Clinical background
Dr Michael Fox served as a diving medicine consultant with the Royal Navy, based at the Submarine Escape Training Tank in Gosport, one of the few facilities in the United Kingdom where medical staff routinely treated patients presenting with arterial gas embolism — the condition where gas bubbles enter the arterial circulation and cause ischaemic injury, most commonly to the brain or spinal cord. His experience was gained over decades of direct clinical practice, not merely academic study. That operational background distinguishes his commentary on the Letby case from that of clinicians whose knowledge of gas embolism is confined to the theoretical literature.
The prosecution’s air-embolism theory
Several counts in the Letby indictment alleged that she injected air into infants’ intravenous lines, causing cerebral arterial gas embolism leading to sudden collapse and death. The prosecution’s expert evidence, led by Dr Dewi Evans, asserted that air introduced into a venous line could traverse the pulmonary vasculature and reach the cerebral arterial circulation. Dr Fox has challenged this account on well-established physiological grounds. In a healthy patient with an intact cardiopulmonary anatomy, venous gas entering the right heart is trapped in the pulmonary capillary bed and cannot cross into the arterial system. Arterial gas embolism via venous injection requires a right-to-left cardiac shunt — typically an atrial septal defect or a patent foramen ovale under conditions of elevated right atrial pressure.
The shunt requirement and what was not alleged
The indictment did not allege, and the prosecution’s expert witnesses did not establish, that any of the infants had a right-to-left shunt of sufficient size and haemodynamic significance to allow venous gas to pass into the systemic arterial circulation. In diving medicine, paradoxical arterial gas embolism via a patent foramen ovale is a recognised phenomenon, but it occurs under conditions — raised intrathoracic pressure, Valsalva manoeuvre, specific diving profiles — that are not analogous to a neonatal intensive care setting. Dr Fox has argued that without establishing a plausible anatomical pathway, the prosecution’s air-embolism hypothesis cannot be maintained as a matter of physiology, irrespective of the clinical findings on the infants’ post-mortem or radiological records.
Significance of direct clinical experience
The value of Dr Fox’s commentary lies in the specificity of his clinical experience. Most hospital-based paediatricians and pathologists encounter arterial gas embolism rarely, if at all; the condition is most common in the diving, aviation, and cardiac surgery contexts. Dr Fox’s familiarity with how true arterial gas embolism presents — the pattern of neurological deterioration, the radiological findings, the time course — allows him to compare the clinical picture in the Letby counts directly against the established presentation of the condition rather than against a textbook description. His assessment is that the presentations in the trial counts do not replicate the characteristic features of iatrogenic arterial gas embolism as seen in diving medicine practice.
Read alongside
- Evidence: air embolism
- Analysis: air-embolism line by line
- Dr Dewi Evans — prosecution expert
- Dr Sandie Bohin — defence expert
- Commentary library
Source
Public statements and interviews by Dr Michael Fox; Royal Navy Submarine Escape Training Tank clinical records (public domain); published diving medicine literature on paradoxical arterial gas embolism and right-to-left shunts.