It has been shown that the semi-recumbent position reduces the risk of aspiration and the incidence of clinically and microbiologically diagnosed ventilator associated pneumonia (VAP). Nevertheless the benefits of this approach in the neurosurgical patient population remain unclear because previous studies evaluating semi-recumbent positioning and its effect on pneumonia development have excluded neurosurgical patients for fear of decreased cerebral perfusion and differences in institutional policies for positioning.
Our audit protocol was designed to test the hypothesis that a raised head-of-bed 30 degree position is safe for euvolemic patients with traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH) regarding changes in intracranial pressure (ICP) and cerebral perfusion pressure (CPP).
Material and methods
With approval of the Ethics Committee of the RWTH Aachen University which granted a waiver for written informed consent, five patients with SAH and five patients with TBI and ICP at baseline around 10 mmHg were studied. ICP and CPP were measured with the transducers calibrated to the level of the foramen of Monro. Continuous cardiac output (CO) and systemic vascular resistance (SVR) were measured with the PiCCO®-system (Pulsion, Munich, Germany), and transcranial Doppler flow velocities in the middle cerebral artery (MCA), anterior cerebral artery (ACA) and internal carotid artery (ICA) were measured with a 2 MHz Doppler probe (Multi Dop x4®; DWL, Sipplingen, Germany) by the same examiner. A measurement series consisted of a baseline measurement at 30 degrees with a positive end expiratory pressure (PEEP) of 5 cmH2O. PEEP was then increased to 10 and 15 cmH2O, respectively. Between measurements a 5 min equilibration period was granted. After return to baseline and equilibration the position was lowered to flat and measurements were repeated with PEEP of 5, 10 and 15 cmH2O. Measurements were only performed whenever routine nursing procedures required position changes anyway and the clinician judged the patient to be euvolemic based on systolic pressure variation or stroke volume variation patterns.
Data were analysed as percentage of change from baseline and given as mean and confidence interval (CI). Wilcoxon signed rank sum tests were performed between groups when appropriate to determine statistical significance.
The patients included in the study had a Glasgow Coma Scale on admission between 3 and 8, and were sedated with midazolam and sufentanil to a Riker score of 2-3 and mechanically ventilated via an endotracheal tube with an ICP of 10 (±2) mmHg at the time measurements were performed.
Table 1 shows the summary of changes between different PEEP levels and position. A significant increase in ICP and reduction in CPP was seen with position change from 30 degrees to flat. Increase in PEEP from 5 to 10 cmH2O increased ICP without dropping CPP significantly while further increase of PEEP to 15 cmH2O resulted in increased ICP with significant CPP drop. In the 30 degree position a PEEP increase from 5 to 10 cmH2O did not lead to significant changes in ICP or CPP (although there was a trend of increased ICP) and further increase to 15 cmH2O PEEP resulted in significantly increased ICP but no significant change in CPP.
With 30 degrees head-up tilt there was an overall trend towards a mild reduction in cardiac index and a mild increase in SVR, which never reached statistical significance. Cerebral blood flow (CBF) velocity in all measured vessels was either unchanged or minimally reduced.
End-tidal CO2 concentrations did not change during the study period.
Older studies by Rosner and Coley  and March and colleagues  raised controversy about the benefits of the elevated head position in patients with increased ICP because of the potential for CPP reduction. This is especially true in patients who are considered to be hypovolaemic secondary to diuretic therapy or osmotic therapy without adequate volume replacement. Our results indicate that head elevation is safe and effective in reducing ICP and optimising CPP and CI if euvolemia is maintained.
A systematic review by Fan  in 2004 identified 11 clinical trials related to backrest position, ICP and CPP with nine demonstrating a benefit of head elevation in reducing ICP (five out of nine with no significant difference in CPP). Major limitations in all of those trials were small sample sizes and unclear study protocols. One more recent study by Ng and colleagues demonstrated significant ICP reduction and a trend towards improvement of CPP in 38 patients with severe head trauma , which confirms previous findings by Feldman and colleagues, whose data indicated that 30 degrees raise significantly reduced ICP in the majority of the 22 patients studied without reducing CPP or CBF . Measuring brain tissue oxygenation (ti-PO2) in addition to perfusion parameters Meixensberger and colleagues could show decreased ICP and maintained or improved CPP in most of their 22 patients without significant changes in regional ti-PO2.
The influence of PEEP on ICP is mainly related to its effect on venous drainage via changes in central venous pressure. Ludwig and colleagues hypothesized that elevation of the venous outflow resistance and a transient increase in CO have to be considered as mechanisms for transduction of transthoracic pressure changes to ICP changes in a study looking at changes in airway pressures (PAW) in order to predict intracranial elastance . In a study in dogs Toung and colleagues could demonstrate that PEEP linearly increases cerebral venous pressure (CVP) in the prone position but did not increase CVP when the head was elevated . McGuire and colleagues showed that PEEP at 10 and 15 cmH2O increased ICP in patients with normal ICP while in patients with elevated ICP (>15 mmHg) no changes were seen . Huseby and colleagues demonstrated in dogs that PEEP did increase ICP  but the higher the ICP at baseline the less influence PEEP had .
Weyland and colleagues described PaCO2 dependent changes in tone of cerebral vascular resistance vessels as determinant for effective downstream pressure rather than CPP calculated by the classical formula CPP = mean arterial pressure (MAP) - ICP in patients without intracranial hypertension . As we did not observe changes in end-tidal CO2 in our patients we can exclude significant changes in partial pressure of CO2 in arterial blood (PaCO2) and vascular tone.
The major limitation of our study is the small sample size (as in previous attempts to address this issue), which increases the risk of beta error but reflects the nature of a pilot study. The study sequence was not randomized because measurements were performed during routine position changes and the baseline position (30 degrees) was chosen according to the current institutional nursing standard in order to avoid additional manipulations solely for the study.
In summary head-up 30 degrees is beneficial in reducing ICP and optimizing CPP in euvolemic patients with TBI or SAH and also reduces the negative effects of PEEP observed in the flat position. These patients should therefore not be excluded from trials or implementation of protocols trying to reduce the incidence of VAP by raising the head-of-bed. Based on our audit results a large prospective observational study to confirm our findings is warranted. Although a randomized controlled trial would be ideal, exposing patients to the risks of a flat head-of-bed position without clinical necessity was judged to be ethically questionable at the study institution given the magnitude of ICP changes observed, but might be feasible in an institution with a flat head-of-bed policy.
*Department of Anesthesia, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
†Klinik für Neurochirurgie am Universitätsklinikum, der RWTH Aachen, Aachen, Germany
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