Methaemoglobin production in normal adults inhaling low concentrations of nitric oxide

Safety of inhaled nitric oxide withdrawal in severe chronic pulmonary hypertension

Inhaled nitric oxide (iNO) is a potent and selective pulmonary vasodilator with a safety concern due to rebound pulmonary hypertension (PH) associated with its withdrawal. We report short-term pulsed iNO in patients with severe pulmonary arterial hypertension (PAH) and nonoperable chronic thromboembolic PH (nCTEPH). This is a retrospective analysis of 33 patients: 22 with PAH and 11 with nCTEPH. We assessed hemodynamic, echocardiographic, and other noninvasive variables to evaluate safety and efficacy of iNO. We performed an iNO withdrawal test during right heart catheterization and after 3 days of iNO treatment. iNO significantly improved all variables examined in 22 patients with PAH and 11 with nCTEPH. Two patterns of response were observed after sudden iNO withdrawal. Twenty-nine patients (88%) showed minimal hemodynamic, oxygenation and clinical changes. Four patients (12%) had a reduction in cardiac index ≥20% and PaO2 ≥ 5%, three patients did not show clinical deterioration, and one patient developed hemodynamic collapse that needed iNO administration. This retrospective study suggests that short-term iNO improves hemodynamics and clinical conditions in some patients with PAH an nCTPEH. However, pulsed iNO withdrawal PH rebound could be a serious concern in these patients. Given the lack of evidence, we do not recommend the use of pulsed iNO in the treatment of patients with chronic PH.

Pulmonary Vasodilator and Inodilator Drugs in Cardiac Surgery: A Systematic Review With Bayesian Network Meta-Analysis

OBJECTIVE

The authors performed a systematic review to evaluate the effect of pharmacologic therapy on pulmonary hypertension in the perioperative setting of elective cardiac surgery (PROSPERO CRD42023321041).

DESIGN

Systematic review of randomized controlled trials with a Bayesian network meta-analysis.

SETTING

The authors searched biomedical databases for randomized controlled trials on the perioperative use of inodilators and pulmonary vasodilators in adult cardiac surgery, with in-hospital mortality as the primary outcome and duration of ventilation, length of stay in the intensive care unit, stage 3 acute kidney injury, cardiogenic shock requiring mechanical support, and change in mean pulmonary artery pressure as secondary outcomes.

PARTICIPANTS

Twenty-eight studies randomizing 1,879 patients were included.

INTERVENTIONS

Catecholamines and noncatecholamine inodilators, arterial pulmonary vasodilators, vasodilators, or their combination were considered eligible interventions compared with placebo or standard care.

MEASUREMENTS AND MAIN RESULTS

Ten studies reported in-hospital mortality and assigned 855 patients to 12 interventions. Only inhaled prostacyclin use was supported by a statistically discernible improvement in mortality, with a number-needed-to-treat estimate of at least 3.3, but a wide credible interval (relative risk 1.26 × 10-17 - 0.7). Inhaled prostacyclin and nitric oxide were associated with a reduction in intensive care unit stay, and none of the included interventions reached a statistically evident difference compared to usual care or placebo in the other secondary clinical outcomes.

CONCLUSIONS

Inhaled prostacyclin was the only pharmacologic intervention whose use is supported by a statistically discernible improvement in mortality in the perioperative cardiac surgery setting as treatment of pulmonary hypertension. However, available evidence has significant limitations, mainly the low number of events and imprecision.

Initiation of Inhaled Nitric Oxide by Air Transport Team in Adult COVID-19 Respiratory Failure

The coronavirus disease 2019 (COVID-19) pandemic has caused a significant increase in the volume of critical care flight transports between outlying referral hospitals and tertiary care facilities. Because of the tropism of severe acute respiratory syndrome coronavirus 2, flight crews are often asked to transport mechanically ventilated patients in refractory hypoxemic respiratory failure. The authors present a case series of 5 patients with COVID-19 acute respiratory distress syndrome (ARDS) who were initiated on inhaled nitric oxide (iNO) by the transport team before rotor wing transport and survived the journey in stable or improved condition upon arrival. Previously, no case reports have described adults with COVID-19 ARDS transported after iNO initiation by the transport team. This case series shows the feasibility of iNO initiation by trained air medical transport teams and suggests a short-term stabilizing effect of iNO in patients with ARDS from COVID-19.

Recent Developments in Nitric Oxide Donors and Delivery for Antimicrobial and Anti-Biofilm Applications

The use of nitric oxide (NO) is emerging as a promising, novel approach for the treatment of antibiotic resistant bacteria and biofilm infections. Depending on the concentration, NO can induce biofilm dispersal, increase bacteria susceptibility to antibiotic treatment, and induce cell damage or cell death via the formation of reactive oxygen or reactive nitrogen species. The use of NO is, however, limited by its reactivity, which can affect NO delivery to its target site and result in off-target effects. To overcome these issues, and enable spatial or temporal control over NO release, various strategies for the design of NO-releasing materials, including the incorporation of photo-activable, charge-switchable, or bacteria-targeting groups, have been developed. Other strategies have focused on increased NO storage and delivery by encapsulation or conjugation of NO donors within a single polymeric framework. This review compiles recent developments in NO drugs and NO-releasing materials designed for applications in antimicrobial or anti-biofilm treatment and discusses limitations and variability in biological responses in response to the use of NO for bacterial eradiation.

Interpreting sulfhemoglobin and methemoglobin in patients with cyanosis: An overview of patients with M-hemoglobin variants

INTRODUCTION

Methemoglobin (MetHb) and sulfhemoglobin (SHb) measurements are useful in the evaluation of cyanosis. When one or both values are elevated, additional analysis is important to establish the etiology of the disorder. Methemoglobinemia occurs from acquired or hereditary causes with diverse treatment considerations, while true sulfhemoglobinemia is only acquired and treatment is restricted to toxin removal. Some toxic exposures can result in a dual increase in MetHb and SHb. Hereditary conditions, such as M-Hemoglobin variants (M-Hbs), can result in increased MetHb and/or SHb values but are clinically compensated and do not require treatment if they are cyanotic but otherwise clinically well.

METHODS

Herein, we report 53 hemoglobin variant cases that have associated MetHb and SHb levels measured by an adapted Evelyn-Malloy laboratory assay method.

RESULTS

Our data indicate M-Hbs cause variable patterns of MetHb and SHb elevation in a fairly reproducible pattern for the particular variant. In particular, α globin chain M-Hbs can mimic acquired sulfhemoglobinemia due to an isolated increased SHb value.

CONCLUSION

If the patient appears clinically well other than cyanosis, M-Hbs should be considered early in the evaluation process to differentiate from acquired conditions to avoid unnecessary testing and treatment regimens and prompt genetic counseling.

The Interplay between Molten Globules and Heme Disassociation Defines Human Hemoglobin Disassembly

Hemoglobin functions as a tetrameric oxygen transport protein, with each subunit containing a heme cofactor. Its denaturation, either in vivo or in vitro, involves autoxidation to methemoglobin, followed by cofactor loss and globin unfolding. We have proposed a global disassembly scheme for human methemoglobin, linking hemin (ferric protoporphyrin IX) disassociation and apoprotein unfolding pathways. The model is based on the evaluation of circular dichroism and visible absorbance measurements of guanidine-hydrochloride-induced disassembly of methemoglobin and previous measurements of apohemoglobin unfolding. The populations of holointermediates and equilibrium disassembly parameters were estimated quantitatively for adult and fetal hemoglobins. The key stages are characterized by hexacoordinated hemichrome intermediates, which are important for preventing hemin disassociation from partially unfolded, molten globular species during early disassembly and late-stage assembly events. Both unfolding experiments and independent small angle x-ray scattering measurements demonstrate that heme disassociation leads to the loss of tetrameric structural integrity. Our model predicts that after autoxidation, dimeric and monomeric hemichrome intermediates occur along the disassembly pathway inside red cells, where the hemoglobin concentration is very high. This prediction suggests why misassembled hemoglobins often get trapped as hemichromes that accumulate into insoluble Heinz bodies in the red cells of patients with unstable hemoglobinopathies. These Heinz bodies become deposited on the cell membranes and can lead to hemolysis. Alternatively, when acellular hemoglobin is diluted into blood plasma after red cell lysis, the disassembly pathway appears to be dominated by early hemin disassociation events, which leads to the generation of higher fractions of unfolded apo subunits and free hemin, which are known to damage the integrity of blood vessel walls. Thus, our model provides explanations of the pathophysiology of hemoglobinopathies and other disease states associated with unstable globins and red cell lysis and also insights into the factors governing hemoglobin assembly during erythropoiesis.

Effect of nitric oxide on postoperative acute kidney injury in patients who underwent cardiopulmonary bypass: a systematic review and meta-analysis with trial sequential analysis

BACKGROUND

The effect of nitric oxide (NO) on renal function is controversial in critical illness. We performed a systematic meta-analysis and trial sequential analysis to determine the effect of NO gas on renal function and other clinical outcomes in patients requiring cardiopulmonary bypass (CPB). The primary outcome was the relative risk (RR) of acute kidney injury (AKI), irrespective of the AKI stage. The secondary outcome was the mean difference (MD) in the length of ICU and hospital stay, the RR of postoperative hemorrhage, and the MD in levels of methemoglobin. Trial sequential analysis (TSA) was performed for the primary outcome.

RESULTS

54 trials were assessed for eligibility and 5 studies (579 patients) were eligible for meta-analysis. NO was associated with reduced risk of AKI (RR 0.76, 95% confidential interval [CI], 0.62 to 0.93, I2 = 0%). In the subgroup analysis by NO initiation timing, NO did not decrease the risk of AKI when started at the end of CPB (RR 1.20, 95% CI 0.52-2.78, I2 = 0%). However, NO did significantly reduce the risk of AKI when started from the beginning of CPB (RR 0.71, 95% CI 0.54-0.94, I2 = 10%). We conducted TSA based on three trials (400 patients) using KDIGO criteria and with low risk of bias. TSA indicated a CI of 0.50-1.02 and an optimal information size of 589 patients, suggesting a lack of definitive conclusion. Furthermore, NO does not affect the length of ICU and hospital stay or the risk of postoperative hemorrhage. NO slightly increased the level of methemoglobin at the end of CPB (MD 0.52%, 95% CI 0.27-0.78%, I2 = 90%), but it was clinically negligible.

CONCLUSIONS

NO appeared to reduce the risk of postoperative AKI in patients undergoing CPB. Additional studies are required to ascertain the finding and further determine the dosage, timing and duration of NO administration.

Inhaled therapy for the management of perioperative pulmonary hypertension

Patients with pulmonary hypertension (PH) are at high risk for complications in the perioperative setting and often receive vasodilators to control elevated pulmonary artery pressure (PAP). Administration of vasodilators via inhalation is an effective strategy for reducing PAP while avoiding systemic side effects, chiefly hypotension. The prototypical inhaled pulmonary-specific vasodilator, nitric oxide (NO), has a proven track record but is expensive and cumbersome to implement. Alternatives to NO, including prostanoids (such as epoprostenol, iloprost, and treprostinil), NO-donating drugs (sodium nitroprusside, nitroglycerin, and nitrite), and phosphodiesterase inhibitors (milrinone, sildenafil) may be given via inhalation for the purpose of treating elevated PAP. This review will focus on the perioperative therapy of PH using inhaled vasodilators.

Pharmacological interventions in acute respiratory distress syndrome

Pharmacological interventions are commonly considered in acute respiratory distress syndrome (ARDS) patients. Inhaled nitric oxide (iNO) and neuromuscular blockers (NMBs) are used in patients with severe hypoxemia. No outcome benefit has been observed with the systematic use of iNO. However, a sometimes important improvement in oxygenation can occur shortly after starting administration. Therefore, its ease of use and its good tolerance justify iNO optionally combined with almitirne as a rescue therapy on a trial basis. Recent data from the literature support the use of a 48-h infusion of NMBs in patients with a PaO2 to FiO2 ratio <120 mmHg. No strong evidence exists on the increase of ICU-acquired paresis after a short course of NMBs. Fluid management with the goal to obtain zero fluid balance in ARDS patients without shock or renal failure significantly increases the number of days without mechanical ventilation. On the other hand, patients with hemodynamic failure must receive early and adapted fluid resuscitation. Liberal and conservative fluid strategies therefore are complementary and should ideally follow each other in time in the same patient whose hemodynamic state progressively stabilizes. At present, albumin treatment does not appear to be justified for limitation of pulmonary edema and respiratory morbidity. Aerosolized β2-agonists do not improve outcome in patients with ARDS and one study strongly suggests that intravenous salbutamol may worsen outcome in those patients. The early use of high doses of corticosteroids for the prevention of ARDS in septic shock patients or in patients with confirmed ARDS significantly reduced the duration of mechanical ventilation but had no effect or even increased mortality. In patients with persistent ARDS after 7 to 28 days, a randomized trial showed no reduction in mortality with moderate doses of corticosteroids but an increased PaO2 to FiO2 ratio and thoracopulmonary compliance were found, as well as shorter durations of mechanical ventilation and of ICU stay. Conflicting data exist on the interest of low doses of corticosteroids (200 mg/day of hydrocortisone) in ARDS patients. In the context of a persistent ARDS with histological proof of fibroproliferation, a corticosteroid treatment with a progressive decrease of doses can be proposed.

A phase I clinical study of inhaled nitric oxide in healthy adults

BACKGROUND

Nitric oxide (NO) is an approved pulmonary vasodilator for neonates and full term infants up to a dose of 80 ppm. At 100 ppm to 200 ppm, NO has potent antimicrobial activities in vitro and in animal studies which suggest its therapeutic use for infectious diseases in humans. However, whether inhaled NO is safe at 160 ppm in healthy human adults is unknown. The aim of the phase I study was to assess the safety of delivery and the physiologic effects of intermittent 160 ppm NO in healthy human adults.

METHODS

Ten healthy adult volunteers (5 males, 5 females; 20-62 years) were recruited and inhaled 163.3 ppm (SD: 4.0) NO for 30 min, 5 times daily, for 5 consecutive days. Lung function and blood levels of methemoglobin, nitrites/nitrates, prothrombin, pro-inflammatory cytokines and chemokines were determined before and during treatment.

RESULTS

All individuals tolerated the NO treatment courses well. No significant adverse events occurred and three minor adverse events, not attributable to NO, were reported. Forced expiratory volume in 1 sec % predicted and other lung function parameters, serum nitrites/nitrates, prothrombin, pro-inflammatory cytokine and chemokine levels did not differ between baseline and day 5, while methemoglobin increased significantly during the study period to a level of 0.9% (SD: 0.08) (p<0.001).

CONCLUSION

These data suggest that inhalation of 160 ppm NO for 30 min, 5 times daily, for 5 consecutive days, is safe and well tolerated in healthy individuals.

Acute, sublethal cyanide poisoning in mice is ameliorated by nitrite alone: complications arising from concomitant administration of nitrite and thiosulfate as an antidotal combination

Sodium nitrite alone is shown to ameliorate sublethal cyanide toxicity in mice when given from ∼1 h before until 20 min after the toxic dose as demonstrated by the recovery of righting ability. An optimum dose (12 mg/kg) was determined to significantly relieve cyanide toxicity (5.0 mg/kg) when administered to mice intraperitoneally. Nitrite so administered was shown to rapidly produce NO in the bloodsteam as judged by the dose-dependent appearance of EPR signals attributable to nitrosylhemoglobin and methemoglobin. It is argued that antagonism of cyanide inhibition of cytochrome c oxidase by NO is the crucial antidotal activity rather than the methemoglobin-forming action of nitrite. Concomitant addition of sodium thiosulfate to nitrite-treated blood resulted in the detection of sulfidomethemoblobin by EPR spectroscopy. Sulfide is a product of thiosulfate hydrolysis and, like cyanide, is known to be a potent inhibitor of cytochrome c oxidase, the effects of the two inhibitors being essentially additive under standard assay conditions rather than dominated by either one. The findings afford a plausible explanation for an observed detrimental effect in mice associated with the use of the standard nitrite-thiosulfate combination therapy at sublethal levels of cyanide intoxication.

Fast measurement of blood T1 in the human jugular vein at 3 Tesla

Current T(1) values for blood at 3T largely came from in vitro studies on animal blood or freshly drawn human blood. Measurement of blood T(1) in vivo could provide more specific information, e.g., for individuals with abnormal blood composition. Here, blood T(1) at 3T was measured rapidly (<1 min) in the internal jugular vein using a fast inversion-recovery technique in which multiple inversion time can be acquired rapidly due to constant refreshing of blood. Multishot EPI acquisition with flow compensation yielded high resolution images with minimum partial volume effect. Results showed T(1) = 1852 ± 104 msec among 24 healthy adults, a value higher than for bovine blood phantoms (1584 msec at Hct of 42%). A second finding was that of a significant difference (P < 0.01) between men and women, namely T(1) = 1780 ± 89 msec (n = 12) and T(1) = 1924 ± 58 msec (n = 12), respectively. This difference in normal subjects is tentatively explained by the difference in Hct between genders. Interestingly, however, studies done on sickle cell anemia patients with much lower Hct (23 ± 3%, n = 10) revealed similar venous blood T(1) = 1924 ± 82 msec, indicating other possible physical influences affecting blood T(1).

Covalent modifications of hemoglobin by nitrite anion: formation kinetics and properties of nitrihemoglobin

The green nitrihemoglobin (α(2)β(2) tetramer, NHb) was prepared by the aerobic reaction of excess nitrite with human hemoglobin A(0) under mildly acidic conditions. A rate equation was determined and found to depend on nitrite, hydrogen ion, and oxygen concentrations: -d[HbNO(2)]/dt = [k(1) + k(2)(K(a)[HNO(2)])[O(2)](1/2)][HbNO(2)], where k(1) = (2.4 ± 0.9) × 10(-4) s(-1), k(2) = (1 ± 0.2) × 10(5) M(-5/2) s(-1), and K(a) is the acid dissociation constant for nitrous acid (4.5 × 10(-4) M). Also, the chemical properties of NHb are compared to those of the normal hemoglobin (including the addition products of common oxidation states with exogenous ligands, the alkaline transitions of the ferric forms, and the oxygen binding characteristics of the ferrous forms) and were found to be nearly indistinguishable. Therefore, the replacement of a single vinyl hydrogen with a nitro group on the periphery of each macrocycle in hemoglobin does not significantly perturb the interaction between the hemes and the heme pockets. Because nonphotochemical reaction chemistry must necessarily be most dependent on electronic ground states, it follows that the clearly visible difference in color between hemoglobin A(0) and NHb must be associated primarily with the respective electronic excited states. The possibility of NHb formation in vivo and its likely consequences are considered.

A prospective, randomized, crossover pilot study of inhaled nitric oxide versus inhaled prostacyclin in heart transplant and lung transplant recipients

OBJECTIVE

Inhaled nitric oxide has been shown to reduce pulmonary vascular resistance in patients undergoing cardiothoracic surgery, but it is limited by toxicity, the need for special monitoring, and cost. Inhaled prostacyclin also decreases pulmonary artery pressure, is relatively free of toxicity, requires no specific monitoring, and is less expensive. The objective of this study was to compare nitric oxide and prostacyclin in the treatment of pulmonary hypertension, refractory hypoxemia, and right ventricular dysfunction in thoracic transplant recipients in a prospective, randomized, crossover pilot trial.

METHODS

Heart transplant and lung transplant recipients were randomized to nitric oxide or prostacyclin as initial treatment, followed by a crossover to the other agent after 6 hours. Pulmonary vasodilators were initiated in the operating room for pulmonary hypertension, refractory hypoxemia, or right ventricular dysfunction. Nitric oxide was administered at 20 ppm, and prostacyclin was administered at 20,000 ng/mL. Hemodynamic and oxygenation parameters were recorded before and after initiation of pulmonary vasodilator therapy. At 6 hours, the hemodynamic and oxygenation parameters were recorded again, just before discontinuing the initial agent. Crossover baseline parameters were measured 30 minutes after the initial agent had been stopped. The crossover agent was then started, and the hemodynamic and oxygenation parameters were measured again 30 minutes later.

RESULTS

Heart transplant and lung transplant recipients (n = 25) were randomized by initial treatment (nitric oxide, n = 14; prostacyclin, n = 11). Nitric oxide and prostacyclin both reduced pulmonary artery pressure and central venous pressure, and improved cardiac index and mixed venous oxygen saturation on initiation of therapy. More importantly, at the 6-hour crossover trial, there were no significant differences between nitric oxide and prostacyclin in the reduction of pulmonary artery pressures or central venous pressure, or in improvement in cardiac index or mixed venous oxygen saturation. Nitric oxide and prostacyclin did not affect the oxygenation index or systemic blood pressure. There were no complications associated with nitric oxide or prostacyclin.

CONCLUSION

In heart transplant and lung transplant recipients, nitric oxide and prostacyclin similarly reduce pulmonary artery pressures and central venous pressure, and improve cardiac index and mixed venous oxygen saturation. Inhaled prostacyclin may offer an alternative to nitric oxide in the treatment of pulmonary hypertension in thoracic transplantation.

Long-term inhaled nitric oxide plus phosphodiesterase 5 inhibitors for severe pulmonary hypertension

BACKGROUND

Inhaled nitric oxide (iNO) is a potent pulmonary vasodilator, but therapeutic experience in patients with severe pulmonary hypertension is scarce.

METHODS

Eleven patients with severe pulmonary hypertension, 6 due to pulmonary arterial hypertension and 4 due to chronic thromboembolic disease, were selected for iNO therapy. A phosphodiesterase type 5 inhibitor (PDE5i) was added in cases of clinical worsening. In this study we evaluate the clinical effectiveness and safety of long-term treatment with iNO either alone or combined with a PDE5i.

RESULTS

After 1 month of iNO administration, improvements were observed in World Health Organization functional class, Borg scale (p = 0.003), brain natriuretic peptide levels (p = 0.002) and 6-minute walk test (p = 0.003). After 6 months of treatment, 7 patients had clinical deterioration that was reversed upon adding a PDE5i. One of these patients died in Month 8 and another underwent pulmonary transplantation in Month 9. The clinical condition of the remaining 9 patients was unchanged after 1 year. A second right catheterization showed improvement in mean pulmonary arterial pressure (66 +/- 15 mm Hg to 56 +/- 18 mm Hg; p = 0.01), pulmonary vascular resistance (1,234 +/- 380 dyn/s/cm(5) to 911 +/- 410 dyn/s/cm(5); p = 0.008) and cardiac index (2.0 +/- 0.4 liters/min/m(2) to 2.5 +/- 0.4 liters/min/m(2); p = 0.04). There was no significant increase in methemoglobin, no worsening of pulmonary function and no sudden withdrawal syndrome.

CONCLUSIONS

We suggest that iNO therapy alone or in combination with a PDE5i could be a therapeutic alternative for severe pulmonary hypertension.

Effects of inhaled aerosolized iloprost and inhaled NO on pulmonary circulation and edema formation in ovine lung injury

Although inhaled NO (iNO) has been shown to lower pulmonary pressures and edema accumulation in experimental acute lung injury, its clinical use has been questioned because of a lack of improvement in outcome, rebound phenomena, and potential toxicity. We investigated the effects of aerosolized iloprost, a stable prostacyclin analogue, compared with iNO on pulmonary pressures and lung edema in 20 female sheep with oleic acid lung injury. The most effective dose of iloprost was determined in healthy animals before the experiment. Anesthetized and ventilated sheep received a central venous oleic acid infusion and were continuously infused with Ringer lactate to achieve a positive fluid balance (5 mL.kg(-1).h(-1)). In the iNO group (n = 6), iNO (20 ppm) was administered continuously for 8 h. Animals in the iloprost group (n = 6) received aerosolized iloprost (40 microg 2 h(-1)). Animals in the control group (n = 6) had no further intervention. Oleic acid infusion was associated with impaired oxygenation, pulmonary hypertension, and lung edema in all groups. Although iNO significantly decreased pulmonary vascular resistance index, effective pulmonary capillary pressure, and extravascular lung water index, these parameters were unaffected by iloprost. Oxygenation index (Pao2/Fio2) increased significantly both during NO and iloprost inhalation but also tended to improve in the control group over time. In contrast to iNO, the investigated dose of iloprost was ineffective to attenuate acute lung injury-induced changes in pulmonary hemodynamics and lung edema in this experimental model.

Gaseous nitric oxide bactericidal activity retained during intermittent high-dose short duration exposure

Previously, we have shown that gaseous Nitric oxide (gNO) has great potential as an effective topical anti-infective agent for non-healing wounds due to its non-specific antimicrobial properties. These same antimicrobial attributes may be useful for pulmonary infections. However, gNO would have limited usefulness as an inhaled antimicrobial agent as continuous exposure to the concentration required for a bactericidal effect (160-200 ppm) leads to methemoglobinemia. To overcome this problem, we investigated whether a thirty minute exposure of 160 ppm every four hours would retain the same antimicrobial effect as continuous delivery. In vitro, exposure of clinical multi-drug resistant Staphylococcus aureus and Escherichia coli strains isolated from the lungs of nosocomial pneumonia patients and a lethal antibiotic-resistant strain of Pseudomonas aeruginosa, isolated from a deceased cystic fibrosis patient resulted in over a 5 log(10) reduction in bacterial load after multiple thirty minute treatments (4 cycles) every four hours to 160 ppm gNO. The intermittent regimen required 320 (SD=0)ppm h for 100% lethality whereas the continuous exposure required 800 (SD=160)ppm h. We have also shown that selection for a gNO resistant phenotype did not lead to decrease sensitivity to gNO therapy (p>0.05). In addition, no host cellular toxicity was observed in human THP-1 monocytes and macrophages following intermittent delivery of a high concentration of gNO, and the proliferation and migration of pulmonary epithelial cells was not adversely affected by the administration of intermittent high-dose gNO. These results justify further studies that should focus on whether intermittent delivery of 160 ppm of gNO every four hours can technically be administered while keeping inhaled NO(2) levels less than 2 ppm and methemoglobin saturation less than 2.5 percent.

A novel method of measuring reduction of nitrite-induced methemoglobin applied to fetal and adult blood of humans and sheep

The reaction of nitrite with deoxyhemoglobin results in the production of nitric oxide and methemoglobin, a reaction recently proposed as an important oxygen-sensitive source of vasoactive nitric oxide during hypoxic and anoxic stress, with several animal studies suggesting that nitrite may have therapeutic potential. Accumulation of toxic levels of methemoglobin is suppressed by reductase enzymes present within the erythrocyte. Using a novel method of measuring methemoglobin reductase activity in intact erythrocytes, we compared fetal and adult sheep and human blood. After nitrite-induced production of 20% methemoglobin, the blood was equilibrated with carbon monoxide, which effectively stopped further production. Methemoglobin disappearance was first order in nature with specific rate constants (k x 1,000) of 12.9 +/- 1.3 min(-1) for fetal sheep, 5.88 +/- 0.26 min(-1) for adult sheep, 4.27 +/- 0.34 for adult humans, and 3.30 +/- 0.15 for newborn cord blood, all statistically different from one another. The effects of oxygen tensions, pH, hemolysis, and methylene blue are reported. Studies of temperature dependence indicated an activation energy of 8,620 +/- 1,060 calories/mol (2.06 kJ/mol), appreciably higher than would be characteristic of processes limited by passive membrane diffusion. In conclusion, the novel methodology permits absolute quantification of the reduction of nitrite-induced methemoglobin in whole blood.

Nitric oxide and nursing: a review

AIMS AND OBJECTIVES

This paper, therefore, aimed to review published literature in this area of pharmacological exploitation, to look at the therapeutic applications and clinical relevance and, by so doing, provide an accessible source for nurses to gain insight into the role of nitric oxide in the clinical setting.

BACKGROUND

Nitric oxide is a chemical mediator fundamental in the maintenance of adequate tissue perfusion and effective cardiovascular function; a major endogenous regulator of vascular tone. The use of nitrates are well established as pharmacological agents but it is only recently that it has been recognized that they act as a source of nitric oxide. Although widely addressed within the medical literature, there appears to be a paucity of nursing literature that explores either its physiological action, or its relevance to nursing practice.

CONCLUSIONS

This literature review provides an overview of the use of nitric oxide and its implications for nursing practice and patient outcomes.

RELEVANCE TO CLINICAL PRACTICE

Knowledge of nitric oxide and its action is pertinent to nurses across diverse specialities. It helps in understanding the principles of many nitrogen-derived medications which nurses administer to their patients on a daily basis. In terms of oral medication, this is demonstrated by greater insights into the action of nitrates, the appreciation of surprising developments in medications such as sildenafil and the development of new drug opportunities such as nitric oxide-non-steroidal anti-inflammatory drugs. Equally, the use of inhaled nitric oxide therapy in adult and neonatal critical care units appears to be an increasingly valuable source of treatment. A particular research challenge is found in the attempt at nitric oxide inhibition in the management of septic shock. The authors argue that understanding such esoteric areas of therapeutic developments is increasingly to be part of the repertoire of knowledge and skills for nurses in the 21st century.

The role of nitric oxide in treatment of acute lung injury after surgery with extracorporeal circulation

Postoperative acute lung injury (ALI) compromises oxygen transfer across alveolar-capillary membrane with consecutive hypoxia, one of its indicators being reduction of oxygenation index PaO2/FiO2 below 40 kPa (300 mm Hg). Management of ALI includes different procedures like mechanical lung ventilation (MLV), drugs and others. One of the new possibilities for treatment of ALI is nitric oxide (NO) inhalation. The aim of this prospective study was to examine the role of NO inhalation in treatment of ALI. 14 patients with ALI developed immediately after operation with extracorporeal circulation (ECC) were included in the study. Group A (n = 8) inhaled NO and group B (n = 6) did not inhale NO during treatment of ALI. All other therapeutic measures were the same in both groups. The groups were similar in relation to demographic data, type of surgery and duration of ECC. PaO2/FiO2 was calculated before operation (T1), immediately after surgery (T2) and after lung recovery, when the need for MLV stopped (T3). The duration of MLV was also registered. PaO2/FiO2 (kPa) in referent times was in group A 54,9 ? 1,6, 33,8 ? 1,2 and 46,2 ? 0,8 and in group B 52,2 ? 1,1, 33,5 ? 1,5 and 47,3 ? 0,9, respectively. There was a statistically significant decrease of PaO2/FiO2 in T2 and T3 vs T1 in both groups (p < 0,05), while the difference between the groups was not statistically significant. The duration of MLV (h) in group B (28,5 ? 1,6) was statistically significantly shorter than in group A (63,1 ? 8,7) (p < 0,01). According to the results of this study we conclude that NO inhalation during ALI after surgery with ECC significantly reduces the duration of MVL and improves pulmonary recovery .

S-nitrosothiol repletion by an inhaled gas regulates pulmonary function

NO synthases are widely distributed in the lung and are extensively involved in the control of airway and vascular homeostasis. It is recognized, however, that the O(2)-rich environment of the lung may predispose NO toward toxicity. These Janus faces of NO are manifest in recent clinical trials with inhaled NO gas, which has shown therapeutic benefit in some patient populations but increased morbidity in others. In the airways and circulation of humans, most NO bioactivity is packaged in the form of S-nitrosothiols (SNOs), which are relatively resistant to toxic reactions with O(2)/O(2)(-). This finding has led to the proposition that channeling of NO into SNOs may provide a natural defense against lung toxicity. The means to selectively manipulate the SNO pool, however, has not been previously possible. Here we report on a gas, O-nitrosoethanol (ENO), which does not react with O(2) or release NO and which markedly increases the concentration of indigenous species of SNO within airway lining fluid. Inhalation of ENO provided immediate relief from hypoxic pulmonary vasoconstriction without affecting systemic hemodynamics. Further, in a porcine model of lung injury, there was no rebound in cardiopulmonary hemodynamics or fall in oxygenation on stopping the drug (as seen with NO gas), and additionally ENO protected against a decline in cardiac output. Our data suggest that SNOs within the lung serve in matching ventilation to perfusion, and can be manipulated for therapeutic gain. Thus, ENO may be of particular benefit to patients with pulmonary hypertension, hypoxemia, and/or right heart failure, and may offer a new therapeutic approach in disorders such as asthma and cystic fibrosis, where the airways may be depleted of SNOs.

Methemoglobinemia: Toxicity of inhaled nitric oxide therapy

Elevation in methemoglobin is a known toxicity of inhaled nitric oxide (NO) therapy. This article describes two significant episodes of methemoglobinemia. These cases illustrate the probable cause and the treatment strategies for the potential for delivery of high concentrations of NO, resulting in methemoglobinemia with moderate and even low-dose delivered NO. We propose mechanisms for this occurrence and means of prevention.

Left ventricular chamber function during inhaled nitric oxide in patients with dilated cardiomyopathy

Inhaled nitric oxide is a potent and selective pulmonary vasodilator. However, when used in patients with congestive cardiac failure, the decrease in pulmonary vascular resistance is associated with an increase in pulmonary capillary wedge pressure (PCWP). This study examined load-independent indexes of left ventricular chamber function during inhaled nitric oxide in 10 patients with dilated cardiomyopathy (mean ejection fraction, 30.2+/-7.8%, mean +/- SD). Etiology of cardiomyopathy was idiopathic in six and ischemic in four. Pulmonary hemodynamics in seven patients revealed normal resting pulmonary vascular resistance. Chamber function was defined by recording pressure-volume loops at steady state and during inferior vena caval occlusion during inhalation of 20 ppm nitric oxide for 10 min. We found no effect of inhaled nitric oxide on steady-state left ventricular pressures, volumes, contractility (end-systolic elastance or preload recruitable stroke work), contraction duration, or active (tau, dP/dt(min)) or passive (end-diastolic pressure-volume relation) diastolic function. Right heart filling pressures did not change. We therefore conclude that 20 ppm inhaled nitric oxide does not affect left ventricular chamber function in patients with controlled heart failure. Previously described elevations in PCWP during inhaled nitric oxide are most likely due to altered left ventricular loading conditions related to secondary pulmonary hypertension in severe heart failure.

Diarrhoea and nitrogen oxides

It is hypothesized that higher indoor nitrogen dioxide levels cause diarrhoea in infants and that this is the result of a direct action of oxides of nitrogen on the gut. This hypothesis is tested by reviewing the reported association between methaemoglobin and diarrhoea in children and two recent reports on indoor air and diarrhoea in infants. The collection of further empirical data is now needed. Studies which measure indoor levels of nitrogen dioxide could usefully collect data on infants symptoms that are not exclusively respiratory. Similarly, studies which are collecting diary information on children's health symptoms should consider collecting data on indoor air quality with respect to the oxides of nitrogen.

Intravenous almitrine combined with inhaled nitric oxide for acute respiratory distress syndrome. The NO Almitrine Study Group

Inhaled nitric oxide (iNO), a selective pulmonary vasodilator and intravenously administered almitrine, a selective pulmonary vasoconstrictor, have been shown to increase PaO2 in patients with acute respiratory distress syndrome (ARDS). This prospective study was undertaken to assess the cardiopulmonary effects of combining both drugs. In 48 consecutive patients with early ARDS, cardiorespiratory parameters were measured at control, after iNO 5 ppm, after almitrine 4 micrograms. kg-1. min-1, and after the combination of both drugs. In 30 patients, dose response to 2, 4, and 16 micrograms. kg-1. min-1 of almitrine with and without NO was determined. Almitrine and lactate plasma concentrations were measured in 17 patients. Using pure O2, PaO2 increased by 75 +/- 8 mm Hg after iNO, by 101 +/- 12 mm Hg after almitrine 4 micrograms. kg-1. min-1, and by 175 +/- 18 mm Hg after almitrine combined with iNO (p < 0.001). In 63% of the patients, PaO2 increased by more than 100% with the combination of both drugs. Mean pulmonary artery pressure (Ppa) increased by 1.4 +/- 0.2 mm Hg with almitrine 4 micrograms/kg/ min (p < 0.001) and decreased by 3.4 +/- 0.4 mm Hg with iNO and by 1.5 +/- 0.3 mm Hg with the combination (p < 0.001). The maximum increase in PaO2 was obtained at almitrine concentrations <= 4 micrograms. kg-1. min-1, whereas almitrine increased Ppa dose-dependently. Almitrine plasma concentrations also increased dose-dependently and returned to values close to zero after 12 h. In many patients with early ARDS, the combination of iNO 5 ppm and almitrine 4 micrograms. kg-1. min-1 dramatically increases PaO2 without apparent deleterious effect allowing a rapid reduction in inspired fraction of O2. The long-term consequences of this immediate beneficial effect remain to be determined.

Elevated methemoglobin in patients with sepsis

BACKGROUND

It has been reported that large amounts of nitric oxide (NO) are released in patients with sepsis. NO is converted to methemoglobin and nitrate. This study was designed to determine whether blood methemoglobin levels were increased in patients with sepsis or septic shock.

METHODS

Forty-five critically ill patients including 8 with sepsis but without shock, 6 with septic shock and 31 non-septic patients were enrolled in the study. For septic and septic shock patients, blood methemoglobin concentrations were measured during sepsis or septic shock and at the time of recovery or just before the onset of sepsis. For the remaining non-septic patients, methemoglobin concentrations were measured at ICU admission and discharge.

RESULTS

Blood methemoglobin levels in the presence of sepsis or septic shock were significantly (P < 0.05) higher than those in non-septic patients and those at recovery or just before the onset of sepsis in both septic and septic shock patients.

CONCLUSIONS

Blood methemoglobin concentration may be useful as a marker of the onset of sepsis or septic shock.

Induction of chromosome aberrations in peripheral blood lymphocytes after short time inhalation of nitric oxide

INTRODUCTION

inhalation of nitric oxide (INO) leads to vasodilation of pulmonary vasculature in ventilated regions of the lung. The clinical use of INO, although not formally approved as a drug, is widespread. NO may rapidly form nitrogen dioxide (NO2) in an oxygen containing gas mixture. NO2 has been shown to induce chromosome aberrations and mutations in both animal and bacterial test systems. We investigated whether a 2-h exposure to NO would increase frequencies of cells with chromosome aberrations in peripheral blood lymphocytes of human volunteers.

METHODS

10 volunteers were exposed to inhaled NO 40 parts per million (ppm) for 2 h. Pre- and post-exposure blood samples were analysed.

RESULTS

no statistically significant differences (p</=0.05) in chromosome aberrations were observed between pre- and post-exposure samples.

CONCLUSION

no detectable increase of chromosome aberrations in human peripheral blood lymphocytes after 2 h of NO-inhalation 40 ppm was found.

Pulmonary hypertension and selective pulmonary vasodilators in acute lung injury

The pulmonary circulation and the mechanisms which generate pulmonary hypertension are reviewed. The role of these mechanisms in the common pulmonary hypertensive states are analysed, particularly those in acute lung injury. Management options are discussed, with particular emphasis on the use of selective pulmonary vasodilators.

UK guidelines for the use of inhaled nitric oxide therapy in adult ICUs. American-European Consensus Conference on ALI/ARDS

OBJECTIVE

Although unlicensed, inhaled nitric oxide (NO) therapy is now widely used in the United Kingdom. Our aim was to produce guidelines for the clinical application of inhaled NO in adult intensive care practice, based upon the current level of published information.

METHODS

The published data regarding the use of inhaled NO in the acute respiratory distress syndrome and right-sided cardiac failure was presented, analysed and discussed. Recommendations based on these data as well as on current experience in the United Kingdom were formulated.

DESIGN

An expert group comprising intensive care specialists from within the United Kingdom, representatives from the European Society of Intensive Care Medicine and the Society of Critical Care Medicine and individuals from the Departments of Health and Industry related to the field was assembled.

RESULTS

United Kingdom guidelines for the indications, contraindications, dose, delivery, monitoring and scavenging of inhaled NO therapy were produced.

CONCLUSIONS

The need for additional quality research to establish evidence of efficacy and safety was emphasized. The guidelines are designed to act within the context of current practice and knowledge and should be revised as further data emerge.

Improved oxygenation by nitric oxide is enhanced by prior lung reaeration with surfactant, rather than positive end-expiratory pressure, in lung-lavaged rabbits

OBJECTIVES

The inhalation of nitric oxide increases oxygenation by improving the ventilation/perfusion ratios in neonates with respiratory distress syndrome and those ratios in adults with acute respiratory distress syndrome. There is evidence that inhaled nitric oxide is ineffective when the lung remains atelectatic and poorly inflated. This study aimed to enhance nitric oxide delivery by improving lung aeration by means of exogenous surfactant or by increasing positive end-expiratory pressure.

DESIGN

Experimental, comparative study.

SETTING

Research laboratory of a large university.

SUBJECTS

Twenty-eight adult New Zealand white rabbits, weighing 2.7 +/- 0.3 kg.

INTERVENTIONS

Lung injury was induced by repeated whole-lung lavage with saline. The animals were mechanically ventilated with a tidal volume of 10 mL/kg, an FIO2 of 1.0, and a positive end-expiratory pressure of 6 cm H2O. Forty-five minutes after the last lavage, the animals were randomly assigned to five groups. In two groups, lung aeration was first increased either by instillation of a low dose of exogenous surfactant (25 mg/kg) or by increasing the positive end-expiratory pressure to 10 cm H2O, before inhalation of nitric oxide was started. In each of these animals, five different nitric oxide concentrations (4 to 20 parts per million) were inhaled for 30 mins, followed by a 30-min washout period. The other three groups served as controls and received only one treatment protocol: nitric oxide (4 to 20 parts per million), or surfactant (25 mg/kg), or positive end-expiratory pressure (10 cm H2O).

MEASUREMENTS AND MAIN RESULTS

Before and after lavage, blood gases and lung mechanics were measured every 30 mins. Both strategies to increase lung aeration improved PaO2 values from 61 +/- 13 torr (8.1 +/- 1.7 kPa) to 200 to 300 torr (26.6 to 39.9 kPa) in 30 mins. After inhalation of nitric oxide, additional increases of oxygenation were seen only in the animals that received a low dose (25 mg/kg) of surfactant. The control group that inhaled nitric oxide showed no significant change in oxygenation, and four of the six animals did not survive the observation period. In the two groups in which positive end-expiratory pressure was increased to 10 cm H2O, half of the animals developed a pneumothorax during the observation period.

CONCLUSION

These data indicate that inhaled nitric oxide is able to improve arterial oxygenation after alveolar recruitment by means of a low dose of exogenous surfactant, and not by increase of positive end-expiratory pressure from 6 to 10 cm H2O, in lung-lavaged rabbits.

Nitrogen dioxide, the oxides of nitrogen, and infants' health symptoms. ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood

In this cross-sectional postal study, the authors measured nitrogen dioxide levels inside infants' bedrooms and outside their homes. During the 2-wk monitoring period, the authors investigated the association between nitrogen dioxide levels and 20 infant symptoms. The subjects were 1,200 women who had infants aged 3-12 mo. Median levels of indoor and outdoor nitrogen dioxide were 6.8 and 12.6 ppb, respectively. Environmental factors that were associated significantly with indoor levels were gas cooking, cigarette smoking, reported traffic levels, and presence of a kerosene heater; use of a cooker hood was associated negatively with indoor nitrogen dioxide levels. There was no evidence for any short-term significant association between prevalence of respiratory symptoms and nitrogen dioxide levels. Diarrhea, the only symptom associated significantly and positively with indoor nitrogen dioxide levels, had unadjusted and adjusted odds ratios of 1.48 (95% confidence interval: 1.13, 1.95) and 1.38 (1.11, 1.70), respectively. This association is discussed in terms of a proposed mechanism with nitric oxide. No association between a gas cooker in the home and diarrhea was found. The association between diarrhea and nitrogen dioxide level might have been a chance finding; the authors investigated 20 symptoms, and at least 1 was expected to be significant at the .05 level. The finding, however, was similar to that reported in a previous study in which a gas cooker was a proxy for nitrogen dioxide exposure.

Delivery and monitoring of inhaled nitric oxide

Inhaled nitric oxide is rapidly gaining popularity as a selective pulmonary vasodilator in patients with acute lung injury and pulmonary hypertension. The development of nitric oxide as a drug has bypassed the usual regulatory and commercial processes, and as a result clinicians have devised a wide range of delivery and monitoring systems. This review describes these systems, and discusses their advantages, disadvantages and safety. The monitoring of nitric oxide metabolites is also discussed.