The effect of moderate hypovolemia on cardiopulmonary function in dogs

Abstract

Objective: To collate canine cardiopulmonary measurements from previously published and unpublished studies in instrumented, unsedated, normovolemic and moderately hypovolemic dogs. Design: Collation of data obtained from original investigations in our research laboratory. Setting: Research laboratory, School of Veterinary Medicine. Subjects: Sixty-eight dogs. Interventions: Subjects were percutaneously instrumented with an arterial catheter and a thermodilution cardiac output catheter. A femoral artery catheter was percutaneously placed for blood removal. Measurements and main results: Body weight, arterial and mixed-venous pH and blood gases, arterial, pulmonary arterial, pulmonary artery occlusion, and central venous blood pressure, cardiac output, and core body temperature were measured. Body surface area, bicarbonate concentration, standard base excess, cardiac index (CI), stroke volume, systemic and pulmonary vascular resistance, left and right ventricular work and stroke work indices, left and right rate-pressure product, alveolar PO 2 , alveolar-arterial PO 2 gradient, arterial and mixed-venous and pulmonary capillary oxygen content, oxygen delivery, oxygen consumption, oxygen extraction, venous admixture, arterial and venous blood carbon dioxide content, arterial-venous carbon dioxide gradient, carbon dioxide production were calculated.In 68 dogs, hypovolemia sufficient to decrease mean arterial blood pressure (ABPm) to an average of 62 mmHg, was associated with the following changes: arterial partial pressure of carbon dioxide (PaCO 2 ) decreased from 40.0 to 32.9 mmHg; arterial base deficit (BDa) increased from À 2.2 to À 6.3 mEq/L; lactate increased from 0.85 to 10.7 mM/L, and arterial pH (pHa) did not change. Arterial partial pressure of oxygen (PaO 2 ) increased from 100.5 to 108.3 mmHg while mixed-venous PO 2 (PmvO 2 ) decreased from 49.1 to 34.1 mmHg. Arterial and mixed-venous oxygen content (CaO 2 and CmvO 2 ) decreased from 17.5 to 16.5 and 13.8 to 9.6 mL/dL, respectively. The alveolar-arterial PO 2 gradient (A-a PO 2 ) increased from 5.5 to 8.9 mmHg while venous admixture decreased from 2.9% to 1.4%. The ABPm decreased from 100 to 62 mmHg; pulmonary arterial pressure (PAPm) decreased from 13.6 to 6.4 mmHg; and pulmonary arterial occlusion pressure (PAOP) decreased from 4.9 to 0.1 mmHg. CI decreased from 4.31 to 2.02 L/min/m 2 . Systemic and pulmonary vascular resistance (SVRI and PVRI) increased from 1962 to 2753 and 189 to 269 dyn s/cm 5 , respectively. Oxygen delivery (DO 2 ) decreased from 787 to 340 mL/min/m 2 while oxygen consumption (VO 2 ) decreased from 172 to 141 mL/min/m 2 . Oxygen extraction increased from 20.9% to 42.3%. Conclusions: Moderate hypovolemia caused CI and oxygen delivery to decrease to 47% and 42% of baseline. Oxygen extraction, however, doubled and, therefore, oxygen consumption decreased only to 82% of baseline. (J Vet Emerg Crit Care 2005; 15(2): 100-109)

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