The continuous measurement of cerebrospinal fluid gas tensions in critically ill neurosurgical patients: a prospective observational study

Abstract

Objective: To determine the feasibility and usefulness of continuous cerebrospinal fluid pH and gas tension monitoring in critically ill neurosurgical patients. Design: Prospective, observational study. Setting: Neurosurgical intensive care unit in a teaching hospital. Patients: Five critically ill neurosurgical patients (GCS < 8) requiring intensive care intracranial pressure monitoring and intermittent positive pressure ventilation. Interventions: Placement of a Paratrend 7 sensor into the external ventricular drain. Measurements and main results: The cerebrospinal fluid (CSF) pH, PCO₂ and PO₂ were recorded at 1-min intervals. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were recorded at 15-min intervals. The mean baseline CSF pH, O₂ and PO₂ values were 7.28 ± 0.08 pH units, 44 ± 6 torr and 43 ± 27 torr, respectively. The ranges of CSF pH, PCO₂ and PO₂ observed during the study were 6.3–7.8 pH units, 37–150 torr and 4–150 torr, respectively. A statistically significant correlation between ICP, CPP and CSF gas tensions occurred in patient 3. Significant changes in CSF PO₂ and pH were observed with augmentation of CPP and preceded clinical improvement in patient 4. There were no complications attributable to sensor placement. CSF gas tensions and pH values obtained from patients 3 and 4 suggest that these measurements may be an indicator of cerebral perfusion. Conclusions: Continuous CSF gas tension measurements in critically ill patients are possible and may be an indicator of adequacy of cerebral perfusion. The relative merits and limitations of the technique are discussed.