Preloading alkalinized lidocaine in the endotracheal tube (ETT) cuff significantly decreases emergence cough after general anesthesia in surgeries lasting less than an hour. The investigators also found an inverse relationship between opioid dose and the incidence of coughing.
“In the early 2000s, European studies showed that alkalinized lidocaine would diffuse out of the endotracheal tube cuff after 90 to 120 minutes,” said Papu Nath, MD, a pediatric anesthesiologist at the University of Montreal. “Soon after, it was shown that alkalinized lidocaine can actually be used to reduce cough and throat pain at emergence. And although we know it usually takes 90 to 120 minutes for lidocaine to cross the endotracheal tube cuff membrane, its usefulness in shorter-duration surgery is unknown.
“So our objective was to test the efficacy of preloading an endotracheal tube for at least 90 minutes prior to surgery to allow the PVC [polyvinyl chloride] to become saturated with lidocaine and see what happens in surgeries in less than two hours.”
With that in mind, Dr. Nath and his colleagues enrolled 200 patients with American Society of Anesthesiologists physical status class I to III into the trial; participants were randomly assigned to receive either alkalinized lidocaine or saline (n=100 each) to inflate the ETT cuff. Cuffs were prefilled at least 90 minutes before intubation with either 2 mL of 2% lidocaine and 8 mL of 8.4% bicarbonate or 10 mL of normal saline, and then emptied immediately before intubation. After intubation, the same solutions were injected into the ETT cuff until there was no air leak.
Anesthesia was maintained with desflurane (Suprane, Baxter) and rocuronium. Either fentanyl or sufentanil could be administered to maintain vital signs within 20% of baseline values. Opioids were specifically proscribed for extubation cough prophylaxis.
“Did you consider standardizing the opioid regimen?” asked session moderator Marie-Hélène Tremblay, MD, professor of anesthesia at Laval University, in Quebec City.
“We didn’t, because we’ve had incidents where anesthesiologists in our department didn’t want to participate in studies because the protocols for opioids were too restrictive,” Dr. Nath replied. “So we told them to perform their anesthetic as they normally would, so there’s no bias. The only difference would be the lidocaine.”
The investigators used a standardized “no-touch” emergence technique. A blinded assessor noted any cough above 0.2 minimum alveolar concentration (MAC) of expired desflurane. At 0.2 MAC, patients were instructed to open their eyes every 30 seconds; extubation occurred once a direct response was noted.
As Dr. Nath explained at the 2016 annual meeting of the Canadian Anesthesiologists’ Society (abstract 152970), the presence or absence of cough was measured in absolute terms. “If the patient started coughing at 0.8 MAC, that was considered positive for cough. But in all of our cases at 0.2 MAC or less, the moment they opened their eyes and started coughing, the tube was pulled out. That was not considered coughing because it was simply the patient waking up and the tube being pulled out.”
Figure. Incidence of emergence cough.
Either way, the study’s results were, as Dr. Nath put it, “quite unambiguous, as we were able to lower emergence cough by over 40%, with a significant Pvalue” (Figure). Indeed, while 22% of patients in the saline group experienced emergence cough, only 12% of their counterparts in the alkalinized lidocaine group did (P=0.04). Although emergence cough was not significantly influenced by smoking (P=0.16) or the use of angiotensin-converting enzyme inhibitors (P=0.71), opioid dosage was inversely correlated with the incidence of cough (P=0.01). Neither preloading time (P=0.67) nor age (P=0.28) showed a significant correlation with emergence cough.
“With respect to duration of surgery, most of our surgeries were less than 60 minutes,” Dr. Nath reported. Opioid dosage was not significantly different between groups.
As part of the trial, the researchers also measured ETT cuff pressures, with interesting results. “Because the cuff is filled with liquid, you can’t really use a standard ETT cuff manometer to measure the pressure,” Dr. Nath explained. “So we attached an arterial line connector to the cuff and found that we never exceeded 13 cm of water.” The integrity of the ETT cuffs also was tested; the researchers found they could withstand up to 300 mL of fluid before they burst.
“So we can confidently say that preloading alkalinized lidocaine in the ETT cuff significantly diminishes cough in surgeries shorter than 90 minutes,” Dr. Nath concluded.