Barbiturate coma - side effects

 Q: Which of the following is NOT a side-effect of pentobarbital induced coma? 

 A) delay in brain death determination 

 B) need of vasopressor 

 C) aadynamic ileus 

 D) risk of ventilator-associated pneumonia 

 E) severe acidosis from ethylene-glycol toxicity 

Answer: E

The induction of barbiturate coma is a common practice in neuro-surgical ICUs. In severe cases of high intracranial pressure (ICP), it helps in decreasing cerebral metabolic demand, Cerebral Blood Flow (CBF), and cerebral blood volume. Its infusion is monitored by continuous electroencephalography (EEG) monitoring, with the objective of a burst-suppression pattern. Barbiturate coma comes with its own price of various side-effects. Due to its very long half-life, there is frequently a delay in brain death determination. Hypotension is a norm and the need for pressor(s) is universal which may lead to arrhythmias as well as organs dysfunction. It also causes ileus. Poor mucus clearance increases the risk for ventilator-associated pneumonia (VAP). Pentobarbital is often prepared in propylene-glycol (not ethylene-glycol - choice E) and longer infusions may result in severe metabolic acidosis.

The objective of the above question is to highlight the dangers of iatrogenic propylene glycol toxicity in ICUs which is used as a diluent in many intravenous infusions including phenytoin, diazepam, and lorazepam besides pentobarbital.

#pharmacology

References:

1. Zosel A, Egelhoff E, Heard K. Severe lactic acidosis after an iatrogenic propylene glycol overdose. Pharmacotherapy. 2010;30(2):219. doi:10.1592/phco.30.2.219 

2. Miller MA, Forni A, Yogaratnam D. Propylene glycol-induced lactic acidosis in a patient receiving continuous infusion pentobarbital. Ann Pharmacother 2008; 42:1502.

3.  Roberts I, Sydenham E. Barbiturates for acute traumatic brain injury. Cochrane Database Syst Rev 2012; 12:CD000033. 

4. Brain Trauma Foundation, American Association of Neurological Surgeons, Congress of Neurological Surgeons, et al. Guidelines for the management of severe traumatic brain injury. XI. Anesthetics, analgesics, and sedatives. J Neurotrauma 2007; 24 Suppl 1:S71.