1 Background

Sedation is used to avoid agitation-related harm, mitigate stress and improve patient comfort [1]. With various sedation goals, sedative regimens are administrated selectively in different patients. The 2013 PAD guidelines suggest using nonbenzodiazepines (such as propofol and dexmedetomidine) over benzodiazepines (such as midazolam and lorazepam) for sedation in adult critically ill patients, for their advantages in shortening ICU length of stay, and decreasing the incidence of delirium [2].

With their own distinct pharmacological properties and limitations, sedation regimens used intravenously including midazolam, dexmedetomidine, propofol and lorazepam, haloperidol are available for common clinical use in ICU. Many studies comprehensively analyze the role of each sedative for critically ill patients [3,4,5,6,7,8]. However, the latest randomized, controlled study [9] showed that in ventilated patients, using dexmedetomidine for sedation did not result in lower 90-day mortality than usual care, which showed difference with previous studies.

Bayesian network analysis provides evidence from direct and indirect comparisons. In this study, we aim to perform a Bayesian network analysis for the effect of sedation regimens on outcome in adult critically ill patients.

2 Material and Methods

The protocol was registered in the International prospective register of systematic reviews (CRD42019137705).

2.1 Search Strategy

We searched the following databases: Elsevier, Cochrane Central Register of Controlled Trials, Medline and Web of Science databases. We used keywords as searching terms: ‘sedative’ or ‘sedation’ or ‘dexmedetomidine’ or ‘propofol’ or ‘benzodiazepine’ or ‘midazolam’ or ‘lorazepam’ and ‘critical ill’ or ‘critical illness’ or ‘intensive care units’ or ‘intensive care’ or ‘ICU’ or ‘critical care’ or ‘ventilated’ or ‘mechanical ventilation’. Studies published from inception to June 11, 2019 were searched. Additional files or supplemental materials of the studies were reviewed if available. Additional file 1—Search strategy showed search strategies.

2.2 Study Selection

Potential eligible studies were screened, and relevant full-text manuscripts were acquired. Two reviewers assessed studies for the inclusion and exclusion criteria, independently. If there were disagreements, we discussed with another reviewer.

2.3 Inclusion and Exclusion Criteria

Features of the included studies were as follows:

  1. 1.

    Type of studies were prospective and randomized trials;

  2. 2.

    Population were adult patients who admitted to ICU;

  3. 3.

    Regimens were used intravenously for sedation;

  4. 4.

    Studies reported all-cause mortality, including ICU or hospital mortality, 28-day or 90-day mortality, or mortality at other time points.

Studies with theses features were excluded:

  1. 1.

    Who were not published as original articles;

  2. 2.

    Studies compared sedation regimens with other sedation methods, eg. music therapy;

  3. 3.

    Studies with no data of mortality;

  4. 4.

    Full-text articles were unachievable.

Primay outcome was as follows:

Longest mortality, if there are different mortality data published in one study, for example, 28-day and 90-day mortality were both recorded, the longest complete followup was preferentially used.

Secondary outcome were grouped as follows:

  1. 1.

    ICU length of stay

  2. 2.

    Incidence of delirium

  3. 3.

    Incidence of bradycardia and hypotension

2.4 Quality Assessment

Two reviewers assessed study quality independently. If there were disagreements, a discussion was performed with another reviewer. Six aspects were performed for assessing the risk of bias, including allocation concealment, random sequence generation, blinding, incomplete outcome data, selective reporting and other bias. The risk of bias was assesseed as low risk, unclear risk, or high risk.

2.5 Data Extraction

Data including mortality were extracted by two reviewers. If there were disagreements, a discussion was performed with another reviewer. If there were different morality values, the longest mortality was used. An e-mail contact to the authors was perfomed if information was insufficient.

2.6 Statistical Analysis

Data were analyzed using Stata version 14. For dichotomous data, the odd ratio (OR) was reported. For continuous data, mean difference (MD) a with 95% confidence intervals (CIs) were reported. Most continuous data were displayed by mean ± standard deviation (SD). If continuous data were reported in median and interquartile ranges, they were converted to mean ± SD by the following equation: median instead of mean, and SD was equal to interquartile range divided by 1.35.

We performed pair-wise meta-analyses firstly, and used forest plots to investigate the statistical heterogeneity and the I2 statistic. Bayesian network using Markov chain Monte Carlo methods in WinBUGS was used to assess dichotomous data in all arms of each study. We used p value < 0.05 and 95% CIs to assess significance.

To assess consistency, when the inconsistency factors were close to 0, and the 95% CI contained the neutral value, as well as the random effects variance and the inconsistency variance were roughly equal, the data were seemed as consistent. The consistency model was used.

The probability of best sedatives, the second and the third best was assessed by calculation of the OR for each sedation regimen when compared with another.

In the cumulative meta-analysis, considering type-I errors always resulting from an increased risk of error, trial sequential analysis (TSA; TSA software version 0.9 Beta; Copenhagen Trial Unit, Copenhagen, Denmark) was used to combine size estimation with an adjusted threshold for total statistical significance. Calculated as diversity-adjusted information size, information size was suggested by the relative risk reduction of the intervention.

3 Results

3.1 Study Location and Selection

A number of 8,635 records were shown by initial search, and 2,016 records as duplicates. Then the rest 6,619 records were screened, and 67 eligible studies were included. Among them, 35 studies were excluded for no data on mortality; 3 studies were excluded for the study type; 2 studies were excluded for the improper control group and administration route. Finally, 27 studies [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34] including 8,599 critically ill adult patients were gathered in the meta-analysis. The flow diagram is shown in Fig. 1.

Fig. 1
figure 1

Flow diagram of the search process and study selection

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Additional file 2—Excluded articles showed the detailed excluded articles.

3.2 Patient and Public Involvement

No patient involved.

3.3 Characteristics of the Studies

Characteristics of the studies are presented in Table 1. Half of the studies were carried out in the United States and Europe; five studies were performed in more than one country; and half of the studies were multi-center studies. Overall, five sedation regimens, usual care and placebo were analyzed. Eight studies had more than 100 participants per group, 23 studies had two-arms and 4 studies had three-arms involving two different sedatives compared with placebo or usual care. Level of sedation are shown in Additional file 3. Detailed longest mortality data and other outcome are shown in Additional file 3 and 4.

Table 1 General characteristics of the studies included in the Bayesian network analysis
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Quality assessments are shown in Fig. 2. Risk of bias graph is shown in Additional file 5.

Fig. 2
figure 2

Quality assessment for all included trials

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Network graph for the longest mortality is shown in Fig. 3. In a network plot, direct comparisons between sedatives including lorazepam, midazolam, propofol, dexmedetomidine, haloperidol and placebo or usual care are represented by edges, and the nodes represent a sedation strategy. Each two-arm study contributes to one comparison. The edge thickness is proportional to inverse standard error of random effects model comparing different sedation strategy, nodes are weighted according to the number of studies.

Fig. 3
figure 3

Network graph for the longest mortality. Direct comparisons between five sedatives including lorazepam, midazolam, propofol, dexmedetomidine, haloperidol and placebo or usual care are represented by edges in a network plot, and the nodes represent a sedation strategy. Each two-arm study contributes to one comparison. The thickness of the edge is proportional to inverse standard error of random effects model comparing different sedation strategy, nodes are weighted according to the number of studies. Usual care defined as midazolam combined with propofol were used for sedation

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3.4 The Impact of Different Sedatives on Longest Mortality and ICU Length of Stay

The effects of different sedation regimens on longest mortality are summarized by Fig. 4. For longest mortality, no significant differences were found among different sedatives. However, when compared with dexmedetomidine, placebo, propofol and usual care, midazolam group had significantly longer ICU length of stay.

Fig. 4
figure 4

Longest mortality and ICU length of stay of sedation regimens. Sedation regimens are shown in alphabetical order. Results are the ORs in the column-defining treatment compared with the ORs in the row-defining treatment. For longest mortality, ORs higher than 1 favor the column-defining treatment. For ICU length of stay, ORs lower than 1 favor the first drug in alphabetical order. Significant results are shown in bold and underscored

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TSA was performed with α = 0.05 and β = 0.20 (power 80%) to correct for random error and repetitive testing of sparse data. Based on the intervention effect, diversity-adjusted information size was suggested using a random effects model (with a relative risk reduction of 12% regarding mortality and 5141 patients). TSA indicated lack of reliable evidence for a beneficial effect of dexmedetomidine for mortality (Additional file 6), considering the monitoring boundary not surpassed and the required information size not reached.

3.5 The Impact of Different Sedation Regimens on Incidence of Delirium in Adult Critically ill Patients

The effect of different sedatives on delirium are summarized by Fig. 5. When compared with midazolam, dexmedetomidine group had a significantly lower incidence of delirium.

Fig. 5
figure 5

Incidence of delirium for sedation regimens. Sedation regimens are shown in alphabetical order. Results are the ORs in the column-defining treatment compared with the ORs in the row-defining treatment. ORs higher than 1 favor the column-defining treatment

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3.6 The Impact of Different Sedation Regimens on Hypotension and Bradycardia

The effects of different sedation regimens on the incidence of hypotension and bradycardia in adult critically ill patients are reported by Additional file 7. When compared with usual care, dexmedetomidine group and propofol group had higher incidence of hypotension. When compared with midazolam and placebo, dexmedetomidine group had higher incidence of bradycardia.

3.7 The Impact of Different Sedation Regimens on Outcome in Sepsis patients

Detailed characteristics of the studies which included sepsis patients are summarized by Additional file 8 (Table S8-1). For longest mortality (Figs. S8-1, S8-2), ICU length of stay, no significant differences were found among sedatives in sepsis patients.

No significant differences were found for longest mortality (Fig. S8-3), ICU length of stay (Fig. S8-4), incidence of delirium (Fig. S8-5) among sepsis patients who used dexmedetomidine compared with other sedatives.

3.8 The impact of Different Sedation Regimens on Outcome in Invasive Ventilated Patients

Detailed characteristics of the studies which included invasive ventilated patients are summarized by Additional file 9 (Table S9-1). For longest mortality, no statistically significant differences were found among sedatives in invasive ventilated patients by pair-wise meta-analyses (Fig. S9-1).

No statistically significant differences were found for longest mortality (Fig. S9-2) and incidence of delirium (Fig. S9-4) among invasive ventilated patients who used dexmedetomidine compared with other sedatives. However, compared with sedatives other than dexmedetomidine, dexmedetomidine for sedatives shortened ICU length of stay (Fig. S9-3) and duration of mechanical ventilation significantly (Fig. S9-5).

3.9 The Impact of Different Sedation Regimens on Outcome in Postoperative Patients

Detailed characteristics of the studies which included postoperative patients are summarized by Additional file 10 (Table S10-1). For longest mortality, dexmedetomidine group reduced longest mortality significantly when compared with placebo, however, no other significant differences were found among sedatives in postoperative patients (Fig. S10-1).

No significant differences were found for longest mortality (Fig. S10-2) and ICU length of stay (Fig. S10-3) among postoperative patients who used dexmedetomidine or other sedatives. However, there was a trend toward lower incidence of delirium (Fig. S10-4) for postoperative patients who used dexmedetomidine (p = 0.05), when compared with sedatives other than dexmedetomidine.

3.10 The Impact of Different Sedation Regimens on Outcome in Patients with a Higher Severity of Disease

The effects of different sedation regimens on outcome in severe critically ill patients are summarized by Additional file 11. In 19 studies, the severity of disease was reported, 17 studies by the acute physiology and chronic health evaluation II score (APACHE II score). The distinction between higher and lower severity was differentiated by the means or medians of APACHE II scores. For higher severity of disease (APACHE II score ≥ 20), the detailed characteristics of the studies are presented by Table S10-1. No significant differences were found among sedatives for mortality in more severe patients (Fig. S11-1).

No significant differences were found for longest mortality (Fig. S11-2), ICU length of stay (Figure S11-3), incidence of delirium (Figure S11-4) among patients with a higher severity of disease who used dexmedetomidine compared with other sedatives.

4 Discussion

This is an integrate analysis for mortality, ICU length of stay, incidence of delirium, common adverse events including hypotension and bradycardia when compare different intravenous sedatives in adult critically ill patients and common type of ICU patients (including all critically ill patients, sepsis patients, mechanical ventilated patients, postoperative patients and patients with higher severity of disease). In this study, no significant differences were found for mortality of different sedatives. However, when compared with midazolam, dexmedetomidine group had a shorter ICU length of stay and a lower incidence of delirium significantly. Meanwhile, midazolam group have a longer ICU length of stay when compared with placebo, propofol and usual care. When compared with usual care, dexmedetomidine group and propofol group had a significantly higher incidence of hypotension. When compared with midazolam and placebo, dexmedetomidine group had a significantly higher incidence of bradycardia.

There are many network meta-analyses exploring the effectiveness of sedatives in the critically ill [7, 35,36,37]. However, this is the first network analysis to evaluate the effect of sedatives on mortality, ICU length of stay and incidence of delirium in critically ill patients, moreover, subgroup analyses were performed in sepsis, ventilated and postoperative patients, which covering most kinds of patients admitted to ICU. Second, other drugs which not commonly used for sedation were excluded for comparison, as management of pain and sedation should use for different objectives. In this meta-analysis, TSA indicated lack of firm evidence due to considerable heterogeneity between groups. More randomized, controlled trials are needed to determine the effects.

In subgroup analyses, comparisons of different sedatives were performed in sepsis, ventilated and postoperative patients, as well as patients with a higher severity of disease, respectively. In sepsis patients, no statistically significant differences were found among sedatives in sepsis patients for longest mortality, ICU length of stay and the incidence of delirium. In invasive ventilated patients, no significant differences were found for longest mortality and incidence of delirium among who used dexmedetomidine or other sedatives. However, compared with sedatives other than dexmedetomidine, dexmedetomidine for sedatives shortened ICU length of stay significantly.

In postoperative patients, dexmedetomidine reduced longest mortality significantly when compared with placebo, however, no other statistically significant differences were found among sedatives. However, there was a trend toward lower incidence of delirium for postoperative patients who used dexmedetomidine, when compared with sedatives other than dexmedetomidine, which were consistent with another network analysis [38].

The latest guideline recommends early goal-directed sedation, which targeted effective analgesia and light sedation. So it is difficult to compare the drugs used for sedation without considering the level of sedation. Most of the ongoing research in this field does take this into account. Although included studies used different method to assess the sedation level, only few studes targeted deep sedation, most studies targeted light sedation, as a result, we still need more studies to observe the relationship between sedation level and outcome.

Interactions between sedation and ventilation are a topic of the highest importance when comparing the sedation regimens, however, few studies shown the detailed ventilatory settings in the study, so it is hard to find the relationship between them.

There are some limitations in the study. Firstly, critically ill patients who enrolled in the network analysis were heterogeneous. That’s why subgroup analysis was performed to seek the appropriate sedatives for the right patients. Secondly, the controlled sedatives were different, which may have an influence on the results. Last but not the least, this analysis included both direct and indirect comparisons, which lead to the reduced statistical power and uncertainty. Meanwhile, studies were included only if they published in English, which may introduce bias.

5 Conclusions

In this Bayesian network analysis, the results suggested clinically important differences exist between commonly prescribed sedation regimens for both ICU length of stay and incidence of delirium in favor of dexmedetomidine and usual care.

However, TSA indicated lack of firm evidence for the results, more powered, randomized, controlled trials are needed to determine the effects.