Helmut Suppan, ECCP, Werner Londer, ECCP, Stefan Huber, MD, Peter Rehak, Ph.D, Heinrich Mächler, MD, Bruno Rigler, MD
Division of Cardiac
Surgery
I. University Clinic of Surgery
Auenbruggerplatz 29
8036 Graz / Austria
The correct citation of this article for reference is:
Suppan H, Londer W, Huber S, Rehak P, Maechler H, Rigler B: Oxygen Extraction Rate As A Tool To Control The Effect Of Hemodilution During Cardiopulmonary Bypass. The Internet Journal of Thoracic and Cardiovascular Surgery 1999; Vol2 N2: http://www.ispub.com/journals/IJTCVS/Vol2N2/oxygen.htm ; Published July 1, 1999; Last Updated July 1, 1999.
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Introduction
Methods
Statistics
Results
Discussion
References
Introduction (back to Quick Links)
Despite recent advances in blood conservation techniques, up to 30% to 80% of patients
undergoing open heart operations require allogeneic blood transfusions 1. The following methods of reducing
allogeneic blood transfusions are well known: autologous blood donation, isovolemic
hemodilution, hemodilution at the beginning and during extracorporeal circulation (ECC),
hemofiltration and ultrafiltration to increase hemoconcentration, cell saver
autotransfusion, reinfusion of blood from drainages, pharmacological influence on
hemostasis, use of coated perfusion systems in extracorporeal perfusion, use of
centrifugal pumps in extracorporeal perfusion, etc.
A prospective, randomized study was performed to test the effect of withdrawing blood
during ECC by the perfusionist while controlling the oxygen extraction rate. The aim was
to evaluate if a withdrawal of blood (400 ml) is tolerable concerning the O2-extraction
rate since a crucial upper limit of 22% - 30% during ECC has been postulated 2.
Methods (back to Quick Links)
40 male patients (62–78 years, mean age 69 years) undergoing CABG-procedures were randomized to either withdrawal of 400 ml blood from the cardiotomy reservoir with simultaneous substitution of cristalloid solutions 10 minutes after cross-clamping of the aorta (group I, n= 20) or performance of coronary artery bypass with standard ECC technique (group II, control group, n = 20). In both groups the oxygen extraction rate was measured.
In group I 400 ml of blood were temporarely stored in biopack-bags (Biotrans®,
Holland) during the ECC – with simultaneous substitution of cristalloid solutions
– and controlled retransfusion during the rewarming or the post-bypass period was
performed if the extraction rate increased up to more than 25%.
In the control group (group II) CABG surgery was performed without hemodilution using
standard ECC technique.
The oxygen extraction rate was calculated with the following formula 3 using a conventional software program
(Excel®, Microsoft®, USA):
(1,39 x Hb) x art. saturation + (PaO2 x 0,003) = ml O2 / 100 ml blood = CaO2
(1,39 x Hb) x ven. saturation + (PvO2 x 0,003) = ml O2 / 100 ml blood = CvO2
CaO2 x CO x 10 = DO2
CaO2 - CvO2 = avDO2 (O2 / 100ml blood)
avDO2 x CO x 10 = VO2
VO2 / DO2 = oxygen extraction rate in %
Abbreviations:
PaO2 = arterial O2 pressure (mm Hg) CaO2 = arterial oxygen concentration
PvO2 = venous O2 pressure (mm Hg) CvO2 = venous oxygen concentration
DO2 = capacity of oxygen transport CO = cardiac output
avDO2 = arterio-venous difference in oxygen concentration
VO2 = oxygen consumption / min
Points of measurement in both groups:
Point I: at 30°C blood temperature (at cross-clamping of the aorta)
Point II: at 30°C blood temperature (10 min after withdrawal of 400 ml blood from the
cardiotomy reservoir
Point III: regaining 37°C blood temperature and after the end of the cross clamping
period
Statistics (back to Quick Links)
The hematocrit and the oxygen extraction rate were calculated by analysis of variance (ANOVA) with repeated measurements. In each group the oxygen extraction at different points of measurement was calculated with the student T-test.
Results (back to Quick Links)
A significant difference (p<0,05) was seen regarding the oxygen extraction rate at
point II between both groups. (Fig. 1, 2). In group I a significant difference (p: 0,02)
was evident between points I and II (Fig. 1). No significant difference was seen regarding
the hematocrit between any points in any of the two groups (Fig. 1, 2).
In 15% of the patients (n = 3) the withdrawn blood had to be retransfused to the
cardiotomy reservoir due to extraction rate values more than 25%. In 85% the stored
biopack bags could be handed over for further use.
Fig. 1
Fig. 2 
Fig. 1 and 2: all the values at points I, II and III are mean values ± standard deviation. Abbreviations: HCT = hematocrit in g/100 ml, O2Ext = O2-extraction in %
Discussion (back to Quick Links)
The preoperative autologous blood donation 4 is considered to be the safest and
best method and should be applied in elective cardiac surgery. However, there are several
contraindications as in patients with unstable angina, left main stenosis, heart failure
in stage of decompensation, in aortic and mitral valve stenosis of higher degree (III
– IV), in the case of a hemoglobin concentration less than 11 g/dl, in defects in
hemostasis and in hemophilia or in congenital and aquired erythrocytal defects.
Additionally, the costs for storage must not be left out of consideration.
Isovolemic hemodilution reflects one of the major methods in reducing blood
transfusions 4.
However, the simultaneous volume exchange with high-molecular or cristalloid solutions
decreases the hematocrit and has several wellknown disadvantages like reduction of vital
substances in the plasma, promotion of defects of hemostasis, increasing the perioperative
risk of infection (immunosuppressive effect) or increasing the accumulation of
extracellular/interstitial fluid (capillary leak syndrome).
Additionally, the equation of Fox 5 should be kept in mind that in case of low hematocrit
levels a further increase of an already high blood flow will only lead to minimal changes
in systemic oxygen consumption. Experimentially, at hematocrit values less than 17% - 20%
an increase of cardiac output cannot maintain adequate oxygen distribution, as shown in
healthy canine hearts 6.
The fact that a crucial lower limit of the hematocrit level exists is wellknown, however,
the O2-extraction rate is the limiting factor to control hemodilution.
Our method of measuring the oxygen extraction rate after withdrawing blood from the
cardiotomy reservoir after initiation of ECC seems to be a good tool to provide
information concerning the current O2–consumption during ECC. The disadvantage is
that the method can only be applied in about 85% of the patients.
Limitations of the study are that there was no long term evaluation of the morbidity at
the intensive care unit (ICU) and that we cannot present results with isovolemic
hemodilution. Additionally, measurements of lactate parameters after arrival at the ICU
were not considered.
In conclusion, a priming free of allogeneic blood, a low volume in priming and an
additional blood withdrawal during ECC with hemodilution while controlling the oxygen
extraction rate might reduce the need for allogeneic blood transfusions during open heart
operations.
References (back to Quick Links)
1. Shapira OM, Aldea GS, Treanor PR,
Chartrand RM, DeAndrade KM, Lazar HL, Shemin RJ. Reduction of allogeneic blood transfusion
after open heart operations by lowering cardiopulmonary bypass prime volume. Ann Thorac
Surg 1998; 65: 724 – 30 (back to
text)
2. Cardiovascular terms and formulas:
Oxygen-transport variables. www.dhep.astate.edu/patho/Cardiovascular/cardioterm.htm (back to text)
3. Reich DL. Hemodynamic Monitoring In
Kaplan JA (ed) , Cardiac Anesthesia 1993; 3rd edn: 289 (back to text)
4. Gombotz H, Kulier A. Reduktion des
Fremdblutverbrauchs in der operativen Medizin. Anaesthesist 1995; 44: 191 – 218
(back to text)
5. Igarashi T, Sonehara D, Iwahashi K, Asahara H, Konishi A, Suwa K.
Hemodynamics and oxygen consumption during warm heart surgery. J. Anesthesiology 1996; 10:
16 - 21 (back to text)
6. Crystal GJ. Myocardial oxygen supply-demand relations during
isovolemic hemodilution Adv Pharmacology 1994; 31: 285 - 300 (back to text)
© Internet Scientific Publications, L.L.C., 1996 to 1999.
First Published: October 1996
The Internet Journal of Anesthesiology