How is respiratory suppression assessed during sedation?

Updated: Nov 06, 2018
  • Author: Arul M Lingappan, MD; Chief Editor: Erik D Schraga, MD  more...
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The clinician must use visual observation to assess the patient's level of consciousness (ie, level of sedation), in conjunction with vital signs, oxygen saturation through pulse oximetry, and cardiac rhythm monitoring. However, these are not enough.

Exhaled carbon dioxide levels may prove very useful in assessing respiratory suppression. End-tidal carbon dioxide concentration (ET CO2) is already a standard assessment tool in the ICU and the OR, but studies in the ED setting are scarce. While pulse oximetry is useful in detecting hypoxemia, it is not useful at detecting the hypercapnia that often precedes hypoxemia in a patient with respiratory suppression. Hypoxia is a late marker of inadequate ventilation.

In a small study of 63 adult patients undergoing procedural sedation breathing room air, desaturation detectable by pulse oximeter usually occured before overt changes in capnometry were identified. [35]

An increase in exhaled CO2 might be the only clue of respiratory compromise. ET CO2 detects respiratory depression earlier than standard practice criteria (ie, clinical markers, oximetry, and hemodynamic monitoring). [36, 37] Another study showed that providing supplemental oxygen via nasal cannula may mask respiratory depression in patients receiving moderate sedation with midazolam and fentanyl. [38] This delay did not result in adverse events, so the clinical significance of this remains unclear.

The bispectral index (BIS) may also be very useful. BIS was once only used by anesthesiologists. Encephalographic wave patterns are used to determine sedation depth, measured on a 100-point scale, 1 being no brain activity and 100 being full alertness. A BIS score below 60 corresponds with a low probability of response to verbal stimuli. [39, 40]

Studies have been performed to validate BIS as a reliable marker for respiratory suppression. [40, 41] One such observational study showed that BIS scores between 70 and 85 provided adequate amnesia and analgesia while minimizing risk of respiratory depression. [40] A follow-up sought to show that knowledge of the BIS value changed clinician behavior. [41] In this prospective randomized study, the incidence of propofol-induced respiratory suppression was decreased when the BIS was known to the clinician. Although the latest recommendations from the ACEP state that "there is insufficient evidence to advocate [the routine use of BIS] in procedural sedation and analgesia", future studies will likely assess its utility. [30]

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