The caval index: an adequate non-invasive ultrasound parameter to predict fluid responsiveness in the emergency department?

Abstract

BackgroundFluid therapy is the first important step in patients with signs of shock but assessment of the volume status is difficult and invasive measurements are not readily available in the emergency department. We have investigated whether the respiratory variation in diameter of the inferior vena cava is a reliable parameter to predict fluid responsiveness in spontaneous breathing emergency department patients with signs of shock.MethodsAll patients admitted to the emergency department during a 15 week period were screened for signs of shock. If the attending physician planned to give a fluid challenge, the caval index was determined by transabdominal ultrasonography in supine position. Immediately afterwards 500 ml NaCl 0.9% was administered in 15 minutes and the clinical response was observed. An adequate response was defined as an increase in systolic blood pressure of at least 10 mm Hg. Based on this definition patients were divided into responders and non-responders.ResultsAfter selection a total number of 45 patients was included. A low caval index (< 36.5%) in patients with signs of shock reliably predicted the absence of an adequate response to fluid therapy (negative predictive value 92%). The positive predictive value of a high caval index was much lower (48%) despite the fact that responders had a significantly higher pre-infusion caval index than non-responders (48.7% vs 31.8%, p 0.014).ConclusionsIn spontaneously breathing patients with signs of shock in the emergency department, a high caval index (>36.5%) does not reliably predict fluid responsiveness in our study, while a low caval index (<36.5%) makes fluid responsiveness unlikely. An explanation for the absence of a blood pressure response in the group of patients with a low high caval index might be that these patients represent a group requiring more volume therapy than 500 ml.

COUNTERPOINT: Should Acute Fluid Resuscitation Be Guided Primarily by Inferior Vena Cava Ultrasound for Patients in Shock? No

“…To support the assertion that both IVC collapse and IVC diameter are determined by CVP, the one study which reported on their predictive accuracy for FR found them to have identical AUC's of 0.62, similar to that of CVP (19,25). Of note, the two studies in Table 1 which found even a modest predictive ability of IVC collapse included 38% and 50% of patients with baseline, overt hypovolemic insults respectively (29,31).…”

Does respiratory variation of inferior vena cava diameter predict fluid responsiveness in spontaneously ventilating children with sepsis

“…Multiple studies in spontaneously ventilating adults have reported the accuracy of respiratory variation in IVC diameter as a predictor of fluid responsiveness, [34][35][36][37][38][39][40] with a pooled AUROC of 0.76. 24 The majority of these studies enrolled mixed patient populations, including those with trauma, dehydration and postoperative surgical patients.…”

Ultrasound assessment of the inferior vena cava for fluid responsiveness: easy, fun, but unlikely to be helpful

“…[30][31][32] Two others yielded borderline results, with the authors commenting that the ''IVC cannot reliably predict FR'' in one 33 and ''caval index does not reliably predict FR'' in the other. 34 The first positive result comes from a study requiring patients to perform a standardized and quantitative inspiratory effort, 35 a technique that cannot be applied to patients who are dyspneic, supine, confused, or intubated, greatly limiting its applicability to critical care. The second 36 is a relatively large (n = 124) emergency department study, which yielded a strong positive result but was criticized for the use of a somewhat controversial tool to estimate FR (thoracic bioreactance), the late enrolment of patients (16 hr after presentation, having already received 4 L of fluid on average), and the low inter-rater reliability (0.67) between experts.…”