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The incidence of sub-optimal sedation in the ICU: a systematic review

  • 1Email author,
  • 2,
  • 2 and
  • 3
Critical Care200913:R204

  • Received: 20 July 2009
  • Accepted: 16 December 2009
  • Published:



Patients in intensive care units (ICUs) are generally sedated for prolonged periods. Over-sedation and under-sedation both have negative effects on patient safety and resource use. We conducted a systematic review of the literature in order to establish the incidence of sub-optimal sedation (both over- and under-sedation) in ICUs.


We searched Medline, Embase and CINAHL (Cumulative Index to Nursing and Allied Health Literature) online literature databases from 1988 to 15 May 2008 and hand-searched conferences. English-language studies set in the ICU, in sedated adult humans on mechanical ventilation, which reported the incidence of sub-optimal sedation, were included. All abstracts were reviewed twice by two independent reviewers, with all conflicts resolved by a third reviewer, to check that they met the review inclusion criteria. Full papers of all included studies were retrieved and were again reviewed twice against inclusion criteria. Data were doubly extracted. Study aims, design, population, comparisons made, and data on the incidence of sub-optimal, optimal, over-sedation or under-sedation were extracted.


There was considerable variation between included studies in the definition of optimal sedation and in the scale or method used to assess sedation. Across all included studies, a substantial incidence of sub-optimal sedation was reported, with a greater tendency toward over-sedation.


Our review suggests that improvements in the consistent definition and measurement of sedation may improve the quality of care of patients within the ICU.


  • Intensive Care Unit
  • Sedative Drug
  • Optimal Sedation
  • Sedation Scale
  • Sedation Protocol


The majority of mechanically ventilated patients within the intensive care unit (ICU) receive sedative drugs. Sedation is administered to ensure patient comfort, reduce anxiety, and facilitate treatments. Optimising sedation management is recognised as important in improving patient outcomes [1]. Under-sedated patients may become agitated and distressed and are at risk of adverse events such as extubation [24], whereas over-sedation can prolong time to recovery [1, 5].

Assessment of sedation level is carried out mainly by nurses or critical care physicians by assessing patient responses to simple stimuli. Sedation scales such as the Ramsay scale or the Richmond Agitation-Sedation Scale (RASS) are widely used [68]. However, there is no universally accepted standard, and this can make comparison between different studies or ICUs difficult [2]. Furthermore, some of these scales have not been fully validated in ICU patients [4]. Recently, devices such as the bispectral index monitor (BIS), which aim to assess sedation levels more objectively, have been introduced. However, most studies of BIS have been performed in surgical settings, and to date its effectiveness is not fully proven [810].

Available guidelines on sedation typically provide limited guidance on optimal sedation monitoring and levels. This is at least partly because optimal sedation levels differ between patients according to their clinical circumstances, and therefore sedation practice is ideally individually tailored to each patient, as recommended by several guidelines [2, 11, 12]. However, among guidelines that do recommend an optimal level of sedation, there are discrepancies, indicating a lack of consensus on this issue. For example, of a survey of available guidelines, one [13] recommended a sedation level of 2 or 3 on the Ramsay scale, whereas one recommended a goal of RASS -3 for an intubated patient [14] and a second recommended a goal of RASS 0 to -2 [15]. A number of guidelines stress the importance of establishing a set protocol for the sedation of ICU patients [16, 17] but do not set out such a protocol in detail, leaving it to individual institutions, and more recent guidelines recognise the benefit of regular (daily) interruption of sedation for eligible patients [11, 14, 18, 19] within sedation protocols.

It is recognised that optimising sedation practice is a recognised quality marker for intensive care treatment, and procedures designed to optimise patient sedation state, such as daily sedation breaks and more frequent monitoring, are key elements of recent quality improvement initiatives. However, despite these recent efforts to improve the quality of sedation practice in the ICU, the epidemiology of sedation, and specifically the prevalence of over- or under-sedation, is unclear. To investigate this further, we carried out a systematic review of the publicly available literature to identify the reported incidence of sub-optimal sedation.

Materials and methods


Medline, Embase and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases were searched from 1988 to 15 May 2008 using terms for sedation, ICU, sedation quality management, and sub-optimal sedation. The standard Scottish Intercollegiate Guidance Network (SIGN) filters for randomised controlled trials (RCTs), economic studies and observational studies [20] were combined to capture all study designs relevant to the study question. Full details of the search strategy used are available from the authors on request. Conference proceedings from 2005 through 2008 were hand-searched for relevant studies. All results were uploaded into a bespoke internet SQL (structured query language)-based database.

Selection criteria

Inclusion of studies was according to a predetermined set of criteria. To be included, studies had to be in adult humans who were sedated and undergoing mechanical ventilation within the ICU and furthermore had to report the incidence of sub-optimal sedation, over- or under-sedation, or of optimal sedation, as defined by the study. Studies that reported the impact of sedation practice on outcomes were also included; these data are reported separately. In addition, short-term studies (including only patients sedated less than 24 hours) were excluded. Only English-language studies were included. To check that they met the review inclusion criteria, all abstracts were reviewed twice by two independent reviewers, with all conflicts resolved by a third reviewer. Full papers of all included studies were retrieved and were again reviewed twice to ensure that they met inclusion criteria. Studies included at this stage were classified as to which aspect of the review question they met, and appropriate data were extracted, summarised and analysed.

Data extraction

Data were extracted by two reviewers and checked by a third reviewer against the original studies. For all studies, the following data were extracted: country, sponsor, study design, patient population, objective, number of patients in the study, details of comparisons made (such as between different treatment arms or between different sedation monitoring systems), and the proportion of measurements, patients, or time in which patients were judged to be optimally sedated, sub-optimally sedated, over-sedated, or under-sedated.

Quantitative data synthesis

Due to the wide range of included study types, no studies were suitable for quantitative data synthesis.


Systematic review study flow

The flow of studies through the systematic review is documented in the QUOROM (Quality of Reporting of Meta-Analyses) diagram in Figure 1. Seventy-five primary and seven secondary studies met the inclusion criteria. Of these, 18 did not provide any data; either they did not contain data on the outcomes extracted in this review or they did not provide these data in quantitative form. Thirty-six studies reported data on the incidence of sub-optimal sedation. The remainder reported the impact of sedation practice on outcomes; these data are reported separately. Of the included studies, three were cohort studies that specifically investigated the epidemiology of sedation, 23 were studies investigating anaesthetic drugs (of which 19 were RCTs and four were observational studies), six studies compared sedation monitoring devices or scales (of which one was an RCT and the remainder were observational studies), three studies investigated the introduction of sedation guidelines, and one did not fit any of these categories. The majority of studies (20) were published after 2002, indicating the increasing interest in the practice of sedation quality in recent years, in particular following the publication of updated sedation guidelines from the American College of Critical Care Medicine [2, 6].
Figure 1
Figure 1

The QUOROM (Quality of Reporting of Meta-Analyses) diagram illustrates the flow of studies through the systematic review.

Definitions of adequate sedation

To assess the incidence of sub-optimal sedation, it is necessary to consider the definition of what constitutes optimal sedation. We used the definition of optimal sedation (and consequently of what constituted sub-optimal sedation) provided by individual studies due to the fact that optimal sedation levels will vary according to study setting (for example, between neurological ICU and medical ICU).

Across all of the studies, 13 different sedation scales were used to assess sedation quality; additionally, nurse assessment of sedation quality simply as over-sedated, under-sedated, or adequate was used three times (Table 1). The Ramsay scale was the most commonly used scale, in 14 studies, with a variant used in a further 7 studies. This is illustrated in Figure 2.
Figure 2
Figure 2

The frequency with which each sedation scale was used in the studies included in our systematic review. ICU, intensive care unit; MAAS, Motor Activity Assessment Scale; OAAS, Observer's Assessment of Alertness/Sedation Scale; RASS, Richmond Agitation Sedation Scale; SAS, Riker Sedation-Agitation Scale.

Table 1

Incidence of optimal and sub-optimal sedation in included studies


Study design and comparisons made


Treatment arms (if relevant)

Incidence of sub-optimal sedation

Incidence of over-sedation

Incidence of under-sedation

Incidence of optimal sedation

Sedation scale/monitoring system used

Definition of optimal sedation

Weinert, et al., 2007 [44]

Cohort study



326 (2.6%) of 12,414 assessments.

111 patients (40%) had ≥ 1 rating of over-sedation. Patients were unarousable/minimally arousable 32% of the time.

1,731 (13.9%) of 12,414 assessments.

211 (76.2%) had ≥ 1 rating of under-sedation.

10,357 (83%) of 12,414

Minnesota Sedation Assessment Tool -- nurse assessment

Arousal level 3-5 (of 6-point scale)

Martin, et al., 2006 [30]

Cohort study

305 (from 220 ICUs)


42.6% of 49 patients sedated 24-72 hours, 39.5% of 157 patients sedated >72 hours, and 43.9% of 57 patients under weaning had significantly deeper sedation than desired level

5.2% of 157 patients sedated >72 hours and 3.5% of 57 patients under weaning had significantly lower sedation than desired level

In patients sedated >72 hours, the desired Ramsay score was 0-4 in 44% of cases -- this was achieved in 28%; in 55% of patients, the desired value was 4-5, which was achieved in 68%; in 1% of patients, the desired score was 6, which was achieved in 6%.

Ramsay scale

Individual to each patient

Payen, et al., 2007 [43]

Cohort study



258 (57%) of 451 patients on sedation day 2; 169 (48%) of 355 patients on day 4; 109 (41%) of 266 patients on day 6


Multiple: most commonly Ramsay, RASS, Sedation-Agitation scale

Over-sedation defined as Ramsay 5-6, RASS -5 or --4, Sedation-Agitation scale 1-2

Sandiumenge, et al., 2000 [36]

RCT/observational study of sedative drugs



19 (7%) of 266 hours


247 (93%) of 266 hours

Modified Ramsay scale

Equivalent of Ramsay 5-6 (for deep sedation)


2% propofol

14 (9%) of 156 hours


142 (91%) of 156 hours


Carrasco, et al., 1993 [26]

RCT (with economic study) of sedative drugs



18% of time (hours)


82% of time (hours)

Ramsay scale; Glasgow coma scale (modified by Cook and Palma)

Ramsay scale 2-5, Glasgow coma scale 8-13



7% of time (hours)


93% of time (hours)


McCollam, et al., 1999 [23]

RCT of sedative drugs



32% of assessments

14% of assessments

18% of assessments

68% of assessments

Ramsay scale

Ramsay scale 2-4



21% of assessments

6% of assessments

16% of assessments

79% of assessments



38% of assessments

7% of assessments

31% of assessments

62% of assessments


Chinachoti, et al., 2002 [40]

RCT of sedative drugs



28% of patients; 17.3% of time (hours)

13% of time (hours)

4% of time (hours)

78% of patients (without midazolam), 83% of time (hours) (maintenance phase)


SAS 4 with no or mild pain



27% of patients; 16% of time (hours)

13% of time (hours)

3% of time (hours)

73% of patients (without midazolam), 84% of time (hours) (maintenance phase)


Harper, et al., 1991 [25]

RCT of sedative drugs


Alfentanil low, moderate and high doses -- results reported together


4 patients had >10% of time at sedation level 6

3 patients had >10% of time at sedation level 1


Ramsay (assessed hourly)


Manley, et al., 1997 [46]

RCT (and economic study) of sedative drugs


Morphine + midazolam

56.8% of time


43.2% of time

North Staffordshire ICU (modification of Ramsay/Addenbrooke's scores)



Alfentanil + propofol

57.8% of time


42.2% of time


Millane, 1992 [21]

RCT of sedative drugs


Isoflurane for 24 hours followed by propofol



Ramsay plus subjective nurse assessment

2-3 (plus subjective nurse assessment)


Propofol for 24 hours followed by isoflurane



Muellejans, et al., 2004 [41]

RCT of sedative drugs



11.7% of time (hours)


88.3% of time (hours)





10.7% of time (hours)


89.3% of time (hours)


Muellejans, et al., 2006 [47]

RCT of sedative drugs


Remifentanil -- propofol

41% of time

28% of time

13% of time

59% of time

3 level sedation score specific to study

Level 2


Midazolam -- fentanyl

30% of time

19% of time

11% of time

70% of time


Chamorro, et al., 1996 [45]

RCT of sedative drugs



332 assessments -- 3% (after first hour)


332 assessments -- 76.5% effective, 20.5% acceptable

Study-specific (modified Glasgow coma scale). Patients monitored at 1 and 6 hours and then every 12 hours.

4 = effective, 3 = acceptable

less than 3 = ineffective



355 assessments -- 7.6%


355 assessments -- 66.2% effective, 26.2% acceptable


Barr, et al., 2001 [34]

RCT of sedative drugs



51% of time

47% of time


49% of time

Modified Ramsay

3-4 (5-6 = over-sedation)



31% of time

22% of time


69% of time


Finfer, et al., 1999 [33]

RCT of sedative drugs


Diazepam (intermittent)

9 (64.3%) of 14 patients; 15.0% of time (hours)

2.8% of time (hours)

21.1% of time (hours)

5 (35.7%) of 14 patients;

85.0% of time (hours)

Modified Ramsay



Midazolam (continuous)

6 (35.3%) of 17 patients; 40.8% of time (hours)

14.8% of time (hours)

0% of time (hours)

11 (64.7%) of 17 patients;

59.2% of time (hours)


Richman, et al., 2006 [37]

RCT of sedative drugs



Mean 9.1 hours/day (SD 4.9)


Modified Ramsay

Individual to each patient


Midazolam and fentanyl

Mean 4.2 hours/day (SD 2.4)


Karabinis, et al., 2004 [39]

RCT of sedative drugs



4.4% of time


95.6% of time (median)





1.9% of time


98.1% of time (median)



1.0% of time


99.0% of time (median)


Pandharipande, et al., 2007 [48], Pandharipande, et al., 2006 [59]

RCT of sedative drugs



20% of patients according to nurse goals; 33% according to physician goals

15% of patients


80% of patients within 1 point of nurse goal; 67% within 1 point of physician goal

RASS, confusion-assessment method for the ICU (CAM-ICU)

Individual to each patient



33% of patients according to nurse goals; 45% according to physician goals

33% of patients


67% within 1 point of nurse goal; 55% within 1 point of physician goal


Swart, et al., 1999 [50]

RCT of sedative drugs



13% of time


87.0% of time (SD 10.5)

Addenbrooke's Hospital's ICU sedation scale

Individual to each patient



34% of time


66.2% of time (SD 23.1)


Carson, et al., 2006 [22]

RCT of sedative drugs


Intermittent lorazepam

42.8% (ventilator hours)

37.9% (ventilator hours)

15.1% (ventilator hours)





Continuous propofol

49.9% (ventilator hours)

38.6% (ventilator hours)

11.5% (ventilator hours)


Anis, et al., 2002 [31], Hall, et al., 2001 [60]

RCT of sedative drugs



39.8% of time

12.0% of time

11.2% of time

60.2% of time


Individual to each patient



56.0% of time

18.4% of time

8.1% of time

44.0% of time


Park, et al., 2007 [49]

RCT of sedative drugs

134 (111 analysed)

Analgesia-based sedation

50% of time


50% of time on SIMV (median)

Assessor judgement

Adequate judged as awake or easily rousable


Hypnotic-based sedation

81% of time


19% of time on SIMV (median)


Cigada, et al., 2005 [32]

Observational study of sedative drugs


Propofol or midazolam with enteral hydroxyzine with or without supplemental lorazepam. IV drugs were tapered after 48 hours.

36.9% of assessments as judged by Ramsay score; 17% by nurse assessment

421 (24.6%) of 1,711 assessments (Ramsay score)

42 (7.3%) of 577 assessments (nurse judgement)

211 (12.3%) of 1,711 assessments (Ramsay score)

56 (9.8%) of 577 assessments (nurse judgement)

1,079 (63.1%) of 1,711 assessments (Ramsay score)

479 (83%) of 577 assessments (nurse judgement)

Ramsay score plus nurse assessment

Adequate sedation defined as the achievement of the planned Ramsay score or nurse judgement as adequate

Barrientos-Vega, et al., 2001 [29]

Observational study of sedative drugs


2% propofol (compared with historical cohort on 1% propofol -- not reported here)

8 (15.6%) of 51 patients judged therapeutic failure on 2% propofol (inadequate level of sedation)


Ramsay score


MacLaren, et al., 2007 [42]

Observational study of sedative drugs


Dexmedetomidine as adjunct to lorazepam/midazolam/propofol

35% of patients with dexmedetomidine; 52% without

12 (30%) patients with dexmedetomidine; 9 (23%) without

4 (10%) patients with dexmedetomidine; 12 (30%) without

65% of patients with dexmedetomidine; 48% without



Shehabi, et al., 2004 [24]

Observational study of sedative drugs


Dexmedetomidine with supplemental midazolam if required

455 (33%) of 1,381 assessments

97 (7%) of 1,381 assessments were Ramsay level 6

137 (10%) of 1,381 assessments were Ramsay level 1

926 (67%) of 1,381



Sackey, et al., 2004 [51]

RCT of sedation devices


Isoflurane using AnaConDa

46% of time; nursing staff estimate 11% of time

44% of time

2% of time

54% of time;

nursing staff estimate 89% of time

Bloomsbury scale

- 1 to +1


IV midazolam

41%; nursing staff estimate 13% of time

37% of time

4% of time

59% of time; nursing staff estimate 87% of time


Walsh, et al., 2008 [52]

Observational study of sedation devices


All sedated patients


137 (32.9%) of 416 assessments (Ramsay score 5-6)

5 (1.2%) of 416 assessments (Ramsay score 1)


Entropy Module/Modified Ramsay scale

None stated. Refers to guidelines suggesting 2-3 is adequate and heavy/over-sedated is 5-6.

Hernández-Gancedo, et al., 2006 [28]

Observational study of sedation scales



44% (66 cases) -- Ramsay level 6


25% (38 cases)

Ramsay, Observer's Assessment of Alertness and Sedation

Ramsay 3-4

Roustan, et al., 2005 [27]

Observational study of sedation scales


All sedated patients -- treated with midazolam and morphine


93 (61.6%) of 151 records

19 (12.6%) of 151 records


Ramsay, Comfort score, EEG

Ramsay 3-4

McMurray, et al., 2004 [38]

Observational study of sedation scales


Propofol-containing regimens

15.6% of time

Mean 5.0% of time (SD 12.7)

Mean 10.6% of time (SD 14.5)

Mean 84.4% of time (SD 18.0)

Modified Ramsay

Individual to each patient

Detriche, et al., 1999 [53]

Before-after study of introduction of sedation protocol




20 (30%) of 67 assessment days


Brussels sedation scale



After protocol introduction


9 (12%) of 77 assessment days


Costa, et al., 1994 [54]

RCT of controlled and empirical sedation



17% of time


83% of time

Ramsay, and Glasgow coma scale modified by Cook and Palma



65% of time


35% of time


MacLaren, et al., 2000 [35]

Before-after comparison of sedation protocol




22.4% (experience of anxiety or pain)


Modified Ramsay





11.0% (P < 0.001)


Tallgren, et al., 2006 [3]

Before-after comparison of sedation protocol


Before reinforcement


Median Ramsay level was 4 during the day and 5 at night, in contrast to the study's stated aim of Ramsay level 2-3 during the day and 3-4 at night




After reinforcement


Median Ramsay level was 4 during the day and 5 at night, in contrast to the study's stated aim of Ramsay level 2-3 during the day and 3-4 at night


Samuelson, et al., 2007 [61], Samuelson, et al., 2006 [62]

Observational study



50% of patients had MAAS 0-2 (although 2 was target for study, 0-1 could be viewed as over-sedated)


39% of patients achieved MAAS 3 in ventilated period


Stated 2-3 but results reported for patients achieving 3

EEG, electroencephalogram; ICU, intensive care unit; IV, intravenous; MAAS, Motor Activity Assessment Scale; RASS, Richmond Agitation-Sedation Scale; RCT, randomised controlled trial; SAS, Riker Sedation-Agitation Scale; SD, standard deviation; SIMV, synchronised intermittent mandatory ventilation.

In addition to the variation in scales used to assess sedation, there was variation in the recommended range of optimal sedation levels stated. Sedation requirements obviously differ among patients; nevertheless, the variation in recommended ranges in included studies indicates some uncertainty in what constitutes optimal sedation. Of the studies using the Ramsay scale, recommended ranges were 2 to 3 (recommended in two studies [21, 22]), 2 to 4 (two studies [23, 24]), 2 to 5 (two studies [25, 26]), 3 to 4 (two studies [27, 28]) and 4 to 5 (one study [29]), while three studies did not recommend specific levels but recommended that levels be optimised for each individual patient [3032]. This variation was reflected in the other scales used; for studies recommending a modified Ramsay scale, recommended ranges were 1 to 4 [33], 3 to 4 [34], 4 [35], and 5 to 6 (the last range being specifically for seriously injured patients [36]) or targets optimised for each patient [37, 38]. The stated SAS (Riker Sedation-Agitation Scale) target level was 1 to 3 [39], 4 [40, 41], or 3 to 4 [42]. Due to the number of studies recommending that optimal sedation state be determined individually for each patient, there was no comparison possible for other scales.

Incidence of sub-optimal sedation

Table 1 lists the study design, sedation assessment scale or tool used, and incidence of sub-optimal sedation reported by studies. As stated above, we used individual study definitions of optimal and sub-optimal sedation because of the fact that optimal sedation levels are likely to vary by study setting.

The three observational studies that investigated the epidemiology of sedation were considered to be the most relevant to the study question as their specific aim was to investigate clinical sedation practice rather than practice within the confines of a trial, where more frequent monitoring and the Hawthorne effect could contribute to improving standards.

A survey of practice across 44 ICUs in France also found a high incidence of deep sedation, in 41% to 57% of readings over a 6-day period [43]. This study highlighted the risks of prolonged deep sedation, which, however, was not specifically defined as over-sedation. Results from these three studies indicate that 30% to 60% of sedation assessments indicate 'deep' or 'over' sedation, although precise description of the prevalence is confounded by imprecise definition or health care worker perceptions. These studies clearly indicate an excess of over-sedation compared with under-sedation.

Martin and colleagues [30] conducted a postal survey of 220 ICUs in Germany. This study found that 42.6% of patients sedated between 24 and 72 hours and 39.5% of patients sedated over 72 hours were over-sedated; the incidence of under-sedation was much lower (<6%).

In the US-based study of Weinert and colleagues [44], the aim was to compare subjective and objective ratings of sedation. Subjects provided 12,414 sedation assessments and were judged by nurses to be sub-optimally sedated in 17% of assessments, over-sedated in 2.6%, and under-sedated in 13.9%. Critically, however, patients were unrousable or minimally rousable just under one third of the time, indicating a high incidence of deep sedation. This finding illustrates the importance of the perception of the health care worker or assessor or both in describing the prevalence of sub-optimal sedation.

The remaining included studies comprised studies of sedative drugs [2126, 29, 3134, 36, 37, 3942, 4550], studies investigating different sedation devices or scales [27, 28, 38, 51, 52], and studies looking at the introduction of a sedation guideline or protocol [3, 35, 53, 54]. Studies varied by design and aim, by sedatives used, by scales and definitions of sub-optimal sedation used, and by the way incidence was reported (as a proportion of measurements, patients, or time). While these studies did not necessarily have the incidence of sub-optimal sedation as their primary focus, the data in such studies were considered to be of interest to the inclusive scope of this review. Although studies of sedative drugs or of the introduction of guidelines or protocols may not give an accurate estimate of the incidence of sub-optimal sedation within routine clinical practice, they nevertheless show that it does occur and can give an impression of the extent to which it may be a problem, even in settings that could be reasonably expected to be more controlled than in routine practice. The incidence of sub-optimal sedation reported in these studies is summarised in Figure 3 (separated by study and treatment arm where relevant). The reported incidence varied from 1% [39] to 75% [28], with the majority reporting an incidence of over 20%. The incidence of over- and under-sedation was similarly variable, and figures of between 2.8% and 44% for over-sedation [28, 33, 51] and between 2% and 31% for under-sedation [23, 51] were reported. A further study [2] that looked at the introduction of a sedation guideline did not record the incidence of sub-optimal sedation but recorded the median Ramsay scale values. These were 4 during the day and 5 at night, in contrast to the study's stated aim of Ramsay levels of 2 to 3 during the day and 3 to 4 at night; this study again noted a possible tendency toward over-sedation of patients. Importantly, there was no change in this tendency before and after reinforcement of the guideline, suggesting that this was insufficient to improve sedation practice [3].
Figure 3
Figure 3

Incidence of sub-optimal sedation across included studies. The plot shows the percentage of measurements, patients, or time in which patients were sub-optimally sedated according to each included study's definition of optimal sedation and measurements reported. Studies are grouped by study design. Where more than one group was reported by a study (for example, a comparison of two different treatment arms), separate points are shown for each group. RCT, randomised controlled trial.


Our systematic review identified few studies that specifically described the epidemiology of sedation during ICU care. Description of the incidence of sub-optimal sedation and over- and under-sedation was difficult due to variation in the use of these terms within individual studies. Overall, available data suggest a high incidence of over-sedation in ICUs, potentially present at 40% to 60% of assessments. A lower reported incidence of sub-optimal sedation across most studies suggests that health care workers consider deep levels of sedation appropriate for many patients.

The quality of published studies was low. There was wide variation in the method used to assess sedation state, the frequency of measurement, and the stated response to evaluations. In addition, the completeness of data in relation to entire ICU populations was usually not stated, introducing the potential for selection bias. Only three cohort studies were found. The importance of selection or inclusion bias was lowest with this study design. All of these indicated a substantial incidence of sub-optimal sedation, with over-sedation being more common (33% to 57%). Notably, one study reported that nurse assessment of sedation found a low incidence of over-sedation, which appeared at odds with the fact that in one third of measurements patients were unrousable or minimally rousable. A difference in perceptions of what constitutes optimal sedation between different health care worker groups and between individual health care workers is also likely to affect the reported incidence of sub-optimal sedation. This finding emphasises the importance of using sedation-assessment methods that have high validity and low inter-rater variability. Many of the scales in current use have not been subjected to formal evaluation. The RASS has been shown to have good construct validity and high levels of consistency among health care workers [55] but was used infrequently in the published literature.

When non-cohort studies were considered, a wide range of incidence of sub-optimal sedation levels was reported (from 1% to 75%). These studies were randomised or non-randomised trials of the efficacy of sedative drugs [2126, 29, 3134, 36, 37, 3942, 4550], or were studies that evaluated sedation devices or scales [27, 28, 38, 51, 52] to monitor sedation levels, or looked at the introduction of sedation guidelines [3, 35, 53, 54]. Overall, the chance of selection and investigator bias, and of study effects, in these studies was high. Drug trials in particular were considered less relevant to our study question as practice within a clinical trial may differ from standard care and is more likely to be controlled. Despite these factors, the majority of studies found an incidence of sub-optimal sedation, using study-specific definitions, of greater than 20%. These studies confirm the findings of the observational cohort studies and suggest high levels of sub-optimal sedation during routine care.

Improving sedation management through sedation protocols and interventions such as daily interruption of sedation is an increasing focus of quality improvement initiatives in critical care in some health care systems [1, 56, 57]. Sedation protocols and scales are increasingly, though not universally, used. A review of German hospitals by Martin and colleagues [6] showed increases in the use of sedation protocols (from 21% of hospitals to 46%) and in the use of sedation scales (from 8% to 51%) over the period of 2002 to 2006. In Finland, Tallgren and colleagues [3] reported that reinforcing a sedation guideline increased the percentage of expected Ramsay scale recordings made, but only to 71% of expected recordings that were actually made, indicating that formal sedation assessments were still not carried out as regularly as they should have been. These studies suggest that, despite recent evidence supporting the avoidance of over-sedation [57, 58], the use of systematic approaches to measure sedation state and optimise sedation for individual patients is not universal. The high prevalence of sub-optimal sedation and high incidence of over-sedation in published studies indicate potential for significant quality improvement in this aspect of care. This is likely to translate into substantial patient benefit.

There are several limitations to our review. As with any systematic review, studies may have been missed; this review was confined to English-language publications and therefore may be biased toward the US and UK in focus. Despite the inclusion of conference searching, there may be relevant grey literature that we did not search. As previously discussed, many of the included studies did not investigate the quality of sedation practice as their primary aim, limiting the relevance of the information provided.


Our review indicates the poor quality of epidemiological data concerning current sedation practice and the incidence of sub-optimal sedation. A key issue is the standardisation of methods of assessment and definitions of optimal sedation. Despite this, available data suggest that many patients in ICUs are considered sub-optimally sedated and, specifically, that the incidence of over-sedation remains high. The strong associations between sedation practice, especially over-sedation, and adverse patient outcomes suggest that a more uniform approach to monitoring depth and quality of sedation will improve quality of care.

Key messages

  • The literature shows that, within the intensive care unit (ICU), a substantial proportion of patients experience inappropriate levels of sedation (that is, under- or over-sedation).

  • There is a greater tendency toward over-sedation in particular.

  • There is a lack of consensus in the literature as to what constitutes optimal sedation practice within the ICU, with little standardisation of either assessment methods or definitions.

  • Improvements in the definition and measurement of optimal sedation may have a positive impact on patient outcomes.

Authors' information

TW is a professor of anaesthetics and critical care at Edinburgh University. DLJ is head of health economics, EMEA (Europe, the Middle East and Africa), at GE Healthcare. CWP is a consultant at Heron Evidence Development Ltd, a health outcomes research consultancy. KFC is a health outcomes analyst at Heron Evidence Development Ltd.



bispectral index monitor


intensive care unit


Richmond Agitation-Sedation Scale


randomised controlled trial.



This review was funded by GE Healthcare. The work was performed at Heron Evidence Development Ltd, UK.

Authors’ Affiliations

GE Healthcare, Pollards Wood, GE Healthcare, Chalfont St. Giles,Nightingales Lane, HP8 4SP, UK,Bucks
Heron Evidence Development Ltd, Luton, Building 210A, Butterfield Technology and Business Park, LU2 8DL, UK
Royal Infirmary of Edinburgh, Edinburgh, Old Dalkeith Road,51 Little France Crescent, EH16 2SA, UK


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