Ventilatory Response to a Hyperoxic Test Is Related to the Frequency of Short Apneic Episodes in Late Preterm Neonates

Abstract

ABSTRACT:Chemoreception is frequently involved in the processes underlying apnea in premature infants. Apnea could result from a decrease in carotid body effectiveness. However, increased carotid body activity could also initiate apnea through hypocapnia following hyperventilation when the receptors are stimulated. The aim of this study was to analyze the relationship between carotid body effectiveness and short apneic episodes in older preterm neonates. Carotid body effectiveness was assessed at thermoneutrality in 36 premature neonates (2.07 Ϯ 0.26 kg) by performing a 30-s hyperoxic test during sleep, the oxygen inhalation involving a ventilation decrease. Blood O 2 saturation (Sp O2 ) and ventilatory parameters were monitored before and during the hyperoxic test. Short episodes of apnea (frequency and mean duration) were recorded during the morning's 3-h interfeeding interval. Pretest Sp O2 was not related to any of the measured respiratory parameters. A higher frequency of short apneic episodes was linked to a greater ventilation decrease in response to the hyperoxic test ( ϭ Ϫ0.32; p ϭ 0.01). Increased carotid body response is correlated with greater apneic episodes frequency, even in the absence of concomitant oxygen desaturation. Fetal or early postnatal hypoxemia could have increased peripheral chemoreceptor activity, which could initiate a "overshoot/ undershoot" situation, which in turn could induce a critical P O2 /P CO2 combination and apnea. (Pediatr Res 62: 591-596, 2007) S hort apneic episodes [defined as a respiratory pause of at least 3 s (1,2)] are common respiratory events in premature neonates, with an incidence of 25% in infants weighing Ͻ2500 g at birth and 84% in those weighing Ͻ1000 g (3).After birth, apnea frequency decreases progressively once chemoreception control is sufficiently developed to initiate the appropriate ventilatory responses to changes in arterial blood gas status (3-6). Chemoreception control is carried out by central and peripheral chemoreceptors that differ in their anatomical location and type of stimulation: peripheral chemoreceptors (mainly carotid bodies) are sensitive to variations in the levels of O 2 and (to a lesser extent) CO 2 , whereas central chemoreceptors are especially sensitive to variations in CO 2 and pH.It is accepted that abnormal functioning of the peripheral chemoreceptors can promote apnea even though the mechanism underlying this altered chemoreceptor activity is still subject to much debate. Provision of oxygen to infants suffering from bronchopulmonary dysplasia delays the peripheral chemoreceptor response and might induce more apnea (7). In preterm neonates, an increase in the chemoreceptor gain during the postnatal period has also been suggested. The latter can initiate an "overshoot/undershoot" situation: the apnea results from a central depression in inspiratory motor drive, which is mainly due to hypocapnia. This concept has been described in adult dogs to explain periodic breathing (8) and extended to the newborn lamb (9), but physiolog...

Relationship Between Functional Residual Capacity and Oxygen Desaturation During Short Central Apneic Events During Sleep in “Late Preterm” Infants

“…As a result, respiratory instability and increased apnea frequency may be observed. These findings are consistent with the "overshoot/undershoot" concept (29) explaining periodic breathing and according to which increased carotid body activity can promote respiratory instability and apnea when the PCO 2 falls below the apneic threshold (27). The greater tonic activity of the peripheral chemoreceptors in AS than in QS (30) may exaggerate this phenomenon during the former sleep state.…”

“…Although we measured SpO 2 only, the latter parameter is thought to accurately reflect the simultaneous PaO 2 (26); in our work, SpO 2 was negatively correlated with FRC. Recent studies (27,28) have reported that a low PaO 2 magnifies the peripheral chemoreceptors' contribution to breathing and induces major ventilatory changes. As a result, respiratory instability and increased apnea frequency may be observed.…”

Intermittent Hypoxic Episodes in Preterm Infants: Do They Matter?

“…Reactive oxygen species have been implicated in these findings. Such an increase in carotid body excitation in response to hypoxic exposure may destabilize breathing, as has been shown in human preterm infant studies [32,33] . Future study should focus on the possible relationship between neonatal intermittent hypoxia, subsequent hyperoxia, and the genesis of unstable breathing patterns in later life.…”

Apnea of prematurity: pathogenesis and management strategies

“…There is also evidence linking carotid chemoreceptor over stimulation to the persistence of AOP. [19][20][21] Current evidence suggests that both increased and decreased carotid chemoreceptor activity can predispose the preterm infants to apnea.…”