Critical values of hematocrit and mixed venous oxygen saturation as parameters for a safe cardiopulmonary bypass.
OBJECTIVE
Mixed venous oxygen saturation (SvO2) is high despite a low hematocrit implies that the relationship between oxygen demand and supply is in a safe state. This study was sought to determine the critical values for hematocrit and SvO2 for safe cardiopulmonary bypass.


METHODS
Study 1: To evaluate the limit of hemodilution without cardiopulmonary bypass, normovolemic hemodilution with Dextran 40 (10%) was performed in 14 rabbits. SvO2 was monitored from the right atrium, and the hemodynamic parameters were recorded continuously. Study 2: To determine the critical values for hematocrit and SvO2 during cardiopulmonary bypass, normothermic and hypothermic cardiopulmonary bypass were performed in 13 rabbits and hemodynamic parameters were corrected.


RESULTS
Study 1: The heart rate decreased to unsafe levels abruptly, when the SvO2 was < or = 43% or the hematocrit was < or = 10%. The lactate concentration increased when the SvO2 was < or = 46% or the hematocrit was < or = 12%. Study 2: When the hematocrit was < or = 12%, the SvO2 decreased gradually. Even when weaning was possible, the animals with a hematocrit < or = 12% collapsed hemodynamically within 40 minutes after cardiopulmonary bypass. Most of the animals could not be weaned from cardiopulmonary bypass during either normothermic or hypothermic cardiopulmonary bypass when the SvO2 was < or = 46%.


CONCLUSIONS
Continuous monitoring of hematocrit and SvO2 provides evidence-based guidelines for safe cardiopulmonary bypass. The lower limits of critical range for a safer cardiopulmonary bypass are hematocrit of 12% and SvO2 of 46%.
Second Department of Surgery, Faculty of Medicine, Yamanashi University, Yamanashi, Japan.
Hiroshi
H
Osawa
Shinpei
S
Yoshii
Samuel J K
SJ
Abraham
Shigeru
S
Hosaka
Shoji
S
Suzuki
Koji
K
Ogata
Okihiko
O
Akashi
Hiroji
H
Higuchi
Yusuke
Y
Tada
D000818:Animals; D002315:Cardiopulmonary Bypass; D006400:Hematocrit; D006438:Hemodilution; D010100:Oxygen / Q000097:blood*; D011817:Rabbits
D010100:Oxygen