Pre-hospital continuous positive airway pressure after blast lung injury and hypovolaemic shock: a modelling study

Mistry, Sonal; Das, Anup; Hardman, Jonathan G.; Bates, Declan G.; Scott, Timothy E.

Abstract

Background
In non-traumatic respiratory failure, pre-hospital application of CPAP reduces the need for intubation. Primary blast lung injury (PBLI) accompanied by haemorrhagic shock is common after mass casualty incidents. We hypothesised that pre-hospital CPAP is also beneficial after PBLI accompanied by haemorrhagic shock.

Methods
We performed a computer-based simulation of the cardiopulmonary response to PBLI followed by haemorrhage, calibrated from published controlled porcine experiments exploring blast injury and haemorrhagic shock. The effect of different CPAP levels was simulated in three in silico patients who had sustained mild, moderate, or severe PBLI (10%, 25%, 50% contusion of the total lung) plus haemorrhagic shock. The primary outcome was arterial partial pressure of oxygen (Pao2) at the end of each simulation.

Results
In mild blast lung injury, 5 cm H2O ambient-air CPAP increased Pao2 from 10.6 to 12.6 kPa. Higher CPAP did not further improve Pao2. In moderate blast lung injury, 10 cm H2O CPAP produced a larger increase in Pao2 (from 8.5 to 11.1 kPa), but 15 cm H2O CPAP produced no further benefit. In severe blast lung injury, 5 cm H2O CPAP inceased Pao2 from 4.06 to 8.39 kPa. Further increasing CPAP to 10–15 cm H2O reduced Pao2 (7.99 and 7.90 kPa, respectively) as a result of haemodynamic impairment resulting from increased intrathoracic pressures.

Conclusions
Our modelling study suggests that ambient air 5 cm H2O CPAP may benefit casualties suffering from blast lung injury, even with severe haemorrhagic shock. However, higher CPAP levels beyond 10 cm H2O after severe lung injury reduced oxygen delivery as a result of haemodynamic impairment.

Citation

Mistry, S., Das, A., Hardman, J. G., Bates, D. G., & Scott, T. E. (2022). Pre-hospital continuous positive airway pressure after blast lung injury and hypovolaemic shock: a modelling study. British Journal of Anaesthesia, 128(2), e151-e157. https://doi.org/10.1016/j.bja.2021.10.012

• Journal Article Type: Article
• Acceptance Date: Oct 14, 2021
• Online Publication Date: Dec 2, 2021
• Publication Date: Feb 1, 2022
• Deposit Date: Dec 10, 2021
• Publicly Available Date: Dec 3, 2022
• Journal: British Journal of Anaesthesia
• Print ISSN: 0007-0912
• Electronic ISSN: 1471-6771
• Publisher: Elsevier BV
• Peer Reviewed: Peer Reviewed
• Volume: 128
• Issue: 2
• Pages: e151-e157
• DOI: https://doi.org/10.1016/j.bja.2021.10.012
• Keywords: Anesthesiology and Pain Medicine
• Public URL: https://nottingham-repository.worktribe.com/output/6917134
• Publisher URL: https://www.bjanaesthesia.org/article/S0007-0912(21)00657-7/fulltext