Article 4

Acid-Base Response to High

Volume Haemofiltration in the Critically Ill


Lim Ju Boo



The effects of acid-base balance on the body buffers, lung function and kidney function are well established. Disturbances in the acid-base balance may be featured by mild CNS (central nervous system) dysfunction and abnormalities of respiration. Acidosis may be suggested by a marked decline in conscious level with confusion and irritability. A classical sign is Kussmaul’s respiration (deep, sighing breathing). Clinical signs are rare in alkalosis (blood pH shifted towards alkalinity), but severe alkalosis may be accompanied by depression of conscious level and hypoventilation. Tetany (muscle spasms due to muscular hyperexcitability) may be present due to low ionised calcium.

The acid-base and cardiorespiratory effects of intermittently pumped high-volume veno-venous haemofiltration (HVHF) using replacement fluid containing lactate as the source of biocarbonate in critically ill-patient was studied (haemofiltration is a form of haemodialysis which requires the same access to the blood circulation as haemodialysis. The patient’s cardiac output drives the blood through a small, highly permeable filter: this permits the isolation of fluid and solutes: this haemofiltrate is measured, discarded, and is replaced with an isotonic solution).

It was demonstrated that there was a significant hyperlactataemia (too much of lactic acid in the blood) throughout the procedure, but there was no deterioration in acid-base status, haemodynamics (the forces involved in circulating blood round the body), or oxygen delivery. These observations suggest that the worsening of acidosis and hypotension that have been described with this technique can be avoided by appropriate monitoring and resuscitation prior to haemofiltration, and may be due to unrecognized inadequacies in the oxygen transport system as shown by Nimmo (1). It is known that in critically ill patients with inadequate ventilation, and hypoperfusion, there will be shift in normal cellular energy transfer from aerobic to anarobic metabolism, resulting in metabolic acidosis. The relationship between elevated serum lactic acid and hypovolemic shock and even death is well known, as shown long ago by Huchabee (2), and more lately by Weil, et al (3).


Reference:

1. Nimmo, G.R; Mackenzie, S.J; Walker, S; Nicol, M; Grant, I.S. Nephrol-Dial-Transplant. 1993; 8(9): 854-7.

2 Huckabee W. Relationships of pyruvate and lactate during anaerobic metabolism: Effects of infusion of pyruvate or glucose and of hyperventilation. J Clin Invest (1958) 37:244

3 Weil M, Afifi A. Experimental and clinical studies on lactate and pyruvate as indication of the severity of acute circulatory failure. Circulation (1990), 41:989