Successful use of nitroglycerin to treat postoperative pulmonary hypertension

Nitrates for the prevention of cardiac morbidity and mortality in patients undergoing non-cardiac surgery

BACKGROUND

Cardiac complications are not uncommon in patients undergoing non-cardiac surgery, especially in patients with coronary artery disease (CAD) or at high risk of CAD. Perioperative cardiac complications can lead to mortality and morbidity, as well as higher costs for patient care. Nitrates, which are among the most commonly used cardiovascular drugs, perform the function of decreasing cardiac preload while improving cardiac blood perfusion. Sometimes, nitrates are administered to patients undergoing non-cardiac surgery to reduce the incidence of cardiac complications, especially for patients with CAD. However, their effects on patients' relevant outcomes remain controversial.

OBJECTIVES

• To assess effects of nitrates as compared with other interventions or placebo in reducing cardiac risk (such as death caused by cardiac factors, angina pectoris, acute myocardial infarction, acute heart failure and cardiac arrhythmia) in patients undergoing non-cardiac surgery.• To identify the influence of different routes and dosages of nitrates on patient outcomes.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and the Chinese BioMedical Database until June 2014. We also searched relevant conference abstracts of important anaesthesiology or cardiology scientific meetings, the database of ongoing trials and Google Scholar.We reran the search in January 2016. We added three potential new studies of interest to the list of 'Studies awaiting classification' and will incorporate them into our formal review findings for the review update.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing nitrates versus no treatment, placebo or other pharmacological interventions in participants (15 years of age and older) undergoing non-cardiac surgery under any type of anaesthesia.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane. Two review authors selected trials, extracted data from included studies and assessed risk of bias. We resolved differences by discussion and, when necessary, sought help and suggestions from a third review author. We used a random-effects model for data analysis.

MAIN RESULTS

We included 27 randomized controlled trials (RCTs) (8244 participants analysed). Investigators reported 12 different comparisons of three different nitrates (nitroglycerin, isosorbide dinitrate and nicorandil) versus no treatment, placebo or other pharmacological interventions. All participants were older than 15 years of age. More than half of the trials used general anaesthesia. Surgical procedures in most trials were at low to moderate risk for perioperative cardiac complications. Only two comparisons including three studies reported the primary outcome - all-cause mortality up to 30 days post operation. Researchers reported other morbidity outcomes and adverse events in a variable and heterogeneous way, resulting in limited available data for inclusion in the meta-analysis. We determined that the overall methodological quality of included studies was fair to low, in accordance with risk of bias in most domains.In summary, we found no difference in the primary outcome - all-cause mortality up to 30 days post operation - when nitroglycerin was compared with no treatment (one study, 60 participants, 0/30 vs 1/30; (risk ratio (RR) 0.33, 95% confidence interval (CI) 0.01 to 7.87, very low-quality evidence based on GRADE criteria) or with placebo (two studies, 89 participants, 1/45 vs 0/44; RR 2.81, 95% CI 0.12 to 63.83, very low-quality evidence). Regarding our secondary outcomes, we noted no statistically significant differences in angina pectoris, acute myocardial infarction, acute heart failure, cardiac arrhythmia or cardiac arrest in any comparisons. In comparisons versus nitroglycerin, although more events of cardiac ischaemia were observed in participants receiving no treatment or placebo, we found no statistically significant differences in any comparisons, except the comparison of nicorandil versus placebo. One study revealed a potential dose-dependent protective effect of nicorandil for cardiac ischaemia.Adverse events were reported in a heterogeneous way among the comparisons. In general, more participants treated with nitrates had hypotension, tachycardia and headache, but investigators reported no statistically significant differences between groups in any comparisons.

AUTHORS' CONCLUSIONS

This systematic review suggests that nitroglycerin or isosorbide dinitrate is not associated with improvement in mortality and cardiac complications among patients undergoing non-cardiac surgery. Limited evidence suggests that nicorandil may reduce the risk of cardiac ischaemia in participants undergoing non-cardiac surgery. Additional studies are needed to consolidate the evidence.However, the data included in many of the analyses in this review are sparse - that is, adequate data are few - resulting in very low power to detect differences between nitrates and comparators. Thus, a more objective conclusion would state that available evidence is insufficient to show whether nitrates are associated with improvement in mortality and cardiac complications among patients undergoing non-cardiac surgery.Over the past decade, no high-quality studies have focused on association of cardiac mortality and morbidity with use of nitrates during non-cardiac surgery. This review underlines the need for well-designed trials in this field.

Nitrates and nitrites in the treatment of ischemic cardiac disease

The organic nitrite, amyl of nitrite, was initially used as a therapeutic agent in the treatment of angina pectoris, but was replaced over a decade later by the organic nitrate, nitroglycerin (NTG), due to the ease of administration and longer duration of action. The administration of organic nitrate esters, such as NTG, continues to be used in the treatment of angina pectoris and heart failure since the birth of modern pharmacology. Their clinical effectiveness is due to vasodilator activity in large veins and arteries through an as yet unidentified method of delivering nitric oxide (NO), or a NO-like compound. The major drawback is the development of tolerance with NTG, and the duration and route of administration with amyl of nitrite. Although the nitrites are no longer used in the treatment of hypertension or ischemic heart disease, the nitrite anion has recently been discovered to possess novel pharmacologic actions, such as modulating hypoxic vasodilation, and providing cytoprotection in ischemia-reperfusion injury. Although the actions of these 2 similar chemical classes (nitrites and organic nitrates) have often been considered to be alike, we still do not understand their mechanism of action. Finally, the nitrite anion, either from sodium nitrite or an intermediate NTG form, may act as a storage form for NO and provide support for investigating the use of these agents in the treatment of ischemic cardiovascular states. We review what is presently known about the use of nitrates and nitrites including the historical, current, and potential uses of these agents, and their mechanisms of action.

Methemoglobin levels during prolonged combined nitroglycerin and sodium nitroprusside infusions in infants after cardiac surgery

Nitroglycerin (NTG) and sodium nitroprusside (SNP) are routinely used perioperatively in infants with congenital heart defects. In this study, NTG and SNP were infused in the operating room to increase venous capacitance, reduce systemic and pulmonary afterload, facilitate weaning off cardiopulmonary bypass, stabilize hemodynamics for transport to the intensive care unit (ICU), and reduce the fluid resuscitation needed upon arrival in the ICU. Because of the risk for accumulation of methemoglobin (MetHb) and cyanmethemoglobin (cyan-MetHb) during prolonged continuous infusion of NTG and SNP, it was decided to (1) quantify ICU use, (2) measure % MetHb at 12-hour intervals, and (3) look indirectly for the accumulation of cyan-MetHb by comparing simultaneous pulse oximetry (SpO2) (Nellcor N-100 [Nellcor, Haywood, CO]) and CO-oximetry (SaO2) (Corning 270 [Corning, Medfield, MA]). A total of 69 arterial samples were obtained from 16 infants (median age 4.4 months) following cardiac surgery with bypass. Median doses of NTG, 6.0 mg/kg (range 0.7 to 27.5), and SNP, 3.3 mg/kg (range 0.6 to 33.4), were infused over a median of 64.5 hours (range 12 to 183) (N = 16 patients). The median MetHb was 0.6% (range 0.0 to 1.5) after infusions of NTG, 1.8 micrograms/kg/min (range 0.5 to 4), and SNP, 1.3 micrograms/kg/min (range 0.3 to 8.4) (N = 69 measurements). Regression analysis of oximetry data yielded the equation: SpO2 = 1.04 SaO2 - 3.7%, r = 0.97. The mean difference between SpO2 and SaO2 data pairs was 0.0% (bias) with a SD (precision) of +/- 2.3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of prostaglandin E1 to treat peri-anaesthetic pulmonary hypertension associated with mitral valve disease

Severe pulmonary hypertension (PH) can be a critical problem during and after cardiac surgery, since it increases right ventricular afterload resulting in decreased cardiac output. A case of pulmonary hypertension associated with mitral valve disease and resistant to glyceryl trinitrate therapy during surgery is reported. The case was treated successfully with prostaglandin E1 (PGE1), indicating that PGE1 can be used peri-operatively in a patient with refractory PH resistant to glyceryl trinitrate treatment.

Intratracheal administration of pulmonary vasodilator agents

We compared intravenous and intratracheal administration of histamine (0.4 and 1.6 micrograms/kg, respectively) and nitroglycerin (5.0 and 20.0 micrograms/kg, respectively) in seven hypoxemic 2 week old lambs, during right lung only perfusion, to see if intratracheal administration could limit their vasodilator action to the pulmonary vessels. The hemodynamic variables: pulmonary artery pressure (Ppa), left atrial pressure (Pla), pulmonary blood flow per kilogram (Q/kg), and aortic pressure (Pao) were measured at baseline and in each experimental state, then pulmonary vascular resistance (PVR) and systemic vascular input resistance (SVR) were determined. We found that intravenous histamine showed some pulmonary vasodilator selectivity in that it caused a 19% decrease of Ppa from baseline (P less than 0.002), a 23% decrease of PVR from baseline (P less than 0.002), and an 8% decrease of SVR from baseline (P less than 0.05). Intratracheal histamine produced smaller effects, decreasing Ppa by 11% from baseline (P less than 0.02), and PVR by 14% from baseline (P less than 0.02), while SVR was unaffected. Intravenous nitroglycerin decreased cardiac output by 16% from baseline (P less than 0.02), and also decreased SVR by 8% while producing a small increase in PVR. Intratracheal nitroglycerin caused a similar 17% (P less than 0.01) decrease in cardiac output, and again an increased PVR but a decreased SVR. This study confirms that histamine has some intrinsic pulmonary vasodilator selectivity. Furthermore, the data suggest that intratracheal administration may accentuate pulmonary selectivity by lessening systemic effects. Nitroglycerin, on the other hand, had untoward hemodynamic effects in the presence of hypoxia.