Year : 2010 | Volume
: 13 | Issue : 3 | Page : 189--191
Neuromuscular blockade and outcome in cardiac anesthesia
Thomas M Hemmerling1, Cedrick Zaouter2,
1 NRG (Neuromuscular Research Group) Laboratory, Department of Anesthesia, McGill University, Montreal, Canada
2 Department of Anesthesia, University Hospital Pisa, University Pisa, Italy
Thomas M Hemmerling
NRG Laboratory, Montreal General Hospital, 1650 Cedar Avenue, Montreal, H3G 1B7, Canada
|How to cite this article:|
Hemmerling TM, Zaouter C. Neuromuscular blockade and outcome in cardiac anesthesia.Ann Card Anaesth 2010;13:189-191
|How to cite this URL:|
Hemmerling TM, Zaouter C. Neuromuscular blockade and outcome in cardiac anesthesia. Ann Card Anaesth [serial online] 2010 [cited 2022 Oct 7 ];13:189-191
Available from: https://www.annals.in/text.asp?2010/13/3/189/69035
Neuromuscular blockade (NMB) and monitoring in the context of cardiac surgery is a forgotten art; the use of neuromuscular blocking agents (NMBA) in cardiac surgery occurs in a complex environment where anesthesiologists' vigilance is focused on hemodynamic management of a patient population of ever increasing age, decreasing renal and hepatic function, undergoing complex surgery - with or without stopping the normal circulation, with or without significant hypothermia - and receiving concomitantly various drugs interfering with action and metabolism of NMBAs. There still is a tendency to use long acting NMBAs, such as pancuronium, even in continuous infusion. Neuromuscular monitoring is often absent or neglected during the use of NMBAs in cardiac surgery, and extubation delayed by prolonged (or unexpected?) NMB. Two cases published in 2005 highlight some of the pitfalls of this practice. 
Cammu raised a question recently how rational muscle relaxation is in cardiac surgery;  however, the title should not be misunderstood: NMB should not be abandoned in cardiac surgery, but the use of NMBAs in the context of cardiac surgery must be even more sophisticated than in any other type of surgery.
NMBAs are used for induction of anesthesia and maintenance of NMB during surgery. In recent years, some studies have shown that insertion of an endotracheal tube is possible without the aid of NMBAs;  insertion of a laryngeal mask airway (LMA) can easily be achieved without or with little NMB. The introduction of the LMA has changed our daily practice and the use of NMBAs,  even in certain cardiac surgery procedures, such as pacemakers or implantable cardioverter-defibrillator insertion.
The question remains: what is the impact of NMB on the surgical or anesthetic conditions, and what is the impact of NMB on postoperative outcome?
There are very few studies focusing on the importance of NMB in cardiac surgery; in fact, only one study by Cammu  looked at the importance of continuous NMB throughout cardiac surgery. This study clearly showed that a continuous infusion of NMBAs during cardiac surgery, a common practice, is not necessary, as with any other type of surgery. NMB should be titrated to clinical needs; it is necessary to achieve a sufficient NMB during certain periods of cardiac surgery, e.g. suturing of the distal grafts, but less so during other periods of cardiac surgery, e.g. dissection of the saphenous vein.
It seems appropriate to evaluate the impact of no NMB on perioperative cardiac surgery management, during various periods of cardiac surgery, based on clinical and scientific findings.
Insertion of an Endotracheal Tube Without The Aid of Neuromuscular Blockade
Several studies have shown that by using specific anesthetic recipes, insertion of an endotracheal tube is feasible without the aid of NMB. ,, However, these strategies usually necessitate rather profound hypnosis and analgesia;  this carries the risk of hemodynamic instability. One study has also shown that NMB significantly improves the intubation conditions;  especially in the context of cardiac surgery induction, the goal is to establish secure airways quickly and with best hemodynamic stability. Therefore, it can be concluded that the use of NMB during the induction improves the outcome by reducing stress, improving intubation conditions (thus potentially reducing the time of intubation) and allowing better hemodynamic stability by avoiding profound hypnosis and analgesia.
Neuromuscular Blockade During Surgery
In the absence of any study showing the benefit of NMB during cardiac surgery, we would like to examine again why, clinically, NMB is necessary and which adverse effects can be seen with insufficient or no NMB.
Let us for didactical purposes distinguish between off-pump cardiac surgery and on-pump cardiac surgery. Most centers and surgeons practicing off-pump techniques are specialized teams; they have a high volume of cases and are specifically skilled to do these procedures. Off-pump cardiac surgery is a favorite area of fast track or ultra-fast track techniques; immediate extubation is very often facilitated using anesthetic drugs with short half-lives and regional techniques.  This means that surgery time is very often short and hypnosis and analgesia less prolonged than in conventional surgery. However, the success of surgery is dependent on establishing excellent operating conditions during the beating heart grafting period. In addition to using specific stabilizers and/or reduced heart rate, profound NMB is necessary. Any inadvertent small movement of the patient would impair the success of the grafting. It is of clinical importance that patients whose NMB has worn off show very significant muscular reactions during electric conversions in any form of surgery; every cardiac anesthesiologist will have had the same experience of patients "jumping" off the operating table when electrically converted by the surgeons.
Despite the more widespread use of depth of consciousness monitors, exact titration of hypnosis and analgesia can be challenging in on-pump surgery with its distinctly different periods of surgery - before, during and after extracorporeal circulation. Neuromuscular blockade titrated using neuromuscular monitoring can help to maintain good or excellent operating conditions during these different periods.
Neuromuscular Blockade After Cardiac Surgery
In general, NMB is not necessary for postoperative ventilation; in fact, some studies have shown that prolonged use of NMB during ICU stay can lead to neuromyopathy  and muscle weakness. However, short acting NMBAs play an important role for interventional procedures in the postoperative period, such as bronchoscopy or broncholavage; very difficult ventilation patterns for specific conditions, such as acute respiratory distress syndrome, might also necessitate a certain degree of NMB. 
The need for objective neuromuscular monitoring during the perioperative period, including postoperative ventilation, cannot be overemphasized. Whenever NMBAs are used or have been used, objective monitoring should be done. Titration to objective monitoring can reduce the use of NMBAs, avoid unnecessarily profound NMB and allow titration of NMBAs to specific needs. Any NMBA with the risk of accumulation, such as pancuronium, should be abandoned. The use of NMBAs with a predictable onset and length of action is as important as NMB is for cardiac surgery. Cisatracurium for patients with impaired renal or hepatic function and rocuronium - especially with the more widespread availability of sugammadex in the future - should be the preferred NMBAs for cardiac surgery.
Let us summarize the reasoning in favor of NMB during different periods of perioperative cardiac surgery:
NMB for induction of anesthesia
The use of NMBAs for insertion of endotracheal airways allows the rapid establishment of good to excellent intubation conditions in the majority of the patients without excessive use of hypnotic or analgesic drugs. This guarantees stable hemodynamic conditions in a patient population where hemodynamic stability is of vital importance.
Importance of objective neuromuscular monitoring and maintenance of NMB during surgery
It is important to continue to regard neuromuscular monitoring as one of the standard monitoring parameters in good clinical practice. Whereas monitoring of the adductor pollicis muscle is relevant for establishing return of neuromuscular transmission at the end of surgery or ICU, but before extubation, neuromuscular monitoring of the corrugator supercilii muscle - which is easily accessible during cardiac surgery - can be used to titrate NMBA dosing to achieve NMB of the core muscles, such as the diaphragm or the larynx.  Clinical outcome, even the success of surgery, might be dependent on sufficient NMB during key periods of cardiac surgery, e.g. grafting during off-pump cardiac surgery. Any inadvertent patient movement should be avoided at key moments of surgery.
Reversal of NMB
Before extubation, neuromuscular transmission should be determined at the adductor pollicis muscle, since it is one of the last muscles to recover from NMB. Any train-of-four response of less than 0.9 should be reversed. Sugammadex in a dose of at least 2 mg/kg (see review in this issue) is the ideal choice of reversal drug at this point; presently, high costs might prevent the widespread use of it. Current reversal drugs shall be carefully titrated to avoid either bradycardia by cholinesterase inhibitors or tachycardia by atropine or glycopyrrolate. Any reversal of NMB, whether it is achieved using sugammadex or any other reversal drug, should be followed by another determination of sufficient neuromuscular transmission before extubation.
Use of NMBAs in the postoperative period and importance of neuromuscular monitoring in the ICU setting
Neuromuscular monitoring is rarely performed in the ICU. This is a serious mistake. Any patient on longer term ventilation should, regardless of whether he or she has received NMBAs, undergo intermittent determination of neuromuscular transmission to exclude critical illness neuromyopathy. Any patient ventilated after cardiac surgery should be monitored and neuromuscular transmission determined before any weaning from ventilation is attempted. Postoperative residual paralysis is a significant problem in cardiac surgery. In general, NMB is not necessary for postoperative ventilation; however, in some patients who develop severe pulmonary complications after cardiac surgery, NMB of a certain degree might be necessary to allow aggressive ventilation protocols. Short-acting NMBAs, whose metabolism is independent from organ failure, such as cisatracurium, are the NMBAs of choice. Choosing long-acting NMBAs with the propensity to accumulate, such as pancuronium, has a negative impact on outcome by delaying extubation, prolonging the period of ventilation and causing significant pulmonary complications. ,,
In summary, NMB as well as neuromuscular monitoring are necessary for cardiac surgery; the absence of appropriate NMB can impair the outcome in cardiac surgery. Good pharmacologic knowledge of the various NMBAs and how different muscles react to NMBAs, as well as the skilful use of available neuromuscular monitoring methods during and after surgery are as important for cardiac anesthesiologists as mastering transesophageal echocardiography. The use of sugammadex might reduce postoperative complications due to insufficient reversal of NMB using the current reversal drugs.
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