Acta Anaesthesiol Scand 2002; 46: 51–56 Copyright C Acta Anaesthesiol Scand 2002 Printed in Denmark. All rights reserved ACTA ANAESTHESIOLOGICA SCANDINAVICA ISSN 0001-5172 Temperature-related fluid extravasation during cardiopulmonary bypass: An analysis of filtration coefficients and transcapillary pressures J. K. HELTNE, J. BERT, T. LUND, M.-E. KOLLER, M. F ARSTAD, S. E. RYNNING and P . HUSBY Department of Anesthesia and Intensive Care, University of Bergen, Haukeland University Hospital, Bergen, Norway and 1 Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, Canada Background: Cardiopulmonary bypass (CPB) as used for car- diac surgery and for rewarming individuals suffering deep acci- dental hypothermia is held responsible for changes in microvas- cular fluid exchange often leading to edema and organ dysfunc- tion. The purpose of this work is to improve our understanding of fluid pathophysiology and to explore the implications of the changes in determinants of transcapillary fluid exchange during CPB with and without hypothermia. This investigation might give indications on where to focus attention to reduce fluid ex- travasation during CPB. Methods: Published data on ‘‘Starling variables’’ as well as re- ported changes in fluid extravasation, tissue fluid contents and lymph flow were analyzed together with assumed/estimated values for variables not measured. The analysis was based on the Starling hypothesis where the transcapillary fluid filtration rate is given by: F LUID AND SOLUTE distribution and transport be- tween the microvascular space and tissues in pa- tients treated on cardiopulmonary bypass (CPB) are complex and poorly understood. Overhydration and tissue edema are often present after prolonged CPB, leading to vital organ dysfunction. Recently we docu- mented an increased fluid extravasation in piglets on CPB, especially if hypothermic conditions were used during bypass (1). Several investigators have focused on a generalized inflammatory response to the ex- posure of blood to foreign surfaces during CPB in order to explain the increased fluid leak into tissues (2, 3). The fluid shifted into the extravascular space has recently been found to be relatively protein poor, consisting mainly of water and small solutes (4, 5). This is not what would be expected secondary to an inflammatory reaction where a protein-rich exudate is typical (6). Based on these recent findings (1, 4), we analyzed further the nature of fluid transport during nor- 51 J V ΩK f [P c ªP i ªs(COP p ªCOP i )]. Here K f is the capillary fil- tration coefficient, s the reflection coefficient, P and COP are hydrostatic and colloid osmotic pressures, and subscript ‘c’ re- fers to capillary, ‘i‘ to the interstitium and ‘p’ to plasma. Results and conclusion: The analysis indicates that attempts to limit fluid extravasation during normothermic CPB should ad- dress primarily changes in K f , while changes in both K f and P c must be considered during hypothermic CPB. Received 26 February, accepted for publication 25 May 2001 Key words: Extracorporeal circulation; capillary filtration coef- ficient; interstitial fluid pressure; colloid osmotic pressure; capil- lary pressure; reflection coefficient; fluid transport. c Acta Anaesthesiologica Scandinavica 46 (2002) mothermic and hypothermic CPB. In particular, we assessed transcapillary pressure driving forces and transport properties of the capillary wall using avail- able data and information along with the well-estab- lished Starling’s hypothesis. Starling’s hypothesis relates transcapillary fluid ex- change to driving forces and transport parameters as follows: J v ΩK f (P c ªP i ªs(COP p ªCOP i )) (1) Where: J v is the transcapillary fluid filtration rate, K f is the fluid filtration coefficient P c is the capillary hydrostatic pressure, P i is the interstitial fluid hydrostatic pressure, s is the capillary wall reflection coefficient (a value of zero describes a capillary wall which is freely per- meable to a specific macromolecule and a value of