How to Manage Critically Ill Patients After Cardiac Surgery
Acute heart failure after cardiac surgery is a pathophysiologic state in which the heart cannot sufficiently pump blood for tissue requirements. Low cardiac output after cardiac surgery can be related to previous deteriorated ventricular function and perioperative myocardial damage due to ischemia. The principal mechanism responsible for low postoperative cardiac output has been attributed to myocardial damage during cardiopulmonary bypass (CPB). Reduction in oxygen supply relative to demand may cause hypoxia and ischemia, which determines myocardial structural damage manifested by contractility impairment, malignant ventricular arrhythmias and low cardiac output. Acute mechanical contractility dysfunction owing to ischemia may take different amounts of time to recover according to the type of lesion involved (1). Contractility dysfunction that is rapidly reversible with pharmacological agents which are able to reduce oxygen demand indicates viable myocardium defined as “hibernating”. On the other hand, contractile dysfunction associated with a short time of ischemia, if slowly reversible, and persisting for days to weeks is termed “stunned myocardium”. Therefore, the basic difference between stunned and hibernating myocardium is related to pathophysiological mechanisms and time necessary to recover the contractility. In the stunned myocardium, the period of contractility impairment is slowly reversed and associated to ischemia. In hibernating myocardium the decrease in the contractility is associated to a period of low coronary flow and characterizes to be rapidly reversible (2-4). In addition to increased oxygen demand in the face of reduced supply, another cause of myocardial dysfunction after CPB is the presence of down-regulation of 6-adrenergic receptors. Cardiopulmonary bypass has been known to be a potent stimulus for the release of endogenous catecholamines, and it has been experimentally demonstrated that a reversible 6-adrenergic receptor down-regulation may contribute to difficulty in weaning from CPB after completion of cardiac surgery as well as transitory postoperative cardiac dysfunction (5).
KeywordsCardiac Index Inspiratory Flow Stun Myocardium Peak Inspiratory Pressure Pressure Control Ventilation
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- 19.Carvalho MJ, Auler Jr JOC, Saldiva PHN, Barbas CSB, Zin WA (1991) The effect of positive end-expiratory pressure (PEEP) on respiratory system mechanics. Annals of 11th International Symposium on Intensive Care and Emergency Medicine, Brussels, Belgium 83Google Scholar
- 24.Boysen PG, McGough E (1988) Pressure-control and pressure-support ventilation: flow patterns, inspiratory time, and gas distribution. Resp Care 33:126–134Google Scholar
- 25.Kosecioglu J, Tibboel D, Lachmann B (1994) Advantages and rationale for pressure controlled ventilation. In: Vincent JL (ed) Yearbook of intensive care and emergency medicine. Springer, Berlin Heidelberg New York, pp 524–533Google Scholar
- 27.Auler Jr JOC, Carvalho MJ, Silva AMPR, Silva MHC, Dias CA, Jatene AD (1992) Pressure controlled ventilation in patients submitted to cardiac surgery. 12th International Symposium on Intensive Care and Emergency Medicine. Brussels, Belgium. Clin Intensive Care [Suppl]3:64Google Scholar
- 28.Freedman RJ (1992) Myoconservation in cardiogenic shock — the use of intra-aortic balloon pumping and other treatment modahties. Cardiac Assists 6:1–10Google Scholar