The relationships between cerebral blood flow (CBF), cerebral metabolism (cerebral metabolic rate of oxygen, CMRO2) and cerebral oxygen extraction (arteriovenous difference of oxygen, AVDO2) are discussed, using the formula CMRO2 = CBF × AVDO2. Metabolic autoregulation, pressure autoregulation and viscosity autoregulation can all be explained by the strong tendency of the brain to keep AVDO2 constant. Monitoring of CBF, CMRO2 or AVDO2 very early after injury is impractical, but the available data indicate that cerebral ischemia plays a considerable role at this stage. It can best be avoided by not "treating" arterial hypertension and not using too much hyperventilation, while generous use of mannitol is probably beneficial. Once in the ICU, treatment can most practically be guided by monitoring of jugular bulb venous oxygen saturation. If saturation drops below 50%, the reason for this must be found (high intracranial pressure, blood pressure not high enough, too vigorous hyperventilation, arterial hypoxia, anemia) and must be treated accordingly.

Electroencephalography (EEG) and evoked potential studies are established monitoring tools in the neurological intensive care unit (ICU). These neurophysiologic techniques provide information on physiological state and response to therapy, and may aid diagnosis and prognosis. Serial studies or continuous monitoring may enable changes to be detected prior to irreversible deterioration in the patient's condition. Current computer technology allows simultaneous display and correlation of electrophysiologic parameters, cardiovascular state and intracranial pressure (ICP). Continuous EEG monitoring in the ICU has been shown to have a decisive or contributing impact on medical decision making in more than three-quarters of patients. In addition, continuous EEG monitoring has revealed previously unsuspected non-convulsive seizures in one-third of patients. SEPs and BAEPs can provide useful prognostic information in coma - however, these tests are etiologically nonspecific and must be carefully integrated into the clinical situation. Motor evoked potentials offer a potentially useful tool for evaluating motor system abnormalities in the ICU.

This paper describes the development and testing of a computer algorithm to automate the process of peak identification and somatosensory evoked potential (SSEP) grading. We tested the accuracy of computerized peak detection and evaluated grading schemes using a test set of 60 SSEPs ranked from worst to best by the programmer (RJM) and a blinded grader (PO). The computer algorithm recognized 95% of peaks identified by visual inspection. Twelve percent of peaks identified by the computer were noise. Summed peak to peak amplitude gave the most accurate ranking of SSEPs. Rank correlation between computer and blinded and unblinded expert grading was r = .82 for PO, r = .92 for RJM, p < .0001 for both. Computer and manually summed amplitudes were highly correlated (Pearson r = .98, p < .0001). Correlation between the 2 expert graders was .86, p < .0001. Computer graded SSEPs were significantly related to clinical outcome at 3 months, p < .0001. Automatic grading of SSEPs using summed peak to peak amplitude is highly correlated with expert grading. The measure is objective, continuous, and well suited to statistical analysis.

Guillain-Barré syndrome causes, in addition to paralysis and respiratory failure, many general medical problems that have great bearing on outcome. The main features of daily care that require attention are: respiratory and urinary tract infections, gastrointestinal dysfunction, hyponatremia, pain control, and the potential for pulmonary embolism. Dysautonomic problems that arise specifically in the intensive care unit include: hyper- and hypotension, cardiac arrhythmias, and ileus. Throughout the illness, certain psychological aberrations and communication problems must be addressed. The experience reviewed herein provides a practical approach to these problems.

Disorders of both the central and peripheral nervous systems are important causes of respiratory insufficiency. However, simple clinical observations and pulmonary function measurements may fail to identify the location and type of disorder. This can often be accomplished by the newly-developed technique of phrenic nerve conduction and needle electromyography of the diaphragm which delineate the various disturbances of central drive, axonal or demyelinating neuropathies of the phrenic nerves and certain myopathies. These studies have been preformed safely and with little discomfort on adults, children or infants, and in out-patient and general ward settings. We have found they are of particular value in the intensive care unit.