Helicopter emergency medical services use of thoracic point of care ultrasound for pneumothorax: a systematic review and meta-analysis

BACKGROUND: Auscultating for breath sounds to assess for pneumothorax in the helicopter emergency medical services (HEMS) settings can be extremely challenging. Thoracic point of care ultrasound (POCUS) offers a seemingly more useful visual (rather than audible) alternative. This review critically and quantitatively evaluates the use of thoracic POCUS for pneumothorax in the HEMS setting. METHODS: A systematic literature review with meta-analysis was conducted. Only papers reporting on patients undergoing POCUS for pneumothorax in the helicopter or pre-hospital setting were included. Primary outcome was accuracy, focusing on sensitivity and specificity. Secondary outcome was practicality. PubMed, Embase and the Cochrane Library were searched. The Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) was used to assess validity of studies. RESULTS: Twelve studies reporting on n = 1,936 images from medical and trauma patients were included in qualitative synthesis. Studies were nearly all observational designs. Most images were acquired by nurses or paramedics who were previously novices to ultrasound. The reference standard was predominantly CT. Specificity results were unanimously precise and very high, whereas sensitivity results were imprecise and extremely variable. Meta-analysis of eight studies involving n = 1,713 images yielded pooled sensitivity 61% (95% CI: 27–87%; I(2) = 94%) and pooled specificity 99% (95% CI: 98–100%; I(2) = 89%). Six studies involving n = 315 images reported practicality. The highest or second highest categorisation of image quality was reported in around half of those images. CONCLUSION: Thoracic POCUS is highly specific but has extremely variable sensitivity for pneumothorax when performed in the HEMS setting. This is from purely a diagnostic (not clinical) perspective. Sensitivity increases when only clinically significant pneumothoraces are considered. Case reports reveal thoracic POCUS can appropriately alter treatment and triage decisions, but only for a small number of patients. It appears predominantly useful in mitigating against unnecessary interventions. More research reporting patient focused outcomes is required. In the meantime, thoracic POCUS appears to offer a more appropriate visual alternative to auscultation for breath sounds when assessing for pneumothorax in the HEMS setting.