Pain from surgical trauma consistently elicits increased sympathetic nervous system activity and adrenal catecholamine secretion. As a consequence, blood pressure, heart rate, and cardiac output increase. This leads to enhanced myocardial oxygen consumption which can be detrimental in patients with underlying cardiac disease. Inadequate treatment of pain in such patients increases the risk of perioperative myocardial ischemia. Additionally, an increased sympathetic tone may lower the heart's fibrillation threshold and render it more susceptible to arrhythmic events. The incidence of cardiovascular complications is reduced by effective pain relief (Kehlet, ,1993).
In the peripheral circulation, increased sympathetic stimulation may alter regional blood flow. Decreased blood flow will reduce oxygen delivery, resulting in local acidosis and impaired wound healing. Together with changes in coagulability, this may also lead to venous thrombosis and pulmonary embolism. Epidural analgesia can prevent these sequelae and improve outcome („Kehlet,,1993).
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