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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Review Course Lecture 23 Bariatric Times • May 2018 with MO than in other patients. The ultimate choice of airway management will also depend on the locally available equipment, expertise, and experience. PATIENT POSITIONING IN MORBID OBESITY Irrespective of the plan, appropriate positioning of patients with MO is probably the most important aspect of airway management. 21 Patients with MO should be positioned in the head up or head elevated laryngoscopy position (HELP), before and during induction of anesthesia. The HELP position is different from the standard "sniffing" position. In addition to flexion of the lower cervical spine and extension at the sub occipital joint, the HELP position is achieved when the patient's sternum and ear are aligned in a horizontal line parallel to the ground. This position facilitates intubation by improving the laryngoscopy view and is of vital importance for both spontaneous and assisted ventilation. The HELP position can be achieved by either tilting the table, stretcher, or bed into a reverse trendelenburg position or using a propriety positioning device. Newer inflatable devices allow for some degree of customization to the degree of elevation and can be considered. PREOXYGENATION IN THE MORBID OBESITY AND DIFFICULT AIRWAYS In patients with MO, the importance of adequate preoxygenation cannot be over emphasized. In MO, anesthetic induction and neuromuscular blockade coupled with poor positioning and inadequate preoxygenation can lead to rapid oxyhemoglobin desaturation and profound hypoxemia. 22 On the contrary, as evident from busy bariatric anesthesia practices, even in patients with MO who have an anticipated DA, with meticulous attention to both positioning and preoxygenation, the incidence of hypoxia can be greatly minimized. Preoxygenation can be initiated well before anesthetic induction, outside the operating rooms with nasal prongs applied to the patient in a sitting position. 23 This approach has been shown to significantly increase the subsequent safe apnea time during airway manipulation, presumably by maximizing both the FRC and oxygen reserves. Additional evidence for the continuation of passive flow of oxygen during the period of apnea (apneic oxygenation) suggests that this can delay hypoxia by continual replenishment of the alveolar oxygen content by passive uptake. 24 Studies have confirmed benefit from this simple maneuver, and other more sophisticated delivery systems are being developed. Another popular technique that is often considered an extension of preoxygenation is the application of positive pressure mechanical ventilation with a tight-fitting face mask in the awake patient for a few minutes. 25 This can then be continued uninterrupted through the anesthetic induction and replaced with recruitment and PEEP immediately after tracheal intubation. A word of caution : patients at risk for regurgitation and aspiration (such as emergency, inadequately fasted, symptomatic GERD, and pregnancy) might not be ideal candidates for this CPAP technique but would still benefit from the previously mentioned passive oxygen flow with nasal prongs. PLANNING THE TRACHEAL INTUBATION Direct laryngoscopy (DL) has remained a common and remarkably successful technique for intubation in patients with MO. Widespread availability and familiarity with this highly efficient and economical technique coupled with simplicity in use of adjuncts, such as tracheal tube stylet or flexible bougies, ensure its continued use in patients with MO who have fewer predictors of DA. Preloading bougies combined with McCoy type DL blades other fairly effective options when more diffculty is anticipated. In the last decade, with the introduction and widespread use of videolaryngoscopy (VL) in patients with anticipated DA, both DL and awake fiberoptic intubation (FOI) has been reduced. The benefits of VL are most obvious in patients with MO who have predictors of difficult laryngoscopy (such as MP and ULBT). In patients with MO, studies comparing VL to DL demonstrate improved laryngeal views, decreased time to tracheal intubation, and fewer situations with oxyhemoglobin desaturation. 26–28 Another advantage of VL is that if the DA prediction suggests both difficult face mask ventilation and challenging DL, VL can afford an invaluable addition to the management paradigm the ability to perform an "awake look" laryn goscopy. This might provide a more detailed evaluation of the airway and allow for practical decision making in further management of the patient. Further experience and research with this technique will no doubt impact the future of DA management in patients with MO. OTHER AIRWAY OPTIONS While supraglottic airway devices (SAD) are part of conventional DA algorithms, these have not always been considered ideal rescue devices in patients with MO. The well-known NAP4 report also highlights multiple complications with SAD use in patients with anticipated DA, a major proportion of whom were patients with MO. Quite the contrary to this rather unsatisfactory experience, multiple other studies have reported the safe and successful use of SADs in patients with MO, either as the primary airway device or as a tool for ventilation prior to tracheal intubation. 29 Newer SADs with gastric ports might provide higher sealing pressures and result in effective positive pressure ventilation while reducing gastric insufflation. It is therefore reasonable to recommend that in patients with MO, if SADs are either used electively or needed in a rescue situation, devices with gastric ports should be used. Once again, it is important to emphasize in patients with MO that SAD use does not preclude or circumvent the need for attention to the previously mentioned importance of positioning and preoxygenation. Fiberoptic intubation (FOI) is a well-described technique in all DA algorithms. This is often considered a "gold standard," and in the technical advantage, the safety of FOI lies both in keeping the patient awake and breathing spontaneously. 30 In patients with MO, FOI can be challenging due to the distortion of the upper airway and other problems with sedation and topicalization. For further guidance on advanced FOI techniques that would be useful in patients with MO, the reader is referred to other excellent resources on this subject. 31 As expected, there is limited evidence in patients with MO for elective or rescue surgical airways or Front of Neck Access (FONA). Studies of tracheostomies, including percutaneous tracheostomies, do, however, suggest that when compared to lean patients, these FONA techniques are more difficult, might take longer, and are associated with more post operative complications in patients with MO. The use of ultrasound to identify landmarks and guide needle-based techniques is promising and will undoubtedly increase the safety of FONA in patients with MO. Overall, DA management in patients with MO has to be tempered with the acknowledgment that all the three well -known DA "rescue techniques"— SADs, FOIs, and FONA—are known to be difficult with increased failures in MO. It is therefore imperative that the assessment and management of any potential DA in patients with MO be systematic and meticulous, as their limited cardiorespiratory reserve can contribute to additional and often serious morbidity and mortality. PHARMACOLOGY OF AIRWAY MANAGEMENT IN MORBID OBESITY The appropriate dose of pharmacological agents needs to be carefully chosen in patients with MO for the induction, maintenance, and reversal of anesthesia. These have been described in detail elsewhere. 32 In patients with MO, where no difficulty in either face mask ventilation or laryngoscopy and intubation are anticipated, the standard balanced anesthetic induction with non depolarising neuromuscular blockade can be used. When difficult face mask ventilation is anticipated, it might be appropriate to consider anesthetic induction followed by tracheal intubation but avoiding neuromuscular blockade. This has been described using short acting agents, such as a combination of remifentanil and propofol. When delivered as an infusion, remifentanil can be titrated to effect with ideal intubating conditions that avoids chest wall rigidity and safe return of adequate ventilation almost immediately on discontinuation. For anticipated difficult laryngoscopy, the "awake look" approach previously mentioned might be appropriately combined with topical local anesthetic or remifentanil. More recently, the increasing experience with infusions of dexmedetomidine, providing sedation without respiratory depression for VL assessment and attenuation of hemodynamic responses to intubation, appears to be a promising addition to the available DA management strategies in patients with MO. These pharmacological approaches can also be applied to FOI techniques. NEUROMUSCULAR BLOCKADE IN MODA The risks and benefits of using neuromuscular blockers in MO have been discussed elsewhere. There is a growing debate in this patient population that challenges the routine use of succinylcholine in elective, fasted patients who have low regurgitation aspiration risk. On one hand, the long standing and well- established use of succinylcholine (with or without RSI) in patients with MO was aimed at using deep and profound neuromuscular blockade to achieving excellent intubating conditions and being able to rapidly secure the airway while reducing the risk of oxyhemoglobin desaturation. This dogmatic approach has also touted the rapid onset and short duration of neuromuscular blockade as a 'safety net' for its use and promoted its use to avoid the dreaded cannot intubate cannot oxygentate (CICO) situation. 33 Contrary to this view are the multiple serious concerns with the routine use of succinylcholine in patients with MO. 34–35 Succinylcholine (recommended dose 1 to 2mg/kg total body weight) can lead to significantly In patients with MO, the importance of adequate preoxygenation cannot be overemphasized.

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