Adequacy of Perfusion during Hypothermia: Regional Distribution of Cardiopulmonary Bypass Flow, Mixed Venous and Regional Venous Oxygen Saturation

Abstract

Background: Hypothermia during CPB is used to reduce metabolic activity, thus protecting organs and tissues. The aim of this study was to investigate the relationship between regional and mixed venous oxygen saturation and distribution of pump flow with respect to hypothermia. Methods: Twenty-five patients undergoing a Ross procedure were included in a prospective, controlled study. During standard CPB, temperature was reduced stepwise to 28° C. Blood gases (a-stat regimen) were analysed in samples from the inferior (IVC) and the superior vena cava (SVC), arterial and mixed venous blood. Flow was detected separately in the SVC, IVC, arterial, and collecting venous line. Samples were taken, and flows were measured before CPB, during hypothermia, during rewarming, and 30 min after CPB discontinuation. Results: Oxygen saturation in the IVC was lower than in the SVC and in mixed venous blood at all times (max. difference - 17.3 ± 3.0 % during hypothermia, - 23.8 ± 2.9 % during rewarming, p < 0.01). There was a statistical correlation of mixed and IVC venous oxygen saturation (r = 0.79, p < 0.001) but not of SVC venous blood. Hypothermia had a major influence on pump flow distribution as backflow from the SVC decreased significantly in favour of IVC flow with increasing degree of hypothermia (increase of flow difference from 1.15 ± 0.23 l/min to 1.49 ± 0.36 l/min, p < 0.01). Temperature profiles were similar when detected in aorta, pulmonary artery, tympanum and nasopharygeum, but differed significantly from other sites. Conclusions: During hypothermic CPB, regional deoxygenation occurs in spite of normal mixed venous saturation. The level of hypothermia has a major impact on bypass flow distribution with cerebral perfusion reduction. Methods of regional oxygenation assessment are needed, and altered strategies during hypothermia have to be taken into consideration.

Key words

Cardiopulmonary bypass - hypothermia - pump flow distribution - oxygen tension and saturation

References

• 1 Parolari A, Alamanni F, Gherli T. et al . Cardiopulmonary bypass and oxygen consumption: oxygen delivery and hemodynamics.  Ann Thorac Surg. 1999;  67 1320-1327
• 2 Routsi C, Vincent J L, Bakker J. et al . Relation between oxygen consumption and oxygen delivery in patients after cardiac surgery.  Anesth Analg. 1993;  77 1104-1110
• 3 Swan H, Sanchez M, Tyndall M. et al . Quality control of perfusion: monitoring venous blood oxygen tension to prevent hypoxic acidosis.  J Thorac Cardiovasc Surg. 1990;  99 868-872
• 4 Baraka A. The effect of perfusion flow on oxidative metabolism during cardiopulmonary bypass.  Anesth Analg. 1993;  76 1191-1194
• 5 Dantzker D R, Foresman B, Gutierrez G. Oxygen supply and utilisation relationships. A reevaluation.  Am Rev Resp Dis. 1991;  143 675-679
• 6 Vaughn S, Puri V K. Cardiac output changes and continuous mixed venous oxygen saturation measurement in the critically ill.  Crit Care Med. 1988;  16 495-498
• 7 Fiddian-Green R G, Gantz N M. Predictive value of the stomach wall pH for complications after cardiac operations.  Crit Care Med. 1987;  15 153-156
• 8 Hassan E, Green J A, Nara A R. et al . Continuous monitoring of mixed venous oxygen saturation as an indicator of pharmacologic intervention.  Chest. 1989;  95 406-409
• 9 Wippermann C F, Schmid F X, Kampmann C. et al . Evaluation of gastric mucosal pH during and after cardiac surgery.  Eur J Cardiothorac Surg. 1997;  12 190-194
• 10 Nakajima T, Kuro M, Hayasi Y. et al . Clinical evaluation of cerebral oxygen balance during cardiopulmonary bypass: on-line continuous monitoring of jugular venous oxyhemoglobin saturation.  Anesth Anal. 1992;  74 630-635
• 11 Croughwell N D, Frasco P, Blumenthal J A. et al . Warming during cardiopulmonary bypass is associated with jugular bulb desaturation.  Ann Thorac Surg. 1992;  53 827-832
• 12 Prough D S, Stump D A, Roy R C. et al . Response of cerebral blood flow to changes in carbon dioxide tension during hypothermic cardiopulmonary bypass.  Anesthesiology. 1986;  64 576-581
• 13 Murkin J M, Farrar J K, Tweed W A. et al . Cerebral autoregulation and flow/metabolism coupling during cardiopulmonary bypass.  Anesth Analg. 1987;  66 825-832
• 14 Miyamoto T A, Miyamoto K J. Alpha-stat strategy: cause of ischemia in brains with old cerebral infarction despite selective cerebral hypothermic antegrade perfusion.  J Thorac Cardiovasc Surg. 2002;  124 1260-1261
• 15 Baraka A, Baroody M, Haroun S. et al . Continuous venous oximetry during cardiopulmonary bypass: influence of temperature changes, perfusion flow and hematocrit levels.  J Cardiothorac Anesth. 1990;  4 35-38
• 16 Miyano H, Inagaki M, Hashimoto N. et al . Regional cerebral blood flow during rewarming of cardiopulmonary bypass correlates with posthypothermic regional glucose use.  J Thorac Cardiovasc Surg. 1998;  116 503-510
• 17 Cook D J, Boston U S, Orszulak D A. et al . Carbon dioxide management and the cerebral response to hemodilution during hypothermic cardiopulmonary bypass in dogs.  Ann Thorac Surg. 2001;  72 1331-1335
• 18 Alston R P, Singh M, McLaren A D. et al . Systemic oxygen uptake during hypothermic cardiopulmonary bypass. Effect of flow rate, flow character, and arterial ph.  J Thorac Cardiovasc Surg. 1989;  98 757-768