Critical closing pressure during midazolam-induced sleep

Abstract

The critical closing pressure (Pcrit) is the airway pressure at which the airway collapses and reflects the anatomical contribution to the genesis of obstructive sleep apnea. Pcrit is usually determined during non-rapid eye movement sleep at night, but has been determined under midazolam sedation during the day in the absence of sleep stage monitoring. Indeed, little is known about the effects of midazolam on sleep architecture. Moreover, deeper sedation with midazolam can decrease upper airway muscle activity and increase collapsibility compared with natural sleep. Pcrit under sedation has not been systematically compared with the usual method performed during natural sleep. Therefore, this study aimed to test the hypothesis that Pcrit following low doses of midazolam during the day would be comparable to Pcrit measured during natural sleep in the same patient. Fifteen men (age 54 ± 10 yr, body mass index 30 ± 4 kg/m(2)) with obstructive sleep apnea underwent a baseline standard overnight polysomnogram (apnea-hypopnea index 38 ± 22 events/h, range: 8-66 events/h), and Pcrit was determined during natural sleep and following midazolam. Sleep induction was obtained with low doses of midazolam (2.4 mg, range 2.0-4.4 mg), and sleep architecture was comparable to natural sleep. Natural sleep and induced sleep Pcrit were similar (-0.82 ± -3.44 and -0.97 ± 3.21 cmH(2)O, P = 0.663) and closely associated (intraclass correlation coefficient = 0.92; 95% confidence interval, 0.78-0.97, P < 0.001). Natural and midazolam-induced Pcrit correlated with obstructive sleep apnea severity, indicating that both Pcrit measures provided meaningful physiological information. Pcrit determined during the day with sleep induction is similar to natural overnight sleep and is a valid alternative approach in which to determine Pcrit.

Fig. 1.

Nasal pressure (Pn) and flow of a representative pressure drop for 5 breaths.

Fig. 2.

Flow [peak inspiratory flow (V̇i_max)] vs. Pn and linear regression of a representative critical closing pressure (Pcrit) determination.

Fig. 3.

A: example of a hypnogram from a Pcrit study performed after sleep induction. The arrows indicate the timing of midazolam intermittent infusions in this patient. B: example of a hypnogram from a Pcrit study performed during natural sleep at nightime (same patient as A). W, wakefulness; REM, rapid eye movement; N1–N3, non-REM stages 1–3.

Fig. 4.

Bland-Altman plot comparing natural and induced sleep Pcrit.

Fig. 5.

A: relationship between natural sleep Pcrit and apnea-hypopnea index (AHI), according to the predominance of respiratory event. B: relationship between induced sleep Pcrit and AHI, according to the predominance of respiratory event.

Fig. 6.

A: relationship between natural sleep Pcrit and minimum oxygen saturation, according to the predominance of respiratory event. B: relationship between induced sleep Pcrit and minimum oxygen saturation, according to the predominance of respiratory event.