1695 VULNERABILITY OF PRETERM INFANTS TO NASAL OBSTRUCTION

Abstract

This study was designed to determine cardiopulmonary responses to nasal obstruction in different sleep states. 8 healthy preterm infants (wt 1.8±.1Kg) were studied at a corrected G.A. of 35±2 wks by multiple 10 sec occlusions during active (AS) and quiet (QS) sleep, via nasal prongs fitted with a thermistor to measure airflow. Heart rate (HR), mouth airflow, transcutaneous PO2 (Tc PO2), chest wall movements, respiratory frequency (f) and sleep state were continuously monitored. Nasal occlusion was invariably accompanied by a fall in TcPO2, which was greater during AS than QS (8±2 vs 5±3 mmHg, p<.01). In contrast, HR fell with only 54% of occlusions, more in AS than QS (35±15 vs 21±7/min, p<.05). During obstruction the frequency of respiratory efforts decreased from 45±10 to 35±7/min (p<.001) compared to preocclusion levels, while mouth airflow was only sporadic and did not influence the fall in TcPO2 or HR. In the initial 5 sec following occlusion, f returned to preocclusion levels. During the subsequent 5 sec, f decreased from 47±10 to 35±13/min (p<.03) in AS and from 41±9 to 31±16/min (p<.03) in QS, as compared to preocclusion levels. Furtheremore, in the 20 sec following occlusion (vs preocclusion) the duration of respiratory pauses ≥2 sec increased in both AS and QS (p<.01). We conclude that 1) preterm infants are more vulnerable to nasal obstruction in AS with a greater fall in PO2 and HR, 2) airway obstruction may enhance susceptibility to the subsequent development of central apnea, and 3) since obstruction may not be accompanied by a fall in HR, routine cardio-respiratory monitoring may fail to detect many episodes.