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American Journal of Critical Care. 2009;18: 42-51 doi:10.4037/ajcc2009509
Copyright © 2009 by the American Association of Critical-Care Nurses.
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CE Article

Autonomic Nervous System Function and Depth of Sedation in Adults Receiving Mechanical Ventilation

By Takeshi Unoki, RN, PhD, Mary Jo Grap, RN, PhD, ACNP, Curtis N. Sessler, MD, Al M. Best, PhD, Paul Wetzel, PhD, Anne Hamilton, MS, RN, FNP, Karen G. Mellott, RN, MS and Cindy L. Munro, RN, PhD, ANP. Takeshi Unoki is a senior assistant professor in the Department of Adult Nursing, School of Nursing, St Luke’s College of Nursing, Tokyo, Japan. Mary Jo Grap and Cindy L. Munro are professors, Anne Hamilton is a PhD student, and Karen G. Mellott is a doctoral candidate in the School of Nursing, Virginia Commonwealth University, Richmond, Virginia. Curtis N. Sessler is a professor and Al M. Best is an associate professor in the Department of Internal Medicine and the Biostatistics Department, School of Medicine, and Paul Wetzel is an associate professor in the Biomedical Engineering Department, School of Engineering, at Virginia Commonwealth University.

Corresponding author: Takeshi Unoki, RN, PhD, Senior Assistant Professor, Department of Adult Nursing, School of Nursing, St Luke’s College of Nursing, Tokyo, Japan (e-mail: tunoki{at}slcn.ac.jp).

Background The effect of the depth of sedation on the function of the autonomic nervous system is not well known.

Objectives To describe the effect of level of sedation on heart rate variability as a marker of the function of the autonomic nervous system in patients receiving mechanical ventilation.

Methods This pilot study was part of a larger study in which sedation level was measured continuously for up to 24 hours. The sample consisted of 14 patients receiving mechanical ventilation. The R-R interval was measured continuously via electrocardiography. Sedation level was determined by using the Patient State Index and was categorized as deep (<60) or light (=60). Continuous heart rate data of 5 to 10 minutes for each sedation level for each patient were analyzed.

Results Parasympathetic activity as indicated by root mean square of successive difference of the R-R interval, the high-frequency component, and the percentage of differences of successive N-N intervals (intervals due to normal sinus depolarization) that differed more than 50 milliseconds was significantly lower for deep sedation than for light sedation. The markers indicating sympathetic activity, including the low-frequency component and the ratio of the low-frequency component to the high-frequency component, did not differ significantly between the 2 levels of sedation. Most patients were receiving benzodiazepines.

Conclusions Deep sedation may be associated with depression of parasympathetic function in patients receiving mechanical ventilation. Use of benzodiazepines most likely contributed to this finding.

Notice to CE enrollees: A closed-book, multiple-choice examination following this article tests your understanding of the following objectives:
  1. Identify 3 conditions associated with changes in heart rate variability.
  2. Describe patient state index values in relation to sedation.
  3. Discuss the effects of parasympathetic activity during deep sedation.
To read this article and take the CE test online, visit www.ajcconline.org and click "CE Articles in This Issue." No CE test fee for AACN members.






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