Ziya L. Gokaslan

Cerebral blood flow, arteriovenous oxygen difference, and outcome in head injured patients.

Cerebral blood flow (CBF) and other physiological variables were measured repeatedly for up to 10 days after severe head injury in 102 patients, and CBF levels were related to outcome. Twenty five of the patients had a reduced CBF [mean (SD) 0.29 (0.05) ml/g/min]; 47 had a normal CBF, (0.41 (0.10) ml/g/min); and 30 had a raised CBF (0.62 (0.14) ml/g/min). Cerebral arteriovenous oxygen differences were inversely related to CBF and averaged 2.1 (0.7) mumol/ml in the group with reduced CBF, 1.9 (0.5) mumol/ml in the group with normal CBF, and 1.6 (0.4) mumol/ml in the group with raised CBF. Patients with a reduced CBF had a poorer outcome than patients with a normal or raised CBF. Mortality was highest in patients with a reduced CBF, and was 32% at three months after injury, whereas only 21% of the patients with a normal CBF and 20% of the patients with a raised CBF died. There were no differences in the type of injury, initial score on the Glasgow Coma Scale, mean intracranial pressure (ICP), highest ICP, or the amount of medical treatment required to keep the ICP less than 20 mm Hg in each group. Systemic factors did not significantly contribute to the differences in CBF among the three groups. A logistic regression model of the effect of CBF on neurological outcome was developed. When adjusted for variables which were found to be significant confounders, including age, initial Glasgow Coma Score, haemoglobin concentration, cerebral perfusion pressure and cerebral metabolic rate of oxygen, a reduced CBF remained significantly associated with an unfavourable neurological outcome.

Dynamic Pressure Volume Index via ICP Waveform Analysis

Intracranial pressure (ICP) monitoring is used as an early sign of neurological deterioration in the management of patients with a variety of neurosurgical conditions. Mean ICP is the most commonly used for this purpose; however, mean ICP is a relatively late indicator of many secondary injury processes, and neurological deterioration may occur in the presence of normal ICP.

Barbiturates, Cerebral Blood Flow and Intracranial Hypertension

Although their efficacy in improving outcome from severe head injury is difficult to prove (Ward et al. 1985; Schwartz et al. 1984; Miller 1979), it has conclusively shown that in certain patients barbiturates can reduce intracranial hypertension (ICH) refractory to conventional measures (Marshall et al. 1979; Rockoff et al. 1979; Rea and Rockswold 1983; Eisenberg et al. 1988). The mechanism of this effect remains unclear. It has been demonstrated that under normal physiological conditions, barbiturates in anesthetic doses, decrease cerebral blood flow (CBF) (Michenfelder and Milde 1975) and cerebral metabolic rate of oxygen (CMRO2) (Michenfelder and Milde 1975) and lactate (CMRL) (Carlsson et al. 1975). This prospective study was undertaken to ascertain the effects of barbiturates on these parameters in patients with ICH with the aim of deriving mechanistic insights and possibly identifying features that would characterize patients responsive to barbiturates (responders).

Intracranial Compliance Monitoring with Computerized ICP Waveform Analysis in 55 Comatose Patients

A computerized system that estimated the intracranial compliance (ICC) from an analysis of the frequency content of the intracranial pressure (ICP) waveform has been previously described as a means of monitoring ICC continuously and avoiding the volumetric manipulations of the cerebrospinal fluid (CSF) system (Bray et al. 1976). We have reported earlier that shifts within the frequency range of 4 to 15 Hz were related to changes in the compliance of the brain (Bray et al. 1976). The power weighted mean frequency within this range was defined as the High Frequency Centroid (HFC = C2 centroid) and was shown to have an excellent inverse relationship to the pressure volume index (PVI). A HFC of 6.5–7.0 Hz was normal, and a HFC of 9.0 Hz corresponded to a critical reduction in the PVI to approximately 13 ml (Bray et al. 1976).