INTERACTIONS BETWEEN HEMODYNAMIC AND HORMONAL MODIFICATIONS DURING PEEP-INDUCED ANTIDIURESIS AND ANTINATRIURESIS

The interactions between hemodynamic and hormonal modifications during antidiuresis and antinatriuresis induced by positive end-expiratory p ressure (PEEP) were studied in six patients under 15 cm H2O PEEP befor e PEEP and after the addition of lower body positive pressure (LBPP) t o PEEP (PEEP+LBPP). We measured or calculated the following: cardiac i ndex, systemic arterial, right atrial, pulmonary arterial, and pulmona ry artery occlusive pressures; indexed renal blood now (iodohippurate 131 sodium clearance); total blood volume (chromium 51 radiolabeled RB Cs); glomerular filtration rate; urinary output; fractional excretion of sodium (FE Na+); plasma concentrations of antidiuretic hormone (ADH ), plasma renin activity (PRA), norepinephrine and epinephrine; urinar y concentration of PGE(2) (PGE(2)u). Although LBPP application correct ed PEEP deleterious effects on systemic and renal hemodynamics, sustai ned fall in Vu and in FE Na+ were observed. Antidiuresis was not due t o ADH release. Sympathetic activation and high PRA appeared the main d eterminants of renal function alterations in PEEP ventilation.