A Different View of Surfactant Development

In Reply.— Dr Kattwinkel suggests in his letter that there has been no serious effort by investigators in neonatology and pulmonary biology to identify the best possible surfactant for use for replacement therapy in hyaline membrane disease. Furthermore, he implies that there has been a national or perhaps international conspiracy to ignore natural human surfactant in the large clinical trials done to date. In reaching these opinions, Dr Kattwinkel seems to have ignored several facts of which he should be aware.</jats:p

Nonuniform distribution of microspheres in blood flowing through a medium-size artery

Suspensions of rigid microspheres, varying from 7.5 to 80 μ diameter, were injected into the left ventricle or ascending aorta of five anesthetized rabbits. After injection, an exposed branch of the femoral artery was frozen ultrarapidly, then removed; after histologic preparation, serial cross sections were studied microscopically. The radial distribution of the spheres within the vessel lumen was uneven, with a progressively decreasing concentration peripherally. This appeared to be proportional to sphere diameter and extended too far in from the periphery to be explained by entrance effect only. Microspheres of 7.5 to 10 μ diameter had the radial distribution which most closely approached that of erythrocytes in these same arteries. </jats:p

Exchange Transfusions: Blood Volume, Increment Volume, Efficiency

We wish to call attention to an apparently common misconception about the efficiency of exchange transfusions. The mechanics of the procedure are: a substance (bilirubin and/or antibody-coated red cells) is washed out of a compartment (the baby's blood volume) by the removal of a fraction of that compartment and its replacement by an equal volume of diluent (donor blood). This flushing process is repeated many times, usually until the total volume replaced is 2 to 3 times the volume of the compartment itself.</jats:p

Newborn Risk Factors and Costs of Neonatal Intensive Care

To understand the sources of the high costs of neonatal intensive care, financial and medical information on 1,185 admissions to an intensive care nursery was gathered. Multiple regression analysis showed that a significant portion of the variation in individual costs was explained by three measures of risk: low birth weight, surgical intervention, and assisted ventilation. There was a highly skewed distribution of costs. Nearly half of all admissions had none of the above risk factors, had an average cost of about $2,000, and accounted for only 13$19,800, and accounted for nearly 60% of the total costs. Models that predict costs and length of stay on a basis of seven risk factors were developed to allow for differences in patient populations.</jats:p