Pathological respiratory consequences are hypoxia manifested by a drop in oxygen saturation below 80% (Figure 17.1) and hypercapnia. Pathological cardiovascular changes are bradycardia manifested by a 20% drop below baseline (Figure 17.1), tachycardia, arrhythmia, asystole, and arterial hypotension or hypertension. Pathological neurological findings are lethargy, seizures, and hypotonia.
Obstructive-central respiratory pauses are not usually seen in normal neonates, hence they are considered apnea regarless of the absence of any other parameter.
Respiratory pauses without pathological consequence lasting from 10 to 19 seconds in a premature infant, or from 10 to 15 seconds in a fullterm neonate, are considered pathological if they add up to more than 2 minutes per hour.

Figure 17.1.— Central apnea (cessation of airflow at the nose and mouth, and absence of thoracic and abdominal movements). Sleep stage: quiet sleep (tracé alternant and regular respiration), bradycardia, and desaturation.

Periodic breathing (Figure 17.2) refers to respiratory pauses lasting from 3 to 10 seconds without pathological consequences, interrupted by at least5periodsofnormalbreathing lasting less than 5 seconds each. Periodic breathing is abnormal if it occupies more than 3% of the recording time in a fullterm infant.

Figure 17.2.— Polysomnogram demonstrating (epoch of 2 minutes) periodic breathing.