Effect of neuromediators on the acid-base balance

Acute and chronic experiments on dogs showed correlation between the state of the adrenergic, cholinergic, and serotoninergic systems, on the one hand, and the acid-base balance of the animal on the other hand. An excess of each mediator was accompanied by respiratory alkalosis and a deficiency by mixed respiratory and metabolic acidosis.Laboratory of Pathological Physiology, Kazan' Research Institute of Traumatology and Orthopedics, Ministry of Health of the RSFSR. (Presented by Academician of the Academy of Medical Sciences of the USSR N. A. Fedorov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 11, pp. 525–528, November, 1978.     

Impact of continuous veno-venous hemofiltration on acid-base balance

BACKGROUND: Continuous veno-venous hemofiltration (CVVH) appears to have a significant and variable impact on acid-base balance. However, the pathogenesis of these acid-base effects remains poorly understood. The aim of this study was to understand the nature of acid-base changes in critically ill patients with acute renal failure during continuous veno-venous hemofiltration by applying quantitative methods of biophysical analysis (Stewart-Figge methodology). METHODS: We studied forty patients with ARF receiving CVVH in the intensive care unit. We retrieved the biochemical data from computerized records and conducted quantitative biophysical analysis. We measured serum Na+, K+, Mg2+, Cl-, HCO3-, phosphate, ionized Ca2+, albumin, lactate and arterial blood gases and calculated the following Stewart-Figge variables: Strong Ion Difference apparent (SIDa), Strong Ion Difference Effective (SIDe) and Strong Ion Gap (SIG). RESULTS: Before treatment, patients had mild acidemia (pH: 7.31) secondary to metabolic acidosis (bicarbonate: 19.8 mmol/L and base excess: -5.9 mEq/L). This acidosis was due to increased unmeasured anions (SIG: 12.3 mEq/L), hyperphosphatemia (1.86 mmol/L) and hyperlactatemia (2.08 mmol/L). It was attenuated by the alkalinizing effect of hypoalbuminemia (22.5 g/L). After commencing CVVH, the acidemia was corrected within 24 hours (pH 7.31 vs 7.41, p<0.0001). This correction was associated with a decreased strong ion gap (SIG) (12.3 vs. 8.8 mEq/L, p<0.0001), phosphate concentration (1.86 vs. 1.49 mmol/L, p<0.0001) and serum chloride concentration (102 vs. 98.5 mmol/L, p<0.0001). After 3 days of CVVH, however, patients developed alkalemia (pH: 7.46) secondary to metabolic alkalosis (bicarbonate: 29.8 mmol/L, base excess: 6.7 mEq/L). This alkalemia appeared secondary to a further decrease in SIG to 6.7 mEq/L (p<0.0001) and a further decrease in serum phosphate to 0.77 mmol/L (p<0.0001) in the setting of persistent hypoalbuminemia (21.0 g/L; p=0.56). CONCLUSIONS: CVVH corrects metabolic acidosis in acute renal failure patients through its effect on unmeasured anions, phosphate and chloride. Such correction coupled with the effect of hypoalbuminemia, results in the development of a metabolic alkalosis after 72 hours of treatment.     

Pre and interdialytic acid-base balance in hemodialysis patients

In an observational study, nine hemodialysis patients using 35 mmol/l bicarbonate dialysate were studied over a 44-hour interdialytic interval. Serum bicarbonate was measured at regular intervals at home and the mean time averaged concentration was 27.0+/-1.2 mmol/l. Seven of the nine patients showed a slow linear decline in bicarbonate whilst in two patients levels were unchanged. In 8 of 9 patients the average of the post and predialysis bicarbonate accurately predicted the time-averaged (area under the curve) bicarbonate concentration. In addition, predialysis serum bicarbonate was measured in 46 patients after both a 2 and 3-day interdialytic interval. The serum bicarbonate was significantly lower after the 3-day interdialytic interval (3-day, 22.1+/-0.6 vs 2-day, 23.0+/-0.5 mmol/l, p<0.05). The results from this study emphasize the importance of standardization of bicarbonate measurement in order to avoid spurious acidosis.     

Switching from three times a week to short daily online hemodiafiltration: effects on acid-base balance

AIMS: This study examines the effect of a change from the standard 4-5 hours 3 times a week of online hemodiafiltration (OL-HDF) to 2-2.5 hours daily (6 times a week) OL-HDF, on acid-base balance, and attempts assess the modifications of acid-base parameters, ionic concentration, and electrical charges of albumin and phosphate available for diffusion and convection mechanisms across the membrane and subsequent infusion. METHODS: In 18 patients on online HDF, blood gas, electrolytes (Na, K, Cl), lactate, phosphate, albumin, apparent strong ion difference (SIDa), effective strong ion difference (SIDe), strong ion gap (SIG), anion gap (AG), and bicarbonate and pH time-averaged concentration (TAC) and time-averaged deviation (TAD) variables were evaluated at baseline, and 1, 3, 6, 9, and 12 months after patients were switched to daily OL-HDF. Additionally, in 12 patients, the same parameters measured simultaneously at dialyzer inlet, outlet, and after reinfusion were studied. RESULTS: Throughout the study, weekly single-pool Kt/V, equilibrated Kt/V, and TAC urea remained constant. However, standard Kt/V increased and TAD urea decreased on daily OL-HDF. There were no statistical differences during the time span of 12 months in pH, cations (Na, K), anions (Cl, HCO3(-) AG, and lactate), or SIDa, SIDe, and SIG pre-HDF; while pH and HCO3(-) TAD decreased from 0.02 and 1.02 +/- 0.74 mEq/L, to 0.01 and 0.64 +/- 0.52 mEq/L, respectively (p<0.01). Net albumin charge and AG increased significantly at dialyzer outlet and decreased after reinfusion. CONCLUSIONS: We did not observe changes in the acid-base balance in patients who switched from 3 times a week to short daily OL-HDF. The main benefit observed was a lower pH and bicarbonate TAD. This shows a better physiology for daily OL-HDF.     

Comparison of the acid-base balance in cisternal and lumbar cerebrospinal fluid

Summary Although the arterial blood showed no indication of respiratory or metabolic changes, the mean pH value of the cisternal CSF was found to be 0.021 pH units higher, and the mean 2.53 mm Hg lower, than the corresponding values in simultaneously sampled lumbar CSF.     

Ventilation and acid-base balance during graded activity in lizards

Arterial PCO2, hydrogen ion ([H+]a), and lactate ([L]a) concentrations, rates of metabolic CO2 production (VCO2) and O2 consumption (VO2), and effective alveolar ventilation (Veff) were determined in the lizards Varanus exanthematicus and Iguana iguana at rest and during steady-state treadmill exercise at 35 degrees C. In Varanus, VCO2 increased ninefold and VO2 sixfold without detectable rise in [L]a at running speeds below 1.0 to 1.5 km x h-1. In this range, Veff increased 12-fold resulting in decreased levels of PaCO2 and [H+]a. At higher speeds [L]a rose. Increments of 5 mM [L]a were accompanied by hyperventilation, reducing PaCO2 and thus maintaining [H+]a near its resting level. When [L]a increased further, [H+]a increased. Sustainable running speeds (0.3-0.5 km x h-1 and below) were often associated with increased VO2, VCO2, and [L]a in Iguana. Sixfold increases in VCO2 and 9-mM increments in [L]a were accompanied by sufficient increase in Veff (9-fold) to maintain [H+]a at or below its control level. When [L]a increased further, [H+]a increased. These results indicate that both lizard species maintain blood acid-base homeostasis rather effectively via ventilatory adjustments at moderate exercise intensities.