We have compared the EEG and auditory evoked wave P300 with psychometric tests in assessing vigilance after flumazenil antagonism of midazolam sedation in 12 healthy volunteers. Measurements were made before and after midazolam 0.1 and 0.2 mg kg-1 i.v., and immediately and 30, 60, 120 and 240 min after administration of flumazenil 1 mg. The sedative effects of midazolam and antagonism by flumazenil resulted in alterations in EEG, P300 and psychometric tests (syndrome short test, letter cancellation, choice reaction and recognition). However, 60 and 120 min after flumazenil a decrease in test performance indicating rebound sedation was seen only in P300 mapping. Thus P300 mapping was a sensitive method of detecting subtle differences in vigilance. Rebound sedation occurred even when midazolam 0.2 mg kg-1 was antagonized with an adequate dose of flumazenil. We suggest that it is advisable to supervise patients for at least 240 min after flumazenil antagonism of midazolam 0.2 mg kg-1.

Objective parameters are needed to quantify cerebral dysfunction following cardiac surgery in outcome and comparative studies. In this investigation we assessed the value of the late auditory evoked potentials N100 and P300 to measure the neuropsychological deficit after coronary artery bypass grafting (CABG). N100, an exogenous potential is influenced by the stimulus pattern (frequency, intensity and stimulus presentation rate). P300, an endogenous potential, depends on the cognitive processing invoked by the stimulus. With approval of the Human Investigation Committee and the patients' consents, 52 subjects undergoing elective CABG were enrolled. Operation, extracorporal circulation, anesthesia and postoperative intensive care were standardized. Twenty-channel recordings of N100 and P300 were obtained for off-line analysis. P300 was elicited using an oddball paradigm with rare target tones interspersed among frequent non-target tones. Additionally, neuropsychological tests (syndrome short test SKT and letter cancellation test) were carried out. Neurological examination and all tests were compared preoperatively and one week postoperatively. A significant deterioration in cerebral function was documented by the SKT score (P = 0.04), an increase in P300 latency (P = 0.004) and an increase of mistake rate in counting the P300 target tone (P = 0.02). No differences between preoperative and postoperative testing were found for letter cancellation, P300 amplitude and any N100 parameter. No correlation was found between the preoperative/postoperative changes in SKT score and P300 latency. P300 was proved to be an objective neurophysiological parameter that allows for the quantification of cerebral function after CABG.

SummaryThe cf;f;.ct ( Key wordsHaernoglobin; half-saturatio? pressure, oxygen transport, oxyhaemoglobin dissociation curve. Pso. Oxygen; oxygen-haemoglobin affinity.Many factors affect the oxygen supply to the tissues. These include the pattern of the capillary network, the magnitude and the distribution of the capillary flow, the presence of oxygen stores (myoglobin), diffusion rates, and the instantaneous oxygen consumption; but essentially the oxygen supply is determined by the arterial oxygen tension and the shape and the position of the oxygen-haemoglobin association/dissociation curve. A right-shift, expressed by an increase of the Pso (tension at 509, saturation of haemoglobin). usually enhances oxygen release. whereas a left-shift represents an increase in oxygenhaemoglobin affinity and impedes the unloading of oxygen. Stimulated by a short article written by Tien, I the quantitative effects that different Pso values would theoretically exert on oxygen release were studied. and the conditions under which the dissociation curve of healthy adults with a Pso of 3.53 kPa is most appropriate were determined. This study started because the author was intcrested to discovcr the effects outlined above. The results seem of sufficient general educational intercst to justify a wider audience and the results are presented in order LO achieve this. MethodsThe calculations are based on Hill's equation

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