Comparison of two induction regimens using or not using muscle relaxant: impact on postoperative upper airway discomfort

Br J Anaesth 2007;99:276-281

Combes X, Andriamifidy L, Dufresne E, Suen P, Sauvat S, Scherrer E, Feiss P, Marty J, Duvaldestin P

 

 

Abstract

Purpose            The purpose of this study was to compare hoarseness and sore throat after induction of general anesthesia and endotracheal intubation with, or without, a nondepolarizing muscle relaxant. A secondary purpose was to assess the ease of intubation and hemodynamic changes associated with intubation.

Background            Paralysis is indicated during induction of general anesthesia to assist endotracheal intubation. Relaxation of the vocal cords moves them out of the way reducing the likelihood of injury when the endotracheal tube (ETT) is passed between them. Paralysis also prevents laryngeal trauma due to bucking and ETT movement. It is possible to intubate patients in whom general anesthesia has been induced with propofol without muscle relaxant and without bucking. Studies of ETT placement without paralysis have produced conflicting results. Some report a higher incidence of postoperative vocal cord dysfunction in patients intubated without paralysis. Others have shown no difference. Factors other than intubation influence the incidence of post-extubation complaints, including, for example: ETT cuff pressure, placement of a gastric tube, ETT diameter, gender, head and neck movement, and the surgical procedure.

Methodology            This prospective, randomized, double-blind study included 300 ASA class I and II adults undergoing elective peripheral surgical procedures. All surgeries were performed in the supine position, with the head and neck in a neutral position, and were expected to require less than 2 hours to perform. Exclusion criteria included the possibility of a difficult intubation, surgery in the throat, and a history of sore throat or hoarseness prior to the procedure.

In the control group, general anesthesia was induced with 2.5?mg/kg propofol, 40 ?g/kg alfentanil, and a volume of saline equal to the volume of rocuronium given to the rocuronium group. In the rocuronium group, anesthesia was induced with 2.5 mg/kg propofol, 15??g/kg alfentanil, and 0.6 mg rocuronium. An experienced laryngoscopist commenced intubation 90 seconds after administration of the rocuronium or saline placebo. Male patients received an 8.0 mm ETT. Female patients received a 7.5 mm ETT. The ETT cuff was inflated to between 20 and 30 cm H2O as measured by a manometer. All patients received a Guedel airway.

Intubating conditions were assessed at the time of intubation. Blood pressure and heart rate were recorded every 3 minutes for 15 minutes then every 15 minutes for the duration of the case. The incidence and severity of hoarseness and sore throat were assessed 2 and 24 hours post-extubation.

Result            One patient was lost to follow up at the 24 hour assessment. Patients in the control group had a higher incidence of hoarseness and sore throat than patients in the rocuronium group (P<0.05). At two hours post extubation, 57% of control patients reported hoarseness and/or sore throat compared to 43% of rocuronium patients. At 24 hours post extubation, 38% of control patients reported hoarseness and/or sore throat compared to 26% of rocuronium patients. There was no difference in the severity of the symptoms between groups.

In the control group 18 patients (12%) were difficult to intubate compared to only 1 patient in the rocuronium group (0.7%) (P<0.05). Intubating conditions were “poor” in 49% of control patients and 13% of rocuronium patients (P<0.05). Laryngeal pressure was applied during laryngoscopy in 73% of control patients and 65% of rocuronium patients. Despite the rate of difficulty with intubation, 78% of control patients and 91% of rocuronium patients were intubated in a single attempt. Patients who were difficult to intubate were significantly more likely to report post-extubation hoarseness or sore throat; 79% of difficult intubations vs. 48% of other intubations at two hours (P<0.05).

Systolic blood pressure and heart rate decreased more following induction in the control group than in the rocuronium group and, thus, received more ephedrine or atropine.

Conclusion            Compared to intubation without a muscle relaxant, using a nondepolarizing muscle relaxant for intubation resulted in less post-extubation hoarseness and sore throat, produced better intubating conditions, and reduced the rate of adverse hemodynamic events.

 

Comment

Whether or not you are willing to believe this study will probably depend upon whether you view it from the perspective of clinical anesthesia in general or through the eyes of a specific anesthetist looking at a specific patient. The investigators focus on the administration of a muscle relaxant for intubation but the real issue may be overall intubating conditions. To see what I’m talking about let’s look at the conclusions more closely.

Using a nondepolarizing muscle relaxant produces better intubating conditions and results in less post-extubation hoarseness and sore throat. The investigators compared muscle relaxant to one other way of optimizing intubating conditions and appeared to generalize that administering a muscle relaxant directly caused a reduction in hoarseness and sore throat.

It is easy to accept that a smooth, gentle, quick, atraumatic intubation is least likely to cause hoarseness or sore throat. And, because a muscle relaxant aids in this process, in general terms one can accept the statement that using a muscle relaxant facilitates optimal intubating conditions and results in fewer post-extubation complaints. But aren’t we are really talking about optimal intubating conditions, rather than the muscle relaxant per se?

A muscle relaxant probably helps prevent hoarseness and sore throat by improving intubating conditions, not by any characteristic peculiar to the muscle relaxant itself. It is a tool. There are other ways to optimize intubating conditions besides administering a muscle relaxant. If someone was in the middle of a mask case with a patient deep on inhalation agent and decided to place an ETT I don’t think any of us would believe there was much to gain by administering a muscle relaxant for intubation. Also, I have, on occasion, intubated on propofol alone at significantly larger doses than the 2.5 mg/kg used in this study. Doing so wouldn’t be appropriate or effective for all patients, but in the hands of some anesthetists it provides great intubating conditions in selected patients. (Of course, not having examined my results with intubating on propofol alone systematically, I may believe them to be better than they really are.)

It would have been nice to see a study that examined the incidence of hoarseness and sore throat in patients who had a smooth, gentle, quick, atraumatic intubation compared to those who did not. Muscle relaxation is, in general, a great aid to intubation. But while fewer patients who receive a muscle relaxant reported hoarseness or sore throat 24 hours post-extubation, 26% of the rocuronium group still did. One thing this study shows is that a muscle relaxant doesn’t eliminate the problem. The question is, what are the actual causes of hoarseness and sore throat post-extubation.

Please don’t misunderstand me. As a general rule muscle relaxation is useful during intubation and probably does play a role in reducing the rate of complications associated with intubation. I’m simply cautioning against over generalizing the role of muscle relaxants in preventing complications and pointing out that there are probably other legitimate ways of preventing complications in at least some situations. Muscle relaxants are not without risk of morbidity and mortality. If we can learn how to optimize intubating conditions and prevent post-extubation complications without a muscle relaxant our patients may be better off.

Using a nondepolarizing muscle relaxant reduces the rate of adverse hemodynamic events. This conclusion is clearly not supported by the results of the study. Patients in both groups received 2.5 mg/kg of propofol. In addition, patients in the control group received 40 ?g/kg of alfentanil while patients in the rocuronium group received only 15 ?g/kg of alfentanil. It should come as no surprise that control patients who received 2.7 times more alfentanil had a lower HR and systolic BP and were given more ephedrine or atropine as a result. Further supporting this point, the HR and BP figures in the original article show “railroad tracks” for HR and systolic BP in patients who received the larger dose of alfentanil while those who received the smaller dose had variability in both vital signs. This is suggestive of a more pronounced opioid effect in the high dose alfentanil patients. It is difficult to imagine that 0.6 mg/kg of rocuronium produced some hemodynamic effect that outweighed the difference in the alfentanil dose.

Does this study have anything to teach us? Yes. As a general rule, with what we know now, the chance of a patient experiencing post-extubation sore throat or hoarseness is somewhat lower when intubation is performed in the presence of profound skeletal muscle relaxation.

Michael Fiedler, PhD, CRNA