POINT: Should Acute Fluid Resuscitation Be Guided Primarily by Inferior Vena Cava Ultrasound for Patients in Shock? Yes

The role of point-of-care ultrasound to monitor response of fluid replacement therapy in pregnancy

Fluid management in obstetrical care is crucial because of the complex physiological conditions of pregnancy, which complicate clinical manifestations and fluid balance management. This expert review examined the use of point-of-care ultrasound to evaluate and monitor the response to fluid therapy in pregnant patients. Pregnancy induces substantial physiological changes, including increased cardiac output and glomerular filtration rate, decreased systemic vascular resistance, and decreased plasma oncotic pressure. Conditions, such as preeclampsia, further complicate fluid management because of decreased intravascular volume and increased capillary permeability. Traditional methods for assessing fluid volume status, such as physical examination and invasive monitoring, are often unreliable or inappropriate. Point-of-care ultrasound provides a noninvasive, rapid, and reliable means to assess fluid responsiveness, which is essential for managing fluid therapy in pregnant patients. This review details the various point-of-care ultrasound modalities used to measure dynamic changes in fluid status, focusing on the evaluation of the inferior vena cava, lung ultrasound, and left ventricular outflow tract. Inferior vena cava ultrasound in spontaneously breathing patients determines diameter variability, predicts fluid responsiveness, and is feasible even late in pregnancy. Lung ultrasound is crucial for detecting early signs of pulmonary edema before clinical symptoms arise and is more accurate than traditional radiography. The left ventricular outflow tract velocity time integral assesses stroke volume response to fluid challenges, providing a quantifiable measure of cardiac function, which is particularly beneficial in critical care settings where rapid and accurate fluid management is essential. This expert review synthesizes current evidence and practice guidelines, suggesting the integration of point-of-care ultrasound as a fundamental aspect of fluid management in obstetrics. It calls for ongoing research to enhance techniques and validate their use in broader clinical settings, aiming to improve outcomes for pregnant patients and their babies by preventing complications associated with both under- and overresuscitation.

SHoC-IVC: Does assessment of the inferior vena cava by point-of-care ultrasound independently predict fluid status in spontaneously breathing patients with undifferentiated hypotension?

BACKGROUND

Accurately determining the fluid status of a patient during resuscitation in the emergency department (ED) helps guide appropriate fluid administration in the setting of undifferentiated hypotension. Our goal was to determine the diagnostic utility of point-of-care ultrasound (PoCUS) for inferior vena cava (IVC) size and collapsibility in predicting a volume overload fluid status in spontaneously breathing hypotensive ED patients.

METHODS

This was a post hoc secondary analysis of the SHOC-ED data, a prospective randomized controlled trial investigating PoCUS in patients with undifferentiated hypotension. We prospectively collected data on IVC size and collapsibility for 138 patients in the PoCUS group using a standard data collection form, and independently assigned a fluid status (volume overloaded, normal, volume deplete) from a composite clinical chart review blinded to PoCUS findings. The primary outcome was the diagnostic performance of IVC characteristics on PoCUS in the detection of a volume overloaded fluid status.

RESULTS

One hundred twenty-nine patients had completed determinant IVC assessment by PoCUS, with one hundred twenty-five receiving successful final fluid status determination, of which one hundred and seven were classified as volume deplete, thirteen normal, and seven volume overloaded. A receiver operating characteristic (ROC) curve was plotted using several IVC size and collapsibility categories. The best overall performance utilized the combined parameters of a dilated IVC (> 2.5 cm) with minimal collapsibility (less than 50%) which had a sensitivity of 85.7% and specificity of 86.4% with an area under the curve (AOC) of 0.92 for predicting an volume overloaded fluid status.

CONCLUSION

IVC PoCUS is feasible in spontaneously breathing hypotensive adult ED patients, and demonstrates potential value as a predictor of a volume overloaded fluid status in patients with undifferentiated hypotension. IVC size may be the preferred measure.

Caudal vena cava measurements and fluid responsiveness in hospitalized cats with compromised hemodynamics and tissue hypoperfusion

OBJECTIVE

To evaluate the use of the caudal vena cava collapsibility index (CVCCI) and the inspiratory/minimum and expiratory/maximum diameters of the vena cava to predict fluid responsiveness in hospitalized, critically ill cats with hemodynamic and tissue perfusion abnormalities.

DESIGN

Diagnostic test study in a prospective cohort of hospitalized cats.

SETTING

Private practice referral hospital.

ANIMALS

Twenty-four hospitalized cats with spontaneous breathing and compromised hemodynamics and tissue hypoperfusion.

INTERVENTIONS

Ultrasonographic examination before and after fluid expansion with 10 ml/kg of lactated Ringer's solution.

MEASUREMENTS AND MAIN RESULTS

Fluid responsiveness was evaluated using the velocity-time integral (VTI) of the subaortic blood flow, by measuring it before and after a fluid load of 10 ml/kg of lactated Ringer's solution. The CVCCI was calculated using the following formula: (maximum diameter - minimum diameter / maximum diameter) × 100. Ten cats were fluid responders (42 %) and 14 were nonresponders (58 %). The area under the receiver operating characteristic curve (AUROC) with their 95% confidence interval for the predictors and the best cutoff values were as follows: CVCCI, AUROC = 0.83 (0.66-1.00) and cutoff = 31%; inspiratory/minimum diameter, AUROC = 0.86 (0.70-1.00) and cutoff = 0.24 cm; expiratory/maximum diameter, AUROC = 0.88 (0.74-1.00) and cutoff = 0.22 cm. A significant lineal correlation was observed between the percentage of increase in VTI after expansion and CVCCI (r_s  = 0.68, P < 0.001), expiratory/maximum diameter (r_s  = -0.72, P < 0.001), and inspiratory/minimum diameter (r_s  = -0.71, P < 0.001). The intraobserver and interobserver variability was low for VTI, and the expiratory/maximum diameter and inspiratory/minimum diameter were high for CVCCI.

CONCLUSIONS

Caudal vena cava measurements could be useful to predict the response to fluids in hospitalized cats with hemodynamic and tissue perfusion alterations. Additional studies are required to draw definitive conclusions about the role of these variables to guide fluid administration in cats.

Ultrasonographical Assessment of Caudal Vena Cava Size through Different Views in Healthy Calves: A Pilot Study

Ultrasonographic measurements of the caudal vena cava (CVC) and aorta (Ao) are known as reliable tools to assess intravascular volume status in humans. The aim of this study was to evaluate the feasibility of obtaining ultrasonographical measurements of CVC and Ao in two different views, assess intra- and interobserver variability, and study the effect of sex, age, body weight, and breed on measurements in healthy calves. The diameter and area of CVC and Ao were measured by a single investigator in two anatomic sites (subxiphoid and paralumbar window) in 48 calves aged less than 60 days and then repeated 2.5 months after the first assessment. For intra- and interobserver variability assessment, CVC and Ao measurements were repeated by three observers on five randomly selected calves. CVC and Ao measurements were easily obtained in PV and more difficult to obtain in SV. CVC and Ao area in PV showed high repeatability and reproducibility. A positive correlation was highlighted between age and CVC and Ao measurements in both sites. In conclusion, CVC size assessment by point of care ultrasound can be easily performed at a paralumbar site in calves under 4 months of age and could be used to assess intravascular volume status.

How I Do It: Risks and Benefits of Fluid Administration as Assessed by Ultrasound

For patients in shock, decisions regarding administering or withholding IV fluids are both difficult and important. Although a strategy of relatively liberal fluid administration has traditionally been popular, recent trial results suggest that moving to a more fluid-restrictive approach may be prudent. The goal of this article was to outline how whole-body point-of-care ultrasound can help clarify both the possible benefits and the potential risks of fluid administration, aiding in the risk/benefit calculations that should always accompany fluid-related decisions.

Critical Care Echocardiography: A Primer for the Nephrologist

Critical care echocardiography (CCE) refers to the goal-directed use of transthoracic or transesophageal echocardiography and represents one of the most common applications of critical care ultrasound. CCE can be performed at the point of care, is easily repeated following changes in clinical status, and does not expose the patient to ionizing radiation. Nephrologists who participate in the care of patients in the intensive care unit will regularly encounter CCE as part of the decision-making and bedside management of ICU patients. The four primary indications for CCE are the characterization of shock, evaluation of preload tolerance, evaluation of volume responsiveness, and serial hemodynamic assessment to evaluate response to therapeutic interventions. This article provides an overview of the anatomical structures that are routinely assessed in basic CCE, describes how these findings are incorporated into the clinical assessment of critically ill patients, and introduces some common applications of advanced CCE.

Inferior vena cava dilation predicts global cardiac dysfunction in acute respiratory distress syndrome: A strain echocardiographic study

PURPOSE

Limited data exist on the utility of ultrasonographic evaluation of inferior vena cava (IVC) in acute respiratory distress syndrome (ARDS). We studied the value of IVC diameter in assessing cardio-circulatory performance in ARDS using strain echocardiography.

MATERIALS AND METHODS

Retrospective cross-sectional analysis of Doppler echocardiograms of patients with moderate-severe ARDS was performed. Right ventricle (RV) parameters, IVC diameter, and left ventricle (LV) systolic and diastolic parameters were collected. RV free wall strain (RVFWS) and LV global longitudinal strain (LVGLS) were calculated.

RESULTS

Fifty-one patients were dichotomized into two groups: with IVC > 2.1 cm (dilated) and with IVC ≤ 2.1 cm (nondilated). The dilated IVC group presented worse hypoxemic profile, hypotension, and poor perfusion markers. No significant associations with positive end-expiratory pressure or lung mechanics were observed. Dilated IVC was associated with impaired RV function, high central venous pressure, elevated pulmonary artery pressure, and LV systolic and diastolic dysfunctions. Strongest predictors of a dilated IVC were RVFWS, LVGLS, and tissue Doppler mitral annular early diastolic velocity. Dilated IVC predicted a global cardiac dysfunction defined by strain echocardiography (GCDS) with high sensitivity and specificity.

CONCLUSIONS

In ARDS, strain echocardiography analyses demonstrated that a dilated IVC is associated with GCDS and impaired hemodynamics independent of lung mechanics. A dilated IVC should be considered a marker of circulatory distress, signaling the potential necessity for improved hemodynamic optimization.

Differences in pharmacological property between combined therapy of the vasopressin V2-receptor antagonist tolvaptan plus furosemide and monotherapy of furosemide in patients with hospitalized heart failure

BACKGROUND

Tolvaptan has been shown to improve congestion in heart failure patients. The purpose of this study was to evaluate the pharmacology and clinical efficacy of combined tolvaptan and furosemide therapy.

METHODS

This study included 40 patients with systemic volume overload who were hospitalized for heart failure. Patients who showed no improvement in the condition after receiving 20 mg intravenous furosemide were included and were randomly selected to receive tolvaptan as an add-on to furosemide or to receive an increased dose of furosemide. We evaluated the bioelectrical impedance analyzer parameters, the parameters of the inferior vena cava using echocardiography, vital signs, body weight, urine output, and laboratory data for 5 days.

RESULTS

In the changes from baseline between intracellular water volume (ICW) and extracellular water volume (ECW) after additional use of tolvaptan or furosemide from Day 1 to Day 5, there were no significant differences observed between ICW and ECW over 5 days in the tolvaptan + furosemide group, although differences were found in the furosemide group from Day 2 onward. Changes in the respiratory collapse of inferior vena cava increased significantly, and systolic blood pressure decreased significantly only in the furosemide group.

CONCLUSIONS

The present study clearly demonstrates that combined therapy with tolvaptan and furosemide removed excess ICW and ECW to an equal extent, while furosemide alone primarily removed ECW, including intravascular water.

Development of a Focused Cardiac Ultrasound Image Acquisition Assessment Tool

Background: Focused cardiac ultrasound (FCU) is widely used by healthcare providers to answer specific questions about cardiac structure and function at the bedside. Currently, no widely accepted FCU image acquisition checklist exists to assess learners with varying skill levels from different specialties.

Objective: The primary objective of this project was to develop a consensus-based FCU image acquisition checklist using a multispecialty group of point-of-care ultrasound (POCUS) experts.

Methods: The essential components of an FCU examination were identified on the basis of published recommendations from echocardiography and international ultrasound societies. A checklist of the essential components of an FCU examination was drafted. A panel of POCUS experts from different medical specialties in the United States and Canada was convened to vote on each checklist item by answering two questions: 1) Is this item important to include in a checklist of essential FCU skills applicable to any medical specialty? and 2) Should the learner be required to successfully complete this item to be considered competent? A modified Delphi approach was used to assess the level of agreement for each checklist item during four rounds of voting. Checklist items that achieved an agreement of 80% or greater were included in the final checklist.

Results: Thirty-one POCUS experts from seven different medical specialties voted on sixty-five items to be included in the FCU image acquisition assessment tool. The majority of POCUS experts (61%) completed all four rounds of voting. During the first round of voting, 59 items reached consensus, and after revision and revoting, an additional 3 items achieved 80% or greater consensus. A total of 62 items were included in the final checklist, and 57 items reached consensus as a requirement for demonstration of competency.

Conclusion: We have developed a multispecialty, consensus-based FCU image acquisition checklist that may be used to assess the skills of learners from different specialties. Future steps include studies to develop additional validity evidence for the use of the FCU assessment tool and to evaluate its utility for the translation of skills into clinical practice.

Influence of head-of-bed elevation on the measurement of inferior vena cava diameter and collapsibility

PURPOSE

Inferior vena cava (IVC) diameter and variation are commonly measured in the supine position to estimate intravascular volume status of critically ill patients. Many scientific societies describe the measurement of IVC diameter in the supine position. However, critically ill patients are rarely placed supine due to concerns for aspiration risk, worsened respiratory mechanics, increases in intracranial pressure, and the time it takes to change patient position. We assessed the influence of head-of-bed (HOB) elevation on IVC measurements.

METHODS

We conducted a prospective observational study of critically ill patients undergoing critical care ultrasound. With HOB at 0°, IVC maximum (IVCmax0°) and minimum (IVCmin0°) diameters were measured. Measurements were then repeated with HOB elevated to 30° and 45°. Collapsibility index (CI), defined as (IVCmax - IVCmin)/IVCmax, was calculated for each HOB elevation. Mean differences were then compared.

RESULTS

A convenience sample of 95 patients was studied, of whom 45% were on vasopressors and 44% were spontaneously breathing. The CI did not significantly differ between the three positions. We found a significant difference (P ≤ .0001) between IVCmax at 45° (2.09 cm) and 0° (1.96 cm), IVCmin at 45° (1.75 cm) and 0° (1.59 cm), IVCmax at 45° (2.09 cm) and 30° (1.97 cm), and IVCmin at 45° (1.75 cm) and 30° (1.61 cm).

CONCLUSIONS

In a population of critically ill patients undergoing goal-directed ultrasound examinations, elevating HOB to 30° did not significantly alter IVC measurements or CI. At 45°, however, IVCmax and IVCmin diameters increased significantly, albeit with no significant change in CI. Performing ultrasound measurements of the IVC with HOB elevated to 30° is unlikely to produce clinically meaningful changes.

Assessing Extravascular Lung Water With Ultrasound: A Tool to Individualize Fluid Management?

Aggressive fluid resuscitation has become standard of care for hypotensive patients with sepsis. However, sepsis is a syndrome that occurs in patients with diverse underlying physiology and a one-size-fits-all approach to fluid administration seems misguided. To individualize fluid management, several methods to assess fluid responsiveness have been validated, but even in fluid responsive patients, fluid administration may still be harmful and lead to pulmonary edema. Hence, to individualize fluid management, in addition to fluid responsiveness, fluid tolerance needs to be assessed. This article examines whether lung ultrasound can be useful to detect excess extravascular lung water (EVLW) and thus assess fluid tolerance. The physiology of EVLW and the principles of lung ultrasound are briefly described. Articles examining the correlation between EVLW and lung ultrasound findings in various clinical settings are carefully reviewed. Overall, lung ultrasound has been found to be an excellent tool to detect EVLW, but large outcome studies investigating lung ultrasound-guided fluid management are still lacking.

Consensus Document of the SEMI, semFYC, SEN, and SEC on Focused Cardiac Ultrasound in Spain

This document summarizes the concept of focused cardiac ultrasound, the basic technical aspects related to this technique, and its diagnostic objectives. It also defines training requisites in focused cardiac ultrasound. This consensus document has been endorsed by the Spanish Society of Internal Medicine (SEMI), the Spanish Society of Family and Community Medicine (semFYC), the Spanish Society of Neurology (SEN), and the Spanish Society of Cardiology (SEC).

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

OBJECTIVE

The intent of fluid bolus therapy (FBT) is to increase cardiac output and tissue perfusion, yet only 50% of septic children are fluid responsive. We evaluated respiratory variation of inferior vena cava (IVC) diameter as a predictor of fluid responsiveness.

METHODS

A prospective observational study in the ED of The Royal Children's Hospital, Melbourne, Australia. Patients were spontaneously ventilating children treated with FBT for sepsis-induced acute circulatory failure. IVC ultrasound was performed prior to FBT. Trans-thoracic echocardiography was performed prior to, 5 and 60 min after FBT. IVC collapsibility index and stroke distance were calculated by a blinded Paediatric Emergency Physician and blinded Paediatric Cardiologist, respectively.

RESULTS

Thirty-nine fluid boluses were recorded in 33 children, 28/39 (72%) of which met criteria for fluid responsiveness at 5 min, which was sustained in 2/28 (7%) of initial fluid responders at 60 min. Sensitivity and specificity (95% confidence interval) of IVC collapsibility index were 0.44 (0.25-0.65) and 0.33 (0.10-0.65) with an area under the receiver operator characteristics curve (95% confidence interval) of 0.38 (0.23-0.55) at 5 min. Test characteristics 60 min after fluid bolus administration were not meaningful because of the infrequency of sustained fluid responsiveness in this patient group. There was no significant correlation between IVC collapsibility and fluid responsiveness at 5 or 60 min.

CONCLUSIONS

IVC collapsibility has poor test characteristics for predicting fluid responsiveness in spontaneously ventilating children with sepsis.

Intraabdominal Hypertension, Abdominal Compartment Syndrome, and the Open Abdomen

Abdominal compartment syndrome (ACS) is the end point of a process whereby massive interstitial swelling in the abdomen or rapid development of a space-filling lesion in the abdomen (such as ascites or a hematoma) leads to pathologically increased pressure. This results in so-called intraabdominal hypertension (IAH), causing decreased perfusion of the kidneys and abdominal viscera and possible difficulties with ventilation and maintenance of cardiac output. These effects contribute to a cascade of ischemia and multiple organ dysfunction with high mortality. A few primary disease processes traditionally requiring large-volume crystalloid resuscitation account for most cases of IAH and ACS. Once IAH is recognized, nonsurgical steps to decrease intraabdominal pressure (IAP) can be undertaken (diuresis/dialysis, evacuation of intraluminal bowel contents, and sedation), although the clinical benefit of such therapies remains largely conjectural. Surgical decompression with midline laparotomy is the standard ultimate treatment once ACS with organ dysfunction is established. There is minimal primary literature on the pathophysiological underpinnings of IAH and ACS and few prospective randomized trials evaluating their treatment or prevention; this concise review therefore provides only brief summaries of these topics. Many modern studies nominally dealing with IAH or ACS are simply epidemiologic surveys on their incidence, so this paper summarizes the incidence of IAH and ACS in a variety of disease states. Especially emphasized is the fact that modern critical care paradigms emphasize rational limitations to fluid resuscitation, which may have contributed to an apparent decrease in ACS among critically ill patients.