Drugs and brain death

Fast, Simple, and Validated Gas Chromatographic-Mass Spectrometric Assay for Quantification of Drugs Relevant to Diagnosis of Brain Death in Human Blood Plasma Samples

In addition to total anamnesis, one of the important aspects in diagnosis of brain death is the exclusion of effective plasma concentrations of drugs that might mimic brain death. A minimum consensus for toxicological analysis in this context includes relevant analytes (thiopental, pentobarbital, methohexital, phenobarbital, diazepam, nordazepam, and midazolam) and proposes limits of quantification. Propofol is another relevant drug. After liquid-liquid extraction of 200 microL of plasma using 50 microL of a solution of deuterated internal standards in butyl acetate and 50 microL of butyl acetate, 2 microL of the organic phase was analyzed by gas chromatography-mass spectrometry using selected-ion monitoring mode. Validation included the parameters selectivity, calibration model, precision and accuracy, and extraction efficiency. Accuracy and precision data obtained using 6-point and 1-point calibration were compared. The abovementioned analytes were separated within 10 minutes and sensitively detected. No interfering peaks were observed in blank samples from 10 different sources. The linearity ranges were 0.5-6 mg/L for propofol, 0.25-10 mg/L for pentobarbital and thiopental, 0.125-10 mg/L for methohexital, 2.5-50 mg/L for phenobarbital, 0.05-2.5 mg/L for diazepam and nordazepam, and 0.01-0.5 mg/L for midazolam. Extraction efficiency ranged from 85% to 111%. The acceptance criterion for accuracy and precision (99% confidence interval of measured mean within +/-50% of target value) was fulfilled for all analytes, even with 1-point calibration using a calibrator close to the center of the linearity range. The assay was applied to analysis of real brain death cases. In conclusion, the described assay allowed fast and reliable determination of analytes relevant to diagnosis of brain death, and 1-point calibration kept the workload low.

Survey of Intensive Care Units and Availability of Drug Assays in Australasia

The availability of drug assays, toxicologic screens, or both can play a significant role in the clinical decision-making processes affecting comatose patients with brain injury, including the decision to continue life support. However, with the widespread trend to reduce such comprehensive laboratory services down to core routine drugs, many clinical staff are finding it increasingly difficult to obtain such assay results in a time-frame relevant to the clinical needs of their patients and families. The authors have surveyed the intensive care units in Australasia to assess their perspectives in this area. The results from 53% of units responding showed there was insufficient clinical pharmacologic support available. Whereas the majority of centers had ready access to the standard immunoassays and urine drug screens, few had access to more complex assays, especially in the time-frame that was required. Interestingly, there was wide variability between centers as to the time to terminate life support in the absence of other indices (e.g., 4-vessel angiography). The use of basic pharmacokinetic principles including drug half-life was practiced in some centers, albeit probably inappropriately in this patient subpopulation. There is generally insufficient availability of specialized drug assay laboratories to meet clinical demands, primarily because of reduction in services and financial constraints in the public hospital system.

Determination of midazolam in human plasma by solid-phase microextraction and gas chromatography/mass spectrometry

A new method is described for the qualitative and quantitative analysis of midazolam, a short-acting 1,4-imidazole benzodiazepine, in human plasma. It involves a plasma deproteinization step, solid-phase microextraction (SPME) of midazolam using an 85-microm polyacrylate fiber, and its detection by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode, using pinazepam as internal standard. The assay is linear over a midazolam plasma range of 1.5-300 ng/mL, relative intra- and inter-assay standard deviations at 5 ng/mL are below 7%, and the limit of detection is 1 ng/mL. The method is simple, fast and sufficiently sensitive to be applied in clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring.

Drugs and brain death

IN THE EARLY HOURS of the morning, a fit young man leaves a party, where drugs are reported to have been consumed, to walk home. A short time later he is found unconscious by the roadside, with severe head injuries. En route to hospital by ambulance, he suffers a cardiac arrest and is successfully resuscitated. On arrival at the Emergency Department he has obvious head injuries and is deeply unconscious, but shows spontaneous ventilatory movements. Available history is that he is a 20-year-old student with well-controlled epilepsy for which he takes phenytoin. It is not known how he sustained his injuries. Pupils are equal, small and react sluggishly to light. There is generalised flaccidity and an extensor-plantar response to painful stimuli. Skull x-rays show no fractures and computed tomography shows early cerebral oedema and scattered cerebral contusions with evidence of subarachnoid haemorrhage. He is transferred to the intensive care unit and measures to inhibit cerebral oedema, including mannitol, are commenced. An N-methyl-D-aspartate (NMDA) inhibitor is administered for neuroprotection and ventilatory support is commenced. Over the next 24 hours haemodynamic support is needed with fluid loading and vasopressors. A urine drug screen by Toxilab (Toxilab Incorporated, Irvine, Calif.) shortly after arrival shows the presence of phenytoin and morphine. The report states that the presence of benzodiazepines is suspected. Plasma phenytoin concentration at the time of arrival was 78 mumol/L (optimal range, 40-80 mumol/L). Forty hours after admission his condition has deteriorated. His pupils are at midposition, no longer reactive to light and his lower limbs exhibit only spinal reflexes. His relatives begin to prepare themselves for the fact he may not survive and raise the issue that he would have been keen to donate organs under such circumstances. What is the opinion regarding withdrawal of life support at this time?