What Is the Optimal Airway Management in Patients Undergoing Gastrointestinal Endoscopy?

Introduction

A growing number of diagnostic and therapeutic procedures are performed outside the operating room. This increase is especially noticeable in the field of gastroenterology. There is an ever increasing demand for adequate sedation or general anesthesia for successful completion of endoscopic procedures on the gastrointestinal (GI) tract, especially for the more complicated ones. These procedures can cause significant pain or discomfort in addition to preoperative anxiety. Patient comfort and cooperation are critical to the success of both therapeutic and diagnostic procedures. The endoscopy setting is challenging as a result of many factors, including patient comorbidities, type and duration of the procedure, and the need to achieve appropriate depth of sedation/anesthesia at all times, sometimes with the patient in a prone position. However, unlike most anesthesia care practiced outside of operating room settings, sharing the airway and dealing with anesthetic-associated upper airway collapse are unique to GI endoscopy.

Unfortunately, very little evidence exists as to the most appropriate method of managing the airway for these procedures, especially under propofol anesthesia. GI endoscopy anesthesia is an area of work selected by few anesthesiologists; the airway challenges and ever increasing patient comorbidities seem to be the primary reason. Most of the guidelines are based on available evidence and one author’s extensive experience with these patients over many years. Particular focus will be on the airway devices and ventilation methods used to overcome respiratory compromise during these procedures.

Four stages of sedation have been described: minimal, moderate, deep, and general anesthesia. At moderate sedation, patients can maintain their cardiopulmonary functions and respond purposefully to verbal or tactile stimulation. At deep sedation, patients cannot be easily aroused and airway support may be required; however, patients may still respond purposefully to repeated or painful stimulation. Finally, during general anesthesia, patients are not aroused by painful stimuli, and cardiopulmonary functions are impaired. Sedative medications commonly used alone or in combination, including midazolam, fentanyl, remifentanil, propofol, ketamine, and dexmedetomidine, have detrimental effects on ventilation.

Minimal to moderate sedation, wherein the patients maintain their airway with little or no help, is sufficient for the majority of endoscopic procedures like diagnostic esophagogastroduodenoscopy (EGD) and screening colonoscopy. However, there are always patients who might be extremely sensitive to the effects of sedative medications, which may lead to obstruction even with small doses. At the other end of the spectrum are patients who have been administered maximal allowable sedative drug doses (based on the nursing and GI departmental protocols) and are still inadequately sedated. Our emphasis will be on managing the airways of patients requiring deep sedation bordering on general anesthesia, with associated loss of consciousness and airway compromise.

Evidence and Options

The American Society of Anesthesiologists (ASA) practice guidelines emphasize that patients progress from one level of sedation to the next in a fluid manner. During sedation, respiratory compromise is commonly in the form of airway obstruction rather than apnea. Hillman and coworkers investigated the upper airway during anesthesia. Upper airway obstruction is common during both anesthesia and sleep. Obstruction, either partial or complex, is caused by the loss of pharyngeal muscle tone, which is present in the awake state. The velopharynx, which connects the nasopharynx and trachea and is a particularly narrow and compliant segment, is especially predisposed to obstruction. Magnetic resonance imaging (MRI) and pharyngeal manometry evidence have elegantly demonstrated this aspect of the airway. During sedation and anesthesia, in addition to the decrease in muscle tone associated with loss of wakefulness, drug-induced impairment of both the upper airway and neuromechanical behavior and suppression of protective arousal responses occur.

Eastwood and coworkers examined the effect of increasing depth of propofol anesthesia on the upper airway. The pressure at which the pharynx collapses is called the critical pressure, or P _crit. P _critdefines the susceptibility of the upper airway to collapse. Sedative and anesthetic medications adversely affect the collapsible pharynx by dynamic effects of negative intraluminal pressures during inspiration, resulting in its occlusion. It is obvious that such an adverse effect is especially pronounced and detrimental in patients with obstructive sleep apnea, obesity, or both.

Having established the mechanisms of airway obstruction, what are the measures available to prevent and treat such an airway collapse? It is important to recognize and treat such drug-induced airway collapse by various maneuvers and devices before they become life-threatening. If the efforts fail, one has to decide on a more definitive mode of airway control (e.g., laryngeal mask airway [LMA] or endotracheal intubation); however, it is critical to make the decision early and request that the endoscopist withdraw the scope to institute appropriate measures. Often bag-mask ventilation might be all that is necessary to tide over the crisis.

Three areas need to be addressed in relation to airway collapse: various mechanical maneuvers, the use of various devices, and newer monitoring techniques to aid early detection of airway collapse.

Optimizing head and neck position is the simplest but often neglected element of airway support. It is based on optimizing the geometry of the airway by improvement of head position. It commonly involves placing the head in the “sniffing-the-morning-breeze” position (i.e., lower cervical flexion, upper cervical extension, and full extension of the neck, when possible, to increase longitudinal tension on the upper airway and decrease its collapsibility). A chin lift with mouth closure increases the pharyngeal dimensions by increasing the anteroposterior distance between the tongue base and the posterior pharyngeal wall. Forward mandibular advancement is shown to increase the pharyngeal airway size and decrease airway collapsibility in sedated and anesthetized patients. Inazawa et al reported that mandibular advancement stiffens the pharyngeal airway, as indicated by a decrease in P _critin healthy adults during sedation with midazolam.

Mandibular advancement can also be obtained by external jaw thrusting with the use of mechanical devices. Two such devices are the Jaw Elevation Device (JED Hypnoz Therapeutics ) shown in Figure 17-1 and the Jaw Support Device shown in Figure 17-2 . Both are applied externally and are unsuitable for prolonged use because of the risk of nerve damage.

Increasing intramural pressure is another approach for preventing airway collapse. Hillman and coworkers used continuous positive airway pressure (CPAP) to splint and maintain upper airway patency when investigating upper airway collapsibility during slow induction of anesthesia with propofol. The application of CPAP in sufficient quantities can generally overcome obstruction. Although this can be easily achieved with a tight fitting face mask with or without an airway during colonoscopy, it is difficult to achieve in upper GI endoscopy. An airway adjunct that permits application of CPAP during upper endoscopy is the VBM endoscopy mask (VBM Medical); with sedation it allows a pain free insertion of the endoscope through the hole in the membrane ( Figure 17-3 ).

Additionally, a VBM endoscopy mask permits the use of volatile anesthetic agents in situations in which intravenous access is problematic. The mask is used during upper endoscopy in pediatric patients. CPAP may serve as a stent to keep open the upper airway, maintain alveolar recruitment, and facilitate delivery of manual pressure-support.

The definitive airway device for bypassing the collapsible segment is the endotracheal tube, which requires general anesthesia and possible use of a muscle relaxant during the endoscopic procedure. The indications for general anesthesia and intubation, which protect the patient’s airway, include the presence of persistent vomiting or severe gastroesophageal reflux disease. Many other patients, in whom indications for intubation are relative, can be managed with supraglottic airway devices. Both standard LMA and ProSeal LMA are used in upper GI endoscopy procedure, including endoscopic retrograde cholangiopancreatography (ERCP).

Providing supplemental oxygenation is universal in GI endoscopy sedation. The nasal cannula remains a popular method. Carbon dioxide monitoring is recommended by the ASA in all cases of GI endoscopy sedation. Although it is shown to be unreliable in upper GI endoscopy, many newer devices that allow both oxygen delivery and capnometry are available ( Figures 17-4 and 17-5 ).