ISSN NUMBER: 1938-7172
Issue 7.11 VOLUME 7 | NUMBER 11

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Penelope S Benedik, PhD, CRNA, RRT
Mary A Golinski, PhD, CRNA
Alfred E Lupien, PhD, CRNA, FAAN
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 2013

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

OBSTETRIC ANESTHESIA
Combined spinal and epidural anaesthesia and maternal intrapartum temperature during vaginal delivery: a randomized clinical trial
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What factors affect intrapartum maternal temperature? A prospective cohort study: maternal intrapartum temperature
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PEDIATRIC ANESTHESIA
Surgical outcome in children undergoing hypospadias repair under caudal epidural vs penile block
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PHARMACOLOGY
Intraoperative methadone improves postoperative pain control in patients undergoing complex spine surgery
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Who is at risk for postdischarge nausea and vomiting after ambulatory surgery?
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The 50% and 95% effective doses of desflurane for removal of the classic laryngeal mask airway in spontaneously breathing anaesthetized adults
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Obstetric Anesthesia
Combined spinal and epidural anaesthesia and maternal intrapartum temperature during vaginal delivery: a randomized clinical trial

Br J Anaesth 2011;107:762-8

de Orange FA, Passini R, Amorim MMR, Almeida T, Barros A


Abstract

Purpose The purpose of this study was to compare the incidence of intrapartum fever in women who received combined spinal-epidural analgesia (CSE group) for labor to women who received only non-pharmacologic methods of analgesia (control group).

 

Background Epidural analgesia during labor has been reported to be associated with intrapartum maternal fever. The exact mechanism is unclear; however, epidural analgesia may contribute to changes in maternal thermoregulation. The problem with increased maternal temperature secondary to epidural analgesia is that this may result in unnecessary maternal and neonatal evaluation to eliminate the possibility of infection. CSE has become a popular technique for labor analgesia; however, the relationship between CSE use and maternal fever has not been evaluated. The investigators of this study wanted to determine if there was a relationship between CSE and increased maternal intrapartum temperature and fever.

 

Methodology This was a prospective, randomized, clinical trial of 70 parturients undergoing vaginal delivery to examine the incidence of intrapartum fever. Inclusion criteria included singleton pregnancy, full-term fetus, and cervical dilation of 3-6 cm. High risk pregnancies and women with a preexisting fever or who were on antibiotics were excluded.

 

Parturients were randomized to receive either Combined Spinal Epidural analgsia or no neuraxial or intravenous analgesia. The CSE group received 2.5 mg of 0.5% hyperbaric bupivacaine with sufentanil 5 µg, followed 30 minutes later with a 5 mL bolus of bupivacaine 0.05% with sufentanil 0.2 µg/mL, then intermittent boluses every 30 minutes as needed. Women in the control group received no neuraxial or intravenous analgesia.

 

All women were monitored hourly and their temperature, blood pressure, heart rate and respiratory rate were recorded. Temperature was measured in the axilla on all patients. The primary outcome was the incidence of maternal fever between the two groups, which was defined as temperature ≥38°C. Secondary outcomes included maternal and neonatal temperature, cesarean delivery rate, instrumental delivery rate, use of oxytocin, duration of the first and second stage of labor, maternal or neonatal infection, need for maternal or neonatal antibiotic therapy, Apgar scores and umbilical cord blood pH. Sample size calculations and statistical analysis were appropriate. A P < 0.05 was considered significant.

 

Result A total of 68 subjects completed the study (N = 34 each group). There were no significant differences in demographics between groups. The average age was 22 with 69% being primaparas at an average 39.2 weeks gestation. The instrumental delivery rate was 11.4% in the CSE group and 0% in the control group (P = NS). The cesarean delivery rate was 11.4% in the CSE group and 20.6% in the control group (P = NS). The duration of the first stage of labor was 85 minutes longer in the control group (P = 0.01).

 

Subjects in the CSE group had a significantly higher incidence of fever (14.3% vs. 0%, P = 0.027). In the CSE group the temperature was significantly higher starting the first hour after CSE placement and continuing until the sixth hour (P < 0.05; Figure 1). There were no cases of chorioamnionitis or signs of maternal infection in either group. No parturient required antibiotic therapy. Apgar scores and cord gases were similar in both groups, and no neonate born to a mother with fever developed neonatal sepsis or required antibiotic therapy.

 

 

Figure 1. Comparison of Temperature

Figure 1

Note. Median (10-90th percentiles).

 

 

Conclusion The use of CSE was associated with a significant increase in maternal temperature and fever. However, this increase was not associated with complications in the mother or neonate.

 

Comment

This is the second study recently to evaluate the relationship between neuraxial analgesia and maternal fever / neonatal outcomes. In a retrospective study, Greenwell et al (1). reported that women who received epidural analgesia and had a temperature >38.3ºC (101ºF) had a 2 to 6 fold increase in neonatal adverse events. In contrast, this randomized clinical trial found no adverse events in any neonate. However, it must be pointed out that the current study sample size was too small to evaluate differences in neonatal outcomes in women who received CSE. A much larger, multi-center, clinical trial would be needed to truly determine if neuraxial analgesia is associated with serious neonatal adverse outcomes.

 

Overall, this was a well-designed clinical trial. It is the first study to examine maternal fever in association with CSE rather than epidural analgesia for labor. The mechanism is most likely similar, and some authors suggest neuraxial analgesia is associated with an inflammatory response with subsequent release of cytokines which contribute to maternal fever. (1) It may be that with CSE the onset of temperature elevation is earlier than with epidural analgesia. The authors of this study report previous investigations have found delayed onset of temperature elevation and fever in women undergoing epidural analgesia for labor.

 

I would have liked to have seen an epidural analgesia group included in this study because it would have helped determine how soon the temperature elevation occurs with these two techniques (CSE vs. epidural). Also I believe a limitation of this study is that temperatures were taken in the axilla as opposed to orally. Nonetheless, I found this to be a good start investigating this phenomenon … but only a start. At this point we are beginning to accumulate data that neuraxial analgesia during labor is somehow associated with maternal fever. We do not yet know if it is the cause of fever and we don’t know if the increase in maternal temperature is harmful in any way.

Dennis Spence, PhD, CRNA


1. Pediatrics. 2012;129:e447-54.


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 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013





What factors affect intrapartum maternal temperature? A prospective cohort study: maternal intrapartum temperature

Anesthesiology 2012;117:302-8

Frölich MA, Esame A, Zhang K, Wu J, Owen J


Abstract

Purpose The purpose of this study was to identify factors associated with noninfectious maternal temperature elevation during active labor.

 

Background Maternal infections are the most common cause of intrapartum temperature elevation. Recent research has suggested an association between epidural analgesia and temperature elevation during active labor. Additionally, some reports suggest intrapartum temperature elevation may be associated with poor neonatal outcomes. There are conflicting results in the literature; some suggesting epidural analgesia may be the cause of maternal fever, while others have not reported this finding.

 

The theories suggested explaining the association between maternal fever and epidural analgesia are based on the concept that epidural analgesia may suppress heat-dissipating mechanisms such as pain-associated hyperventilation, or that epidural analgesia may promote placental inflammatory processes which in turn trigger maternal fever. However, sympathetic blockade from epidural analgesia should result in hypothermia secondary to redistribution of heat from the core to the periphery. Furthermore, other factors besides epidural use may influence temperature changes during labor. For example, prolonged labor in patients receiving oxytocin who have a long time from rupture of membranes to delivery may result in an inflammatory process. This could explain the temperature elevation seen in some parturients.

 

This study sought to evaluate the time course of maternal temperature changes and examine whether or not duration of labor, epidural analgesia, oxytocin dose, body mass index (BMI), or length of time from rupture of membranes where associated with maternal temperature elevation.

 

Methodology This was a prospective cohort study of 81 women scheduled for induction of labor. Patients were excluded if they had conditions that would affect normal temperature regulation, such as chorioamnionitis, or received medications such as acetaminophen, prostaglandins, or ibuprofen; had active cardiac disease, pulmonary disease, or neurologic disease. Epidural analgesia consisted of bupivacaine 0.1% with 2 µg/mL fentanyl administered via patient controlled epidural analgesia using a basal rate of 8 mL/hr and a demand bolus of 4 mL every 20 minutes. Oxytocin was titrated by nurses based on a standard protocol. After rupture of membranes, an intrauterine pressure catheter was placed in all patients. Temperature was measured orally every hour. Statistical analysis and sample size calculation were appropriate.

 

Result A total of 81 patients completed the study. Average labor duration was 14 ± 7 hours, length of rupture of membranes was 8 ± 5.6 hours, and BMI was 34.6 ± 9 kg/m2. Median duration of labor was 8 hours. The majority of patients were white (47%) and then African American (40%). Approximately 56% of patients were GBS positive (Group B Streptococcus). The most common parity (number of vaginal births) was 0 (40%) and next most common was 1 (31%).

 

A mixed linear regression model was used to estimate the temperature slope, or change in temperature per hour. The temperature increased 0.017° C per hour which indicated the temperature increased significantly over time (P = 0.009). Fifty-four percent (54%) of patients had a positive temperature slope (increasing temperature over time) and 46% had a negative temperature slope. Patients with increased BMI had a larger increase in temperature over time (P = 0.0008). Similarly, in patients whose temperatures increased, time from rupture of membranes was associated with a much larger temperature change over time (slope). Total oxytocin dose was not associated with temperature change over time.

 

In patients who received epidural analgesia, temperature slopes were compared for the four hours before and after epidural initiation. No significant difference was found in the temperature slope before or after initiation of epidural analgesia. Epidural analgesia had no effect on the change in temperature over time.

 

Conclusion In this study, induced labor was associated with a small temperature increase over time. Patients with a higher BMI and longer duration from rupture of membranes to delivery were more likely to experience temperature elevations during labor. Epidural analgesia had no effect on maternal temperature.

 

Comment

I thought this was a well done cohort study. Temperature studies are difficult to conduct, and the investigators did a good job of controlling for many of the factors that may confound their results (i.e., excluded patients with chorioamnionitis or those who received prostaglandins or acetaminophen; measured temperature orally). Therefore, this study provides some reassuring evidence to anesthesia providers that epidural analgesia use is NOT associated with increasing temperature during labor.

 

It is probably not surprising that prolonged rupture of membranes was associated with a more pronounced temperature elevation. Prolonged rupture of membranes may trigger an inflammatory response or subclinical infection that probably contributes to the temperature elevation seen. The finding of an association between increasing BMI and temperature elevation is interesting, and it may be that obesity as well contributes to an inflammatory response and secondary temperature elevation, as previous research on obesity has found a link between obesity and inflammation.

 

One limitation of this study was that the investigators did not report the total amount of local anesthetic administered, or whether or not patients required additional top-up boluses of stronger concentrations of local anesthesia for labor analgesia. This could have potentially influenced the results. I also would have liked to have known about the neonatal outcomes. However, this would have required a much larger sample size. Nonetheless, I still think this was a good study that provides us some evidence demonstrating epidural analgesia has no effect on maternal temperature.

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 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013




Pediatric Anesthesia
Surgical outcome in children undergoing hypospadias repair under caudal epidural vs penile block

Pediatric Anesthesia 2012;22:707-712

Kundra P, Yuvaraj K, Agrawal K, Kishnappa S, Kumar LT


Abstract

Purpose The purpose of this study was to compare the success, quality, and complication rate of caudal epidural and penile block when used for postoperative pain relief in children undergoing hypospadias repair.

 

Background Both caudal epidural and penile blocks are common anesthetic techniques used for postoperative pain relief in children undergoing hypospadias repair. Caudal anesthesia continues to be preferred over penile block by most anesthesia providers even though previous studies have indicated that penile block is superior to caudal anesthesia for the following reasons:

  • lower complication rate
  • improved analgesia
  • longer duration of block
  • less peripheral venous engorgement

This study sought to clarify previous studies on the subject.

 

Methodology This was a randomized, double blind study on healthy children ages 4 to 12 undergoing primary hypospadias repair. Children were allocated to one of two groups. Group P contained 27 subjects who received penile blocks for postoperative pain relief. Group C contained 27 subjects who received caudal anesthesia for postoperative pain relief. Both groups received the same preoperative sedation and general anesthesia technique for the surgical procedure. After induction of general anesthesia, the penile block or caudal anesthesia was administered according to the randomization protocol. Penile blocks were administered at the dorsal root nerve with 0.5 mg/kg of 0.25% bupivacaine. The caudal epidurals were administered with the same dose of bupivacaine. In the first 48 hours of the postoperative period, nurses who were blinded to the type of postoperative pain block given to each patient administered intravenous morphine 0.1 mg/kg to patients that reported a visual analog scale (VAS) pain score greater than 5 on a 0 to 10 scale. After 48 hours, patients were given acetaminophen on demand. The differences between groups were analyzed with a two way repeated measure analysis of variance (ANOVA) with significance considered at P < 0.05.

 

Result VAS scores demonstrated that penile blocks provided better postoperative analgesia than caudal epidurals, and this conclusion was supported by less morphine consumption in the penile block group. In addition, the penile blocks lasted significantly longer on average than the caudal epidurals. Penile blocks provided 5-6 hours of postoperative pain relief while the caudal epidurals provided 4 hours. Acetaminophen consumption was similar in both groups for the period 48 hours after surgery. In addition, while there were no failures in the penile block group, there was one block failure in the caudal epidural group. Five patients developed postoperative urethral fistulas, and all of those patients were in the caudal epidural group. 

 

Conclusion This study of children undergoing hypospadias repair demonstrated that penile blocks provided superior and longer lasting postoperative pain relief compared to caudal epidural blocks. All patients who developed postoperative urethral fistula were in the caudal epidural group.

 

Comment

This study asks an interesting question about an issue that occurs in anesthesia as well as other health care settings.  Why do we continue to use a particular technique when evidence suggests that there is a better technique available? In this case, it appears that using a caudal anesthetic for hypospadias repair is less effective and has greater risk of complications than using a penile block. Other studies have supported this conclusion as well.  It is not so much the marginal benefit of pain relief one technique has over the other (6 hours for penile blocks vs 4 hours for caudal epidurals), but the significant postoperative complication of urethral fistula developed by those patients who received a caudal anesthetic. Venous engorgement from peripheral dilatation caused by caudal anesthesia is suggested to contribute to this complication. So why, as the article indicates, do anesthesia providers prefer to use caudal anesthesia for this procedure? This may be an example of providers not keeping up with evidence based practice. This also may be an example of providers using techniques that they are most comfortable with, even though there are other techniques that might have greater benefits with less risk. Regardless of the reason, it is important to periodically evaluate one’s techniques and make an effort to acquire new skills; choosing those that are best suited for the patient instead of clinging to “routine” techniques.

Steven R Wooden, DNP, CRNA


© Copyright 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013




Pharmacology
Intraoperative methadone improves postoperative pain control in patients undergoing complex spine surgery

Anesth Analg 2011;112:218-223

Gottschalk A, Burjeux M, Nemergut E


Abstract

Purpose The purpose of this study was twofold:  1) to explore the efficacy of a single dose of methadone in providing post-operative pain management for those who have major thoraco-lumbar spine surgery, and 2) to asses the side effects related to using methadone in this scenario.

 

Background Methadone is a long-acting opioid frequently administered to those with chronic pain.  It has been limited in its use in the surgical setting as it has great potential to cause unwanted post-operative side effects which include prolonged sedation, respiratory depression, nausea, and vomiting.  The benefits of using methadone following spine surgery are related to its long duration of action. This patient population typically requires large doses of opioids for an extended period of time following surgery. It is postulated that if post-operative pain is managed to the physiologic safety and psychological satisfaction of the patient, the risk for developing complications would be minimized.

 

Methodology The study was carried out as a prospective, single blind, randomized clinical trial. Patients scheduled for elective thoracolumbar spine surgery (n = 30) with instrumentation and fusion, were consented and randomized in to one of two groups:

  • Sufentanil Group: received 0.75 µg/kg initial loading dose of sufentanil before surgical incision followed by sufentanil infusion of 0.25 µg/kg/h
  • Methadone Group: received 0.2 mg/kg subsequent to intubation

Both groups were treated intraanesthetically with a sufentanil bolus of 0.1 µg/kg IV every 2.5 minutes at the discretion of the provider if additional analgesia was needed based on vital signs. Anesthetic induction and maintenance drugs were standardized. Anesthesia was maintained with a propofol infusion; no potent inhalation agent was used.

The sufentanil infusion was discontinued at the time surgical wound closure was initiated.  Patients were extubated based on meeting extubation criteria at the appropriate time.

The following parameters were measured:

  • Pain rating via visual analogue scale
  • Preoperative opioid consumption (in morphine equivalents)
  • Time after surgery to first pain medication
  • Cumulative opioid requirement at 24, 48 and 72 hours postoperatively (in morphine equivalents)
  • Complications defined as:
    • hypotension (MAP < 50 mm Hg)
    • need for vasopressors
    • incidence of respiratory depression
    • respiratory arrest
    • need for naloxone
  • The incidence of hypoxemia or desaturation or the need for supplemental oxygen
  • The incidence of cardiac arrhythmias, MI, PONV and any treatment that was given

 

Results One patient was excluded due to reasons unrelated to the study. Data was collected on 29 patients; Sufentanil Group (n = 16) and Methadone Group (n = 13). Significant findings included:

  • Methadone Group reported less pain after 48 hours after surgery (P < 0.05)
  • Methadone Group patients had lower postoperative opioid requirements (morphine equivalents) at both 48 and 72 hour postoperatively (P < 0.05)

 

There were no significant differences in the demographic profile of the two groups, the specifics related to the surgical/anesthetic techniques (blood loss, blood transfusion, etc), or the incidence of complications and/or side effects.

 

Conclusion Opioid consumption during the first 24 hours postoperatively (measured as morphine equivalents) was not clinically or statistically different between the two groups. However, the administration of a single IV dose of methadone prior to surgical incision controlled postoperative pain significantly better 48 hours postoperatively.  Additionally, methadone reduced opioid requirements significantly 48-72 hours postoperatively. Reported side effects and/or complications (which were minimal in both groups) of those who received methadone were no different in quantity compared to those who received sufentanil.

 

Comment

Typically, those who have extensive spine surgeries present with significant pain prior to surgery, and are very uncomfortable following their surgical procedure. Their pain scores can be very high.  Many of these patients experience hyperalgesia phenomenon.  Providing the proper level of analgesia is an extremely complicated process and while it may be possible to totally alleviate pain with large doses of narcotics, it is these large doses which cause numerous complications, some of which can be lethal.  Numerous case studies have reported post-operative respiratory depression and respiratory arrest in these patients, typically the result of trying to manage pain with high doses of narcotics.  With such large doses of narcotics, it may be impossible to eliminate these side effects, even when preventative drugs are given.  Leaving a patient intubated, ventilated and narcotized due to the inability to manage pain seems antiquated and barbaric yet so does emerging a patient and denying pain medication because of the potential complications.  There has to be a better way.  Here enters methadone, a drug with some unique properties. Methadone can attenuate or even prevent opioid tolerance and it has a long duration of action. These traits are beneficial in this specific patient population.

 

The results of this study were surprising; patients who received methadone derived the greatest benefit between 48 and 72 hours postoperatively - not in the initial 24 hours postoperatively.  The investigators had a meaningful response to this:  Is the primary advantage of methadone not in its ability to provide analgesia, but rather in its ability to attenuate opioid tolerance and hyperalgesia?

 

Mary A. Golinski, PhD, CRNA

Mary A Golinski, PhD, CRNA


Hyperalgesia- A greater than normal sensitivity to pain.

 

Analgesia Tolerance- The phenomenon whereby chronic exposure to a drug diminishes its antinociceptive or analgesic effect, or creates the need for a higher dose to maintain this effect.  The tolerant person is less susceptible to the pharmacologic effects of a drug as a consequence of its prior administration.


© Copyright 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013





Who is at risk for postdischarge nausea and vomiting after ambulatory surgery?

Anesthesiology 2012;117:475-86

Apfel CC, Phillip BK, Cakmakkaya OS, Shilling A, Shi YY, Leslie JB, Allard M, Turan A, Windle P, Odem-Forren J, Hooper VD, Radke OC, Ruiz J, Kovac A


Abstract

Purpose The purpose of this study was to identify risk factors and develop a risk score for postDischarge nausea and vomiting (PDNV) after ambulatory surgery.

 

Background Approximately 25% of all surgical patients will develop postoperative nausea and vomiting (PONV). While there are published consensus guidelines to help identify and treat patients at risk for PONV, further research is needed to identify risk factors for the development of postDischarge nausea and vomiting. This is especially important given that more than 60% of surgeries in the United States are now performed on an ambulatory basis. Having a simplified risk score would help anesthesia providers tailor prophylactic regimens to prevent PDNV in at-risk patients.

 

In this study the investigators examined the incidence of PONV and PDNV. They also identified risk factors and a risk score for the development of PDNV in a group of ambulatory surgery patients. PONV was defined to include the time period from PACU admission until discharge home. PDNV was defined to include the time period from discharge home until 48 hours after emergence from anesthesia.

 

Methodology This was a multicenter study conducted on 2,493 adults at 12 ambulatory surgery centers in academic centers around the United States. All patients were scheduled for outpatient surgery in which general anesthesia with intubation or laryngeal mask airway placement was anticipated. Anesthetic agents/techniques and PONV antiemetic prophylactic regimens used were based on local institution standards. Nausea and/or vomiting were evaluated in the PACU at 30, 60 and 120 min after surgery using an 11-point verbal numeric rating scale. Severe nausea was defined as a score of 7 or greater on the scale, and severe vomiting as three or more emetic episodes during any given time interval. Patients were provided with a diary and they recorded the severity and incidence of nausea and/or vomiting after discharge home for 48 hours after emergence from anesthesia.

 

The primary outcome was the percentage of patients with PDNV until 48 hours after emergence from anesthesia. Secondary outcomes included:

  1. percentage of patients with vomiting after discharge
  2. percentage of patients with nausea after discharge
  3. percentage of patients with PONV in PACU
  4. PONV and PDNV severity incidence

Multiple logistic regression was used to identify risk factors and develop a risk score for postDischarge. Sample size calculation was appropriate.

 

Result A total of 2,170 patients were included in the analysis. The average age of patients was 50 yrs. A majority of patients were nonsmoking (85%), Caucasian (74%), female (65%) with 30% having a history of PONV.

The four most common surgical procedure types included:

  1. general surgery (20%) (41% of general surgery = laparoscopic cholecystectomy)
  2. gynecological surgery (11%)
  3. arthroscopic knee surgery (11%)
  4. breast surgery (10%)

Laparoscopic approaches were used in 38% of all surgeries. A majority of patients (66%) received sevoflurane. A prophylactic serotonin receptor antagonist antiemetic was administered to 77% of patients, 48% received dexamethasone, 13% a dopamine antagonist, and 2.5% a histamine antagonist. Total intravenous anesthesia was not used, although 752 patients (35%) received additional boluses or infusions of propofol. There were 35% who received two intraoperative antiemetics and 12% who received three intraoperative antiemetics.

 

The overall incidence of postDischarge nausea and vomiting was 37%. The overall incidence of PONV was 21%. (See Figure 1). During both time periods the following factors were independent predictors of PONV and PDNV (Table 1):

  1. female gender
  2. age < 50
  3. history of PONV
  4. opioid use in the PACU

Additional predictors that increased the risk of PONV included >125 mcg of fentanyl intraoperatively, and arthroscopic and laparoscopic surgical approaches. Ondansetron administration intraoperatively decreased PONV incidence.

 

The only additional predictor of PDNV was nausea in the PACU. Patients who experienced nausea in the PACU had a 3-fold increased risk for PDNV.

 

Risk factors that were not independent predictors of PONV or PDNV included a history of motion sickness or migraines, ASA physical status, drinking status, and adjuvant peripheral nerve blocks.

 

A simplified risk score for PDNV in ambulatory surgery patients demonstrated that when zero, one, two, three, four, and five risk factors were present the incidence of PDNV was 11%, 18%, 31%, 49%, 59%, and 80% respectively.

 

 

Figure 1. Incidence of PONV and PDNV.

Figure 1

Note: The incidence of severe vomiting was 0.2% in the PACU.

 

Table 1. Independent Predictors of PONV and PDNV

PONV Period

Adjusted OR

PDNV Period

Adjusted OR

Patient Factors

Female gender

2.19

Female gender

1.54

Age <50 yrs

1.79

Age < 50 yrs

2.17

PONV hx

1.43

PONV hx

1.50

Intraoperative Variables

>125 µg fentanyl in surgery

1.48

 

 

Ondansetron

0.70

 

 

Surgical Approach

Arthroscopy

1.97

 

 

Laparoscopy

2.39

 

 

Postoperative

Opioids in PACU

1.51

Opioids in PACU

1.93

 

 

Nausea in PACU

3.14

Note: OR = odds ratio

 

Conclusion Almost 40% of patients experienced PDNV. Anesthesia providers can use the simplified risk score developed in this study to identify patients who may be at risk for PDNV and thus benefit from prophylactic long-acting antiemetics.

 

Comment

PDNV is not a new problem, however it is a less well understood phenomenon compared to PONV. In this study, 37% of patients experienced PDNV, with over 13% experiencing severe nausea. These results tell me that we need to do a better job of identifying and prophylactically treating patients with long-acting antiemetics (e.g., aprepitant, scopolamine) using evidence-based guidelines.

 

The use of simplified risk scores, where each risk factor is given one point, make it easy for anesthesia providers to quantify a given patients’ risk of PONV or PDNV. However, these risk scores do not tell us which factors are most significant. For example, the strongest risk factor for PONV was a laparoscopic procedure (i.e., cholecystectomy). These patients had a 2.4-fold increased risk of PONV. For PDNV, nausea in the PACU was the strongest predictor, which increased the risk 3-fold. I think anesthesia providers should keep these factors in mind when deciding which patients should receive prophylaxis.

 

It is not surprising that ondansetron and dexamethasone did not reduce the incidence of PDNV up to 48 hours after emergence from anesthesia. These medications have a relatively short half-life when compared to long acting agents such as aprepitant or scopolamine. I think this brings home the point that we should start thinking more about utilizing some of these long acting antiemetic agents in high-risk patients. Anesthesia providers should use the risk factors and risk scoring system to help in the prevention of PDNV.

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 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013





The 50% and 95% effective doses of desflurane for removal of the classic laryngeal mask airway in spontaneously breathing anaesthetized adults

Anaesthesia 2011;66:274-277

Hui MT, Subash S, Wang CY


Abstract

Purpose The purpose of this study was to determine the 50% and 95% effective dose (ED) at which the classic LMA could safely be removed in anesthetized adults who were spontaneously breathing desflurane.

 

Background LMAs are used extensively for airway management in patients presenting for outpatient surgery requiring general anesthesia. Some recommend removing the LMA when the patient is still deeply anesthetized, while others only recommend removal after the patient is awake. The rationale for removing the LMA when the patient is still deeply anesthetized is that this minimizes the incidence of coughing, bucking, breath holding, biting on the tube, bronchospasm, and laryngospasm. Desflurane has a rapid recovery profile for return of upper airway reflexes, and some investigators recommend removing the LMA when the patient is still deeply anesthetized because airway reflexes return quickly.

 

Methodology This was a prospective, descriptive study of 38 adult (18-44 years) ASA I or II patients presenting for elective minor surgery under general anesthesia with an LMA.  Patients with a history of GERD, substance abuse, neck pathology, reactive airway disease, suspected difficult airway or BMI > 35 kg/m2 were excluded. After informed consent was obtained, unsedated patients were transported to the operating room for induction of anesthesia. Anesthesia was induced with propofol 3.5 mg/kg, then an LMA size 4 for males and size 3 for females was placed according to the manufactures recommendations. Anesthesia was maintained with 50% nitrous oxide and 50% oxygen at 2 LPM and desflurane. Paracoxib 40 mg was given after induction. Local anesthesia or regional blockade was performed on all patients. No opioids were administered.

 

At the end of the surgery the nitrous oxide was discontinued and oxygen increased to 6 LPM. The end-tidal desflurane concentration for patient number one was set to 6% for 10 minutes before removal of the LMA. All LMAs were removed after suctioning and lifting the jaw (authors did not state if cuff was deflated). The patient was then given oxygen via face mask at 10 LPM.

 

Using the Dixon up-down method, each subsequent patient had the desflurane concentration increased or decreased in increments of 0.1%, depending on the previous patient’s response. Successful removal of the LMA was defined as: absence of coughing, gagging, clenched teeth, biting on tube, airway obstruction, body movement within 1 minute of removal, breath holding, laryngospasm or desaturation to SPO2 <90%, and bronchospasm. If removal was successful the next patient had their end-tidal concentration decreased by 0.1%, if removal was unsuccessful the concentration was increased by 0.1%. This continued until at least 6 crossover pairs occurred. The ED50 and ED95 were determined using Probit analysis.

 

Result A total of n = 38 subjects completed the study. Three were excluded; 1 had a severe laryngospasm on induction and the other 2 required opioids to facilitate LMA placement. This left n = 35 for the analysis. Seventy-one percent of subjects were female with a mean age of 27 ± 6 years, weight of 56 ± 12 kg, and height of 161 ± 0.1 cm. Surgical duration was 49 ± 26 minutes. The most common surgical procedure was breast biopsy (66%), followed by minor orthopedic procedures (28%), inguinal hernia repair (13%), and lipoma excision (3%). None of the patients reported pain after completion of the surgeries. 

 

There were 13 subjects who had failed LMA removal. The reasons for failed LMA removal are listed in Table 1. The desflurane ED50 for smooth LMA removal was 5.29% (95% CI: 5.13-5.38%) and the desflurane ED95 for smooth LMA removal was 5.55% (95% CI: 5.43-6.39%) (Figure 1). The MAC ratio for the ED50 was 0.88 and for the ED95 was 0.93.

 

Conclusion In unpremedicated ASA I and II patients who received desflurane and no opioid for maintenance, the effective concentration for safe LMA removal in 50% and 95% of patients was 5.29% and 5.55%, respectively.

 

Comment

This is the second study this year published on the safe removal of the classic LMA when desflurane was used. This study was conducted in Malaysia and the previous study by Sahiner et al in Turkey.1 Both studies are reviewed in this edition of Anesthesia Abstracts.

 

In both investigations, the methodology and patient populations were similar, with the exception that this current study had a higher proportion of women when compared to the study by Sahiner et al.1 In both studies nitrous oxide was used but turned off 10 minutes before beginning to change the desflurane concentration. The major differences I see between the studies are that the desflurane concentration started at 6% in this current study and was titrated down in 0.1% increments. Whereas in the Sahiner et al1 study the desflurane concentration was set at 4% and titrated up or down in 0.5% increments. Additionally, in this current study more events were used to classify “LMA removal failure.” In the Sahiner et al1 study unsuccessful LMA removal was defined as the occurrence of the following complications: coughing, teeth clenching, gross purposeful movements, breath holding, laryngospasm, or desaturation <90% within 1 minute of LMA removal.

 

 

Table 1. Causes of failed LMA removal in n = 13 subjects

Gross purposeful movement

8     (62%)

Airway obstruction

6     (46%)

Clenching of teeth

6     (46%)

Coughing

4     (31%)

Biting on LMA

3     (23%)

Breath holding

2     (15%)

Gagging

1     (8%)

Laryngospasm

1     (8%)

Bronchospasm

0     (0%)

Desaturation < 90%

0     (0%)

Note. Data is n (%). Some subjects experienced more than one event.

 

In the Sahiner et al1 study the ED50 and ED95 were 2.1% (95% CI: 1.1-2.9%) and 3.9% (95% CI: 3.1-7.9%), respectively. The ED50 and ED95 to the MAC ratio of desflurane were 0.4 and 0.7, respectively. However, in this current study the ED50 and ED95 were considerably higher at 5.29% and 5.55%, respectively. These results make me scratch my head as to why one would see such dramatic differences. I think the broader list of events defined as LMA failure is probably the most likely explanation for the higher ED50 and ED95 found in this current study. This would result in more events being defined as a failure unless anesthetic depth was increased. The higher desflurane concentration at which the first patient started may have influenced the results in some way as well.

 

Limitations to this study include that the investigators did not report the frequency of smoking in their sample. Additionally, the investigators did not state if the LMA was removed inflated or deflated. If the LMA was removed deflated, it is possible this could have contributed to the higher MAC ratios as compared to the Sahiner et al study. In the Sahiner et al1 study the LMA was removed inflated.

 

 

Figure 1. ED50 and ED95 for Safe LMA Removal with Desflurane

Figure 1

 

So at what desflurane concentration can one safely remove an LMA? Well, I think it is probably somewhere between 4%1 and 6%, which is the ED95 in both studies. It is important to point out that in both studies the patients did not receive any opioids. Given opioids blunt the airway response, I think if the patient has a good opioid load on board, one could safely remove the LMA when the patient is at a lower concentration. If minimal or no opioids are used then I would go at closer to 6%. Of course, one must consider the patient’s comorbidities and other surgical/anesthetic factors when deciding to remove the LMA deep. I tend to leave the LMA in until the patient is fully awake, however results of this study and the one by Sahiner et al1 at least provide me with some evidence to support removal of the LMA deep in a patient who received desflurane.

Dennis Spence, PhD, CRNA


1. Sahiner Y, Özkan D, Akkaya T, Göral N, Alptekin A, Gümüs H. The end-tidal desflurane concentration for smooth removal of the laryngeal mask airway in anaesthetised adults. Eur J Anaesthesiol 2011;28:187-89.


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 2013 Anesthesia Abstracts · Volume 7 Number 11, November 30, 2013