THE RELATIONSHIP BETWEEN BRADYCARDIA, APNEA, AND HYPOXEMIA IN PRETERMINFANTS

The pathogenesis of bradycardias in preterm infants is poorly understo od. Because their pathogenesis may involve both apnea and hypoxemia, w e set out to analyze the proportion of bradyeardias that were associat ed with an apneic pause and/or a fall in arterial oxygen saturation (S aO2), and the temporal sequence of the three phenomena, in overnight t ape recordings of SaO2 (Nellcor N100 in beat-to-beat mode), breathing movements, nasal airflow, and ECG in 80 preterm infants at the time of discharge from hospital. A bradycardia was defined as a fall in heart rate of greater-than-or-equal-to 33% from baseline for greater-than-o r-equal-to 4 s, an apneic pause as a cessation of breathing movements and/or airflow for greater-than-or-equal-to 4 s, and a desaturation as a fall in SaO2 to less-than-or-equal-to 80%. A total of 193 bradycard ias were found in 46 (58%) of the recordings (median, three per record ing; range 1-18). There was a close relationship between bradycardias, apneic pauses, and desaturations: 83% of bradycardias were associated with apneic pauses and 86% with desaturations. Where all three phenom ena occurred in combination, the time from the onset of apnea to the o nset of the fall in SaO2 was shorter (median interval, 0.8 s; range -4 .9-+11.5 s) than that from the onset of apnea to the onset of bradycar dia (median, 4.8 s; range -4.0-+14.0 s). Hence, most bradycardias (86% ) commenced after the onset of the fall in SaO2. We conclude that brad ycardia, apnea, and hypoxemia are closely linked phenomena in preterm infants.