Cerebral acid-base changes during reduced cranial blood flow

Subarachnoid hemorrhage in the rat: cerebral blood flow and glucose metabolism during the late phase of cerebral vasospasm

A double-isotope technique for the simultaneous measurement of CBF and CMRglu was applied to a subarachnoid hemorrhage (SAH) model in the rat. Cisternal injection of 0.07 ml blood caused a rather uniform 20% reduction in CBF together with an increase in glucose utilization of 30% during the late phase of vasospasm. In one-third of the SAH animals, there were focal areas where the flow was lowered to 30% of the control values and the glucose uptake increased to approximately 250% of control. We suggest that blood in the subarachnoid space via a neural mechanism induces the global flow and metabolic changes, and that the foci are caused by vasospasm superimposed on the global flow and metabolic changes. In the double-isotope autoradiographic technique, [14C]iodoantipyrine and [3H]deoxyglucose were used for CBF and CMRglu measurements, respectively, in the same animal. In half of the sections, the [14C]iodoantipyrine was extracted using 2,2-dimethoxypropane before the section was placed on a 3H- and 14C-sensitive film. The other sections were placed on x-ray film with an emulsion insensitive to 3H. The validity of the double-isotope method was tested by comparing the data with those obtained in animals receiving a single isotope. The CBF and metabolic values obtained in the two groups were similar.

Cerebrospinal fluid lactate levels in term infants with perinatal hypoxia

The prognostic value of cerebrospinal fluid (CSF) lactate concentration after an hypoxic-ischemic brain insult was evaluated. Three groups of neonates were studied and followed. Group 1A included 19 asphyxiated neonates who subsequently developed normally, Group 1B included 6 asphyxiated neonates who died or developed neurologic sequelae, and Group 2 consisted of 20 control (comparison) infants. A CSF sample was obtained within the first day of life for cytochemical analysis, culture, and lactate determination with simultaneous determination of serum lactate. The mean CSF lactate level in Group 1B (4.5 mmol/L) was significantly higher than in Group 1A (2.5 mmol/L) (p less than .001). In comparison to the highest CSF lactate concentrations in the normal range in Group 2 (2.7 mmol/L), all Group 1B neonates had elevated CSF lactate levels, and eight neonates (34%) of Group 1A had increased levels. A correlation was found between blood and CSF lactate levels in asphyxiated infants (r = .42, p less than .05), but its meaning is uncertain. We conclude that CSF lactate determinations may be helpful in the evaluation of perinatal hypoxic-ischemic encephalopathy.

Cerebrospinal fluid lactate and pyruvate concentrations in patients with malignant hypertension

Lactate and pyruvate concentrations and acid-base parameters in cerebrospinal fluid (CSF) and arterial blood were measured in 21 patients with malignant hypertension ( MHT ), 19 with benign hypertension (BHT) and 21 normotensive subjects (NT). Average values for CSF lactate and lactate/pyruvate (L/P) ratio were significantly higher in MHT (1.90 +/- 10 mM/1, 19.2 +/- 1.0) than in either BHT (1.50 +/- 0.05 mM/l, 15.7 +/- 0.7) or NT (1.44 +/- 0.04 mM/1, 15.7 +/- 0.4). There was a linear correlation between CSF lactate and CSF pressure (r = 0.565, P less than 0.01), and the latter was also related to mean arterial pressure exceeding 150 mm Hg (r = 0.553, P less than 0.01). Such increases in the acid metabolites in CSF indicate that brain metabolism becomes anaerobic in MHT , probably due to increased intracranial pressure. Increased cerebrovascular permeability is also discussed as participating in causal mechanisms.

Electrolyte composition of cerebrospinal fluid in acute acid-base disorders

Electrolyte composition of cisternal CSF was measured during 4 hours of respiratory and metabolic acid-base disturbance in anesthetized dogs. Three groups of dogs were studied: (1), isocapnic metabolic alkalosis; (2), acute respiratory acidosis; and (3), combined respiratory acidosis and metabolic alkalosis. Cisternal CSF [K+] remained unchanged despite significant changes in plasma [K+], PCO2 and [HCO3-]; suggesting that mechanisms involved in regulation of CSF [K+] continue to operate normally under such conditions. Cisternal [Na+] and osmolality remained unchanged with almost identical reciprocal equimolar changes in CSF concentration of Cl- and HCO3- during the acid-base disorders studied. The regulatory mechanisms involved in this Cl- -HCO3- exchange may be different in different acid-base disorders, but since CSF [Na+] is kept constant, CSF [HCO3-] in any acid-base disorder equals the difference between CSF [Na+] and CSF [Cl-].

Role of PCO2 as determinant of CSF [HCO-3] in metabolic acidosis

To study regulation of CSF [HCO-3] in metabolic acidosis and in particular the role of CSF PCO2 in establishing CSF bicarbonate level, acute metabolic acidosis was induced by the intravenous infusion of HCl in three groups of anesthetized dogs for six hours when PaCO2 was changed at different rates. Plasma [HCO-3] was lowered to 12 +/- 2 meq/L within one hour and maintained at that level thereafter in all groups. (I) Seven dogs were kept isocapnic while metabolic acidosis was induced. The cisternal CSF [HCO-3] fell by only 2.6 meq/L after six hours and was not significantly different from control. (II) In 11 dogs metabolic acidosis was induced while the dogs breathed spontaneously. There was a gradual drop in PaCO2 accompanied by a similar drop in CSF PCO2 of 14.5 torr. CSF [HCO-3] fell significantly by 6.1 meq/L at 6 hours and in parallel with the fall in CSF PCO2. (III) In order to show interdependence of the rate of fall in CSF [HCO-3] with rate of fall in cisternal PCO2 six dogs were mechanically hyperventilated and PaCO2 reduced to 21 torr rapidly and maintained there for six hours. CSF PCO2 followed PaCO. CSF bicarbonate fell rapidly and by 5 meq/L. In groups II and III the fall in cisternal [HCO-3] paralleled the drop in PCO2. Therefore, in metabolic acidosis the rate of the fall in cisternal bicarbonate appears to be a function of the rate of fall in CSF PCO2. It is speculated that the coupling of CSF [HCO-3] reduction in metabolic acidosis to CSF PCO2 fall is primarily for the benefit of CNS H+ homeostasis.

The CSF HCO3 increase in hypercapnia relationshp to HCO3, glutamate, glutamine and NH3 in brain

To study the role of carbonic anhydrase in the CSF [HCO3] increase in respiratory acidosis and its effect on brain ammonia, anesthetized rats were subjected to hypercapnia (7% CO2) for 2 hours. The animals received periodic intraventricular injections of either 'mock' CSF or 'mock' CSF and acetazolamide for 45 minutes prior and during hypercapnia when: (a) plasma [HCO3-] was allowed to increase normally and (2) plasma [HCO3] increase was prevented by i.v. HC1 infusion, CSF [HCO3] increased 8.5 mM/L after 2 hours of hypercapnia (delta PCO2 40) in the rats with intraventricular 'mock' CSF injections, and only 6 mM/L in the animals with acetazolamide injections. CSF [HCO3-] increased 7 mM/L during hypercapnia and HCl infusion with intraventricular 'mock' CSF injections, but only 2 mM/L with acetazolamide injections. Changes in total brain CO2 (increase) and brain glutamic acid (decrease) in hypercapnia were not affected by intraventricular acetazolamide and i.v. HCl. The increase of brain NH4+ and glutamine in hypercapnia was reduced in these conditions. It is concluded that there are at least two sources for the CSF [HCO3-] increase in hypercapnia; one formed in the CNS and dependent on carbonic anhydrase, and the other derived from plasma [HCO3-] increase.

Cerebrospinal fluid and arterial lactate, pyruvate and acid-base balance in patients with intracranial hemorrhages

Lactate and pyruvate concentrations and acid-base balance in cerebrospinal fluid (CSF) and arterial blood were determined in patients with intracranial hemorrhages (28 subarachnoid hemorrhages and 15 intracerebral hemorrhages). A greater increase in CSF lactate and lactate-pyruvate ratio (L/P ratio) was observed in patients with impairment of consciousness, focal neurological deficits, poor prognosis, or CSF pressures higher than 300 mm H2O. A combination of CSF lactate greater than 2.5 mM per liter, L/P ration above 20, bicarbonate less than 20.4 mEq per liter, pH below 7.276, or arterial PCO2 below 31.5 mm Hg seems to indicate poor prognosis from intracranial hemorrhage. The mechanism of hyperventilation in acute cerebrovascular diseases and of CSF pH regulation in acid-base disturbances was also discussed.