Postoperative analgesia for thoracotomy patients

Severe postoperative pain, which may persist for up to 3 days and may lead to postoperative complications, due to the patient's inability to breathe deeply and cough, is frequently experienced in the area of the incision and chest tubes by thoracotomy patients. Eighteen patients undergoing routine thoracotomies were tested preoperatively for arterial blood gases and pulmonary function and given chest x-rays. Anesthesia consisted of thiopental, succinylcholine, N2O, enflurane, and pancuronium. Before incision closure, 6 intercostal spaces were injected by the surgeon with 3 ml of a randomly determined drug mixture. Patients received either bupivacaine and saline solution, bupivacaine and LMW dextran 40, or saline and LMW dextran 40. Arterial blood gases, pulmonary function, chest x-rays, narcotic dosage, sensory level, and subjective responses were evaluated for 3 days postoperatively. Results demonstrate that intercostal nerve blocks can markedly reduce postoperative pain and improve pulmonary function in such patients. Significant differences from controls were seen in Pao2, Paco2, vital capacity, forced expiratory flow rates, analgesic requirements, and patient comfort. The duration of the block with bupivacaine and saline was less than 12 hours, while the mean duration of the block with bupivacaine and dextran 40 was 36 hours.

The renin--angiotensin--aldosterone system during cardiac surgery with morphine--nitrous oxide anesthesia

Ten consecutive adult patients undergoing elective cardiac surgery with extracorporeal circulation were anesthetized using morphine (1-3 mg/kg) and nitrous oxide. Pre-bypass plasma renin activity showed a 3.5-fold elevation (P smaller than 0.001) over baseline values. This correlated with maximal blood pressure elevation. Plasma renin activity remained elevated during bypass. High baseline aldosterone levels increased 3.4-fold (P smaller than 0.001) after 15 minutes on bypass and 4.0-fold by the end of bypass. Plasma potassium decreased from 3.9 mEq/1 before bypass to 3.2 mEq/1 (P smaller 0.0001) during bypass, and the fractional urinary excretion of potassium was 32 per cent before bypass with a mean of 34.4 per cent during bypass. Urinary output remained high during bypass despite a progressive decrease in glomerular filtration rate. Catecholamine levels showed no significant change. The data suggest that the renin-angiotensin-aldosterone system may play a role in blood pressure regulation during cardiopulmonary bypass and may result in the excessive urinary excretion of potassium and decrease in plasma potassium levels.

Inhibition of angiotensin conversion and prevention of renal hypertension

Renal artery constriction in the unilaterally nephrectomized, trained dog, with maintained renal arterial hypotension, produces a prompt increase in systemic renin activity and blood pressure. The hypertension normally induced by renal artery stenosis is prevented by prior treatment with the nonapeptide Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro (SQ 20, 881), which blocks conversion of angiotensin I to angiotensin II. Constant intravenous infusion of the inhibitor over several days of renal artery constriction prevents the development of chronic renovascular hypertension. Furthermore, a single injection of the nonapeptide restores blood pressure to normal in the early phase of renovascular hypertension, but becomes progressively less effective as salt and water retention occurs in the chronic stage when plasma renin activity returns to control levels. These data provide strong evidence that the renin-angiotensin system is responsible for the initiation of renovascular hypertension in the one-kidney Goldblatt dog, but that other factors become increasingly important in chronic renovascular hypertension.

Inhibition of angiotensin conversion in experimental renovascular hypertension

Constriction of the renal artery and controlled reduction of renal perfusion pressure is followed by a prompt increase in systemic renin activity and a concomitant rise in blood pressure in trained, unanesthetized dogs. The elevated blood pressure induced by the renal artery stenosis can be prevented by prior treatment with the nonapeptide Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro, which blocks conversion of angiotensin I to angiotensin II. Further, the nonapeptide can restore systemic pressure to normnal in the early phase of renovascular hypertension. These results offer strong evidence that the renin-angiotensin system is responsible for the initiation of hypertension in the unilaterally nephrectomized dog with renal artery constriction.