Title: Clinical Profile of Persistent Pulmonary Hypertension in Neonates with Role of Sildenafil in its Outcome: Rural India NICU Experience

Background: Persistent pulmonary hypertension of newborn (PPHN) result from failure of normal fall in pulmonary vascular resistance at or shortly after birth. It is associated with high mortality and morbidity. Objectives: To estimate incidence, risk factors; and outcome within limited resources – conventional ventilation, sildenafil, dobutamine and milrinone therapy. Methods: This prospective study was carried out on cases of PPHN admitted between March 2017 to August 2018. PPHN was suspected clinically, and then confirmed by echocardiography. Results: Out of 2811 inborn live births 12 (0.43%) developed PPHN. Out of total 942 NICU admissions, PPHN was diagnosed in 40(4.2%). 32 (80%) were full term, 6 (15%) were late preterm and 2(5%) were post term neonates. 25(62.5%) were male. Major etiological factors were asphyxia Original Research Article Pathak et al.; JPRI, 33(52A): 324-336, 2021; Article no.JPRI.75974 325 19(47.5%), EOS (early onset sepsis) 18(45%) and MAS (meconium aspiration syndrome) 12(30%). 20(50%) responded to oral sildenafil and dobutamine therapy, 6 more responded with addition of milrinone. The overall survival rate was 26(65%) and poor outcome in 14 (35%) in our study. Median duration of respiratory support was 1.5(1 – 6) days in those with poor outcome and 6(4 – 7) in those survived. Duration of hospital stay was 1.5(1 – 6) days in poor outcome and 17(13 – 22) in those survived. Conclusions: Asphyxia, EOS and MAS are common causes of PPHN. Severity of respiratory distress on admission is correlated with mortality rather than etiological factors. Conventional ventilation, dobutamine, sildenafil and milrinone therapy are mainstay of treatment of PPHN cases in resource limited settings, and helps to reduce mortality to some extent.


INTRODUCTION
Persistence of pulmonary hypertension (PPHN) in neonates was described initially by Gersony and colleagues in 1969 as persistent fetal circulation [1]. Persistent pulmonary hypertension of the newborn can be defined as a failure of normal fall in pulmonary vascular resistance (PVR) at or shortly after birth, leading to shunting of unoxygenated blood into the systemic circulation across foramen ovale or ductus arteriosus [2]. Increased pulmonary vascular resistance and decreased pulmonary blood flow prevents adequate gas exchange in the lungs resulting in severe respiratory distress and hypoxemia in the neonate [3].
Its incidence is estimated at around 2 per 1000 live births worldwide [4,5]. Despite the progress in treating PPHN, it remains a potentially fatal disease, especially in resource-limited settings [6]. The reported overall mortality ranges from 4% to 33% in developed countries4 and from 25% to 48% in developing countries [7,8]. The mortality rate about 10-20% of affected infants despite of treatments such as nitric oxide, extracorporeal membrane oxygenation (ECMO) and advanced modes of mechanical ventilation [9]. In addition, infants who survive PPHN at increased risks for long-term sequelae including chronic lung disease, seizures, and neurological developmental problems [10,11].
PPHN is suspected when there is a considerable difference between preductal and post-ductal oxygen saturation, in combination with severe hypoxaemia that does not improve when the infant is subjected to 100% supplemental oxygen. As it is difficult to differentiate PPHN from cyanotic congenital heart disease on clinical grounds alone, echocardiography is usually required to confirm a diagnosis of PPHN [5,14].
The main goals of treatment of PPHN are to decrease pulmonary vascular resistance and increase pulmonary blood flow. This is carried out by correcting the underlying disease, good supportive care, and selective pulmonary vasodilators such as inhaled nitric oxide (iNO), Magnesium sulphate (MgSO4) and Oral sildenafil [15]. In resource-limited facilities, sildenafil, milrinone and magnesium sulphate have been shown to be safe, effective pulmonary vasodilators for improving oxygenation when iNO is not available [16,17,18,19]. The current mainstay of PPHN treatment when conventional ventilatory support alone fails, consists of a combination of high frequency oscillatory ventilation (HFOV) and administering iNO. ECMO is used as a rescue therapy for neonates in respiratory failure and who are unresponsive to other therapies [20,21,22,23].
As there were no outcome data from our centre, we conducted a prospective study to determine incidence, risk factors, etiological factors & survival rate. We also aimed to analyse role of sildenafil, dobutamine, milrinone and conventional ventilation in management of PPHN, as also factors influencing outcome. Diagnostic criteria for echocardiography used were increased pulmonary artery pressure (measured by tricuspid regurgitation jet), with right to left shunt or bidirectional shunt across patent ductus arteriosus (PDA) or persistent foramen ovale (PFO) or paradoxical ventricular septal movement. All the neonates with PPHN started with head box oxygen, oral sildenafil and dobutamine infusion along with specific therapy based on etiology, and other supportive management based on standard protocol guidelines. Conventional ventilation was given based on oxygen saturation (SpO2) / arterial blood gas (ABG) &/or clinically based on respiratory distress severity. In poor responders milrinone infusion was added.

Statastical Analysis
Data collected was entered in Microsoft excel sheet. Then it was analysed and summarized by percentage, mean & standard deviation; and median and IQR(inter quartile range). Relative risk and p value calculation was done to find association between variables. Mann Whitney U test was used to find out p value from median.
Risk of PPHN was 3.7% in inborn asphyxiated neonates, while it was 16.49% in outborn asphyxiated. Risk among MAS cases was 23.08% in inborn while 45% in outborn. Risk of PPHN among EOS cases was 10.42% in inborn and 13.33% in outborn.
All the neonates required ventilator therapy (conventional ventilator). Out of 26 neonates who showed good response, post extubation CPAP (continuous positive airway pressure ventilation) was required in 17 (42.5%) neonates. 9 were directly extubated to head box oxygen. All (40) the neonates were given sildenafil and dobutamine, of which 20 showed good response, and remaining 20 did not show good response. of which milrinone was added in 17 neonates. 26 (65%) were successfully discharged. 9 (22.5%) were expired. 5 (12.5%) left against medical advice (LAMA), they left NICU in moribund state.   We analyzed relative risk of poor outcome among various factors, e.g. outborn Vs inborn, LSCS delivered Vs vaginally delivered, born before 37 weeks Vs born after 37 weeks, PPHN due to asphyxia Vs PPHN due to cause other than asphyxia, etc. We were not able to find any significance among them. We found statistically significant increased risk of poor outcome among those who presented with severe respiratory distress than those who presented with mild/moderate respiratory distress; RR 7.0 (95% CI 1.02 -3.43), p = 0.048.
We were not able to find correlation of any factor associated with either good or poor outcome except post maturity; which was associated with poor outcome; p value of 0.05. Mean gestational age was 37.62 (1.11) in neonates with good outcome, as against mean gestational age of 38.57 (1.4) in neonates with poor outcome; p value 0.024.
Duration of hospital stay was statistically very significant between the two outcome groups, with mean duration of 3.36 days in those with poor outcome and of 17.77 days in those with good outcome. As also duration of respiratory support was significantly different between the two outcome groups. Those with poor outcome, outcome came very early with mean 3.36 (3.41) days and median days of 1.5 (1 -6) days of admission.
One case with associated surgical conditionesophageal atresia with tracheoesophageal fistula in whom surgery was done was removed from analysis. Thus, total 17 cases of EOS with PPHN were analyzed.
We could not find any effect of associated problem along with EOS in relation with either poor or good outcome. We also could not find any statistically increased relative risk of poor outcome when EOS is associated with other conditions causing PPHN.   One case with associated surgical conditionesophageal atresia with tracheoesophageal fistula in whom surgery was done was removed from analysis. Thus, total 18 cases of asphyxia with PPHN were analyzed.
We could not find any effect of associated problem along with asphyxia in relation with either poor or good outcome. We also could not find any statistically increased relative risk of poor outcome when asphyxia is associated with other conditions causing PPHN. One case with associated surgical conditiondiaphragmatic hernia in whom surgery was done was removed from analysis. Thus, total 11 cases of MAS with PPHN were analyzed.
We could not find any effect of additional associated conditions along with MAS in relation with either poor or good outcome. We found relatively low risk of poor outcome when MAS is associated with other conditions causing PPHN, but we had only one isolated MAS case and overall sample size was less to conclude.  [29].
All (100%) the neonates in our study were mechanically ventilated with CMV. And dobutamine and oral sildenafil were started in all (100%) as a pulmonary vasodilator. Our findings are consistent with reports that assisted ventilation constitutes mainstay of PPHN management [14,21,30,31,32]. The high proportion of neonates treated with mechanical ventilation in our study may reflect the severity of their disease, although we were unable to calculate the neonates' oxygenation indices as a measure of the severity of respiratory failure. None of the neonates were treated with HFOV, iNO or ECMO as our we did not have these treatment modalities. 20 (50%) responded to oral sildenafil and dobutamine therapy. In 17 (42.5%) non-responders we added milrinone, of which 6 (35.29%) responded. In study by Abdel et al 62.5% responded with oral sildenafil [8]. Columbian pilot study by Baquero et al. stated that oral sildenafil was administered easily and tolerated well and improved oxygenation index in infants with severe PPHN; showed 6/7 survival in sildenafil group vs 1/6 survival in placebo group [19]. In a study by Arturo et al observed better oxygenation parameters after 7 hours of sildenafil treatment, but no significant changes were found in the placebo group. Mortality was higher in the placebo group (40%) than in those infants who received sildenafil (6%; p = 0.004). concluded that sildenafil may be a useful adjuvant therapy for term infants with pulmonary hypertension in centers lacking inhaled nitric oxide and extracorporeal membrane oxygenation [33]. In a study by Dinakara et al. oral sildenafil was administered easily and tolerated improved OI in infants with severe PPHN, which suggests that oral sildenafil may be effective in the treatment of PPHN [34]. All of our cases tolerated sildenafil well, and none of them developed any adverse events suspected to be due to sildenafil. Khorana et al in a retrospective study concluded that sildenafil may be useful adjuvant therapy for term infants with pulmonary hypertension in centers lacking iNO and ECMO [35].
The overall survival rate was 65% and poor outcome in 35% in our study. Harish et al noted 57.1% survival having similar kind of resource limited instrumental facilities [27]. In study by Harerimana et al 34.7% did not survive [29]. Similar kind of high mortality is reported from other resource limited settings [6,7,8]. High mortality rate in resource limited settings may be attributed to non-availability of newer modalities of therapy [5,20,21]. In our case it was also attributed to late presentation of many of outborn neonates with severe respiratory distress. The duration of both ventilation and hospital stay was longer for those having good outcome than those with poor outcome (p 0.00452 & <0.0001 respectively), probably because of early poor outcome. Those having poor outcome had poor outcome very early with mean 3.36 (3.41) days and median days of 1.5 (1 -6) days of admission. We tried to analyze various factors probably associated with either good or poor outcome. Out of many factors only post maturity and higher gestational age was found to be associated with significantly poor outcome. We analyzed relative risk of poor outcome between various risk factors and etiological factors, but could not find any statistically significant difference. Those presented with severe respiratory distress had significantly higher risk of poor outcome compared to presented with mild to moderate distress. We tried to find association of additional problems or those having multiple etiologies with increased risk of poor outcome than those having single etiology (isolated asphyxia or EOS or MAS as a cause) without additional problem. But we could not find any such association. Surprisingly we found relatively low risk of poor outcome when MAS is associated with other additional conditions causing PPHN, but we had only one isolated MAS case and overall sample size was less to conclude.

CONCLUSION
Asphyxia, EOS and MAS are common causes of PPHN. Severity of respiratory distress on admission is correlated with mortality rather than etiological factors. Prevention of asphyxia, EOS and MAS by good antenatal and intrapartum obstetric care, & reducing post term births helps in reduction of PPHN cases. Conventional ventilation, dobutamine, sildenafil and milrinone therapy are mainstay of treatment of PPHN cases in resource limited settings, and helps to reduce mortality to some extent.

LIMITATIONS OF STUDY
We had service of visiting pediatric cardiologist. Cardiologists who were on regular service were adult cardiologist. Echocardiography was done by any of the available cardiologist. Though echocardiography was done in all, in many of the patients echocardiography was done after management of PPHN was started on clinical grounds. ABG could not be done frequently. So, we were not able to measure severity of PPHN based on echocardiographic findings or oxygenation index.

DISCLAIMER
The products used for this research are commonly and predominantly use products in our area of research and country. There is absolutely no conflict of interest between the authors and producers of the products because we do not intend to use these products as an avenue for any litigation but for the advancement of knowledge. Also, the research was not funded by the producing company rather it was funded by personal efforts of the authors.

CONSENT AND ETHICAL APPROVAL
Ethical approval was obtained for the study topic from Sumandeep Vidyapeeth Institutional Ethics Committee (SVIEC/UN/MEDI/BNPG16). Those are involved in the study, were asked to read and willingly sign on the informed consent form.