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The Use of Neuromuscular Blocking Drugs in Adult Cardiac Surgery: Results of a National Postal Survey

Murphy, Glenn S., MD*,; Szokol, Joseph W., MD*,; Vender, Jeffery S., MD*,; Marymont, Jesse H., MD*,; Avram, Michael J., PhD

doi: 10.1097/00000539-200212000-00012
CARDIOVASCULAR ANESTHESIA: Research Report
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Available data suggest that the choice of neuromuscular blocking drugs (NMBDs) can influence early clinical recovery of the fast-track cardiac surgical patient. The aim of this study was to use a survey tool to determine practice patterns of anesthesiologists for the use of NMBDs in the cardiac surgical setting. We mailed a survey to one third of the 3295 active members of the Society of Cardiovascular Anesthesiologists. A follow-up letter and survey were sent to each individual who did not respond to the initial mailing. After the second mailing, 459 surveys were returned, yielding a response rate of 43%. Pancuronium was listed as the primary NMBD used in the majority of patients undergoing cardiopulmonary bypass (69%) and off-pump (41%) procedures. Only 28% of respondents routinely used a peripheral nerve stimulator to monitor neuromuscular blockade in the operating room. Residual neuromuscular blockade was routinely reversed before tracheal extubation by only 9% of cardiac anesthesiologists. This survey demonstrates that long-acting NMBDs are often administered to fast-track cardiac patients. Peripheral nerve stimulator monitoring is rarely used in the operating room or intensive care unit, and reversal drugs (anticholinesterases) are infrequently administered in the postoperative period.

*Department of Anesthesiology, Evanston Northwestern Healthcare, Illinois; and †Department of Anesthesiology, Northwestern University Feinberg School of Medicine (get address)

The mailing list of members of the Society of Cardiovascular Anesthesiologists was provided by the Society.

August 21, 2002.

Address correspondence and reprint requests to Glenn S. Murphy, MD, Department of Anesthesiology, Evanston Northwestern Healthcare, 2650 Ridge Ave., Evanston, IL 60201. Address e-mail to dgmurphy@core.com.

Significant advances in the anesthetic management of the cardiac surgical patient have occurred during the last two decades. During this time, most hospitals performing cardiac surgery in North America and Europe have initiated fast-track programs that promote early tracheal extubation and reductions in length of hospital stay. An essential component of all fast-track anesthesia protocols is a reduction in the dose of narcotics administered to the patient in the operating room to prevent prolonged intubation in the intensive care unit (ICU). However, the choice of nondepolarizing neuromuscular blocking drugs (NMBDs) may also play an important role in the recovery of the cardiac surgical patient. Recent clinical studies have demonstrated that long-acting NMBDs are associated with a frequent incidence of residual neuromuscular blockade, delays in tracheal extubation, and symptoms of muscle weakness in the early postoperative period (1–3).

Relatively little is known about the use of NMBDs in the fast-track cardiac patient. The purpose of the present study was to use a survey instrument to identify factors associated with practitioner use of NMBDs in patients undergoing cardiopulmonary bypass (CPB) and off-pump coronary artery bypass graft (OPCAB) surgical procedures. This postal survey was conducted to assess current clinical practice in drug selection, methods of monitoring in the operating room and ICU, and reversal of neuromuscular blockade during postoperative recovery.

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Methods

This study was approved by the Evanston Northwestern Healthcare IRB. Surveys were mailed and received between the months of July and December of 2001 to a sample of active members of the Society of Cardiovascular Anesthesiologists (SCA) who currently practice in the United States. No residents were included in the survey. The SCA membership list was obtained from the SCA’s management company with the society’s permission. Of 3295 eligible members, surveys were mailed to every third member on the list, yielding 1098 potential respondents.

The survey solicited information from the practitioners regarding their use of NMBDs in adult cardiac surgical patients. Eighteen simple questions were asked about the characteristics of the clinical practice, the choice of NMBDs, mode of delivery and monitoring of NMBDs in the operating room, and management of neuromuscular blockade in the ICU (Appendix). A cover letter explaining the objectives of the study and a stamped, self-addressed return envelope accompanied each questionnaire.

Sequential numbering of the return envelopes provided a mechanism for determining which members had responded to the survey. To ensure that responses remained anonymous, no identifying information was recorded on the questionnaires. Ten weeks after the initial mailing, an identical questionnaire was mailed to all individuals who did not respond to the initial survey.

Responses to all questions are presented as the number providing a given response to each question as well as the percent of all anesthesiologists providing given responses to each question. Spearman rank order correlations were performed to identify relationships between variables. Selected frequency data were compared using 2 × 2 χ2 analysis. Responses of anesthesiologists stratified on the basis of the reported use of either pancuronium or an intermediate-acting muscle relaxant as the primary muscle relaxant in patients requiring CPB were compared using the Mann-Whitney U-test. The criterion for rejection of the null hypothesis was P < 0.05 after the Bonferroni correction for multiple applications of the test to the same data.

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Results

Nineteen surveys were returned by the postal service as undeliverable. Four-hundred-fifty-nine of the remaining 1079 surveys were returned, yielding a response rate of 43%. Twenty-two respondents noted that they did not perform adult cardiac surgery at their institution and were excluded from analysis. Thus, the sample size for most questions was 437.

Fifty-seven percent (n = 249) of responding SCA members practiced in a community hospital, 25% (n = 109) worked in a university teaching hospital, and 18% (n = 79) were affiliated with a university or Veterans Affairs hospital. Forty-three percent (n = 187) of respondents practiced at small cardiac centers (<500 cases/yr), 34% (n = 148) practiced at medium-sized cardiac centers (500–1000 cases/yr), and 23% (n = 102) worked at large cardiac centers (>1000 cases/yr). Nearly two thirds of respondents (n = 285) indicated that 50% or less of their clinical practices were devoted to cardiac anesthesia.

OPCAB surgery was performed infrequently at most institutions, with 60% (n = 263) of the anesthesiologists surveyed reporting that it was used in <20% of coronary revascularization procedures. Only 14% (n = 59) of SCA respondents reported that an OPCAB approach was used in more than half of the cardiac surgical cases.

Most respondents noted that the majority of their OPCAB patients were tracheally extubated within 2 h (37% [n = 158]) or 2–4 h (39% [n = 170]). However, when CPB was used, only 6% (n = 25) of respondents indicated that tracheal extubation was achieved within 2 h (P < 0.001 versus OPCAB). Most patients requiring CPB were tracheally extubated within 2–4 h (37% [n = 160]) or 4–8 h (43% [n = 191]). A statistically significant association between surgical method (CPB versus OPCAB) and time to tracheal extubation (0–2 h versus 2 to >12 h;P < 0.05) was noted. Clinicians who primarily administered intermediate-acting muscle relaxants reported that they tracheally extubated cardiac surgical patients earlier than practitioners who used pancuronium. The duration of action of the primary NMBD used in the operating room (all intermediate-acting drugs versus the long-acting drug pancuronium) was correlated with the reported time to tracheal extubation after both OPCAB and CPB (ρ = 0.191 for OPCAB, P < 0.05 and ρ = 0.135 for CPB, P < 0.05).

Pancuronium was listed as the primary NMBD used in the majority of patients undergoing CPB (Fig. 1). Pancuronium was used less frequently in OPCAB surgery (P < 0.05 versus CPB patients). The most frequently cited criterion that determined selection of NMBDs was duration of action in both OPCAB (51% [n = 222]) and CPB (40% [n = 173]) procedures (Fig. 2). Pancuronium use was more frequent in larger institutions. The duration of action of the primary NMBD used in the operating room for both OPCAB and CPB (all intermediate-acting drugs versus the long-acting drug pancuronium) was correlated with the number of cases performed annually at the respondents’ institution (ρ = 0.204 for OPCAB, P < 0.05 and ρ = 0.200 for CPB, P < 0.05), confirmed by the Mann-Whitney U-test (P < 0.05). No other practice variable was associated with choice of NMBD.

Figure 1

Figure 1

Figure 2

Figure 2

Ninety-nine percent (n = 431) of respondents indicated that the primary mode of delivery of NMBDs in the operating room was by intermittent bolus. The decision to provide maintenance doses was based upon peripheral nerve stimulation by only 38% (n = 161) of the respondents. Only 28% (n = 122) of the SCA members surveyed stated that they routinely (>70% of the time) use a peripheral nerve stimulator in the cardiac operating room (Fig. 3). No correlation was observed between the frequency of neuromuscular monitoring and the use of long- or intermediate-acting NMBDs.

Figure 3

Figure 3

Few (1% [n = 6]) anesthesiologists administer muscle relaxants in the ICU after surgery. All of the surveyed anesthesiologists stated that sedative drugs were used in the early postoperative period. Propofol was the primary sedative used in the majority of ICUs (50% [n = 219]).

Recovery of neuromuscular function before weaning from mechanical ventilation and tracheal extubation was determined by clinical criteria according to 88% (n = 378) of respondents. Only 8% (n = 36) of the SCA members used a peripheral nerve stimulator to measure the degree of residual paralysis in the ICU. In addition, residual neuromuscular blockade was infrequently reversed in the postoperative period (Fig. 4). Only 9% (n = 38) of respondents reported that anticholinesterase drugs were routinely (>70% of the time) administered to cardiac surgical patients. Clinicians who used neuromuscular monitoring in the operating room were more likely to use a peripheral nerve stimulator to monitor neuromuscular function in the ICU (ρ = 0.215;P < 0.05) and to administer reversal drugs before tracheal extubation (ρ = 0.368;P < 0.05).

Figure 4

Figure 4

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Discussion

There is currently no consensus regarding the most appropriate method of choosing, monitoring, or dosing NMBDs in the fast-track cardiac surgical patient. The results of our study demonstrate that the majority of cardiac anesthesiologists continue to use pancuronium in their clinical practices. Neuromuscular function is infrequently monitored in the operating room and ICU. In addition, reversal drugs are rarely administered to patients after cardiac surgical procedures.

The majority of respondents to our survey reported that pancuronium was the primary drug used to maintain muscle relaxation in patients undergoing OPCAB and CPB procedures. The advantages of pancuronium use are its inexpensive cost and long duration of action. In addition, the sympathomimetic/vagolytic effects of pancuronium can counteract the bradyarrhythmias that may develop after opioid induction and restore heart rate and cardiac index to baseline levels (4,5). However, the use of pancuronium has also been associated with increases in heart rate and an increased incidence of myocardial ischemia (6,7). Furthermore, the administration of pancuronium in the operating room may result in prolonged neuromuscular blockade in the ICU, which can persist for up to eight hours (1–3).

Routine perioperative monitoring with a peripheral nerve stimulator has been demonstrated to reduce the incidence of postoperative residual neuromuscular blockade (8–10). Neuromuscular monitoring may also be useful in the ICU care of the cardiac surgical patient; full recovery of muscle strength can be documented and the hazards of residual paresis avoided (2,11). The current study found that peripheral nerve stimulators are rarely used in the cardiac operating room or ICU. Only 28% of the SCA members surveyed routinely use a nerve stimulator in the operating room. In addition, only 8% of respondents reported that neuromuscular function was monitored in the ICU. These results are surprising. At many institutions, peripheral nerve stimulators are used routinely whenever a NMBD is administered to a patient (12).

The risks associated with residual paralysis can be reduced if muscle relaxants are routinely reversed in the postoperative period. Because small degrees of blockade are difficult to assess clinically, some authors recommend that all cardiac patients should receive anticholinesterase drugs at the conclusion of surgery (1,13). Only 9% of the respondents reported that neuromuscular blockade was routinely reversed before tracheal extubation in the ICU. We did not assess the reasons for the infrequent use of anticholinesterase drugs in this patient population. It is likely that most clinicians believe that neuromuscular function will fully recover spontaneously by the time weaning and tracheal extubation are accomplished. However, when long-acting NMBDs are used, available data do not support this belief (1–3).

Several clinical studies have examined the impact of the choice of NMBD on early recovery after cardiac surgery. In a retrospective analysis of a database of 1094 CABG patients, Butterworth et al. (14) examined the influence of long- and intermediate-acting NMBDs on ICU and hospital length of stay. No differences were observed between patients who received vecuronium and pancuronium in the duration of intubation or postoperative length of stay. McEwin et al. (1) measured train-of-four (TOF) ratios in the ICU in subjects randomized to receive either pancuronium or rocuronium in the operating room. All of the patients in the pancuronium group had measured TOF ratios <0.7 on arrival to the ICU, and severe residual weakness was present seven hours after the last dose was administered. In the rocuronium group, approximately half of the subjects had TOF ratios >0.7 at ICU admission, and full recovery of neuromuscular function occurred within 2 hours of last dosing. Patients in the pancuronium group remained tracheally intubated four hours longer than subjects in the rocuronium group. Van Oldenbeek et al. (2) measured TOF ratios in postoperative cardiac patients who had received pancuronium. When criteria for discontinuation of sedation and tracheal extubation were met, the median TOF ratio was 0.23. An additional 2 hours elapsed before neuromuscular function recovered fully and tracheal extubation was achieved. Murphy et al. (3) randomized 110 patients undergoing CPB to receive either pancuronium or rocuronium. Significant reductions in the duration of weaning of ventilatory support and in the duration of tracheal intubation were observed in the rocuronium subjects. In addition, symptoms of residual muscle weakness in the ICU were significantly reduced in the rocuronium group.

Several techniques were incorporated into the study design to improve the accuracy of our results. To improve response rates, we provided all study participants with a personalized cover letter explaining our study, a self-addressed stamped envelope, a structured survey with defined answers, and a follow-up letter and survey to each individual who did not respond to the initial mailing. Eighteen simple multiple-choice questions were designed by the authors to reflect the current clinical practices of cardiac anesthesiologists. Each question was reviewed for content validity and interrater reliability by pretesting the survey on a group of five cardiac anesthesiologists (from two medium-sized cardiac practices). It is unlikely a selection bias occurred among respondents in this study because all cardiac anesthesiologists use muscle relaxants in their practices. Responses from the group that returned the survey after the first mailing were not significantly different from the responses obtained after the second mailing.

There are limitations to the current investigation. Data obtained using a survey instrument are subject to recall bias and potential inaccurate estimates. Respondents may not accurately recall all aspects of the intraoperative and postoperative management of the cardiac surgical patient. Outcome data, such as tracheal extubation times, may be based on estimates by the clinician and not necessarily upon objective assessments. Our survey questionnaire did not collect information regarding the role of the anesthesiologist in the management of the cardiac patient in the ICU. Postoperative patient care may occur independently of the anesthesiologist. Therefore, respondents’ data may be derived from information provided by the surgical or ICU teams instead of from direct patient care. Finally, the practice patterns outlined in this study reflect those currently reported by active members of the SCA in the United States. These results should not be generalized to practitioners in other parts of the world.

In summary, the results of this survey demonstrated that pancuronium is the primary muscle relaxant used to maintain neuromuscular blockade in cardiac surgical patients. Further, cardiac anesthesiologists infrequently monitor neuromuscular blockade and rarely reverse the residual effects of muscle relaxants in the perioperative period. Recent clinical studies suggest that the administration of pancuronium to cardiac surgical patients is associated with prolonged neuromuscular impairment and delays in recovery (1–3). Methods to reduce the risk of residual neuromuscular blockade should be considered in the fast-track patient population, including the use of intermediate-acting NMBDs, routine peripheral nerve monitoring, and postoperative reversal of residual neuromuscular blockade.

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Appendix

Survey on the Use of Neuromuscular Blocking Drugs During Adult Cardiac Surgery

Note: The following questions apply only to adult cardiac surgical patients.

□ Adult cardiac surgical procedures are not performed at our institution.

Please check only one box per question.

  1. Type of hospital in which you practice.
    • (a) University teaching hospital □
    • (b) Community hospital □
    • (c) University-affiliated hospital □
    • (d) Veterans Affairs hospital/military □
  2. Number of cardiac cases performed annually at your hospital.
    • (a) <100 □
    • (b) 100–500 □
    • (c) 500–1000 □
    • (d) >1000 □
  3. Percentage of your clinical practice devoted to cardiac anesthesia.
    • (a) <20% □
    • (b) 20–50% □
    • (c) 50–80% □
    • (d) >80% □
  4. Percentage of cardiac surgery done “off-pump” at your institution.
    • (a) <20% □
    • (b) 20–50% □
    • (c) 50–80% □
    • (d) >80% □
  5. Most of your patients requiring cardiopulmonary bypass are extubated in
    • (a) the operating room □
    • (b) <2 hours □
    • (c) 2–4 hours □
    • (d) 4–8 hours □
    • (e) 8–12 hours □
    • (f) 12>hours □
  6. Most of your patients undergoing “off-pump” cardiac surgery are extubated in
    • (a) the operating room □
    • (b) <2 hours □
    • (c) 2–4 hours □
    • (d) 4–8 hours □
    • (e) 8–12 hours □
    • (f) >12 hours □
  7. The primary drug used to maintain neuromuscular blockade in patients requiring cardiopulmonary bypass is
    • (a) Pancuronium □
    • (b) Rocuronium □
    • (c) Vecuronium □
    • (d) Atracurium/Cisatracurium □
    • (e) Doxacurium/Pipecuronium □
  8. The primary drug used to maintain neuromuscular blockade in patients having “off-pump” cardiac surgery is
    • (a) Pancuronium □
    • (b) Rocuronium □
    • (c) Vecuronium □
    • (d) Atracurium/Cisatracurium □
    • (e) Doxacurium/Pipecuronium □
  9. In patients undergoing cardiopulmonary bypass, the primary factor determining the choice of muscle relaxants is
    • (a) Cost □
    • (b) Hemodynamic properties □
    • (c) Duration of action □
    • (d) Drug metabolism □
    • (e) Other □
  10. In patients undergoing “off-pump” cardiac surgery, the primary factor determining the choice of muscle relaxant is
    • (a) Cost □
    • (b) Hemodynamic properties □
    • (c) Duration of action □
    • (d) Drug metabolism □
    • (e) other □
  11. The primary mode of delivery of muscle relaxants in your cardiac operating room is
    • (a) Continuous infusion □
    • (b) Intermittent bolus □
  12. If intermittent boluses are used, how do you decide when to administer additional boluses?
    • (a) Additional boluses are provided at certain points during the operation (i.e., on initiation of bypass, during rewarming, or separation from bypass) □
    • (b) Additional boluses are provided at certain time intervals (e.g., 1–2 mg Pancuronium every 30–60 min) □
    • (c) on the basis of neuromuscular monitoring □
  13. How often do you use a nerve stimulator to monitor neuromuscular blockade during cardiac surgery cases?
    • (a) Never □
    • (b) Occasionally (<20%) □
    • (c) Frequently (20–70%) □
    • (d) Routinely (>70%) □
  14. Are you more likely to use a peripheral nerve stimulator during an “off-pump” cardiac case than a cardiopulmonary bypass case?
    • (a) Yes □
    • (b) No □
  15. Do you routinely provide an additional bolus of muscle relaxant in the ICU?
    • (a) Yes □
    • (b) No □
  16. Recovery of neuromuscular function is monitored in the ICU.
    • (a) by clinical criteria (i.e., five-second head lift, negative inspiratory force > 40 cm H2O, etc.) □
    • (b) by use of a peripheral nerve stimulator □
    • (c) other □
  17. How often are reversal agents (anticholinesterases) given to cardiac surgical patients prior to extubation in the ICU?
    • (a) Never □
    • (b) Occasionally (<20%) □
    • (c) Frequently (20–70%) □
    • (d) Routinely (>70%) □
  18. The primary drug used to provide sedation to patients following cardiac surgery is
    • (a) None □
    • (b) Propofol □
    • (c) Midazolam □
    • (d) Lorazepam □
    • (e) Opiates □
    • (f) other □
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References

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© 2002 International Anesthesia Research Society