Usefulness of focused cardiac ultrasonography for predicting fluid responsiveness in conscious, spontaneously breathing dogs

Abstract

OBJECTIVE To evaluate the diagnostic usefulness of focused cardiac ultrasonography and selected echocardiographic variables for predicting fluid responsiveness in conscious, spontaneously breathing dogs with various clinical conditions. ANIMALS 26 dogs (15 males and 11 females) with a median age of 84 months (range, 12 to 360 months) and median body weight of 8 kg (range, 2 to 35 kg) referred for various clinical conditions. PROCEDURES Left ventricular end-diastolic internal diameter normalized to body weight (LVIDDn), left ventricular volume score (LVVS), left ventricular end-diastolic volume index (EDVI), aortic velocity time integral (VTIAo), and aortic peak flow velocity (VmaxAo) were echocardiographically measured before and after IV administration of a bolus of lactated Ringer solution (4 mL/kg) over a 1-minute period. Dogs were classified on the basis of the observed change in aortic stroke volume following fluid administration as responders (≥ 15%) or nonresponders (< 15%) to fluid administration. Receiver operating characteristic curves were generated for the ability of LVVS, LVIDDn, EDVI, VTIAo, and VmaxAo to predict responder status. RESULTS 13 dogs were classified as responders and 13 as nonresponders. Areas under the receiver operating characteristic curves (95% confidence intervals) for predicting fluid responsiveness were as follows: VTIAo, 0.91 (0.74 to 0.99); LVIDDn, 0.85 (0.66 to 0.96); EDVI, 0.85 (0.65 to 0.96); LVVS, 0.85 (0.65 to 0.96); and VmaxAo, 0.75 (0.54 to 0.90). CONCLUSIONS AND CLINICAL RELEVANCE The evaluated echocardiographic variables were useful for noninvasive prediction of fluid responsiveness in conscious dogs and could be valuable for informing clinical decisions regarding fluid therapy.

Assessment of Volume Status and Fluid Responsiveness in Small Animals

“…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). These findings are similar to human ICU studies that also demonstrate the ability of a change in HR to predict fluid responsiveness is quite variable (62,63).…”

“…Dynamic Markers below. 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).…”

“…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.…”

“…Moreover, hyperlactatemia secondary to an anaerobic cellular metabolism in hypovolemic patients only occurs when a certain threshold of hypoperfusion has been reached; it is not sensitive at accurately identifying mild hypo-or even severe hypervolemia. Although lactate has been studied in veterinary medicine as a prognostic indicator in many disease states, research regarding the ability of lactate to discriminate between fluid responders and non-responders is lacking; a single study in spontaneously breathing dogs failed to demonstrate a difference in lactate between responders and non-responders (15). There is even less research regarding lactate and volume status in cats; it has been shown that hypotensive cats with normal lactate have a greater chance of survival than hypotensive cats with hyperlactatemia (39), however, lactate has not been studied as a hemodynamic marker of volume status or fluid response in cats.…”

“…At a more advanced level CO can be directly calculated based on the cross-sectional area of the descending aorta and the left ventricular outflow tract volume time integral (LVOT VTI), which has been used to predict fluid responsiveness in both humans and dogs (15,116). The product of these factors is equal to the column of blood that is ejected from the heart during each contraction.…”