The combination of lactate and bicarbonate buffers in continuous venovenous hemodiafiltration and its impact on serum lactate levels and homeostasis

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Introduction

The buffer substitution of dialysis and hemofiltration is usually performed using either lactate or bicarbonate solutions. Bicarbonate works as a diuretic and it has certain renal tubular protective properties. The use of lactate containing solutions can interfere with the monitoring of lactate as a tissue oxygenation parameter.

Methods

Twelve septic ventilated patients were treated with continuous venovenous hemodiafiltration (CVVHDF). They were monitored before the treatment was started and after 24 and 48 h. The dialysis fluid contained 35 mmol/l of Na-lactate as a buffer. The hemofiltration substitution fluid was Ringer's solution and 8.4% bicarbonate was infused at the average rate of 16.0 ml/h. The dose was calculated initially and it was adjusted later to reach positive BE and mild hypernatremia up to 150 mmol/l. In all patients the dose of furosemide was reduced to 1 mg/kg.day after commencing of the treatment. Hemodynamic monitoring was performed with transesophageal echocardiography in all patients. Systemic oxygen delivery (DO₂) was calculated, oxygen extraction was approximated according to central venous pO₂ (cvpO₂).

Results

Lactate levels were found to be significantly elevated 24 h and 48 h after commencing the treatment: 1.77± 0.68 mmol/l vs 2.70± 0.88 mmol/l (P<0.001) vs 2.52± 1.06 mmol/l (P<0.03). No significant relationship was found between arterial lactate and cvpO₂ before the treatment, but there was an indirect relationship between arterial lactate and cvpO₂ during CVVHDF (correl. coeff.r=-0.5 P=0.01 n=23). The regression equation of the estimate of arterial lactate using cvpO₂ was derived:lactate =6.9-0.81^*cvpO₂.Average DO₂ changed little(777.2± 187.0 ml/min vs 741.5± 171.8 ml/min vs 760.1± 149.6 ml/min). Average sodium did not change but the standard deviation of sodium levels decreased (147.6± 11.4 vs 148.7± 6.9 vs 146.2± 1.9) as well as the standard deviation of base excess (0.83± 5.29 vs 2.24± 4.00 vs 1.74± 3.48). Eight patients (67%) had preserved sufficient residual renal functions. The average time of CVVHDF was 3.83 (3-5) days in six patients who survived (50%).

Conclusion

Lactate remains a valuable marker of tissue hypoxia in patients treated with CVVHDF with constant input of lactate by dialysis. The stabilization of serum tonicity and acid-base balance was recorded. Continuous bicarbonate infusion during early CVVHDF can probably reduce the dose of other diuretics and promote the residual renal functions.