Effects of variable Impella CP® flows on analogue mean systemic filling pressure.
Creators: name: Yastrebov, Konstantin
name: Brunel, Laurencie
name: Williams, Zoe
name: Paterson, Hugh
name: Burrows, Christopher
name: Wise, Innes
name: Bannon, Paul
Publisher: name: UNSW Sydney
Year: 2020
Subjects: subject: 0903 Biomedical Engineering

description: Introduction and rational: Mean systemic filling pressure (Pms) represents the equalization pressure within systemic circulation following cardiac arrest. It is a pressure exerted by the stressed volume of blood on cardiovascular walls, therefore reflecting volume status of the patient and global cardiovascular compliance. There is currently no ideal technique to estimate Pms for patients with preserved systemic blood flow. Analogue mean systemic filling pressure (Pmsa) has been used in research and in limited clinical intensive care settings as a surrogate for Pms and as an alternative estimate of intravascular volume status in humans with beating hearts. It has been used to guide fluid therapy and administration of vasopressors aiming to alter the stressed volume of blood. It is calculated using the equation: Pmsa = (0.96 x CVP) + (0.04 x MAP) + (c x CO) where c is an anthropometric constant. We previously reported c=2.65 ± 1.08 in an ovine model. Impella CP® left ventricular assist device is used for patients with severe left ventricular systolic failure as a temporary mechanical circulatory support. The impact of variable Impella® flows on Pmsa has not been investigated. We hypothesized that Pmsa is unaffected by the variability in flows provided by the Impella®. Methods: We conducted a translational interventional study to investigate the impact of Impella CP® on changes in Pmsa. The study was approved by the University of Sydney (Australia) Animal Research Ethics Committee. Five female adult merino cross sheep underwent implantation of Impella CP® under general anaesthesia following mitral valve surgery as a part of an unrelated investigation. Invasive measurements of haemodynamic parameters were recorded to allow calculation of Pmsa at variable Impella® settings with flows gradually changed from no flow to the maximum achievable by the pump. Total cardiac output was monitored with a Transonic Flowmeter positioned around the main pulmonary artery. Results: A total of 96 sets of flows were analyzed against Pmsa. The mean Pmsa was 22.34 ± 2.27 mmHg at zero Impella® flows and 23.79 ± 1.77 mmHg at maximum. A weak but statistically significant correlation was found between Impella® flows and Pmsa (rho = 0.20, 95% CI 0.004 - 0.389, p=0.046) representing a 1.45 mmHg (6.5%) increase from the baseline Pmsa after reaching maximum flows with Impella CP®. Conclusions: The effect of variable flows of Impella CP® on Pmsa values is small and is unlikely to be clinically significant in terms of guiding fluid or vasomotor therapy. Further data analysis is required to ascertain the validity of the Pmsa equation in patients with Impella® therapy. Acknowledgements: The authors acknowledge the facilities and the scientific and technical assistance of Sydney Imaging, a Core Research Facility at the Charles Perkins Centre, University of Sydney.
description: 31st Annual ELSO Conference; USA, virtual; 2020-09-25 - 2020-09-26