Controlling the Airway

IN 1874, Jacob Heiberg wrote that during chloroform anesthesia, noisy, obstructed breathing, particularly during inspiration, could be prevented by pulling the jaw forward. He was not sure how this worked and proposed freezing a corpse to find out. Unfortunately, I have not been able to find any report of this proposed study, which was conceived without the advantage of modern imaging methods. Even earlier, writers had suggested that obstruction of the airway in unconscious subjects often could be overcome by pulling the tongue forward, and they suggested that the “inelastic ligaments” between the tongue and epiglottis would act on the epiglottis, which was considered to be the cause of the problem. If this method failed, then intubation of the trachea was advocated, which could explain why we are perhaps more skilled in using instruments to keep the airway patent than we are informed about how the body does it. Indeed, tracheal intubation has been with us for a millennium. It is only now, with modern methods of investigation and imaging, that we are unraveling the complexities of how the airway is controlled. Thus, in an early study, Boidin used a fiberscope to show how head position affected the epiglottis, and Nandi et al. showed how the epiglottis moved with head extension. This issue of ANESTHESIOLOGY contains two studies of the airway during anesthesia. Such investigations are important for several reasons, despite the increasing variety of apparatuses being marketed to hold the upper airway open. First, all of the devices that we could choose have disadvantages, from minor morbidity caused by an apparatus in the airway, to the dangers associated with misplacement and blockage, to the apparent risk of transmission of serious disease, of which, in Europe, variant Creutzfeldt–Jakob disease is the latest worry. Simple, safe methods of airway management with minimal intrusion could have many advantages. Second, after anesthesia, the control of the airway has to be relinquished to the patient, and in many other circumstances, patients’ control systems may be impaired, either by disease or deliberately during sedation. In some cases, the consequences of poor airway control are striking and disastrous, but in others, the consequences of inadequate airway control are not clear. In patients with overt, sleep-disordered breathing, a study conducted over 4 yr showed a “dose” relationship with hypertension. Perhaps airway obstruction is a cardiovascular stress that plays a part in complications such as postoperative myocardial ischemia and infarction. Anesthesiologists are ideally positioned to study and understand these phenomena. We spend our career maintaining the airway, often with our own hands. We attempt to predict, maybe optimistically, when we may encounter difficulties with the airway; we address the consequences of returning control of the airway to the patient after anesthesia; and we are aware that sedation may lead to adverse events. An early study of the upper airway muscles concluded, “The simultaneous contraction of opposing muscles maintains airway patency.” The reality is more complex: the activity of the pharyngeal muscles is not simple, and there are clear differences between the different muscles. In conscious subjects, muscle activation is affected by factors such as breathing route, posture, and blood pressure. The control of pharyngeal muscle activity has both central and reflex components. Anesthesia of the airway reduces airway muscle activity in patients with sleep-disordered breathing and can induce airway obstruction during sleep in normal subjects. General anesthetics reduce the central component of this control. The coordination of the respiratory muscles is complex, particularly the interaction of some of the less accessible muscles of the velopharynx, but the muscles in this region are vital in the interaction between the jaw, the pharynx, and airway resistance. Studies of anesthetic actions in this field have been few. In the past, the pharynx has been a “border post” between specialties, and studies of the respiratory system were usually conducted after the upper airway had been bypassed and “secured.” When obstructive sleep apnea became recognized as an important cause of morbidity, research on airway control impairment in this condition accelerated, and we gained knowledge of how the normal airway is controlled. However, there are important differences between the normal airway and the airway in sleep apnea and associated conditions such as obesity. One striking difference is in the shape of the pharyngeal airway, which is narrowed from the side in obesity. In obese subjects, the circumference of the This Editorial View accompanies the following articles: Isono S, Tanaka A, Nishino T: Lateral position decreases collapsibility of the passive pharynx in patients with obstructive sleep apnea. ANESTHESIOLOGY 2002; 97:780–5; and Eastwood PR, Szollosi I, Platt PR, Hillman DR: Collapsibility of the upper airway during anesthesia with isoflurane. ANESTHESIOLOGY 2002; 97:786–93.