Use of aortic flow indexes derived from transthoracic echocardiography to evaluate response to a fluid challenge in anesthetized dogs

Objective To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs. Study design Prospective experimental study. Animals A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery. Methods Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg(-1) intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (Delta SVTPTD) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (Delta SVTPTD <= 15%). When Delta SVTPTD was >15% after the first FC, additional FC were administered until Delta SVTPTD was <= 15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (Delta VTIFC) and maximum acceleration (Delta Vmax(FC))] and in mean arterial pressure (Delta MAP(FC) ) were compared with Delta SVTPTD. Results After one FC, 24 animals were responders. For nonresponders, Delta SVTPTD was <= 15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased Delta SVTPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of Delta VTI (FC) (0.901) was larger than the AUROCs of Delta Vmax(FC) (0.774, p = 0.041) and Delta MAP(FC) (0.519, p < 0.0001). Delta MAP(FC) did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for Delta VTIFC and >8.6 (-0.3 to 14.7)% for Delta Vmax(FC). Animals within the gray zone were 17% (Delta VTIFC) and 50% (Delta Vmax(FC)). Conclusions and clinical relevance Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy.