Respiratory drive and pulmonary mechanics during haemodialysis with ultrafiltration in ventilated patients

Abstract

The improvements of respiratory drive and pulmonary mechanics which follow haemodialysis with ultrafiltration in mechanically ventilated renal failure patients seem predictable but have not been studied before. In this study, 14 renal failure patients with stable haemodynamics mechanically ventilated with pressure support ventilation (PSV) were enrolled. Respiratory drive (represented as PO.1), pulmonary mechanics, breathing pattern, arterial blood gas and haemodynamics were measured according to the time schedule; pre-dialysis (Time 0), and at 60, 120, 180, 240 minutes thereafter. Following the removal of excess lung water during haemodialysis, auto-PEEP and patient's work of breathing (WOBp) decreased gradually. PO.1 lessened progressively along with the improvements in pulmonary mechanics. The changes in auto-PEEP and WOBp correlated closely to the pre- and post-dialysis decline of PO.1 (ΔPO.1). There was a negative, moderately significant correlation between the amount of fluid ultrafiltrated during dialysis (ΔUF) and the ΔPO.1 (R = -0.54). The breathing pattern remained stable during dialysis. No hypoventilation or hypoxaemia occurred despite the development of metabolic alkalosis induced by bicarbonate dialysate. We have shown that respiratory drive decreases gradually during bicarbonate haemodialysis. The improvements of pulmonary mechanics, rather than the rapid alkalization of body fluids, responds to the decrease of PO.1 in renal failure patients ventilated with PSV.