Objective: Although extensively studied in children, the safety and tolerability of ketone supplementation in adults is unclear, particularly in the acute brain injury population. The purpose of this study was to examine the feasibility and safety of inducing ketosis using an enteric ketogenic formulation and determine its impact on intracranial and cerebral perfusion pressures and metabolic parameters.Methods: Prospective interventional Phase II trial of ventilated critically ill patients with acute brain injury administered a ketogenic feed over a 6 day period.Results: 20 patients were recruited, 5 females and 15 males, 3 with stroke, 2 with subarachnoid haemorrhage and 15 with traumatic brain injury. Feeds were well tolerated with 19 patients completing study. There was a significant increase in both plasma beta-hydroxybutyrate and acetoacetate from 0.24± 0.31 mmol/l and 0.19 ± 0.16 mmol/l to 0.61 ± 0.53 mmol/l (p =0.0005) and 0.52 ± 0.40 mmol/l (p<0.0001) respectively over the 6 day period. Total daily Ketocal® caloric intake was positively correlated with plasma beta-hydroxybutyrate concentrations (p=0.0011). There was no significant correlation between the cerebral hypertension and cerebral hypoperfusion indices and plasma ketone concentrations. In 95% of patients there were no clinically significant changes in acid/base status over the 6 days with pH remaining within normal range.Conclusion: In patients with acute brain injury, an enterally administered ketogenic formulation increased plasma ketone concentrations, was well tolerated, did not impact on cerebral hemodynamics and can be safely administered.Clinical trial registered at the Australian New Zealand Clinical Trials Registry (ACTRN12616000332426)Abbreviations: BHB: betahydroxybutyrate; AcAc: acetoacetate; ABI: acute brain injury; TBI: traumatic brain injury; CSF: cerebrospinal fluid; SAH: subarachnoid injury; CVA: cerebrovascular accidents; ICP: intracranial pressure; CPP: cerebral perfusion pressure; ICU: intensive care unit; EVD: external ventricular device; CHI: cerebral hypoperfusion index; IHI: intracranial hypertension index; GCS: Glasgow Coma Scale.