The effect of changing from pressure support ventilation to volume control ventilation on renal function.
OBJECTIVE
Mechanical ventilation increases intrathoracic pressure and decreases cardiac output, and the associated hormonal changes may affect the free water, sodium and creatinine clearance. We sought to establish if there was any difference in creatinine clearance, urine volume and fractional excretion of sodium (FE(Na)) between pressure support ventilation (PSV) and volume controlled (VC) ventilation.


METHODS
The study took place in a 10 bedded metropolitan intensive care unit that admitted both medical and surgical patients. The study was a within subjects, non-randomised, controlled procedures design. Patients were included if they were ventilated on volume control ventilation (VC) with a constant positive end expiratory pressure (PEEP) and suitable for pressure support ventilation (PS), a mean arterial pressure of > 65 mmHg, a normal serum creatinine, well-hydrated and catheterised. Exclusion criteria were administration of a loop diuretic or renal dopamine in the six hours preceding the onset of the study, clinical adrenal dysfunction or clinically unstable requiring a change in intravenous fluid therapy. Eight patients completed four hours of VC ventilation and had renal functions monitored and then changed to PS ventilation for a one hour washout period. Four hours of PS were maintained and renal function monitored over a second four hour period. Patients remained on PS and then after a one hour washout on VC the final four hour monitored period on VC was completed. Urine and serum samples were collected for urine volume, fractional excretion of sodium and creatinine clearance during each four hour cycle on VC and PS ventilation.


RESULTS
Friedman's test statistical analysis revealed no significant difference in creatinine clearance (p = 0.54), fractional excretion of sodium (p = 0.58) or urine volume (p = 0.42).


CONCLUSIONS
VC ventilation had no adverse effects on renal indices in comparison to spontaneous PS ventilation.
Intensive Care Unit, Frankston Hospital, Frankston, Victoria.
J
J
Botha
P
P
Mudholkar
V
V
Le Blanc