Comparison of heart rate responses during cortical and subcortical arousals in term and preterm infants

Impact of diaper change frequency on preterm infants' vital sign stability and skin health: A RCT

BACKGROUND

Bundling nurse caregiving interventions are promoted to minimize infant stress.

PURPOSE

To evaluate impact of bundled nursing care and diaper change frequency on vital sign stability and skin health of preterm infants born ≤32 weeks gestation.

METHOD

Stable preterm infants on a 3-hour feeding schedule were randomly assigned to 3- vs. 6-hour diaper changes. Diapers were changed prior to 6 h if stool was present. Direct observation of bundled care events (BCE) identify caregiving activities during each BCE. Skin pH, transepidermal water loss (TEWL), and neonatal skin condition scores (NSCS) were obtained. Vital sign data (HR, RR, O₂ saturation) was downloaded from bedside monitors.

RESULTS

Forty-six infants contributed to 605 BCEs. BCEs lasted on average 28 min and included nine different activities (e.g., vital signs, feeding). Significant increases in heart rate during BCEs occurred in approximately half of the observations. Among observations with a diaper change increases in heart rate during diapering occurred in over 74% of observations Infants who were awake at the beginning of BCEs had 48% lower odds of having a change in heart rate than infants who were sleeping (p = .02). There were no group differences (3- vs. 6-hour diaper change) in skin health outcomes (TEWL, pH, NSCS).

CONCLUSION

Reducing diaper change frequency without stool present should be considered to minimize caregiving stress in preterm infants. Additional research should evaluate the intrusiveness and clusters of activities that significantly impact physiologic stability to better individualize the timing of routine yet intrusive activities. Clinicaltrials.gov registry # NCT03370757.

Arousal from sleep pathways are affected by the prone sleeping position and preterm birth: preterm birth, prone sleeping and arousal from sleep

OBJECTIVES

Preterm infants exhibit depressed arousability from sleep when compared with term infants. As the final cortical element of the arousal process may be the most critical for survival, we hypothesized that the increased vulnerability of preterm infants to the Sudden Infant Death Syndrome (SIDS) could be explained by depressed cortical arousal (CA) responses. We evaluated the effects of preterm birth on stimulus-induced arousal processes in both the prone and supine sleeping positions.

STUDY DESIGN

10 healthy preterm infants were studied with daytime polysomnography, in both supine and prone sleeping positions, at 36 weeks gestational age, 2-4 weeks, 2-3 months and 5-6 months post-term corrected age. Sub-cortical activations and cortical arousals (CA) were expressed as proportions of total arousal responses. Preterm data were compared with data from 13 healthy term infants studied at the same corrected ages.

RESULTS

In preterm infants increased CAs were observed in the prone position at all ages studied. Compared to term infants, preterm infants had significantly fewer CAs in QS when prone at 2-3 months of age and more CAs when prone at 2-4 weeks in AS. There were no differences in either sleep state when infants slept supine.

CONCLUSIONS

Prone sleeping promoted CA responses in healthy preterm infants throughout the first six months of post-term age. We have previously suggested that in term infants enhanced CA represents a critical protection against a potentially harmful situation; we speculate that for preterm-born infants the need for this protection is greater than in term infants.

The carotid body and arousal in the fetus and neonate

Arousal from sleep is a major defense mechanism in infants against hypoxia and/or hypercapnia. Arousal failure may be an important contributor to SIDS. Areas of the brainstem that have been found to be abnormal in a majority of SIDS infants are involved in the arousal process. Arousal is sleep state dependent, being depressed during AS in most mammals, but depressed during QS in human infants. Repeated exposure to hypoxia causes a progressive blunting of arousal that may involve medullary raphe GABAergic mechanisms. Whereas CB chemoreceptors contribute heavily to arousal in response to hypoxia, serotonergic central chemoreceptors have been implicated in the arousal response to CO(2). Pulmonary or chest wall mechanoreceptors also contribute to arousal in proportion to the ventilatory response and decreases in their input may contribute to depressed arousal during AS. Little is known about specific arousal pathways beyond the NTS. Whether CB chemoreceptor stimulation directly stimulates arousal centers or whether this is done indirectly through respiratory networks remains unknown. This review will focus on arousal in response to hypoxia and CO(2) in the fetus and newborn and will outline what we know (and do not know) about the involvement of the carotid body in this process.

Arousal from sleep mechanisms in infants

Arousals from sleep allow sleep to continue in the face of stimuli that normally elicit responses during wakefulness and also permit awakening. Such an adaptive mechanism implies that any malfunction may have clinical importance. Inadequate control of arousal in infants and children is associated with a variety of sleep-related problems. An excessive propensity to arouse from sleep favors the development of repeated sleep disruptions and insomnia, with impairment of daytime alertness and performance. A lack of an adequate arousal response to a noxious nocturnal stimulus reduces an infant's chances of autoresuscitation, and thus survival, increasing the risk for Sudden Infant Death Syndrome (SIDS). The study of arousability is complicated by many factors including the definition of an arousal; the scoring methodology; the techniques used (spontaneous arousability versus arousal responses to endogenous or exogenous stimuli); and the confounding factors that complicate the determination of arousal thresholds by changing the sleeper's responses to a given stimulus such as prenatal drug, alcohol, or cigarette use. Infant age and previous sleep deprivation also modify thresholds. Other confounding factors include time of night, sleep stages, the sleeper's body position, and sleeping conditions. In this paper, we will review these different aspects for the study of arousals in infants and also report the importance of these studies for the understanding of the pathophysiology of some clinical conditions, particularly SIDS.

Cardiovascular control during sleep in infants: Implications for Sudden Infant Death Syndrome

In infants the cardiorespiratory system undergoes significant functional maturation after birth and these changes are sleep-state dependent. Given the immaturity of these systems it is not surprising that infants are at risk of cardiorespiratory instability, especially during sleep. A failure of cardiovascular control mechanisms in particular is believed to play a role in the final event of Sudden Infant Death Syndrome (SIDS). The "triple risk model" describes SIDS as an event that results from the intersection of three overlapping factors: (1) a vulnerable infant, (2) a critical development period in homeostatic control, and (3) an exogenous stressor. This review summarises normal development of cardiovascular control during sleep in infants and describes the association of impaired cardiovascular control with the three overlapping factors proposed to be involved in SIDS pathogenesis.

Stabilizing immature breathing patterns of preterm infants using stochastic mechanosensory stimulation

Breathing patterns in preterm infants consist of highly variable interbreath intervals (IBIs) that might originate from nonlinear properties of the respiratory oscillator and its input-output responses to peripheral and central signals. Here, we explore a property of nonlinear control, the potential for large improvement in the stability of breathing using low-level exogenous stochastic stimulation. Stimulation was administered to 10 preterm infants (postconceptional age: mean 33.3 wk, SD 1.7) using a mattress with embedded actuators that delivered small stochastic displacements (0.021 mm root mean square, 0.090 mm maximum, 30-60 Hz); this stimulus was subthreshold for causing arousal from sleep to wakefulness or other detectable changes in the behavioral state evaluated with polysomnography. We used a test-retest protocol with multiple 10-min intervals of stimulation, each paired with 10-min intervals of no stimulation. Stimulation induced an approximately 50% reduction (P = 0.003) in the variance of IBIs and an approximately 50% reduction (P = 0.002) in the incidence of IBIs > 5 s. The improved stability of eupneic breathing was associated with an approximately 65% reduction (P = 0.04) in the duration of O(2) desaturation. Our findings suggest that nonlinear properties of the immature respiratory control system can be harnessed using afferent stimuli to stabilize eupneic breathing, thereby potentially reducing the incidence of apnea and hypoxia.

Unchanged heart rate-respiratory frequency ratio in preterm infants during spontaneous arousals

AIM

To find out whether a correlation of heart rate (HR) and respiratory frequency (RF) defined as HR-RF-ratio (HRR) may be helpful to identify arousals in term and preterm infants.

METHODS

Polygraphic recordings were performed in 25 term infants (gestational age 40.1 +/- 1.1 weeks) and 25 preterm infants (gestational age 31.1 +/- 1.3 weeks) during undisturbed daytime sleep. Arousals were scored as suggested by the 'International Paediatric Work Group on Arousals' and divided into cortical arousals and subcortical arousals. HRR was defined as HR over RF. Arousals were compared to a 30-sec period preceding an arousals.

RESULTS

Two hundred arousals were scored (100 cortical arousals and 100 subcortical arousals). HRR increased during arousals in term infants (p < 0.001). This was true for cortical arousals (p < 0.001) and subcortical arousals (p < 0.05) of term infants. In contrast, in preterm infants HRR remained unchanged during cortical arousals and subcortical arousals.

CONCLUSION

An increase of HRR during arousals is a simple parameter to identify arousals in term infants, but not in preterm infants suggesting that an unchanged HRR might be an indicator of an immature arousal response.