Edmund A. Egan

Lung surfactant replacement in premature lambs with extracted lipids from bovine lung lavage: effects of dose, dispersion technique, and gestational age.

ABSTRACT: Extracted bovine calf lung lipids (CLL) with minimal protein (approximately 1 %) were instilled prior to ventilation in groups of premature lambs of average gestational ages of 127 and 133 days. Aqueous dispersions of CLL were prepared by two techniques prior to instillation: sonication in an ice bath (S) and mechanical vortexing at room temperature (V). A low surfactant dose (15 mg CLL/kg animal weight) and a high dose (100 mg/kg) were investigated for each dispersion technique. Following tracheal instillation of surfactant, lambs were ventilated with 100% oxygen for 2 h with umbilical circulation intact, and for up to an additional 10 h after separation. A clear improvement in blood oxygenation and lung compliance was found over controls for lambs given 15 mg/kg and 100 mg/kg CLL(V), and 100 mg/kg CLL(S). Lambs treated with 15 mg/kg CLL(S) failed to improve over controls. Experimental groups treated with equal doses of CLL(V) and CLL(S) had similar amounts of lung lavage phospholipid, with values progressively declining during ventilation. Analyses of in vitro surface properties showed that both vortexed and sonicated CLL dispersions adsorbed to equilibrium surface pressures of 45–47 dynes/cm in seconds at concentrations > 0.25 nig CLL/ml. Both dispersions also lowered surface tension to less than 1 dyne/cm under dynamic compression at 37° C in 100% humidity, although CLL(V) showed some enhancement over CLL(S) in dynamic surface activity at low subphase concentration (0.5 mg/ml). Moreover, CLL(V) and CLL(S) differed markedly in their effects on pressure-volume mechanics in a surfactant-deficient excised rat lung model. Instilled CLL(V) dispersions improved excised lung pressure-volume mechanics at significantly lower concentrations than CLL(S) dispersions.

Pathophysiology of congenital diaphragmatic hernia III: Exogenous surfactant therapy for the high-risk neonate with CDH

Exogenous surfactant therapy (EST) in surfactant-deficient premature infants has been shown to improve lung compliance, decrease morbidity, and improve survival. Reports have demonstrated that newborns with congenital diaphragmatic hernia (CDH) have lung compliance, pressure-volume curves, and hyaline membrane formation resembling those changes seen in surfactant deficient premature newborns. We hypothesize that EST may also benefit infants with CDH. All high risk cases of prenatally diagnosed CDH at Childrens Hospital of Buffalo from November 1988 to February 1991 were prospectively evaluated for EST. In those families who chose to participate, the surfactant preparation, Infasurf (100 mg/kg), was instilled into the newborns lungs prior to the first breath. The remainder of the perinatal, neonatal, and surgical care was performed in a routine manner. Three high-risk prenatally diagnosed newborns with left CDH were treated with EST. All showed signs of decreased pulmonary compliance, but could still be adequately oxygenated and ventilated. Surgical correction was performed after stabilization and all required patch closures. Two of the three infants suffered no life-threatening episodes of pulmonary hypertension and all survived. These infants had many known indicators for poor outcome in CDH with an expected survival of less than 20%. We believe that EST in these neonates with CDH contributed to their survival with minimum morbidity. These results suggest that surfactant replacement for the high-risk neonate with CDH warrants further consideration and a randomized clinical trial is being planned.

Instillation of calf lung surfactant extract (calfactant) is beneficial in pediatric acute hypoxemic respiratory failure

OBJECTIVE Prospective study of the efficacy of calf lung surfactant extract in pediatric respiratory failure. DESIGN Multi-institutional, prospective, randomized, controlled, unblinded trial. SETTING Eight pediatric intensive care units (ICU) of tertiary medical centers. PATIENTS Forty-two children with acute hypoxemic respiratory failure characterized by diffuse, bilateral pulmonary infiltrates, need for ventilatory support, and an oxygenation index of >7. INTERVENTION Instillation of intratracheal surfactant (80 mL/m2). MEASUREMENTS AND MAIN RESULTS Ventilator parameters, arterial blood gases, and derived oxygenation and ventilation indices were recorded before and at intervals after surfactant administration. Complications and outcome measures, including mortality, duration of mechanical ventilation, and length of pediatric ICU and hospital stay, were also examined. Patients who received surfactant demonstrated rapid improvement in oxygenation and, on average, were extubated 4.2 days (32%) sooner and spent 5 fewer days (30%) in pediatric intensive care than control patients. There was no difference in mortality or overall hospital stay. Surfactant administration was associated with no serious adverse effects. CONCLUSIONS Administration of calf lung surfactant extract, calfactant, appears to be safe and is associated with rapid improvement in oxygenation, earlier extubation, and decreased requirement for intensive care in children with acute hypoxemic respiratory failure. Further study is needed, however, before widespread use in pediatric respiratory failure can be recommended.

Lung inflation and alveolar permeability to non-electrolytes in the adult sheep in vivo.

1. Experiments were performed on adult sheep to determine the effect of lung distension on the passive permeability of alveoli to water soluble non‐electrolytes. With the animal breathing oxygen spontaneously, a segment of one lung was isolated by passing a balloon‐tipped catheter through a tracheostomy into a distal bronchus. This isolated atelectatic segment was filled with an isosomotic saline solution containing radio‐labelled solutes of known molecular size: [125I]albumin, [14C]inulin, [14C]‐sucrose, [3H]mannitol, and [14C]urea. The segment was inflated with oxygen either to a preselected pressure, or to a predetermined fraction of its capacity. Inflation was then maintained for several 10‐15 min periods between which the oxygen supply was disconnected and the saline sampled, allowing the tracer concentrations to be measured. 2. At low inflating pressures (20‐32 cmH2O) and at low volumes (24‐54% of capacity), alveolar permeability to water soluble solutes was slight and could be characterized in terms of a membrane penetrated by cylindrical water filled pores of 0‐5‐1‐6 nm radius. In all experiments showing restricted diffusion, absorption of saline occurred. 3. There was a positive correlation between the degree of lung inflation and pore radius in both the pressure controlled and volume controlled experiments. At high inflating pressures and at inflation volumes which were close to the total capacity of the isolated segment, restriction of solute diffusion was lost; in five out of six such experiments there was a net movement of liquid into the alveoli. 4. These results can be explained by postulating that as the lung epithelium is progressively stretched there is an opening up of water filled channels between alveolar cells. At peak inflation, restriction of diffusion of water soluble solutes is lost, and the alveolar epithelium ceases to function as a barrier between the circulation and air spaces.

Changes in non‐electrolyte permeability of alveoli and the absorption of lung liquid at the start of breathing in the lamb.

1. Experiments were done on mature foetal lambs, 135–145 days in gestation, exteriorized at Caesarean section, and on new‐born lambs aged 12–60 hr. In the foetal lambs, test substances were added to lung liquid and then spontaneous ventilation was induced or the lungs were statically inflated with gas or saline. In the new‐born lambs, the left lung was ventilated in order to maintain respiratory gas‐exchange, while foetal lung liquid, taken from previous experiments and containing test substances, was introduced into the right lung, which was then inflated with gas and used for permeability measurements. In both foetuses and new‐borns, the gas used was O2 or N2O and, at 20 min intervals, ventilation or static inflation was interrupted, the gas in the lungs absorbed into the circulation and the remaining liquid sampled through the trachea. The following test substances were used in various combinations: [14C]‐erythritol, [3H]sucrose, [14C]inulin, [131I]albumin, and the polymer [131I]‐PVP. The last of these was separated, after the experiments, by gel filtration with Sephadex G200 or G50, into fractions of defined molecular radius. [131I]albumin, or a large molecule fraction of [131I]PVP, was used as a volume marker. 2. Spontaneous ventilation was associated with the absorption of liquid and with an alteration in the foetal pattern of non‐electrolyte permeability that could be characterized by postulating an opening up of water‐filled cylindrical pores to 34–56 A in radium. In the new‐born lambs, the results suggested pores 7–14 A in radius. 3. Static inflation of the foetal lungs with gas, to pressures of 25–35 cmH2O, gave permeabilities appropriate for pores 5‐5–12 A in radius. Static inflation with gas, to pressures of 41–49 cmH2O, produced changes appropriate for much larger channels, more than 125 A in radius and possibly much larger. With one exception, expansion with saline produced changes similar to those obtained by gas inflation to 25–35 cmH20. 4. It was concluded that in the initial stages of pulmonary ventilation a change takes place in alveolar epithelial cells. The increase in size would be sufficient to allow for rapid liquid absorption, but is not so great as to permit significant penetration by plasma albumin. The results obtained in the lung of the new‐born lamb statically inflated to 25–32 cmH2O suggest that, following the initial adaptation, alveolar permeability returns towards the foetal pattern, although the pores remain larger than in the foetus. The change in permeability pattern at birth appears to depend on the degree of lung expansion with gas.

The correlation of maternal cytomegalovirus infection during varying stages in gestation with neonatal involvement

An obstetric population was prospectively followed for evidence of primary maternal cytomegalovirus infection during gestation. The cord serum of infants whose mothers had serologic evidence of infection was analyzed for the level of IgM and for the presence of specific anticytomegalovirus IgM antibodies. The progeny were cultured for cytomegalovirus. In the four cases of maternal infection identified, the cord sera were found to be positive by immunofluorescence for anticytomegalovirus IgM immunoglobulins and correlated with recovery of virus in the immediate neonatal period or beyond. There was a direct correlation between severity of neonatal infection and presumed duration of disease in utero. These observations suggest that cytomegalovirus is capable of infecting the products of conception irrespective of gestational age, and that the clinical manifestations of congenital cytomegalovirus infection appear to be primarily a reflection of the duration of infection in utero.

Prevention of neonatal necrotizing enterocolitis

Small premature infants are often hypochlorhydric, and frequently their stomachs are colonized by enteric, gram-negative bacteria. We tested a hypothesis that gastric pH affected the colonization of the stomach with enteric bacteria and that this colonization was causally related to the risk or severity of necrotizing enterocolitis. A prospective, double-blind study was conducted that compared a group of infants supplemented with 0.01–0.02 ml of 1 N HCl/ml of milk to a group with a similar supplement of water. Gastric pH, gastric enteric bacteria counts, and the incidence and severity of necrotizing enterocolitis were monitored. The median gastric pH of the HCl-supplemented group was lower (3.0) than controls (4.0) throughout the study (p < 0.001). The gastric enteric bacterial colonization rate and the quantitative bacterial counts were strongly correlated with gastric pH over 4 (p < 0.001). Somatic growth rates in infants in the HCl-supplemented group were equal to, or exceeded, those in the control group. There was 1 case of necrotizing entero-colitis among the 34 infants in the HCl-supplemented group and 8 cases among the 34 in the control group (p = 0.02). It appears that acidifying the feedings of small premature infants to a pH low enough to inhibit bacterial proliferation in the stomach significantly lowers the risk of necrotizing enterocolitis.

A prospective controlled trial of oral kanamycin in the prevention of neonatal necrotizing enterocolitis

Alimentary kanamycin, 15 mg/kg/day, was given as prophylaxis for neonatal necrotizing enterocolitis in a prospective study. Newborn infants of less than 1,500 gm birth weight who survived until initiation of alimentary nutrition at the University of Florida Neonatal Intensive Care Unit were admitted to a control or study group based on the last digit of the hospital number. Alimentary kanamycin was not absorbed; all blood levels determined were less than 0.5 μg/ml. The two groups had similar gestational ages, birth weights, severity of neonatal illness, and frequency of therapeutic procedures. In the study group of 35 infants, none developed neonatal necrotizing enterocolitis, whereas five cases occurred in the 40 control infants (p=0.038).

Component-specific surface and physiological activity in bovine-derived lung surfactants.

Composition, surface activity and effects on pressure-volume (P-V) mechanics are examined for lavaged calf lung surfactant (LS) and the clinical exogenous surfactants Infasurf and Survanta. Lavaged LS and Infasurf had closely-matching compositions of phospholipids and neutral lipids. Survanta had higher levels of free fatty acids and triglycerides consistent with its content of added synthetic palmitic acid and tripalmitin. Infasurf and Survanta both contained less total protein than LS because of extraction with hydrophobic solvents, but the total protein content relative to phospholipid in Survanta was about 45% lower than in Infasurf. This difference was primarily due to surfactant protein (SP)-B, which was present by ELISA at a mean weight percent relative to phospholipid of 1.04% in LS, 0.90% in Infasurf, and 0.044% in Survanta. Studies on component fractions separated by gel permeation chromatography showed that SP-B was a major contributor to the adsorption, dynamic surface activity, and P-V mechanical effects of Infasurf, which approached whole LS in magnitude. Survanta had lower adsorption, higher minimum surface tension, and a smaller effect on surfactant-deficient P-V mechanics consistent with minimal contributions from SP-B. Addition of 0.05% by weight of purified bovine SP-B to Survanta did not improve surface or physiological activity, but added 0.7% SP-B improved adsorption, dynamic surface tension lowering, and P-V activity to levels similar to Infasurf. The SP-B content of lung surfactants appears to be a crucial factor in their surface activity and efficacy in improving surfactant-deficient pulmonary P-V mechanics.

A multicenter randomized, masked comparison trial of natural versus synthetic surfactant for the treatment of respiratory distress syndrome

OBJECTIVE To compare the efficacy and safety of two surfactant preparations in the treatment of respiratory distress syndrome (RDS). METHODS We conducted a randomized, masked comparison trial at 21 centers. Infants with RDS who were undergoing mechanical ventilation were eligible for treatment with two doses of either a synthetic (Exosurf) or natural (Infasurf) surfactant if the ratio of arterial to alveolar partial pressure of oxygen was less than or equal to 0.22. Crossover treatment was allowed within 96 hours of age if severe respiratory failure (defined as two consecutive arterial/alveolar oxygen tension ratios < or = 0.10) persisted after two doses of the randomly assigned surfactant. Four primary outcome measures of efficacy (the incidence of pulmonary air leak (< or = 7 days); the severity of RDS; the incidence of death from RDS; and the incidence of survival without bronchopulmonary dysplasia (BPD) at 28 days after birth) were compared by means of linear regression techniques. RESULTS The primary analysis of efficacy was performed in 1033 eligible infants and an analysis of safety outcomes in the 1126 infants who received study surfactant. Preentry demographic characteristics and respiratory status were similar for the two treatment groups, except for a small but significant difference in mean gestational age (0.5 week) that favored the infasurf treatment group. Pulmonary air leak (< or = 7 days) occurred in 21% of Exosurf- and 11% of infasurf-treated infants (adjusted relative risk, 0.53; 95% confidence interval, 0.40 to 0.71; p < or = 0.0001). During the 72 hours after the initial surfactant treatment, the average fraction of inspired oxygen (+/-SEM) was 0.47 +/- 0.01 for Exosurf- and 0.39 +/- 0.01 for infasurf-treated infants (difference, 0.08; 95% confidence interval, 0.06 to 0.10; p < 0.0001); the average mean airway pressure (+/-SEM) was 8.6 +/- 0.1 cm H2O; for Exosurf- and 7.2 +/- 0.1 cm H2O for Infasurf-treated infants (difference, 1.4 cm H2O; 95% confidence interval, 1.0 to 1.8 cm H2O; p < 0.0001). The incidences of RDS-related death, total respiratory death, death to discharge, and survival without bronchopulmonary dysplasia at 28 days after birth did not differ. The number of days of more than 30% inspired oxygen and of assisted ventilation, but not the duration of hospitalization, were significantly lower in Infasurf-treated infants. CONCLUSION Compared with Exosurf, Infasurf provided more effective therapy for RDS as assessed by significant reductions in the severity of respiratory disease and in the incidence of air leak complications.