- Delirium is a common complication of admission to critical care1.
- Sedative drugs, in particular benzodiazepines, may contribute to the development of delirium2.
- We audited the depth of sedation in our ICU patients and examined the relationship between depth of sedation, sedative drug use and delirium.
- Data was collected retrospectively for all patients admitted over a five-week period to our teaching hospital ICU.
- Depth of sedation was recorded hourly using the Richmond Agitation-Sedation Scale score (RASS), along with twice daily delirium screening (using CAM-ICU).
- Our guidelines recommend RASS 0 to -2 but recognise that deep sedation (RASS ≤ -3) is appropriate in the following situations:
- During the hours directly following major surgery
- If there is evidence of hypoxic respiratory failure (FiO2 ≥ 0.5)
- If muscle-relaxants are used
- We recorded the total daily dose of all sedative, analgesic, anxiolytic, antipsychotic and muscle relaxant drugs used. This was adjusted for patient weight.
- Statistical association between doses of common sedative drugs, duration of deep sedation and delirium was assessed using multivariate logistic regression.
- 61 patients were admitted to ICU during the study period.
- 24 patients (39.3%) developed delirium during their stay.
- In total, 36.0% of time was spent deeply sedated (RASS ≤ -3).
- 47.1% of deep sedation was considered to be indicated according to our guidelines.
- The drugs most commonly used for sedation in our unit were propofol and remifentanil.
- We found some evidence of association between the number of days of deep sedation and the development of delirium (odds ratio (OR) 1.50, p=0.06) (Figure 1).
- There was also a suggestion of an association between delirium and the maximum daily dose (mg/kg/day) of propofol (OR 1.03, p=0.13) but not remifentanil (OR 0.16, p=0.51) (Figure 1).
- For each patient, the CAM-ICU score throughout their stay was plotted together with the doses of propofol and remifentanil (Figure 2). This shows the temporal relationship between sedative drugs, depth of sedation and delirium in individual patients.
- Our results show an association between the duration of deep sedation and the development of delirium.
- Overall, 52.9% of the time spent in deep sedation was potentially avoidable. There were a number of patients who were deeply sedated at the start of their admission who subsequently developed delirium. In some of those patients, deep sedation was judged to have been potentially avoidable.
- This study has led us to review the use of sedation on our unit as well as strategies to minimise unnecessary periods of deep sedation.
- Our results also suggest that higher doses of propofol may be associated with the development of delirium. This merits further investigation and may support the increased use of alternative drugs such as alpha-2 agonists.
1. Ely EW, Shintani A, Truman B, Speroff T, Gordon SM, Harrell FE, et al. Delirium as a predictor of mortality in mechanically ventilated patients in the intensive care unit. JAMA. 2004 Apr 14;291(14):1753–62.;
2. Pisani MA, Murphy TE, Araujo KLB, Slattum P, Van Ness PH, Inouye SK. Benzodiazepine and opioid use and the duration of intensive care unit delirium in an older population. Crit Care Med. 2009 Jan;37(1):177–83.