Changes in brain surface and cisternal fluid pH during Na-pentobarbital induced cardiac arrest in dogs

This paper describes the changes in the brain surface pH and cisternal cerebrospinal fluid (CSF) acid-base variables during Na-pentobarbital induced cardiac arrest in anesthetized dogs. Brain surface pH, reflecting brain extracellular fluid (ECF) pH was measured by rapidly responding flat surface pH electrodes. Cardiac arrest was induced by intravenous injection of large amounts of Na-pentobarbital (60 to 400 mg/kg). The mean arterial blood pressure fell from 138 +/- 20.8 (mean +/- 1 SD; n = 5) to 33.0 +/- 9.8 mmHg within 30 s after bolus injection of pentobarbital, indicating a rapid fall in cerebral blood flow. Brain surface pH fell abruptly and profoundly; 1 1/2 and 3 min after induction of cardiac arrest, the mean pH had fallen from 7.34 to, respectively, 7.05 and 6.81. Cisternal CSF pH changes were considerably slow with the mean pH falling from 7.35 to 7.00, 10 min after induction of cardiac arrest. This study demonstrates that during stagnant hypoxia there is abrupt and profound cerebral acidosis; more importantly, however, the data indicate that cisternal CSF pH changes lag behind brain ECF pH changes under such circumstances; analysis of cisternal CSF will grossly underestimate the magnitude of severity of brain metabolic derangement up to 10 min after cardiac arrest.