Cerebrospinal Fluid and Arterial Acid–Base Equilibrium of Spontaneously Breathing Patients with Aneurismal Subarachnoid Hemorrhage

Abstract

Background Hyperventilation resulting in hypocapnic alkalosis (HA) is frequently encountered in spontaneously breathing patients with acute cerebrovascular conditions. The underlying mechanisms of this respiratory response have not been fully elucidated. The present study describes, applying the physical–chemical approach, the acid-base characteristics of cerebrospinal fluid (CSF) and arterial plasma of spontaneously breathing patients with aneurismal subarachnoid hemorrhage (SAH) and compares these results with those of control patients. Moreover, it investigates the pathophysiologic mechanisms leading to HA in SAH. Methods Patients with SAH admitted to the neurological intensive care unit and patients (American Society of Anesthesiologists physical status of 1 and 2) undergoing elective surgery under spinal anesthesia were enrolled. CSF and arterial samples were collected simultaneously. Electrolytes, strong ion difference (SID), partial pressure of carbon dioxide (PCO2), weak noncarbonic acids (ATOT), and pH were measured in CSF and arterial blood samples. Results Twenty spontaneously breathing patients with SAH and 25 controls were enrolled. The CSF of patients with SAH, as compared with controls, was characterized by a lower SID (23.1 ± 2.3 vs. 26.5 ± 1.4 mmol/L, p < 0.001) and PCO2 (40 ± 4 vs. 46 ± 3 mm Hg, p < 0.001), whereas no differences in ATOT (1.2 ± 0.5 vs. 1.2 ± 0.2 mmol/L, p = 0.95) and pH (7.34 ± 0.06 vs. 7.35 ± 0.02, p = 0.69) were observed. The reduced CSF SID was mainly caused by a higher lactate concentration (3.3 ± 1.3 vs. 1.4 ± 0.2 mmol/L, p < 0.001). A linear association (r = 0.71, p < 0.001) was found between CSF SID and arterial PCO2. A higher proportion of patients with SAH were characterized by arterial HA, as compared with controls (40 vs. 4%, p = 0.003). A reduced CSF-to-plasma difference in PCO2 was observed in nonhyperventilating patients with SAH (0.4 ± 3.8 vs. 7.8 ± 3.7 mm Hg, p < 0.001). Conclusions Patients with SAH have a reduction of CSF SID due to an increased lactate concentration. The resulting localized acidifying effect is compensated by CSF hypocapnia, yielding normal CSF pH values and resulting in a higher incidence of arterial HA.

Cerebrospinal fluid and arterial acid–base equilibria in spontaneously breathing third-trimester pregnant women

“…We recently described a reduced DPCO 2 in patients with aneurismal subarachnoid haemorrhage and hypothesised reduced cerebral metabolism as the cause of this finding. 17 However, we do not think that increased cerebral metabolism could explain the finding in the present context, as several studies described a normal cerebral CO 2 production during physiological pregnancy. 9 In pregnant women, the reduction in arterial PCO 2 was marked, whilst CSF PCO 2 varied only slightly.…”

“…Isolated reduction of CSF SID, representative of local CSF metabolic acidosis, is associated with development of sustained hyperventilation both in experimental and clinical settings. 17 , 19 , 20 In this context, central chemoreceptors sense CSF metabolic acidosis and trigger hyperventilation to lower CSF P co 2 and restore physiological CSF pH. 21 During pregnancy, physiological hormonal changes adapt the mother's physiology to fetal development and needs, 5 , 6 , 18 progressively modifying the electrolytes of plasma and CSF.…”

“… 16 The differences between CSF and arterial SID (ΔSID) and CSF and arterial P co 2 (Δ P co 2 ) were computed. 17 The CSF:plasma ratio of the concentrations of sodium and chloride was calculated, and the expected chloride concentration ( ) resulting from blood dilution was estimated as where and were the average values of plasma chloride and sodium, respectively, measured in controls, and was the actual plasma sodium concentration measured for each pregnant woman. Average values of plasma sodium and chloride of controls were chosen as a reference, as they were measured by the same method and are representative of a population of the same sex and similar age.…”

“…16 The differences between CSF and arterial SID (DSID) and CSF and arterial PCO 2 (DPCO 2 ) were computed. 17 The CSF:plasma ratio of the concentrations of sodium and chloride was calculated, and the expected chloride concentration (exp½Cl À ) resulting from blood dilution was estimated as…”

Relationship between the mean of 24-h venous blood glucose and in-hospital mortality among patients with subarachnoid hemorrhage: A matched cohort study

“…Previous researchers have discovered risky factors related to unsatisfactory prognoses (3)(4)(5)(6). BG contents are usually increased on admission posterior to SAH, which might indicate a stress reaction to the bleeding (7)(8)(9)(10)(11).…”