The reason for cardiac output reduction after aortic cross-clamping

Classic Papers Revisited: My Love Affair with the Venous System

The Pathophysiology of Aortic Cross-clamping and Unclamping. By Gelman S. ANesthesiology 1995; 82:1026–60. Reprinted with permission.

Aortic cross-clamping (AoX) and unclamping are associated with severe hemodynamic disturbances in virtually all organs and systems. The main hemodynamic changes induced by AoX result from an increase in impedance to aortic flow, an increase in systemic vascular resistance and afterload, blood volume redistribution caused by collapse and constriction of venous vasculature distal to the aortic clamp, and a subsequent increase in preload. Preload may not increase if the aorta is clamped distal to the celiac artery; in that case, blood volume from distal venous vasculature may be redistributed to the splanchnic vasculature without associated increases in preload. Increases in afterload and preload demand an increase in contractility, which results in an autoregulatory increase in coronary blood flow. Without increases in coronary blood flow and myocardial contractility, decompensation may occur. Aortic cross-clamping is associated with the formation and release of many mediators which constitute a double-edged sword: they may mitigate or aggravate the harmful hemodynamic effects of AoX and unclamping. Injuries to the lungs, kidneys, spinal cord, or abdominal viscera are caused mainly by ischemia and reperfusion of organs distal to aortic cross-clamping. A clear understanding of the pathophysiologic mechanisms involved in these processes should help to promote rational, well-focused, and effective measures to prevent and treat homeostatic disturbances occurring during AoX and unclamping.

Extending resuscitative endovascular balloon occlusion of the aorta: Endovascular variable aortic control in a lethal model of hemorrhagic shock

BACKGROUND

The duration of use and efficacy of resuscitative endovascular balloon occlusion of the aorta (REBOA) is limited by distal ischemia. We developed a hybrid endovascular-extracorporeal circuit variable aortic control (VAC) device to extend REBOA duration in a lethal model of hemorrhagic shock to serve as an experimental surrogate to further the development of endovascular VAC (EVAC) technologies.

METHODS

Nine Yorkshire-cross swine were anesthetized, instrumented, splenectomized, and subjected to 30% liver amputation. Following a short period of uncontrolled hemorrhage, REBOA was instituted for 20 minutes. Automated variable occlusion in response to changes in proximal mean arterial pressure was applied for the remaining 70 minutes of the intervention phase using the automated extracorporeal circuit. Damage-control surgery and whole blood resuscitation then occurred, and the animals were monitored for a total of 6 hours.

RESULTS

Seven animals survived the initial surgical preparation. After 20 minutes of complete REBOA, regulated flow was initiated through the extracorporeal circuit to simulate VAC and provide perfusion to distal tissue beds during the 90-minute intervention phase. Two animals required circuit occlusion for salvage, while five animals tolerated sustained, escalating restoration of distal blood flow before surgical hemorrhage control. Animals tolerating distal flow had preserved renal function, maintained proximal blood pressure, and rapidly weaned from complete REBOA.

CONCLUSION

We combined a novel automated, extracorporeal circuit with complete REBOA to achieve EVAC in a swine model of uncontrolled hemorrhage. Our approach regulated proximal aortic pressure, alleviated supranormal values above the balloon, and provided controlled distal aortic perfusion that reduced ischemia without inducing intolerable bleeding. This experimental model serves as a temporary surrogate to guide future EVAC catheter designs that may provide transformational approaches to hemorrhagic shock.

The pathophysiology of aortic cross-clamping

During open aortic surgery, interrupting the blood flow through the aorta by applying a cross-clamp is often a key step to allow for surgical repair. As a consequence, ischemia is induced in parts of the body distal to the clamp site. This significant alteration in the blood flow is almost always associated with hemodynamic changes. Upon release of the cross-clamp, the blood flow is restored, triggering an ischemia-reperfusion response, leading to many pathophysiological processes such as inflammation, humoral changes, and metabolite circulation that could lead to injury in many organ systems and may significantly influence the postoperative outcome. It is therefore important to understand these processes and how they can be treated in order to allow for safe surgical aortic repairs while ensuring the best possible outcomes.

Bilateral femoral artery compression as a technique to increase vital organ perfusion during intraoperative hypotension

Intraoperative hypotension is associated with adverse outcomes. The preferred treatment for intraoperative hypotension is to address its cause. In the interim the blood pressure can be supported by the anesthesia team with volume resuscitation and vasopressors. Additionally, preferential perfusion of vital organs, such as the myocardium and cerebrum, at the expense of non-vital vascular beds, such as the extremities, is desirable. In the state of shock, the flight or fight response will ensure perfusion of the extremities in order to prepare the organism for a physical confrontation. However, in the context of intraoperative hypotension this response is counter-productive. Therefore we propose bilateral femoral artery compression as a new technique to increase vital organ perfusion during intraoperative hypotension. This results in shunting of blood flow from the legs and towards the vital organs. Bilateral femoral artery compression can be employed by the surgical team to immediately improve blood pressure until other counter-measures against intraoperative hypotension take effect.

Hemodynamic variations during thoracic and abdominal stop-flow regional chemotherapy

AIMS

The aim of this study was to study hemodynamic modifications during thoracic and abdominal stop-flow regional chemotherapy and to evaluate the need for routine hemodynamic monitoring during such kind of procedures.

METHODS

Thirty patients, aged 17-67 years, ASA physical status II-III, scheduled for thoracic (group A, n = 15), and abdominal (group B, n = 15) stop-flow regional chemotherapy were enrolled. Heart rate (HR), electrocardiogram lead I and V(5), end tidal carbon dioxide (ETCO(2)), arterial oxygen saturation (SaO(2)), systolic, diastolic and mean arterial pressure (SBP, DBP, MAP), mean pulmonary arterial pressure (MPAP), pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), cardiac output (CO), stroke volume (SV), stroke index (SI), systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), left cardiac work (LCW), right cardiac work (RCW), left cardiac work index (LCWI), right cardiac work index (RCWI), cardiac index (CI), and body O(2) consumption (VO(2)) were recorded.

RESULTS

After aortic and inferior vena cava endovascular occlusion (T(1)), a significant reduction of CO and SV, associated with an increase of CVP, MAP, PAPM and PCWP were observed. A concomitant reduction of CI and increase of SVR and PVR were registered. The VO(2) was significantly reduced compared to basal values in both groups. After deflating aortic and vena cava balloons (T(2)), CO, SV and CI increased with respect to basal value p < 0.05) whereas MAP, CVP, PAPM, PCWP and calculated parameters (SVR, PVR) showed a significant reduction compared to T(1). The oxygen consumption was significantly higher than that of basal values p < 0.05. After hemofiltration (T(3)), all hemodynamic variables were comparable with the basal values. Modifications of direct and calculated parameters, during the stop-flow period, showed a similar trend in both study groups, without any statistically significant difference. No ST modifications at ECG were noted during all perioperative period.

CONCLUSIONS

The results of this study have confirmed in both groups, the safety of stop-flow regional chemotherapy procedure, despite endovascular occlusion of the aorta and inferior cava vein. The hemodynamic and oxygenation changes are reversible and did not produce any ST modifications at ECG during all perioperative period. Routine pulmonary artery catheterization is thus unnecessary, except in high cardiac risk patients.

Dopexamine hydrochloride does not modify hemodynamic response or tissue oxygenation or gut permeability during abdominal aortic surgery

PURPOSE

To assess the effects of intraoperative infusion of dopexamine (a DA-1 and B2 adrenoreceptor agonist) on hemodynamic function, tissue oxygen delivery and consumption, splanchnic perfusion and gut permeability following aortic cross- clamp and release.

METHODS

In a randomised double blind controlled trial 24 patients scheduled for elective infrarenal abdominal aortic aneurysm repair were studied in two centres and were assigned to one of two treatment groups. Group I received a dopexamine infusion starting at 0.5 microg x kg(-1) x min(-1) increased to 2 microg x kg(-1) x min(-1) maintaining a stable heart rate; Group II received a placebo infusion titrated in the same volumes following induction of anesthesia. Measured and derived hemodynamic data, tissue oxygen delivery and extraction and gut permeability were recorded at set time points throughout the procedure.

RESULTS

Dopexamine infusion (0.5 -2 microg x kg x min(-1)) was associated with enhanced hemodynamic function (MAP 65 +/- 5.5 vs 92 +/- 5.7 mm Hg, P = <0.05) only during the period of aortic cross clamping. However, during the most part of infrarenal abdominal aortic surgery, dopexamine did not reduce systemic vascular resistance index, mean arterial pressure nor oxygen extraction compared with the control group. The lactulose/ rhamnose permeation ratio was elevated above normal in both groups (0.22 and 0.29 in groups I and II respectively).

CONCLUSIONS

Dopexamine infusion (0.5 -2 microg x kg(-1) x min(-1)) did not enhance hemodynamic function and tissue oxygenation values during elective infrarenal abdominal aortic aneurysm repair.

Hemodynamics, intramucosal pH and regulators of circulation during perioperative epidural analgesia

PURPOSE

To evaluate the effects of perioperative epidural analgesia on hemodynamics, splanchnic perfusion and regulators of circulation.

METHODS

Twenty patients undergoing aortic surgery were randomised into two groups: epidural analgesia group (EAG): epidural analgesia with bupivacaine (15 ml, 0.125%) was started before surgery. Eight and 16 hr postoperatively 10 ml bupivacaine 0.125% and 1 mg morphine were given. Control group (COG): patients received no epidural catheter. Monitoring included pulmonary artery catheter and gastric tonometer. Norepinephrine, epinephrine, renin, ADH, ANP and endothelin were measured: before epidural analgesia (T0), before aortic clamping (T1), 20 min after aortic clamping (T2), after declamping the first leg (T3), at end of surgery (T4), one hour (T5) and 24 hr postoperatively (T6).

RESULTS

At T5 mean arterial blood pressure decreased in EAG compared with baseline (86 +/- 16 to 75 +/- 8 mmHg) and compared with COG (75 +/- 8 vs 84 +/- 11 mmHg). At T2 pulmonary capillary wedge pressure and cardiac index increased and at T6 decreased in both groups. Systemic vascular resistance decreased at T I and at T3-T5 in EAG compared with COG and at T1 and T3-T6 to baseline (1472 +/- 448 to 1027 +/- 184 dyn x sec x cm(-5) x m(-2)). In EAG and in COG, pHi decreased compared with baseline but without group differences. In both groups, epinephrine, norepinephrine, renin, and ADH levels increased from baseline. Endothelin and ANP levels showed no changes.

CONCLUSIONS

Perioperatively administrated epidural bupivacaine has no beneficially effects on hemodynamics, pHi or release of regulators of circulation.

A prolonged spinal cord ischaemia model in pigs. Passive shunting offers stable central haemodynamics during aortic occlusion

OBJECTIVES

to evaluate the effect of a modified aortic shunt on central haemodynamic variables during experimental thoracic aortic occlusion in a prolonged spinal cord ischaemia model.

MATERIAL AND METHODS

central haemodynamic variables were evaluated during aortic cross-clamping. In the shunt group (n=11), after the placement of proximal and distal aortic clamps, distal aortic perfusion was restored through an aortoiliac shunt via the left subclavian artery. In the no-shunt group (n=11), spinal cord ischaemia was achieved with only proximal aortic cross-clamping. The clamping time was 60 minutes in the shunt group and 30 minutes in the no-shunt group.

RESULTS

in the no-shunt group, all animals needed inotropic support, vasodilators and buffers during the experiment. None of these drugs were needed in the shunt group. In the no-shunt group, cross-clamping caused a significant increase in mean arterial pressure and heart rate compared to baseline values. These variables were stable in the shunt group during aortic occlusion. In the reperfusion period cardiac output, heart rate and arterial pCO(2)were significantly higher in the no-shunt than in the shunt group.

CONCLUSION

the present experimental spinal cord ischaemia model, using double aortic cross-clamping with shunt, offers improved central haemodynamics. This enables the study of prolonged selective spinal cord ischaemia without interaction from vasoactive drugs or systemic reperfusion.

Respiratory mechanics during and after anaesthesia for major vascular surgery

To evaluate the effects of major vascular surgery on respiratory mechanics, 11 patients undergoing general anaesthesia for abdominal aortic surgery were studied. Before aortic cross-clamping, chest wall elastance and resistance both increased (by 126% and 58%, respectively) when surgical retractors were placed. After aortic cross-clamping, lung elastance increased by 29%, accompanied by a decrease in cardiac index (22%) and an increase in pulmonary (17%) and systemic (15%) vascular resistance. After aortic unclamping, lung elastance decreased, although it remained higher than baseline values (by 12%). All cardiovascular variables returned to the values obtained before aortic cross-clamping.

Fractured cervical spine and aortic transection

A 17-year-old victim of a road traffic accident presented. Following investigation diagnoses of fractured first cervical vertebra, aortic transection, diffuse cerebral oedema, fractured right ribs 2-4 and pubic rami were made. Management of this case presented a number of anaesthetic dilemmas: management of the airway, use of cross-clamp vs. shunting or heparinization and bypass, cardiovascular and neurological monitoring, maintenance of cardiovascular stability during and post cross-clamp, minimizing the risk of post-operative renal and neurological dysfunction.

Cardiac function in patients with treated hypertension during aortic aneurysm repair

OBJECTIVES

To investigate the impact of arterial hypertension on cardiac function during aortic cross-clamping and declamping.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty treated hypertensive males with slight left ventricular hypertrophy and 10 normotensive controls undergoing elective repair of an abdominal aortic aneurysm.

INTERVENTIONS

Using transesophageal echocardiography, the mitral inflow profile was evaluated during aortic cross-clamping and declamping.

MEASUREMENTS AND MAIN RESULTS

During the clamping period, the ratio of peak atrial to peak early filling velocity (PA/PE) was significantly higher in the hypertensive patients. One minute after aortic cross-clamping, mean arterial pressure (MAP) and pulmonary artery occlusion pressure significantly increased in the hypertensive patients, whereas they did not change in the normotensive group. Cardiac index and heart rate significantly decreased after cross-clamping, and increased after clamp release in both groups. PA/PE significantly dropped in both groups after aortic declamping, and returned to baseline values thereafter. MAP also decreased significantly in both groups after clamp release, but the fall of MAP tended to be more pronounced in the hypertensive patients.

CONCLUSIONS

In the treated hypertensive patients, more pronounced hemodynamic and echocardiographic responses to aortic cross-clamping probably mirror the altered diastolic left ventricular function in these patients. With respect to intraoperative management, however, the treated hypertensive patients did not react grossly differently from the normotensive controls.

Hemodynamic effects of isovolemic hemodilution during descending thoracic aortic cross clamping and lower torso reperfusion

BACKGROUND

Isovolemic hemodilution has been suggested for blood conservation and to improve hemodynamic tolerance to abdominal aortic cross clamping. However, the hemodynamic effects of hemodilution during descending thoracic aortic cross clamping (DAC) have not been established. We evaluated them in anesthetized swine.

METHODS

Hemodilution (n = 7) was produced by the isovolemic exchange of blood for 6% hetastarch to a target hematocrit of 20%. Hematocrit in control pigs (n = 7) remained at 30%. DAC was performed at the T9 level for 45 minutes. During a 60-minute reperfusion period, control pigs were infused with lactated Ringer's solution; shed blood was returned to hemodilution pigs, followed by lactated Ringer's. If hypotension occurred despite left atrial pressure of 10 mm Hg or greater, boluses of phenylephrine were given to keep mean arterial pressure above 60 mm Hg.

RESULTS

Hemodilution caused a marked reduction in hematocrit and in global oxygen delivery (DO2). DAC produced a significant increase in proximal arterial pressure, cardiac index, and DO2 and oxygen consumption (VO2) was markedly reduced in both groups. A significant increase in systemic vascular resistance during DAC occurred only in control pigs. After reperfusion, vascular resistance was significantly lower than baseline in hemodilution pigs, requiring a sixfold greater dose of phenylephrine to avoid hypotension. A lower global DO2 and supply-limited VO2 were also observed in hemodilution pigs.

CONCLUSIONS

Isovolemic hemodilution maintains hemodynamic stability during DAC. During lower torso reperfusion, however, hemodilution caused hemodynamic instability, decreased global DO2, and limited VO2, which may offset its potential benefits.

Trimethaphan versus sodium nitroprusside for the control of proximal hypertension during thoracic aortic cross-clamping: the effects on spinal cord ischemia

Sodium nitroprusside (SNP) has been used to control the proximal hypertension associated with thoracic aortic cross-clamping (TACC) during thoracic aortic surgery. It worsens neurologic outcome, presumably by further decreasing distal arterial pressure and increasing cerebrospinal fluid (CSF) pressure, thereby worsening the spinal cord perfusion pressure (SCPP). Trimethaphan does not increase CSF pressure. Therefore, the present study investigates the effect of trimethaphan versus SNP to control proximal hypertension during TACC on neurologic outcome. Two groups, each with eight mongrel dogs, were studied. All animals underwent descending TACC for 45 min. The mean proximal aortic blood pressure was maintained at 95-100 mm Hg by the use of SNP or trimethaphan. Distal aortic pressure was allowed to vary. The dogs were neurologically evaluated 24 and 48 h later by a blinded observer. During cross-clamping, there was no difference in mean proximal aortic pressure between groups. After 10 min of cross-clamping, distal aortic pressure was higher (P < 0.01), CSF pressure was lower (P < 0.01), and SCPP was higher (P < 0.005) in the trimethaphan group as compared with the SNP group (group effect). Neurologic outcome as assessed by Tarlov's score was better at 24 and 48 h in the trimethaphan group (P < 0.05). Histopathologic injury trended with worsened neurologic outcome. We conclude that 1) trimethaphan produced higher SCPP than SNP, and 2) neurologic outcome was better in the trimethaphan group.

Effects of halothane and isoflurane on transient renal dysfunction associated with infrarenal aortic cross-clamping

Aortic cross-clamping for reconstructive aortic surgery is associated with impairment of renal function. Halothane or isoflurane was used to assess the influence of volatile anesthesia on renal hemodynamics during aortic surgery. Nineteen patients with normal preoperative creatinine clearances who were scheduled for reconstructive aortic surgery were randomly divided into two groups: halothane group (n = 9) and isoflurane group (n = 10). Induction of anesthesia consisted of midazolam, fentanyl, and pancuronium. Anesthesia was maintained with fentanyl and halothane or isoflurane in nitrous oxide and oxygen (50/50). Systemic hemodynamics were similar in both groups throughout surgery. Before aortic cross-clamping, effective renal plasma flow (ERPF) (131I-hippuran clearance) and glomerular filtration rate (GFR) (99Tc-DTPA clearance) were significantly lower in the halothane group (118.4 +/- 25.6 and 19.7 +/- 5.2 mL/min, respectively) than in the isoflurane group (253.4 +/- 51.5 and 44.9 +/- 8.4 mL/min) (P less than 0.05 for both). During cross-clamping, the renal variables were not markedly affected in either group and remained higher in the isoflurane-anesthetized patients (232.9 +/- 47.1 and 49.5 +/- 1.2 mL/min for ERPF and GFR, respectively) than in the halothane-anesthetized patients (132.4 +/- 31.6 and 14.8 +/- 3.7 mL/min, respectively) (P less than 0.05). After aortic unclamping, ERPF increased markedly in both groups (467.8 +/- 122 and 362.5 +/- 57.7 mL/min in the halothane and isoflurane groups, respectively), as did GFR (74.8 +/- 22 and 71.8 +/- 13.1 mL/min, respectively). These results suggest that anesthesia with halothane is associated with transient renal vasoconstriction during abdominal surgery. In contrast, aortic cross-clamping during isoflurane anesthesia was not associated with renal hemodynamic impairment.

Humoral factors and hemodynamics during cross-clamping of the thoracic aorta

The present study was designed to test the hypothesis that vasoactive compounds produced in the ischemic part of the body below an occluded aorta are responsible for the hemodynamic changes observed during cross-clamping of the thoracic aorta. The experiments were performed on 32 rabbits anesthetized with halothane that underwent experiments with cross-circulation; the blood from the inferior caval veins of rabbits A was pumped into the inferior caval veins of rabbits B. Simultaneously, exactly the same amount of blood was pumped from the jugular vein of rabbits B into the jugular vein of rabbits A. The aorta and inferior vena cava were exposed and then simultaneously cross-clamped directly below the diaphragm. The cross-clamping of the aorta and inferior vena cava in rabbits A was associated with a 29% to 44% increase in mean arterial pressure in rabbits B. The experiments support the hypothesis and suggest that endogenously produced humoral factors are responsible for at least one third to one half of the arterial hypertension that usually develops during aortic cross-clamping.

Cerebral haemodynamics during proximal aortic cross-clamping

This study was carried out to examine cerebral blood flow, including the microcirculation and intracranial pressure during cross-clamping (XC) of the thoracic aorta in pigs. Blood flow in the internal carotid artery was measured by electromagnetic flowmetry. Cerebral microcirculation was studied by the laser Doppler technique, and intracranial pressure measured by applying a fibre optic pressure monitoring catheter in the same craniotomy. Maximal and mean blood flow velocity of the middle cerebral artery was recorded using a transcranial Doppler and cardiac output measured by thermodilution. The thoracic aorta was cross-clamped distal to the left subclavian artery for 30 min. During aortic XC the internal carotid artery blood flow increased 191% (p less than 0.05). Simultaneously mean and maximal blood flow velocity of the middle cerebral artery both increased 125% (p less than 0.01). Intracranial pressure increased 163% (p less than 0.05), and there was an increase in cerebral flux of 23% (p less than 0.05). Within the first minutes following the release of XC, all values decreased to preocclusive values. In conclusion, we observed a significant increase in cerebral blood flow during XC of the thoracic aorta. This is in accordance with the finding of a simultaneous increase in cardiac output. These haemodynamic changes support the theory that an increased blood flow via the proximal feeding system to the anterior spinal artery might be important in avoiding neurological sequelae following proximal aortic XC.

Anaesthesia for abdominal aortic surgery--a review (Part II)

Patients presenting for abdominal aortic surgery have a high incidence of vascular disease elsewhere, manifested primarily by hypertension, coronary and cerebrovascular disease, as well as co-existing respiratory, renal and metabolic disorders. Routine clinical assessment, electrocardiogram, chest roentgenograms, resting and exercise radionuclide ventriculography and echocardiography, dipyrdiamole-thallium scanning are all designed to assess the functional status of the myocardium and to detect the presence of significant coronary artery disease. Patients with no abnormalities on physical examination, routine evaluation and no redistribution on dipyridamole-thallium scanning should proceed to surgery with the expectation of very low perioperative cardiac risk. Patients with evidence of coronary artery disease and significant redistribution on dipyridamole-thallium scan should undergo coronary angiography and possible myocardial revascularization before definitive aortic vascular surgery. For high cardiac risk patients with no bypassable lesions presenting for abdominal aortic aneurysm resection a conservative policy of serial three monthly ultrasound or CT assessment may be adopted, with selective resection for rapid aneurysm expansion or symptom development. A variety of extra-anatomical and angioplastic techniques is available for similar high cardiac risk patients with aortoiliac occlusive disease. The haemodynamic consequences of aortic cross-clamping, especially in aneurysm patients, include a significant reduction in stroke volume, cardiac index, and myocardial oxygen consumption with an increased systemic vascular resistance. Patients with coronary artery disease may respond to aortic cross-clamping by increasing pulmonary capillary wedge pressure and by demonstrating ECG evidence of myocardial ischaemia. Pulmonary artery catheterization is especially indicated in patients with a history of previous myocardial infarction, angina or signs of cardiac failure and in patients with evidence of diminished ejection fraction, abnormal ventricular wall motion or myocardial redistribution on preoperative scanning. The more widespread application of intraoperative transoesophageal two-dimensional echocardiography and radionuclide cardiography monitoring techniques into anaesthetic practice will enable measurement of left ventricular dimensions, myocardial performance and wall motion. Suggested guidelines for anaesthetic management are presented in Table VI. A combined opiate-oxygen-volatile anaesthetic agent technique will best ensure a hypodynamic circulation with preservation of myocardial oxygenation.(ABSTRACT TRUNCATED AT 400 WORDS)

Hemodynamic and hormonal changes in patients pretreated with captopril for surgery of the abdominal aorta

Cardiovascular and hormonal responses to aortic cross-clamping (ACC) and declamping (ADC) were studied in 20 patients undergoing reconstructive aortic surgery anesthetized with fentanyl and droperidol. Ten of the patients served as a control group, and 10 patients were treated with oral captopril (25 mg the day before operation and 25 mg one hour before anesthesia) to prevent intraoperative and postoperative hypertension. After the induction of anesthesia in the captopril group, hypotension was seen in four patients and bradycardia in three patients. In both groups, the most important changes in hemodynamics after the ACC were an increase in systemic vascular resistance and decreases in cardiac and stroke index. After the ADC, the cardiac index (CI) improved nearly to the level before the ACC. The urine output during anesthesia was 46 +/- 5 mL/h in the control group and 73 +/- 11 mL/h (P less than 0.05) in the captopril group. Postoperatively, patients in both groups were hypertensive and tachycardic. In the control group, plasma renin activity rose significantly during the ACC, indicating activation of the renin-angiotensin system (RAS). In both groups, significant increases in plasma vasopressin (PAVP), epinephrine, and norepinephrine were also observed before the ACC and during the postoperative period. The results suggest that oral captopril increases the risk of hypotension and bradycardia after induction of anesthesia, and does not prevent postoperative hypertension.