Michael T. Beriault

Science, pseudoscience and Sellick.

ULMONARY aspiration of gastric contents remains a much-feared complication of anesthesia. Anesthesiologists commonly refer to patients as being at ‘high risk’ of pulmonary aspiration. Risk means that an unpleasant or dangerous outcome may occur. The frequency of that outcome quantifies the risk. We accept assumptions about ‘risk factors’ that will reduce or increase that frequency, while giving little attention to the evidence. We take steps to prevent aspiration and are satisfied that our knowledge and technical expertise appear to be effective. Management strategies are based on those assumptions but, if the assumptions are not evidencebased, logical deductions may lead to invalid or erroneous conclusions. We have made pilgrimages to many shrines in the past 40 years, always in search of the amulet that will ward off aspiration, and the demons of blame and litigation. How ‘high’ is the ‘high risk’ that we fear? Epidemiological evidence suggests that because our fear of aspiration is exaggerated, all strategies appear to be effective. In 1946, Mendelson 1 published his retrospective review of anesthetic related morbidity and mortality in more than 44,000 pregnancies from 1932 to 1945 at the Lying-In Hospital in New York. He described the typical clinical and radiological changes following liquid aspiration. All anesthetics in these cases were nitrous oxide and ether, without tracheal intubation, and were often given by inexperienced interns. There were 66 cases of aspiration. No deaths occurred in the 40 who aspirated liquid, but two of five patients who aspirated solids succumbed. No deaths occurred in those cases in which the aspirated material was not recorded. In 1986, Olsson 2 reported 83 aspirations with four deaths in 185,358 anesthetics (1:45,454). Two of the four were already very ill, one had a failed intubation, and one vomited under spinal anesthesia. In 1993, Warner 3 reported three deaths, all in ASA III-V patients, in 215,488 general anesthetics (1:71,829). He defined aspiration as bilious secretions or particulate matter in the tracheobronchial tree or a new infiltrate on postoperative chest x-ray. The incidence varied from 1:9,229 for ASA I patients undergoing elective surgery to 1:895 for all emergency surgery. Obstetric patients were the only ones who received routine antacids, H 2 receptor blockers and gastrokinetic medications. More than half (18 of 29) of those who had specific risk factors and aspirated had received pharmacological prophylaxis. The most consistent contributing factors were gagging and vomiting during laryngoscopy (33%) or gagging and vomiting during emergence from anesthesia (36%). Vomiting is the forcible expulsion of gastric contents into the pharynx as the lower and upper esophageal sphincters relax. It requires skeletal muscle activity. Regurgitation is a passive process. Recommended anesthetic techniques for the ‘full stomach’ patient in the 1950s, before the days of succinylcholine, halothane and cricoid pressure, now sound bizarre. 4 Nevertheless, they were based on physiological principles and appeared to prevent pulmonary aspiration. The Newcastle technique was based on the premise that a patient cannot hyperventilate and vomit at the same time. An inhalation induction of nitrous oxide, oxygen, carbon dioxide and ether was used to produce hyperventilation until anesthesia was deep enough for tracheal intubation. Other techniques involved a 20 head-down tilt, or head-down tilt in the lateral position that assisted drainage of fluid away from the glottis, but these made laryngoscopy difficult. The 40° head-up tilt position raised the larynx 19 cm above the lower esophageal sphincter. 4 This strategy was based on O’Mullane’s clinical studies, 5 which showed that, even with 500–1,000 mL saline in the stomach, the intragastric pressure did not exceed 18 cm water. The head-up tilt would therefore prevent passive reflux into the phar

Airway management in obstructive sleep apnea: local solutions

To the Editor, After reading the Continuing Professional Development Module on the management of sleep apnea, I suggest two additional airway management strategies to minimize short-term adverse outcomes in selected intubated patients with obstructive sleep apnea (OSA). First, to reduce the incidence of airway irritation with its attendant coughing and breath holding, I use lidocaine gel on the external cuff of the endotracheal tube as well as intracuff lidocaine (2% preservative free lidocaine 3 mL, no alkalinization). The patient is placed in a semi-upright position and, despite being under a light plane of anesthesia, tolerates the endotracheal tube. The use of local anesthetics prevents, or at least attenuates, troublesome airway reflexes that compromise functional residual capacity (cough, breath holding) or airway patency (laryngospasm). The emerging patient’s tidal volumes can be kept well above closing capacity without disruptive emergence airway reflexes by employing a ventilator pressure support mode or hand-bag assisted ventilation until the patient is ‘‘fully conscious’’. Second, to avoid relapse into a pathologic snoring (obstructive breathing) pattern in the early post-extubation period, I place an appropriately sized nasal airway (coated with lidocaine gel) into the ‘‘best-fit’’ nares immediately after intubation. This step allows any traumatic epistaxis to subside prior to the end of the procedure; insertion of the device at extubation could lead to a bloody airway, which may further compromise extubation. After I started applying these techniques in practice, recovery room nurses developed a new sign of ‘‘full recovery’’. When patients remove the airway device or complain of its presence, it is a good indication that they will maintain their own airway from that point onwards. The foregoing strategy is contraindicated in selected patients undergoing procedures such as transphenoidal pituitary resection. Repatriating a fully controlled airway to spontaneous unassisted breathing constitutes an inherently unstable transition period in an anesthetic plan, particularly in OSA patients. While contemporary anesthesiologists may take full advantage of current ultra-short-acting pharmacological agents for OSA patients, and may heed such good advice as verifying full reversal of neuromuscular blockade prior to emergence, simple techniques may also play a role in the smooth and successful airway management of these patients.

Another technique to facilitate insertion of the ProSeal™ laryngeal mask airway

I have been using a variation of this reported technique for several years now and it is a slight refinement of Dr. Lee’s description. The por-tion of the stylet that is not advanced into the gastric port (esophageal lumen) can be bent 180° back onto itself to form a short arm. The short arm is advanced into the ventilation port. The configuration of the stylet is now akin to the stylet used for double lumen tube insertion for lung isolation procedures. The advantages of this configuration are that it resists rotation of the ProSeal on its short axis (avoiding direction into a pyri-form fossa), prevents the stiff stylet from inadvertently protruding beyond the gastric port distal outlet, and finally, allows the styletted ProSeal to be bent into the same curve as an intubating laryngeal mask airway if the operator prefers that method of insertion. Michael Beriault