Summary of findings for the main comparison. Altered backrest position for severe traumatic brain injury.

Altered backrest position for severe traumatic brain injury
Patient or population: people with severe traumatic brain injury (adults and children) Settings: intensive care Intervention: altered backrest position (head‐of‐bed elevation (HBE)) Comparison: any other backrest position (the studies used a flat position or 30 degree elevation as the baseline)
Outcomes	Results	No of participants (studies)	Quality of the evidence (GRADE)	Comments
Mortality	Out of a total of 20 participants who served as their own control, there was one death at final follow‐up 28 days after hospital admission	20 (3 studies)	⊕⊝⊝⊝ Very low1,2	We are uncertain about the effects of altered backrest position in participants with severe TBI
Intracranial pressure (ICP) Follow‐up: ≤ 1 h	The findings across these three small studies were inconsistent, with two showing no evidence of an effect of HBE on ICP, and one showing a negative linear association with high intra‐study heterogeneity	20 (3 studies)	⊕⊝⊝⊝ Very low1,2,3	Due to the unclear risk of bias, inconsistency and the very small number of participants, we are uncertain about the effect of altered backrest position on ICP in participants with severe TBI
Cerebral perfusion pressure (CPP) Follow‐up: ≤ 1 h	These three small studies showed no effect of HBE on CCP	20 (3 studies)	⊕⊝⊝⊝ Very low1,2	Due to the unclear risk of bias, and in particular the very small number of participants, we are uncertain about the effect of altered backrest position on CPP in participants with severe TBI
Quality of life; Glasgow Coma Score; Disability	No studies measured quality of life, Glasgow Coma Score or disability
Adverse events	All three studies reported adverse events, and none occurred. One participant experienced an increase in ICP in response to the intervention, which resolved when the height of the bed was returned to the baseline position.	20 (3 studies)	⊕⊝⊝⊝ Very low1,2	We are uncertain about the adverse effects of altered backrest position in participants with severe TBI
CPP: cerebral perfusion pressure; HBE: head‐of‐bed elevation; ICP: intracranial pressure; TBI: traumatic brain injury
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

¹Downgraded one level due to limitations in design and execution leading to risk of bias: there are methodological aspects that are unclear (allocation concealment, blinding of participants and personnel, and outcome assessment).
 ²Downgraded two levels due to a high imprecision: the number of participants is very low and the confidence intervals very wide.
 ³Downgraded one level due to inconsistency: the three studies that measured this outcome had inconsistent results.