Clinical PotpourriInferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients
Introduction
Assessing fluid responsiveness is key to the successful resuscitation of critically-ill patients. While under-resuscitation is associated with worse clinical outcomes [1], there is a growing body of evidence that over-resuscitation may be harmful to patients with septic shock [2] and the acute respiratory distress syndrome [3]. As physicians re-examine the paradigm of aggressive intravenous fluid (IVF) resuscitation, there are calls for an individualized, evidence-based, IVF resuscitation strategy [4], [5].
Despite the prevailing practice of early and aggressive IVF resuscitation in critically-ill patients, only 50% of patients will respond to an IVF bolus with an increase in their cardiac index [6], [7], [8]. Traditional methods of assessing fluid status, such as vital signs and physical examination, do not reliably identify fluid responders [9], [10]. The use of a pulmonary artery catheter (PAC) is invasive, exposes patients to potential harm, and has questionable efficacy [11]. The Non-Invasive Cardiac Output Measurement device (NICOM™) offers an alternative to the PAC. NICOM has been validated against the PAC in multiple studies [12], [13], [14] and produces comparable hemodynamic data when compared to stroke volume variation [15]; however, its clinical use is limited to resource-rich practice environments. Consequently, an accurate, adaptable non-invasive alternative to help guide the IVF resuscitation of critically-ill patients is needed.
Emergency and critical care physicians have readily adopted point-of-care ultrasound (POCUS) for a spectrum of diagnostic and therapeutic uses [16], [17], [18]. Proficiency with POCUS among clinicians can be established with limited additional training [19], [20], and the accuracy of POCUS has been demonstrated in multiple domains [21], [22], [23]. If a sonographic method of determining fluid responsiveness is shown to be valid, POCUS could obviate the need for other invasive or non-invasive methods.
POCUS can estimate central venous pressure (CVP) [24]; however, CVP is a static measure of volume status and has little clinical value in guiding the resuscitation of critically-ill patients [25]. Measurement of the collapsibility of the inferior vena cava (cIVC) during respiration, also known as the caval index, has been proposed as a non-invasive means to measure a patient's response to an IVF volume challenge or following a passive leg raise (PLR). Research has demonstrated that cIVC can be used to predict fluid responsiveness in mechanically ventilated patients (receiving tidal volumes of 10 ml/kg) [26], [27], [28]. However, evidence supporting the use of cIVC in spontaneously breathing critically-ill patients has been limited to smaller trials [29], [30], [31]. In 2016, the Society of Critical Care Medicine (SCCM) released updated guidelines for the use of POCUS in the evaluation of critically-ill patients. With a lack of robust evidence, the guideline panel was unable to make a recommendation for or against the use of cIVC among spontaneously breathing patients [23]. Despite this absence, the 2015 Surviving Sepsis Campaign bundle calls for an assessment of patient volume status and suggests POCUS as a clinical option [32]. Many emergency physicians and intensivists have already adopted the practice of using POCUS to guide IVF resuscitation (with or without an IVF challenge or PLR) among spontaneously breathing critically-ill patients into their practice [33], [34] despite the limited evidence.
The primary aim of this study was to assess the ability of cIVC to detect fluid responsiveness among spontaneously breathing critically-ill patients undergoing resuscitation, as measured using NICOM. Secondary aims were to establish an optimum cutoff value for cIVC, compare this value to previously suggested cutoffs, and determine if incorporating a PLR with cIVC assists in detecting fluid responsiveness.
Section snippets
Study setting and population
This prospective observational investigation was performed in the emergency departments and medical intensive care units (ICUs) of two urban adult academic hospitals in the United States. From August 2014 until July 2016, we enrolled a convenience sample of spontaneously breathing patients with signs of acute circulatory failure being admitted to the ICU. Patients were enrolled within 36 h of presentation to the emergency department during the resuscitative phase of care. Acute circulatory
Study population and fluid administration
Fig. 1 illustrates the recruitment, enrollment, and final study sample (n = 124). Table 1 provides patient demographic characteristics, clinical characteristics, and discharge diagnoses. Sixty-one participants (49.2%) were fluid responders. There were no differences between fluid responders and non-responders at baseline, except patients with COPD were more likely to be fluid responders while patients with pulmonary hypertension were more likely to be non-responders. The median time from ED
Discussion
The results of this investigation support the use of cIVC measured by POCUS to predict fluid responsiveness among spontaneously breathing critically-ill patients. Our cIVC AUC of 0.84 [0.76–0.91] is similar to the AUC of 0.84 [0.81–0.87] reported in a meta-analysis of stroke volume variation, an alternative more invasive method, to detect fluid responsiveness [36]. A comparison of results from studies using similar techniques as ours shows that a cIVC of 25% produced fewer misclassified
Conclusion
cIVC, as measured by POCUS, is able to detect fluid responsiveness and may be used to guide IVF resuscitation among spontaneously breathing critically-ill patients.
The following are the supplementary data related to this article.
Author's Contributions
KC: study concept and design, patient enrollment, ultrasound review, data analysis and interpretation, drafting and revision of manuscript; NG: patient enrollment, ultrasound review, and revision of manuscript; JR: data analysis and revision of manuscript; AL: patient enrollment and revision of manuscript; DC: data collection and patient enrollment; RM: study design, data analysis and interpretation, and revision of manuscript; ML: study design and revision, data interpretation, and revision of
Conflicts of interests
KC has no conflicts of interest. NG has no conflicts of interest. JR has no conflicts of interest. AL has no conflicts of interest. DC has no conflicts of interest. RM has no conflicts of interest. ML has no conflicts of interest. AN has no conflicts of interest.
Funding
This work was supported by the Division of Pulmonary and Critical Care and the Department of Emergency Medicine, Alpert Medical School of Brown University.
Acknowledgements
We would like to extend a special thanks to Dr. Otto Leibmann who provided ultrasound support and Dr. Gregory Jay who provided research personnel support for the study.
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