Melinda S. Kwong

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.

Validation of [57Co] cyanocobalamin as an extracellular fluid marker and measurement of albumin exclusion from the interstitium in the rabbit

The use of [57Co]cyanocobalamin as an extracellular marker has been validated. Its simultaneous use with 51Cr-labeled erythrocytes and 125I-human serum albumin allows quantitative measurement of tissue water and the fractional exclusion of albumin from the interstitial compartment. The extravascular extracellular spaces of rabbit tissue are lung, 32 +/- 4%; heart, 25 +/- 2%; gut, 24 +/- 4%; and muscle, 13 +/- 1%. The fractional excluded albumin spaces are lung, 0.78 +/- 0.05; heart, 0.37 +/- 0.03; gut, 0.69 +/- 0.05; and muscle 0.58 +/- 0.03. The oversimplification that the extravascular extracellular space is a homogeneous region defined by a small tracer molecule and has the composition of lymph must be reconsidered. Albumin has a vastly different distribution in the interstitial spaces of different organs. Use of the three tracers reported here allows efficient measurement of blood volume, interstitial space, and interstitial albumin exclusion in whole tissues and organs, and thus can lead to further understanding of the in vivo changes occurring in various physiologic and disease states.

Rabbit tissue composition: Developmental aspects of tissue fluid and fractional exclusion of albumin

The maturational changes in tissue water spaces and in the fractional exclusion of albumin from the interstitial gel were studied in the developing rabbit using multiple radioactive tracers. Total tissue water and extracellular water decrease with age in all organs studied. Intracellular water decreases in the heart and brain, transiently increases in the muscle, and is unchanged in the ileum and lung. However, the percentage of extravascular water located in the cell increases with age in all organs. Fractional exclusion of albumin is unchanged in the muscle and brain, fluctuates in the lung, increases in the ileum, and decreases in the heart. Possible mechanisms for regional differences in fluid and albumin changes with maturation are discussed. Until the role of the fractional exclusion of albumin in the interstitial matrix in the maintenance of tissue fluid balance is elucidated, the physiological impact of these developmental changes will not be evident.

113 CARDIOVASCULAR ADJUSTMENTS DURING RECOVERY FROM CHRONIC NEONATAL ASPHYXIA IN PIGLETS

Prolonged, repeated episodes of asphyxia were induced in newborn piglets to, determine cardiovascular adjustments in the post-asphyxial period. Ten piglets (<24 hours age) had catheters placed in the right, and left ventricles and the descending aorta under general anesthesia. Animals were subjected to 8 episodes of asphyxia by rebreathing into a bag to last gasp over a 2 hour period. Immediately after the last episode, the pH and base deficit were 7.01±.12 and -20±3. The insult induced prolonged seixures and persistent changes in activity in 9 of 10 animals and organ hemorrhage in 4. .Organ blood flow was measured prior to asphyxiation and 1 hour after recovery by radioactive microsphere; injection. Arterial blood gases prior to and 1 hour post-asphyxia were respectively pH-7, 44±.08, pCO2-42±5 Torr. pO2-61±10 Torr, B.D.-2±1; pH-7.20±.21, pCO2-32±12 Torr, PO2-75±19 Torr, B.D.-l4±3. Blood flow one hour post-asphyxia increased significantly to the heart, adrenal and liver and decreased significantly to the small bowel, large bowel, kidney, spleen and skin. Blood flow to the brain decreased from 86±13 cc/100 gm to 45±5 cc/100 gm (p<.0) and was no longer related to paCO2. In spite of normal heart rate, hemodynamic pressures, arterial oxygenation, and ventilation at one hour post-asphyxia, there are major changes in organ perfusion, and the distribution of cardiac output, and autoregulation of brain blood flow.

1379 SURFACTANT REPLACEMENT AND PATENCY OF THE DUCTUS ARTERIOSUS (DA) IN LAMBS

Extracted calf lung lipids (CLL) instilled into 127-129 day gestation lambs at birth prevents respiratory failure; we sought to determine the early status of the DA in such animals. Lambs were delivered by hysterotomy, tracheotomized, and catheters placed in the main pulmonary artery (PA) 1 cm beyond the valve under fluroscopy, the ascending aorta and descending aorta. CLL was instilled in 6 lambs, saline in 5, mechanical ventilation was started and umbilical cord severed. Blood gases and aortic PGE2 levels were obtained hourly. DA status was determined by the PA to aorta pressure gradient, aorta-PA xoygen difference, and microsphere trapping in the lung after left ventricular injection. Only 1 of the 5 control animals survived to 6 hours, 4 showed some transient constriction of the DA, and one of the 4 functional closure for 2 hours. In the treated animals, all showed constriction of the DA, 3 were functionally closed for 6 hours, 2 were constricted, 1 had re-opened. DA status was not correlated with aortic PGE2 levels, which declined during the experiment in all animals, nor with PaO2. Prevention of respiratory failure by CLL instillation at birth is associated with constriction of the DA in the first 6 hours.

1378 CLINICAL TRIAL OF TRACHEAL INSTILLATION OF CALFLUNG LIPID (CLL) AT BIRTH T0 PREVENT HYALINE MEMBRANE DISEASE (HMD)

A double blind clinical trial is in progress to determine if 100 mg of CLL instilled into the. trachea of 24-28 weeks gestation infants who had no prenatal steroid treatment can prevent HMD. The trial has been conducted at Childrens Hospital of Buffalo between 6-1-83 and 7-31-84. During the 14 months, 24 patients were enrolled in the trial, 24 were excluded because of prenatal steroid treatment. HMD was prospectively defined as death before 48 hours or an infant at 48 hours of age with x-ray criteria, on more than 20 breaths/min of artificial ventilation, mean airway pressure >7 torr, and FiO2 >0.3. The CLL treated group had a 17% incidence of HMD and the saline control group 60% (p=.043 Fishers exact test). The incidence of HMD was 25% in prenatal steroid treated infants, and 76% in. those unenrolled who did not receive prenatal steroids. Among survivors CLL treated infants had a lower incidence of bronchopulmonary dysplasia than saline controls, 18% to 63% (p=.06 Fishers exact test). The CLL treated group had fewer deaths, intraventricular hemorrhages, and air leaks, but these were not enough different to reach statistical significance with the present numbers. Patent ductus arteriosus incidence was the same in all groups. CLL instillation at birth. appears to induce a major reduction in the incidence of HMD and in some or many of. its related complications in extremely premature infants.

EFFECTIVENESS OF EXTRACTED COW LUNG LIPID (CLL) IN INDUCING AND SUSTAINING NORMAL LUNG FUNCTION IN SURFACTANT DEFICIENT PREMATURE LAMBS

Sterilized CLL was studied in premature lambs 132-134 days G.A. to determine if pre-breathing instillation could induce and sustain normal lung function for 2 days. CLL is a chloroform methanol extract of lavage of calfs lung containing 1% protein and flash autoclaved for sterility. We delivered 4 fetal lambs by hysterotomy, incubated them, took 10 ml of fetal lung liquid, instilled 100mg/kg of CLL in 10 ml of saline, and ventilated them immediately. Three control lambs were treated with 10 ml of saline. The lambs, sedated with nembutal, were managed using a clinical protocol. All CLL animals survived for 36-48 hours in good condition. Two control animals had a pneumothorax and 1 died at 21 hours. CLL treated lambs required mean airway pressures (MAP) of 10-15 cm H20 for 2 hours; average MAP was ≤10 cm H2O thereafter to maintain a PaC02 30-45. Control animals required an average MAP ≥20 cm H2O for 2 hours and 10-20 cm H2O thereafter. FiO2 requirements became <.4 by 7 hours in the CLL treated lambs. Control lambs required FiO2 >.4 until 21 hours age. Lavage of the lung at sacrifice revealed 49±10uM of alveolar surfactant in CLL lambs and 17±2uM in controls. CLL treatment before breathing induces and sustains normal lung function for 36-48 hours. This appears to be a surfactant preparation and protocol appropriate for a human clinical trial.