Original contributionThe effects of head and body positioning on upper airway collapsibility in normal subjects who received midazolam sedation☆
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).
Section snippets
Materials and methods
The experimental protocols described below were approved by the Human Investigation Committee of the Nagasaki University School of Dentistry. Informed written consent was obtained from all subjects. Normal subjects without evidence for upper airway obstruction during sleep (snoring and OSA) were recruited.
Subject characteristics
Measurement of Pcrit was performed in 14 men in the first experiment (age, 23.5 ± 0.8 years; body weight, 65.5 ± 2.0 kg; and body mass index, 22.9 ± 1.2) and 16 men in the second experiment (age, 22.4 ± 0.9 years; body weight, 66.7 ± 1.0 kg; and body mass index, 21.7 ± 1.5). All subjects were free of any sleep complaints, including severe snoring.
Sedation
There was no difference in SpO2 or etco2 before, during, and after induction of sedation. The initial dose of midazolam was 4.9 ± 0.2 mg (0.068 ±
Discussion
The aim of the present study was to investigate the influence of head and body position on upper airway patency (Pcrit and 1/Rua) using pressure-flow relationships. This study indicates three important findings. First, reduction of nasal pressure induced flow-limited inspiration during midazolam-conscious sedation generating a linear pressure-flow relationship, which may affect Pcrit and upper airway resistance. Second, the 30° of body elevation decreased Pcrit without changing upstream
Acknowledgment
The authors thank Terumi Ayuse for technical assistance. This study was supported by grants-in-aid for Scientific Research no. 11470441 from the Japanese Ministry of Education, Science, Sports and Culture.
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Note: This article is based on a study first reported in the Journal of Japanese Dental Society of Anesthesiology 2003;31(2):112-121.