Glycine and ammonia plasma concentrations during sedation with remifentanil in critically ill patients

To investigate glycine and ammonia plasma concentrations during a 72-h remifentanil infusion and the relationship between glycine concentration and remifentanil infusion rate.

A prospective open-label observational clinical trial in a trauma and a neurosurgical intensive care unit in a university teaching hospital.

Nine consecutive patients requiring sedation and ventilatory support for at least 72 h. One was excluded due to acute cardiac failure.

Patients were sedated with remifentanil and propofol. Glycine and ammonia plasma concentrations were measured every 12 h during an intravenous remifentanil infusion performed over 72 h, and 24 h after the end of the infusion. Cumulative remifentanil dose and rate of infusion were recorded for each patient. Clinical and biological signs of glycine toxicity were evaluated.

Glycine and ammonia plasma concentrations did not exceed the toxic threshold at any time. Plasma glycine concentration measured at the end of remifentanil infusion was significantly correlated with the mean weighted rate of remifentanil infusion and with the cumulative remifentanil dose. A correlation between plasma glycine concentration and creatinine clearance at the end of remifentanil infusion was also documented.

Plasma glycine concentration was correlated with the remifentanil cumulative dose and the infusion rate and did not reach the toxic threshold. As glycine concentration was also correlated with creatinine clearance and because remifentanil was the only source of exogenous glycine, additional data are necessary to ascertain the safety of remifentanil infusion in ICU patients.