Investigation of intrapartum clearance of the upper airway in the presence of meconium contaminated amniotic fluid using an animal model.

In order to define as effective a procedure as possible for the intra- and post-partum clearance of the upper airways of meconium contaminated infants, three methods of suction clearance, nasal, oral and combined nasal and oral, were carried out on each of five kittens aged between 17 to 19 weeks. There was an interval of at least one week between each investigation. The animals were anaesthetized with ketamine intramuscularly. The pressure changes during delivery were simulated using a compressed blood pressure cuff around the kittens thorax. During the first minute of thoracic compression Tc 99 labeled synthetic sputum was introduced into both the oro- and nasopharynx, then during the 2nd minute the instilled fluid was removed using a conventional extractor with mucus trap. Solely oral or solely nasal routes were used, suction was carried out for 60 secs, whereas when the combined technique was applied the oral and nasal cavities were cleared for only 30 secs each. At the end at the 2nd minute thoracic compression was released and a deep inspiration occurred. After five minutes the radioactivity remaining after suction was documented using a gamma-camera. We attempted to answer the following questions: How much mucus could be extracted with each different method, and where the remaining amount was later distributed? Nasal suction alone was found to be inefficient; using this route an average of 13% (only an eight of the amount instilled) could be removed. Oral suction led to the recovery of an average of 52% of the material instilled, the combined technique much as 56%. After re-establishment of spontaneous respiration, it could be clearly seen that, independent of the efficacy of the technique used, the majority of the remaining radioactivity (55 relative percent) is localized in the head and neck area. Absolute values are 45% for nasal suction, 26% for oral, and 24% for the combined oro-nasal route. The other part of the remaining radioactivity was found in the lung or in the stomach. It must be pointed out that the aspirate need not be disturbed in both of the parts, both the stomach and the lungs can be solely involved. Five minutes after spontaneous respiration had been resumed the lungs revealed only a centrally distributed radioactivity. This corresponds anatomically to the trachea and major bronchi. The peripheral area of the lungs was free of aspirate at this point in time.(ABSTRACT TRUNCATED AT 400 WORDS)