Effect of Head Elevation on Passive Upper Airway Collapsibility in Normal Subjects during Propofol Anesthesia

Abstract

Background Head elevation can restore airway patency during anesthesia, although its effect may be offset by concomitant bite opening or accidental neck flexion. The aim of this study is to examine the effect of head elevation on the passive upper airway collapsibility during propofol anesthesia. Method Twenty male subjects were studied, randomized to one of two experimental groups: Fixed-jaw or Free-jaw. Propofol infusion was used for induction and to maintain blood concentration constant at a target level between 1.5 and 2.0 μg/ml. Nasal mask pressure (PN) was intermittently reduced to evaluate the upper airway collapsibility (passive PCRIT) and upstream resistance (RUS) at each level of head elevation (0, 3, 6, & 9 cm). We measured the Frankfort plane (head flexion) and the mandible plane (jaw opening) angles at each level of head elevation. Analysis of variance was used to determine effect of head elevation on PCRIT, head flexion and jaw opening within each group. Results In both groups the Frankfort plane and mandible plane angles increased as with head elevation (P < 0.05), although the mandible plane angle was lower in the Free-jaw group (i.e., increased jaw opening). In the Fixed-jaw group, head elevation decreased upper airway collapsibility (PCRIT ~ −7 cmH2O at greater than 6 cm elevation) compared to the baseline position (PCRIT ~ −3 cmH2O at 0 cm elevation; P < 0.05). Conclusion We demonstrate that elevating the head position by 6 cm while ensuring mouth closure (centric occlusion) produces substantial decreases in upper airway collapsibility and maintains upper airway patency during anesthesia.

Upper‐airway collapsibility and compensatory responses under moderate sedation with ketamine, dexmedetomidine, and propofol in healthy volunteers

“…Arousals can therefore interfere with the assessment of compensatory upper‐airway and respiratory timing responses. We have previously reported that passive measurements of upper‐airway collapsibility in sedated subjects were similar to those in non‐REM sleep (Ayuse et al., 2004; Hoshino et al., 2009; Inazawa et al., 2005; Kobayashi et al., 2011). Active compensatory neuromuscular responses to partial upper‐airway obstruction have also been characterized in anesthetized subjects (Hoshino et al., 2009).…”

“…Airflow ( V ̄ ) was measured using a pneumotachometer (model 3,830, Hans Rudolph, Inc., Kansas City, MO, USA) and nasal pressure ( P N ) was measured using a differential pressure transducer (model 1100, Hans Rudolph, Inc.). The outflow from the valve attached to the nasal mask was then connected in series to the pneumotachometer and nasal mask, as described in a previous study (Kobayashi et al., 2011). Air leaks from the mouth were prevented by applying surgical tape across the lips.…”

“…The upper‐airway pressure‐flow relationship was analyzed to determine upper‐airway collapsibility. At each level of P N , breaths were evaluated for the presence of inspiratory airflow limitation, as previously described (Ayuse et al., 2004; Boudewyns et al., 2000; Hoshino et al., 2009, 2011; Kobayashi et al., 2011; Schwartz, Smith, Wise, Gold, & Permutt, 1988). Breaths that were associated with arousal evaluated with sudden change of increase in BIS value associated with change if raw EEG trace was excluded from analysis.…”

“…Upper airway obstruction during sedation can result from changes in either the passive structural properties of the pharynx or from disturbances in neuromuscular control (Ayuse, 2010, 2016; Ayuse et al., 2009; Hoshino et al., 2009; Kobayashi et al., 2011), similar to the mechanism in sleep (Patil et al., 2007; Schneider et al., 2009). Methods for quantifying the contribution of anatomic alterations have been established in both sleeping and anesthetized subjects.…”

Understanding Phenotypes of Obstructive Sleep Apnea: Applications in Anesthesia, Surgery, and Perioperative Medicine

“…Anesthetizing and recovering patients without OSA in the head position elevated up to 6 cm from horizontal increases the stability of the airway. 122 It is useful to have patients with supine-related OSA in lateral or semiupright positions throughout the perioperative period. Although the role of fluid shift in worsening of OSA is not studied in the perioperative period, it may be prudent to restrict perioperative fluid administration in the elderly OSA patients and those with fluid retention states.…”