Inhaled nitric oxide in children with severe lung disease: results of acute and prolonged therapy with two concentrations

Inhaled Nitric Oxide Treatment for Aneurysmal SAH Patients With Delayed Cerebral Ischemia

Background

We demonstrated experimentally that inhaled nitric oxide (iNO) dilates hypoperfused arterioles, increases tissue perfusion, and improves neurological outcome following subarachnoid hemorrhage (SAH) in mice. We performed a prospective pilot study to evaluate iNO in patients with delayed cerebral ischemia after SAH.

Methods

SAH patients with delayed cerebral ischemia and hypoperfusion despite conservative treatment were included. iNO was administered at a maximum dose of 40 ppm. The response to iNO was considered positive if: cerebral artery diameter increased by 10% in digital subtraction angiography (DSA), or tissue oxygen partial pressure (PtiO₂) increased by > 5 mmHg, or transcranial doppler (TCD) values decreased more than 30 cm/sec, or mean transit time (MTT) decreased below 6.5 secs in CT perfusion (CTP). Patient outcome was assessed at 6 months with the modified Rankin Scale (mRS).

Results

Seven patients were enrolled between February 2013 and September 2016. Median duration of iNO administration was 23 h. The primary endpoint was reached in all patients (five out of 17 DSA examinations, 19 out of 29 PtiO₂ time points, nine out of 26 TCD examinations, three out of five CTP examinations). No adverse events necessitating the cessation of iNO were observed. At 6 months, three patients presented with a mRS score of 0, one patient each with an mRS score of 2 and 3, and two patients had died.

Conclusion

Administration of iNO in SAH patients is safe. These results call for a larger prospective evaluation.

Efficacy study of pulmonary surfactant combined with assisted ventilation for acute respiratory distress syndrome management of term neonates

The clinical efficacy of pulmonary surfactant (PS) combined with assisted ventilation was assessed for acute respiratory distress syndrome (RDS) management of term neonates. The total sample size was of 60 subjects. Group I: Experimental group, 30 cases were treated with standard of care with tracheal intubation, mechanical ventilation and PS (100-200 mg/kg). In case of hypoxaemia present even after 12 h standard of care was administered again, up to 4 times. Group II: Control group, 30 cases treated with conventional tracheal intubation and mechanical ventilation. PaO₂, PaO₂/FiO₂ and X-ray were compared between the two groups after 24-h treatment. Analysis of the results indicate that the PS combined with ventilation can improve the clinical symptoms and blood gas analysis index of ARDS neonates. The PaO₂, PaCO₂, PaO₂/FiO₂ levels were improved in the two groups after treatment, the improvement effect of the experimental group was better than in the control group, P<0.05. The surfactant therapy is proved to be effective as preventive and rescue treatment of NRDS in term neonates. This result is supported by conventional concepts and clinical confirmation in patients with lung injury-associated respiratory failure.

Pediatric Acute Respiratory Distress Syndrome: Fibrosis versus Repair

Clinical and basic experimental approaches to pediatric acute lung injury (ALI), including acute respiratory distress syndrome (ARDS), have historically focused on acute care and management of the patient. Additional efforts have focused on the etiology of pediatric ALI and ARDS, clinically defined as diffuse, bilateral diseases of the lung that compromise function leading to severe hypoxemia within 7 days of defined insult. Insults can include ancillary events related to prematurity, can follow trauma and/or transfusion, or can present as sequelae of pulmonary infections and cardiovascular disease and/or injury. Pediatric ALI/ARDS remains one of the leading causes of infant and childhood morbidity and mortality, particularly in the developing world. Though incidence is relatively low, ranging from 2.9 to 9.5 cases/100,000 patients/year, mortality remains high, approaching 35% in some studies. However, this is a significant decrease from the historical mortality rate of over 50%. Several decades of advances in acute management and treatment, as well as better understanding of approaches to ventilation, oxygenation, and surfactant regulation have contributed to improvements in patient recovery. As such, there is a burgeoning interest in the long-term impact of pediatric ALI/ARDS. Chronic pulmonary deficiencies in survivors appear to be caused by inappropriate injury repair, with fibrosis and predisposition to emphysema arising as irreversible secondary events that can severely compromise pulmonary development and function, as well as the overall health of the patient. In this chapter, the long-term effectiveness of current treatments will be examined, as will the potential efficacy of novel, acute, and long-term therapies that support repair and delay or even impede the onset of secondary events, including fibrosis.

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.

High-frequency oscillatory ventilation associated with inhaled nitric oxide compared to pressure-controlled assist/control ventilation and inhaled nitric oxide in children: Randomized, non-blinded, crossover study

PURPOSE

To compare the acute oxygenation effects of high-frequency oscillatory ventilation (HFOV) plus inhaled nitric oxide (iNO) with pressure-controlled assist/control ventilation (PCACV) plus iNO in acute hypoxemic respiratory failure (AHRF) children.

METHODS

Children with AHRF, aged between 1 month and 14 years under PCACV with PEEP ≥ 10 cmH(2) O were randomly assigned to PCACV (PCVG, n = 14) or HFOV (HFVG, n = 14) in a crossover design. Oxygenation indexes and hemodynamic variables were recorded at enrollment (Tind), 1 hr after PCACV start (T0) and then every 4 hr (T4h, etc.).

RESULTS

PO(2)/FiO(2) significantly increased after 4 hr compared to enrollment in both groups [(PCVG-Tind: 111.95 ± 37 < T4h: 143.88 ± 47.5 mmHg, P < 0.05; HFVG-Tind: 123.76 ± 33 < T4h: 194.61 ± 62.42 mmHg, P < 0.05)] without any statistical differences between groups. At T8h, PO(2)/FiO(2) was greater for HFVG compared with PCVG (HFVG: 227.9 ± 80.7 > PCVG: 171.21 ± 52.9 mmHg, P < 0.05). FiO(2) could be significantly reduced after 4 hr for HFVG (HFVG-T4h: 0.53 ± 0.09 < Tind: 0.64 ± 0.2; P < 0.05) but only after 8 hr for PCVG. Comparing groups at T8h, it was observed that FiO(2) decrease was greater for HFVG (HFVG: 0.47 ± 0.06 < PCVG: 0.58 ± 0.1; P < 0.05).

CONCLUSION

Both ventilatory techniques with iNO improve oxygenation. HFOV causes earlier FiO(2) reduction and increased PO(2)/FiO(2) ratio compared to PCACV at 8 hr. However, at the end of the protocol, there was no significant difference and no clinical improvement derived from the application of both ventilatory strategies with iNO. It is not possible to say what would have happened if a different conventional ventilatory mode and a fully protective ventilatory strategy had been used, given the fact that our study is non-blind, and that a limited number of patients were included in each group.

Mean airway pressure and response to inhaled nitric oxide in neonatal and pediatric patients

Inhaled nitric oxide (iNO) can improve oxygenation and ventilation-perfusion (V/Q) matching by reduction of shunt (Qs/Qt) in patients with hypoxemic lung disease. Because the improvement in V/Q matching must occur by redistribution of pulmonary blood flow, and because high airway pressure (Paw) increases physiologic dead space (Vd/Vt), we hypothesized that high Paw may limit the improvement in V/Q matching during iNO treatment. iNO 0-50 ppm was administered during mechanical ventilation. Mechanical ventilator settings were at the discretion of the attending physician. Qs/Qt and Vd/Vt were derived from a tripartite lung model with correction for shunt-induced dead space. Data from 62 patients during 153 trials were analyzed for effects of Paw and iNO on Qs/Qt and Vd/Vt. Baseline Qs/Qt was slightly increased at Paw 16-23 cmH2O (p < 0.05), while Vd/Vt increased progressively with higher Paw (p < 0.002). Therapy with iNO significantly reduced Qs/Qt (p < 0.001) at all levels of mean Paw, reaching a maximum reduction at 16-23 cmH2O (p < 0.05), such that Qs/Qt during iNO treatment was similar at all levels of Paw. During iNO treatment, a reduction in Vd/Vt occurred only at Paw of 8-15 cmH2O (p < 0.05), and the positive relationship between Vd/Vt and Paw was maintained. These differential effects on Qs/Qt and Vd/Vt suggest that both high and low Paw may limit improvement in gas exchange with iNO. Analysis of gas exchange using this corrected tripartite lung model may help optimize ventilatory strategies during iNO therapy.

Acute and sustained effects of early administration of inhaled nitric oxide to children with acute respiratory distress syndrome

OBJECTIVE

To determine the acute and sustained effects of early inhaled nitric oxide on some oxygenation indexes and ventilator settings and to compare inhaled nitric oxide administration and conventional therapy on mortality rate, length of stay in intensive care, and duration of mechanical ventilation in children with acute respiratory distress syndrome.

DESIGN

Observational study.

SETTING

Pediatric intensive care unit at a university-affiliated hospital.

PATIENTS

Children with acute respiratory distress syndrome, aged between 1 month and 12 yrs.

INTERVENTIONS

Two groups were studied: an inhaled nitric oxide group (iNOG, n = 18) composed of patients prospectively enrolled from November 2000 to November 2002, and a conventional therapy group (CTG, n = 21) consisting of historical control patients admitted from August 1998 to August 2000.

MEASUREMENTS AND MAIN RESULTS

Therapy with inhaled nitric oxide was introduced as early as 1.5 hrs after acute respiratory distress syndrome diagnosis with acute improvements in Pao(2)/Fio(2) ratio (83.7%) and oxygenation index (46.7%). Study groups were of similar ages, gender, primary diagnoses, pediatric risk of mortality score, and mean airway pressure. Pao(2)/Fio(2) ratio was lower (CTG, 116.9 +/- 34.5; iNOG, 62.5 +/- 12.8, p <.0001) and oxygenation index higher (CTG, 15.2 [range, 7.2-32.2]; iNOG, 24.3 [range, 16.3-70.4], p <.0001) in the iNOG. Prolonged treatment was associated with improved oxygenation, so that Fio(2) and peak inspiratory pressure could be quickly and significantly reduced. Mortality rate for inhaled nitric oxide-patients was lower (CTG, ten of 21, 47.6%; iNOG, three of 18, 16.6%, p <.001). There was no difference in intensive care stay (CTG, 10 days [range, 2-49]; iNOG, 12 [range, 6-26], p >.05) or duration of mechanical ventilation (TCG, 9 days [range, 2-47]; iNOG, 10 [range, 4-25], p >.05).

CONCLUSIONS

Early treatment with inhaled nitric oxide causes acute and sustained improvement in oxygenation, with earlier reduction of ventilator settings, which might contribute to reduce the mortality rate in children with acute respiratory distress syndrome. Length of stay in intensive care and duration of mechanical ventilation are not changed. Prospective trials of inhaled nitric oxide early in the setting of acute lung injury in children are needed.

Inhaled nitric oxide for acute hypoxic respiratory failure in children and adults: a meta-analysis

We systematically reviewed randomized controlled trials examining inhaled nitric oxide (INO) for the treatment of acute respiratory distress syndrome or acute lung injury in children and adults. Qualitative assessments of identified trials were made, and metaanalyses were performed according to Cochrane methodology. Five randomized controlled trials (n = 535) met entry criteria. One study demonstrated significant improvement in oxygenation in the first 4 days of treatment, with no difference after this. There was no difference in ventilator-free days between treatment and placebo groups, and no specific dose of INO was more advantageous than any other. INO had no effect on mortality in trials without crossover of treatment failures to open-label INO (relative risk, 0.98; 95% confidence interval, 0.66-1.44). Other clinical indicators of effectiveness, such as duration of hospital and intensive care stay, were inconsistently reported. Lack of data prevented assessment of all outcomes. If further trials assessing INO in acute respiratory distress syndrome or acute lung injury are to proceed, they should be stratified for primary etiology, incorporate other modalities that may affect outcome, and evaluate clinically relevant outcomes before any benefit of INO can be excluded.

The effect of inhaled nitric oxide and oxygen on the hydroxylation of salicylate in rat lungs

Inhaled nitric oxide (iNO) is used as a selective pulmonary vasodilator, and often under conditions when a high fraction of inspired oxygen is indicated. However, little is known about the potential toxicity of iNO therapy with or without concomitant oxygen therapy. NO can combine with superoxide (O2-) to form peroxynitrite (ONOO-), which can in turn decompose to form hydroxyl radical (OH.). Both OH. and ONOO- are involved in various forms of lung injury. To begin evaluation of the effect of iNO under either normoxic or hyperoxic conditions on OH. and/or ONOO- formation, rats were exposed for 58 h to either 21% O2, 21% O2 + 10 parts per million (ppm) NO, 21% O2 + 100 ppm NO, 50% O2, 90% O2, 90% O2 + 10 ppm NO, or 90% O2 + 100 ppm NO. We used a salicylate hydroxylation assay to detect the effects of these exposures on lung OH. and/or ONOO- formation measured as the appearance of 2,3-dihydroxybenzoic acid (2,3-DHBA). Exposure to 90% O2 and 90% O2 + 100 ppm NO resulted in significantly (p < 0.05) greater lung wet weight (1.99 +/- 0.14 g and 3.14 +/- 0.30 g, respectively) compared with 21% O2 (1.23 +/- 0.01 g). Exposure to 21% O2 + 100 ppm NO led to 2.5 times the control (21% O2 alone) 2,3 DHBA formation (p < 0.05) and exposure to 90% O2 led to 2.4 times the control 2,3-DHBA formation (p < 0.05). However, with exposure to both 90% O2 and 100 ppm NO, the 2,3-DHBA formation was no greater than the control condition (21% O2). Thus, these results indicate that, individually, both the hyperoxia and the 100 ppm NO led to greater salicylate hydroxylation, but that the combination of hyperoxia and 100 ppm NO led to less salicylate hydroxylation than either did individually. The production of OH. and/or ONOO- in the lung during iNO therapy may depend on the ratio of NO to O2.

[Effects of prone position, inhaled nitric oxide and surfactant in children with hypoxemic pulmonary disease]

OBJECTIVE

To analyze the therapeutic response to prone position, inhaled nitric oxide (NO) and surfactant in children with hypoxemic pulmonary disease.

PATIENTS AND METHODS

We studied the effect of prone position, NO, and surfactant in critically ill children with acute hypoxemic pulmonary disease unresponsive to conventional therapy. We analyzed PaO2, SatO2, the PaO2/FiO2 ratio, oxygenation index and PaCO2 before and after each treatment, as well as the subsequent clinical course. An increase of more than 20 % in the PaO2/FiO2 ratio was considered a positive response.

RESULTS

Ninety treatments were administered in 56 patients: 55 patients were treated with NO, 18 with prone position and 17 with surfactant. All three treatments substantially improved oxygenation. The mean increase in the PaO2/FiO2 ratio was 35 % with nitric oxide, 33 % with prone position and 50 % with surfactant. The mean decrease in oxygenation index was 22 % with nitric oxide, 24 % with prone position and 17 % with surfactant. Seventy-one percent of patients treated with NO, 61 % of patients treated with prone position, and 64 % of patients who received surfactant were responders. The three treatments produced a slight decrease in PaCO2 (2.5 mmHg with nitric oxide, 4.7 mmHg with prone position and 5.1 mmHg with surfactant).

CONCLUSIONS

Inhaled NO, prone position and surfactant improve oxygenation in some children with hypoxic pulmonary disease.

Tratamientos complementarios: óxido nítrico, posición en prono y surfactante

The management of hypoxic respiratory failure is based on oxygen delivery and ventilatory support with lung-protective ventilation strategies. Better understanding of acute lung injury have led to new therapeutic approaches that can modify the outcome of these patients. These adjunctive oxygenation strategies include inhaled nitric oxide and surfactant delivery, and the use of prone positioning. Nitric oxide is a selective pulmonary vasodilator that when inhaled, improves oxygenation in clinical situations such as persistent pulmonary hypertension of the newborn, pulmonary hypertension associated with congenital heart disease, and acute respiratory distress syndrome (ARDS). When applied early in ARDS, prone positioning improves distribution of ventilation and reduces the intrapulmonary shunt. The surfactant has dramatically decreased mortality caused by hyaline membrane disease in premature newborns, although the results have been less successful in ARDS. Greater experience is required to determine whether the combination of these treatments will improve the prognosis of these patients.

Inhaled nitric oxide for acute hypoxemic respiratory failure in children and adults

BACKGROUND

Acute hypoxemic respiratory failure affects all age groups and may result from a number of systemic diseases. It continues to be associated with high mortality and morbidity. Initial studies examining the effect of inhaled nitric oxide in respiratory failure demonstrated transient improvement in oxygenation but did not examine mortality or other significant morbidity outcomes.

OBJECTIVES

To systematically examine randomized controlled trials addressing the effect of inhaled nitric oxide, compared with placebo inhaled gas, on mortality and morbidity in patients with acute hypoxemic respiratory failure.

SEARCH STRATEGY

Randomized controlled trials were identified from electronic databases: The Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 2, 2002;MEDLINE (January 1966-August 2002); EMBASE (1980-March 2001); CINAHL (1982-July 2002), as well as from bibliographies of retrieved articles. Relevant journals and conference proceedings were hand searched and authors published in this field were contacted for knowledge of unpublished ongoing trials.

SELECTION CRITERIA

Randomized controlled trials comparing inhaled nitric oxide with maximal conventional therapy and inhaled placebo, in either children or adults with acute hypoxemic respiratory failure.

DATA COLLECTION AND ANALYSIS

Qualitative assessment of each trial was made and analyses performed according to statistical methods in Review Manager MetaView 4.1. A sub-group analysis was performed to assess the impact of inhaled nitric oxide at varied doses.

MAIN RESULTS

Five randomized controlled trials were evaluated, assessing 535 patients with acute hypoxemic respiratory failure (Age range not provided). Lack of data prevented assessment of all outcomes. There was no significant difference of nitric oxide on mortality in trials without cross-over (RR 0.98, 95%CI 0.66,1.44). Published evidence from one study demonstrated nitric oxide to transiently improve oxygenation in the first 72 hours of treatment. Limited data demonstrated no significant difference in ventilator-free days between treatment and placebo groups, and no specific dose of nitric oxide was significantly advantageous over another. Other clinical indicators of effectiveness, such as duration of hospital and intensive care stay, were inconsistently reported. There were no significant complications directly attributable to this treatment.

REVIEWER'S CONCLUSIONS

Nitric oxide did not demonstrate any statistically significant effect on mortality and transiently improved oxygenation in patients with hypoxemic respiratory failure. Lack of data prevented assessment of other clinically relevant end points. If further trials comparing inhaled nitric oxide with an inhaled placebo are to proceed, they should be stratified for primary disease, assess the impact of other combined treatment modalities for respiratory failure, and must specifically evaluate clinically relevant outcomes, before any benefit of inhaled nitric oxide for respiratory failure can be excluded.

Critical care of the severely injured child

It is the responsibility of the surgeon committed to care of these critically injured patients to understand the nature of injuries being treated, and to orchestrate this treatment in a manner that maximizes recovery, avoids unnecessary morbidity, and assures the injured child the best quality of life humanly possible.

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.

Inhaled nitric oxide and prevention of pulmonary hypertension after congenital heart surgery: a randomised double-blind study

BACKGROUND

Pulmonary hypertensive crises (PHTC) are a major cause of morbidity and mortality after congenital heart surgery. Inhaled nitric oxide is frequently used as rescue therapy. We did a randomised double-blind study to investigate the role of routinely administered inhaled nitric oxide to prevent pulmonary hypertension in infants at high risk.

METHODS

We enrolled 124 infants (64 male, 60 female; median age 3 months [IQR 1-5]), 76% with large ventricular or atrioventricular septal defects, who had high pulmonary flow, pressure, or both, and were undergoing corrective surgery for congenital heart disease. They were randomly assigned continuous low-dose inhaled nitric oxide (n=63) or placebo (n=61) from surgery until just before extubation. We measured the numbers of PHTC, time on study gas, and hours spent in intensive care. Analysis was done by intention to treat.

FINDINGS

Compared with placebo, infants receiving inhaled nitric oxide had fewer PHTC (median four [IQR 0-12] vs seven [1-19]; relative risk, unadjusted 0.66, p<0.001, adjusted for dispersion 0.65, p=0.045) and shorter times until criteria for extubation were met (80 [38-121] vs 112 h [63-164], p=0.019). Time taken to wean infants off study gas was 35% longer in the nitric oxide group than in the placebo group (p=0.19), but the total time on the study gas was still 30 h shorter for the nitric oxide group (87 [43-125] vs 117 h [67-168], p=0.023). No important toxic effects arose.

INTERPRETATION

In infants at high risk of pulmonary hypertension, routine use of inhaled nitric oxide after congenital heart surgery can lessen the risk of pulmonary hypertensive crises and shorten the postoperative course, with no toxic effects.

Randomized controlled study of inhaled nitric oxide after operation for congenital heart disease

BACKGROUND

Inhaled nitric oxide selectively decreases pulmonary vascular resistance. This study was performed to determine whether inhaled nitric oxide decreases the incidence of pulmonary hypertensive crises after corrective procedures for congenital heart disease.

METHODS

Patients with a systolic pulmonary arterial pressure of 50% or more of the systolic systemic arterial pressure during the early postoperative period were randomized to receive 20 parts per million inhaled nitric oxide (n = 20) or conventional therapy alone (n = 20). Acute hemodynamic and blood gas measurements were performed at the onset of therapy. The efficacy of sustained therapy was determined by comparing the number of patients in each group who experienced a pulmonary hypertensive crisis.

RESULTS

In comparison to controls, there were no significant differences in the baseline and 1-hour measurements of patients who were treated with nitric oxide. Four patients in the control group and 3 patients in the nitric oxide group experienced a pulmonary hypertensive crisis.

CONCLUSIONS

Nitric oxide did not substantially improve pulmonary hemodynamics and gas exchange immediately after operation for congenital heart disease. Nitric oxide also failed to significantly decrease the incidence of pulmonary hypertensive crises.

Prevention of rabbit acute lung injury by surfactant, inhaled nitric oxide, and pressure support ventilation

Improvement of pulmonary perfusion and blood oxygenation and prevention of acute lung injury (ALI) may rely on ventilation strategy. We hypothesized that application of a combined surfactant, inhaled nitric oxide (iNO), and pressure support ventilation (PSV) should more effectively protect the lungs from injury. Anesthetized and intubated adult rabbits weighing 2.8 +/- 0.3 kg were allowed to breathe room air while receiving oleic acid intravenously (60 microl/kg). Within 90 min this caused a reduction of Pa(O(2)) from 94 +/- 7 to 48 +/- 3 mm Hg and dynamic lung compliance (Cdyn) from 1.59 +/- 0.22 to 0.85 +/- 0.10 ml/cm H(2)O/kg (both p < 0.01), and increase of intrapulmonary shunting (Q S/Q T) from 9.4 +/- 1.2 to 27 +/- 5% (p < 0.05). PSV was subsequently applied with 3 cm H(2)O of continuous positive airway pressure and FI(O(2)) of 0.3, and the animals were randomly allocated to four groups, receiving: (1) PSV only (Control, n = 10); (2) iNO at 20 ppm (NO, n = 9); (3) surfactant phospholipids at 100 mg/kg (Surf, n = 8); and (4) surfactant at 100 mg/kg and iNO at 20 ppm (SNO, n = 8). PSV level was varied to maintain a tidal volume of 8 to 10 ml/kg for another 12 h or until early animal death. Five animals in the SNO, three each in the NO and Surf group, and one in the Control group survived 12 h (SNO versus Control, p < 0.05). The NO, Surf, and SNO groups had significantly improved mean Pa(O(2)) (> 70 mm Hg, p < 0.05), and reduced Q S/Q T (15, 19, and 17%, respectively, p < 0.05) at 6 and 12 h, but not in the Control group. The SNO group had the highest values of Cdyn at 12 h, alveolar aeration and disaturated phosphatidylcholine-to-total protein ratio in bronchoalveolar lavage fluid, and the lowest wet-to-dry lung weight ratio and lung injury score (p < 0.05). The results indicate that early alleviation of ALI by surfactant, iNO, and PSV is due to synergistic effects, and only PSV in this model had limited effects.

Inhaled nitric oxide fraction is influenced by both the site and the mode of administration

OBJECTIVE

Inhaled nitric oxide (NO) can be delivered continuously or sequentially (= during inspiration) at different locations of the ventilation circuit. We have tested the influence of locations, modes of NO administration and the ratio of the inspiratory time over the respiratory cycle time (I/I + E ratio) on the accuracy of NO fractions, delivered by 2 devices: Opti-NO and Flowmeter.

METHODS

We used a simplified lung model consisting of a ventilation circuit with a Y piece, a tracheal tube, a 150 ml dead-space volume and a 5 liter balloon. Three fractions (3, 6, 9 ppm) were administered continuously or sequentially, in controlled volume, in 4 different sites on the inspiratory branch above the Y piece: i) just after the water trap, ii) just before the Y piece; below the Y piece: iii) just after the Y piece, iv) into the endotracheal tube. In addition, different I/I + E ratios (25, 33, 50, 80%) were studied. The delivered NO fractions were measured in the balloon by chemiluminescence (CLD 700, Ecophysics). A linear regression analysis was used to test the relationship between administered and measured NO fractions for the 3 fractions (3, 6 and 9 ppm) in sequential and continuous modes. Intercept values were compared to zero and slopes to the identity line.

RESULTS

When NO was administered in the continuous mode upstream the Y piece, NO fractions measured in the balloon corresponded to the administered fractions. In contrast, below the Y piece, the measured NO fractions were significantly lower than the administered NO fractions. In the sequential mode, above and below the Y piece, the delivered NO fractions were within the manufacturer's range.

CONCLUSIONS

For the continuous NO delivery, locations above the Y piece are mandatory. However, locations below the Y piece imposes a sequential system, which can also be used for the sites located above the Y piece.

Nitric oxide and nitrogen dioxide concentrations during in vitro high-frequency oscillatory ventilation

PURPOSE

The purpose of this study was to measure nitric oxide (NO) and nitrogen dioxide (NO2) concentrations, at various ventilatory settings and sampling sites, during in vitro inhaled NO and high-frequency oscillatory ventilation therapy [iNO-HFOV].

MATERIALS AND METHODS

We used a high-frequency oscillatory ventilator (model 3100A, SensorMedics, Yorba Linda, CA), a test lung (model VT-2A Ventilator Tester, Bio-Tek Instruments, Inc., Winooski, VT), nitric oxide delivery and NO/NO2 monitoring (Pulmonox II, Pulmonox, Tofield, Canada), and scavenging systems in this study. The ventilator frequency, amplitude, and inspired oxygen concentration were systematically changed at a fixed flow of NO. The concentrations of NO and NO2, sampled at four sites, were determined by an electrochemical method (Pulmonox II). The NO and NO2 concentrations were measured at the proximal part of the inspiratory limb (site 1), near the Y-piece (site 2), the carina of the test lung (site 3), and the bellows of the test lung (site 4).

RESULTS

The concentration of NO decreased significantly (P < .001) from the proximal port (site 11 of the inspiratory circuit (86.16 +/- 0.38 ppm) through the lung bellows (site 4) (70.08 +/- 0.23 ppm). The concentration of NO2 increased significantly (P < .001) from site 1 (3.25 +/- 0.04 ppm) through site 4 (19.4 +/- 0.19 ppm). However, the total concentration of NO + NO2 (NOx) remained unchanged at both site 1 and site 4. Increasing the frequency and amplitude of the ventilator significantly altered NO and NO2 concentrations. The NO2 concentration increased significantly (P < .0001) from 5.6 ppm to 18.1 ppm at site 4 when the fraction of inspired oxygen was increased from 0.25 to 0.93. The NO2 concentration also increased significantly (P < .0001) from 0.6 ppm to 18.7 when NO concentrations were independently increased from 12 ppm to 80 ppm.

CONCLUSIONS

During HFOV, the concentrations of NO and NO2 vary between sampling sites and also are influenced by the frequency, amplitude, and inspired oxygen concentration. NO2 concentrations in the lung were significantly increased above commonly accepted toxic concentrations during ventilation with high concentrations of NO (80 ppm) and high fractional concentrations of oxygen. The excessive increase in NO2 concentration at the "alveolar" level in our test lung model warrants confirmation in an in vivo model.

Inhaled nitric oxide, oxygen, and alkalosis: dose-response interactions in a lamb model of pulmonary hypertension

Inhaled nitric oxide (NO) is currently used as an adjuvant therapy for a variety of pulmonary hypertensive disorders. In both animal and human studies, inhaled NO induces selective, dose-dependent pulmonary vasodilation. However, its potential interactions with other simultaneously used pulmonary vasodilator therapies have not been studied. Therefore, the objective of this study was to determine the potential dose-response interactions of inhaled NO, oxygen, and alkalosis therapies. Fourteen newborn lambs (age 1-6 days) were instrumented to measure vascular pressures and left pulmonary artery blood flow. After recovery, the lambs were sedated and mechanically ventilated. During steady-state pulmonary hypertension induced by U46619 (a thromboxane A2 mimic), the lambs were exposed to the following conditions: Protocol A, inhaled NO (0, 5, 40, and 80 ppm) and inspired oxygen concentrations (FiO2) of 0.21, 0.50, and 1.00; and Protocol B, inhaled NO (0, 5, 40, and 80 ppm) and arterial pH levels of 7.30, 7.40, 7.50, and 7.60. Each condition (in randomly chosen order) was maintained for 10 min, and all variables were allowed to return to baseline between conditions. Inhaled NO, oxygen, and alkalosis produced dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). Systemic arterial pressure remained unchanged. At 5 ppm of inhaled NO, alkalosis and oxygen induced further dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). At inhaled NO doses > 5 ppm, alkalosis induced further dose-independent decreases in mean pulmonary arterial pressure, while oxygen did not. We conclude that in this animal model, oxygen, alkalosis, and inhaled NO induced selective, dose-dependent pulmonary vasodilation. However, when combined, a systemic arterial pH > 7.40 augmented inhaled NO-induced pulmonary vasodilation, while an FiO2 > 0.5 did not. Therefore, weaning high FiO2 during inhaled NO therapy should be considered, since it may not diminish the pulmonary vasodilating effects. Further studies are warranted to guide the clinical weaning strategies of these pulmonary vasodilator therapies.

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.

Electroencephalogram changes during inhalation with nitric oxide in the pediatric intensive care patient--a preliminary report

OBJECTIVES

Although endogenous nitric oxide (NO) is an excitatory mediator in the central nervous system, inhaled NO is not considered to cause neurologic side effects because of its short half-life. This study was motivated by a recent case report about neurologic symptoms and our own observation of severe electroencephalogram (EEG) abnormalities during NO inhalation.

DESIGN

Blind, retrospective analyses of EEGs which were registered before, during, and after NO inhalation. EEG was classified in a 5-point rating system by an independent electroencephalographer who was blinded to the patients' clinical histories. Comparisons were made with the previous evaluation documented at recording. Other EEG-influencing parameters such as oxygen saturation, hemodynamics, electrolytes, and pH were evaluated.

SETTING

Pediatric intensive care unit of a tertiary care university children's hospital.

PATIENTS

Eleven ventilated, long-term paralyzed, sedated children (1 mo to 14 yrs) who had EEG or clinical assessment before NO treatment and EEG during NO inhalation. They were divided into two groups according to the NO-indication (e.g., congenital heart defect, acute respiratory distress syndrome).

MEASUREMENTS AND MAIN RESULTS

All 11 patients had an abnormal EEG during NO inhalation. EEG-controls without NO showed remarkable improvement. EEG abnormalities were background slowing, low voltage, suppression burst (n = 2), and sharp waves (n = 2) independent of patients' age, NO-indication, and other EEG-influencing parameters.

CONCLUSIONS

These preliminary data suggest the occurrence of EEG-abnormalities after application of inhaled NO in critically ill children. We found no correlation with other potential EEG-influencing parameters, although clinical state, medication, or hypoxemia might contribute. Comprehensive, prospective, clinical assessment regarding a causal relationship between NO-inhalation and EEG-abnormalities and their clinical importance is needed.

Randomised trial of three doses of inhaled nitric oxide in acute respiratory distress syndrome

BACKGROUND

Inhaled nitric oxide (iNO) is a potential therapeutic agent for the management of acute respiratory distress syndrome (ARDS). Concerns remain, however, regarding the potential toxicity from iNO and/or its oxidative derivatives and methaemoglobinaemia.

AIMS

To determine the risk of toxicity from iNO, which includes worsening of lung injury, a prospective study evaluating the acute effects of three concentrations of iNO on gas exchange and haemodynamics in 12 children with ARDS was performed in a tertiary paediatric intensive care unit.

INTERVENTION

iNO was administered for one hour at three concentrations (1, 10, and 20 parts per million (ppm)) in a random order of possible dosing schedules to avoid dose accumulation bias. Arterial blood gas, methaemoglobin concentrations, and haemodynamic parameters were obtained at baseline before commencement of iNO, at the end of each study hour, and after iNO was discontinued. Nitric oxide and nitrogen dioxide concentrations were continuously monitored during the study.

RESULTS

iNO significantly improved the oxygenation ratio (Pao2/Fio2) from a mean (SEM) baseline of 11.9 (1.7) kPa to 20 (3.9) kPa, 24 (4.5) kPa, and 21.6 (3.9) kPa at 1, 10, and 20 ppm iNO, respectively. There was no significant difference in the improvement in oxygenation achieved between the three concentrations. Correspondingly, there was a significant improvement in oxygenation index (pre-iNO 28.3 (5) v post-iNO 18 (3) (1 ppm), 15 (3) (10 ppm), 16 (3) (20 ppm)). No toxicity from methaemoglobinaemia or nitrogen dioxide was seen during iNO administration.

CONCLUSION

The results show that a low concentration of iNO (1 ppm) is as effective as higher concentrations (10 and 20 ppm) in improving oxygenation in children with ARDS and may be important in minimising toxicity during iNO use.

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.

Aerosolization of novel nitric oxide donors selectively reduce pulmonary hypertension

OBJECTIVES

Inhaled nitric oxide (NO) reduces pulmonary hypertension in acute respiratory failure. Soluble nitric oxide donors (NO/nucleophile adducts-NONOates) are less cumbersome to deliver and may offer clinical advantage compared with inhaled NO. The objective of this study was to examine the pulmonary and systemic hemodynamic effects of tracheal aerosolization of a new class of NONOates in a porcine model of experimentally induced pulmonary hypertension.

DESIGN

Prospective, randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Yorkshire pigs (n = 18), weighing 11.4 to 16.4 kg.

INTERVENTIONS

In anesthetized, mechanically ventilated, instrumented pigs, steady-state pulmonary hypertension (SSPH) was induced using a thromboxane agonist (U46619). Control animals received tracheal aerosolization of saline (n = 6); EP/NO animals received tracheal aerosolization of ethylputreanine NONOate (EP/ NO, n = 6); and DMAEP/NO animals received aerosolized 2-(dimethylamino) ethylputreanine NONOate (DMAEP/NO, n = 6).

MEASUREMENTS AND MAIN RESULTS

Mean pulmonary (MPAP) and mean systemic arterial pressures (MAP), atrial pressures, cardiac output, and arterial blood gases were measured following drug instillation. DMAEP/NO animals had significant reductions in pulmonary vascular resistance index (PVRI) and MPAP at all time points compared with SSPH and control animals (p < .05), while systemic vascular resistance index did not change. EP/NO animals had a significant reduction in PVRI and MPAP at some time points compared with SSPH and control animals. For both NONOate-treated animal groups, MAP and cardiac index did not change significantly compared with SSPH and control animals (p < .05).

CONCLUSIONS

In this porcine model of pulmonary hypertension, intratracheal aerosolization of soluble NO donors results in sustained reduction of pulmonary hypertension without reducing systemic arterial pressure. Intermittent aerosolization of NONOates may be an alternative to continuously inhaled NO in the treatment of acute pulmonary hypertension.

Combined surfactant therapy and inhaled nitric oxide in rabbits with oleic acid-induced acute respiratory distress syndrome

Intratracheal administration of surfactant and inhaled nitric oxide (INO) have had variable effects in clinical trials on patients with acute respiratory distress syndrome (ARDS). We hypothesized that combined treatment with exogenous surfactant and INO may have effects in experimental ARDS. After intravenous infusion of oleic acid in adult rabbits and 4-6 h of ventilation, there was more than a 40% reduction in both dynamic compliance (Cdyn) of the respiratory system and functional residual capacity (FRC), a 50% increment of respiratory resistance (Rrs), a 70% reduction in PaO2 /FIO2, and an increase in intrapulmonary shunting (Q S/Q T) from 4.4 to 33.5%. The animals were then allocated to groups receiving (1) neither surfactant nor INO (control), (2) 100 mg/kg of surfactant (S) administered intratracheally, (3) 20 ppm INO (NO), or (4) 100 mg/kg of surfactant and 20 ppm INO (SNO), and subsequently ventilated for 6 h. After the period of ventilation, the animal lungs were used for analysis of disaturated phosphatidylcholine (DSPC) and total proteins (TP) in bronchoalveolar lavage fluid (BALF), and for determination of alveolar volume density (VV). The animals in the control group had the lowest survival rate, and no improvement in lung mechanics and blood oxygenation, whereas those in the S group had a modest but statistically significant improvement in Cdyn, Rrs, PaO2 and FRC, reduced Q S/Q T, lowered minimum surface tension (gammamin) of BALF, and increased DSPC/ TP and alveolar VV. The NO group had increased PaO2 and reduced Q S/Q T. The SNO group showed improved Cdyn, Rrs, FRC, DSPC/TP, alveolar VV, and gammamin of BALF comparable to the S group, but there was a further increase in survival rate and PaO2, and additional reduction in Q S/Q T and TP in BALF. These results indicate that, in this animal model of ARDS, a combination of surfactant therapy and INO is more effective than either treatment alone.

The use of inhaled nitric oxide in a wide variety of clinical problems

Inhaled nitric oxide (NO) clearly decreased pulmonary vascular resistance in pediatric patients with pulmonary hypertension, regardless of the underlying origin of the pulmonary hypertension. In persistent pulmonary hypertension of the neonate (PPHN) and CHD, the use of inhaled NO appears to improve the outcome of these patients. In acute respiratory distress syndrome (ARDS) and surfactant deficiency the role of inhaled NO therapy remains unclear. The use of inhaled NO is safe in a carefully monitored setting with a delivery system designed to minimize the generation of NO2.

Inhaled nitric oxide versus conventional therapy: effect on oxygenation in ARDS

A randomized, controlled clinical trial was performed with patients with acute respiratory distress syndrome (ARDS) to compare the effect of conventional therapy or inhaled nitric oxide (iNO) on oxygenation. Patients were randomized to either conventional therapy or conventional therapy plus iNO for 72 h. We tested the following hypotheses: (1) that iNO would improve oxygenation during the 72 h after randomization, as compared with conventional therapy; and (2) that iNO would increase the likelihood that patients would improve to the extent that the FI(O2) could be decreased by > or = 0.15 within 72 h after randomization. There were two major findings. First, That iNO as compared with conventional therapy increased Pa(O2)/FI(O2) at 1 h, 12 h, and possibly 24 h. Beyond 24 h, the two groups had an equivalent improvement in Pa(O2)/FI(O2). Second, that patients treated with iNO therapy were no more likely to improve so that they could be managed with a persistent decrease in FI(O2) > or = 0.15 during the 72 h following randomization (11 of 20 patients with iNO versus 9 of 20 patients with conventional therapy, p = 0.55). In patients with severe ARDS, our results indicate that iNO does not lead to a sustained improvement in oxygenation as compared with conventional therapy.

Intratracheal instillation of a novel NO/nucleophile adduct selectively reduces pulmonary hypertension

We examined the pulmonary and systemic hemodynamic effects of administering soluble nitric oxide (NO) donor compounds (NO/nucleophile adducts, i.e., NONOates) directly into the trachea of animals with experimentally induced pulmonary hypertension. Steady-state pulmonary hypertension was created by using the thromboxane agonist U-46619. Yorkshire pigs were randomly assigned to one of four groups: group 1, intratracheal saline (control; n = 8); group 2, intratracheal sodium nitroprusside (n = 6); group 3, intratracheal ethylputreanine NONOate (n = 6); and group 4, intratracheal 2-(dimethylamino)-ethylputreanine NONOate (DMAEP/NO; n = 6). Pulmonary and systemic hemodynamics were monitored after drug instillation. Group 4 had significant reductions in pulmonary vascular resistance index (PVRI) at all time points compared with steady state and compared with group 1 (P < 0.05), whereas systemic vascular resistance index did not change. The mean change in mean pulmonary arterial pressure in group 4 was -33.1 +/- 1.2% compared with +6.4 +/- 1.3% in group 1 (P < 0.001), and the mean change in mean arterial pressure was -9.3 +/- 0.7% compared with a control value of -0.9 +/- 0.5% (P < 0.05). Groups 2 and 3 had significant decreases in both PVRI and systemic vascular resistance index compared with steady state and with group 1. In conclusion, intratracheal instillation of a polar-charged tertiary amine NONOate DMAEP/NO results in the selective reduction of PVRI. Intermittent intratracheal instillation of selective NONOates may be an alternative to continuously inhaled NO in the treatment of pulmonary hypertension.

A randomized, controlled study of the 1-hour and 24-hour effects of inhaled nitric oxide therapy in children with acute hypoxemic respiratory failure

STUDY OBJECTIVE

To determine whether 24 h of inhaled nitric oxide improves oxygenation greater than conventional therapy alone in children with acute hypoxemic respiratory failure.

DESIGN

Prospective, randomized, controlled study.

SETTING

Twenty-six-bed pediatric ICU in a tertiary children's hospital.

PATIENTS

Twenty-four patients with acute bilateral lung disease requiring a positive-end expiratory pressure >6 cm H2O and a fraction of inspired oxygen >0.5 for >12 h.

INTERVENTIONS

Twelve patients were treated with 10 ppm inhaled nitric oxide from the onset of randomization and 12 control patients were initially maintained on a regimen of conventional therapy alone. After a period of 24 h, control patients were also treated with 10 ppm inhaled nitric oxide. Hemodynamic and blood gas measurements were performed at baseline, at 1 h after randomization, and at 24-h intervals for 2 days.

MEASUREMENTS AND RESULTS

Inhaled nitric oxide decreased the ratio of pulmonary to systemic vascular resistance and improved oxygenation indexes during the initial hour following randomization. However, 24 h after randomization, the oxygenation indexes of 11 surviving treated patients were not improved in comparison to baseline or the oxygenation indexes of 10 surviving control patients. Oxygenation indexes acutely improved in control patients when inhaled nitric oxide was started after 24 h of conventional therapy. Oxygenation indexes remained improved in the initial control patients after 24 h of inhaled nitric oxide.

CONCLUSIONS

Pulmonary vascular resistance and systemic oxygenation are acutely improved by 10 ppm inhaled nitric oxide in some children with severe lung disease. However, a sustained improvement in oxygenation may not occur during prolonged therapy. Thus, inhaled nitric oxide may have a limited therapeutic role in children with acute hypoxemic respiratory failure.

Effects of inhaled nitric oxide and extracorporeal membrane oxygenation on pulmonary hemodynamics and lymph flow in oleic acid lung injury in sheep

OBJECTIVE

To compare the effects of inhaled nitric oxide (NO) and extracorporeal membrane oxygenation (ECMO) on oxygenation, hemodynamics, and lymphatic drainage in an oleic acid lung injury model in sheep.

DESIGN

Prospective, randomized study.

SETTING

Animal research laboratory.

ANIMALS

Thirty female sheep, weighing 35 to 40 kg.

INTERVENTIONS

Acute lung injury was induced by central venous injection of oleic acid (0.5 mL/kg body weight). A chronic lymph fistula had been prepared through a right thoracotomy 3 days before the experiment. Animals were assigned randomly to the NO group (n = 14) or the ECMO group (n = 16). When a lung injury score of > 2.5 was achieved, the animals were given NO in dosage increments of 2, 5, 10, 20, and 40 parts per million (ppm), or placed on ECMO with an FIO2 of 0.21 (ECMO-21) and then 1.0 (ECMO-100) at the oxygenator. Mechanical ventilator parameters were kept constant to isolate the effects of NO and ECMO on systemic and pulmonary hemodynamics, cardiac output, oxygenation parameters, lymph/plasma protein ratio, and lymph flow. Measurements and calculations were performed after 1 hr at each individual step of NO concentration or FIO2.

MEASUREMENTS AND MAIN RESULTS

In the ECMO group, PVRI and MPAP did not change and were significantly different from the NO group. In the NO group, there was a dose-dependent decrease in venous admixture, maximal at 10 ppm NO and decreasing from 40 +/- 6% to 23 +/- 10% (p < .05). This decrease was significantly different from the ECMO group, where there was no change. There was a significant increase in PaO2/FIO2 in the NO group, maximal at 10 ppm NO (84 +/- 11 to 210 +/- 90, p < .05), but a greater increase in PaO2/FIO2 on ECMO-21 (81 +/- 14 to 265 +/- 63) and a further increase on ECMO-100 (398 +/- 100) (p < .05). The lymph/plasma protein ratio remained unchanged in both groups after induction of lung injury by oleic acid. However, lymph flow decreased by 11 +/- 6% in the NO group, whereas it increased by 14 +/- 17% in the ECMO group (p < .05).

CONCLUSIONS

In an oleic acid-induced sheep model of acute lung injury, there were significant differences between the effects of NO and ECMO on acute pulmonary hypertension, hypoxemia, hypercarbia, and lymph flow. NO significantly decreases pulmonary hypertension, whereas pulmonary hemodynamics were not substantially affected by ECMO. Both interventions reversed hypoxemia, but ECMO did so to a greater degree, and only ECMO improved hypercarbia. Only NO decreased lymph flow, possibly as an effect of decreased microvascular filtration pressure. This study did not attempt to evaluate the impact of these interventions on ventilatory requirements, barotrauma, or outcome. However, this model suggests that NO therapy may moderate pulmonary hypertension and improve lymph flow in acute lung injury. Clinical studies are needed to assess whether NO therapy might be beneficial in treatment of severe acute lung injury in older children and adults.

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.

Dose response to inhaled nitric oxide in pediatric patients with pulmonary hypertension and acute respiratory distress syndrome

OBJECTIVE

To determine the pulmonary vascular functional dose response to inhaled nitric oxide (NO) for infants and children with acute respiratory distress syndrome and pulmonary artery hypertension.

DESIGN

Prospective, clinical observational study.

SETTING

Thirteen-bed pediatric intensive care unit at a 168-bed children's hospital.

PATIENTS

Infants and children requiring mechanical ventilation with an oxygenation index greater than 10.

METHODS

Children with severe acute respiratory distress syndrome received inhalation therapy with NO after conventional mechanical ventilation failed to result in improvement. Inhaled NO was sequentially titrated from 10 parts per million to 20, 40, 60, and 80 ppm at 10-minute intervals. A reduction of at least 30% in the pulmonary vascular resistance index (PVRI), or a reduction in mean pulmonary artery pressure of at least 10%, or an increase in the hypoxemia score of at least 20%, or a decrease in the oxygenation index of at least 20% from pretreatment values was considered a therapeutic response. After sequential titration, children who responded received continuous inhaled NO at the lowest dose associated with a therapeutic response.

RESULTS

Fourteen children received 15 trials with inhaled NO (median age, 63.4 months; range, 0.4 to 201 months). One patient's condition deteriorated during the titration phase, unrelated to NO treatment, and the patient was withdrawn from the study protocol. The mean (+/- SD) pretreatment oxygenation index was 35 +/- 15, which decreased to 32 +/- 20 at 80 ppm of inhaled NO (p = 0.01). Ten children had pulmonary artery catheter measurements. The PVRI decreased by 30% or greater in seven children (70%). One child had a minimal decrease in PVRI during the titration phase but demonstrated an increase of more than 30% after NO therapy was discontinued. Mean pretreatment PVRI (270 +/- 106) decreased to 207 +/- 92 dynes/sec per cubic centimeter per square meter at 80 ppm of inhaled NO (p = 0.06). Pretreatment mean pulmonary artery pressure (31 +/- 7) decreased to 28 +/- 5 mm Hg at 80 ppm of inhaled NO (p = 0.04). Six trials (43%) showed an increase of 20% or greater in their hypoxemia score. Maximum improvement in the hypoxemia score and reduction in OI, PVRI, and mean pulmonary artery pressure occurred at 20 to 40 ppm of NO. Ten trials led to continuous inhaled NO therapy ranging from 7 to 661.5 hours, with a median of 47 hours. Systemic hypotension was not observed in any patient, and the maximum methemoglobin level was 5%.

CONCLUSION

Inhaled NO appears to be a safe, although variably effective, therapy for the treatment of infants and children with acute respiratory distress syndrome. The maximum dose response occurs between 20 and 40 ppm of inhaled NO. Systemic side effects did not occur in any child who received NO therapy.

Effects of inhaled nitric oxide and nebulized prostacyclin on hypoxic pulmonary vasoconstriction in anesthetized sheep

OBJECTIVES

Inhaled nitric oxide has been shown to be a selective pulmonary vasodilator, leading to reduced pulmonary arterial pressure and improved ventilation/perfusion ratio in the acute respiratory distress syndrome. This local pulmonary vasodilation theoretically can be achieved by the airway application of a short-acting vasodilator, such as prostacyclin. We hypothesized that nebulized prostacyclin has the same properties for selective pulmonary vasodilation as inhaled nitric oxide.

DESIGN

Prospective, experimental study in sheep.

SETTING

Investigational intensive care unit in a university hospital.

SUBJECTS

Six adult ewes of the Merino breed.

INTERVENTIONS

Sheep (n = 6) were surgically prepared for chronic study. After 5 days of recovery, the sheep had tracheostomies performed under anesthesia. Intubation with a modified Robert-Shaw tube allowed side-separated ventilation. The entire left lung was ventilated with pure nitrogen, whereas the right lung was ventilated with pure oxygen. Nitric oxide and prostacyclin were added in different concentrations to the nitrogen, with which the left lung was ventilated.

MEASUREMENTS AND MAIN RESULTS

The blood flows to the left and right lungs were measured with ultrasonic flow probes on the common and left pulmonary artery. Measurements were taken after each compound had been administered for 10 mins at a predefined dose. Both inhaled nitric oxide and nebulized prostacyclin caused effective, selective, dose-dependent pulmonary vasodilation. Inhaled nitric oxide was able to abolish hypoxic pulmonary vasoconstriction when insufflated into the animals at a concentration of 50 ppm of nitrogen, but 100 ppm of nitric oxide had no further effect. Prostacyclin, at a dosage of 10 micrograms/min, showed maximum pulmonary vasodilation, which could not be further increased by doubling the dosage. However, prostacyclin produced less dilation than high doses of nitric oxide, and its maximum pulmonary vasodilation was comparable with that effect obtained under ventilation with 20 ppm of nitric oxide.

CONCLUSIONS

Both drugs selectively dilated the pulmonary vasculature in ventilated alveoli. Prostacyclin nebulization is an excellent tool to reduce pulmonary hypertension and to improve the ventilation/perfusion ratio. Prostacyclin nebulization can be used without the highly sophisticated technical equipment that is needed for controlled nitric oxide inhalation, and may therefore become a new, noninvasive therapeutic approach for treatment of adult respiratory distress syndrome in hospitals that cannot provide nitric oxide inhalation.