|Vol.11 No. 1|
Editors: Dr. Sam SP Lau
Dr. Kwong Ngai Shan
Department of Paediatrics, Tuen Mun Hospital
Exogenous surfactant is primarily meant for use in premature babies with surfactant deficiency. Other conditions which surfactant replacement may be beneficial include meconium aspiration syndrome, severe pneumonia, acute respiratory distress syndrome, etc. In this article, I will focus the discussion on its use in respiratory distress syndrome for preterm infants and share my personal view on the practical aspect of about this treatment.
Indications for Using Surfactant in Preterm Babies
Prophylaxis treatment is meant for babies who are at high risk of developing RDS, and studies including babies <30 weeks have shown that maximum benefit is seen when surfactant is instilled immediately after delivery.1 All the included studies note an initial improvement in respiratory status and a decrease in the risk of respiratory distress syndrome in infants who receive prophylactic treatment when compared with control. There is a decrease in the risk of pneumothorax (typical relative risk (RR) 0.35, 95% confidence interval (CI) 0.26, 0.49; typical risk difference (RD) -0.15, 95% CI -0.20, -0.11), a decrease in the risk of pulmonary interstitial emphysema (typical RR 0.46, 95% CI 0.35, 0.60; typical risk difference -0.19, 95% CI -0.25, -0.13), a decrease in the risk of neonatal mortality (typical RR 0.60, 95% CI 0.44, 0.83; typical RD -0.07, 95% CI -0.12, -0.03). There is also a decrease in risk of bronchopulmonary dysplasia or death (typical RR 0.84, 95% CI 0.75, 0.93; typical RD -0.10, 95% CI -0.16, -0.04). There are no differences in risk of intraventricular haemorrhage, patent ductus arteriosus, necrotising enterocolitis or retinopathy of prematurity. However, doctor attending standby has to get the medication and equipment ready beforehand and the dose has to be given intra-tracheally right after intubation on site. Prior arrangement has to be secured with the delivery room staff. SpO2 monitoring should be available during and after dosing.
Prophylactic use of surfactant had been shown to have better result when compared with early selective regime1,2 in babies <30 weeks. Prophylaxis use showed a decrease in risk of pneumothorax that was of borderline statistical significance (RR 0.57, 95% CI 0.32, 1.03; RD -0.05, 95% CI -0.10, 0.00), decrease in risk of pulmonary interstitial emphysema (RR 0.46, 95% CI 0.22, 0.98; RD -0.08, 95% CI -0.15, -0.00). There is however no difference in risk of NEC, PDA, PIVH BPD or ROP. It also results in decreased mortality and BPD in those less than 30 weeks gestation.
When comparing early (surfactant administration within first 2 hours after birth) versus delayed (surfactant administration after 2 hours after birth in established RDS cases) selective regimes2 in babies of all gestation ages, it was well shown that outcome is better in the early treatment group, with significant reductions in risk of pneumothorax (RR 0.70, 95% CI 0.59, 0.82; RD -0.05, 95% CI -0.08, -0.03), risk of pulmonary interstitial emphysema (RR 0.63, 95% CI 0.43, 0.93; RD -0.06, 95% CI -0.10, -0.01), neonatal mortality (RR 0.87, 95% CI 0.77, 0.99; RD -0.03, 95% CI -0.06, -0.00), chronic lung disease at 36 weeks (RR 0.70, 95% CI 0.55, 0.88; RD -0.03, 95% CI -0.05, -0.01). There is a trend toward risk reduction in BDP or death at 28 days (RR 0.94, 95% CI 0.88, 1.00; RD -0.04, 95% CI -0.07, -0.00). No differences were found in other complications of RDS or prematurity.
|Prophylactic use of surfactant had been shown to have better result when compared with early selective regime in babies <30 weeks.|
Early selective treatment should be based on clinical ground. There is no need to wait for chest radiograph to assess the severity of RDS, as the ultimate aim of surfactant use is to replace what is lacking rather than depends on how bad the CXR looks. The time spent while waiting for radiograph, no matter how short it is, can cause irreversible damage to the lung, or prolonging the hypoxaemia state.
However there is one prerequisite before instillation of exogenous surfactant, that is to make sure the ETT is properly positioned. Make sure you check the baby's air entry by listening to both sides of the chest and watching for symmetrical chest rise with each breath. A useful formula to guide ETT depth of insertion at the upper lip = [BW (kg) + 6] cm
Survanta4 is what we are using in Tuen Mun Hospital. It is a modified natural bovine lung extract containing phospolipids, neutral lipids, fatty acids, and surfactant-associated proteins B and C, to which colfosceril palmitate (DPPC, the major lipid component of natural surfactant), palmitic acid, and tripalmitin are added. It is suspended in normal saline (0.9% sodium chloride) and heat sterilised. Animal metabolism studies show that most of a dose becomes lung-associated within hours of administration, and lipids enter endogenous surfactant pathways of reuse and recycling.
When using surfactant in NICU, make sure the followings are secured before you give surfactant:
Administration of Survanta should best be performed in a close circuit system using in-line catheter, with minimal disturbance of the ventilatory circuit and interruption of distending pressure. The recommended volume (4 ml/kg) should be given as 4 aliquots. Follow the manufacturer's instruction if conditions allow. If baby is critical and labile, do not manipulate too much. The total dose of surfactant can be safely given in aliquots while maintaining baby in supine position. There is no proven evidence that positioning will help redistribution of administered surfactant once it is attached to lung tissue. Prolonged administration by instillation, either as very slow injection or infusion, via a special adaptor, worsens the distribution, however.
In between instillation, the ventilatory settings should be maintained. If possible, avoid hand bagging, as the inflation pressure may be increased unnoticed and causing baro-trauma and volu-trauma. Sufficient time should be allowed for the baby to stabilised in between. Watch closely the vital signs from the monitors.
As the lung compliance rapidly improves, and one should promptly readjust the ventilatory settings. The first improvement will usually be SpO2, and so FiO2 can be decreased cautiously, basing on the SpO2 readings. Always keep tight control in the range of (88% to 95%), by fine tuning the FiO2. The next improvement will be compliance, and in turn, the tidal volume, so the CO2 will drop. It is important to obtain an arterial blood gas within 30 minutes after surfactant dose. PaCO2 of 45 mmHg to 50 mmHg will be fine. There is no need to lower CO2 level below 40 mmHg as hypocarbia is harmful to the brain, and the price of using high PIP and tidal breathing to achieve such CO2 level is not justified. PIP can hence be reduced slowly, basing on the extent of chest excursion and CO2 level. TcCO2 monitoring is helpful for trending.
|As the lung compliance rapidly improves, one should promptly readjust the ventilatory settings.|
It is important to keep a reasonable PEEP since initiation of IMV. A starting PEEP of 6 cm water for RDS is recommended, irrespective of gestational age and weight. PEEP is the single most important parameter to keep the lung recruited and stabilised. It should then be adjusted according to subsequent progress and CXR findings. If PEEP is lowered prematurely, the lung will be de-recruited, and clinically will manifest as increasing FiO2 requirement and increasing respiratory rate and insucking of chest wall.
After giving the first dose of surfactant, do not suction the infant for at least 1 hour after dosing unless signs of significant airway obstruction occur. Frequent endotracheal suctioning will worsen the clinical status as it results in loss of distending pressure, trauma to the airway, and nocosomial infection. More important, the procedure itself causes cardiovascular instability, and increases chance of periventricular haemorrhage.
Second and subsequent doses of surfactant can be given at 6 hourly intervals when indicated, basing on similar clinical parameters set up above. Up to 4 doses can be given within first 48 hours.
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