Clinical evaluation of intravenous nitroglycerin for neurosurgery

Controlled arterial hypotension during resection of cerebral arteriovenous malformations

Background

Resection of cerebral arteriovenous malformations (AVM) is technically demanding because of size, eloquent location or diffuse nidus. Controlled arterial hypotension (CAH) could facilitate haemostasis. We performed a study to characterize the duration and degree of CAH and to investigate its association with blood loss and outcome.

Methods

We retrospectively analysed intraoperative arterial blood pressure of 56 patients that underwent AVM-resection performed by the same neurosurgeon between 2003 and 2012. Degree of CAH, AVM size, grading and neurological outcome were studied. Patients were divided into two groups, depending on whether CAH was performed (hypotension group) or not (control group).

Results

The hypotension group consisted of 28 patients, which presented with riskier to treat AVMs and a higher Spetzler-Martin grading. CAH was achieved by application of urapidil, increasing anaesthetic depth or a combination thereof. Systolic and mean arterial blood pressure were lowered to 82 ± 7 and 57 ± 7 mmHg, respectively, for a median duration of 58 min [25% percentile: 26 min.; 75% percentile: 107 min]. In the hypotension group, duration of surgery (4.4 ± 1.3 h) was significantly (p <  0.001) longer, and median blood loss (500 ml) was significantly (p = 0.002) higher than in the control group (3.3 ± 0.9 h and 200 ml, respectively). No case fatalities occurred. CAH was associated with a higher amount of postoperative neurological deficits.

Conclusions

Whether CAH caused neurological deficits or prevented worse outcomes could be clarified by a prospective randomised study, which is regarded as ethically problematic in the context of bleeding. CAH should only be used after strict indication and should be applied as mild and short as possible.

Risks and benefits of deliberate hypotension in anaesthesia: a systematic review

This systematic review was performed to investigate and review the evidence on the risks and benefits of hypotensive anaesthesia in order to answer the following question: 'Should deliberate hypotension be used routinely during orthognathic surgery?' An electronic search on MEDLINE and the Cochrane Library database was carried out for all relevant articles using specific search keywords. All articles were classified by their levels of evidence. Studies with highest level of evidence and rated to have the lowest risk of bias were reviewed. Regarding the benefits of hypotensive anaesthesia, three studies reported significant decrease of blood loss in patients receiving hypotensive anaesthesia. Two studies reported a significant decrease in transfusion rate. Two studies demonstrated improved surgical field and significant reduction in operation time. In terms of risk, no significant changes in cerebral, cardiovascular, renal and hepatic functions in patients receiving hypotensive anaesthesia compared to control were reported. In conclusion, hypotensive anaesthesia appears to be effective in reducing blood loss. Serious consequences due to organ hypoperfusion are uncommon. Hypotensive anaesthesia can be justified as a routine procedure for orthognathic surgery especially bimaxillary osteotomy. Patient selection and appropriate monitoring are mandatory for this technique to be carried out safely.

In vitro effects of new generation fungal derived nitric oxide donors on rabbit basilar artery

The fungal derived nitric oxide donors, (E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409) and N-[(E)-4-ethyl-3-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl]-3-pyridinecarboxamide (FR144420), were evaluated for the treatment and prevention of cerebral vasospasm induced by subarachnoid hemorrhage (SAH) by an in vitro study using rabbit basilar artery. The tension-relaxation of a 3 mm-long artery segment was carried out in a micro-tissue organ bath with a real-time recorder to record the tension-relaxation curve. Steady contraction of the specimens was induced by KCI (n = 12) and oxyhemoglobin (oxyHb) (n = 12). Sodium nitroprusside was used for comparison. Each of the agents was added in ascending concentration. Relaxation caused by FK409 and FR144420 was significantly greater (p < 0.05) than that by sodium nitroprusside. Relaxation effects of FK409 and FR144420 on the KCl-induced steady contraction were better than those on the oxyHb-induced contraction. FK409 and FR144420 have potential uses for the treatment and prevention of SAH-induced cerebral vasospasm.

Treatment modalities for hypertensive patients with intracranial pathology: options and risks

OBJECTIVES

To review the cerebrovascular pathophysiology of hypertension, and the risks and benefits of antihypertensive therapies in the patient with intracranial ischemic or space-occupying pathology.

DATA SOURCES

Review of English language scientific and clinical literature, using MEDLINE search.

STUDY SELECTION

Pertinent literature is referenced, including clinical and laboratory investigations, to demonstrate principles of pathophysiology and controversies regarding the treatment of hypertension in patients with intracranial ischemic or space-occupying pathology.

DATA EXTRACTION

The literature was reviewed to summarize the pathophysiology, risks, and benefits of antihypertensive therapies in the patient with intracranial ischemic or space-occupying pathology. Treatment strategies were outlined with a particular emphasis on how antihypertensive agents may affect the brain.

DATA SYNTHESIS

Cerebral autoregulation typically occurs over a range of cerebral perfusion pressures between 50 and 150 mm Hg. Chronic hypertension results in adaptive changes that allow cerebral autoregulation to occur over a high range of pressures. Acute hypertension (rapid increase in perfusion pressure above the autoregulatory limit) may result in cerebral edema, persistent vasodilation, and brain injury. Treatment of a hypertensive emergency must be undertaken conservatively since the chronically hypertensive patient is at risk for ischemic brain injury when perfusion pressure is rapidly decreased beyond autoregulatory limits. In the patient with head injury or primary neurologic injury, acute antihypertensive intervention can result in further brain injury. Selection of appropriate antihypertensive therapy necessitates the careful consideration of agent-specific effects on cerebral blood flow, autoregulation, and intracranial pressure. For example, some vasodilators treat hypertension but also dilate the cerebral vasculature, and increase cerebral blood volume and intracranial pressure while decreasing cerebral perfusion pressure. Pharmacologic blockade of alpha 1- or beta 1-adrenergic receptors can reduce arterial blood pressure with little or no effect on intracranial pressure within the autoregulatory range. Like the direct peripheral vasodilators, calcium-channel antagonists are limited by cerebral vasodilation and increased intracranial pressure. Angiotensin converting enzyme inhibitors can also be used for mild to moderate hypertension but have the potential to further increase intracranial pressure in patients with intracranial hypertension. Barbiturates offer an alternative antihypertensive therapy since they decrease blood pressure as well as cerebral blood flow and oxygen metabolism.

CONCLUSIONS

The treatment of acute hypertension in the patient with intracranial ischemic or space-occupying pathology requires an understanding of the pathophysiology of hypertension and determinants of cerebral perfusion pressure. Individual agents should be selected based on their ability to promptly and reliably decrease blood pressure, while considering effects on cerebral blood flow and intracranial pressure.

Effects of intravenous nitroglycerin combined with dopamine on intracranial pressure and cerebral arteriovenous oxygen difference in patients with acute subarachnoid haemorrhage

The effects of intravenous nitroglycerin (NTG) combined with dopamine on intracranial pressure (ICP) and cerebral arteriovenous oxygen difference (AVDO2) were studied in 11 patients with acute subarachnoid haemorrhage (SAH). The study was performed on Days 1 to 3 of SAH after aneurysmal clipping. Treatment consisted of an intravenous drip infusion of NTG in increasing incremental doses of 0.5, 1.0, 1.5, 2.0, and 2.5 micrograms/kg/min at one-hour intervals. Dopamine (5 to 10 micrograms/kg/min) was also given concurrently to maintain systemic blood pressure. ICP values before NTG administration ranged from 7 to 24 mmHg (mean. 11.91 +/- 5.30 mmHg). ICP began to increase immediately after the administration of NTG 0.5 microgram/kg/min and peaked at 14.64 +/- 5.93 mmHg 10 minutes after onset of infusion. Thereafter, ICP gradually returned to pretreatment levels. Increasing the dose of NTG failed to induce further significant rises in ICP. Mean AVDO2 before NTG administration was 4.69 +/- 0.62 ml/dl. This parameter showed no significant change during NTG infusion, although cerebral perfusion pressure decreased to between 75% to 94% of the control value after NTG administration. These results indicate that continuous NTG infusion combined with dopamine does not have adverse effects on ICP (the ICP increase is minimal and transient) and may even have beneficial effects on CBF in patients with acute SAH.

Effects of hypotension on cutaneous and subcutaneous blood flow in anaesthetized humans

The aim of this study was to determine the effect of controlled hypotension on subcutaneous and cutaneous haemodynamics in humans. Moderate hypotension was achieved with nitroglycerin (NTG) and sodium nitroprusside (SNP) infusion during narconeuroleptanalgesia in seven patients. Subcutaneous and cutaneous blood flow were measured by a superficial and deep heat clearance (HC) technique. The mean arterial pressure (BPa) decreased by 23%-30% and heart rate (fc) increased but only during NTG infusion (+22%; P less than 0.02). Subcutaneous and cutaneous blood flows remained unchanged despite a significant decrease in calculated cutaneous resistance (NTG: -26%, P less than 0.01; SNP: -34%, P less than 0.02] and subcutaneous vascular resistance changed only with SNP (-31%, P less than 0.02). After hypotension was discontinued the subcutaneous blood flow decreased (-13%, P = 0.05), whereas subcutaneous vascular resistance returned to its control values. An inverse relationship was found between fc and BPa (NTG: r = -0.525, P less than 0.01; SNP: r = -0.622, P less than 0.01) as well as with subcutaneous blood flow (NTG: r = -0.653, P less than 0.001; SNP: r = -0.573, P less than 0.01). In addition, we found oscillatory changes in deep HC values which differed in magnitudes (NTG 0.22 (SEM 0.09) W.m-1.degree C-1 vs SNP 0.42 (SEM 0.1) W.m-1.degrees C-1, P less than 0.01) and frequencies (NTG 0.02 (SEM 0.006) Hz vs SNP 0.01 (SEM 0.002) Hz, P less than 0.01). Despite unchanged blood flow, the effects of controlled hypotension on cutaneous and subcutaneous haemodynamics were different depending on the type of drug. These differences may have been related to counterregulatory responses and/or to direct vascular effects.

Influence of controlled hypotension by adenosine triphosphate or nitroglycerin on the neuromuscular blocking effect of atracurium in dogs

The neuromuscular blocking effect of atracurium under the influence of controlled hypotension by adenosine triphosphate (ATP) or nitroglycerin (NTG) was studied in mongrel dogs under halothane anesthesia. Under hypotensive state (60 +/- 5 mmHg) elicited by ATP (0.5 mg/kg/min) or NTG (1 microgram/kg/min), the neuromuscular blockade produced by atracurium (30 micrograms/kg, i.v.) was significantly potentiated and prolonged. The maximal depression of twitch contraction of the gastrocnemius-soleus muscle increased from 10 +/- 3% to 36 +/- 10% (ATP group) and 56.0 +/- 2.4% (NTG group), while the duration of neuromuscular blockade was prolonged from 663 +/- 96 s to 1060 +/- 277 s (ATP group), and 1375 +/- 441 s (NTG group). The potentiation and prolongation of neuromuscular blockade by atracurium was still apparent upon reversal of the hypotensive effect of ATP, but not of NTG, by dopamine infusion. We suggest that ATP may prolong and augment the effect of atracurium by reducing the presynaptic release of acetylcholine at the neuromuscular junction.

Treatment of intraoperative hypertensive emergencies in patients with intracranial disease

In patients with neuropathologic processes leading to disturbed cerebrovascular autoregulation, sudden increases in arterial blood pressure may lead to a sudden elevation in cerebral blood flow and intracranial pressure. Therefore, sudden increases in arterial pressure should be assiduously avoided in the perioperative period. Hypertensive episodes may occur at any time during anesthesia, but are more likely to occur (1) during laryngoscopy and intubation, (2) at the time of skin incision, (3) at extubation, and (4) during awakening. In patients with cardiovascular disease, such hypertensive episodes may also cause deterioration of the cardiovascular situation. Catecholamines are the principal mediators of such intraoperative hypertensive reactions. There are 2 options available to the anesthesiologist: (1) attempt to suppress this response after it has occurred, or (2) prevent its occurrence at the outset. Treatment of hypertension often relies on agents that relax vascular smooth muscle. In patients with compromised intracranial compliance, however, cerebral vasodilation must be avoided because it leads to an increase in cerebral blood volume. This, in turn, may raise intracranial pressure and result either in herniation of brain contents or a decrease in cerebral perfusion pressure leading to brain ischemia. Different pharmacologic means of preventing or suppressing such intraoperative hypertensive reactions are reviewed. Many of the drugs reviewed resulted in adverse effects that could preclude their use in patients with reduced intracranial compliance. Alpha- and beta-adrenergic receptor blockers can safely be administered to such patients.

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.

Glyceryl trinitrate as a hypotensive agent in middle-ear surgery

A total of 47 patients having microsurgery of the middle-ear under general anaesthesia received an infusion of glyceryl trinitrate to produce controlled hypotension. The operating field was evaluated by the surgeon by means of a simple scoring system. Using this technique satisfactory conditions were achieved in all patients without complications.

Effects of hypotension induced by adenosine on brain surface oxygen pressure and cortical cerebral blood flow in the pig

Six pigs were anaesthetized with ketamine in combination with fentanyl and droperidol and paralysed with pancuronium. The pigs were tracheotomized and ventilated mechanically. Mean arterial blood pressure, MABP, was lowered from 97 +/- 21 mmHg stepwise to 58 +/- 2, 33 +/- 4 and 22 +/- 4 mmHg by intravenous infusion of adenosine (4-8 mg kg-1 min-1). Regional cerebral blood flow (rCBF) was measured directly onto the cortex of the brain by local atraumatic application of 133xenon. Brain surface oxygen pressure (PtO2) was obtained using a multiwire oxygen surface electrode. At the level of 60 mmHg, rCBF showed a significant increase, while flow values were not changed from initial values with further hypotension. Ten minutes after adenosine was discontinued, rCBF showed a rebound effect with higher values than initially. During normotension mean cortical PtO2 varied between 2.1 KPa and 3.9 kPa. During adenosine infusion PtO2 was increased at MABP-levels of 60 and 30 mmHg, while at 20 mmHg a decrease was seen in all animals. After discontinuation of the adenosine infusion, PtO2 values were higher than those measured at the initial normotension, a similar rebound phenomenon as seen with rCBF. During the experiments all hypotensive levels could be maintained at constant level without progressively increasing infusion rates, indicating no tachyphylaxis during these time periods. After discontinuation of the drug, blood pressure did not fully reach pre-hypotensive level within 10 min. Thus, hypotension induced by adenosine down to a MABP of 30 mmHg in animal experiments does not cause deterioration in either cerebral blood flow or oxygen pressure.

Crossover from intravenous to transdermal nitroglycerin therapy in unstable angina pectoris

The present study was designed to examine the safety and efficacy of titrating a nitroglycerin infusion to a fixed hemodynamic endpoint as initial therapy for patients admitted to a coronary care unit for medically refractory unstable angina, and to test the hypothesis that patients, responding to the addition of intravenous (i.v.) nitroglycerin to their previous antianginal regimen, could be crossed over to nitroglycerin administered by a new transdermal delivery system. In 9 patients the nitroglycerin infusion titrated upward at 3- to 10-minute intervals until a 10% reduction in mean arterial pressure was achieved. This titration schedule and hemodynamic endpoint proved safe and effective for controlling episodes of chest pain at rest in all 9 patients. Subsequently, this treatment strategy was tested in 17 consecutive patients with unstable angina treated in our coronary care unit during a 1-month period. In 10 of 15 successfully treated patients ischemia was the cause of chest pain as documented by cardiac catheterization. No change was made in antianginal or vasoactive drugs during the period of i.v. nitroglycerin administration or during crossover to transdermal therapy. In this well defined subgroup of patients with unstable angina, nitroglycerin infusion decreased the mean arterial pressure from 101 +/- 18 to 87 +/- 11 mm Hg (mean +/- standard deviation), using an infusion rate of 84 +/- 74 micrograms/min (range 10 to 200). The mean duration of i.v. therapy was 36 +/- 12 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic management of acute intracranial hypertension

Acute intracranial hypertension requires aggressive treatment with physiologic and pharmacologic measures guided by intracranial pressure monitoring devices. Therapy involves the use of diuretics, corticosteroids, and barbiturates in combination with hyperventilation, ventricular drainage, and general supportive measures. This review focuses on the pathophysiology of increased intracranial pressure and the pharmacologic agents used in its management.

Intravenous glyceryl trinitrate (nitroglycerin). A review of its pharmacological properties and therapeutic efficacy

The recently introduced preparation of intravenous glyceryl trinitrate (nitroglycerin) provides a rapid steady therapeutic blood concentration of nitrates during continuous infusion. Intravenous glyceryl trinitrate causes venodilation at low doses, but at higher doses dilates both arteries and veins. Its principal haemodynamic effects at therapeutic dosages include a decrease in blood pressure in preload (left ventricular filling pressure) and in determinants of afterload, and a decrease in myocardial oxygen demand. Human pharmacokinetic data are few and difficult to interpret due to wide interstudy and interindividual variation. There is no close correlation between infusion rate, blood concentration and haemodynamic effects. The nature of the patient population treated with intravenous glyceryl trinitrate has largely precluded the use of a placebo, but in open trials the drug has been used successfully in the treatment of unstable angina, left ventricular failure accompanying acute myocardial infarction and in the control of hypertension associated with cardiac surgery at dosages titrated to achieve a specific end-point. Favourable haemodynamic responses have been achieved in very short term studies in congestive heart failure, and preliminary studies suggest that institution of intravenous glyceryl trinitrate early after acute myocardial infarction may limit ischaemic damage. However, use of the drug in acute myocardial infarction remains controversial. Intravenous glyceryl trinitrate is generally well tolerated, although hypotension and headache occur occasionally, and sinus tachycardia and bradycardia less frequently. Careful titration of dosage is required (beginning at 5 micrograms/min), and if the infusion sets contain polyvinylchloride, the delivered dose is lower than that calculated, because of adsorption of glyceryl trinitrate onto the plastic tubing.

Toxicology studies with a stable intravenous formulation of nitroglycerin

The preclinical toxicologic profile of Nitrostat, a stable parenteral formulation of nitroglycerin, was determined in mice, rats, rabbits and dogs. Single-dose i.v. studies in rodents yielded LD50 values of 17.3 and 18.2 mg kg-1 in male and female mice, and 24.4 and 23.2 mg kg-1 in male and female rats, respectively. Subacute i.v. studies in rats at doses of 2.5, 5.0 and 10.0 mg per kg per day, and in dogs at doses 1.0 and 3.0 mg per kg per day for two weeks, elicited minimal reactions. In rats, suppression of body-weight gain and food consumption occurred among treated and vehicle-control animals. Mild tissue irritation at injection sites was noted in treated and vehicle-control groups. There were no clearly drug-related clinical or pathological findings in dogs. In rabbits, repeated intravenous administration of Nitrostat did not induce significant local venous irritation. The results of these studies indicated that the stabilized parenteral formulation of nitroglycerin did not elicit unusual toxic properties in intravenous infusion studies.

Effects of intravenous nitroglycerin on the intracranial pressure and volume pressure response

Ventricular fluid pressure (VFP) and volume-pressure response were measured during nitroglycerin (NTG) infusion in nine patients anesthetized with N2O and fentanyl. The patients' ventilation was controlled, and PaCO2 was kept at 32 +/- 4 mm Hg. When an infusion of 0.01% NTG was given intravenously to decrease the mean blood pressure to 95.1%, 84.7%, and 78.2% of control, the VFP increased from control levels of 9.94 +/- 2.14 mm Hg to 12.89 +/- 2.25, 15.6 +/- 2.85, and 14.43 +/- 3.45 mm Hg, respectively. The volume-pressure response showed a significant increase when blood pressure decreased to 84.7% and 78.2% of control. These results suggest that intravenous NTG caused an increase in the intracranial pressure and a decrease in the intracranial compliance.

A profile of intravenous nitroglycerin use in cardiopulmonary bypass surgery

We studied the indications for use, time to onset of effect, approximate effective concentration and therapeutic success of commercially prepared intravenous nitroglycerin (NTG) in 50 patients undergoing cardiopulmonary bypass (CPB) surgery. Nitroglycerin was used to treat systemic or pulmonary hypertension, myocardial ischaemia and ventricular failure. Twenty-one patients had more than one indication for NTG use. Nineteen of 22 patients with pulmonary hypertension, 12 of 13 patients with ischaemic changes, and 13 of 15 patients with ventricular failure improved during intravenous NTG administration. Hypertension during CPB was ameliorated in only six of ten instances. The time to onset of effect ranged from 4.1 +/- 0.8 to 7.8 +/- 2.8 minutes and the mean approximate effective NTG concentration varied from 1.7 +/- 0.3 to 2.9 +/- 0.7 micrograms . kg-1.min-1 (doses only approximate due to our use of an infusion system which absorbs NTG). Complications from intravenous NTG administration were not seen. We conclude that this NTG preparation facilitates treatment of prebypass hypertension, pulmonary hypertension, myocardial ischaemia and ventricular failure but is less effective for the treatment of hypertension during CPB.

Cerebral and systemic circulatory effects of arterial hypotension induced by adenosine

In six dogs anesthetized with halothane and nitrous oxide, mean arterial pressure (MAP) was lowered to 40 mm Hg for an average of 90 minutes by intravenous infusion of adenosine. The hypotensive effect of the adenosine was potentiated by administering dipyridamole to block its intravascular inactivation. Blood flow to the brain, spinal cord, heart, kidneys, and skeletal muscle was measured six times in each animal using the radioactive microsphere technique. Determinations were made before, during, and 30 minutes after the hypotensive period. During the hypotensive period, MAP was decreased 61% and was related to a proportional decrease in peripheral vascular resistance. Cardiac index decreased 14%. Total cerebral blood flow (CBF) decreased an average of 28% and cerebral vascular resistance decreased 53%. The reduction in CBF was heterogeneous; the cerebral cortex and corpus callosum were most affected and the brain stem least affected. No change occurred in the cerebral metabolic rate of oxygen usage (CMRO2). Left ventricle flow increased 147% and right ventricle flow increased 271%. Blood flow to the kidneys decreased 70%, and to the liver decreased to 6% of control. Jejunum blood flow increased 138% during recovery, while stomach flow varied but showed no statistical change. There was no tachyphylaxis, rebound hypertension, or toxicity associated with the adenosine-induced hypotension. These properties suggest that adenosine may be a useful agent for inducing arterial hypotension in neurosurgical patients.

Pharmacologically induced profound arterial hypotension in the anesthetized dog

✓ The purpose of this study was to compare the behavioral, hematological, and biochemical effects of profound arterial hypotension induced by adenosine potentiated with dipyridamole with those of hypotension induced by trimethaphan camsylate or sodium nitroprusside. Twenty dogs were anesthetized with halothane and nitrous oxide, paralyzed with pancuronium, and ventilated to an arterial pCO2 of 40 torr. Arterial pressure and heart rate were monitored continuously. The animals were divided into four groups of five dogs each. The first group served as controls, while in the remaining groups the mean arterial pressure (MAP) was lowered to 40 mm Hg with adenosine/dipyridamole, trimethaphan, or nitroprusside for 1 hour, following which the animals were allowed to recover from the anesthetic and observed for 48 hours. Determinations of arterial blood gases and hematological and biochemical parameters were made immediately prior to and at the completion of the 1-hour hypotensive period and 48 hours later.

Reduction of MAP to 40 mm Hg was readily achieved with adenosine/dipyridamole. There was no tachyphylaxis to this drug, and arterial pressure promptly returned toward control levels without overshoot after the infusion was discontinued. In contrast, hypotension of this degree could be produced only with toxic doses of nitroprusside. Trimethaphan was more effective in producing hypotension than nitroprusside, but the dose required was extremely variable, and prolonged intervals were required for pressure to return toward normal after the agent was stopped. The control animals and those that received adenosine/dipyridamole recovered promptly from the anesthetic and were neurologically intact. The animals that received trimethaphan recovered more slowly but were neurologically normal within 12 hours. All of the animals that received nitroprusside died without recovering from the anesthesia. Aside from a mild transient metabolic acidosis and transient elevation of blood urea nitrogen and creatinine in the dogs that received adenosine/dipyridamole or trimethaphan, no specific cardiovascular, hematological, hepatic, or renal toxic effects were noted. Evidence of fatal cyanide toxicity was present in the nitroprusside group.

These data suggest that hypotension using adenosine/dipyridamole is readily induced, maintained, and reversed, and is not associated with any apparent hematological, or biochemical evidence of toxicity. Further studies leading to a clinical trial of adenosine-induced hypotension appear to be indicated.

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.

The use of intravenous nitroglycerin in cardiovascular disease

The development of an intravenous form of nitroglycerin has further enhanced the role of nitrates in the therapy of cardiovascular disorders. This new preparation permits prompt initiation of therapy and rapid attainment of high systemic levels; because of its short half-life, rapid dose titration is both feasible and safe. The antianginal effects of intravenous nitroglycerin are useful in the treatment of coronary vasospasm and unstable angina pectoris. Its hemodynamic effects are of benefit in the therapy of congestive heart failure and in the control of peri-operative hypertension. Recent data suggest that, with appropriate monitoring, intravenous nitroglycerin can be safely administered to patients with evolving myocardial infarction to reduce the extent of myocardial damage.

The effects of molsidomine on intracranial pressure in anaesthetized dogs

Measurements of intracranial liquor pressure were made during i.v. molsidomine administration in pentobarbital anaesthetized beagle dogs without thoracotomy, and compared with those after nitroglycerin. The administration of 100 micrograms/kg molsidomine decreased blood pressure by 14 mmHg and increased intracranial pressure by 3.7 cm H2O (P less than 0.05). No changes in heart rate and the alveolar end-tidal CO2 concentration were noted. The i.v. administration of 5 micrograms/kg nitroglycerin, however, decreased systolic blood pressure by 41 mmHg (p less than 0.05), increased heart rate by 40 bpm (p less than 0.01), elevated intracranial pressure by 3.2 cm H2O (p less than 0.05), and caused marked hyperventilation indicated by increased end-tidal CO2 concentration. Larger increases in intracranial pressure were related to larger pressure reductions. Thus, molsidomine produced significant increase in intracranial liquor pressure of longer duration (60 to 90 min of observation time). Nitroglycerin increased liquor pressure with a short duration of action and was about twenty time more effective with respect to intracranial pressure increase. In contrast to molsidomine, this was accompanied by significant decrease in systolic peripheral blood pressure.

Intravenous nitroglycerin perfusion techniques--clinical implications

Two types of intravenous nitroglycerin (NTG) perfusion sets were studied using laboratory techniques. A known concentration of NTG was placed in each of these sets, and an evaluation was made as to the dose of NTG actually received by the patient after passage of the NTG solution through the sets. Set number one consisted of a glass container and polyvinyl chloride (PVC) tubing. After passage through this set, there was a rapid and significant decrease in the NTG concentration, i.e. the dose actually received by the patient is less than the dose theoretically administered. Set number two consisted of a polypropylene syringe and polyethylene tubing. After passage through this set, there was no significant change in the NTG concentration, i.e. the patient receives the full theoretical dose.

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.

Plasma levels and cardiovascular effect of nitroglycerin in pregnant sheep

The cardiovascular effects and blood levels of intravenous nitroglycerin in mother and foetus were studied in normotensive and hypertensive ewes. Although nitroglycerin produced a reduction in uterine blood flow following a decrease in blood pressure, there was little if any incidence of adverse effects in the foetus. Nitroglycerin was detected in all but two samples of foetal arterial blood but the foetal/maternal artery ratio was only 0.04. Nitroglycerin merits further evaluation for the treatment of acute hypertensive episodes in the preeclamptic patient.

Intracranial pressure during nitroglycerin-induced hypotension

Nitroglycerin was given intravenously to five anesthetized, hyperventilated (PaCO2 25 to 30 torr) patients during craniotomy, to facilitate surgery by creating a relatively bloodless field, and to decrease the potential need to blood transfusion. A subarachnoid screw and an indwelling radial artery catheter were inserted to monitor intracranial pressure (ICP) and mean arterial pressure (MAP). As MAP decreased from 10.4 +/- 4.0 (SE) to 69.0 +/- 1.8 torr, ICP increased from 14.2 +/- 0.7 (SEM) to 30.8 +/- 1.1 torr. Cerebral perfusion pressure decreased from 90.2 +/- 3.6 (SEM) to 38.2 +/- 2.3 torr (p < 0.0005). We attribute this nitroglycerin-induced ICP increase to capacitance vessel dilation within the relatively noncompliant cranial cavity, with subsequent cerebral blood volume increase.