This study will be targeting patients suffering from acute brain injury (ABI), including those with severe trauma brain injury (sTBI) and those with aneurysmal sub arachnoid hemorrhage (aSAH).

This clinical study is an open-label, non-randomized, single-center, exploratory metabolic study.

The primary objective is to determine changes from baseline (before enteral administration of Peptamen AF) in plasma and brain extracellular levels of MCFAs and Ketone bodies in sTBI patients upon Peptamen AF nutritional support.

Inclusion Criteria:

• Comatose patients (defined by an initial Glasgow Coma Scale (GCS) < 9) following sTBI or aSAH.
• Female or male, aged >18.
• Abnormal head CT-Scan (contusions, hematoma).
• Intracranial monitoring with CMD, [PbtO2] and [ICP] probes as part of standard of care.
• Written informed consent from an independent physician (not associated to the research project) who provides medical follow-up and defends patient's interests.
• Written informed consent from patient relative/legal representative confirming the presumed patient willingness to participate in the study

Exclusion Criteria:

• Signs of brain death or expected brain death within 48h.
• Pregnancy.
• Hemodynamic instability (circulatory shock, requiring vasopressors).
• Renal or liver insufficiency .
• Chronic intestinal disease.
• Patients requiring parenteral nutrition .
• Currently participating or having participated in another clinical trial during the month preceding the study