ISSN NUMBER: 1938-7172
Issue 2.8 VOLUME 2 | NUMBER 8

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Mary A. Golinski, PhD, CRNA
Alfred E. Lupien, PhD, CRNA
Steven R. Wooden, MS, CRNA


Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2008

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


Airway

Neilipovitz D, Crosby E


 

Evidence-Based Clinical update: no evidence for decreased incidence of aspiration after rapid sequence induction

Can J Anesth 2007;54:748-764

Neilipovitz D, Crosby E

 

Abstract

Purpose            The purpose of this article was to review the literature to determine if accepted “Rapid Sequence Induction” techniques decrease the risk of aspiration or other complications of airway management.

Background            It is appropriate to limit the amount of time an airway remains unprotected during anesthesia induction.  Rapid Sequence Induction (RSI) with cricoid pressure is the standard of care in situations where patients are at risk for aspiration. This study reviewed the literature to determine what evidence there was that RSI reduced the risk of aspiration and what other risks and benefits there were in using the technique.

Methodology            A MEDLINE search was performed to determine whether “Rapid Sequence Induction had any impact on the incidence, severity or consequences of pulmonary aspiration.” The search also looked for studies that addressed other emergency airway intervention techniques, oxygenation issues, and drug issues. The search included both anesthesia and non-anesthesia related literature from 1966 to 2006. Two investigators independently reviewed 184 studies that addressed the questions.

Result            The incidence of aspiration in patients induced for emergency procedures was 1:600 to 900 for elective procedures 1:3000 to 4000. There was a 7 fold increase incidence of aspiration in physical status IV and V patients as well as most deaths from aspiration occurring in those same patients. Other factors that were shown to increase the risk of aspiration were a history of gastric reflux, hiatus hernia, obesity, difficult intubation, increased age, reduced consciousness, neurologic disease, gastric obstruction, recent meal, and critical illness.

The review found insufficient evidence to address the primary questions of whether RSI reduced the incidence of aspiration. There was simply not enough information to answer the question in a statistically significant way. With that being addressed, the review turned toward the secondary questions.

1. Does RSI improve the outcomes of emergency airway interventions compared to other airway management techniques?

Succinylcholine and other neuromuscular blocking agents provided for more successful intubations and a lower rate of complications. The use of RSI in the out of hospital environment showed increased mortality and delayed time of transport without improved intubation success rates as compared to those patients transported to the hospital using alternative airway management techniques.

2. What is the preferred preoxygenation technique for RSI?

All techniques used 100% oxygen prior to the induction of anesthesia. Both tidal volume ventilation and 8 deep breaths provided similar improvement in oxygen saturation during the apneic period following induction. The 4 deep breath technique was less successful.

3. Should all drugs be rapidly administered during RSI?

No studies were found that compared the consequences of titrating induction drugs as compared to the rapid administration of a preselected amount of induction drugs for RSI.

4. Which is the best induction drug for RSI?

Studies did not find any single induction drug that was ideal for every patient. Other studies showed that successful intubation was more likely with thiopental, methohexital, or propofol compared to a decreased success rate with etomidate, ketamine, or midazolam. Additional studies suggested that thiopental was the single best overall induction drug.

5. Which muscle relaxant should be used for RSI?

Succinylcholine has historically been the choice for RSI due to its rapid onset and short duration. Some studies have found the benefit of succinylcholine’s short duration to be inconsequential in regards to a patient’s ability to resume spontaneous ventilation before critical oxygen desaturation was reached. This theory was not supported in most studies.

Some providers have recommended the use of non-depolarizing agents in order to avoid succinylcholine related complications.  Although succinylcholine >1.0mg/kg provides excellent intubating conditions more often than rocuronium 0.6-0.7mg/kg, higher doses of rocuronium (0.9-1.2mg/kg) have been shown to have an equivalent onset and excellent intubating conditions similar to succinylcholine.

6. Should adjuvant drugs be routinely employed during RSI?

Opioids have been used during RSI in conjunction with other drugs to suppress the hemodynamic effects of sympathetic stimulation. They can also provide better control of intraocular and intracranial pressures. Lidocaine has also been suggested as an agent used both intravenously and topically in the airway to suppress the sympathetic response. Studies of lidocaine used in this manner have provided conflicting evidence. Esmolol, a short acting beta blocker has been shown to effectively suppress the negative response to sympathetic stimulation during intubation.

7. Should cricoid pressure be used routinely in all patients undergoing RSI?

Although cricoid pressure has been considered an important part of RSI, no evidence was found to support or contradict its effectiveness. Because of anecdotal evidence and expert opinion, cricoid pressure has become a standard of care even without scientific evidence. Studies using radiologic imaging indicated that as many as half of the cricoid pressure maneuvers evaluated were inadequate because of lateral displacement of the esophagus or airway occlusion.

8. Should bag and mask ventilation be routinely avoided during RSI?

It is thought that positive pressure ventilation prior to rapid sequence intubation increases the risk of regurgitation and aspiration. However, the review could not find any evidence to support this theory. Proper positive pressure ventilation should produce airway pressures below 20 cm H2O and is not likely to increase the risk of aspiration. Positive pressure ventilation with 100% can reduce the risk critical hypoxia during apnea.

Conclusion            The review of literature does not support the routine use of Rapid Sequence Induction to reduce the risk of aspiration. It is recommended only in cases where the risk of aspiration is moderate or high, and different components of the technique should be altered to fit the situation. It is recommended that muscle relaxants be used to improve intubation conditions; however the routine use of succinylcholine over rocuronium is not recommended. A single induction drug could not be recommended and the rapid administration of drugs should be avoided in hemodynamically vulnerable patients. The use of pre-oxygenation by either 3 minutes tidal volume ventilation or 8 deep breaths should be utilized. Finally, because there does not appear to be any substantial risk, and there might be benefits, routine use of cricoid pressure is still recommended. However, if it should distort the airway it is acceptable to release cricoid pressure.

Comment

Many health care providers routinely use Rapid Sequence Induction (RSI) when a risk of aspiration exists. The accepted technique is to have the patient spontaneously breath 100% oxygen, rapidly administer a pre-calculated dose of induction drug with succinylcholine, apply cricoid pressure, and intubate the trachea.  This is often done without consideration to the risks of such a procedure because of a misplaced theory, in my opinion, that aspiration prevention is a priority over other risk considerations. I really enjoyed reading this review and the author’s comments concerning the routine use of RSI. I can remember vividly the clinical staff instructions to me in school concerning RSI. They all seemed convinced that the technique was a life saving maneuver that had to be used in every patient that was at risk of aspiration. The more interesting lecture was the one when we were told that for a variety of reasons, all patients were at risk of aspiration. When I asked why we did not use RSI for all patients in that case, I was told that we probably should. Now a review of 40 years of medical literature does not provide any scientific evidence to support the routine use of RSI.

I have always felt that the practice of anesthesia is as much of an art as it is a science, and in the absence of scientific evidence we must use our best judgment and balance the risk and benefits of any technique to fit the individual patient and situation. I have always recognized the risks of the rapid administration of very powerful drugs, the often ineffective use of cricoid pressure, and the counter intuitive nature of not ventilating an apnic patient. This review supports the use of judgment as opposed to the routine use of any technique. It is critical that the provider understand the impact that a drug or technique might have on a patient and balance the risks and benefits to best fit the situation.

I do not agree with the suggestion that there is no clear indicated role for the use of midazolam in RSI. Midazolam, in combination with appropriate agents to suppress sympathetic response, provides for less patient recall during a potentially frightening experience as well as using the powerful synergistic effects of midazolam to reduce the effective doses of other drugs. In addition, I do not agree that cricoid pressure does not have any apparent risk and that it should be routinely used. Cricoid pressure applied prematurely can stimulate the airway and increase the risk of retching, it can delay intubation, and it is not always necessary. The bottom line is that a good provider uses good judgment, and I think this review supports that view.

 

Steven R Wooden, MS, CRNA

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008




General

Wong PF, Kumar S, Bohra A, Whetter D, Leaper DJ


 

Randomized clinical trial of perioperative systemic warming in major elective abdominal surgery

Br J Surg 2007;94:421-426

Wong PF, Kumar S, Bohra A, Whetter D, Leaper DJ

 

Abstract

Purpose            The purpose of this study was to determine if ‘active’ warming of patients pre-operatively, intra-operatively, and post-operatively with a conductive carbon polymer mattress (in addition to standardized forced-air and fluid warming during surgery) would prevent hypothermia and therefore reduce negative outcomes related to hypothermia, compared to the use of the customary intra-operative warming modalities alone.

Background            Hypothermia in the surgical setting is defined as a core body temperature less than 36 degrees centigrade. The body’s temperature is determined by the balance between heat loss and heat gain.  Anesthesia itself causes hypothermia due to its action on thermoregulatory control mechanisms in the body.  Exposure to a cold external environment, such as the operating room proper, is also a major cause of heat loss.  The adverse effects of intra-operative hypothermia are numerous and include:  prolonged duration of drug action, coagulopathies, myocardial dysrhythmias, ischemia, and increased incidence of post-operative surgical site infections.  Previous research has demonstrated that intra-operative localized and systemic warming reduces peri-operative complications.  This study placed emphasis on extending the ‘warming period’ to include the pre-operative and immediate post-operative time frames using a warming mattress, with a goal to assess whether or not extension of the warming period was efficacious in preventing hypothermia.

Methodology            This was conducted as a randomized controlled clinical trial.  Patients scheduled for elective major abdominal surgery requiring bowel resection were consented to participate; all patients were placed on an Inditherm Warming Mattress (see notes) 2 hours prior to transfer to the operating room.  The experimental group had the mattress turned on for 2 hours prior to surgery, kept on during surgery, and up to 2 hours post-operatively. Control group patients were placed on the mattress but it was not turned on at any time period.  All patients received a forced air warming device and fluid warming during the surgical procedure as well as a standardized anesthetic.  Temperatures were measured before and immediately after surgery using a tympanic thermometer. During surgery temperatures were measured continuously with a nasopharyngeal probe.  Data was collected regarding patient demographics as well as all other important intra-operative variables such as surgical time, blood loss, need for transfusion, etc.  Additional data was gathered by an independent observer unaware of the group assignments.  Patients were evaluated on their surgical wounds, wound healing or complications daily during hospitalization and again at 6-8 weeks following surgery.  The operating surgeons determined day of discharge for each patient; timing was based on routine surgical considerations including any wound infections or problems with post-operative recovery.

Result            During a 14 month period, 103 patients were recruited into the study.  Fifty-six were enrolled in the control group and 47 in the peri-operative warming (experimental) group. Demographic data did not differ statistically between groups.   The great majority of the patients had major abdominal surgery for colorectal cancer and right hemi-colectomy was the most common procedure performed. Upon culmination of the pre-operative systemic warming, the patients in the experimental group demonstrated significantly higher temperatures (p<0.001) compared with the control group.  Additionally, the experimental group exhibited higher temperatures 2 hours after surgery but this was not statistically significant.   The median time for the surgical procedure was comparable between groups; this was also true of the total anesthesia time.  While the amount of intravenous fluid infused during surgery and urine output was similar between groups, patients in the warming or experimental group had statistically significantly less blood loss than the control group.  The most common complication observed post-operatively was surgical-site infection, followed by pneumonia.  Significantly fewer patients in the experimental group developed any complications compared with the control group (p=0.027).

Conclusion            In this study, expanding the warming period (with use of the warming mattress) to 2 hours pre-operatively and up to 2 hours post-operatively demonstrated significance in terms of less total blood loss as well as fewer total complications post–operatively.

Comment

We all know and clearly understand why surgical outcomes are poor when the patient is not maintained in a normothermic state.  Yet with all the knowledge we have acquired in understanding the physiologic responses to hypothermia and with the plethora of devices that we have access to use, we still struggle daily as anesthesia providers trying to maintain a state of normothermia for our patients.  While that seems perplexing for the more routine surgical procedures, there do exist those times when total body exposure is necessary for a prolonged period of time, and fluid-warming is the only way to actively warm the patient.  It simply isn’t efficacious.  This polymer mattress appears to have great promise, especially for those procedures that mandate the total exposure, and it is ‘user friendly’.  I encourage everyone to access the website and learn more about this device.

 

Mary A. Golinski, PhD, CRNA

 

To learn more about the Inditherm warming mattress, which is a conductive carbon polymer mattress, access their website at www.inditherm.com

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008





Levy J H, Tanaka K A, Dietrich W


 

Perioperative Hemostatic management of patients treated with vitamin K antagonists

Anesthesiology 2008;109:918-26

Levy J H, Tanaka K A, Dietrich W

Abstract

Purpose            The purpose of this article was the review of available clinical options for the reversal of common oral anticoagulation therapy.

Background            Anesthesia providers are confronted with an increased number of patients being treated with oral anticoagulants such as warfarin. Warfarin acts as a vitamin K antagonist inhibiting the actions of factors II, VII, IX, and X, and proteins C and S preventing the binding of Calcium ions on negatively charged phospholipid surfaces. The therapeutic benefits are great, but potential hemorrhagic complications exist because of the narrow therapeutic range of the drug. The target therapeutic range of warfarin is an international normalized ratio (INR) of 2.0 to 3.0. The target is sometimes difficult to reach and maintain because of various metabolic, physiologic and dietary factors that influence the uptake, distribution, and clearance of the drug. Approximately 4% of patients treated with oral anticoagulation therapy develop major bleeding problems. The potential of hemorrhagic problems for patients on oral anticoagulation therapy poses a particular risk for surgical patients.

Warfarin is routinely discontinued 4 days prior to surgery with a goal of reducing the INR to 1.3-1.5 in some cases, and normalizing it to near 1.0 when the risk of thrombolytic problems is less likely. When a surgical patient presents with an unacceptably high INR and the procedure cannot be delayed, rapid reversal of anticoagulation may need to be considered.

Result            Therapies available for the reversal of warfarin include holding warfarin therapy, the administration of vitamin K, fresh frozen plasma (FFP), prothrombin complex concentrates (PCC), and recombinant active factor VII (rFVIIa).

Withholding warfarin therapy may take up to 4 days to normalize INR while the administration of vitamin K will take 4-5 hours intravenously and 24 hours orally. These therapies should not be considered for the rapid reversal of warfarin therapy. In addition to the slow onset of reversal, high doses of vitamin K have been associated with a 3% incidence of warfarin resistance after its administration. Specific coagulation factors such as rFVIIa  are indicated for rapid reversal when those factor deficiencies are specifically known. The risk of administration of these specific factors is thrombolitic complications such as myocardial infarction. FFP is the most commonly used product for the rapid reversal of warfarin. It is approved in the United States for such use but carries the risks of viral infections, volume overload, and transfusion related acute lung injury (TRALI).

PCC has been used in Europe for years for rapid reversal of warfarin therapy, but is only approved in the United States for the treatment of hemophilia. Its “off label” use in the rapid reversal of warfarin therapy is being recommended by the American College of Chest Physicians because it is less likely to cause viral infections such as hepatitis, herpes, influenza, West Nile, and other potentially deadly viruses. It is also more concentrated than FPP so volume overload and TRAILI are less likely to occur with PCC when compared to FFP. The primary concern of PCC is the increased possibility of thrombogenic events such as myocardial infarction, pulmonary embolism, disseminated intravascular coagulation, and deep vein thrombosis. A study comparing the mean INR correction times between PCC and FFP showed that PCC normalized INR in an average of 41 minutes compared to 115 minutes for FFP.

Conclusion            Anesthesia providers are finding more patients presenting preoperatively with an elevated INR because of warfarin therapy. Rapid reversal therapy in the United States continues to be the administration of FFP. However, the American College of Chest Physicians is recommending the “off label” use of PCC instead because of its more rapid onset and fewer risks.

 

Comment

Rural providers are generally fortunate to work in environments where the emergency reversal of warfarin therapy is rarely necessary, but it does occur and may occur more frequently in the future. For that reason it is important to periodically review the therapies, risks, and benefits of warfarin reversal because it is true that we are finding more patients being treated with warfarin and some of those patients are presenting for emergency surgery. I found myself in a situation a few months ago when a patient admitted for an emergency appendectomy presented with an INR in excess of 4.0. The surgeon suggested that we give the patient vitamin K and proceed with surgery immediately. I reminded the surgeon that vitamin K is very slow to reverse warfarin therapy so we checked an INR an hour later and it was actually higher. After the infusion of FFP and 3 hours of restraint, the INR was normalized and we proceeded with a successful surgery.

I was reminded during this event that there are several reasons why an INR would be inaccurate. They included sampling problems with the Prothrombin Time (PT), reagent problems, the effects of lupus on some reagents, and lack of reliability of INR values above 4.5. Even being confronted with this information, I found no reason to proceed with surgery until we had some verification that hemostasis would not be a problem.

 

Steven R. Wooden, MS, CRNA

 

 

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008




Pharmacology

Murphy G, Szokol J, Marymont J, Greenberg S, Avram M, Vender J


 

residual neuromuscular blockade and critical respiratory events in the postanesthesia care unit

Anesth Analg 2008;107:130-137

Murphy G, Szokol J, Marymont J, Greenberg S, Avram M, Vender J

Abstract

Purpose            The purpose of this research was to determine the frequency of critical respiratory events (CREs) in the post anesthesia recovery room (PARR) after general anesthesia. A secondary purpose was to determine how many of these critical respiratory events were related to, or highly correlated with, insufficient reversal of neuromuscular blockade.

Background            Residual neuromuscular blockade remains a problem for patients’ post-general anesthesia when neuromuscular blocking agents were used. Many still suffer from inadequate reversal of neuromuscular blocking agents, despite the use of techniques clearly demonstrating efficacy in limiting the degree of residual paralysis. Up to 64% of patients exhibit signs of inadequate neuromuscular recovery on arrival to the PARR. The clinical significance, or how this impacts the safe recovery of these individuals, is less clearly understood.

Numerous studies conducted on volunteers have demonstrated that train-of-four (TOF) ratios  < 0.70-0.90 (see notes) are associated with upper airway obstruction, inadequate recovery of pulmonary function, reduced pharyngeal muscle coordination, increased risk of aspiration, and an impaired hypoxic ventilatory response. Nevertheless, the clinical significance in terms of outcomes, remains unclear. Unfortunately, evidence to support the position that patients do better in the PARR clinically when their train of four ratio is 0.80 or greater compared with ratios <0.50 is lacking, even though we clearly understand the physiologic effects of residual neuromuscular blockade. (See notes section for operational definitions of critical respiratory events).

Methodology            This study was conducted as a quality assurance project. Written informed consent was not needed, however IRB approval was obtained. A case-control study design with prospectively defined cases was performed. During the study period, and with the primary outcome variable being a ‘critical’ respiratory event, each case was paired with selected control patients not exhibiting signs of a CRE for comparison.

The cases selected consisted of all patients who received a general anesthetic and who showed signs of a critical respiratory event in the PARR within 15 minutes of arrival. A standardized data collection sheet using a check box format with a comprehensive listing of patient data and of the CRE was completed for each patient who received an anesthetic. The nurses in the PARR were extensively trained about the project and the respiratory outcomes of interest to be identified. If a critical respiratory event was identified by the PARR nurses, a study investigator was immediately notified. The study investigator validated the nurses’ identification of the event. If the investigator agreed that the patient showed signs and symptoms of a CRE, the anesthesia record was reviewed and the TOF fade ratios were immediately measured using a quantified acceleromyography unit.

Patients were categorized into 1 of 3 groups on the basis of the TOF data. A TOF ratio <0.90 constituted ‘acceptable recovery.’ A TOF ratio between 0.70 and 0.90 constituted mild to moderate blockade. A TOF ratio <0.70 constituted severe blockade associated with an increased risk of respiratory complications.

The comparison groups were selected using a methodology that identified those who underwent general anesthesia but did not develop a CRE in the PARR. The controls (comparison group) consisted of patients who also received a neuromuscular blocking agent during the same time period and the cases were matched by age, gender, and surgical procedures. The PARR nurses were instructed to contact an investigator as soon as a control patient arrived in the recovery room. Absence of signs of a CRE was validated and TOF values were measured on each of the control patients also using the acceleromyography unit. Each CRE and TOF ratio (and any interventions needed) were documented and compared with the appropriate control and analyzed clinically and statistically.

Result            Data were collected on 7,459 patients during a one year study period. The incidence of CREs was 0.8% or 61/7,459 patients. The critical events observed most often were seen in those who had non-abdominal general surgery (24.6%), followed by orthopedic surgery (18%), and thoracic surgery (18%). The most frequently observed CRE in these 61 patients was severe hypoxemia (59%), followed by upper airway obstruction (34.4%), and mild hypoxemia (19.7%). Other CREs observed included:

§     Inability to breathe deeply (11.5%)

§     Symptoms of respiratory muscle weakness (9.0%)

§     Signs of respiratory distress (8.2%)

§     Reintubation (6.2%)

In 34.4% of the cases, there were multiple CREs. Eight patients required reintubation and three of the eight patients were reintubated urgently before train-of-four data could be measured.

Demographic data (which was extremely comprehensive) included age, gender, type of surgical procedure, length of surgical procedure and specifics of the anesthetics (including neuromuscular blocking agents used and reversal agents used, fluid administration, narcotic use, etc) were similar between the groups. The researchers were only able to ‘match’ 42 ‘control group’ patients to the CRE group. Numerous providers, including learners, administered the anesthetics and since a large group of providers administered the anesthetics, they were not considered to be a variable in the analysis.

Significant neuromuscular blockade (TOF ratio: 0.62 + 0.20) was observed in the majority of the cases with a CRE. By contrast, nearly complete recovery from neuromuscular blockade was observed in the control group (TOF ratio values of 0.98 + 0.07). This difference was highly statistically significant (p<0.0001). Acceptable neuromuscular blockade recovery, or a TOF ratio >0.90, was seen in 90.5% of those without any evidence of a CRE in the recovery room, versus the CRE group where only 9.5% had a train of four ratio >0.90. The probabilities of upper airway obstruction, severe hypoxemia, and any hypoxemia were found to be related to residual neuromuscular blockade.

Conclusion            Incomplete recovery of neuromuscular blockade was a major causative factor in critical respiratory events seen in the recovery room for this particular study. While opioids and inhalation agents can contribute to upper airway dysfunction it was felt that clinicians in general lacked knowledge relating to clinical assessment of neuromuscular recovery and infrequently monitored the degree of blockade in the peri-operative period. Providers who did monitor neuromuscular blockade used a traditional ‘nerve stimulator’ and the authors suggested that using a quantitative neuromuscular monitoring device, such as the acceleromyography unit, may reduce the incidence of residual paralysis and CREs in the early recovery period

Comment

It is extremely unfortunate that we are still struggling with critical respiratory events in the post anesthesia care unit related to residual neuromuscular blockade!  It is an accepted standard of care that we monitor neuromuscular blockade when neuromuscular blocking agents are used. There is no excuse for not monitoring the effects of these drugs and for not vigilantly ensuring all patients meet extubation criteria, above and beyond what the monitors demonstrate. I thought the authors did a respectful job of showing that patient care remains compromised and is at times related to not adhering to a standard that promotes the use of a very simple and basic process. The goal – to make sure no residual neuromuscular weakness is present via an appropriate monitor and additional important clinical signs. The only way we are going to change practice is to continually show the evidence as this study did, that drives the point home. I challenge all providers to reassess their own practice and have open and constructive dialogue with their colleagues regarding the use of neuromuscular blocking drugs, reversal agents, appropriate monitoring, and clinical signs that must be present before extubation. It is for the safety of practice and for enhancing quality anesthesia care.

 

Mary A. Golinski, PhD, CRNA

 

A review of train of four ratios:

§     Using a neuromuscular blockade monitor, the muscle response after administration of a neuromuscular blockade agent can be quantified with different parameters depending on the type and the level of neuromuscular block

§     Train-of-four ratio (TOF%) is the ratio of the fourth muscle response to the first one. TOF% indicates fade in non-depolarizing block. When fade increases, not all four stimuli produce a measurable response and TOF% cannot be calculated

§     TOF Count, i.e. the number of detected muscle responses, then indicates the level of neuromuscular block. When depolarizing agents are used, no fade occurs, and the height of the four responses indicates the level of block

Operational definitions of a CRE:

§     Upper airway obstruction requiring an intervention (jaw thrust, oral or nasal airway)

§     Mild to moderate hypoxemia (oxygen saturation 93% to 90% on 3L nasal cannula that was not improved after active interventions (increasing the oxygen flows, application of a high flow face mask, verbal commands to breathe deeply, tactile stimulation)

§     Severe hypoxemia (oxygen saturation <90%) on 3L nasal cannula that was not improved after active interventions (same as above)

§     Signs of respiratory distress or impending ventilatory failure

§     Inability to breathe deeply when requested

§     Patient complaining of symptoms of respiratory or upper airway muscle weakness

§     Patient requiring reintubation

§     Clinical evidence or suspicion of pulmonary aspiration

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008





Bekker A, Sturaitis M, Bloom M, Moric M, Golfinos J, Parker E, Babu R, Pitti A


 

The effect of dexmedetomidine on perioperative hemodynamics in patients undergoing craniotomy

Anesth Analg 2008;107:1340-1347

Bekker A, Sturaitis M, Bloom M, Moric M, Golfinos J, Parker E, Babu R, Pitti A

Abstract

Purpose            The purpose of this study was to determine if adding the alpha 2 agonist Dexmedetomidine (DEX) to a standardized anesthetic regime during neurosurgical procedures prevented the often harmful variability in the hemodynamic profile of the patient.

Background            Acute fluctuations of any type in arterial blood pressure can be extremely dangerous for those undergoing neurosurgical procedures. Intracranial hemorrhage can be the result of an acute elevation in blood pressure and the outcomes of the individual can be severely compromised as a result. Irrespective of the most modern management techniques and pharmacologic interventions available, hemodynamic instability is challenging to the anesthetist. Dexmedetomidine is an alpha 2 agonist that possesses sedative, sympatholytic, and analgesic properties. It may have potential as an adjunct agent for neurosurgical cases to improve hemodynamic stability.

Methodology  This study was conducted as a randomized, controlled, double-blind clinical trial. After IRB approval, patients 18-65 years of age who were scheduled for elective resections of brain tumor, intracranial vascular lesions, or an epileptic focus, were consented to be randomized into one of two groups:  sevoflurane-opioid-DEX or sevoflurane-opioid-placebo. Standard monitoring and a BIS depth of anesthesia monitor was used and a standardized anesthetic drug regime was followed. Infusion of the study drug (dexmedetomidine) or a placebo was started after induction of general anesthesia. Patients in the DEX groups received an initial loading dose of 1 mcg/kg of DEX over 10 minutes, followed by a continuous infusion of 0.5 µ/kg/hour. The placebo group received an equivalent volume of normal saline. The loading doses of the study drugs took place before any cranial pinning was done, and fentanyl boluses were administered before pinning and before skin incision. Narcotic boluses, sevoflurane, and any needed vasoactive substances were administered at the discretion of the anesthesia provider as needed. Inhalation agent concentration was titrated to maintain a BIS reading of 50 until the dura mater was closed. The DEX or placebo infusions were stopped 20 minutes before the end of the procedure. The following hemodynamic events were considered to require treatment and as primary outcome variables:

  • Hypotension:  SBP <90 mm Hg
  • Hypertension:  SBP >130 mm Hg
  • Bradycardia HR <50 bpm
  • Tachycardia HR > 90 bpm

The anesthesia provider was permitted to treat hemodynamic events by customary methods, i.e. adjust dose of inhalation agent; give ephedrine, neosynephrine, or beta blockers; administer narcotics; etc. Data were analyzed to assess for demographic differences between the two groups, as well as any pre-operative medications that were used (anti-hypertensives: beta blockers, calcium channel blockers and ACE inhibitors).

Mean pre-induction blood pressures and heart rates were recorded and compared with the arterial blood pressure and heart rate during the operative and post-operative period.

Result            Seventy-two patients were recruited for the study. The two groups were comparable in terms of age, gender, weight, ASA physical status, history of hypertension, and type of surgery

Pre-induction heart rate was higher in the DEX group but this was not clinically significant. Of significance was the Area Under the Curve Systolic Blood Pressure (see notes) that exceeded the target value of 130 mm Hg. This was significantly less for patients in the DEX group. Heart rate was within the goal range for all patients, although slower for DEX group (P = 0.0277). Average end tidal sevoflurane concentrations and BIS values were similar between groups. Mean remifentanil infusion dose used (part of the anesthetic maintenance for both groups) was lower in the DEX group (p<0.05). Significantly fewer patients in the DEX group required pharmacologic intervention to control blood pressure intraoperatively. Of interest was the fact that more patients in the placebo group required treatment with ephedrine (P<0.05). The duration of surgery and emergence time were similar in both groups. While patients in the DEX group had fewer hypertensive episodes (p<0.05), there was no difference in the actual number of hypertensive episodes per hour. Neither group of patients required treatment for bradycardia.

Conclusion            The study was conducted to assess whether or not adding DEX to a commonly administered anesthetic regimen improved hemodynamic stability in patient undergoing craniotomy. It demonstrated that a continuous dexmedetomidine infusion appeared to stabilize arterial blood pressure without affecting heart rate. It also improved hemodynamic stability in the recovery room as well as shortened the recovery room length of stay, compared to patients who received placebo.

 

Comment

This was a very ‘clean’ study; conducted in a straight forward manner with tremendous scientific merit. Controlling perioperative hemodynamics under conditions that are challenging at best, yet absolutely necessary or patients will have poor outcomes, are very much a part of our responsibilities. Dexmedetomidine is showing itself to be a pharmacologic adjunct that may improve patient safety and outcomes. I look forward to further studies assessing the efficacy of this newer alpha 2 agonist.

 

Mary A. Golinski, PhD, CRNA

 

Notes:            The hemodynamic data was obtained from the standard monitoring devices and the anesthesia gas machine. Data was acquired at a frequency of 30 samples per minute (patients all had arterial lines for BP monitoring). ‘Hemodynamic stability’ was assessed by comparing the number of times a recorded systolic blood pressure was above 130 mm Hg or below 90 mm Hg. A database was stored and data was appropriately manipulated for analyzing purposes. Global hemodynamic stability using the coefficient of variability of systolic blood pressure and heart rate. The coefficient of variability was the ratio of the standard deviation of the mean to the mean. It is a statistic that compares the degree of variation from one set of data to another.

Areas under the curve greater than 130 mm Hg or below 90 mm Hg were used to analyze the overall efficacy of an anesthetic in keeping systolic blood pressure and heart rate close to the target or goal.

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008




Quality Improvement

Loftus R, Koff M, Corey B, Schwartzman J, Thorum V, Read M, Wood T, Bearch M


 

Transmission of pathogenic bacterial organisms in the anesthesia work area

Anesthesiology 2008;109:399-407

Loftus R, Koff M, Corey B, Schwartzman J, Thorum V, Read M, Wood T, Bearch M

 

Abstract

Purpose            The purpose of this study was to identify the risk of an anesthesia provider's cross contaminating patients during the normal course of anesthesia care.

Background            Antibiotic resistant infections continue to increase in both the hospital setting and community environment. The fact that 10% of all hospital admissions result in a nosocomial infection is alarming. Little is known about the role the anesthesia environment plays in spreading infection. Contributing to the possibility that the anesthesia environment does spread infection from patient to patient is the routine use of non-disposable anesthesia equipment, pressure to turn over the operating room rapidly, limited disinfection between cases,  practices that can potentially aerosolize bacteria, and an association between anesthesia and immune suppression.

Methodology            The study hypothesized that infection of the anesthesia work area and contaminated intravenous stopcock sets were related. In addition, agent flowmeter dials and pressure limiting dial on the Datex-Ohmeda anesthesia machines were identified as the most likely source of bacteria because of consistently high bacterial counts on these devices. Over 6 days, the first person in each of 61 operating rooms at Dartmouth-Hitchcock Medical Center was used as a baseline source of bacteria. The anesthesia dials in question were terminally cleaned prior to the first patient entering the operating room. These first patients were given a sterile intravenous set with stopcocks and a baseline culture was taken from the stopcocks upon entry into the operating room. The stopcocks were cultured again when the patient left the operating room. A number of variables were also evaluated including anesthesia provider level of training, surgical procedure, duration, anesthesia type, physical status, patient age, and patient sex. All patients with contaminated stopcocks were evaluated postoperatively for the development of a nosocomial infection and associated mortality. In addition, patients who developed nosocomial infections were evaluated for factors that might have contributed including temperature, glycemic control, oxygen issues, and prophylactic antibiotic therapy.

The primary outcome was the presence of bacteria on a stopcock upon leaving the operating room when none was present upon entry. Secondary outcomes included the number of bacteria colonies per surface area sampled (CPSS), bacterial resistance, as well as patient morbidity and mortality.

Result            Cultures of the anesthesia relief dial and flowmeter dials revealed contamination of these devices unassociated with the length of the initial procedure. Contamination on these devices was found in procedures lasting as little as 4 minutes. Cultures from 32% of the patient’s stopcocks at the end of surgery showed potential pathologic bacteria. When comparing the bacteria colonies per surface area sampled (CPSS) on anesthesia work surface dials, it was found that the probability of stopcock contamination was 20% when the work surface CPSS was 10, and increased to 50% when the CPPS was greater than 100. None of the other variables including anesthesia provider level of training, surgical procedure, duration, anesthesia type, physical status, patient age, and patient sex contributed significantly to the risk of contamination. In one case Vancomycin Resistant Enterococcos (VRE) and in two cases Methacillin Resistant Staphylococcus Aureus (MRSA) was found on anesthesia work surfaces and patient stopcocks. Of the patients with contaminated stopcocks, 25% developed nosocomial infections. Of the 3 patients who had stopcocks that cultured positive for VRE or MRSA, 2 died postoperatively. When evaluating the impact that temperature, glucose control, and prophylactic antibiotic therapy had on these patients, there was no significant difference found.

Conclusion            The prevalence of bloodstream infection related to central venous catheter contamination is reported to be between 3% and 7% with a mortality rate among those patients as high as 15%. The average increased cost of each nosocomial infection episode has been reported to be $9,000. This study indicated that contamination of anesthesia work surfaces can occur quickly, is unrelated to case duration, and because of the relationship between stopcock and anesthesia machine dial contamination it is most likely the hands of the provider that are the source of bacteria transfer. The study demonstrated a relationship between the anesthesia machine contamination and patient nosocomial infections.

 

Comment

Nosocomial infection is a preventable problem leading to many unnecessary deaths, morbidity, and significant increase in health care costs. The Center for Medicare and Medicaid Services has identified prevention of nosocomial infection as a priority. They have initiated a payment incentive plan for providers which addresses prevention of infection. They have also indicated that in the near future they will no longer pay for procedures that result in a nosocomial infection. This policy has the potential to have a dramatic and negative financial impact on hospitals, but it also increases the incentive for hospitals to aggressively pursue preventative measures. I believe this study indicates correctly that anesthesia providers and their equipment might play a role in the transmission of infectious material between patients. With that in mind, we might look more closely at what can be done by anesthesia providers to reduce or prevent infection. Although we use far more disposable items than we did in the past, there are still a number of tools at our workstations that have the potential to carry bacteria from patient to patient. Something as simple as a pen can be the source. How many of us dispose of our pens after each case? Laryngoscope handles, arm straps, scrubs, and numerous items placed on our carts and machines throughout the day are just a few of the potential sources. How far do we go to reduce contamination? I doubt we will ever have disposable machines, but you never know when the cost of such an initiative might be worth the effort. When I think back to my education 28 years ago, I can remember reusable endotracheal tubes, anesthesia circuits, needles and syringes. Although we “decontaminated” these items between cases, I wonder today just how effective we were at preventing patient infections. Perhaps 28 years from now we will be thinking the same way about today’s practices. Just like safe anesthesia practice, I believe the best way to address this issue is with vigilance. Be aware of your environment and avoid practices that can potentially infect the patient, use good disinfection practices, and wash your hands regularly.

 

Steven R Wooden, MS, CRNA

© Copyright 2008 Anesthesia Abstracts · Volume 2 Number 8, December 31, 2008