Evaluation of the caudal vena cava diameter to abdominal aortic diameter ratio and the caudal vena cava respiratory collapsibility for predicting fluid responsiveness in a heterogeneous population of hospitalized conscious dogs

Abstract

Fluid responsiveness, defined as the response of stroke volume to fluid loading, is a tool to individualize fluid administration in order to avoid the deleterious effects of hypovolemia or hypervolemia in hospitalized patients. To evaluate the accuracy of two ultrasound indices, the caudal vena cava to abdominal aorta ratio (CVC/Ao) and the respiratory collapsibility of the caudal vena cava (cCVC), as independent predictors of fluid responsiveness in a heterogeneous population of spontaneously breathing, conscious, hospitalized dogs. A prospective, multicenter, observational, cross-sectional study was designed in twenty-five dogs. The accuracy of CVC/ Ao and cCVC in predicting fluid responsiveness was evaluated by the area under the receiver operating characteristic curve (AUROC) in a group of hospitalized dogs after receiving a mini-fluid bolus of 4 ml/kg of Hartmann's solution. Dogs with an increased aortic velocity time integral >15% were classified as fluid responders. Twenty-two dogs were finally included. Ten were classified as responders and 12 as non-responders. The AUROC curves were 0.88 for the CVC/Ao ratio (95% confidence interval, CI, 0.67-0.98; P=0.0001) and 0.54 for cCVC (95% CI 0.32-0.75; P=0.75). The CVC/Ao threshold optimized for best sensitivity (SE) and specificity (SP) values was 0.83 (SE 100%; SP 75%). In spontaneously breathing hospitalized dogs, the CVC/Ao measurement predicted stroke volume increase after a fluid bolus, while the respiratory variations in the cCVC did not discriminate between fluid responders and non-responders.

Assessment of Volume Status and Fluid Responsiveness in Small Animals

“…This is similar to a study in dogs undergoing abdominal surgery that showed a significant decrease in HR following a 10 ml/kg bolus of isotonic crystalloid over 10 min was only detected in fluid responders (18). However, a prospective study in 25 hospitalized dogs found HR decreased significantly in both fluid responders and non-responders following a 4 ml/kg mini isotonic crystalloid bolus, suggesting HR could not differentiate between the two groups (16). Several other studies in spontaneously breathing and anesthetized dogs also found changes in HR failed to differentiate fluid responders and non-responders (15,19,28,32).…”

“…In both the human and veterinary literature, the magnitude of change (increase or decrease) that constitutes a positive response varies from 6 to 36% depending on the physiologic parameter measured and conditions under which the preload challenge is induced (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). In general, there is a trend to define a positive fluid responder as any patient that has an increase in a measured dynamic marker, such as CO, by ≥10-15% following a preload challenge (14,16,25,(28)(29)(30). There are generally two ways to induce a preload challenge; (1) by directly increasing the vascular volume through a traditional or a mini IV fluid bolus, or (2) shifting fluids within the vascular system without actually changing the patients total vascular volume.…”

“…In the veterinary clinical setting, a preload challenge is most often elicited through a traditional IV fluid bolus, typically described as isotonic fluids at a dose of 10-20 mL/kg administered over a period of 10-15 min in both cats and dogs (14,(32)(33)(34). More recently, and in many veterinary research settings, a mini fluid bolus which is often defined as 3-5 ml/kg IV isotonic fluid administered over 1 min (15,16,20,23,35) has been used to induce a preload challenge. However, in clinical practice there will be considerable variation in the volume of fluid administered because of clinician preference, patient characteristics such as species and age, the type of fluid used, and the underlying disease process.…”

“…The gray-zone approach can be calculated for any physiologic parameter used to assess a patient's response to a preload challenge (e.g., heart rate, CO, SV, etc.). More specifically, it is defined as the interval of values (for the physiologic parameter assessed) between a sensitivity or specificity lower than 90% to classify patients as fluid responders or non-responders (16,17,19). The further from the gray zone a measurement lies, the greater the confidence of accurately classifying the patient as a fluid responder or not.…”

“…Although clinical examination findings have been studied and are integral to the assessment of perfusion status and the identification of shock in veterinary patients, studies assessing the accuracy of clinical parameters to specifically estimate volume status and/or volume responsiveness in dogs and cats are very limited (49)(50)(51). Research in anesthetized dogs suggests these parameters are not accurate at differentiating fluid responders from non-responders (16)(17)(18)(19). A recent study in spontaneously breathing dogs with compromised hemodynamics or tissue hypoperfusion found CRT, presence of pale mucous membranes, HR, weak pulses and serum lactate concentrations all failed to differentiate fluid responders and non-responders (25).…”