Alternative methods to central venous pressure for assessing volume status in critically ill patients

Peripheral venous pressure accurately predicts central venous pressure in the adult Fontan circulation

BACKGROUND

Patients with the Fontan circulation lack a subpulmonary ventricular pump and thus the main driver for pulmonary blood flow is a high central venous pressure. Peripheral venous pressure (PVP) measurement has been shown to be a reproducible and fairly accurate surrogate for central venous pressure (CVP), but not specifically for the adult Fontan circulation. This study aims to determine the relationship of PVP to CVP in adult Fontan patients.

METHODS

All adult patients (≥18 yo) with a Fontan circulation undergoing cardiac catheterization were included. Both CVP and PVP were measured during the catheterization. The relationship between the peripheral venous and central venous pressures was assessed using simple linear regression and the Bland-Altman plot analysis for differences.

RESULTS

Thirty-eight adult Fontan patients (mean age 30.7 ± 8.5, range 18-52 years) undergoing 43 cardiac catheterizations were analyzed. The mean CVP was 17.3 +/- 4.7 mmHg. The mean PVP was 18.4 +/- 5 mmHg. CVP and PVP were highly correlated, with an R² value of 0.83 (p < 0.001). The CVP can be estimated with PVP measurements using the formula CVP = (0.86 * PVP) + 1.3. A Bland-Altman plot for PVP and CVP demonstrated that the PVP overestimated CVP by a mean of 1.2 mmHg, with a 95% limit of agreement of -5.2 mmHg to 2.8 mmHg.

CONCLUSIONS

In adult Fontan patients, measuring PVP is a reliable, less-invasive, and accurate method of estimating the CVP during cardiac catheterization procedures. These findings may enable outpatient monitoring of Fontan hemodynamics.

Non-Invasive Venous waveform Analysis (NIVA) for monitoring blood loss in human blood donors and validation in a porcine hemorrhage model

STUDY OBJECTIVE

There is an unmet need for a non-invasive approach to diagnose hemorrhage early, before changes in vital signs occur. Non-Invasive Venous waveform Analysis (NIVA) uses a unique physiological signal (the peripheral venous waveform) to assess intravascular volume. We hypothesized changes in the venous waveform would be observed with blood loss in healthy adult blood donors and characterized hemorrhage using invasive monitoring in a porcine model.

DESIGN

Prospective observational study.

SETTING

American Red Cross donation center.

PATIENTS

50 human blood donors and 12 non-donating controls; 7 Yorkshire pigs.

INTERVENTIONS

A venous waveform capturing prototype (NIVA device) was secured to the volar aspect of the wrist in human subjects. A central venous catheter was used to obtain hemodynamic indices and venous waveforms were obtained using the prototype NIVA device over the saphenous vein during 400 mL of graded hemorrhage in a porcine model.

MEASUREMENTS

Venous waveforms were transformed from the time to the frequency domain. The ratiometric power contributions of the cardiac frequencies were used to calculate a NIVA value representative of volume status.

MAIN RESULTS

A significant decrease in NIVA value was observed after 500 mL of whole blood donation (p < .05). A ROC curve for the ability of the NIVA to detect 500 mL of blood loss demonstrated an area under the curve (AUC) of 0.94. In the porcine model, change in NIVA value correlated linearly with blood loss and with changes in hemodynamic indices.

CONCLUSIONS

This study provides proof-of-concept for a potential application of NIVA in detection of blood loss. NIVA represents a novel physiologic signal for detection of early blood loss that may be useful in early triage and perioperative management.

Undertaking an accurate and comprehensive assessment of the acutely ill adult

Accurate assessment of the acutely ill adult who has recently been admitted to hospital, or an inpatient whose condition begins to deteriorate, is becoming a required skill for nurses as people live longer and with a variety of complex conditions, and as nursing skills continue to evolve and develop. This article emphasises the importance of undertaking an accurate and comprehensive patient assessment to ensure that management strategies are implemented in a timely manner. The article also considers the importance of the National Early Warning Score (NEWS), which is a 'track-and-trigger' tool designed to identify patients who are at risk of deterioration. The presentation of shock is considered and how this can be identified using the NEWS. The patient assessment skills required by nurses are discussed and the main signs of patient deterioration, regardless of cause, are outlined. The article also examines the ABCDE (airway, breathing, circulation, disability and exposure) approach to assessment.

Assessment of central venous physiology of Fontan circulation using peripheral venous pressure

OBJECTIVE

Elevated central venous pressure is a major cause of morbidity and mortality after the Fontan operation. The difference between mean circulatory filling pressure and central venous pressure, a driving force of venous return, is important in determining dynamic changes in central venous pressure in response to changes in ventricular properties or loading conditions. Thus, noninvasive central venous pressure and mean circulatory filling pressure estimation may contribute to optimal management in patients undergoing the Fontan operation. We tested the hypothesis that central venous pressure and mean circulatory filling pressure in those undergoing the Fontan operation can be simply estimated using peripheral venous pressure and arm equilibrium pressure, respectively.

METHODS

This study included 30 patients after the Fontan operation who underwent cardiac catheterization (median 8.6, 3.4-42 years). Peripheral venous pressure was measured at the peripheral vein in the upper extremities. Mean circulatory filling pressure was calculated by the changes of arterial pressure and central venous pressure during the Valsalva maneuver. Arm equilibrium pressure was measured as equilibrated venous pressure by rapidly inflating a blood pressure cuff to 200 mm Hg.

RESULTS

Central venous pressure and peripheral venous pressure were highly correlated (central venous pressure = 1.6 + 0.68 × peripheral venous pressure, R = 0.86, P < .0001). Stepwise multivariable regression analysis showed that only peripheral venous pressure was a significant determinant of central venous pressure. Central venous pressure was accurately estimated using regression after volume loading by contrast injection (R = 0.82, P < .0001). In addition, arm equilibrium pressure measurements were highly reproducible and robustly reflected invasively measured mean circulatory filling pressure (mean circulatory filling pressure = 9.1 + 0.63 × arm equilibrium pressure, R = 0.88, P < .0001).

CONCLUSIONS

Central venous pressure and mean circulatory filling pressure can be noninvasively estimated by peripheral venous pressure and arm equilibrium pressure, respectively. This should help clarify unidentified Fontan pathophysiology and the mechanisms of Fontan failure progression, thereby helping construct effective tailor-made approaches to prevent Fontan failure.