ISSN NUMBER: 1938-7172
Issue 5.8

Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Penelope S Benedik, PhD, CRNA, RRT
Mary A Golinski, PhD, CRNA
Gerard Hogan Jr., DNSc, CRNA
Alfred E Lupien, PhD, CRNA
Lisa Osborne, PhD, CRNA
Dennis Spence, PhD, CRNA
Cassy Taylor, DNP, DMP, CRNA
Steven R Wooden, DNP, CRNA

Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2011

New health information becomes available constantly. While we strive to provide accurate information, factual and typographical errors may occur. The authors, editors, publisher, and Lifelong Learning, LLC is/are not responsible for any errors or omissions in the information presented. We endeavor to provide accurate information helpful in your clinical practice. Remember, though, that there is a lot of information out there and we are only presenting some of it here. Also, the comments of contributors represent their personal views, colored by their knowledge, understanding, experience, and judgment which may differ from yours. Their comments are written without knowing details of the clinical situation in which you may apply the information. In the end, your clinical decisions should be based upon your best judgment for each specific patient situation. We do not accept responsibility for clinical decisions or outcomes.

Table of Contents

Missed steps in the preanesthetic set-up

  Risk factors of post-operative urinary retention in hospitalized patients

The volume of blood for epidural blood patch in obstetrics: a randomized, blinded clinical trial

  A prospective evaluation of bleeding risk of interventional techniques in chronic pain

Incidence and predictors of hypertension during high-dose dexmedetomidine sedation for pediatric MRI

Intramuscular Dexmedetomidine Sedation for Pediatric MRI and CT

Nitrous oxide anesthesia and plasma homocysteine in adolescents

Spinal anesthesia failure after local anesthetic injection into cerebrospinal fluid: a multicenter prospective analysis of its incidence and related factors in 1214 patients



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Equipment & Technology
Missed steps in the preanesthetic set-up

Anesth Analg 2011;113:84-8

Demaria S, Blasius K, Neustein SM


Purpose The purpose of this study was to describe the incidence of missed steps in the preanesthetic setup and to determine what factors were associated with those missed steps.


Background Anesthesia providers are required to perform multiple tasks in a short period of time prior to induction of anesthesia. Rapid case turn-over and production pressures can lead to missed steps in the preanesthetic set-up of the anesthesia machine, resuscitation and airway equipment, and medications. Incomplete or missed steps in the set-up have been associated with patient injury and near misses.


Methodology This was an observational study of 200 surgical procedures to evaluate the preanesthetic room set-up for missed steps before induction of anesthesia. Rooms were randomly selected from 40 operating rooms. Each of the 40 operating rooms were evaluated 5 times during at least one AM and PM shift. Investigators evaluated each room for the presence or absence of the following:

  1. manual ventilation device available
  2. full machine checkout done before first case of the day
  3. adequate suction
  4. emergency airway devices (endotracheal tube, working laryngoscope, laryngeal mask airway), 
  5. emergency drugs (i.e., succinylcholine, and either phenylephrine or ephedrine)
  6. working intravenous line
  7. working standard monitors

An expert panel of anesthesia providers used the Delphi method (see notes at end) to develop the items included in the pre-anesthetic set-up list.


Additional variables collected included time of day, number of cases in the room, experience level of provider, type of case, anesthetic plan, scheduled or unscheduled case, patient age, ASA physical status, and patient gender. Descriptive and inferential statistics were used to analyze the results. The investigators stated they used a Wilcoxon test to evaluate the association between perioperative variables and missed set-up steps (Editor’s note: It appears the investigators used a Chi-square but called it a Wilcoxon test). A P value <0.05 was significant.


Result Of the 200 cases sampled, 50% were evaluated in the morning. Similarly, 50% were the first case of the day. A majority of the cases were scheduled (179 of 200). Four or fewer cases were completed in 119 of the operating rooms from which cases were sampled and five or more cases were completed in 81 of the operating rooms. A majority of the cases were general surgery (n = 148), followed by cardiothoracic (n = 29), and pediatric (n = 23). General anesthesia was used for 132 of the cases, regional anesthesia for 34 cases, and MAC for 34 of the cases. In 87 cases the provider was a 1st year resident, in 51 cases a 2nd year resident, in 35 cases a 3rd year resident, in 13 cases an anesthesiologist working alone, and in 14 cases a CRNA.


A total of 23 missed steps occurred out of 200 sampled room set-ups. There was an 11.5% incidence of at least one missed step. There were 3 double misses. Twice both suction and a manual resuscitation device (Ambu bag) were missing. The other double miss was a missing Ambu bag and a missing working laryngoscope handle in a room with MAC cases. In 6% of cases there was a missing Ambu bag alone. In 3% of cases there was missing suction. In 1% of cases the morning full machine check had not been completed. In 1% of cases there were missing emergency airway devices. In 0.5% of cases there were missing emergency drugs. No case had a nonfunctional intravenous line or absent monitors.


There was no significant association between time of day, case order or type, scheduled or unscheduled case, patient age, or ASA classification and missed steps. Cases scheduled to have regional anesthesia were 5 times more likely to have a missed step when compared to general anesthesia (95% CI: 1.6-13.6, P = 0.005). Rooms with ≥5 cases scheduled were 2.4 times more likely to have a missed step (95% CI: 1.2-12.2, P = 0.04). When an attending anesthesiologist set-up the room the risk of at least one missed step was 5 times greater than if a resident set-up the room (95% CI: 1.3-10.2, P = 0.04).




Table 1. Room Characteristics Associated with at least 1 Missed Step


Missed Steps
(% of sampled rooms)


P value

Time of day




10 (10%)

13 (13%)


Provider experience



Anesthesiologist alone


15 (8.7%)

2 (15.4%)

6 (42.9%)


# of cases in room



7 (5.9%)

16 (19.8%)


Anesthetic Type





7 (5.3%)

14 (41.1%)

4 (11.8%)


Note. Percentages are for those cases with factor involved. For example, 14 cases were set-up by an anesthesiologist working alone and 6 of these cases had a missing step, for a 42.9% missed step rate.



Conclusion This study demonstrated that missed steps in preanesthetic room set-up do occur. Anesthesia providers should allow for enough time for room set-up. A thorough room set-up may help improve the provider’s ability to respond to emergencies. Future investigations should evaluate if an anesthesia time-out before induction reduces the incidence of missed steps in the preanesthetic set-up.



Anesthesia is a lot like flying an airplane. Critical to a safe take-off is going through a pre-flight checklist. Similarly, an anesthesia provider needs to go through a preanesthetic set-up checklist to ensure that critical steps and equipment are completed prior to administering an anesthetic. This study sought to determine the incidence of missed steps or missing equipment in the preanesthetic setup. This was an important study because it highlights one of the most basic, and important steps in administering anesthesia; ensuring the anesthesia machine is working properly and that emergency airway equipment and drugs, suction, monitors, and a functioning intravenous line are available.


The investigators found an 11.5% incidence of missed steps, with the most common missing step being a missing Ambu bag. I found this surprising given that most operating rooms with anesthesia carts I have been at have an Ambu bag hanging on the side of the anesthesia cart. If you exclude the missing Ambu bag, then the incidence of missing steps was 5.5% at this institution, with most providers forgetting to check for working suction (6 out of 200 cases or 3%). In rooms with 5 or more cases or a staff anesthesiologist working alone there was a higher likelihood that critical steps were missing in the room set-up. While these results are from a single academic institution I think similar results would be found at other large institutions. At many large academic centers were staff supervises trainees it is rare that the staff anesthesia provider works alone, so when they do it is not surprising that they might miss certain steps. They are probably used to having the trainee set-up the room. Likewise, in a busy room with a lot of cases and a rapid turnover it is not surprising that a provider might rarely forget to check that the suction is working.


Additionally, if the room had a regional anesthetic planned for the case then there was a higher likelihood of a missed step. It maybe that the anesthesia provider or staff supervising the anesthesia trainee may have felt the equipment or step was not needed for a regional anesthetic (i.e., not drawing up succinylcholine). So it is possible the checklist falsely elevated the incidence of missed steps. The investigators point out that the checklist had never been validated in previous research, however, it was developed by an expert panel and the list has face validity, representing steps or equipment that should be available anytime one administers an anesthetic.


Nonetheless, I think the study is important because it highlights the importance of the “timeout.” The authors used the results of this study to call for an “anesthesia timeout”. I think this would be an important aid to ensuring that we do not miss a critical step, like ensuring one has a working suction canister prior to inducing anesthesia. Previous investigations have demonstrated that the surgical checklist and timeout reduce complications in multiple institutions worldwide1 (see Anesthesia Abstracts, September 2010, volume 4, number 9).


Anesthesia providers should use the results of this study as a reminder to take the time to ensure there are no missed steps prior to starting a case.

Dennis Spence, PhD, CRNA

Weiser TG, Haynes AB, Dziekan G, Berry WR, Lipsitz SR, Gawande AA. Safe surgery saves lives investigators and study group. Effect of a 19-item surgical checklist during urgent operations in a global patient population. Ann Surg 2010;251: 976-80.

Delphi Method The Delphi Method is a consensus building process in which participants provide written responses to questions in two or more rounds. Following each round, a facilitator anonymously reports everyone’s responses and the rational given for their answers. After reading everyone else’s answers the participants again answer the same questions in another round. Having knowledge of other participant's answers encourages individual participants to revise previous answers. The process is intended to encourage a narrowing of the range of answers over several rounds until a consensus is reached.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Risk factors of post-operative urinary retention in hospitalized patients

Acta Anaesthesiol Scand 2011;55:545-548

Hansen BS, Soreide E, Warland AM, Nilsen OB


Purpose The purpose of this study was to identify risk factors associated with post-operative urinary retention.


Background Post-operative urinary retention can cause permanent damage to urinary function. Often defined as a bladder volume greater than 400 mL, Post-Operative Urinary Retention recognition is an important aspect of care in the recovery room. Risk factors that can lead to Post-Operative Urinary Retention include spinal anesthesia, long surgical procedures, and large perioperative fluid infusion. The identification of Post-Operative Urinary Retention is seldom a priority in most recovery room facilities, and the issue is often overlooked. In an effort to identify the prevalence of Post-Operative Urinary Retention and the risk factors associated with it, a quality improvement project was undertaken to collect bladder volume data on consecutive post-operative patients during a defined time period.


Methodology A portable ultrasound device was used to measure the urinary bladder volume in 773 consecutive post-operative patients. All patients were older than 18 years old. Those patients who were catheterized before or during surgery, or who had post-operative epidural pain management were excluded from the study. When a patient was found to have Post-Operative Urinary Retention they were asked to void. If they could not void within 1 hour, they were catheterized. Data collection included bladder volume, age, sex, type of anesthesia, pre-operative voiding, and duration of surgery. A Student’s t test for difference in mean bladder volumes, a Mann-Whitney U-test for difference in medians, and a Fisher’s Exact test for categorical variables were used to compare patients with bladder volumes greater than 400 mL to those patients with smaller post-operative bladder volumes.


Result Upon arrival in the recovery room, bladder scanning revealed that 13% of patients (n=104) had bladder volumes greater than 400 mL. Of those patients, 80% failed to void within an hour and had to be temporarily catheterized. Risk factors associated with Post-Operative Urinary Retention included: failure to void pre-operatively, the use of spinal anesthesia, age greater than 50, prolonged anesthesia time, and emergency surgery (p<0.001).


Conclusion Risk factors found in this study were similar to other studies with the exception that sex was not found to be a risk factor. In addition to identifying those who were at risk for Post-Operative Urinary Retention, this study also revealed that those presenting to the recovery room with bladder volumes greater than 400 mL were very likely to need temporary catheterization. It was also evident that many patients experience Post-Operative Urinary Retention without any clinical symptoms and were unable to void at the time of recovery room discharge. Because there is a risk of permanent damage associated with Post-Operative Urinary Retention, bladder scanning in the recovery room should be part of the recovery room protocol.



This was a simple study, but pointed out an important issue that we may often neglect. Post-operative urinary retention is not a benign problem. As pointed out in the article, it can present without symptoms and cause permanent damage. Although the risk factors presented in this study are probably not a surprise to any anesthesia provider, it is unlikely that many providers place identification of urinary retention at a high level. I suspect few recovery room protocols include checking bladder volume with ultrasound, but it would be prudent to identify patients at risk and make sure the recovery room staff is aware that they need to use whatever tools necessary to evaluate the situation especially if risk factors do exist.


This study did exclude those who had epidural pain management in place in the recovery room. I suspect they excluded these patients because they were at high risk for urinary retention and would skew the data. With that in mind I believe that anyone with epidural pain management in place should be added to the list of those at risk for Post-Operative Urinary Retention. These articles that present simple studies with what appear to be common sense outcomes are valuable in the respect that they remind us that simple issues are worth our attention.

Steven R Wooden, DNP, CRNA

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Obstetric Anesthesia
The volume of blood for epidural blood patch in obstetrics: a randomized, blinded clinical trial

Anesth Analg 2011;113:126-133

Paech MJ, Doherty DA, Christmas T, Wong CA, and Epidural Blood Patch Trial Group


Purpose The purpose of this study was to compare the efficacy and adverse effects of 15, 20, or 30 mL blood patch volumes used to treat postdural puncture headaches in obstetrical patients who underwent epidural analgesia.


Background The most common complication associated with epidural anesthesia in obstetrical patients is a unintentional dural puncture, with 55-80% experiencing a postdural puncture headache (PDPH). Of those who experience a PDPH, over 50% will experience a severe headache for several days or more. Rare, but serious complications such as cranial nerve palsy, subdural hematoma, and chronic headaches can occur. The most common and effective treatment is an epidural blood patch (EBP). Two-thirds of patients with a PDPH receive an EBP. Observational studies suggest that short-term complete or partial relief occurs in 95% of obstetrical patients who receive an EBP. However, only 35-70% remain headache free after several days. There is controversy over the most efficacious amount of blood to administer. This trial sought to compare the three most common volumes of blood used to treat a PDPH in obstetrical patients.


Methodology This was a prospective, randomized, blinded clinical trial that enrolled 121 participants from 10 centers around the world (see note below for centers). Exclusion criteria included age <18 years old, contraindications to an EBP, previous EBP, EBP <24 hours or >5 days after the dural puncture, and a history of low or radicular back pain requiring treatment during pregnancy. The randomization sequence was stratified by timing and study site (≤48 or >48 hours). Participants were randomized to receive 15, 20, or 30 mL of autologous blood for the EBP. The volume of blood could be limited at the discretion of the anesthesia provider based on patient complaints of severe back pain during injection. All EBP were performed in the lateral position. Participants and data collectors were blinded to the EBP volume. Blood was injected at approximately 0.3 mL/s. Participants remained supine for at least 2 hours after the EBP, and were encouraged to drink plenty of liquids and to avoid coughing, heavy lifting, or straining.


Data were collected at 2, 4, 8, 24, 48, and 72 hours and 5 days post-procedure. The primary outcome was a composite of permanent or partial headache relief. Permanent relief was defined as a pain score of 0/10 four hours after the procedure and no reoccurrence. Partial relief was defined as a reduction in the PDPH severity score by at least 50% at 4 hours or initial complete relief but a reoccurrence of the PDPH with a severity score >0 at any time point. Secondary outcomes included the permanent headache relief rate, partial headache relief rate, severity of headache, need for repeat blood patch, incidence and severity of back pain with EBP. Statistical analysis was appropriate. An intention to treat analysis was completed. Because of the small sample size some secondary outcomes were not analyzed.


Result A total of 121 participants were recruited from 10 centers across the world, with 39 of 121 recruited from a single center in Australia. Average age was 31 years, and BMI 27 kg/m2. Over 60% of the needles which produced the PDPH were 17-18 g epidural needles. A catheter was placed in the intrathecal space in 31% of participants. A majority of deliveries were vaginal (71%). No significant differences were found between the groups (Table 1). However, median onset of PDPH was longer in the group randomized to receive a 20 mL blood patch (P = 0.05). Patients in the 30 mL group received significantly less of the allotted volume when compared to the other two groups (P < 0.01; Table 1).



Table 1. Patient Characteristics and Secondary Outcomes


15 mL
n = 41

20 mL
n = 41

30 mL
n = 39

P value

Onset (hours)

15 (7-37)

28 (15-46)

16 (7-35)


Severity (0-10)

8 (7-9)

8 (7-9)

8 (6-9)


Associated symptoms*





Time from dural puncture to EBP

62 (49-85)

77 (48-86)

52 (40-80)


Back pain during EBP





Volume EBP w/ onset of back pain

13 (10-15)

12 (10-18)

16 (9-25)


% received allotted volume





Incidence of back pain after EBP





Back pain onset after EBP

28 (15-42)

27 (14-39)

27 (15-29)


No analgesics required post-EBP





Time to return of PDPH (hours)

100 (88-111)

100 (88-112)

95 (82-108)


Repeat EBP





Note. Results are median (interquartile range) or %. *Associated symptoms included visual or hearing disturbances, nausea.



The incidence of permanent or partial headache relief was highest in the 20 mL group, and lowest in the 15 mL group (15 mL: 61%; 20 mL: 73%; 30 mL: 67%; Figure 1). The odds of permanent or partial relief were 3.15 times greater if the EBP was performed >48 hours after dural puncture (95% CI: 1.39-7.15, P = 0.01). The odds of permanent relief if the EBP was performed >48 hours after dural puncture were not significant (OR: 2.35, 95% CI: 0.84-6.56, P = 0.10). The incidence of permanent PDPH relief was significantly higher in the 20 mL group than the 15 mL group (32.3% vs. 9.8%; OR: 4.49, 95% CI: 1.31-15.42, P = 0.017). No statistically significant difference was found between the 15 mL and 30 mL groups (9.8% vs. 25.6%; OR: 3.56, 95% CI: 0.99-12.73, P = 0.051). The severity of the PDPH 0 to 48 hours after the EBP was significantly less in the 20 mL and 30 mL groups when compared to the 15 mL group (P = 0.01). Median headache severity scores between 0 and 48 hours after EBP were between 1-2 on a 0-10 scale in all groups. Patients in the 20 mL group had a lower incidence of repeat EBP when compared to the other two groups (Table 1). No serious complications occurred in any group.



Figure 1. Comparison of PDPH Relief

Figure 1

Note. The incidence of permanent or partial PDPH relief was 61%, 73.2%, and 66.7% in the 15 mL, 20 mL, and 30 mL groups, respectively.



Conclusion While similar efficacy was seen for permanent or partial PDPH relief with 15, 20, and 30 mL, results overall support the use of 20 mL epidural blood patch volume when treating a PDPH in obstetrical patients after unintentional dural puncture.



The incidence of PDPH is approximately 1% in obstetric patients, with higher rates reported when epidurals are placed by inexperienced providers. In my opinion, management of PDPH is one of the most challenging complications faced by obstetric anesthesia providers. The reason it is challenging is because one must rule out other potential causes of a postoperative headache. Additionally, headache onset may not occur until after delivery, conservative treatment is largely ineffective for severe PDPH, and coordinating when to perform an EBP may be challenging after a patient is discharged from the hospital. While an EBP is considered the “gold standard” for a confirmed PDPH, many patients are fearful about having a repeat procedure, and providers may be reluctant to perform an EBP. Furthermore, the optimal volume for an EBP remains to be determined.


While the optimal volume is still unknown, this study goes a long way in providing strong evidence supporting an attempt to administer 20 mL for an EBP in obstetrical patients. This investigation is probably one of the best designed investigations, with the strongest level of evidence published to date on the efficacy of EBP in patients with a PDPH. Results suggest that permanent or partial relief was higher with 20 mL, and that a little over one third experienced complete relief with this volume of blood. No differences were found with the 30 mL volume, however only 54% of participants in the 30 mL group received the total 30 mL volume, presumably because of patient intolerance of back pain during injection of autologous blood. Furthermore, 42% of participants in the 20 mL group required no analgesics post-EBP as compared to 12% and 21% in the 15 mL and 30 mL groups, respectively. These results indicate to me that 20 mL may be the ideal volume.


What else does this study tell us? First, it is important to point out that all EBP were performed >24 hours after dural puncture. The onset of a PDPH occurs between 7 and 46 hours after dural puncture; this suggest some patients may experience symptoms before discharge. Over 60% of patients who experience a PDPH will have a severe headache, and close to 80% will have associated symptoms of visual or hearing disturbances and/or nausea. These latter symptoms are important because they can aid in the differential diagnosis of a postpartum headache. Over half of all patients will experience back pain during the EBP. Therefore, it is important to inform patients that they may experience back pain. I would inform patients that approximate incidence of permanent or partial headache relief is around 70% when 20 mL is used, and that permanent relief is around 30%. Approximately one-third may require a repeat EBP.


These results suggest that the odds of permanent or partial headache relief were greater if the EBP was done >48 hours after the dural puncture. The authors did not speculate on the mechanism for this difference, but it may be due to development of scar tissue at the site of the dural rent. The best time to perform an EBP is still not known. Anesthesia providers should balance patient desires, logistics, and departmental guidelines when deciding when to perform an EBP. I typically like to perform the EBP before the patient is discharged, because it may be difficult to coordinate performance of the procedure after discharge. In some facilities the patient may need to go to the emergency room to be evaluated, which may increase health care costs. These results may make me rethink the timing of the EBP.

Dennis Spence, PhD, CRNA

The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

A prospective evaluation of bleeding risk of interventional techniques in chronic pain

Pain Physician 2011;14:317-329

Manchikanti L, Malla Y, Wargo BW, Cash KA, McManus CD, Damron KS, Jackson SD, Pampati V, Fellows B


Purpose The purpose of this study was to evaluate subjects who were having interventional pain procedures to determine if withholding their antithrombotic agents prior to the procedure reduced their risk for bleeding complications.


Background Antithrombotic therapy has been shown to reduce the cardiac risk of individuals with coronary artery disease and dysrhythmias. This antithrombotic therapy includes aspirin, clopidogrel (Plavix), and warfarin (Coumadin), among others. Studies have shown that withdrawal of antithrombotic therapy is associated with a 3 fold risk of major adverse cardiac events, especially for individuals with intracoronary stents. The withdrawal of clopidogrel can create hypercoagulability. Even with evidence that discontinuation of antithrombotic therapy can lead to cardiac risk, it remains common practice to withhold such therapy prior to interventional pain management procedures. However, there is lack of evidence that continuation of antithrombotic therapy leads to bleeding complications during or after interventional pain procedures. This study was undertaken to evaluate the risk of bleeding in subjects who continue antithrombotic therapy during interventional pain management procedures.


Methodology This study was conducted at a United States health care institution with IRB approval. A total of 3,179 subjects were enrolled between May 2008 and December 2009. The study was performed prospectively, and without change in the normal course of treatment. The providers who performed the interventional procedures used their normal selection process to determine if a patient should have their antithrombotic therapy withheld or not. All subjects were included that received interventional pain management procedures except those having disc decompression or implantations. Outcome measurements included intravascular entry with a needle, profuse bleeding, localized bleeding, hematoma, oozing, bruising, and postoperative soreness. The results were determined to be significant if the P value was less than 0.05.


Result During the 20 month study, there were 3,179 subjects who underwent 18,472 procedures. Subjects who had their antithrombotics withheld had stopped their warfarin for 3 to 5 days prior to the procedure, and their aspirin and clopidogrel 5 to 7 days prior to the procedure.



Table 1. Demographics of Participants











Clopidogrel (Plavix)



Warfarin (Coumadin)





Antithrombotic Status at time of procedure







The interventional procedures included facet joint injections, sacroiliac joint injections, lumbar sympathetic blocks, stellate ganglion blocks, intercostal nerve blocks, occipital nerve blocks, epidural injections, intraarticular injections, and peripheral nerve blocks. Intravascular entry and oozing were higher in those subjects who continued their antithrombotic therapy, but local bleeding and bruising were higher in those who discontinued therapy. There were no significant differences in complications 48 and 72 hours post procedure.





Table 2. Complications Following Procedure


No Antithrombotic

Therapy Continued

Therapy Discontinued

Intravascular Needle




Profuse bleeding




Local bleeding
















No complication




** indicates P<0.05


Conclusion A previous study indicated that antiplatelet therapy did not pose a significant risk in developing neurologic dysfunction after spinal or epidural anesthesia. In addition, intravascular entry does not appear to carry an increased risk of hemorrhagic complications with or without antithrombotic therapy. Consequently, the risk of stopping antithrombotic therapy may be higher than continuing therapy when it comes to interventional pain management. This study conclude that NSAIDs, which includes aspirin, should not be discontinued prior to interventional techniques and discontinuation of antiplatelet and warfarin therapy should be considered on a case by case basis.



Most of us have routinely removed patients from antithrombotic therapy prior to interventional pain management procedures, for various lengths of time. Concerns about antithrombotics increasing the risk of an epidural hematoma have overshadowed concerns of cardiac complications being created by discontinuing antithrombotic agents. There appears to be little evidence that continuing antithrombotic therapy actually does increase bleeding risk. On the other hand, there is emerging evidence that discontinuing antithrombotic therapy for any length of time increases create cardiac risk in some patients.


It seems prudent to evaluate every patient on a case by case basis, and then consider the risks of discontinuing antithrombotic therapy before routinely doing so. This is especially true for patients with coronary artery stents. Some of my colleagues routinely discontinue all aspirin and other NSAIDS for 7 days prior to an interventional procedure. I have always wondered what kind of risk we are creating for our patients by doing so. For that reason, I have not taken patients off NSAIDs for over 10 years now, and I have not seen a bleeding problem because of that decision. I have continued to follow the guidelines concerning warfarin, and request that those patients remain off the drug for 3 days prior to the procedure and that their INR be below 1.5 at the time of the procedure. I think this decision remains prudent because of the occasional patient who arrives with a grossly elevated INR and does not know it.


Clopidogrel (Plavix) is an entirely different animal. I have had physicians tell me they did not want to remove their patients from the drug, but still wanted them to have the interventional therapy. I believe there is enough evidence that we can safely treat patients on this drug if we monitor them carefully, avoid unnecessary trauma, and inform them of the additional risks. As this article suggests, each patient needs to be evaluated carefully before making such a decision.


Now we have patients coming in on Dabigatran (Pradaxa). This replacement for warfarin has no measurable therapeutic range, has no reversal agent, and we have been given little guidance on how it will impact bleeding problems for interventional procedures. I have been told I can safely treat a patient who has been off the drug for 4 days. Only time will tell what kind of problems this drug will create for us, but until there is a better understanding of how patients on it will respond to interventional treatment, I plan to continue removing them from the drug for 4 days.


We are only just beginning to investigate the risk of bleeding during interventional procedures with various anticoagulants in different types of patients. This particular study diluted the clinical significance, and applicability, of its findings by including a host of procedures where bleeding may not be evident, or where bleeding may not pose a serious risk. Neither did it stratify patients by pathology and history. However, this is at least the second study to call into question the assumption of increased bleeding risk when removing patients from a thromboprophylactic dose of some antithombotics. Could it be that we have been overstating the risk of keeping most patients on these agents prior to their procedure; and understating the risk of withholding them?


The bottom line is that health care is becoming more complex every day. We have to deal with potential risks to each patient in a reasonable manner. We should not consider any procedure routine. Guidelines are helpful, but until they can guarantee removal of all risk, I will continue to consider alternatives if they might be in the best interest of the patient, and the alternatives have reasonable support through evidence. It is time to drop the “sacred cow” and look for better evidence. I consider the management of antithrombotics to be one of those complex situations deserving of a second look, each and every time.

Steven R Wooden, DNP, CRNA

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Pediatric Anesthesia
Incidence and predictors of hypertension during high-dose dexmedetomidine sedation for pediatric MRI

Paediatr Anaesth 2010;20:516-23

Mason K, Zurakowski D, Zgleszewski S, Prescilla R, Fontaine P, Dinardo J



Purpose The purpose of this study was to describe the hypertension effect, if any, during high dose dexmedetomidine as a sole agent for sedation during radiologic studies in the pediatric population.


Background Dexmedetomidine (Precedex) is an alpha 2 adrenoreceptor agonist approved by the FDA for use in adults. It is commonly administered to those needing sedation during both surgical and non-surgical or less invasive diagnostic studies.


While not approved by the FDA for use in the pediatric population, it is being used in the pediatric population when sedation is necessary; such as in the MRI suite. A biphasic dose response effect exists for adults and is characterized by decreases in both mean arterial blood pressure (MAP) and heart rate at low plasma concentrations and increases in MAP at higher plasma concentrations. Cardiovascular effects of dexmedetomidine administration have not been studied in the pediatric population.


Methodology This study was carried out as a retrospective review of quality outcome data specific to institution developed sedation guidelines. Pediatric patients undergoing MRI with high dose dexmedetomidine-only sedation were evaluated for hypertension, bradycardia and any other adverse effects. Dexmedetomidine sedation guidelines included:


  • Bolus of 3 µg/kg -1 over 10 minutes
  • If fail to achieve a Ramsay Sedation Score (RRS) of ≥4, repeat bolus up to 2 more times
  • When RRS ≥4, begin 2 µg/kg/hr -1 infusion until completion of imaging study
  • Monitor at 5 minute intervals:
    • Heart rate
    • Oscillometric blood pressure
    • End tidal CO2
    • SpO2
    • Respiratory rate


Vital signs, pertinent demographic data, total drug usage and duration, and adverse events were recorded and entered in to a computerized database. The database was 

retrospectively reviewed to assess and compare outcomes and associated variables for 3,522 children.


Hypertension was defined as MAP >20% above the upper limit for the specific age:


  • 0-3 months MAP >78 mmHg
  • 3-6 months MAP >88 mmHg
  • 6-12 months MAP > 90 mmHg
  • 1-3 years MAP > 98 mmHg
  • 3-6 years MAP > 104 mmHg
  • 6-12 years MAP > 108 mmHg
  • >12 years MAP > 122 mmHg


Additionally, the association between hypertension and bradycardia was assessed and compared against the 6 age groups, gender, and the number of dexmedetomidine boluses.


Result A total of 3,522 children were included; 172 experienced hypertension for an overall incidence of 4.9%. Of the 3,522 children in the study, 75% received a single bolus followed by an infusion, 24% received 2 boluses followed by an infusion, and 0.65% of children required 3 boluses followed by an infusion. The youngest children (<6 months) had significantly more boluses than the other age groups (P < 0.0001). No child required pharmacologic treatment of hypertension and no adverse events related to hypertension and/or bradycardia were identified.




Table 1: Incidence Of Hypertension by Age




Hypertension Incidence


1 - 6 months


10 (8.5)*


6 - 12 months


21 (7.9)*


1 - 3 years


66 (6.1)*


3 - 6 years


45 (3.7)


6 - 12 years


29 (4.0)


12 - 18 Years


1 (0.9)

NOTE: * Significantly higher incidence than the older age groups (p<0.05)



Conclusion Hypertension occurred with high dose dexmedetomidine sedation in some pediatric patients, but it was not a common occurrence. Children <1 year of age who received multiple boluses had the highest incidence and longest duration of hypertension. The duration of the dexmedetomidine infusion was not a predictor of the incidence or duration of hypertension.



Although hypertension was observed to be a rare and/or non problematic side effect of this alpha 2 adrenoceptor agonist at high plasma concentrations, the potential for hypertension to occur should not be ignored. Administering dexmedetomidine to those in whom a hypertensive episode could create a true catastrophe would be problematic.


This study did note their limitations upfront, which I totally agreed with. Blood pressures taken at 5 minute intervals via cuff may not have identified a ‘short period of hypertension’ as an arterial line would, however shortened time intervals for cuff pressures may have clinically aggravated the pediatric patient. Placing an arterial line would have been inappropriate for such a low risk imaging study. Second, there was no true baseline blood pressure. The behavioral patterns of very young patients simply did not allow the establishment of individual baselines. Any attempts to establish a baseline would have resulted in skewed results. Age-adjusted norms were used instead for comparison purposes. On the plus side, the guidelines developed for dexmedetomidine administration promoted quality and safety considering what was known about the rare side effect of hypertension at high doses. And, if there was any indication that a child was at risk for hypertension or presented with a history which placed them at risk, dexmedetomidine was not used. This emphasizes the need for comprehensive preanesthetic evaluations irrespective of how ‘benign’ an imaging study may seem. In addition, I appreciated the extensive analysis and outcomes assessment that was done; both were appropriately carried out including a description, in detail, of the effects of hypertension when it did occur.


This adds useful information to the body of evidence we have on dexmedetomidine. With the most recent emerging evidence suggesting cellular apoptosis in the pediatric population following the administration of some general anesthetic agents, we need to be cognizant that alternative agents exist and continue to research their side effect profiles. In this case, we’ve learned that even when used only for sedation, small children may require quite large doses of dexmedetomidine, but even then the overall rate of hypertension is fairly low and caused no harm.

Mary A Golinski, PhD, CRNA

Editor’s Note: compare these dosing guidelines from the manufacturer with those used in this study for context.

Dosing Guidelines from – For adult sedation during surgical and other procedures:  After administration of a 1 µg/kg loading dose, the maintenance dose of dexmedetomidine is initiated at 0.6 µg/kg/hr and titrated to achieve the desired clinical effect, with doses ranging from 0.2 to 1 µg/kg/hr.


Ramsay Sedation Scale

1 Patient is anxious and agitated or restless, or both

2 Patient is co-operative, oriented, and tranquil

3 Patient responds to commands only

4 Patient exhibits brisk response to light glabellar tap or loud auditory stimulus

5 Patient exhibits a sluggish response to light glabellar tap or loud auditory stimulus

6 Patient exhibits no response

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Intramuscular Dexmedetomidine Sedation for Pediatric MRI and CT

Am J Roentegnol 2011;197:720-5

Mason K, Lubisch N, Robinson F, Roskos R


Purpose The purpose of this study was to describe intramuscular dexmedetomidine sedation used in the pediatric population undergoing MRI and CT imaging studies.


Background Infants and young children often require sedation to ensure motionless conditions while undergoing imaging studies such as MRI and CT scans. More traditional, older sedative medications such as pentobarbital and chloral hydrate have numerous disadvantages; for example, an extremely long duration of action that has been linked to prolonged recovery and several sedation-related side effects. Dexmedetomidine is not labeled for pediatric use however literature is becoming abundant with clinical scenarios describing its effectiveness in the pediatric patient population. It has been administered to children using the IV, nasal, buccal, and subcutaneous routes however the intramuscular (IM) route has only been described in adults. Oftentimes children do not need an intravenous for MRI and CT imaging studies other than to receive sedation. Dexmedetomidine via the IM route has potential for a safe and high quality sedative agent.


Methodology This study was carried out as a retrospective analysis of an institutional dexmedetomidine sedation protocol. The goal was to assess the effectiveness of IM dexmedetomidine administered to pediatric patients when undergoing MRI and CT imaging studies. Children who were undergoing routine brain, seizure, and musculoskeletal imaging received:


1) 4% lidocaine topical lysosomal delivery 20 minutes before the planned IM dexmedetomidine injection (two separate sites)

2) An initial dose of 1-4 µg/kg of undiluted intramuscular dexmedetomidine (4 µg/mL solution) in the deltoid muscle (dose used dependent upon discretion of provider, child’s medical diagnosis, preexisting state of anxiety and agitation)

3) An assessment to determine whether a Ramsay sedation score of 4 was achieved

4) A second reduced dose of dexmedetomidine if a Ramsay score of 4 was not achieved and maintained after a minimum observation of 10 minutes

Quality assurance data entered into an electronic database at 5 minutes intervals included:

  • Blood pressure
  • Heart rate
  • Pulse oximetry values


Additional data collected included the dose of dexmedetomidine administered, time required to achieve adequate sedation, duration of imaging study, time required to meet discharge criteria, total duration of sedation, and adverse events. An age-adjusted deviation beyond 20% of baseline vital signs was plotted for comparison.


Result A total of 65 children received IM dexmedetomidine, completed the imaging studies, and were included in the final analysis. A total of 21 had an MRI and 44 had a CT scan. Nine children, 14%, had hypotension. Only one of those nine received a second dose of the study drug because of the inability to achieve the sedation score required. There was no association between hypotension and the total dose of the study drug. All nine patients exhibited a return to within 20% of baseline/normal vital signs without pharmacologic intervention. There were no other adverse effects noted. The average time to achieve sedation was about 13 minutes.


Conclusion Intramuscular dexmedetomidine, administered in mean dose of between 2.4 - 2.9 µg/kg to children undergoing MRI and CT imaging studies produced adequate sedation with an average onset time of 13 minutes. These doses allowed successful completion of the study, and allowed for a recovery period on average of 30 minutes or less. No adverse events were noted. The study was underpowered for determining if a relationship existed between a child’s medical diagnosis and the incidence of hemodynamic variability.



Far too often the complexity of the anesthetic exceeds the complexity of the procedure requiring the anesthetic, especially in the pediatric population. That just doesn’t seem right but it is very true! Clearly the developmental behavioral patterns and stages of infants and younger children mandate a special way of caring for them by the anesthesia provider. This is the humane way of taking care of young people and is widely accepted. What is exciting about this novel IM dexmedetomidine sedation protocol, is that it meets the special needs of young children. Why start an intravenous line and cause trauma when a topical cream can be used to localize an area where an intramuscular injection is given? Why start an IV when the drug administered has very little potential to create respiratory depression or hemodynamic instability? It truly is a unique way to continue to promote a safe and high quality environment in a very special patient population.


Some may ask: what is the difference then of anesthetizing a young child for myringotomy tube placement using inhalational anesthesia and not placing an IV? The difference is obvious:  dexmedetomidine is an alpha 2 adrenoreceptor agonist that pharmacokinetically and pharmacodynamically works in distinctly different ways than our inhalation agents. Unlike inhalation agents, it does not carry the risk of causing a loss of airway patency or of creating myocardial depression and tachycardia. Therefore, the risk of not placing on IV to treat effects of an anesthetic is very minimal in the case of dexmedetomidine. For minimally invasive diagnostic procedures where immobility is a necessity, such as imaging studies, it appears to be one of the most appropriate ways to sedate children without making the anesthesia risk and associated side effects greater than the procedure risk!

Mary A Golinski, PhD, CRNA

Ramsay Sedation Scale

1 Patient is anxious and agitated or restless, or both

2 Patient is co-operative, oriented, and tranquil

3 Patient responds to commands only

4 Patient exhibits brisk response to light glabellar tap or loud auditory stimulus

5 Patient exhibits a sluggish response to light glabellar tap or loud auditory stimulus

6 Patient exhibits no response

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Nitrous oxide anesthesia and plasma homocysteine in adolescents

Anesth Analg 2011;June 16 Epub ahead of print

Nagele P, Tallchief D, Blood J, Shara A & Kharasch ED


Purpose This study investigated the effects of nitrous oxide on plasma levels of total homocysteine (tHcy) in a pediatric age group.


Background Hyperhomocysteinemia is associated with impaired endothelial function and an increase in vascular risk and thrombosis. Homocysteine can accumulate when the vitamin B12-dependent enzyme, methionine synthase, is inhibited;hese events reliably occur in adults after the administration of nitrous oxide (N2O). The increase in tHcy as a result of N2O is dose- and duration-dependent. Because homocysteine is prothrombotic, acute increases in tHcy levels due to N2O may be detrimental during the perioperative period.


Methodology The study used a convenience sample of 27 pediatric patients aged 10 to 18 years undergoing major elective spine surgery. The study used residual blood samples from a previous IRB approved pharmacokinetic drug study of anesthetic drugs. Patients received general anesthesia with the specific technique at the discretion of the anesthesia team. Twenty-six patients received N2O and were included in this analysis. Plasma levels of tHcy were analyzed at baseline (immediately after induction and IV start) and at 1, 2, 4, 6, 8, 12, 24, 48, 72 and 96 hours after induction. Cumulative exposure to N2O was calculated as the product of the average concentration of N2O used and the duration of N2O exposure in minutes (%N2O x minutes).


Result All patients exposed to N2O had increases in tHcy that were significantly higher than baseline at the 4th, 6th, 8th, and 10th hours, with the highest results generally occurring just after the anesthetic ended. The magnitude of the increase in tHcy was highly correlated with the %N2O x minutes nitrous was used during the case (Pearson r = 0.80, p < 0.0001).


Conclusion Pediatric patients develop significantly increased homocysteine levels after a prolonged exposure to N2O, although the clinical significance of this is unknown.



It is important to lay the groundwork on the physiology and clinical implications of hyperhomocysteinemia. Multiple factors affect tHcy levels including genetic variations, age, lifestyle choices (smoking, caffeine, alcohol consumption, poor nutrition, lack of exercise), pathophysiologic states (renal failure, hypothyroidism) and some drugs including N2O. N2O irreversibly oxidizes the cobalt ion in vitamin B12 (cobalamin) preventing it from acting as a coenzyme to methionine synthase. Because methionine synthase catalyzes the conversion of homocysteine to methionine, its inhibition leads to the accumulation of homocysteine. Increased levels of homocysteine are associated with impaired endothelial function evidenced by an impaired arterial dilation, hypercoaguability, and the development of atherosclerosis and venous thromboembolism.1 These events may occur not only in severe hyperhomocysteinemia but also in mild and moderate cases. Chronically high levels of homocysteine can cause altered DNA and protein synthesis.


It is quite clear that the administration of N2O significantly increases total homocysteine levels after 4 hours of use and into the postoperative period, but is there evidence of a detrimental effect of N2O on perioperative outcome? This retrospective analysis of blood samples from adolescents does not attempt to answer this question. However, studies have demonstrated that an increased duration and concentration of N2O leads to the highest homocysteine levels and those patients with higher baseline values achieve higher peak levels after N2O anesthesia. Although older patients (> 60 years) have higher baseline tHcy levels, younger patients (< 45 years) demonstrate much larger increases in tHcy after N2O anesthesia. But again, what about outcomes?


The original ENIGMA study2 compared 384 patients undergoing major surgery; patients were partitioned into 2 groups, those who received 80% oxygen with balance nitrogen and those who received 70% N2O with balance oxygen. After adjusting for age, ASA status and duration of anesthesia, the authors reported major complications in 17% of patients (67/394, p = 0.007). Six patients had a myocardial infarction (4 in the 80% oxygen/nitrogen group, 2 in the 70% N2O/oxygen group) and three patients died within 30 days of surgery (all in the N2O group).

In a subsequent long-term analysis of the ENIGMA data,3 however, N2O was not associated with an increased risk of death (hazard ratio 0.98, p = 0.82) at a mean of 3.5 years postoperatively. Patients who received N2O were more likely to have a myocardial infarction (OR=1.59, p = 0.04) while the risk of stroke was not significantly increased (OR=1.01, p =0.97). These results and other studies have been used to question the role of N2O as a routine part of anesthesia care.


Based on this preliminary evidence, and while awaiting further research, should the anesthetist consider the possible effects of N2O when planning an anesthetic? Of course. Nitrous oxide has well-defined absolute, relative, and “putative relative” contraindications.4 Patients with known abnormalities of the methionine synthase pathway and those in whom expansion of gas filled organs might be dangerous must absolutely not receive N2O. Accepted relative contraindications include pulmonary hypertension, anesthetics longer than 6 hours, 1st trimester of pregnancy, and patients with a very high risk of postoperative nausea & vomiting. This recent research suggests that a “putative relative” contraindication might be a patient with risk of myocardial ischemia, although the evidence for this remains largely theoretical.


Considering an individual patient’s risk of baseline hyperhomocysteinemia could become part of the standard preoperative assessment. Age-related increases in tHcy may occur due to decreases in renal function and suboptimal vitamin status (folate and cobalamin deficiency) due to dietary or intestinal malabsorption.5 Smoking, coffee (caffeine), alcohol consumption and a sedentary lifestyle are all associated with elevated tHcy levels. Methotrexate, as an antifolate drug, is associated with increased tHcy levels in doses that range from small (rheumatoid arthritis) to large (cancer chemotherapy). Type 2 diabetics being treated with metformin in the absence of folate supplementation develop high tHcy levels. Chronic renal failure, acute lymphocytic leukemia and some other chronic inflammatory diseases are associated with elevated tHcy. Patients with combinations of these disorders are likely to have hyperhomocysteinemia.


The current anesthesia armamentarium allows for a satisfactory anesthetic in the absence of N2O and this may be a prudent choice for patients who are high risk for hyperhomocysteinemia. On the other hand, N2O remains a safe and helpful adjunct in patients with malignant hyperthermia and for pediatric inhalation induction as long as the anesthetist remains aware that an enhanced prothrombotic state may occur. Proceeding with caution, despite the lack of a large and well-conducted study, might be the safest choice if your patient is in a high risk category.

Penelope S Benedik, PhD, CRNA, RRT

1. Myles PS, Chan MT, Kaye DM et al. Effects of nitrous oxide on plasma homocysteine and endothelial function. Anesthesiology 2008;109:657-653.

2. Myles PS, Chan MT, Leslie K, Peyton P, Paech M & Forbes A. Effect of nitrous oxide on plasma homocysteine and folate in patients undergoing major surgery. Br J Anaesth 2008;100:780-6.

3. Leslie K, Myles PS, Chan MT et al. Nitrous oxide and long term morbidity and mortality in the ENIGMA trial. Anesth Analg 2011;112:387–93.

4. Warner DS & Warner MA. Biologic effects of nitrous oxide. Anesthesiology 2008;109:707-722. A thorough and readable review that covers both the mechanisms of action and clinical implications of the drug. Highly recommended.

5. Schneede J, Refsum H & Ueland PM. Biological and environmental determinants of plasma homocysteine. Semin Thromb Hemost 2000;26:263-279.

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011

Regional Anesthesia
Spinal anesthesia failure after local anesthetic injection into cerebrospinal fluid: a multicenter prospective analysis of its incidence and related factors in 1214 patients

Reg Anesth Pain Med 2011;36:1-5

Fuzier R, Bataille B, Fuzier V, Richez A, Magués J, Choquet O, Montastruc J, Lapeyre-Mestre M


Purpose The purpose of this study was to describe the incidence and predictors of failed spinal anesthesia after injection of local anesthetic into the cerebrospinal fluid (CSF).


Background Spinal anesthesia has a high success rate after aspiration of CSF and injection of local anesthetic. Unfortunately, inadequate or failed anesthesia can occur despite aspiration of CSF and injection of local anesthetic. Reported factors associated with spinal anesthesia failure include problems with batches or baricity of local anesthetic.


Methodology This was a prospective, observational study of 1,218 consecutive adult patients undergoing spinal anesthesia at 21 centers in France between 2007 and 2008. Each center was asked to recruit 50 consecutive patients. The primary aim of the study was to determine the incidence of failed spinal anesthesia. The secondary aim was to identify predictors of failed spinal anesthesia. Patients were >18 years old. Patients undergoing obstetric, urologic, abdominal, orthopedic, and vascular surgery were recruited. Exclusion criteria included coagulopathy, local anesthetic allergy, and inability to obtain free flow of CSF or to inject local anesthetic. The spinal procedure and dose was determined by the anesthesia provider.


Failed spinal anesthesia was defined as any surgical procedure that required conversion to general anesthesia. A total failed spinal anesthetic was defined as absence of anesthesia to the trunk and lower extremities, and partial failure as incomplete or complete anesthesia but an inadequate level for the procedure. Descriptive and inferential statistics were used to analyze the results. Multiple logistic regression was used to identify predictors of failed spinal anesthesia (total and partial failures). A P < 0.05 was considered significant.


Result A total of 17 of 21 centers participated in the study, with 1,214 patients included in the analysis. Many centers were teaching hospitals (44%). No significant differences were found in demographics between the two groups (Table 1). The mean age of all patients was 56 ± 20, with a majority being ASA I or II (77%). Patients who had a successfully placed spinal were significantly older (P < 0.05;Table 1).


There were a total of 39 failed spinals (3.2% overall, 95% CI, 2.2-4.2). Partial failure occurred in 59% of the cases, and total failure in 41% of cases. In the failed spinals, 85% were converted to general anesthesia, and 13% underwent a repeat spinal anesthetic. In 1 case an epidural was placed. When a spinal anesthetic failed and a repeat spinal was performed, half the time an inadequate sensory level resulted. The other half of the time the repeat spinal procedure produced no sensory level at all.


A majority of spinals were placed in the sitting position (96%). Bupivacaine was used most often (93% of cases), followed by ropivacaine (7%). The most common local anesthetic concentration was 0.5% (80% of cases). The local anesthetic was hyperbaric in a majority of the spinal injections (68% of cases). The mean volume injected was slightly different between successful spinals and failed spinals; 2.7 mL ± 1.1 mL in the success group and 2.4 mL ± 0.6 mL in the failed group (P = NS). Adjunct agents were used in a majority of the cases (70%); including sufentanil alone (50%) or in combination with morphine (25%) or another agent (8%) (P = NS). The most common needle type was a 25 g pencil point; used in 72% of successful spinals and  69% of failed spinals (P = NS). The success group had a median sensory level of T-9 (range C8-S5).


The odds of a failed spinal were 2.86 times greater if more than 3 attempts were required (95% CI, 1.20-6.79, P = 0.02). Likewise, if no adjuncts were used the odds of failed spinal were 2.32 times greater (95% CI: 1.20-4.50, P = 0.01). The odds of failed spinal were lowest in patients ≥70 years, when compared to patients < 40 years old (OR: 0.3, 95% CI: 0.13-0.70, P = 0.005). For patients between 40 and 69 years old, the odds of failed spinal were 0.43 times less likely when compared to those < 40 years old (95% CI: 0.20-0.93, P = 0.03).



Table 1. Demographics and Results



n = 1175


n = 39

P Value

Male gender




Age (yrs)

<40 yrs

40-69 yrs

≥70 yrs












BMI kg/m2

27 ± 5

26 ± 5


Surgical procedure




























Number of attempts
















Conclusion The overall incidence of failed spinal anesthesia was 3.2%. Independent risk factors for failed spinal anesthesia included 3 or more attempts, absence of adjunct medication, and age < 40. Patients who were > 70 years old had the lowest risk of failed spinal anesthesia.



This study demonstrated that spinal anesthesia is a very reliable anesthetic, with a very high success rate (96.8%). The authors found that patients who were >70 years old had the lowest risk of failed spinal anesthesia, and that if 3 or more attempts were required, or if adjunct agents were not added, the odds of failure were significantly greater. I think these clinical findings are not surprising. I have certainly experienced cases were it took multiple attempts to obtain free flowing CSF, but still had an inadequate or failed spinal. Some speculative causes of a failed spinal despite the presence of CSF might be that the needle is in the subdural space. Another cause may be that the needle moves in or out of the spinal canal after aspiration of CSF. The addition of adjunctive agents such as opioids improves spinal anesthesia success by increasing the density of the block. The finding that older patients have the lowest risk of failure may be due to a higher spread of local anesthetic, possibly due to changes in the spinal canal with aging. I also wonder if patients > 70 years old have increased sensitivity to local anesthetics injected in the spinal canal.


This study does have a number of limitations. First, the procedure was not standardized, and multiple providers performed the spinal anesthetics. This latter point is especially important given most cases occurred in a teaching hospital, were, presumably, the spinals were placed by anesthesia trainees. Additionally, while not statistically significant, the dosage was lower in the failed spinal group (2.4 mL vs. 2.7 mL). This could explain the higher failure rate. The second most common surgical procedure was obstetrical cases (most likely cesarean deliveries). A T-4 level is typically required for adequate surgical anesthesia for cesarean deliveries, and if the spinal anesthetic was under dosed then this could explain the higher failure rate.


In conclusion, I think this is an important study because it reminds us that we need to always have a backup plan in the event of a failed spinal anesthetic. This is especially important if the patient has significant comorbidities (e.g., difficult airway, morbid obesity). I am always a little leery about repeating a spinal if I have a partial block because I am never sure how much to give. A safer option might be conversion to general anesthesia or supplementation with sedation. However, one must balance the risks vs. benefits with these options.

Dennis Spence, PhD, CRNA

The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.

© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 8, August 31, 2011