Kidney injury is a serious complication of cardiac surgery that occurs in up to 30% of
patients and increases the risk of adverse outcomes. Kidney injury initiates when oxygen
supply to the kidney drops below levels that are needed for normal cellular function, causing
tissue oxygen deficiency (hypoxia), activation of the inflammatory cascade, and oxidative
stress. Together, these events further impair tissue oxygenation, culminating in impaired
kidney function due to cellular injury and death.

There are no effective therapies for kidney injury after cardiac surgery, but there is
evidence that recovery is possible if the processes of injury – i.e., impaired oxygen
delivery, increased inflammatory response, and oxidative stress – are ameliorated soon after
the onset of injury. Hyperbaric oxygen therapy (HBOT) – which entails the intermittent
inhalation of 100% oxygen in a hyperbaric chamber at a pressure higher than one absolute
atmosphere (> 760 mmHg) – has been shown to positively affect all of these processes (i.e.,
to improve tissue oxygenation, reduce inflammation, and reduce oxidative stress). Thus, we
hypothesized that HBOT will reduce the severity of kidney injury after cardiac surgery if it
is initiated soon after onset of injury. This hypothesis has not been tested in humans, but
is supported by animal studies.

In this first-in-human, unblinded, controlled pilot trial, 20 adult patients who develop
severe kidney injury soon after cardiac surgery will be randomized (after obtaining informed
consent from the patient or surrogate) to standard-of-care or early HBOT. Severe kidney
injury will be defined as a ≥30% drop in kidney function within 6 hours of surgery (as
determined by change in creatinine from before surgery to Intensive Care Unit (ICU)
admission). This degree of injury occurs in ~ 2% of patients and is associated with a 12-fold
increase in the risk of complete kidney failure (requiring dialysis) or death. Patients will
be excluded if they have any relative or absolute contraindications to HBOT (e.g., severe
ventricular dysfunction, ventricular assist device, severe respiratory dysfunction,
pneumothorax, bronchospasm).