Wide variation and systematic bias in expert clinicians' perceptions of prognosis following brain injury.

BACKGROUND: The heterogeneous nature of traumatic brain injury (TBI) makes outcome prediction difficult. Although a considerable evidence base exists in the form of well-validated predictive models, these models are not widely used. We hypothesised that this prognostic gap, between the availability and use of prognostic data, leads to inaccurate perceptions of patient outcome. We investigated whether outcome predictions in TBI made by expert clinicians were consistent and accurate when compared to a well-validated prognostic model (IMPACT). METHODS: Neurosurgeons and neurointensivists were asked to predict probability of death at 6 months for 12 case vignettes describing patients with isolated TBI. Predictions were compared to IMPACT prognosis for each vignette. To interrogate potential sources of bias in clinical predictions, respondents were given one of two sets of vignettes (A or B) identical apart from one critical factor known to make a large difference to outcome. RESULTS: 27 of 33 questionnaires were returned. Clinicians were consistently more pessimistic about outcomes than the IMPACT model, predicting a significantly greater probability of death (mean difference + 16.3%, 95% CI 13.3-19.4, p < 0.001). There was wide variation between clinicians predicting outcomes for any given vignette (mean range 68.3%), and within the predictions made by each individual: 30% of clinicians were both the most pessimistic respondent, and the most optimistic, for at least one vignette. Clinicians modified their predictions appropriately for most of the factors altered between corresponding vignettes. However when the reported blood glucose was changed, clinicians' predictions deviated widely from IMPACT predictions, indicating that clinicians systematically overlooked the prognostic relevance of this information. CONCLUSION: Clinical experts' predictions of outcome in TBI are widely variable and systematically pessimistic compared to IMPACT. Clinicians overlook important factors in formulating these predictions. Use of well-validated outcome models may add value and consistency to prognostication.

High altitude pulmonary oedema.

High altitude pulmonary oedema (HAPE) is an important and preventable cause of death at high altitudes. However, little is known about the global incidence of HAPE, in part because most cases occur in remote environments where no records are kept. Furthermore, despite international efforts to achieve consensus, there is wide disparity in the diagnostic criteria in clinical and research use. We have reviewed the literature on the incidence and epidemiology of HAPE. There is broad agreement between studies that HAPE incidence at 2500m is around 0.01%, and increases to 1.9% at 3600m and 2.5-5% at 4300m. Risk factors for HAPE include rate of ascent, intensity of exercise and absolute altitude attained, although an individual pre-disposition to developing the condition is also well described and suggests an underlying genetic susceptibility. It is increasingly recognised that clinically-detectable HAPE is an extreme of a continuous spectrum of excess pulmonary fluid accumulation, which has been demonstrated in asymptomatic individuals. There is a continued need to ensure awareness of the diagnosis and treatment of HAPE among visitors to high altitude. It is likely that HAPE is preventable in all cases by progressive acclimatisation, and we advocate a pragmatic "golden rules" approach. Our understanding of the epidemiology and underlying genetic susceptibility to HAPE may be advanced if susceptible individuals register with the International HAPE Database: http://www.altitude.org/hape.php. HAPE has direct relevance to military training and operations and is likely to be the leading cause of death at high altitude.

Passage of pathogenic microorganisms through breathing system filters used in anaesthesia and intensive care.

SUMMARY: Invasive ventilation poses a risk of respiratory infection that can be drug-resistant. One means of reducing transmission of infection is the use of a breathing system filter. Filters are intended to be used with dry gas. Current international standards do not require that filters prevent bacterial transfer when wet. It is not known whether microorganisms pass through wet filters, but theory predicts that this might occur. We tested six filters from three different manufacturers. We passed a suspension of microorganisms through the filters using the least pressure necessary, and incubated a sample of the filtrate on blood agar. All the filters tested allowed free passage of both Candida albicans and coagulase-negative staphylococci. The median (IQR [range]) pressure required for fluid to flow across the filter varied greatly between different filter types (20 (0-48 [0-138]) cmH(2)O). We conclude that even large microorganisms pass across moist breathing system filters in conditions that are found in clinical practice.

Oral antioxidant supplementation does not prevent acute mountain sickness: double blind, randomized placebo-controlled trial.

BACKGROUND: Acute mountain sickness may be caused by cerebrovascular fluid leakage due to oxidative damage to the endothelium. This may be reduced by oral antioxidant supplementation. AIM: To assess the effectiveness of antioxidant supplementation for the prevention of acute mountain sickness (AMS). DESIGN: A parallel-group double blind, randomized placebo-controlled trial. METHODS: The study was conducted in a university clinical research facility and a high altitude research laboratory. Eighty-three healthy lowland volunteers ascended to 5200 m on the Apex 2 high altitude research expedition. The treatment group received a daily dose of 1 g l-ascorbic acid, 400 IU of alpha-tocopherol acetate and 600 mg of alpha-lipoic acid (Cultech Ltd., Wales, UK) in four divided doses. Prevalence of AMS was measured using the Lake Louise Consensus score sheet (LLS). Secondary outcomes were AMS severity measured using a novel visual analogue scale, arterial oxygen saturation and pulmonary artery systolic pressure (PASP). RESULTS: Forty-one subjects were allocated to the antioxidant group, and 42 to the placebo group. There was no difference in AMS incidence or severity between the antioxidant and placebo groups using the LLS at any time at high altitude. At the pre-determined comparison point at Day 2 at 5200 m, 69% of the antioxidant group (25/36) and 66% of the placebo group (23/35) had AMS using the LLS criteria (P = 0.74). No differences were observed between the groups for PASP, oxygen saturation, presence of a pericardial effusion or AMS assessed by VAS. CONCLUSION: This trial found no evidence of benefit from antioxidant supplementation at high altitude. TRIAL REGISTRATION NUMBER: NCT00664001.

Contamination of anaesthetic machines with pathogenic organisms.

Hospital-acquired infections are commonly resistant to antibiotics and cause substantial morbidity and mortality in susceptible populations. Although there is no direct contact between the anaesthetic machine's controls and the patient, there is considerable potential for colonising organisms to be carried between the anaesthetic machine and the patient on the anaesthetist's hands. We performed two cross-sectional studies of bacterial contamination on anaesthetic machines before and after a simple intervention. Without warning, during theatre sessions, bacterial cultures were obtained from anaesthetic equipment. A new departmental policy of cleaning anaesthetic equipment with detergent wipes between cases was then introduced. Six weeks later, again without warning, a further set of cultures was taken. There was significant reduction in the proportion of cultures containing pathogenic bacteria (from 14/78 cultures (18%; 95% CI 9.4-26.5%) before the intervention to 5/77 cultures (6%; 95% CI 1.0-12%) after the intervention (p = 0.03)). The intervention was quick, easy and enthusiastically taken up by the majority of staff. We conclude that cleaning of anaesthetic equipment between cases should become routine practice.