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Respir Care. 2018 Apr;63(4):448-454. doi: 10.4187/respcare.05723. Epub 2017 Dec 5.

Respiratory Volume Monitoring Reduces Hypoventilation and Apnea in Subjects Undergoing Procedural Sedation.

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The University of Texas Medical Branch at Galveston, Galveston, Texas.
Stanford University School of Medicine, Stanford, California.
The University of Texas Medical Branch at Galveston, Galveston, Texas.



The use of monitored anesthesia care for endoscopic procedures increases the risk of respiratory depression, necessitating careful monitoring of patient ventilation. We examined the effectiveness of an impedance-based respiratory volume monitor (RVM) in improving the safety of patients undergoing upper and lower gastrointestinal endoscopies under total intravenous anesthesia. We hypothesized that feedback from the RVM would allow anesthesiologists to maintain adequate ventilation, which would reduce the duration of respiratory depression (ie, hypoventilation and apnea) compared to a blinded control group.


Sixty-five subjects were enrolled in a randomized controlled trial and monitored with a noninvasive impedance-based RVM, which displayed respiratory traces and calculated expiratory minute ventilation (V̇E), tidal volume (VT), and breathing frequency (f) measurements. Prior to induction of anesthesia, a baseline V̇E measurement (V̇E-baseline) was taken as a measurement of normal breathing. V̇E was monitored throughout the procedure for signs of hypoventilation and apnea. Hypoventilation was defined as V̇E < 40% V̇E-baseline, and apneas were defined as V̇E = 0 for > 15 s.


Sixty-five subjects were randomly assigned to either a control (n = 38) or RVM intervention group (n = 27). Subjects in the intervention group had a higher V̇E% for the entire procedure (P = .045), as well as the third and fourth quartile of the procedure compared to the control group (P = .01). Likewise, subjects in the RVM intervention group spent significantly less time below 40% V̇E-baseline compared to the control group throughout the entire procedure (12 ± 15% vs 32 ± 24%, respectively) (P < .001). The median number of apneas per subject was greater in the control group (median 2, interquartile range 1-2, maximum 4) compared to the RVM intervention group (median 1, interquartile range 1-2, maximum 3) (P = .037).


The control group had a higher incidence of hypoventilation and apnea compared to the RVM intervention group. Respiratory monitoring using the RVM can potentially be a useful tool for identifying early signs of respiratory depression and for titrating anesthetics to maintain adequate ventilation while minimizing patient risk.


endoscopy; procedural sedation; respiratory volume monitor; ventilation monitoring


Conflict of interest statement

The authors disclose no conflicts of interest.

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