Contribution of pulmonary surfactant with inhaled nitric oxide for treatment of pulmonary hypertension

BACKGROUND: Combined therapy of inhaled nitric oxide (iNO) with pulmonary surfactant replacement was reported to improve oxygenation in patients or animal models of persistent pulmonary hypertension of the newborn with pulmonary surfactant deficiency lung. To evaluate the potential of iNO for the treatment of persistent pulmonary hypertension of the newborn, pulmonary arterial pressure (PAP) was measured during iNO before and after pulmonary surfactant replacement in an animal model of pulmonary hypertension with surfactant deficiency. METHODS: Seven newborn piglets were injected with L-nitro-arginine-methylester to produce an animal model of pulmonary hypertension. After PAP increased, iNO (30 p.p.m.) was introduced. Then iNO was stopped, and animals were subjected to lung lavage with saline. After recording the effect of iNO, all animals then received exogenous pulmonary surfactant installation. After surfactant treatment, iNO was again introduced. RESULTS: Pulmonary arterial pressure and systemic arterial pressure were increased significantly by >30% after infusion of L-nitro-arginine-methylester. During iNO only PAP was reduced significantly. Respiratory system compliance decreased significantly after lung lavage, and increased significantly after pulmonary surfactant replacement with concomitant increase of PaO2. In contrast, significant reduction of PAP with iNO before and after pulmonary surfactant replacement were also observed. The reduction ratios of PAP under each condition were 75.2 +/- 7.4%, 81.3 +/- 3.1%, and 79.1 +/- 5.3%, respectively (not significant among conditions). CONCLUSION: These results suggest that iNO is still a potent pulmonary arterial vasodilator even under pulmonary surfactant deficiency in an animal model of pulmonary hypertension.     

Variable oxygenation response to inhaled nitric oxide in severe persistent pulmonary hypertension of the newborn

The causes of variable responsiveness to inhaled nitric oxide (NO) in Persistent Pulmonary Hypertension of the Newborn (PPHN) are unknown. The changes in the severity of respiratory failure after the onset of inhaled NO (maximal dose 20ppm) were studied in 13 consecutive neonates with severe PPHN. Response was defined as a sustained decrease of alveolar-arterial oxygen gradient (AaD0₂) by > 20%, or a decrease in oxygenation index (OI) by > 40%. Six neonates had a rapid response within 30min, three had an intermediate response within 8h, and three had a delayed response within 12 h after the onset of NO. Three infants with birth asphyxia responded rapidly to inhaled NO. One infant with sepsis did not respond, and two with suspected sepsis had a delayed response. The infants with Meconium Aspiration Syndrome and idiopathic PPHN had a variable response time. Twelve neonates required 4 to 14 days of mechanical ventilation and survived. Infants with PPHN may benefit from a trial of inhaled NO therapy that exceeds 30min. The variability of the response time to inhaled NO is likely to be multifactorial and dependent on the disease process associated with PPHN.     

Three-year follow up of term and near-term infants treated with inhaled nitric oxide

BACKGROUND: The present study describes the outcome at 3 years in term and near-term infants treated with inhaled nitric oxide (iNO) for persistent pulmonary hypertension of the newborn (PPHN). METHODS: The study population consisted of 18 infants delivered at 34 weeks by best obstetric estimate who were admitted to the neonatal intensive care units with a diagnosis of PPHN. RESULTS: Eighteen infants (mean gestational age 38.5 +/- 2.6 weeks, mean birthweight 3015 +/- 587 g) were treated with iNO. The mean oxygenation index before iNO was 27.2 +/- 15.2. Responses to iNO were classified into three groups: (i) early response in eight infants; (ii) late response in two; and (iii) poor response in eight infants. Three infants died within seven postnatal days. Fifteen surviving infants were followed up to 3 years. The mean developmental scale was 98.4 +/- 9.0. One infant was diagnosed with severe neurodevelopmental disability due to cerebral palsy. Another infant was diagnosed with mild neurodevelopmental disability because of a low developmental scale. No infant showed significant hearing loss. Five infants had reactive airway disease (RAD) at 18 months, these infants required a significantly longer duration of mechanical ventilation in their neonatal period than non-RAD infants (P = 0.02). The frequency of survival with normal neurodevelopmental outcome was significantly higher in the early response group than the late or poor response groups (P = 0.03). CONCLUSION: In iNO-treated PPHN, mortality and neurodevelopmental outcome were associated with response to iNO, and pulmonary outcome was associated with duration of mechanical ventilation.     

Inhaled nitric oxide and extracorporeal membrane oxygenation in persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) may occasionally require an invasive treatment with extracorporeal membrane oxygenation (ECMO). Inhaled nitric oxide (NO) has recently been introduced as a selective pulmonary vasodilator for treatment of PPHN. We describe a case of PPHN in which neither inhaled NO nor ECMO was effective in reversing pulmonary hypertension. The clinical course of the patient suggested a potential role of NO inhalation in predicting the outcome of ECMO treatment for PPHN.     

A prospective clinical study on inhaled nitric oxide therapy for neonates in Japan

BACKGROUND: This is the first report about a prospective clinical investigation to study the efficacy and safety of nitric oxide (NO) inhalation in infants with persistent pulmonary hypertension of the newborn (PPHN) in Japan. METHODS: Patients in the present study had to meet the following entry criteria: (i) they had to be younger than 7 days of age; (ii) they had to have evidence of PPHN as defined by echocardiograph; (iii) they had to have severe systemic hypoxemia under mechanical ventilation at 100% oxygen supplementation; and (iv) they had to have a failure to respond to conventional therapies. Patients were excluded from this trial if they had any of the following: hypoplastic lung, structural cardiac lesions or severe multiple anomalies. RESULTS: Nitric oxide inhalation therapy was performed in 68 infants who had severe PPHN at 18 hospitals between May 1995 and May 1997. At birth, 21 of 68 infants (31%) weighed less than 1,500 g and 39 infants weighed more than 2,500 g. The diagnoses associated with PPHN were as follows: 27 infants had meconium aspiration syndrome, 15 infants had dry lung syndrome, nine infants had congenital diaphragmatic hernia, six infants had respiratory distress syndrome, three infants had pneumonia and eight infants had other diagnoses. The mean oxygenation index (OI) before NO inhalation therapy in 68 infants was 43.2; 55 infants (81%) had good responses. CONCLUSIONS: These results may be valuable for further randomized controlled and double-blind trials in Japan to evaluate whether NO inhalation therapy is more effective than conventional therapy in infants with severe PPHN.     

一氧化氮治疗新生儿持续肺动脉高压42例疗效观察

目的　探讨一氧化氮 (NO)吸入疗法治疗新生儿持续肺动脉高压 (PPHN)的疗效。方法　对 4 2例新生儿PPHN和呼吸衰竭患儿按解剖性血管梗阻和肺血管痉挛分为Ⅰ组和Ⅱ组 ,分别在呼吸机机械通气情况下 ,将NO气源加入呼吸机环路中 ,NO质量浓度从 2 0× 10 -6mg/L(2 0 ppm)开始 ,每经 15～ 30min无效者增加 (5～10 )× 10 -6mg/L(5～ 10 ppm) ,达到 4 0× 10 -6mg/L仍无效者停用。有效者经予吸入较高浓度NO 6h后 ,每 30min降低NO质量浓度 (5～ 10 )× 10 -6mg/L ,如患儿的PaO2 下降不超过 15 % ,可降至 6× 10 -6mg/L后维持 36～ 72h ,治疗时观察全身氧合情况的变化 ,监测心率、血压、吸入前后血高铁血红蛋白 (MHb)定量及凝血功能。结果　Ⅱ组 33例患儿中 2 7例 (81 82 % )治疗后氧合情况显著改善 ;Ⅰ组治疗后氧合情况无改善。两组心率、血压、凝血功能无明显改变 ,MHb定量的改变无临床意义。结论　低浓度短期NO吸入疗法治疗肺血管痉挛所致持续肺动脉高压有显著疗效 ,且未见明显副作用 ,但对解剖性血管梗阻所致持续肺动脉高压疗效欠佳。     

Nitric oxide further attenuates pulmonary hypertension in magnesium-treated piglets

BACKGROUND: Persistent pulmonary hypertension of the newborn (PPHN) commonly appears as a complication of several pulmonary and non-pulmonary diseases. The hypoxia possibly inhibits Ca2+ +/- dependent K+ channels, thus resulting in membrane depolarization of pulmonary smooth muscle cells, which leads to the opening of Ca2+ channels and Ca2+ entry, resulting in contraction of the vascular smooth muscle. However, magnesium (Mg2+) is an antagonist of Ca2+. We studied the effect of magnesium sulfate on the treatment of hypoxia-induced pulmonary hypertension and compared to the site of action of nitric oxide (NO). METHODS: Zero-day-old piglets were used in each experiment. The effects of Mg2+ were tested in each hypoxic, normoxic and hyperoxic states. Once the desired physical state was achieved, Mg2+ was administered at a dose of 100 mg/kg approximately every 10 min. In order to determine the exact mechanism of the Mg2+, Nw-nitro-l-arginine (LNNA), a NO synthase-inhibitor, was administered simultaneously with Mg2+ in some of the experiments. RESULTS: There was a significant correlation between the percent reduction of the pulmonary arterial pressure (PAP) caused by magnesium and the level of oxygen (O2) present in the pulmonary artery. The greatest amount of reduction was seen in the hypoxic condition where the least amount of O2 is found. A further reduction in the PAP was seen when NO was given at the end of the Mg2+ trials. There was no significant reduction seen in the systemic arterial pressure. CONCLUSIONS: Inhaled NO further reduced the PAP in piglets already treated with Mg2+.     

Inhaled nitric oxide in neonates and children with pulmonary hypertension

Fourteen critically ill neonatal and paediatric intensive care patients with various primary diagnoses and signs of associated pulmonary hypertension received inhaled nitric oxide (NO), 20–80 ppm, after failure of conventional therapy to improve oxygenation. NO administration was found to be associated with a significant improvement in postductal arterial oxygen tension (pre-NO: 3.75 (SD 1.39) kPa; post-NO: 6.05 (SD 1.70) kPa; p = 0.004). In 10 patients, NO was found to increase arterial oxygen tension with more than 1 kPa. In 2 of these patients, ECMO treatment could be avoided due to the pronounced improvement in gas exchange seen after the initiation of NO administration. The remaining 4 patients failed to respond to NO administration. One patient developed methaemoglobinaemia (13.9%) which required treatment with methylthionine. Since we were unable to produce any beneficial effect of NO in the late phase of the pulmonary disease process, we believe that, in order to be successful, inhaled NO should be instituted when conventional treatment has failed and the administration of an iv vasodilator is usually considered.     

Weaning strategy with inhaled nitric oxide treatment in persistent pulmonary hypertension of the newborn

AIM—To determine if infants who had become dependent on inhaled nitric oxide treatment could be successfully weaned off it if FIO₂ was increased briefly during withdrawal.
METHODS—Sixteen infants admitted for conditions associated with increased pulmonary vascular resistance responded well to inhaled nitric oxide treatment with a significant increase in PaO₂ (maximum inhaled nitric oxide given 25 ppm). Weaning from inhaled nitric oxide in 5 ppm decrements was initiated once the FIO₂ requirement was less than 0.5. When patients were stable on 5 ppm of inhaled nitric oxide, the gas was then discontinued. If a patient showed inhaled nitric oxide dependence—that is, oxygen saturation fell by more than 10% or below 85%—inhaled nitric oxide was reinstated at 5 ppm and the patient allowed to stabilise for 30 minutes. At this time, FIO₂ was increased by 0.40 and weaning from inhaled nitric oxide was attempted again.
RESULTS—Nine infants were successfully weaned on the first attempt. The seven infants who failed the initial trial were all successfully weaned following the increase in FIO₂. After successful weaning, FIO₂ was returned to the pre-weaning level in mean 148(SD 51) minutes and inhaled nitric oxide was never reinstated.
CONCLUSION—Infants showing inhaled nitric oxide dependency can be successfully weaned by increasing FIO₂ transiently.

     

Disease-related response to inhaled nitric oxide in newborns with severe hypoxaemic respiratory failure

Inhaled nitric oxide (iNO) has been shown to improve oxygenation in severe persistent pulmonary hypertension of the newborn (PPHN). However, PPHN is often associated with various lung diseases. Thus, response to iNO may depend upon the aetiology of neonatal acute respiratory failure. A total of 150 (29 preterm and 121 term) newborns with PPHN were prospectively enrolled on the basis of oxygenation index (OI) higher than 30 and 40, respectively. NO dosage was stepwise increased (10–80 ppm) during conventional mechanical or high-frequency oscillatory ventilation while monitoring the oxygenation. Effective dosages ranged from 5 to 20 ppm in the responders, whereas iNO levels were unsuccessfully increased up to 80 ppm in the nonresponders. Within 30 min of iNO therapy, OI was significantly reduced in either preterm neonates (51 ± 21 vs 23 ± 17, P < .0001) or term infants with idiopathic or acute respiratory distress syndrome (45 ± 20 vs 20 ± 17, P < .0001), `idiopathic' PPHN (39 ± 14 vs 14 ± 9, P < .0001), and sepsis (55 ± 25 vs 26 ± 20, P < .0001) provided there was no associated refractory shock. Improvement in oxygenation was less significant and sustained (OI = 41 ± 16 vs 28 ± 18, P < .001) in term neonates with meconium aspiration syndrome and much less (OI = 58 ± 25 vs 46 ± 32, P < .01) in those with congenital diaphragmatic hernia. Only 21 of the 129 term newborns (16%) required extracorporeal membrane oxygenation (57% survival). Survival was significantly associated with the magnitude in the reduction in OI at 30 min of iNO therapy, a gestational age ≥34 weeks, and associated diagnosis other than congenital diaphragmatic hernia. Conclusion, iNO improves the oxygenation in most newborns with severe hypoxaemic respiratory failure including preterm neonates. However, response to iNO is disease-specific. Furthermore, iNO when combined with adequate alveolar recruitment and limited barotrauma using exogenous surfactant and HFOV may obviate the need for extracorporeal membrane oxygenation in many term infants. Received: 24 April 1997 / Accepted in revised form 3 January 1998     

常频通气联合一氧化氮吸入治疗新生儿持续肺动脉高压

目的 探讨常频通气联合一氧化氮吸入(iNO)治疗新生儿持续肺动脉高压(PPHN)的疗效.方法 对22例确诊为PPHN且入院时采取常频通气疗效不满意的患儿给予iNO.NO初始吸入浓度上,20例为(10～20)×10-6,2例为(20～40)×10-6.当SpO2≥93%并已经稳定20min以上,开始下调呼吸机参数,并逐渐下调NO吸入浓度.当NO吸入浓度降至(5～10)×10-6时,再持续2～3h后,若PaO2>55mm Hg(1 mm Hg=0.133 kPa)、SpO2>93%时停止吸入.在NO吸入前和吸入后1～6 h分别进行血气分析,连续记录生命体征、SpO2和监测NO2值等.结果 20例在吸人NO后5～20 min左右SpO2逐渐升高,临床缺氧状态逐步改善.有效率达91%.吸入NO 1～6 h,SpO2、PaO2分别由吸入前的(76.3±13.3)%、(46.4±10.1)mm Hg升到(94.4±2.9)%和(92.8±24.7)mm Hg,FiO2由(0.9±0.1)降至(0.6±0.1),差异均有非常显著性(P<0.001).患儿生命体征平稳,未发现急性合并症.全组治愈18例,治愈率达82%,自动放弃4例.结论 iNO能有效地缓解PPHN患儿的乏氧状态.提高氧分压和治愈率.NO吸入不良反应小、易操作.iNO初始吸人浓度以(10～20)×10-6开始为宜,极个别病例可以(20～40)×10-6开始.     

Severe persistent pulmonary hypertension of the newborn in a setting where limited resources exclude the use of inhaled nitric oxide: successful treatment with sildenafil

We present the case of a full term neonate with severe persistent pulmonary hypertension of the newborn (PPHN) after birth asphyxia cared for at the St. Elizabeth Hospital in Curacao, Netherlands Antilles. Although the child was ventilated with high pressures and was given high doses of cardiovascular pressors, the arterial oxygen levels remained low with an alveolar-arterial O₂ gradient of 651 mmHg. As a last resort, sildenafil (1.5 mg/kg) was given via a nasogastric tube. This resulted in an immediate and sustained elevation of arterial oxygenation and subsequent complete recovery. After administration of sildenafil there was a transient hypotension which was corrected by a single bolus of saline. Conclusion:We discuss the current treatment modalities of persistent pulmonary hypertension of the newborn and the potential use of phosphodiesterase 5 inhibitors such as sildenafil in a situation where the standard of practice with inhaled nitric oxide and extracorporeal membrane oxygenation is not available.     

加温湿化高流量鼻导管通气在胎粪吸入综合征并肺动脉高压机械通气撤机中的应用研究

目的比较湿化高流量鼻导管通气(HHFNC)和经鼻持续气道正压通气(NCPAP)两种无创通气模式在胎粪吸入综合征(MAS)并持续肺动脉高压(PPHN)患儿机械通气撤机中的应用,探讨HHFNC的临床价值。方法选取78例胎粪吸入综合征合并持续肺动脉高压的患儿,机械通气撤机后随机分为HHFNC组和NCPAP组,分别行HHFNC和NCPAP呼吸支持,比较两组无创通气后的血气、无创通气时间、撤机失败率及鼻部损伤、腹胀和脑室内出血(IVH)等并发症发生情况的差异。结果两组患儿的撤机失败率、应用NCPAP/HHFNC后1 h的PaO_2和PCO_2值、PaO_2/PaO_2、无创通气时间、达全肠道喂养时间、住院时间以及IVH发生率的差异均无统计学意义(P0.05)。HHFNC组鼻损伤发生率(5.0%)低于NCPAP组(31.6%),P0.05;腹胀发生率(7.5%)低于NCPAP组(34.2%),P0.05。结论NCPAP和HHFNC均可在新生儿MAS并PPHN经机械通气撤机后序贯使用,具有确定的效果;但HHFNC更易使患儿耐受,副作用较少、安全性较高。     

Uncertainties about the use of inhaled nitric oxide in preterm infants

Respiratory failure in the premature neonate is frequently complicated by pulmonary hypertension. When conventional therapies including administration of exogenous surfactant, conventional mechanical ventilation or high-frequency oscillatory ventilation using an appropriate high-volume strategy have failed, one should assess the pulmonary circulation status with colour-coded Doppler echocardiography. There is now considerable evidence that the regulation of foetal and postnatal pulmonary circulation occurs via nitric oxide (NO), and that persistent pulmonary hypertension of the neonate may be related to a relative deficiency in NO release. Low-dose (10–20 ppm), short-duration (1–2 d) inhaled NO has generally been shown to improve the oxygenation and relieve pulmonary hypertension in premature neonates with severely hypoxaemic respiratory failure. Whether this therapy (eventually prolonged >1-3 wk?) would improve survival and lessen morbidity (e.g. intracranial haemorrhage and chronic lung disease) remains to be proven by appropriately designed controlled trials. Until these issues can be clarified, NO therapy for premature neonates should be still considered as an experimental drug, and its use restricted to clinical studies.     

Endogenous nitric oxide and endothelin-1 in persistent pulmonary hypertension of the newborn

We studied changes in endogenous nitric oxide (NO) synthesis and endothelin-1 (ET-1) production in infants with persistent pulmonary hypertension of the newborn (PPHN). We determined concentrations of serum NO metabolites, i.e., nitrites and nitrates (NOx), and of plasma ET-1 in five infants with PPHN (PPHN group) and in 25 healthy full-term neonates (control group). In both groups, serum NOx concentrations increased over time and plasma ET-1 concentrations decreased with age. The differences in serum NOx concentrations between groups were not significant at <12 h and 24 h of age; however, they were significantly higher in the PPHN group than in the control group at 5 days of age. The differences in plasma ET-1 concentrations between groups were not significant at 5 days of age, but were significantly higher in the PPHN group than in the control group at <12 h and 24 h of age. Conclusion Limited endogenous nitric oxide synthesis and elevated endogenous endothelin-1 production during the first few days of life may contribute to pulmonary hypertension in infants with persistent pulmonary hypertension of the newborn. Received: 2 September 2000 / Accepted: 15 June 2000