Response to nitric oxide inhalation in early acute lung injury

Inhaled nitric oxide and inhaled prostacyclin in acute respiratory distress syndrome: what is the evidence?

The mortality for acute respiratory distress syndrome remains unacceptably high. Two vasodilators, inhaled prostacyclin and inhaled nitric oxide, are reviewed in this article. Knowledge of inhaled prostacyclin has grown substantially in the past 30 years, but less research exists about its utility in acute respiratory distress syndrome. Inhaled prostacyclin and other prostaglandin derivatives are used in acute respiratory distress syndrome with increasing frequency. Currently, only randomized controlled trials exist for inhaled nitric oxide in acute respiratory distress syndrome patients. Randomized controlled trials with consistent dosing methods are needed for both vasodilators to better define their role in the treatment of acute respiratory distress syndrome.

Successful treatment of acute respiratory distress syndrome after hysterectomy for life-threatening atonic bleeding by inhaled nitric oxide

We report a case of a 33-year-old female who developed severe acute respiratory distress syndrome (ARDS) after emergency hysterectomy for life-threatening atonic bleeding. A marked decline in pulmonary oxygenation was observed during the surgery, which led to a diagnosis of ARDS. Following admission to the intensive care unit, hypoxia became critical, with a PaO(2)/F(I)O(2) value of 52 even after recruitment maneuvers. Inhaled nitric oxide (NO 10 ppm) was administered to the patient as a rescue treatment, resulting in a gradual but dramatic improvement in pulmonary oxygenation. Although several randomized trials have failed to confirm the beneficial effects of NO on morbidity in patients with ARDS, NO administration is worth consideration as treatment prior to invasive treatments, such as extracorporeal membrane oxygenation, for patients with acute lung injury/ARDS.

The initial response to inhaled nitric oxide treatment for intensive care unit patients with acute respiratory distress syndrome

BACKGROUND

Inhaled nitric oxide (INO) can improve hypoxemia and reduce pulmonary hypertension, but there is a wide range of response to INO.

OBJECTIVES

The aim of this study was to evaluate the effect of different INO concentrations in acute respiratory distress syndrome (ARDS) patients.

METHODS

Thirty-two adult ARDS patients who were supported by mechanical ventilator were included. INO was given at a concentration of 1, 5, 10, 20 and 40 ppm, sequentially. Arterial blood gas and mean pulmonary artery pressure (MPAP) were measured 30 min after INO concentrations changed.

RESULTS

There was a significant increase in PaO(2)/FiO(2) (p < 0.0001) and a decrease in pulmonary vascular resistance index and MPAP (p < 0.0001) after INO use. INO concentrations required for improving oxygenation were in the range of 1-20 ppm, whereas concentrations required for decreasing MPAP were in the range of 1-40 ppm. PaO(2)/FiO(2) worsened when the INO dose was adjusted above 20 ppm. Sixty-nine percent of ARDS patients were responders; 31% of them were nonresponders. Among responders, 64% of patients responded at 1 ppm, 36% at 5 ppm.

CONCLUSIONS

The optimal doses for improving oxygenation and reducing PAP differ. The maximum PaO(2)/FiO(2) was observed at a lower INO concentration than that required for the minimal MPAP. There was no further improvement in PaO(2)/FiO(2) when the INO dose was adjusted above 20 ppm. Higher doses of INO treatment worsened oxygenation.

Selective pulmonary vasodilation in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by a marked maldistribution of pulmonary perfusion in favor of nonventilated, atelectatic areas of the lungs, and it is the main cause of pulmonary right-to-left shunting and hypoxemia. Therapeutic interventions to selectively influence pulmonary perfusion in ARDS became feasible with the introduction of inhaled nitric oxide, which provided a means not only to reduce pulmonary hypertension, but also to improve matching of ventilation to perfusion and, thus, hypoxemia. Clinical studies in ARDS subsequently demonstrated that the combination of inhaled nitric oxide with other interventions, such as positive end-expiratory pressure and prone positioning, yielded beneficial and additive effects on arterial oxygenation. Although the available randomized, controlled trials of this novel concept have so far failed to show an improved outcome in ARDS, inhaled nitric oxide is a clinically valuable option for the treatment of severe refractory hypoxemia in ARDS, and largely promoted the concept of selective pulmonary vasodilation in intensive care practice. Currently, aerosolization of various vasodilators, in particular prostaglandins, is under evaluation in models of acute lung injury and human ARDS. Ongoing research aims to augment the effectiveness of vasodilators with specific inhibitors of phosphodiesterases or by combination with intravenous vasoconstrictors. Consequently, several alternative ways to selectively modulate pulmonary vascular tone in patients with ARDS may be available in the near future. Cost-benefit analysis of these therapeutic options will largely determine their future perspective.

Dose-response characteristics during long-term inhalation of nitric oxide in patients with severe acute respiratory distress syndrome: a prospective, randomized, controlled study

Inhaled nitric oxide (NO) improves systemic oxygenation (PaO2/FIO2) in adult patients with acute respiratory distress syndrome (ARDS). However, individual response varies, and previous trials demonstrated no outcome benefit. This prospective, randomized study in 40 ARDS patients analyzed dose-response (DR) characteristics during long-term inhaled NO. Patients were randomized for conventional therapy (control) or continuous treatment with 10 parts per million (ppm) inhaled NO until weaning was initiated. We measured DR curves of PaO2/FIO2 versus the inhaled NO dose at regular intervals. Before treatment (Day 0), peak improvement in PaO2/FIO2 was achieved at 10 ppm for both control and NO-treated patients. After 4 days, the DR curve of the NO-treated patients was left shifted with a peak response at 1 ppm. At higher doses (10 and 100 ppm), oxygenation deteriorated, and the response to inhaled NO disappeared in several patients. This effect was not observed in the control group. There was no effect of inhaled NO on duration of mechanical ventilation or stay at the intensive care unit. In conclusion, long-term inhaled NO with constant doses of 10 ppm leads to enhanced sensitivity after several days and does do not allow reduction of ventilation parameters. Hence, previous trials on therapy with inhaled NO in ARDS should be carefully interpreted, as they used constant NO concentrations, which may have become overdoses leading to deterioration of oxygenation after several days.

[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.

Inhaled nitric oxide in ARDS

The role of nitric oxide (NO) in numerous physiologic systems only recently has been discovered. When used as a gas, inhaled NO (iNO) has many unique properties that cause immediate improvements in pulmonary hemodynamics and oxygenation. Acute benefits in physiologic parameters have been demonstrated in numerous studies of iNO in acute respiratory distress syndrome (ARDS), but recent randomized controlled trials have failed to show improvement in outcome. The addition of other treatments that prolong or enhance the affect of iNO or its use with other ventilator modalities such as prone positioning or high-frequency ventilation offer hope that iNO may be beneficial in select groups of patients.

Acute lung injury: pathophysiology, assessment and current therapy

Acute respiratory distress syndrome (ARDS) is a clinically defined entity describing the severity of diffuse alveolar injury caused by direct or indirect injury to the lung. Pathophysiology, clinical course and outcome of ARDS depend on the underlying cause, the severity of the disease and co-morbidities. Pulmonary function tests show restrictive lung disease, which is characterised by a reduction in lung compliance and functional residual capacity, resulting in marked ventilation-perfusion inequality. Current ventilator strategies aim to minimise ventilator-induced lung injury by targeting mechanical ventilation between the lower and upper inflection point of the pressure volume curve. This includes recruitment manoeuvres and the use of high PEEP to open the atelectatic lung and the use of permissive hypercapnia and the limitation of peak inspiratory pressure below 35 cm H2O to avoid overinflation. The clinical benefit of newer modes of ventilatory support such as inverse ratio ventilation, high frequency oscillatory ventilation, surfactant replacement, prone positioning and inhaled nitric oxide has yet to be determined in children.

Short-term effect of inhaled nitric oxide and prone positioning on gas exchange in patients with severe acute respiratory distress syndrome

OBJECTIVE

To compare the short-term effects of inhaled nitric oxide (NO) and prone positioning in improving oxygenation in acute respiratory distress syndrome (ARDS).

METHODS

Charts of consecutive ARDS patients (lung injury score >2) during a 2-yr period, tested for both inhaled NO and prone positioning efficacy were retrospectively reviewed. Variations in the Pao2/Fio2 ratio induced by inhaled NO and prone positioning were evaluated.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven patients (age, 42+/-17 yrs) were included. Simplified Acute Physiology Score II was 45+/-14. Mortality rate in the intensive care unit was 63%. The causes of ARDS were pneumonia (n = 14), extra-lung infection (n = 5), and noninfectious systemic inflammatory response syndrome (n = 8). Lung injury score was 2.7+/-0.3. At baseline, before the initiation of inhaled NO, the Pao2/Fio2 ratio was 97+/-46 torr and before prone positioning, 92+/-26 torr. Variations in the Pao2/Fio2 ratio were lower at start of NO therapy (11+/-4 ppm) than that observed at prone positioning initiation (23+/-31 vs. 62+/-78 torr, p<.05). An increase in variations in the Pao2/Fio2 ratio of >15 torr was associated with prone positioning in 16 patients (59%) and with NO inhalation in 13 patients (48%) (not significant). An increase in variations in the Pao2/Fio2 ratio of >15 torr was associated with both techniques in only six patients (22%). There was no correlation between the response to prone positioning and the response to inhaled NO (r2 = .005; p = .73).

CONCLUSIONS

Prone positioning improves hypoxemia significantly better than does inhaled NO. The response to one technique is not predictive of the response to the other technique.

Low-dose inhaled nitric oxide improves the oxygenation and ventilation of infants and children with acute, hypoxemic respiratory failure

OBJECTIVE

To describe the effects of inhaled nitric oxide on oxygenation and ventilation in patients with acute, hypoxic respiratory failure and to characterize those who respond to low doses with a significant improvement in PaO2.

DESIGN

Prospective dose response trial of inhaled nitric oxide. Patients who demonstrated a > or =15% improvement in PaO2 were randomized to receive conventional mechanical ventilation with or without prolonged inhaled nitric oxide.

SETTING

Pediatric intensive care unit of a tertiary care children's hospital serving as a regional referral center for respiratory failure.

PATIENTS

Pediatric patients with an acute parenchymal lung disease requiring mechanical ventilation, an F(IO2) of > or =0.5, a positive end-expiratory pressure of > or =7 cm H2O, and whose PaO2/FIO2 ratio was < or =160.

INTERVENTIONS

PaO2, PaCO2, pH, heart rate, blood pressure, and methemoglobin were recorded at baseline and after inhaling 1, 5, 10, and 20 ppm of nitric oxide. Peak expiratory flow rate and mean airway resistance were measured while subjects received 0 and 20 ppm of inhaled nitric oxide. Patients were followed up until extubation or death.

MEASUREMENTS AND MAIN RESULTS

Twenty-six patients (median age, 2.6 yrs [range, 1 mo-18.2 yrs]) were enrolled in the study. PaO2 increased (p< .001) and Pa(CO2) fell (p< .0001) from baseline with the administration of inhaled nitric oxide. There was no statistical difference among 1, 5, 10, and 20 ppm with regard to effects on oxygenation. Sixteen patients (62%) responded to inhaled nitric oxide with a > or =15% improvement in PaO2; 14 of these responses occurred at a dose of 1 or 5 ppm. Response to inhaled nitric oxide was not associated with age, length of intubation, presence of primary lung disease, chest radiograph, or illness severity. Among patients weighing < or =20 kg, responders showed a greater fall in mean airway resistance (p < .05) than nonresponders. Mortality was not influenced by prolonged inhaled nitric oxide when analyzed by intention to treat. Patients receiving prolonged inhaled nitric oxide at doses of < or =20 ppm maintained methemoglobin levels of <3.0% and circuit concentrations of NO2 of <1 ppm.

CONCLUSIONS

Inhaled nitric oxide at doses of < or =5 ppm improves the oxygenation and (to a lesser extent) ventilation of most children with acute, hypoxic respiratory failure. The unpredictable response of patients necessitates individualized dosing of inhaled nitric oxide, starting at concentrations of < or =1 ppm. Inhaled nitric oxide at < or =20 ppm may exert a small salutary effect on bronchial tone. The benefits of prolonged inhaled nitric oxide remain unknown.

Vasodilators in mechanical ventilation

Vasodilators that affect the pulmonary vasculature are appealing adjuncts in many cardiopulmonary conditions that require mechanical ventilation such as ARDS, COPD, PPHN, and cardiothoracic surgery. The adverse systemic effects of parenteral PGE1 and parenteral prostacyclin limit their usefulness in critically ill patients. Liposomal PGE1 has few systemic effects, but thus far has not resulted in a significant clinical benefit in patients with ARDS. Inhaled NO and aerosolized prostacyclin offer the advantage of selective pulmonary vasodilation with minimal systemic effects. Both agents decrease PAP and in many clinical situations improve oxygenation; however, the physiologic effects of inhaled NO and aerosolized prostacyclin have not convincingly led to improved clinical outcomes. Currently, use of vasodilators in mechanically ventilated patients remains investigational.

Efficacy of inhaled nitric oxide in children with ARDS

STUDY OBJECTIVE

Data concerning inhaled nitric oxide (iNO) on pediatric ARDS is rare. We investigated the effects of iNO on pediatric ARDS in order to examine the ability to predict a response to iNO, the optimal concentration of iNO, the effects of < or = 1 ppm nitric oxide (NO), and the effect of iNO on PaCO2.

SETTING

ICU at Kumamoto (Japan) University Hospital.

PATIENTS AND INTERVENTIONS

Seven children with ARDS. The initial responses to 16 ppm NO and the dose-response effects of 0.13 to 16 ppm NO were assessed.

MEASUREMENTS AND RESULTS

Sixteen ppm of iNO improved oxygenation in all seven children. The use of iNO significantly increased the ratio of arterial oxygen tension to the fraction of inspired oxygen (PaO2/FIO2). A correlation between the NO-induced increase in PaO2/FIO2 and the baseline PaO2/FIO2 was observed (r=0.93, p<0.01). Dose-response tests showed that the optimal concentration of iNO was < or = 4 ppm, improvements in PaO2/FIO2 could be observed with concentrations of < or = 1 ppm NO, and iNO induced a slight decrease in PaCO2.

CONCLUSIONS

In children with ARDS, iNO frequently improves oxygenation and induces a slight decrease in PaCO2, with the baseline PaO2/FIO2 functioning as a predictor of all NO response. Improvements of PaO2 and PaCO2 were observed with concentrations of iNO of < or = 1 ppm, a level in which the risk of a toxic reaction in children is minimal. Effects on outcome need verification in larger controlled trials.

The efficacy of inhaled nitric oxide in the treatment of acute respiratory distress syndrome. An evidence-based medicine approach

Nitric oxide is an endothelial relaxing factor. When given as an inhalational agent in the acute respiratory distress syndrome (ARDS), it vasodilates well ventilated areas of lung and improves oxygenation. Nitric oxide is a highly reactive molecule with myriad biologic effects, both potentially beneficial and toxic; its use as an inhalational agent in ARDS is experimental. This article reviews the available studies of inhaled nitric oxide.

Pulmonary function in adult survivors of severe acute lung injury treated with inhaled nitric oxide

BACKGROUND

Following an episode of acute respiratory distress syndrome (ARDS), some degree of measurable pulmonary impairment may be anticipated. ARDS is thought to be the more severe form of acute lung injury (ALI) and a recently proposed addition to conventional therapy in ALI/ARDS is inhaled nitric oxide (INO). We carried out a non-randomised follow-up study with pulmonary function tests on survivors of severe ALI/ARDS treated with INO.

METHODS

Sixteen previously healthy pulmonary patients, survivors of severe ALI/ARDS, were evaluated with pulmonary function tests >8 months after the acute event. The tests included static and dynamic spirometry, diffusion capacity for carbon monoxide (DLCO), blood gas analysis and evaluation of a chest radiograph.

RESULTS

The most common abnormality seen was a low DLCO in 69% of the patients. Abnormally low values were seen in forced vital capacity in 31%, in forced expiratory volume in 1 s in 13%, and in residual volume and total lung capacity in 6%. Blood gas data were within normal limits in 15/16 patients. All chest radiographs showed resolution of the interstitial and alveolar changes present during the acute event.

CONCLUSION

In this non-randomised follow-up study we conclude that a degree of measurable pulmonary impairment after INO treatment in severe ALI/ARDS was common, but did not differ markedly from other published studies on pulmonary function in similar patient material. No late unexpected major abnormalities due to the inhaled nitric oxide treatment could be identified in these survivors.

Pharmacologic strategies in acute respiratory distress syndrome

Treatment of the acute respiratory distress syndrome includes both supportive measures and correction of the underlying cause. Various pharmacological interventions have been proposed to limit the severity of lung injury and enhance the healing process, including exogenous surfactant, inhaled vasodilators (mainly nitric oxide), corticosteroids, prostaglandin E1, antioxidants (N-acetylcysteine), ketoconazole and other substances. Some of these interventions are administered via the airways, for example inhaled nitric oxide or liquid ventilation with perfluorocarbons. Some have beneficial effects on surrogate end-points such as pulmonary gas exchange. However, in large prospective trials none of these pharmacological approaches have resulted in significantly improved survival in acute respiratory distress syndrome patients.

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.

Uptake of inhaled nitric oxide in acute lung injury

BACKGROUND

Despite the widespread use of inhaled nitric oxide (NO), little is known of its pulmonary uptake in patients with acute respiratory failure.

METHODS

Fourteen patients with acute lung injury (ALI) and ongoing NO therapy were studied. Three doses of NO (5, 10 and 40 ppm) were given for 20 min and at each dose level the following parameters were recorded: minute ventilation, inspiratory NO conc., mixed expired NO conc., end-tidal NO conc., mixed expired CO2 conc., end-tidal CO2 conc, and arterial CO2 tension. Total uptake was calculated and correlated to the total amount of NO inhaled, the amount of NO administered to the alveolar space, and the amount of NO administered to the perfused alveolar space.

RESULTS

About 35% of the total amount of NO delivered is taken up by the lungs, 70% of NO administered to the alveolar space is taken up, and 95-100% of the NO administered to perfused alveolar space is taken up. The size of the alveolar dead space varied between 10 and 60% of the alveolar space. At 40 ppm of inhaled NO there was no difference between inspired and mixed expired NO2 concentration, indicating that there is no significant NO2 formation taking place in the lungs during NO inhalation at the concentrations studied.

CONCLUSIONS

Practically all NO administered to the perfused alveolar space is taken up. The total uptake differs from that of healthy persons probably because of differences in the alveolar dead space.

Inhaled nitric oxide in acute respiratory distress syndrome with and without septic shock requiring norepinephrine administration: a dose-response study

BACKGROUND: The aim of this prospective study was to assess whether the presence of septic shock could influence the dose response to inhaled nitric oxide (NO) in NO-responding patients with adult respiratory distress syndrome (ARDS). RESULTS: Eight patients with ARDS and without septic shock (PaO2 = 95 +/- 16 mmHg, PEEP = 0, FiO2 = 1.0), and eight patients with ARDS and septic shock (PaO2 = 88 +/- 11 mmHg, PEEP = 0, FiO2 = 1.0) receiving exclusively norepinephrine were studied. All responded to 15 ppm inhaled NO with an increase in PaO2 of at least 40 mmHg, at FiO2 1.0 and PEEP 10 cmH2O. Inspiratory intratracheal NO concentrations were recorded continuously using a fast response time chemiluminescence apparatus. Seven inspiratory NO concentrations were randomly administered: 0.15, 0.45, 1.5, 4.5, 15, 45 and 150 ppm. In both groups, NO induced a dose-dependent decrease in mean pulmonary artery pressure (MPAP), pulmonary vascular resistance index (PVRI), and venous admixture (QVA/QT), and a dose-dependent increase in PaO2/FiO2 (P </= 0.012). Dose-response of MPAP and PVRI were similar in both groups with a plateau effect at 4.5 ppm. Dose-response of PaO2/FiO2 was influenced by the presence of septic shock. No plateau effect was observed in patients with septic shock and PaO2/FiO2 increased by 173 +/- 37% at 150 ppm. In patients without septic shock, an 82 +/- 26% increase in PaO2/FiO2was observed with a plateau effect obtained at 15 ppm. In both groups, dose-response curves demonstrated a marked interindividual variability and in five patients pulmonary vascular effect and improvement in arterial oxygenation were dissociated. CONCLUSION: For similar NOinduced decreases in MPAP and PVRI in both groups, the increase in arterial oxygenation was more marked in patients with septic shock.