A clinician's guide to predicting fluid responsiveness in critical illness: applied physiology and research methodology

A Review of Central Venous Pressure and Its Reliability as a Hemodynamic Monitoring Tool in Veterinary Medicine

OBJECTIVE

To review the current literature regarding central venous pressure (CVP) in veterinary patients pertaining to placement (of central line), measurement, interpretation, use in veterinary medicine, limitations, and controversies in human medicine.

ETIOLOGY

CVP use in human medicine is a widely debated topic, as numerous sources have shown poor correlation of CVP measurements to the volume status of a patient. Owing to the ease of placement and monitoring in veterinary medicine, CVP remains a widely used modality for evaluating the hemodynamic status of a patient. A thorough evaluation of the veterinary and human literature should be performed to evaluate the role of CVP measurements in assessing volume status in veterinary patients.

DIAGNOSIS

Veterinary patients that benefit from accurate CVP readings include those suffering from hypovolemic or septic shock, heart disease, or renal disease or all of these. Other patients that may benefit from CVP monitoring include high-risk anesthetic patients undergoing major surgery, trending of fluid volume status in critically ill patients, patients with continued shock, and patients that require rapid or large amounts of fluids.

THERAPY

The goal of CVP use is to better understand a patient's intravascular volume status, which would allow early goal-directed therapy.

PROGNOSIS

CVP would most likely continue to play an important role in the hemodynamic monitoring of the critically ill veterinary patient; however, when available, cardiac output methods should be considered the first choice for hemodynamic monitoring.

Corrected flow time is a good indicator for preload responsiveness during living donor liver donation

BACKGROUND

Corrected flow time (FTc) has been utilized as preload indicator in recent literature. Accurate estimation of preload status during living donor liver donation (LDLD) is important due to fluid restriction. We evaluate the effectiveness of FTc as a surrogate of preload indicator during LDLD.

MATERIALS AND METHODS

Twenty-five patients undergoing LDLD were enrolled in the study. Administration of intravenous fluid was restricted before lobectomy was performed. After the organ was harvest, fluid challenge with 500 mL of Voluven (130/0.42, Fresenius, Friedberg, Germany) was performed. Stroke volume (SV) was measured with ultrasonic cardiac output monitor (USCOM; USCOM Pty, Ltd, Sydney, Australia) before and after the fluid challenge. The FTc value obtained with USCOM before fluid challenge was recorded. Fluid responsiveness was defined as an increase in SV of more than 15%. Receiver operating characteristic (ROC) curve was performed.

RESULTS

The area under ROC curve was 0.9. The optimal cutoff FTc value was 340 milliseconds during LDLD.

CONCLUSIONS

FTc is a noninvasive, easily obtainable, and essentially good preload indicator during LDLD.

A comparison of transcutaneous Doppler corrected flow time, b-type natriuretic peptide and central venous pressure as predictors of fluid responsiveness in septic shock: a preliminary evaluation

Aortic corrected flow time (FTc) is easily measured by Doppler techniques. Recent data using transoesophageal Doppler suggest that it may predict fluid responsiveness in critical care. This use of FTc has not previously been evaluated in septic shock, nor have any studies incorporated transcutaneously measured FTc. Furthermore, no comparison has been made between FTc, plasma B-type natriuretic peptide concentration (BNP) or central venous pressure. The aim of this preliminary study was to compare FTc, BNP and central venous pressure as predictors of fluid responsiveness in septic shock patients without cardiac dysrhythmia. This was a prospective study of 10 consecutive adult septic shock patients (in sinus rhythm; 60% mechanically ventilated) treated with intravenous fluid challenge (4% albumin 250 ml over 15 minutes) in a mixed medical/ surgical tertiary intensive care unit. Mean + SD Acute Physiological and Chronic Health Evaluation II score was 21.8 +/- 12.7. Haemodynamic assessment incorporating transcutaneous aortic Doppler (USCOM) occurred before and five minutes after fluid challenge. Concurrent with initial assessment, blood samples were collected for BNP assay (ADIVA Centaur). Four patients demonstrated an increase in stroke volume > or = 15% (responders). Percent change in stroke volume strongly correlated with baseline FTc (r = -0.81, P = 0.004) but not BNP (r = -0.3, P = 0.4) or central venous pressure (r = -0.4, P = 0.2). Baseline FTc < 350 ms discriminated responders from non-responders (P = 0.047). Our data support FTc as a better predictor of fluid responsiveness than either BNP or central venous pressure in septic shock. Transcutaneous aortic Doppler FTc offers promise as a simple, completely non-invasive predictor of fluid responsiveness and should be evaluated further