Barbiturates

Specimen:

5 mL blood in lithium heparin or plain tube.

Method:

Chromatography.

Spectrophotometry is unsuitable as it does not identify specific barbiturates.

Therapeutic Interval:

Definition of the toxic level depends on the type of barbiturate administered.

Application:

Assessment of barbiturate overdose.

See Phenobarbitone for therapeutic monitoring.

In patients with severe head injury thiopentone assay is occasionally required to differentiate reversible CNS depression due to administered thiopentone from brain death.

Interpretation:

Depends on the barbiturate identified and the time since ingestion or administration. 

Brain death cannot be reliably diagnosed if a significant level of thiopentone is still present.

Reference:

Porter WH, Moyer TP. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 2nd ed. Philadelphia: WB Saunders, 1994.