Predicting survival in infants with persistent pulmonary hypertension of the newborn

Predicting mortality in infants with persistent pulmonary hypertension of the newborn with the Score for Neonatal Acute Physiology-Version II (SNAP-II) in Thai neonates

AIM

To evaluate the ability of the Score for Neonatal Acute Physiology-Version II (SNAP-II) to predict mortality in infants with persistent pulmonary hypertension of the newborn (PPHN).

METHODS

A prospective cohort study of 41 infants with PPHN admitted to our neonatal intensive care unit between June 2008 and March 2010, who underwent a SNAP-II test within 12 h of admission.

RESULTS

Of the 41 infants, 14 died (34.1%) and 27 survived (65.9%). The SNAP-II scores were significantly higher in infants who died (50.1 ± 18.5 vs. 35.7 ± 16.8, P=0.02). Each point increase in the SNAP score increased the odds of mortality by 1.04 [95% confidence interval (CI) 1.01-1.07, P<0.01]. Infants who had a SNAP-II score of ≥ 43 had the greatest mortality risk with an odds ratio (OR) of 10.00 (95% CI 1.03-97.50). The SNAP-II model showed moderate discrimination in predicting mortality with a result of 0.72 (95% CI 0.56-0.88) under the receiver operating characteristic curve. The lowest blood pressure, lowest PaO(2)/FIO(2) ratio, and urine output within the first 12 h of admission were also independently found to be good predictors of an increased risk for death.

CONCLUSION

The SNAP-II scoring system significantly predicted mortality. PPHN infants with a SNAP-II score of ≥ 43 had the greatest mortality risk.

Advances in the diagnosis and management of persistent pulmonary hypertension of the newborn

Rapid evaluation of a neonate who is cyanotic and in respiratory distress is essential for achieving a good outcome. Persistent pulmonary hypertension of the newborn (PPHN) can be a primary cause or a contributing factor to respiratory failure, particularly in neonates born at 34 weeks or more of gestation. PPHN represents a failure of normal postnatal adaptation that occurs at birth in the pulmonary circulation. Rapid advances in therapy in recent years have led to a remarkable decrease in mortality for the affected infants. Infants who survive PPHN are at significant risk for long-term hearing and neurodevelopmental impairments, however. This review focuses on the diagnosis, recent advances in management, and recommendations for the long-term follow-up of infants who have PPHN.

Correlation of echocardiographic markers and therapy in persistent pulmonary hypertension of the newborn

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) causes morbidity and mortality in neonates. High-frequency ventilation (HFV), inhaled nitric oxide (iNO), and extracorporeal membrane oxygenation (ECMO) are used when conventional treatment fails. This study aimed to identify echocardiographic predictors of progression to these therapies before clinical deterioration.

METHODS

Echocardiographic parameters were compared for survival and need for ECMO, HFV, iNO, and prolonged mechanical ventilation (MV, >or=10 days).

RESULTS

Of 63 neonates, 95% survived, with 14% requiring ECMO, 52% requiring HFV, 67% requiring iNO, and 35% requiring MV. The following echocardiographic indices reflecting left ventricular output were decreased in sicker infants: (1) A decreased ascending aortic velocity time integral indicated an increased likelihood of ECMO (p=0.02), iNO (p=0.01), or MV (p=0.05), (2) Shorter transverse aortic arch antegrade ejection time indicated HFV (p<0.01), iNO (p<0.01), and MV (p=0.03), (3) Absent or retrograde transverse aortic diastolic flow correlated with HFV (p=0.01, iNO (p=0.01), and MV (p<0.01). These sicker patients were more likely to have smaller left ventricular end-diastolic areas (p<0.03 for all) and right-to-left atrial shunting (ECMO, HFV, and MV). There were no differences in survival.

CONCLUSIONS

Decreased left ventricular size and output correlates with the need for advanced therapies in infants with PPHN. Early identification may allow more effective management and placement of neonates at risk.

Inhaled NO and markers of oxidant injury in infants with respiratory failure

BACKGROUND

Inhaled nitric oxide (iNO) is an effective adjunct in the treatment of infants with respiratory failure. Although there are clear benefits to this therapy, potential toxicity could result from reactive nitrosylated species.

OBJECTIVE

To evaluate whether iNO therapy is associated with increased serum markers of oxidative stress.

DESIGN/METHOD

Multiple markers were prospectively evaluated in the serum of term infants with severe respiratory failure treated with iNO for 1 to 72 hours. These were compared to those of patients exposed to greater than 80% oxygen for more than 6 hours and room air controls.

RESULTS

After 24 hours of exposure, the iNO-treated infants had increased serum lipid hydroperoxides (LPO), protein carbonyls and nitrotyrosine residues as well as increased serum total glutathione (GSH) content. The increase in LPO peaked at 24 hours and correlated with the cumulative dose of iNO whereas other markers did not. The presence of chronic lung disease (CLD) did not correlate with serum markers of oxidative injury.

CONCLUSIONS

In term infants with respiratory failure, prolonged iNO exposure is associated with a transient increase in markers of oxidative stress, but this finding does not appear to predict the development of CLD.

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+.

Three-week neonatal hypoxia reduces blood CGRP and causes persistent pulmonary hypertension in rats

To increase understanding of persistent pulmonary hypertension, we examined chronic pulmonary effects of hypoxia at birth and their relationships with immunoreactive levels of the potent vasodilator, calcitonin gene-related peptide (CGRP). Rats were born in 10% hypobaric hypoxia, where they remained for 1-2 days, or in 15% hypoxia, where they remained for 21 days. All were then reared in normoxia for 3 mo followed by reexposure to 10% hypoxia for 7 days (H-->H) or continued normoxia (H-->N); age-matched normoxic rats were hypoxic for the last 7 days (N-->H) or normoxic throughout (N-->N). Results are as follows. Pulmonary arterial pressure (P(PA)) in 10% H-->N rats was normal at the end of the experiment (13 wk), but in rats reexposed to hypoxia (H-->H), pressure rose to 19% above N-->H controls. In 15% H-->N rats, P(PA) remained high, similar to that of N-->H rats, and increased further by 40% on reexposure (H-->H). Medial thickness of small pulmonary arteries in 10% H-->H rats also increased by 40% over N-->H controls and was equally high in 15% H-->N and H-->H rats. In N-->H rats from both experiments, right ventricular hypertrophy index (RVH) was increased after hypoxia at 15-16 wk. Also, in the 15% study, RVH remained elevated in H-->N rats and increased in H-->H rats by 19% above N-->H controls. Blood CGRP was reduced by neonate and adult hypoxia, and hypoxic reexposure (H-->H) further lowered blood CGRP in the 15% but not 10% study. Declining left ventricular blood CGRP correlated highly with logarithmically increasing P(PA) in the 15% study (r = -0.81, P = 0.000). In conclusion, 1) short perinatal exposure to 10% O(2) exacerbated pulmonary hypertension with hypoxia later in life, 2) 15% O(2) at birth and for 21 days caused persistent pulmonary hypertension and exacerbation with reexposure, and 3) P(PA) correlated highly with declining blood CGRP levels in the 15% study.

Haemodynamic features at presentation in persistent pulmonary hypertension of the newborn and outcome

Thirty four newborns presenting with persistent hypoxaemia in the first three days of life underwent detailed haemodynamic assessment using Doppler echocardiography, including measurements of pulmonary arterial pressure (PAP), left ventricular (LV) function, and left ventricular output (LVO). Results were compared with values from 51 healthy babies, and those of survivors were compared with non-survivors. Four of the 34 babies were excluded from this analysis because one was found to have transposed great arteries, one had a large left-to-right shunt with no evidence of persistent pulmonary hypertension, and two had diffuse skeletal myopathy. Tricuspid regurgitation was present in 70%, permitting systolic PAP estimation. The pulmonary:systemic arterial pressure ratio range was 0.7:1 to 1.83:1 (mean 1.02:1). A patent duct was present in 83%, and flow patterns indicated PAP approaching, or above, systemic pressure in all. Systolic time interval ratio TPV/RVET (time to peak velocity at the pulmonary valve/right ventricular ejection time) was mostly (65%) in the normal range, and did not correlate with other PAP measurements. LV function was below the 10th centile in only 11%, but values for LVO lay below the 10th centile in 41%, and for left ventricular stroke volume index (LSVI) in 66%. Results of 18 survivors were compared with 10 non-survivors (excluding two premature babies who died early with pulmonary interstitial emphysema). There were no significant differences for any parameter of PAP or LV function, but LVO and LSVI were significantly lower in non-survivors: LVO survivors (mean (SD)), 205 (57), non-survivors 138 (63) ml/kg/minute (P < 0.01); LSVI survivors, 1.29 (0.51), non-survivors 0.86 (0.31) ml/kg (P < 0.05). All four babies with LVO < 100 ml/kg/minute died, and 6/7 babies with LSVI < 1 ml/kg died. Detailed echocardiographic evaluation shows that the haemodynamic features of persistent pulmonary hypertension are diverse and that clinical diagnosis can be incorrect. Low LV output and stroke volume, usually with normal LV function, were the only Doppler echocardiographic parameters to predict subsequent death. This correlation with outcome requires further prospective evaluation.

Treatment of severe persistent pulmonary hypertension of the newborn with magnesium sulphate

Eight of nine newborn infants with severe persistent pulmonary hypertension of the newborn (PPHN), and a predicted mortality of 100%, and one infant with a predicted mortality greater than 94% based on alveolar-arterial oxygen tension difference [A-a)DO2) were treated with magnesium sulphate (MgSO4) as a life saving therapy after they failed to improve with conventional treatment. Magnesium at high serum concentrations decreases pulmonary pressures and is a muscle relaxant and sedative. Diluted MgSO4.7H2O solution (200 mg/kg) was given intravenously over 20-30 minutes. No changes in the treatment were made after MgSO4. Mean serum magnesium concentration was maintained between 2.88 and 5.67 mmol/l by continuous intravenous infusion (six infants). Baseline arterial oxygen tension (PaO2) and haemoglobin oxygen saturation had mean (SD) values of 4.66 (1.8) kPa and 60.4 (29.7)% respectively, which started to increase one hour after MgSO4 infusion, and increased significantly at six hours to 12.04 (7.07) kPa and 91.8 (10.88)% respectively. Arterial carbon dioxide tension (PaCO2) decreased and pH increased significantly after one hour compared with the baseline value. PaO2 increases are probably secondary to a decrease in pulmonary vascular resistance and pressure, decrease in a right to left shunt, better ventilation:perfusion ratio, and PaCO2 decrease and pH rise. Seven infants survived (77.8%). These results demonstrate the beneficial effect of magnesium in the management of PPHN when other accepted treatment fails, is contraindicated, or not available.

Ventilatory response to combined high frequency jet ventilation and conventional mechanical ventilation for the rescue treatment of severe neonatal lung disease

High frequency jet ventilation (HFJV) was used to treat 176 infants who were either failing to respond to conventional mechanical ventilation (CMV) or demonstrating pulmonary air leak. The median birthweight for infants treated with HFJV was 1530 g, median gestational age was 31 weeks. Median duration of therapy with HFJV was 3.0, with a range of 0.1 to 27 days. During the first 24 hours of treatment, mean airway pressure decreased from 16.2 +/- 0.3 (Mean +/- SEM) cmH2O to 12.2 +/- 0.3 cmH2O, while mean PaO2 increased from 65.3 +/- 3.0 torr to 93.3 +/- 3.0 torr during the same time period. Simultaneously, mean PaCO2 decreased from 46.4 +/- 1.5 torr to 36.6 +/- 1.0 torr, although peak inflating pressure decreased from 34.3 +/- 0.7 cmH2O to 30.1 +/- 0.8 cmH2O. Ninety-five (54%) infants treated with HFJV survived. Of 123 infants with RDS 75 (61%) survived. The rate of complications for HFJV patients was similar to that seen with CMV in our nursery. This study suggests that HFJV provides improved oxygenation and ventilation of infants at lower mean and peak pressures compared to conventional mechanical ventilation. HFJV combined with CMV may be a valuable adjunct to therapy in infants with severe lung disease.