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Objective: To investigate whether percentage changes in pulse wave transit time (PWTT%Δ) induced by mini-fluid challenges predict fluid responsiveness in mechanically ventilated anesthetized dogs., Design: Prospective experimental trial., Setting: University teaching hospital., Animals: Twelve Harrier hounds., Intervention: Each dog was anesthetized with propofol and isoflurane after premedication with acepromazine, mechanically ventilated, and had a fluid challenge. This was repeated 4 weeks later. The fluid challenge, 10 mL/kg of colloid administration over 13 minutes, consisted of 3 intermittent mini-fluid challenges (1 mL/kg of each over a minute) with a minute interval, and the remaining colloid administration (7 mL/kg) over 7 minutes., Measurements and Main Results: Percentage change in velocity time integral of pulmonary arterial flow by echocardiography was calculated as an indication of change in stroke volume. Fluid responsiveness was defined as percentage change in velocity time integral ≥ 15% after 10 mL/kg colloid. Dogs responded on 14 fluid challenges and did not on 10. After 1, 2, 3, and 10 mL/kg of fluid challenge, PWTT%Δ 1, 2, 3, 10 were measured. Receiver operator characteristic (ROC) curves were generated and areas under ROC curve were calculated for PWTT%Δ 1, 2, 3 . A gray zone approach was used to identify the clinically inconclusive range. The area under the ROC curve for PWTT%Δ 3 was 0.91 (P = 0.001). Cutoff value for PWTT%Δ 3 was -2.5% (sensitivity: 86%, specificity: 90%). The gray zone for PWTT%Δ 3 was identified as between -2.9% to -1.9% for which fluid responsiveness could not be predicted reliably in 6 out of 24 fluid challenges., Conclusions: In mechanically ventilated anesthetized dogs given a mini-fluid challenge of 3 mL/kg of colloid, PWTT%Δ could predict fluid responsiveness although the gray zone should be considered., (© Veterinary Emergency and Critical Care Society 2019.)

Objective: To evaluate whether pulse pressure variation (PPV) and pleth variability index (PVI) are more accurate than central venous pressure (CVP) for predicting fluid responsiveness in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine., Design: Prospective experimental trial., Setting: University teaching hospital., Animals: Twelve Harrier hound dogs., Interventions: Each dog was anesthetized and had a fluid challenge performed. This was repeated 4 weeks later for a total of 24 fluid challenges. After premedication with intramuscular acepromazine, anesthesia was induced with propofol and maintained with isoflurane. The dogs were mechanically ventilated with constant settings. The fluid challenge consisted of 10 mL/kg of 6% hydroxyethyl starch intravenously over 13 minutes., Measurements and Main Results: Before and after the fluid challenge, PPV, PVI, CVP, and other hemodynamics were recorded. Change in velocity time integral of pulmonary arterial blood flow by echocardiography was calculated as an indication of change in stroke volume. A fluid responder was defined as an increase in velocity time integral ≥ 15%. Receiver operator characteristic (ROC) curves were used to determine cutoff values. Areas under ROC curve were calculated and compared. Dogs responded on 14 fluid challenges and did not on 10. Cutoff values for PPV and PVI were 11% (sensitivity 79%; specificity 80%) and 9.3% (sensitivity 86%; specificity 70%), respectively. The areas under the ROC curve of PPV [0.85, 95% confidence interval (CI): 0.70-1.00, P = 0.038] and PVI (0.84, 95% CI: 0.68-1.00, P = 0.043) were significantly higher than CVP (0.56, 95% CI: 0.32-0.81)., Conclusions: PPV and PVI predicted fluid responsiveness more accurately than CVP and may be useful to guide fluid administration in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine., (© Veterinary Emergency and Critical Care Society 2018.)

Objectives: To evaluate the effects of dexmedetomidine (DEX) on changes in pulse pressure variation (PPV) induced by hemorrhage followed by volume replacement (VR) during isoflurane (ISO) anesthesia., Design: Prospective, randomized, crossover study., Setting: Research laboratory at a veterinary teaching hospital., Animals: Eight adult dogs., Interventions: Anesthesia was maintained with 1.3 times the minimum alveolar concentration (MAC) of ISO alone or ISO with DEX (ISO-DEX, 1.6 μg/kg [bolus], followed by 2 μg/kg/h). Atropine was administered 30 minutes prior to hemorrhage in the ISO-DEX treatment. Ventilation was controlled (tidal volume of 12 mL/kg, positive end-expiratory pressure of 7 cm H2 O, respiratory rate of 16-20/min) under neuromuscular blockade. After recording baseline data, progressive withdrawal of 10%, 20%, and 30% of blood volume (HV10 , HV20 , and HV30 , respectively [measurements during hemorrhage, indicating x% of blood volume removed]) was followed by VR with autologous blood., Measurements and Main Results: In 4 of 8 ISO dogs, hemorrhage decreased mean arterial pressure (MAP) < 60 mm Hg. Based on mean arterial pressure after hemorrhage, dogs were assigned to hypotensive (HG) and normotensive (NG) groups post hoc. During ISO, stroke index and cardiac index decreased with hemorrhage (P < 0.05), while VR normalized or increased these variables. The PPV (%, mean [range]) was increased by hemorrhage from 7 (5-9) to 20 (12-27) and 27 (17-40) at HV20 and HV30 , respectively, only in ISO dogs in the HG; PPV returned to baseline after VR. Dexmedetomidine caused increases in systemic vascular resistance (in dogs in HG and NG), and prevented the increase in PPV with hemorrhage., Conclusions: During ISO anesthesia, PPV increases in individuals prone to developing hypotension from hypovolemia. Because DEX prevents the increase in PPV associated with hypovolemia, PPV should not be used to guide VR in dogs that have been given DEX., (© Veterinary Emergency and Critical Care Society 2014.)