Scoring System Predicts Difficult Airways in Obese Patients

A literature review from Canada has concluded that in the current health care environment, alternative assessment and management strategies should be the norm for morbidly obese individuals with difficult airways. Armed with findings from the review, the researchers subsequently constructed a scoring system to predict the likelihood of a difficult airway in morbidly obese patients.

“It has been traditionally believed that all morbidly obese patients will present with a difficult airway,” said Adele Budiansky, MD, a resident at the University of Ottawa, in Ontario. “Looking at previous literature, there was a heavy emphasis on fiber-optic intubation, as well as rapid-sequence induction. But as we gain more experience with morbidly obese patients, and with the increasing use of video laryngoscopes, the question is whether these techniques are necessary and whether there are specific predictors of difficult airway that we can identify in this population.”

First, a Deep Dive Into the Literature

Dr. Budiansky and her co-investigator, Naveen Eipe, MD, searched the peer-reviewed literature, using specific keywords for predictors, management and pharmacology of difficult airways in the morbidly obese population. The researchers then sought expert opinion to develop a consensus for a difficult airway prediction rule that is specific to morbid obesity. The last step of the research was to revise an existing difficult airway algorithm for anticipated difficult airway and customize it with modalities specifically for morbid obesity.

The search yielded multiple predictors of difficult airways in morbid obesity. Interestingly, most of the literature identified body mass index (BMI) as a poor independent predictor of difficult intubation.

“It is suggested that there are other potential characteristics of the obese patient that predispose to a difficult intubation,” Dr. Budiansky noted. “For example, the Society for Obesity & Bariatric Anaesthesia [www.sobauk.co.uk] has suggested that central adiposity more predisposes to a potential difficult airway, because of the links to increased adipose tissue in the airways, increased desaturation due to reduced functional residual capacity, and increased sleep apnea.”

As reported at the 2016 annual meeting of the Canadian Anesthesiologists’ Society (abstract 151155), risk factors for difficult bag mask ventilation included age over 40 years, male sex, sleep apnea with higher pressure settings, BMI greater than 40 and neck circumference greater than 40 cm.

“Independent risk factors for difficult laryngoscopy were the same as for difficult ventilation, with the exception of BMI,” Dr. Budiansky added. “In addition, both an elevated Mallampati score and limited upper lip bite test were independent risk factors for difficult laryngoscopy.”

Second, a Review of Management Options

The review also yielded several insights into how clinicians manage morbidly obese patients. Of these, although awake fiber-optic intubation is still the gold standard for managing a difficult airway in these individuals, it is not the only option in predicted difficult direct laryngoscopy.

“If there’s a patient who has some—but not all—predictors of a difficult airway, then one of the ‘intermediate’ options that has been identified is general anesthetic with video laryngoscopy, either with maintaining spontaneous ventilation or with controlled ventilation,” Dr. Budiansky said. “An alternative is an awake look, and possibly an awake intubation with the video laryngoscope.”

Another significant management question is the use of neuromuscular blockade, particularly succinylcholine. On one side are those who say profound neuromuscular blockade improves the glottic view in morbidly obese individuals, an argument countered by those who say it can lead to serious oxygen desaturation and subsequent complications.

“One of the options discussed in the literature as an alternative to succinylcholine—especially when difficulty is anticipated—is the possibility of using remifentanil, since it’s titratable and can help with the return of spontaneous ventilation more effectively than succinylcholine can after neuromuscular blockade,” she said.

Last, a Scoring System for Predictors of Difficult Airway

As a result of the literature review, the researchers created a scoring system for independent predictors of a difficult airway in morbid obesity. As part of the scoring system, patients were assigned one point for each of the following characteristics:

• age 40 to 60 years;
• female sex;
• waist less than one-half height;
• continuous positive airway pressure (CPAP) 5 to 15 cm H₂O;
• BMI 40 to 60 kg/m²;
• neck circumference 40 to 60 cm;
• Mallampati score less than II; and
• upper lip bite test less than II.

Patients were assigned two points for the following:

• age over 60 years;
• male sex;
• waist more than one-half height;
• CPAP more than 15 cm H₂O;
• BMI more than 60 kg/m²;
• neck circumference more than 60 cm;
• Mallampati score more than II; and
• upper lip bite test more than II.

The algorithm recommends that patients whose total score is less than 5 undergo induction with controlled ventilation and direct laryngoscopy. Scores of 5 to 10 have a recommendation of induction with spontaneous ventilation and video laryngoscopy. The system recommends an awake look or fiber-optic intubation for patients with scores over 10.

“After the scoring system, we tried to create an algorithm that’s based on a traditional difficult airway algorithm, as a guideline to help direct airway management in an elective and fasted morbidly obese patient,” Dr. Budiansky said.

Session co-moderators Adriaan van Rensburg, MD, and Orlando Hung, MD, were quick to note that treatment algorithms should only be viewed as guidelines, because they do not account for patient-specific or situation-specific issues. “Clinically, I think there’s one important factor that’s missing here: whether it’s 9 o’clock in the morning or 11 o’clock at night,” said Dr. van Rensburg, assistant professor of anesthesia at the University of Toronto, in Ontario. “Because if it’s 9 o’clock in the morning and I know there are people around who can help me, I’m going to take a much different approach than 11 o’clock at night when I’m alone. You can look at that in your follow-up, because I think that is the crucial part in managing these patients.”

“Anatomy is also a dynamic problem,” said Dr. Hung, professor of anesthesia, pain management and perioperative medicine at Dalhousie University, in Halifax, Nova Scotia. “So even though someone examined a patient at the initial clinic and said they were fine, I always reassess before I induce the patient. And the reason is that you just don’t know; things can change from one minute to another. So I think it’s very important to understand the context of the patient as well.”