An observational delirium assessment

The Richmond Agitation Sedation Scale (RASS) is a level of consciousness (or arousal) scale that was originally developed to quantify depth of sedation in mechanically ventilated patients.

Its scores range from -5 (unarousable) to +4 (combative), with 0 being normal (alert and calm). The RASS’s verbiage has been modified and evaluated as a delirium screen.

Because the RASS is an observational delirium assessment, it can be assessed by simply observing the patient during routine clinical care and does not require additional cognitive testing.

The modified RASS (mRASS) adds an open-ended question, “How are you feeling today?” to help characterize the presence of inattention, which is incorporated in the mRASS’s verbiage.

A RASS or mRASS other than 0 (normal) is considered to be a positive screen.

Used with permission. Copyright 2012. Vanderbilt University Medical Center.
Sessler CN, et al. Am J Respir Crit Care Med. 2002;166(10):1338–1344.
Ely EW, et al. JAMA. 2003;289(22):2983–2991.
mRASS, modified RASS
RASS, Richmond Agitation Sedation Scale

Senstitivity and specificity

In general, the RASS and mRASS have very good sensitivity and specificity for delirium, especially when considering its brevity and ease of use. Based upon the likelihood ratios, a positive RASS or mRASS moderately increases the likelihood of delirium, while a negative test moderate reduces the likelihood of delirium.

1Han JH, et al. Acad Emerg Med. 2015;22(7):878–882.
2Grossmann FF, et al. Am J Emerg Med. 2017;35(9):1324–1326.
3Chester JG, et al. J Hosp Med. 2012;7(5):450–453.
4Tieges Z, et al. Am J Geriatr Psychiatry. 2013;21(12):1244–1253.
ED, emergency department
LR, likelihood ratio
mRASS, modified RASS
RA, research assistant
RASS, Richmond Agitation Sedation Scale

Advantages and disadvantages of RASS or mRASS


  • Can be assessed during routine clinical care
  • No additional patient interaction required
  • Serial measurements are very easy to perform in ED
  • Changes in RASS or mRASS ↑ sensitivity and specificity


  • Moderate sensitivity and specificity
  • Subjective, moderate inter-observer reliability (κ = 0.63)1
  • Subtler changes in level of consciousness may be missed
  • Does not capture delirium with normal arousal
    • Poorest prognosis2,3
  • Limited validation in ED patients


Performing serial RASS can improve its diagnostic accuracy. If a patient fluctuates between a RASS or an mRASS of -1 and 0, then this is highly indicative of delirium.

The RASS and mRASS do have some disadvantages. Because they are based upon subjective clinical impressions, they are operator dependent and have moderate interobserver reliability. Consequently, their diagnostic accuracies may decrease in raters with limited experience or training.

The RASS and mRASS also do not capture subtler alterations of consciousness, which limits their sensitivities. However, this likely improves the assessments’ specificities.

Lastly, the RASS does not capture delirious patients with normal arousal, which has been associated with higher mortality and poorer 6-month cognition and function.


1Han JH, et al. Acad Emerg Med. 2015;22(7):878–882.

2Han JH, et al. Am J Geriatr Psychiatry. 2017;25(3):233–242.

3Han JH, et al. Psychosomatics. 2019;60(1):27–36.


ED, emergency department

mRASS, modified RASS

RA, research assistant

RASS, Richmond Agitation Sedation Scale