The effects of head and body positioning on upper airway collapsibility in normal subjects who received midazolam sedation

Abstract

Study Objective

To test the hypothesis that the change of body and head position affects upper airway patency during midazolam sedation.

Design

Clinical study using 30 healthy subjects.

Setting

Research unit for sleep study.

Interventions

We used a pressure-flow relationship to evaluate critical closing pressure (Pcrit) and upper airway resistance (Rua) in different condition of body and head position. A pressure-flow relationship was obtained in 3 body postures (supine, 15° elevation, and 30° elevation) and was obtained in 3 head positions (supine with the head in the neutral, supine with head extension, and supine position with head rotated).

Measurements

The pressure and inspiratory flow at subjects' nose mask were recorded. Polysomnographic parameters (electroencephalograms, electrooculograms, submental electromyograms, upper esophageal pressure, and plethysmogram) were also recorded.

Main Results

In experiment 1, 30° elevation of the body significantly decreased Pcrit (P < 0.05) to −13.3 ± 1.3 cm H₂O compared with −8.2 ± 1.4 cm H₂O in supine condition without changing the slope (1/Rua). In experiment 2, head extension significantly decreased Pcrit (−12.5 ± 1.3 cm H₂O) (P < 0.05) compared with the value (−8.2 ± 1.0 cm H₂O) in supine condition without changing the slope (1/Rua).

Conclusions

Our findings indicate that 30° body elevation and head extension significantly decreased upper airway collapsibility during midazolam sedation and established the relative potency of maneuvers that maintain upper airway patency.

Introduction

Monitored anesthesia care is used in patients undergoing minor surgical procedures with regional anesthesia to relieve their anxiety. Among several sedative agents, the benzodiazepine midazolam is widely used to provide the desired level of sedation as well as amnesia and anxiolysis. Several investigators reported that midazolam increases upper airway resistance [1], [2], [3], [4]. Therefore, the maintenance of a patent airway is of critical importance during sedation.

In awake subjects, upper airway patency is dependent on baseline tone and pharyngeal reflexes that activate pharyngeal muscles during inspiration. Sedative agents and general anesthesia may compromise the effectiveness of reflexes that maintain upper airway patency. Therefore, induction of conscious sedation commonly results in airway occlusion at the level of the soft palate, epiglottis, and tongue [3].

In sedated conditions, several methods can be used to stabilize the upper airway and maintain upper airway patency, including lateral body positioning [5], [6] and anterior mandibular repositioning [7], [8], [9]. However, these methods may be difficult to apply when the surgical procedure or examination interferes with the maneuver for technical reasons. There are no data evaluating the effect of head and body position on upper airway patency during midazolam sedation.

The purpose of our study was to examine the control of upper airway patency during midazolam sedation, especially in the patient whose breathing may be restricted to nasal breathing. In this study, we tested the effects of different head and body position on the upper airway patency, as reflected by the pressure-flow relationship during midazolam sedation. We hypothesized that the change of head and body position may improve upper airway patency during midazolam sedation as well as during sleep in patients with obstructive sleep apnea (OSA).