Surfactant bolus instillation: effects of different doses on blood pressure and cerebral blood flow velocities

Surfactant and neonatal hemodynamics during the postnatal transition

Surfactant replacement therapy (SRT) has revolutionized the management of respiratory distress syndrome (RDS) in premature infants, leading to improved survival rates and decreased morbidity. SRT may, however, be associated with hemodynamic changes, which can have both positive and negative effects on the immature cardiovascular system, during the transitional adaptation from fetal to extrauterine environment. However, there is a relative paucity of evidence in this domain, with most of them derived from small heterogeneous observational studies providing conflicting results. In this review, we will discuss the hemodynamic changes that occur with surfactant administration during this vulnerable period, focusing on available evidence regarding changes in pulmonary and systemic blood flow, cerebral circulation and their clinical implications.

Review demonstrates that less invasive surfactant administration in preterm neonates leads to fewer complications

Surfactant treatment of neonatal respiratory distress syndrome (RDS) was introduced in Europe during the 1990s. Meta-analyses have indicated that using less invasive surfactant administration techniques on preterm neonates receiving continuous positive airway pressure (CPAP) results in improved survival rates without bronchopulmonary dysplasia. Surfactant should be administered early and ventilator settings adapted to changing oxygen requirements and lung mechanics. Side effects including initial bradycardia, oxygen desaturation, tube obstruction and isolated cases of pulmonary haemorrhage have been reported.

CONCLUSION

Less invasive surfactant therapy improves pulmonary outcomes in preterm neonates with RDS and should ideally be administered in combination with CPAP.

Current Issues and Challenges in the Use of Aerosolized Surfactant for Respiratory Distress Syndrome in the Newborns

BACKGROUND: Surfactant replacement therapy is a recognized treatment for respiratory distress syndrome (RDS) in the newborns. Over the past 30 years, human and animal trials have been performed regarding administration of aerosolized surfactant to the injured lung, however the result has been unsatisfactory when compared with instilled surfactant delivery via endotracheal tube (ETT). This review aims to investigate the current issues, challenges and future recommendation of aerosolized surfactant therapy.CONTENT: Five randomized clinical trials in humans and 13 animal trials met the inclusion criteria and were reviewed. Most animal trials agree that this method of treatment is feasible. However, human trials presented conflicting results, and generally showed it to be ineffective. When compared with surfactant delivery via ETT, aerosolized surfactant is less effective in improving respiratory function.SUMMARY: The current data from human trials does not support the implementation of aerosolized surfactant therapy to treat newborns with RDS. Further research is necessary to improve nebulization, delivery, distribution and deposition in the lung, to investigate aerosolized surfactant delivery via ETT and to determine the appropriate dose.KEYWORDS: surfactant, aerosol, prematurity, respiratory distress syndrome

Patent ductus arteriosus hemodynamics in very premature infants treated with poractant alfa or beractant for respiratory distress syndrome

OBJECTIVE

Respiratory distress syndrome (RDS), requiring mechanical ventilation and exogenous surfactant treatment, and patent ductus arteriosus (PDA), are common co-morbidities in very premature infants. The effects of intra-tracheal surfactant administration on the cardiovascular and pulmonary systems in very premature infants with RDS and PDAs are not well characterized. We evaluated the effects of poractant alfa and beractant, surfactants with different rapidity of onset and duration of action, in very premature infants with RDS. To assess whether there were differences in PDA hemodynamics in very premature infants with RDS treated with poractant alfa and beractant during the first week of life and to assess whether poractant alfa or beractant had a direct effect on PDAs and PDA hemodynamics following the second dose of surfactant.

STUDY DESIGN

We studied 50 in-born, very premature infants with RDS, 24 0 of 7 to 29 6 of 7 weeks gestation, treated with poractant alfa or beractant, in an open label, 1:1, randomized clinical trial. A subgroup of 16 patients with severe RDS, treated with a second dose of surfactant, had echocardiographical assessments before and 20 to 30 min after the second dose of surfactant.

RESULT

There were 25 infants treated with poractant alfa (27.1±1.6 weeks, birth weight 930±231 g) and 25 treated with beractant (26.7±1.7 weeks, P=0.407 and birth weight 898±282 g, P=0.666). Clinically significant PDAs were diagnosed and treated in 8 of 25 (32%) of the poractant alfa and 19 of 25 (76%) of the beractant group (P=0.002). Indomethacin treatment was slightly earlier (3.4±2.5 days) in the poractant alfa than in the beractant group (5.1±4.9 days, P=0.038). Right ventricle pressure (RVP)/systolic arterial pressure (SAP) ratio in the first week was slightly lower in the poractant alfa (64±20%) than in the beractant (78±26%, P=0.048) group. Following a second dose of surfactant, neither poractant alfa nor beractant changed PDA flow. These hemodynamic observations were associated with less respiratory support in the poractant alfa group, allowing earlier extubation (13 of 25 at 48 h and 15 of 25 at 72 h), than in the beractant group (6 of 25 at 48 h, P=0.044, and 8 of 25 at 72 h, P=0.049).

CONCLUSION

The more rapid improvement in pulmonary function in the poractant alfa-treated infants was associated with a lower RVP/SAP ratio and a corresponding earlier treatment with indomethacin. Neither surfactant had a significant direct effect on PDA hemodynamics. The lower frequency of clinically significant PDAs in the poractant alfa compared with the beractant group may represent an indirect effect of the differences in the pulmonary improvement induced by the two surfactants.

Randomized clinical trial comparing two natural surfactant preparations to treat respiratory distress syndrome

OBJECTIVES

Natural surfactant preparations have been shown to reduce the severity and mortality of respiratory distress syndrome (RDS) in preterm infants. The objective of this study was to compare the efficacy of two natural surfactants, namely SF-RI 1 (Alveofact) and barectant (Survanta), on the incidence of chronic lung disease (CLD) and other associated complications of RDS in preterm infants.

METHODS

Preterm infants with RDS requiring artificial ventilation were randomly selected to receive an initial dose of either Alveofact or Survanta. The two treatment groups were tested for variation in gas exchange, ventilatory settings and neonatal complications such as CLD and mortality.

RESULTS

After 5 days the Survanta-treated infants had a lower fraction of inspired oxygen (FiO2) compared with the Alveofact-treated infants. There were no differences in the ventilatory settings. More infants in the Survanta group were extubated at 3 days and fewer required the use of postnatal steroids. Less CLD and duration of oxygenation were experienced by the Survanta-treated group.

CONCLUSIONS

Improved oxygenation and reduced ventilatory requirements were greater with Survanta compared to Alveofact, which in turn was associated with a trend towards a lower incidence of serious pulmonary complications.

Acute side effects of surfactant treatment

There is increasing evidence from studies on animals and humans that surfactant administration may have a great impact on cerebral perfusion. These effects may result from direct pulmonary or hemodynamic changes (or a combination of both), but may also be due to rapid alterations of blood gases. Type of surfactant and mode of administration seem to play an important role. Results from the pertinent literature are summarised with a special emphasis on how to avoid potentially harmful side effects of surfactant therapy in preterm infants.

Endotracheal surfactant atomization: an alternative to bolus instillation?

OBJECTIVE

To investigate the effect of an intratracheal surfactant fog on oxygenation, blood pressure, distribution, and recovery rate as a pilot study to intratracheal surfactant aerosol.

DESIGN

Prospective, randomized study.

SETTING

University laboratory.

SUBJECTS

A total of 15 New Zealand White rabbits.

INTERVENTIONS

The anesthetized ventilated rabbits were surfactant-deprived by repeated lung lavages and then received 200 mg/kg of a 99mTc-labeled porcine surfactant (Curosurf) either as bolus or as intratracheal surfactant fog.

MEASUREMENTS AND MAIN RESULTS

Blood gases and pressure were measured and distribution as well as recovery rate of the surfactant determined by means of the radio label (gamma camera images and lung processing with subsequent gamma counter measurements). Respiratory function normalized immediately, no difference could be found between the two groups with regard to PaO2, PaCO2, and blood pressure. Even distribution of the radiolabel was found with both methods, the bolus group showing a higher percentage of lung pieces with label concentrations of double average or more. Recovery rates were 82.5%+/-13.1% (mean +/- SD) in the bolus group and 86.5%+/-7.7% in the fog group.

CONCLUSION

Endotracheal surfactant fog application is as effective as bolus instillation and may have a role in the treatment of adult respiratory distress syndrome. It has to be considered as a first step in producing an effective aerosol.

A risk-benefit assessment of natural and synthetic exogenous surfactants in the management of neonatal respiratory distress syndrome

Alveolar surfactant is central to pulmonary physiology. Quantitative and qualitative surfactant abnormalities appear to be the primary aetiological factors in neonatal respiratory distress syndrome (RDS) and exogenous replacement of surfactant is a rational treatment. Available exogenous surfactants have a natural (mammal-derived lung surfactants) or synthetic origin. Pharmacodynamic and clinical studies have demonstrated that exogenous surfactants immediately improve pulmonary distensibility and gas exchange; however, this is achieved more slowly and with more failures with synthetic surfactants. The ensuing advantageous haemodynamic effects are not so striking and they include an inconvenient increased left to right ductal shunt. Two strategies of administration have been used: prophylactic or rescue therapy to treat declared RDS. All methods of instillation require intubation. In addition to the early benefits (improved gas exchange and reduced ventilatory support) the incidence of classical complications of RDS, especially air leak events, is decreased except for the uncommon problem of pulmonary haemorrhage. The incidence of bronchopulmonary dysplasia is neither uniformly nor significantly reduced although the severity appears to be lessened. The overall incidence of peri-intraventricular haemorrhages is not diminished although separate trials have shown a decreased rate. The most striking beneficial effect of exogenous surfactants is the increased survival (of about 40%) of treated very low birthweight neonates. A small number of adverse effects has been described. The long term outcome of survivor neonates with RDS treated with surfactants versus control neonates with RDS not treated with surfactants is similar in terms of physical growth, at least as good in terms of respiratory status, with a similar or slightly better neurodevelopmental outcome. There is not clear benefit of exogenous surfactant therapy in extremely premature infants (< 26 weeks gestational age, birthweight < 750 g). The potential risks of contamination, inflammatory and immunogenic reaction and the inhalation of platelet activating factor remain a theoretical concern of surfactant therapy which has not been confirmed in clinical practice. The optimal timing of treatment favours prophylaxis over rescue treatment and early rescue treatment rather than delayed therapy. Meta-analyses suggest the clinical superiority of natural surfactant extracts over a synthetic one (colfosceril palmitate). The economic impact of surfactant therapy is favourable and the costs per quality-adjusted life year (QALY) for surviving surfactant treated infants are low. In conclusion, the mid and long term benefit/risk ratio clearly favours the use of exogenous surfactants to prevent or to treat RDS in neonates who have a gestational age of > 26 weeks or a birthweight of > 750 g, especially with the prophylactic strategy using natural surfactant extracts.

A randomized comparison of surfactant dosing via a dual-lumen endotracheal tube in respiratory distress syndrome. The Spanish Surfactant Collaborative Group

AIM

To determine if 1-minute instillation of Curosurf via a dual-lumen endotracheal tube without interruption of mechanical ventilation could decrease the incidence of hypoxia (drop in oxygen saturation [SaO2] to <80%, or of transcutaneous partial pressure of oxygen [PtcO2] to <50 mm Hg [6.6 kPa]) and bradycardia (heart rate below 80 beats/minute) at dosing, without affecting the efficacy of the standard bolus delivery.

DESIGN

Prospective, multicenter, randomized, nonblinded clinical trial.

SETTING

Neonatal intensive care units of the Spanish Surfactant Collaborative Group.

PATIENTS AND METHODS

One hundred ninety-eight infants (birth weight 600-2000 g) with respiratory distress syndrome needing mechanical ventilation with a fraction of inspired oxygen [FIO2] 0.40 were randomized before 24 hours to receive 200 mg/kg of Curosurf, either by bolus instillation (n = 99) or by a simplified dosing technique (n = 99), giving the full dose in 1 minute via a dual-lumen endotracheal tube without positioning, interruption of mechanical ventilation, or bagging. Two additional doses (100 mg/kg) were given within 12 and 24 hours of first dose, by the same method, if the infant still needed mechanical ventilation and had a FIO2 0.30. The effects of both procedures on the incidence of acute adverse events at dosing, gas exchange, ventilator requirements, and outcome at 28 days were compared.

RESULTS

Fewer episodes of hypoxia (18 vs 40% of doses), and a smaller decrease in heart rate and SaO2 were observed in the dual-lumen group. Efficacy of surfactant, based on improvement of oxygenation, ventilator requirements, and number of doses required, was similar in both groups. Infants in the dual-lumen group had a lower total time exposure to supplemental oxygen (195+/-199 vs 266+/-221 hours). No differences in the incidence of air leaks, intraventricular hemorrhage, patent ductus arteriosus, bronchopulmonary dysplasia, or survival were observed.

CONCLUSION

A simplified 1-minute Curosurf dosing procedure via a dual-lumen endotracheal tube without fractional doses, ventilator disconnection, changes in the infant's position, or manual bagging was found to reduce the number of dosing-related adverse transient episodes of hypoxia. Although the simplified method appeared to be as effective as bolus delivery, this should be confirmed in a larger trial.

Rate of surfactant administration influences lung function and gas exchange in a surfactant-deficient rabbit model

The aim of this study was to test whether the effect of surfactant treatment on lung function in a surfactant-deficient animal model can be influenced by the rate at which surfactant is administered. Surfactant deficiency was induced in 18 New Zealand white rabbits (weighing approx. 1 kg each) by lung lavage with normal saline. The arterial/alveolar oxygen ratio (a/A ratio), functional residual capacity (FRC), dynamic compliance of the respiratory system (Crs), tidal volume (V(T)), alveolar portion of the tidal volume (V(A)) and arterial P(CO2) (P(a,CO2)) were measured before and after lavage and 15, 30, 60, 90, and 120 min after administration of a single dose of surfactant (Survanta, 100 mg/kg). Two surfactant administration protocols were compared over a 2-h interval: an infusion lasting 4 min and an infusion over 2 min. Both administrations were given during continuous mechanical ventilation. The six lung function and gas exchange parameters improved significantly following surfactant administration over 2 min compared with a control group. However, only the a/A ratio and V(A) improved following the 4-min protocol. Comparison of the two intervention protocols yielded significantly differences in V(A) and P(a,CO2), favoring the shorter administration. These results support the hypothesis that fast (2 min) administration of surfactant will improve its distribution to formerly collapsed alveoli and results in better lung function, improved ventilation, and (to a lesser extent) better oxygenation than prolonged infusions (4 min).

Nitric oxide contributes to surfactant-induced vasodilation in surfactant-depleted newborn piglets

To investigate whether nitric oxide (NO) is involved in surfactant-induced systemic and pulmonary vasodilatation in newborn piglets with surfactant deficiency, 2-6-d-old piglets were subjected to repeated saline lung lavages. They were then randomly assigned to one of two groups (seven in each group): the N(omega)-nitro-L-arginine methyl ester (L-NAME) group received 3 mg/kg L-NAME i.v. 45 min before endotracheal instillation of 200 mg/kg porcine surfactant; the saline group received saline i.v. at the same time point, and instillation of 200 mg/kg surfactant. Mean arterial blood pressure, systemic vascular resistance, pulmonary arterial pressure, and pulmonary vascular resistance increased significantly after injection of L-NAME (all p < 0.01), whereas the cardiac index decreased significantly (p < 0.05). Saline injection did not change any variable. Significant decreases in mean arterial blood pressure (from a mean +/- SD of 66 +/- 10 to 53 +/- 9 mm Hg, p < 0.01), pulmonary arterial pressure (from 29 +/- 6 to 23 +/- 6 mm Hg, p < 0.01), and systemic vascular resistance (from 0.40 +/- 0.13 to 0.33 +/- 0.12 mm Hg/mL/min/kg, p < 0.05) were observed only in the saline group after surfactant instillation, whereas the decrease in pulmonary vascular resistance was not significant after surfactant instillation (p = 0.06). In contrast to the saline group, these variables were not modified in the L-NAME group after surfactant instillation. We conclude that the vasodilatory effect of porcine surfactant instillation in newborn piglets with surfactant deficiency is associated with activation of NO synthase.

Acute effects on systemic and pulmonary hemodynamics of intratracheal instillation of porcine surfactant or saline in surfactant-depleted newborn piglets

Surfactant instillation may affect systemic and pulmonary hemodynamics. The aim of this study was to investigate whether this effect is specific to surfactant or if it can be triggered by instillation of the same volume of saline. Piglets 3-5-d-old were subjected to repeated lung lavage using 20 mL/kg 0.9% saline until the partial pressure of arterial O2 was < 10 kPa and partial pressure of arterial CO2 was between 4.0 and 6.0 kPa with fraction of inspired oxygen (FiO2) 1.0 and peak inspiratory pressure 25 cm H2O. Porcine surfactant 200 mg/kg (80 mg/mL) or the same volume of 0.9% saline was instilled into the lungs through a feeding catheter entered through the endotracheal tube. Mean arterial blood pressure, pulmonary artery pressure, and cardiac output were measured continuously. There was a significant decrease in mean arterial blood pressure from 67 (+/- 13) mm Hg to 52 (+/- 18) mm Hg (p < 0.05) 210 s after instillation of surfactant. Systemic vascular resistance decreased from 0.42 (+/- 0.18) to 0.34 (+/- 0.18) mm Hg x mL-1 x min x kg (p < 0.05) from 0 min to 180 s after instillation of surfactant. In the group receiving saline instillations there were no significant changes in mean arterial blood pressure or systemic vascular resistance. A transient but significant increase in mean pulmonary artery pressure was seen 120 s after instillation in both groups with a return to presurfactant level 240 s after instillation. Pulmonary vascular resistance increased transiently and significantly only in the group receiving surfactant. We conclude that porcine surfactant causes a decrease in systemic vascular resistance, resulting in a decrease in mean arterial blood pressure in newborn lung-lavaged piglets not seen after instillation of the same volume of saline.

Circulatory changes after surfactant bolus instillation in lung-lavaged adult rabbits

Following surfactant instillation in infants treated for respiratory distress syndrome, a mean arterial blood pressure (MABP) decrease is often observed. Its etiology and pathogenesis are still unknown. In this study various circulatory parameters were recorded continuously after surfactant instillation to elucidate the role of pulmonary vascular resistance as one possible cause for the MABP drop. Seven anesthetized adult New Zealand white rabbits were artificially ventilated after tracheotomy. Arterial and right atrial pressure were recorded continuously. Pulmonary artery pressure and cardiac output were determined by means of a thermodilution catheter. After inducing surfactant deficiency by repeated saline lavages, 200 mg/kg body weight of a natural surfactant preparation was administered by tracheal bolus instillation. PaO2 increased rapidly from 8.0 +/- 1.3 kPa to 51.2 +/- 8.8 kPa (mean +/- standard deviation) within 2 min (p < .05). MABP dropped from 12.1 +/- 1.9 kPa to 8.9 +/- 2.3 kPa within 2 min (p < .05). Pulmonary artery pressure, cardiac output, and right atrial pressure did not change during the observation period of 60 min. The results suggest that a peripheral vasodilatation is the most likely cause for the drop in MABP.

Hemodynamics and tissue blood flow after porcine surfactant replacement in surfactant-depleted newborn piglets

In 22 newborn piglets we studied the effect of hypovolemia or hypoxemia on hemodynamics and regional blood flow after instillation of porcine surfactant. Surfactant deficiency was obtained by repeated lung lavage, and blood flow measurements were carried out using radioactive microspheres. Three groups of piglets were studied, controls (n = 8), hypovolemia (n = 7), and hypoxemia (n = 7). Three to five minutes after instillation of surfactant, mean arterial blood pressure decreased significantly in all three groups with a mean decrease (+/- SD) of 31(+/- 12), 33(+/- 9), and 29(+/- 9) mm Hg, respectively (p < 0.01 in all three groups). Systemic vascular resistance decreased significantly in all three groups immediately after surfactant instillation (p < 0.01) and returned to presurfactant level after 60 min. Blood flow did not change after surfactant instillation in any of the three groups, in neither skin, muscle, pancreas, brain, nor retina. In liver, kidney, intestine, and choroidea there was a decrease in blood flow immediately after instillation with return to presur-factant levels within 60 min. Hypoxemia or hypovolemia before surfactant instillation did not increase the hemodynamic instability. The decrease in mean arterial blood pressure was caused by a vasodilation and not by a reduced cardiac output.

[Influence of surfactants on hemodynamics during neonatal respiratory distress syndrome]

The neonatal respiratory distress syndrome tends to delay the circulatory adaptation to extra-uterine life and leads to systematic hypotension. Haemodynamic changes following the instillation of surfactant are not stereotyped. They depend on the type of surfactant, the time of the instillation, the degree of prematurity, the severity of the respiratory disease and the mode of instillation. They are characterized by a transient haemodynamic instability with variable consequences on arterial pressure and systemic blood flow. The use of surfactant tends to decrease pulmonary arterial resistances and pulmonary arterial pressures but this effect is variable and is not obviously accompanied by long-term deleterious effect on the arterial duct. Haemodynamics and blood gases changes due to surfactant instillation have a variable effect on cerebral blood flow. The potential role of blood gas and haemodynamics changes on the occurrence of pulmonary haemorrhage or cerebral damage following instillation of surfactant remains poorly established but has to be taken into account.

[Natural or artificial surfactants? Arguments in favour of natural surfactants]

The use of exogenous surfactant (ES) is an essential component for prevention and treatment of hyaline membrane disease (HMD). The ES available for clinical use are of two therapeutic classes: natural surfactants prepared from mammalian lung and artificial surfactants. The choice between these two classes of ES is controversial. In this overview, we present the arguments in favour of the preferential use of natural ES. The presence of hydrophobic specific proteins (SP-B and SP-C) provides to natural ES better surface tension properties than artificial ES. The in vitro greater efficacy of natural ES has been confirmed in vivo in experimental models of surfactant deficiency, human pharmacodynamic studies, and comparative clinical trials. Furthermore, the excellent clinical tolerance and harmlessness of natural ES has been firmly established. A meta-analysis of the comparative clinical trials between natural ES and one artificial ES (enrolling as many as 4400 babies treated for HMD) suggests that the use of natural ES compared to this artificial ES significantly reduces the neonatal mortality by 20%. In conclusion, all these arguments are in favor of the preferential use of natural ES for prevention and treatment of HMD.

Prevention of intraventricular hemorrhage in preterm infants

Prematurely born infants with intraventricular hemorrhage (IVH) suffer significant morbidity and mortality, particularly those infants with high grade hemorrhage. The more premature infants have a higher incidence, experiencing more severe IVH. Early onset IVH is also likely to be severe and to progress to a higher grade. The etiology of intraventricular hemorrhages is clearly multifactorial, with differing sets of risk factors for early onset and later occurring hemorrhage. Prevention requires multilayered strategies, both prenatal and postnatal. These strategies are discussed in detail, highlighting unresolved controversies. Certain recommendations for prevention can be made. These include efforts to prevent preterm delivery, transfer of high risk mothers to tertiary care centers and antenatal maternal steroid use. Postnatally, the importance of optimal resuscitation and neonatal care practices is stressed, particularly those which minimize cerebral blood flow fluctuation. Postnatal indomethacin use should be considered in most infants. Further investigation of other strategies is necessary, including multicenter randomized trials to further evaluate antenatal pharmacologic agents, as well as the relative efficacy of different modes of delivery. The different risk factors for early onset versus later onset IVH must be more clearly delineated. Most importantly, any strategy must include sustained neurodevelopmental followup.