Inhaled nitric oxide, almitrine infusion, or their coadministration as a treatment of severe hypoxemic focal lung lesions

Treatment for acute respiratory distress syndrome in adults: A narrative review of phase 2 and 3 trials

INTRODUCTION

Ventilatory management and general supportive care of acute respiratory distress syndrome (ARDS) in the adult population have led to significant clinical improvements, but morbidity and mortality remain high. Pharmacologic strategies acting on the coagulation cascade, inflammation, oxidative stress, and endothelial cell injury have been targeted in the last decade for patients with ARDS, but only a few of these have shown potential benefits with a meaningful clinical response and improved patient outcomes. The lack of availability of specific pharmacologic treatments for ARDS can be attributed to its complex pathophysiology, different risk factors, huge heterogeneity, and difficult classification into specific biological phenotypes and genotypes.

AREAS COVERED

In this narrative review, we briefly discuss the relevance and current advances in pharmacologic treatments for ARDS in adults and the need for the development of new pharmacological strategies.

EXPERT OPINION

Identification of ARDS phenotypes, risk factors, heterogeneity, and pathophysiology may help to design clinical trials personalized according to ARDS-specific features, thus hopefully decreasing the rate of failed clinical pharmacologic trials. This concept is still under clinical investigation and needs further development.

Pathophysiology of Acute Respiratory Distress Syndrome and COVID-19 Lung Injury

The pathophysiology of acute respiratory distress syndrome (ARDS) is marked by inflammation-mediated disruptions in alveolar-capillary permeability, edema formation, reduced alveolar clearance and collapse/derecruitment, reduced compliance, increased pulmonary vascular resistance, and resulting gas exchange abnormalities due to shunting and ventilation-perfusion mismatch. Mechanical ventilation, especially in the setting of regional disease heterogeneity, can propagate ventilator-associated injury patterns including barotrauma/volutrauma and atelectrauma. Lung injury due to the novel coronavirus SARS-CoV-2 resembles other causes of ARDS, though its initial clinical characteristics may include more profound hypoxemia and loss of dyspnea perception with less radiologically-evident lung injury, a pattern not described previously in ARDS.

Almitrine Infusion in Severe Acute Respiratory Syndrome Coronavirus 2-Induced Acute Respiratory Distress Syndrome: A Single-Center Observational Study

OBJECTIVES

Treating acute respiratory failure in patients with coronavirus disease 2019 is challenging due to the lack of knowledge of the underlying pathophysiology. Hypoxemia may be explained in part by the loss of hypoxic pulmonary vasoconstriction. The present study assessed the effect of almitrine, a selective pulmonary vasoconstrictor, on arterial oxygenation in severe acute respiratory syndrome coronavirus 2-induced acute respiratory distress syndrome.

DESIGN

Single-center retrospective observational study.

SETTING

ICU of Lille Teaching Hospital, France, from February 27, 2020, to April 14, 2020.

PATIENTS

Patients with coronavirus disease 2019 pneumonia confirmed by positive reverse transcriptase-polymerase chain reaction for severe acute respiratory syndrome-coronavirus 2 and acute respiratory distress syndrome according to Berlin definition. Data focused on clinicobiological features, ventilator settings, therapeutics, outcomes, and almitrine-related adverse events.

INTERVENTIONS

Almitrine was considered in patients with severe hypoxemia (Pao2/Fio2 ratio < 150 mm Hg) in addition to the recommended therapies, at an hourly IV delivery of 10 μg/kg/min. Comparative blood gases were done before starting almitrine trial and immediately after the end of the infusion. A positive response to almitrine was defined by an increase of Pao2/Fio2 ratio greater than or equal to 20% at the end of the infusion.

MEASUREMENTS AND MAIN RESULTS

A total of 169 patients were enrolled. Thirty-two patients with acute respiratory distress syndrome received an almitrine infusion trial. In most cases, almitrine was infused in combination with inhaled nitric oxide (75%). Twenty-one patients (66%) were responders. The median Pao2/Fio2 ratio improvement was 39% (9-93%) and differs significantly between the responders and nonresponders (67% [39-131%] vs 6% [9-16%], respectively; p < 0.0001). The 28-day mortality rates were 47.6% and 63.6% (p = 0.39) for the responders and nonresponders, respectively. Hemodynamic parameters remained similar before and after the trial, not suggesting acute cor pulmonale.

CONCLUSIONS

Almitrine infusion improved oxygenation in severe acute respiratory syndrome coronavirus 2-induced acute respiratory distress syndrome without adverse effects. In a multistep clinical approach to manage severe hypoxemia in this population, almitrine could be an interesting therapeutic option to counteract the loss of hypoxic pulmonary vasoconstriction and redistribute blood flow away from shunting zones.

Surfactant therapy for acute lung injury and acute respiratory distress syndrome

This article examines exogenous lung surfactant replacement therapy and its usefulness in mitigating clinical acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Surfactant therapy is beneficial in term infants with pneumonia and meconium aspiration lung injury, and in children up to age 21 years with direct pulmonary forms of ALI/ARDS. However, extension of exogenous surfactant therapy to adults with respiratory failure and clinical ALI/ARDS remains a challenge. This article reviews clinical studies of surfactant therapy in pediatric and adult patients with ALI/ARDS, focusing on its potential advantages in patients with direct pulmonary forms of these syndromes.

Lack of alteration of endogenous nitric oxide pathway during prolonged nitric oxide inhalation in intensive care unit patients

OBJECTIVE

To compare hemodynamic and gasometric variables and the plasma concentrations of nitric oxide metabolites (cyclic guanosine monophosphate and nitrate and nitrite), endothelin-1, and renin-angiotensin metabolites before and after the start of nitric oxide inhalation, after prolonged nitric oxide inhalation, and before and after nitric oxide withdrawal.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit, university hospital.

SUBJECTS

Patients with acute lung injury and right ventricular failure.

INTERVENTIONS

Nitric oxide inhalation (10-12 ppm) during a median of 2.9 days (12 hrs to 6.5 days).

MEASUREMENTS AND MAIN RESULTS

The pulmonary vasodilator effects of inhaled nitric oxide improved arterial oxygenation in patients with acute lung injury (p < .05) and reduced right atrial pressure in patients with right ventricular dysfunction (p < .01). These beneficial effects lasted the whole period of prolonged inhaled nitric oxide therapy up to 6.5 days. However, when inhaled nitric oxide was withdrawn, pulmonary vasodilator effects rapidly disappeared, and Pao2/Fio2 ratio markedly deteriorated in all studied patients to return to pre-inhaled nitric oxide levels. Changes in plasma cyclic guanosine monophosphate and nitrate and nitrite paralleled those of pulmonary vasodilatory effects. An immediate increase in plasma cyclic guanosine monophosphate with a slightly delayed increase in plasma nitrate and nitrite was observed at inhaled nitric oxide start with no attenuation during the prolonged inhaled nitric oxide therapy. A marked decrease toward pre-inhaled nitric oxide levels was seen within hours of inhaled nitric oxide withdrawal. In addition, no alteration of plasma endothelin-1 or renin-angiotensin mediators was observed during or after inhaled nitric oxide therapy.

CONCLUSIONS

Our study showed a lack of attenuation in the beneficial effects of inhaled nitric oxide and a lack of alteration of endogenous nitric oxide, endothelin-1, and renin-angiotensin pathways during prolonged nitric oxide inhalation.

Acute Respiratory Distress Syndrome

Acute lung injury is a syndrome diagnosed clinically and is one of the most common causes of respiratory failure seen in the intensive care unit. A consensus definition of this and its more severe form, acute respiratory distress syndrome (ARDS), has allowed for better consistency in determining the epidemiology and facilitates consistent clinical trial design to better find therapies to treat or prevent it. Patients who present with ARDS usually show signs of tachpnea or dyspnea and have underlying conditions that promote inflammatory responses. The pathogenesis involves an inflammatory insult that eventually destroys the pulmonary capillary vasculature as well as alveoli. Pathophysiologically, the patient with ARDS may progress through as many as 3 phases: exudative, proliferative, and fibrotic. Treatment options can be either nonpharmacologic or pharmacologic and are limited. Ventilator strategies such as low-tidal-volume ventilation have improved outcomes in these patients, while corticosteroid use is not as established to provide morbidity or mortality benefit. Other therapies have been investigated with inconclusive or disappointing results for the treatment of this fatal syndrome.

Treatment of Hypoxemia During One-Lung Ventilation Using Intravenous Almitrine

We performed this prospective randomized double-blinded study to assess the ability of almitrine to treat hypoxemia during one-lung ventilation (OLV). Twenty-eight patients were anesthetized with propofol, sufentanil, and atracurium; lung separation was achieved with a double-lumen tube. A transesophageal Doppler probe was inserted to evaluate cardiac index. If SpO(2) was equal to or decreased to <95% during OLV (inspired fraction of oxygen of 0.6), patients were included in the study and received a placebo or almitrine (12 microg x kg(-1) x min(-1) for 10 min followed by 4 microg x kg(-1) x min(-1)) infusion until SpO(2) reached 90% or decreased to <90% (exclusion from the study). Eighteen of the 28 patients were included and received either almitrine (n = 9) or a placebo (n = 9). Treatment was discontinued in 1 patient in the almitrine group and 6 in the placebo group (P < 0.05). Treatment was successful (SpO(2) remaining >or=95% during OLV) in 8 patients in the almitrine group and 1 in the placebo group (P < 0.01). Heart rate, arterial blood pressure, and cardiac index did not change throughout the study, but we could obtain an adequate aortic blood flow signal in only half of the patients. Almitrine could be used to treat hypoxemia during OLV.

IMPLICATIONS

IV almitrine improves oxygenation during one-lung ventilation without hemodynamic modification. Such treatment could be used when conventional ventilatory strategy fails to treat hypoxemia or cannot be used.

[Inhaled nitric oxide in the peroperative period and recovery]

OBJECTIVE

To analyse the current knowledge concerning use of inhaled NO (iNO) in anaesthesia and intensive care.

DATA SOURCE

References were obtained from Medline, recent review articles, the library of the department and personal files.

STUDY SELECTION

All categories of articles on this topic have been selected.

DATA EXTRACTION

Articles have been analysed for history, biochemistry, pharmacology, toxicity and clinical use of iNO.

DATA SYNTHESIS

Nitric oxide (NO) is a potent endothelium-dependent vasodilator. Because of its selective action on pulmonary circulation and the lack of effect on the systemic circulation due to its inactivation by haemoglobin, iNO has been presented as a new therapeutic agent in most diseases with pulmonary hypertension. During heart transplantation or surgical correction of congenital heart disease, iNO decreases pulmonary hypertension and improves altered right ventricular function. Studies included however small numbers of patients. Preliminary pharmacological studies demonstrated that iNO was able to decrease pulmonary hypertension and improve systemic oxygenation in adult respiratory distress syndrome. To date, none of the three multicentric studies performed was able to show any significant effect on duration of mechanical ventilation, morbidity or mortality. Finally, the sole demonstrated indication for iNO which remains is the persistent pulmonary hypertension of the newborn. Two multicentric studies have evidenced an improvement in systemic oxygenation and a reduced need for extracorporeal membrane oxygenation. In these two studies global mortality was however unchanged.

CONCLUSION

Persistent pulmonary hypertension is the sole demonstrated indication for iNO. Inhaled nitric oxide may be efficient in pulmonary hypertension, right ventricular dysfunction and severe hypoxemia. Inhaled nitric oxide must be considered as a rescue therapy or needs to be part of research protocols.

Right ventricular response to high-dose almitrine infusion in patients with severe hypoxemia related to acute respiratory distress syndrome

OBJECTIVE

To evaluate the effects of high-dose almitrine infusion on gas exchange and right ventricular function in patients with severe hypoxemia related to acute respiratory distress syndrome (ARDS).

DESIGN

Prospective study.

SETTING

Medicosurgical intensive care department (ten beds).

PATIENTS

Nine patients with ARDS and severe hypoxemia (PaO2/FIO2 ratio, <150 torr [20 kPa]).

INTERVENTION

High-dose almitrine infusion (16 microg/kg/min for 30 mins).

MEASUREMENTS AND MAIN RESULTS

Gas exchange and hemodynamic parameters were recorded before and after almitrine infusion. Right ventricular function was evaluated by using a fast response thermistor pulmonary artery catheter that allowed measurement of right ventricular ejection fraction and calculation of right ventricular end-diastolic and end-systolic volumes. Almitrine did not significantly alter arterial oxygenation and intrapulmonary shunt. Almitrine increased mean pulmonary arterial pressure (MPAP) from 31 +/- 4 to 33 +/- 4 mm Hg (p < .05), pulmonary vascular resistance index from 353 +/- 63 to 397 +/- 100 dyne x sec/ cm5 x m2 (p < .05), and right ventricular end-systolic volume index from 71 +/- 22 to 77 +/- 21 mL/m2 (p < .05); almitrine decreased right ventricular ejection fraction from 36% +/- 7% to 34% +/- 8% (p < .05). Stroke volume index and cardiac index did not change. The almitrine-induced changes in right ventricular ejection fraction were closely correlated with the baseline MPAP (r2 = .71, p < .01).

CONCLUSION

In patients with severe hypoxemia related to ARDS, high-dose almitrine infusion did not improve arterial oxygenation and impaired the loading conditions of the right ventricle. The decrease in right ventricular ejection fraction induced by almitrine was correlated with the baseline MPAP. Thus, high-dose almitrine infusion may be harmful in ARDS patients with severe hypoxemia and pulmonary hypertension.

Inhaled nitric oxide and acute lung injury

The nitric oxide (NO) field has been one of the most exciting scientific ventures over the past 10 years. Among the researches developed, the use of inhalation of NO gas allowed us to propose this therapy in lung diseases with promising results. Because of its property as a "selective" pulmonary vasodilator and because of its apparent clinical safety, inhaled NO has been proposed in acute lung injury (ALI) to improve severe hypoxemia. In this situation, the abnormal ventilation-perfusion ratio is improved by inhaled NO, limiting arterial hypoxia. The major clinical trials performed in adults, however, have failed to show any benefit on mortality and on mechanical ventilation requirements. Inhaled NO has been shown as an efficient therapy in pediatric ALI, probably because of a lower comorbidity. Because of the inhaled NO uptake by the lung, the extra vascular lung effects might be in the future the most important development in relation with platelet anti-agregant and anti-inflammatory properties.

Nitric oxide and almitrine: the definitive answer for hypoxemia

Hypoxia-induced by acute lung injury results from abnormal ventilation/perfusion ratio distribution towards shunt or low ventilation/perfusion zones. Pharmacological modification of pulmonary blood flow distribution improving ventilation/perfusion ratio should correct hypoxia. The development of inhaled nitric oxide therapy had confirmed this concept, but with a relatively high proportion of 'non responders'. Then development of other drugs used alone or in association with nitric oxide may reinforce the benefit of nitric oxide. This has been tested with almitrine bismesylate, a lipophilic drug that reinforce hypoxic pulmonary vasoconstriction. Using inhaled nitric oxide in combination with almitrine, several studies in adult respiratory distress syndrome or acute lung injury patients have shown spectacular results in term of PaO2 and pulmonary shunt reduction. Moreover, the proportion of responders to this combination seems largely great than those observed for each drug alone. In conclusion, pulmonary blood flow manipulation improving ventilation/perfusion mismatching is one of the major strategies to correct severe hypoxia.