Urinary Antidiuretic Hormone Excretion during Mechanical Ventilation and Weaning in Man

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Abstract
Measurements were made of antidiuretic hormone (ADH) excretion and renal and cardiovascular function in 8 patients with flail chest during 4 ventilatory conditions: continuous positive-pressure ventilation (CPPV), intermittent positive-pressure ventilation (IPPV), spontaneous breathing with continuous positive airway pressure (CPAP) and spontaneous breathing (SB). Each condition was maintained for 6-8 days. ADH excretion was significantly greater during CPPV (181 .+-. 14 ng/24 h, mean .+-. SE) than during IPPV (86 .+-. 10), CPAP (83 .+-. 7) and SB (44 .+-. 6). Free-water clearance was more negative during mechanical ventilation than during CPAP and SB, resulting in significant fluid retention during CPPV and IPPV (440 .+-. 88 and 547 .+-. 70 ml/day) and a negative water balance during SB (-154 .+-. 80 ml/day). Arterial and central venous pressures and cardiac output (measured in 4 patients) did not change significantly among ventilatory conditions. ADH excretion is apparently increased during CPPV. This could represent 1 possible mechanism of water retention with this type of ventilation.