Changes in hemodynamic parameters, inotropic state, and myocardial oxygen consumption owing to intravenous application of nitroglycerin

Nitroglycerin-induced hypoxemia does not produce myocardial ischemia

OBJECTIVE

Nitroglycerin has been the drug of choice for relieving myocardial ischemia for more than a hundred years. Several studies have indicated that a significant reduction in arterial oxygen tension (PaO2) occurs after the administration of sublingual nitroglycerin to patients with coronary artery disease breathing room air. Because available oxygen in arterial blood is reduced, it would be reasonable to assume that oxygen delivery to the myocardium would also be impaired. The purpose of this study was to investigate whether nitroglycerin-induced arterial desaturation results in compromised oxidative metabolism of myocardium assessed by coronary sinus lactate concentration and oxygen content in patients with coronary artery disease undergoing coronary artery bypass surgery.

PARTICIPANTS

Ten randomly selected patients undergoing coronary bypass surgery.

SETTING

All studies were performed at Siyami Ersek Cardiovascular and Thoracic Surgery Center.

METHODS

A catheter was inserted into the radial artery to measure blood gases and arterial lactate concentration. After sternotomy, and aortic and venous cannula placement, a coronary sinus catheter was introduced into the coronary sinus to measure oxygen content and lactate concentration. Control coronary sinus and arterial blood samples were obtained before nitroglycerin infusion. Nitroglycerin was then given in a dose of 2 micrograms/kg/min for a period of 5 minutes. At the end of 5 minutes, second samples were obtained from the coronary sinus and arterial catheters.

MAIN RESULTS

It was found that arterial and coronary sinus oxygen tension decreased significantly. Arterial lactate concentration did not change, coronary sinus lactate concentration decreased. Despite a substantial fall in arterial oxygen tension after administration of nitroglycerin, a significant reduction in coronary sinus lactate concentration occurred.

CONCLUSION

Nitroglycerin-induced hypoxia does not compromise oxidative metabolism of myocardium as can be assessed by a concomitant decrease in coronary sinus lactate concentration.

Automated infusion of nitroglycerin to control arterial hypertension during cardiac surgery

OBJECTIVE

To evaluate the feasibility of closed-loop blood pressure control during cardiac surgery.

DESIGN

A closed-loop system regulated peroperative hypertension by controlling the infusion rate of the vasodilator nitroglycerin (NTG). The controller consisted of a regulator which was monitored by a supervisory computer program. Mean arterial pressure (MAP) was calculated every 5 s from measurements of the radial artery pressure signal. The regulator calculated an NTG infusion rate with each new MAP measurement. The supervisory computer program monitored the regulator's actions and adapted or overruled the regulator when required.

SETTING

The cardiac surgery operating room.

PATIENTS

46 patients who were scheduled for cardiac surgery and who developed peroperative hypertension.

INTERVENTIONS

Patients were scheduled for either bypass or valve replacement surgery. The closed-loop system was used to control hypertension before and after cardiopulmonary bypass. The use of the closed-loop system did not require deviation from the protocol normally used during cardiac surgery. All patients received standard continuous anaesthesia with opioids.

MEASUREMENTS AND RESULTS

Initial automatic control was achieved in 9.4 (4.1 SD) min. The percentage of time that MAP remained in a range around the target MAP of +/- 10 and +/- 20 mmHg was 74 and 94%, respectively. The mean NTG infusion rate while MAP was within 5 mmHg of target MAP was 1.14 (0.84 SD) micrograms kg-1 min-1. Target MAP was set between 65 and 90 mmHg. There was a small group of patients (6 out of 46) who did not respond to NTG and required alternative drug therapy.

CONCLUSIONS

The controller provided fast and stable control in all patients. The expert knowledge implemented through the supervisory computer program enabled the controller to respond adequately to the rapid changes in arterial pressures commonly associated with cardiac surgery. We conclude that closed-loop control of arterial pressure is feasible not only in the cardiac surgical care unit but also during cardiac surgery.

Vasodilator properties of atrial natriuretic factor: a comparison with nitroglycerin, nitroprusside, and phentolamine during cardiopulmonary bypass

Thirty-five patients scheduled for coronary artery surgery were studied during hypothermic cardiopulmonary bypass (CPB) to compare the arteriolar and venodilator properties of a bolus dose of atrial natriuretic factor (ANF), 100 micrograms, with those of nitroglycerin, 200 micrograms, sodium nitroprusside, 120 micrograms, phentolamine, 3 mg, and placebo. A decrease observed in mean arterial pressure was used as an indicator of a decrease in systemic vascular resistance (arteriolar dilation), while a decrease in reservoir blood volume of the CPB circuit was considered to indicate an increase in venous capacitance (venodilation). All vasodilators decreased mean arterial pressure, and there was no difference in the maximal decrease of the pressure between the drugs. However, the decrease caused by ANF appeared later than that caused by the other vasodilators and lasted longer than with nitroglycerin and sodium nitroprusside. Nitroglycerin and sodium nitroprusside decreased reservoir blood volume, while ANF and phentolamine had no effect. It is concluded that ANF is an arteriolar dilator with a time profile of its effect differing from those of nitroglycerin, sodium nitroprusside, and phentolamine. ANF seems to have no venodilator activity in patients undergoing hypothermic CPB.

Hemodynamic effects of SIN-1 in acute left heart failure

To assess the hemodynamic effects of SIN-1, the active metabolite of the venodilator molsidomine, after acute as well as chronic intravenous administration, ten patients with exacerbation of chronic heart failure were studied. After a mean bolus dose of 2 mg of SIN-1, mean right atrial pressure (MRAP), mean pulmonary artery pressure (MPAP), and pulmonary capillary wedge pressure (PCAP) decreased significantly up to the 60th minute; pulmonary vascular resistance (PVR) decreased significantly up to the 30th minute, while cardiac index (CI) and systemic vascular resistance (SVR) remained unchanged. During a 24-hour continuous infusion of SIN-1, MRAP, MPAP, and PCAP decreased significantly, while CI, PVR, and SVR remained largely unaltered. No dose adjustment was required to maintain the hemodynamic effects over 24 hours. The absence of noteworthy side effects and tolerance during this prolonged administration indicate that SIN-1 is a potentially useful drug in the management of patients admitted with exacerbation of heart failure.

Comparison of intravenous nitroprusside, nitroprusside-captopril, and nitroglycerin for deliberate hypotension during posterior spine fusion in adults

Three techniques for deliberate hypotension (mean arterial pressure, 60 to 70 mmHg) were prospectively compared in adults undergoing posterior spine fusion. Patients received either IV sodium nitroprusside, sodium nitroprusside with oral captopril pretreatment, or IV nitroglycerin. Patient groups were comparable in age, sex, weight, baseline hemodynamic and laboratory parameters, duration of surgery, and duration of hypotension. Absolute blood loss was significantly less in the group receiving nitroglycerin; however, there were no differences between groups when corrected for operative exposure (milliliter per spine segment exposed). Nitroprusside was effective in producing target blood pressure in all patients. Nitroglycerin was ineffective in two patients and two other patients required greater than 20 micrograms/kg/min. Both groups receiving nitroprusside developed significant postinfusion increases in arterial pressure. Blood pressure fell significantly after induction of anesthesia in patients receiving captopril. Cardiac index, heart rate, pulmonary capillary wedge pressure, intrapulmonary shunt, and arterial blood gases were comparable and did not change significantly in any group. Systemic vascular resistance fell during infusion in all groups and remained depressed after infusion in patients receiving nitroglycerin. Plasma renin activity was significantly increased in the group receiving captopril due to loss of feedback inhibition of renin release and rose significantly during infusion in those patients receiving nitroprusside alone. There were no complications. Nitroprusside with and without captopril pretreatment was associated with postoperative increases in arterial pressure, although not to hypertensive levels, probably due to loss of captopril activity after single-dose administration. The use of nitroglycerin was limited by lack of potency. There was no demonstrable clinical advantage for any of the three techniques.

Myocardial and systemic effects of nitroglycerin, given awake and during anaesthesia in coronary patients

The haemodynamic and myocardial energy-metabolic effects of intravenous nitroglycerin (NTG) were investigated in seven male patients about to undergo coronary artery bypass grafting. Effects of one mg of NTG given at a rate of 100 micrograms . min-1 to sedated, awake hypertensive patients, were compared to effects of the same dose of NTG in the same patients, after sternotomy. Coronary sinus flow was measured by a thermodilution catheter and myocardial oxygen consumption (MVO2) was calculated using the arterio-coronary sinus difference of oxygen content. With the patients awake, cardiac index and stroke volume and work indices fell during NTG administration. There was only a small fall in arterial pressure as heart rate and systemic resistance increased. Pulmonary capillary wedge pressure decreased but not MVO2. With NTG administration during anaesthesia, arterial pressure fell significantly to normal, as systemic resistance decreased, without a change in heart rate or cardiac index. Calculated MVO2 decreased as the arterial-coronary venous difference of oxygen content increased. Both oxygen and lactate balance of the myocardium were maintained. NTG given during anaesthesia was more effective in reducing blood pressure and MVO2 than when given to awake patients.

Cardiovascular effects of nitroglycerin as a hypotensive agent in cerebral aneurysm surgery

The cardiovascular effects of nitroglycerin (TNG) were studied in 20 patients undergoing cerebral aneurysm clipping under controlled hypotension. Total oxygen consumption was also calculated in 15 patients. Mean arterial blood pressure was reduced by 36% from 91 to 58 mmHg (12.1 to 7.7 kPa) by TNG due to decrease in both total peripheral resistance (16%) and cardiac output (24%). Right atrial and pulmonary capillary wedge pressures were reduced during hypotension, indicating a decrease in venous return to the heart. There were no significant changes in total oxygen consumption. It is concluded that the fall in cardiac output results from a reduction in central blood volume due to venous pooling of blood, and that TNG has no major overall metabolic effects.

Intravenous nitroglycerin during surgery for coronary artery disease

Intravenous infusions of nitroglycerin decreased systemic systolic, pulmonary systolic and wedge pressures in β-blocked patients anaesthetised for coronary artery surgery with high dose of fentanyl without changing heart rate, diastolic pressure, or cardiac index, thus leading to an improvement in endocardial viability ratio.

The use of a nitroglycerin bolus to abort an acute myocardial ischaemic episode is described.

Nifedipine blockade of ergonovine-induced coronary arterial spasm: angiographic documentation

To determine whether calcium-flux blockade with nifedipine blunts coronary vasospasm, four patients with angiographically demonstrable coronary arterial spasm in the absence of significant fixed coronary arterial stenosis were evaluated with coronary arteriography before and after treatment with nifedipine. After initial coronary arteriography, ergonovine was administered in successive doses of 0.05, 0.1 and (when necessary) 0.2 mg intravenously at 3 minute intervals. Three patients had symptomatic high grade focal coronary arterial spasm with electrocardiographic changes, and the fourth exhibited asymptomatic 60 percent constriction of the left anterior descending coronary artery. A maximal ergonovine challenge was repeated 30 minutes later after each patient had been pretreated with a 20 mg sublingual dose of nifedipine. Under these conditions, no patient had chest pain or electrocardiographic changes. Furthermore, neither focal nor diffuse coronary arterial spasm was demonstrable angiographically after the second challenge. Thus, in each case, a single dose of nifedipine precluded the angiographic expression of ergonovine-provoked coronary arterial spasm.

Effect of FR 7534, a new calcium antagonist, on myocardial oxygen demand

The actions of FR 7534, a new calcium antagonist, nitroglycerin, and dipyridamole on myocardial oxygen demand have been compared. Six anaesthetized dogs received two infusion levels of each drug which produced equivalent arterial hypotension. All three compounds reduced the tension-time index (TTI). FR 7534 and nitroglycerin but not dipyridamole produced significant decreases in myocardial oxygen consumption (MVO2). FR 7534 demonstrated oxygen-sparing actions comparable to nitroglycerin. FR 7534 may prove beneficial in alleviating myocardial ischemia.