Influence of Ventilation on Response to Fluid Load in Dogs

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Abstract
Beagle dogs sedated with i.v. pentobarbital were ventilated for 46 h with spontaneous ventilation (SV), controlled ventilation (CV), or controlled ventilation with 10 cm H2O end-expiratory pressure (CV + PEEP). Throughout the study period, saline (0.45% with added KCl) was infused at 120 ml/h. The influence of ventilatory mode on the accumulation and organ distribution of body water during continuous fluid loading was determined. Five animals were studied with each ventilatory mode. In all groups body weight increased, but with SV weight increase began only after 28 h and increased by 7.2% of body wt by 46 h. With CV the weight increase was continuous and was 9.2% of initial body wt at 46 h. With CV + PEEP the increase was earlier and greater, reaching 22% by 46 h. Radioisotopic analysis of total body water, extracellular water, and plasma and erythrocyte water demonstrated that the body weight increase was due to water retention principally in the extracellular compartment. Postmortem analysis of the major body organs for water and albumin distribution demonstrated increased water in the muscle and subcutaneous tissue of the CV + PEEP group that accounted for the total difference in water retention compared to the SV or CV animals. Organ extravascular albumin content varied relatively little between ventilatory modes. Ventilation with increased mean intrathoracic pressure was accompanied by marked and prolonged fluid retention. In these otherwise healthy dogs the water accumulation was confined to sites that appeared unlikely to interfere with organ function.