280	B.K. Abraham and N. Ramakrishnan

•Vasopressin

–Diabetes insipidus (DI) should be suspected in a brain-dead patient when urine output is greater than 5 mL/kg/h for two consecutive hours, and this can be associated with hemodynamic instability.

–If urine-specific gravity is less than 1.005, urine osmolality is less than 200 mOsm/kg, serum osmolality is more than 300 mOsm/kg, and serum sodium is more than 145 mEq/L, a diagnosis of DI can be confirmed.

–Once the diagnosis of DI is confirmed, vasopressin needs to be started.

–Therapy is usually initiated with an infusion of vasopressin at 0.5 unit/h and titrated to a maximum of 6 units/h with an aim of bringing urine output down to 0.5–3 mL/kg/h and serum sodium to 135–145 mEq/L.

–Caution—serum sodium values should be checked every 6 h to assist with titration. Side effects of vasopressin include hyponatremia, digital vasoconstriction, and thrombosis.

–Desmopressin (DDAVP) can be an alternative choice. It is usually given at a dose of 1–4 mcg IV followed by 1–2 mcg IV every 6 h until the above-men- tioned targets are met. However, its drawbacks are that it is more difficult to titrate and does not provide significant hemodynamic support.

•There is still no clear consensus about when to initiate hormonal replacement therapy. Some prefer to initiate methylprednisolone and insulin components of hormonal replacement therapy soon after the first brain death declaration, while levothyroxine and/or vasopressin are initiated only if the patient becomes hypotensive or has diabetes insipidus. Others start all hormones simultaneously as soon as brain death is declared, even if they are hemodynamically stable.

Suggested Reading

1.Wijdicks EF, Varelas PN, Gronseth GS, Greer DM. Evidence-based guideline update: determining brain death in adults. Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 74;2010:1911–8.

An update of the 1995 American Academy of Neurology guideline on brain death.

2.Jennifer A, Frontera TK. How I manage the adult potential organ donor: donation after neurological death (Part 1). Neurocrit Care. 2010;12:103–10.

A practical guide for managing brain dead organ donor.

3.Goila AK, Pawar M. The diagnosis of brain death. Indian J Crit Care Med. 2009;13(1):7–11.

4.Wood KE, Becker BN, McCartney JG, D’Alessandro AM, Coursin DB. Care of the potential organ donor. N Engl J Med. 2004;351:2730–9.

A classic article on management of brain death organ donor.

5.Wijdicks EFM. The diagnosis of brain death. N Engl J Med. 2001;344:1215–21.

A classic article on diagnosing brain death.

Websites

1.www.aan.com

American Association of Neurology web sites for professional standards for determining brain death.

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2.www.thamburaj.com/brain_death.htm Neurosurgeons insight into brain death criteria.

3.www.neurologyindia.com

An archive of leading articles on brain death.

Part IV

Gastrointestinal System

Ajay Kumar and Pravin Amin