Pulmonary-renal axis during positive-pressure ventilation.

Controlled mechanical ventilation with positive end-expiratory pressure (PEEP) is generally associated with decreases in urine volume and renal sodium excretion. The resulting positive sodium and water balance is an undesirable side effect of controlled mechanical ventilation with PEEP. The increase in intrathoracic pressure initiates a cascade of hemodynamic, neural, and hormonal changes which, in turn, stimulate the kidney to decrease the glomerular filtration rate and increase tubular reabsorption. The redundancy of these regulatory mechanisms makes it difficult to determine the involvement of only one or two single parameters as causative events of the phenomenon.