Nitroprusside, Nitroglycerin, and Angiotensin-Converting Enzyme Inhibitors

Management of perioperative hypertensive urgencies with parenteral medications

BACKGROUND

Hypertension is the major risk factor for cardiovascular (CV) disease such as myocardial infarction (MI) and stroke. This risk is well known to extend into the perioperative period. Although most perioperative hypertension can be managed with the patient's outpatient regimen, there are situations in which oral medications cannot be administered and parenteral medications become necessary. They include postoperative nil per os status, severe pancreatitis, and mechanical ventilation. This article reviews the management of perioperative hypertensive urgency with parenteral medications.

METHODS

A PubMed search was conducted by cross-referencing the terms "perioperative hypertension," "hypertensive urgency," "hypertensive emergency," "parenteral anti-hypertensive," and "medication." The search was limited to English-language articles published between 1970 and 2008. Subsequent PubMed searches were performed to clarify data from the initial search.

RESULTS

As patients with hypertensive urgency are not at great risk for target-organ damage (TOD), continuous infusions that require intensive care unit (ICU) monitoring and intraarterial catheters seem to be unnecessary and a possible misuse of resources.

CONCLUSIONS

When oral therapy cannot be administered, patients with hypertensive urgency can have their blood pressure (BP) reduced with hydralazine, enalaprilat, metoprolol, or labetalol. Due to the scarcity of comparative trials looking at clinically significant outcomes, the medication should be chosen based on comorbidity, efficacy, toxicity, and cost.

Effect of intravenous nitroglycerin on cerebral saturation in high-risk cardiac surgery

PURPOSE

To determine whether or not intravenous nitroglycerin (IV NTG) can prevent a decrease in near-infrared spectroscopy (NIRS) values during cardiopulmonary bypass (CPB).

METHODS

We conducted a randomized double-blinded study in a tertiary academic center including 30 patients with a Parsonnet score>or=15 scheduled for a high-risk cardiac surgery. The patients were randomized to receive either IV NTG (initial dose of 0.05 microg.kg(-1).min(-1), followed by 0.1 microg.kg(-1).min(-1)) or placebo after anesthetic induction until the end of CPB. The primary outcome was a decrease of 10% in NIRS values during CPB.

RESULTS

Despite the absence of between-group difference in the mean cerebral oxygen saturation during CPB, there was a significant decrease in NIRS values during CPB in the placebo group, whereas mean NIRS values were maintained in the IV NTG group (-16.7% vs 2.3% in the NTG, P=0.019). Major hemodynamic variables were similar at corresponding time periods in both groups, while patients in the IV NTG group had higher CK-MB values and experienced greater blood loss during the first 24 hr postoperatively.

CONCLUSION

Intravenous nitroglycerin administration before and during CPB may prevent a decrease in NIRS values associated with CPB in high-risk cardiac surgery. Further studies are warranted to determine the efficacy and the risks associated with IV NTG infusion for this indication during CPB in high-risk patients.

Elevated carboxyhemoglobin associated with sodium nitroprusside treatment

OBJECTIVE

To report four cases of carboxyhemoglobinemia associated with high doses of sodium nitroprusside after cardiac transplant in children.

PATIENTS

Four children in the pediatric care unit of a university hospital aged 6 months-4 years. Carboxyhemoglonemia developed at levels of 5.5-7.7% in patients receiving high doses of sodium nitroprusside (7-16 microg/kg per minute and no other medication that could caused elevated carboxyhemoglobin). One patient died, and three recovered with no sequelae after discontinuation of sodium nitroprusside.

CONCLUSIONS

High doses of sodium nitroprusside can induce carboxyhemoglobinemia in children after heart transplant, probably by inducing hemeoxygenase, with no other secondary effects.

Cyanide poisoning and its treatment

Cyanide is both widely available and easily accessible throughout the world. Although the compound is not frequently encountered, it has been used as a poison and contaminant in the past and is a potential terrorist agent. Cyanide has the ability to cause significant social disruption and demands special attention to public health preparedness. It can be obtained from a variety of sources, including industrial, medical, and even common household products. Another frequently encountered source of cyanide exposure is residential fires. Exposure to high concentrations of the chemical can result in death within seconds to minutes. Long-term effects from cyanide exposure can cause significant morbidity. The only treatment for cyanide toxicity approved for use in the United States is a kit consisting of amyl nitrite, sodium nitrite, and sodium thiosulfate. Future research aims to find a faster-acting, more effective, and better tolerated treatment for cyanide toxicity.

Methemoglobinemia: an unusual cause of postoperative cyanosis

Methemoglobinemia, although rare, must be considered in surgical patients presenting with acute respiratory distress and cyanosis. We report two cases of methemoglobinemia in patients undergoing aortic reconstruction. The first patient developed methemoglobinemia while on a nitroglycerin infusion, and the second after receiving benzocaine spray before intubation. Both patients were treated with methylene blue and ascorbic acid, with resolution of their hypoxia and cyanosis. The pathophysiology, etiology, diagnosis, and treatment of methemoglobinemia are reviewed.

Cardiopulmonary effects of nebulized sodium nitroprusside in term infants with hypoxic respiratory failure

OBJECTIVE

To study whether nebulized nitroprusside (neb-NP) improves oxygenation in term infants with hypoxic respiratory failure (HRF).

STUDY DESIGN

We studied 22 newborn term infants (gestational age, 39.7+/-0.4 weeks [mean+/-SEM]; birth weight, 3.6+/-0.1 kg) with hypoxia (Pao2<100 mm Hg) during mechanical ventilation (Fio2=1.0). Sodium nitroprusside (5 mg followed by 25 mg) was nebulized into the inspiratory arm of the ventilator circuit. Vital signs and arterial blood gas values were recorded after 20 minutes at each dose and before and after initiation of inhaled nitric oxide (iNO).

RESULTS

Pao2 increased significantly with 5 mg neb-NP (from 64.6+/-5.6 to 90.1+/-15.3 mm Hg, P=.04) and with 25 mg neb-NP (113.2+/-20.4 mm Hg, P=.009). Differences between mean Pao2 at 5 mg versus 25 mg neb-NP were also statistically significant (P=.03). When comparing the effect of neb-NP to iNO, the treatment-induced increases in Pao2 were similar (52.1+/-18.7 vs 62.2+/-18.2 mm Hg, respectively, P=not significant).

CONCLUSIONS

Neb-NP causes a dose-dependent increase in oxygenation in term infants with HRF, similar in magnitude to iNO* Neb-NP may be beneficial in infants with HRF when iNO is not readily available.

The effect of acute hypoxemia and hypotension on adenosine-mediated depression of evoked hippocampal synaptic transmission

The present study was designed to investigate the relative contributions of arterial P(O(2)), local cerebral blood flow, and oxygen delivery to the adenosine A(1) receptor-mediated depression of evoked synaptic transmission recorded in the rat hippocampus. Urethane-anesthetized rats were given a unilateral common carotid artery occlusion and then placed in a stereotaxic apparatus for stimulation and recording of bilateral hippocampal field excitatory postsynaptic potentials (fEPSPs). Arterial blood gases, mean arterial blood pressure (MAP), and bilateral hippocampal blood flow (HBF) were also measured. Arterial P(O(2)), HBF, and oxygen delivery were manipulated using normoxic hypotension, hypoxic hypotension, and hypoxic normotension. Both hypoxic hypotension and normoxic hypotension resulted in decreased HBF, decreased oxygen delivery, and a depression of the evoked fEPSP limited to the hippocampus ipsilateral to the occlusion. The enhanced HBF and oxygen delivery associated with increased MAP resulted in a restoration and maintenance of hippocampal fEPSPs despite sustained hypoxemia. The adenosine A(1) receptor-mediated depression of the fEPSP was more strongly correlated with changes in HBF and oxygen delivery than with arterial P(O(2)). We propose that adenosine plays an important role mediating the depression of neuronal activity associated with reduced oxygen delivery characteristically observed in ischemic brain tissue.

Intravenous nicardipine for treatment of severe hypertension in children

OBJECTIVE

To examine the effect of intravenous nicardipine in the treatment of children with severe hypertension.

METHODS

The medical records of 29 children (mean age 94 months) treated with intravenous nicardipine were retrospectively reviewed. The mean duration of severe hypertension before nicardipine use was 12.5 hours. Most (74%) patients were receiving other antihypertensive agents before nicardipine.

RESULTS

The initial nicardipine dose was 0.8 +/- 0.3 microg/kg/min (mean +/- SD). The mean effective dose was 1.8 +/- 1.0 microg/kg/min (range, 0.3 to 4.0). Blood pressure control was achieved within 2.7 +/- 2.1 hours after nicardipine was started. Nicardipine treatment produced a 16% reduction in systolic blood pressure, a 23% reduction in diastolic blood pressure, and a 7% increase in heart rate. Nicardipine was effective as a single agent on 26 (84%) of 31 occasions. Adverse effects included tachycardia, flushing, palpitations, and hypotension.

CONCLUSIONS

When administered in the intensive care unit setting with close patient monitoring, intravenous nicardipine effectively lowered blood pressure in children with severe hypertension. Larger prospective studies should be conducted to confirm these findings.

Reduction of infarct size by the NO donors sodium nitroprusside and spermine/NO after transient focal cerebral ischemia in rats

Nitric oxide (NO) plays a dual role (neuroprotection and neurotoxicity) in cerebral ischemia. NO promoting strategies may be beneficial shortly after ischemia. Therefore, we have studied the hemodynamic and possible neuroprotective effects of two NO donors, the classical nitrovasodilator sodium nitroprusside (SNP) and the NONOate spermine/NO, after transient focal cerebral ischemia in rats. Parietal cortical perfusion was measured by laser-Doppler flowmetry. The effects of increasing intravenous doses (10-300 microgram) of sodium nitroprusside and spermine/NO on cortical perfusion and arterial blood pressure were assessed. Transient (2 h) focal cerebral ischemia was carried out by the intraluminal thread method. The effects of intraischemic intravenous infusion of SNP (0.11, 1.1 mg/kg) and spermine/NO (0.36, 3.6 mg/kg) on hemodynamic parameters and infarct size developed after 1 week reperfusion were assessed. In control conditions, SNP and, to a lesser extent, spermine/NO induced dose-dependent hypotension and concomitant reduction in cortical perfusion. In focal cerebral ischemia, infusion of SNP (0.11 mg/kg) and spermine/NO (0.36, 3.6 mg/kg) reduced the infarct size. In the case of spermine/NO, cortical perfusion was maintained above the control levels during the ischemic insult. No significant hypotension was elicited by NO donors at the dose-ratios infused. In conclusion, brain damage induced by transient focal ischemia is reduced by intravenous NO donors. Neuroprotective effects of spermine/NO are due at least in part to improvement of brain perfusion, while sodium nitroprusside must provide direct cytoprotection. These results give further support to the protective effect of NO in the early stages of cerebral ischemia and point to the therapeutic potential of NONOates in the management of brain ischemic damage.

The lack of transplacental movement of the cyanide antidote thiosulfate in gravid ewes

A previous study reported that the co-infusion of IV sodium thiosulfate (STS) with sodium nitroprusside (SNP) to near-term gravid ewes prevented both maternal and fetal cyanide toxicity. We questioned whether maternally administered STS crossed the ovine placenta to enhance fetal transulfuration of cyanide, or whether the fetus was dependent on maternal detoxification of cyanide after diffusion of cyanide into the maternal circulation. Ten anesthetized, near-term gravid ewes underwent hysterotomies with delivery of fetal heads for venous catheterization. Five control ewes received IV isotonic sodium chloride solution, whereas five experimental ewes received IV STS (50 mg/kg over 15 min). Serial plasma thiosulfate concentrations in ewes and fetuses were measured over 135 min. Areas under the time-plasma thiosulfate concentration curves were calculated for experimental and control ewes at 2758+/-197 and 508+/-74 min x mg(-1) x L(-1), respectively (P < 0.008). Mean areas under the curve for experimental and control fetuses were 236+/-34 and 265+/-23 min x mg(-1) x L(-1), respectively (P > 0.5). Maternally administered STS may prevent fetal cyanide poisoning from SNP administration without relying on STS crossing the placenta into the fetal circulation. Fetal cyanide may cross down a concentration gradient from fetal to maternal circulation, to be transulfurated to thiocyanate in maternal tissues.

IMPLICATIONS

We evaluated the mechanism of action of sodium thiosulfide (STS) in sodium nitroprusside-induced cyanide toxicity in the ewe. Fetal cyanide poisoning is alleviated by maternal administration of STS, although this cyanide antidote apparently does not cross the placenta.

Prevention of fetal and maternal cyanide toxicity from nitroprusside with coinfusion of sodium thiosulfate in gravid ewes

Coadministration of sodium thiosulfate with sodium nitroprusside (SNP) to children and adults prevents increases in cyanide concentrations during anesthesia or long-term SNP infusions. We wondered whether maternally administered sodium thiosulfate would prevent increases in fetal red cell cyanide concentrations in gravid ewes receiving SNP infusions. Under anesthesia, the fetal head was delivered through a lateral hysterotomy for catheterization of the jugular vein; the fetus was left in utero. Six control ewes near term received SNP at 25 micrograms.kg-1.min-1 for 4 h. Norepinephrine was used to maintain maternal mean arterial pressure at 80% baseline values. Six experimental ewes received the same treatment except that sodium thiosulfate was infused with SNP (1 g sodium thiosulfate per 100 mg SNP). Serial red cell cyanide concentrations in ewes and fetuses were followed. One control fetal death resulted from abruptio placenta, and this ewe and fetus were excluded from analysis. An additional control ewe and fetus died from apparent cyanide poisoning late during the course of the experiment. While control ewes and fetuses suffered progressive increases in red cell cyanide concentrations into the toxic range, experimental ewes and fetuses never developed toxic red cell cyanide levels (ewes P < .003, fetuses P < .004). These data, if applicable to humans, suggest that coadministration of sodium thiosulfate with SNP to pregnant women at doses currently in use for nonpregnant patients will prevent fetal, as well as maternal, cyanide toxicity.

Cardiovascular effects of an ultra-short-acting nitric oxide-releasing compound, zwitterionic diamine/NO adduct, in dogs

BACKGROUND

This study was conducted to clarify the cardiovascular effects of a new NO-releasing compound, NOC-7, and to compare it with other nitrovasodilators, sodium nitroprusside (SNP) and nitroglycerin, in dogs anesthetized with pentobarbital.

METHODS AND RESULTS

A bolus injection of NOC-7 decreased mean aortic blood pressure in a dose-dependent manner. The onset was rapid and the recovery quick. Continuous infusion of NOC-7 decreased mean aortic pressure from 115 +/- 3.9 to 84 +/- 2.9 mm Hg and infusion of SNP, from 118 +/- 3.8 to 87 +/- 3.1 mm Hg. The optimum doses of NOC-7 and SNP were determined to be 2.73 +/- 0.77 and 11.5 +/- 6.1 micrograms.kg-1.min-1, respectively. During infusion of NOC-7, heart rate and cardiac output were increased (P < .05), pulmonary artery pressure was not changed, and systemic and pulmonary vascular resistances were decreased (P < .05). Electromagnetic flowmetry showed that portal venous and internal carotid arterial blood flow were increased (P < .05) and that hepatic and renal arterial blood flows were not changed. These hemodynamic changes during NOC-7 infusion were similar to those with SNP. The plasma level of NO2-/NO3 did not change, but methemoglobin increased slightly (P < .05). Comparison between hypotensive responses before and after a 3.5-hour infusion of NOC-7 or nitroglycerin showed that acute tolerance developed to nitroglycerin but not to NOC-7.

CONCLUSIONS

The results indicate that NOC-7 may be useful as an ultra-short-acting nitrovasodilator that has no major adverse effect or tolerance.

Sodium nitroprusside metabolism in children during hypothermic cardiopulmonary bypass

Ten children, aged 1-7 yr, presenting for repair of complex congenital heart lesions, were prospectively studied. A ketamine, halothane/isoflurane, and fentanyl anesthetic was used. After initiation of hypothermic cardiopulmonary bypass, sodium nitroprusside (SNP) was titrated as necessary to maintain a target mean arterial blood pressure of 35-60 mm Hg. Blood samples drawn immediately prior to starting SNP infusion, every 15 min during infusion, and at 1, 4, and 24 h postinfusion were analyzed for whole blood cyanide (CN-) and serum thiocyanate (SCN-). Blood gas analysis was performed every 30 min during SNP infusion. A maximum CN- level > or = 1.0 micrograms/mL was observed in two children; four others had maximum CN- levels between 0.5 micrograms/mL and 1.0 micrograms/mL (normal, < 0.2 micrograms/mL). No child had a clinically important increase of SCN- subsequent to SNP infusion. There was substantial variability in observed CN- accumulation during SNP infusion. CN- levels during the first 60 min correlated with the average SNP rate of administration (P = 0.02). Cyanide levels rapidly decreased after termination of SNP infusion and were undetectable 4 h postinfusion. Despite the short-term increase of CN- level, no child showed biochemical signs of toxicity (acidosis or increased mixed venous oxygen tension).

Sodium nitroprusside: twenty years and counting

SNP remains an effective, reliable, and commonly used drug for the rapid reduction of significant arterial hypertension regardless of the etiology, for afterload reduction in the face of low CO when blood volume is normal or increased, and for intraoperative induced hypotension. After establishing indwelling arterial monitoring, an initial infusion rate of 0.3-0.5 micrograms.kg-1.min-1 is begun with titration as needed up to 2.0 micrograms.kg-1.min-1. Higher rates for brief periods of time (10 min) are acceptable. The use of alternative drugs to reduce the dose or shorten the duration of infusion should be considered when the 2.0 micrograms.kg-1.min-1 range is exceeded (Table 1). SNP should not be used by individuals unfamiliar with its potency and metabolic pathways, as the many reports of adverse reactions testify. Careful attention to infusion rates, particularly in patients at risk for depleted thiosulfate stores, is mandatory, and the use of other drugs in conjunction with or instead of SNP should always be considered. As with many therapeutic interventions, SNP requires careful administration to appropriately selected patients by a clinician who knows its inherent hazards. Despite its toxicity, SNP is popular because it is often the most (in some cases, the only) effective drug in some difficult clinical circumstances.

Advances in pharmacotherapy: treatment of hypertensive crisis

A hypertensive crisis can be caused by many factors. Frequently, the mechanism involved is complex and highly variable among patients. Without drug therapy, this condition is associated with very high mortality and morbidity. There are a number of oral and intravenous hypotensive agents available, which can effectively control blood pressure in a hypertensive crisis. The relative advantages and disadvantages of each treatment option is discussed.

Cyanide toxicity from sodium nitroprusside: risks and management

OBJECTIVE

To review the risks, manifestations, and treatment of cyanide toxicity from nitroprusside therapy.

DATA SOURCES

All English case reports identified in Index Medicus (MEDLINE) of cyanide intoxication related to nitroprusside from 1970 to the present were reviewed. In addition, literature regarding the incidence, risks, and treatment of cyanide toxicity from nitroprusside is presented.

CONCLUSIONS

Numerous cases of cyanide toxicity associated with nitroprusside have been reported. The overall incidence appears to be infrequent; however, certain patients may be at high risk. Risk factors may include hypoalbuminemia, cardiopulmonary bypass procedures, or the administration of moderate to high doses of nitroprusside. Treatment of cyanide toxicity requires the cessation of nitroprusside and, for severe toxicity, use of the cyanide antidote kit. Cyanide toxicity from nitroprusside may be prevented by concomitant administration of sodium thiosulfate infusions.