Bariatric Times

MAY 2018

A peer-reviewed, evidence-based journal that promotes clinical development and metabolic insights in total bariatric patient care for the healthcare professional

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22 Review Course Lecture Bariatric Times • May 2018 Predicting and Managing MODA: the Morbid Obesity Difficult Airway by NAVEEN EIPE, MD Reprinted with permission. IARS 2017 Review Course Lectures. 2017; 48–51. INTRODUCTION In the general population, morbid obesity (MO) has been frequently identified as a risk factor for challenges in airway management. 1–3 The increasing prevalence of obesity globally, coupled with the widespread use of weight loss (bariatric) surgery as a treatment option, has given investigators the opportunity to study large cohorts of patients with MO undergoing elective surgery. 4–7 These and other studies have begun to identify clinical features related to MO that would more accurately predict difficult airways (DA) and develop appropriate management strategies. In this review, we use our previously described schema of '7Ps' Predicting (difficulty), Planning, Positioning and Preoxygenating (the patient), Preparing (equipment), Pharmacology (appropriate choice) and Postoperative (care). While the circumstances and needs of airway management will vary widely depending on the patient, practitioner, and procedure, this review focuses mainly on tracheal intubation as the primary goal of airway management of patients with MO. PREDICTING DIFFICULT AIRWAYS IN MORBID OBESITY Age, sex, body mass index (BMI), distribution, and obstructive sleep apnea (OSA). It is well known that although BMI is a useful screening tool for obesity, among patients with MO, its use alone cannot predict DA. 8–12 Clearly, other MO-related factors should be sought. Experience from bariatric anesthesia practices has emphasized the importance of distribution of the excessive body mass as a better predictor of DA. 13–14 When the waist circumference exceeds half the height, the distribution is more "central" or "android" and is associated with DA, ventilation, metabolic syndrome, OSA, and increased perioperative morbidity. The "peripheral" or "gynecoid" pattern of MO is when the WC is less than half the height and is much less likely to be associated with DA. 15 As patients with MO get older, apart from age-related changes to their airway anatomy, their comorbidity burden increases and their cardiorespiratory reserve diminishes. There has been an observation of signi ficant difference in the age of patients with MO having uneventful intubation, difficult intubation, and those planned for fiberoptic intubation. 16 Other studies have also confirmed that with increasing age, both difficulty with face mask ventilation and worse direct laryngoscopy views will be encountered. Indeed, as described elsewhere, age and BMI (either or both >50) are the major diagnostic criteria for OSA and other perioperative MO risk scores. In our opinion, when the numerical sum of the age and BMI exceeds 100, difficulty in airway management and other perioperative risk increases considerably. In MO, the patient's sex might also increase the incidence of DA. The central distribution of excessive body mass in male patients has been implicated as an independent predictor of difficult face mask ventilation. OSA is also more prevalent with central obesity and has also been previously identified as a risk factor for both difficult face mask ventilation and difficult intubation. 17–18 We have frequently observed difficulties in face mask ventilation in patients with OSA who have higher positive pressure (continuous positive airway pressure [CPAP] or bilevel positive airway pressure [BiPAP]) settings. Airway examination. Among the specific airway examination findings, the Mallampati score is a well-established measure of available space in the upper airway relative to the MO-related oro pharyngeal soft tissue mass. This explains why it is probably the most consistent DA test reported in multiple studies of patients with MO. Mallampati scores higher than two have been identified as an independent predictor of difficult face mask ventilation and intubation. 19–20 Increasing neck circumference (NC>40cm) has been described as a significant predictor of difficult face mask ventilation. NC has also been proposed as a predictor of difficult tracheal intubation because of increased anterior neck soft tissue. It is also worthwhile to remember that increased NC is also one of the diagnostic criteria for OSA. Patients with MO presenting with this finding are likely to have OSA and should be evaluated for it further. Finally, the upper lip bite test (ULBT) is a simple test that provides an objective assessment of the anatomy and proportion of the lower jaw, its mobility and protrusion, and assessment of the submandibular space. In patients with MO, this test might offer important information with regard to space available for the caudad displacement of the tongue, which improves laryngeal visualization on direct laryngoscopy. The predictors of DA in patients with MO are summarized in Table 1. Taking into consideration the multifactorial etiology of predicting DA in patients with MO, further investigation and validation will be required. MANAGING THE MORBID OBESITY- DIFFICULT AIRWAY (MODA) Following an appropriately detailed DA assessment of a patient with MO, a management plan needs to be formulated. Individual components of the above mentioned predictors might influence specific aspects of the DA management. As a "gestalt," the first four DA predictors—age, sex, BMI, and distribution—might influence the decision whether the airway might be safely secured after the induction of anesthesia or if the patient needs to have an awake intubation. Similarly, when difficult face mask ventilation is predicted, among others, by increasing NC and higher CPAP settings in patients with OSA, profound and/or prolonged neuromuscular blockade might be avoided. Finally, when the airway evaluation suggests difficult direct laryngoscopy (such as Mallampati scores and Upper Lip Bite Tests), videolaryngoscopy should be considered as the primary option. It is, however, essential to appreciate that while some of these predictors might each individually predict some difficulty, they need to be all considered together in any plan where alternative techniques and rescue methods are also clearly identified. Another aspect worth emphasizing is the seeking of expert help and adequate assistance when any difficulty in airway management is anticipated. In our experience, this is probably more important in patients TABLE 1. Predictors of difficult airways in morbid obesity PATIENT CHARACTERISTICS 0 1 2 Age <40 40–60 >60 Sex Women Men Habitus Waist< 1/2Height Waist> 1/2Height Obstructive sleep apnea (OSA) Absent CPAP 5–15cm H 2 O CPAP >15cmH 2 O Body mass index (BMI) <40 40–60 >60 Neck circumference (cm) <40 40–60 >60 Mallampati Score ≤II >II Upper Lip Bite Test (ULBT) ≤II >II The scores (0–2) from each predictor suggested here are additive, can produce total scores that predict increasing difficult airways (DA). Total scores with <5 suggest low probability of DA, 5 to 10 suggests moderate to serious difficulty and >10 suggests considerably serious DA. While goals might vary for each patient and procedure, DA management for the provider depends on the available equipment, expertise, and experience.

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