In this episode, I’ll discuss the connection (or lack thereof) between respiratory drive and sedation depth.
When mechanically ventilated patients have spontaneous respiratory effort, it is often assumed that providing a deeper level of sedation will depress the respiratory effort and allow compliance with the ventilator.
This is a logical assumption because a main side effect of most ICU sedatives is to cause respiratory depression. However we have all probably encountered patients that still have spontaneous respiratory effort despite high doses of sedation, which defies this logic.
Researchers recently published in Critical Care Medicine a prospective cohort study in patients from 5 different ICUs that examined respiratory drive in relation to depth of sedation on the Richmond Agitation Sedation Scale. The authors attempted to analyze the association between the two.
56 patients were involved in the analysis. The authors found that respiratory drive was not significantly correlated with the Richmond Agitation Sedation Scale.
The authors concluded:
Sedation depth is not a reliable marker of respiratory drive during critical illness. Respiratory drive can be low, moderate, or high across the range of routinely targeted sedation depth.
In this patient population and across the range of routinely targeted sedation depth, respiratory drive among patients could be low, moderate, or high. Not only did deep sedation often not suppress respiratory drive, light sedation often did not ensure that a patient’s respiratory effort was preserved.
SCCM guidelines on ICU sedation do not recommend monitoring respiratory drive specifically. The authors suggest that adding monitoring of respiratory drive could help assess whether the intended depth of sedation is having the desired effect. This could allow for lighter sedation if a patient fails to respond with a lower respiratory drive when deep sedation is attempted, but should be subjected to prospective study before being routinely adopted.
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