Evaluation of Hemodynamic Changes in Normovolemic Hypotensive Dogs Treated With Fluids Alone or in Combination With...

Normovolemic hypotension occurs due to vasodilation or loss of vascular tone in conditions such as distributive or neurogenic shock. Studies have shown that fluid therapy alone is insufficient in restoring blood pressure in normovolemic hypotension, necessitating the use of complementary drugs.

This study aimed to evaluate the effects of fluid therapy with Ringer's solution combined with ephedrine or dobutamine in normovolemic dogs undergoing hypotension induced by isoflurane anaesthesia.

Anaesthesia in 29 mixed-breed dogs was induced with propofol (6 mg/kg) titration and maintained with inspired 1.5% isoflurane in 100% oxygen. A total of 15 min after instrumentation (30 min), hypotension (mean arterial blood pressure [MAP] below 60 mmHg) was induced by 3% isoflurane, confirming a direct MAP reading below 60 mmHg for 10 min. Dogs were given one of five treatments of Ringer's solution (1 mL/kg/min, n = 5), Ringer's plus ephedrine (0.2 mg/kg, n = 6), Ringer's plus dobutamine (5 µg/kg/min, n = 6), ephedrine (dosage 0.2 mg/kg, n = 6) and dobutamine (5 µg/kg/min, n = 6). If direct MAP reached over 60 mmHg and was maintained for 10 min, treatment was discontinued, and the data were recorded. If treatment did not achieve the target of 60 mmHg within 15 min, it was continued for another 15 min. Following the second attempt, drug administration was halted after another 15 min, regardless of the direct MAP level, and the data were recorded. Cardiorespiratory (heart rate, blood pressure, central venous pressure, end tidal CO₂, SPO₂ and rectal temperature) and blood gas values were monitored across multiple time points.

Three dogs in the R, two in the D and one in the RE, RD and E treatments needed re-administration of therapy. Three dogs in R and one in RD and D did not show direct MAP > 60 mmHg after re-treatment until the isoflurane concentration decreased. After treatment, heart rate was significantly higher in Ringer's plus dobutamine than in dobutamine (p = 0.007) and ephedrine (p = 0.016). Respiratory and metabolic acidosis were observed in all treatments.

While ephedrine and dobutamine improved hemodynamic variables, crystalloid fluid therapy alone was ineffective in managing normovolemic hypotension in dogs. Future studies with larger samples must assess the combined promising effects of fluid therapy and ephedrine.