Influence of thermal drive on central sleep apnea in the preterm neonate

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a common breathing disorder in sleep in which the airways narrow or collapse during sleep, causing obstructive sleep apnea. The prevalence of OSAS continues to rise worldwide, particularly in middle-aged and elderly individuals. The mechanism of upper airway collapse is incompletely understood but is associated with several factors, including obesity, craniofacial changes, altered muscle function in the upper airway, pharyngeal neuropathy, and fluid shifts to the neck. The main characteristics of OSAS are recurrent pauses in respiration, which lead to intermittent hypoxia (IH) and hypercapnia, accompanied by blood oxygen desaturation and arousal during sleep, which sharply increases the risk of several diseases. This paper first briefly describes the epidemiology, incidence, and pathophysiological mechanisms of OSAS. Next, the alterations in relevant signaling pathways induced by IH are systematically reviewed and discussed. For example, IH can induce gut microbiota (GM) dysbiosis, impair the intestinal barrier, and alter intestinal metabolites. These mechanisms ultimately lead to secondary oxidative stress, systemic inflammation, and sympathetic activation. We then summarize the effects of IH on disease pathogenesis, including cardiocerebrovascular disorders, neurological disorders, metabolic diseases, cancer, reproductive disorders, and COVID-19. Finally, different therapeutic strategies for OSAS caused by different causes are proposed. Multidisciplinary approaches and shared decision-making are necessary for the successful treatment of OSAS in the future, but more randomized controlled trials are needed for further evaluation to define what treatments are best for specific OSAS patients.

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review

BACKGROUND AND OBJECTIVES

Heat stress and hyperthermia are common findings in sudden infant death syndrome (SIDS) victims. It has been suggested that thermal stress can increase the risk of SIDS directly via lethal hyperthermia or indirectly by altering autonomic functions. Major changes in sleep, thermoregulation, cardiovascular function, and the emergence of circadian functions occur at the age at which the risk of SIDS peaks-explaining the greater vulnerability at this stage of development. Here, we review the literature data on (i) heat stress and hyperthermia as direct risk factors for SIDS, and (ii) the indirect effects of thermal loads on vital physiological functions.

RESULTS

Various situations leading to thermal stress (i.e., outdoors temperatures, thermal insulation from clothing and bedding, the prone position, bed-sharing, and head covering) have been analyzed. Hyperthermia mainly results from excessive clothing and bedding insulation with regard to the ambient thermal conditions. The appropriate amount of clothing and bedding thermal insulation for homeothermia requires further research. The prone position and bed-sharing do not have major thermal impacts; the elevated risk of SIDS in these situations cannot be explained solely by thermal factors. Special attention should be given to brain overheating because of the head's major role in body heat losses, heat production, and autonomic functions. Thermal stress can alter cardiovascular and respiratory functions, which in turn can lead to life-threatening events (e.g., bradycardia, apnea with blood desaturation, and glottal closure). Unfortunately, thermal load impairs the responses to these challenges by reducing chemosensitivity, arousability, and autoresuscitation. As a result, thermal load (even when not lethal directly) can interact detrimentally with vital physiological functions.

CONCLUSIONS

With the exception of excessive thermal insulation (which can lead to lethal hyperthermia), the major risk factors for SIDS appears to be associated with impairments of vital physiological functions when the infant is exposed to thermal stress.

Treating Apnea of Prematurity

Premature babies often suffer apnea of prematurity as a physiological consequence of an immature respiratory system. Hypercapnia may develop, and neonates with apnea of prematurity are at an increased risk of morbidity and mortality. The long-term effects of apnea of prematurity or their treatments are less clear. While a number of treatment options exist for apnea of prematurity, there is no clear-cut "first-line" approach or gold standard of care. Effective treatments, such as caffeine citrate, carbon dioxide inhalation, nasal continuous positive airway pressure, nasal intermittent positive pressure ventilation, and others, may be associated with safety concerns. More conservative treatments are available, such as kangaroo care, postural changes, and sensory stimulation, but they may not be effective. While apnea of prematurity resolves spontaneously as the respiratory system matures, it can complicate neonatal care and may have both short-term and long-term consequences. The role, if any, that apnea of prematurity may play in mortality of preterm neonates is not clear.

Association between hypothermia in the first day of life and survival in the preterm infant

OBJECTIVE

Hypothermia is associated with elevated mortality in the preterm infant. The preterm infant's thermoregulatory capacity is limited, and the thermal environment in an incubator is often perturbed by nursing procedures. We evaluated the incidence of a postnatal low body temperature and hypothermia in preterm infants and its association with mortality.

METHODS

We measured the lowest body temperature during the first 24h of life (T_{Body Nadir 24h}) and hypothermia (T_{Body Nadir 24h}<36.0°C) in preterm infants (gestational age: 23⁰-31⁶ weeks) in a neonatal intensive care unit. Prenatal and neonatal characteristics associated with mortality were identified in univariate and multivariable analyses.

RESULTS

A total of 102 preterm infants were included, with a mean gestational age at birth of 28.4±2.3 weeks. The incidence of hypothermia during the first 24h was 53%. A Cox multivariate regression model indicated that T_{Body Nadir 24h} (hazard ratio (HR) [95% confidence interval]: 0.57 [0.36-0.90]; P=0.017), gestational age (0.62 [0.50-0.76]; P<0.001), and amine use (4.55 [2.01-10.28]; P=0.001) were significantly associated with mortality. When considering a threshold for T_{Body Nadir 24h}, a value of 35.0°C had the highest HR (3.30 [1.42-7.68]; P<0.01).

CONCLUSION

In preterm infants, the incidence of hypothermia during the first 24h of life was 53%. T_{Body Nadir 24h} had an influence on mortality, independently of other factors (notably birth weight and amine use). Within the framework of a quality improvement strategy, the implementation of a thermoregulation bundle is required to prevent hypothermia and decrease mortality in preterm infants.

The newborn infant's thermal environment in the delivery room when skin-to-skin care has to be interrupted

OBJECTIVE

Newborns are prone to hypothermia immediately following birth. Hypothermia is associated with increased morbidity and mortality rates. We sought to assess the thermal environment and metabolic costs associated with exposure to various situations in the delivery room when skin-to-skin care (SSC) has to be curtailed.

METHODS

Environmental variables (air temperature: T _a; relative humidity: RH; radiative temperature: T _r; and air convection velocity) were recorded during sequences reproducing SSC, in the maternity unit's various rooms ("passive environments") and in incubators ("active environments"). Analytical calorimetry was then used to calculate the body heat loss (BHL) from these data.

RESULTS

The analysis of 1280 measurements of T _a, RH, T _r, and air convection velocity in SSC, passive and active environments revealed that (i) the thermohygrometric environment during SSC was optimal (T _a: 32.7 ± 3.2 °C; RH: 50.9 ± 5.6%), (ii) BHL rose when SSC had to be interrupted, and (iii) the use of a radiant incubator prevented hypothermia and reduced dry BHL but not humid BHL (9.4 ± 1.5 kcal/kg/h; p < .001), relative to SSC (5.8 ± 2.0 kcal/kg/h; p < .001).

CONCLUSION

The newborn infant's thermohygrometric environment is optimal during SSC in the delivery room. When SSC was interrupted, T_a and RH always decreased, and BHL increased in all passive environments.

Sleep and prematurity: sleep outcomes in preterm children and influencing factors

BACKGROUND

Sleep undergoes changes from birth to adulthood, while sleep disorders are associated with various cognitive deficiencies in childhood. In parallel, prematurity is known to predispose to poor neurodevelopmental outcomes. Our aim is to provide literature data about factors influencing sleep in the premature infants and sleep outcomes in this population.

METHODS

A systematic review was conducted using a variety of health-related databases. Original research papers were considered and no year-of-publication restriction was placed.

RESULTS

In total, 22 articles fulfilled our selection criteria. Available studies present remarkable heterogeneity in terms of methodological design. Compared to full term, premature infants exhibit significant differences in sleep structure, which mainly include differences in electroencephalographic spectral values, in total sleep time and in arousal threshold. Furthermore, prematurity seems to be a risk factor of sleep breathing disorders in childhood and adolescence. Data about the effect of methylxanthines and the environment of neonatal intensive care unit is controversial. With regard to the impact of prematurity-related sleep disorders on future neurodevelopment, available research papers are generally few.

CONCLUSIONS

The alterations in sleep patterns are an outcome of prematurity (immaturity of nervous system) as well as of postnatal factors and comorbidities. Sleep problems in this population of infants seems to be a missing piece of the puzzle of impaired neurodevelopment. Future studies should focus on interventions to improve sleep hygiene and limit neurodevelopmental problems.

Sleep and salivary cortisol in preterm neonates: a clinical, randomized, controlled, crossover study

ABSTRACT Objective: Analyze the influence of ear protectors on the baseline levels of salivary cortisol and response and total sleep time of preterm neonates during two periods of environmental management of a neonatal intermediate care unit. Method: A clinical, randomized, controlled and crossover study conducted with 12 preterm neonates. The use of ear protectors was randomized in two periods. Sleep evaluation was performed using one Alice 5 Polysomnography System and unstructured observation. Results: No significant difference was observed between the baseline levels of salivary cortisol and response in preterm neonates from the control and experimental groups, and no statistical significance was observed between the total sleep time of both groups. No relationship was observed between the baseline levels of cortisol and response and total sleep time. Conclusion: Ear protectors in preterm neonates did not influence the salivary cortisol level and total sleep time in the studied periods.

A mean body temperature of 37°C for incubated preterm infants is associated with lower energy costs in the first 11 days of life

AIM

This randomised trial compared the energy costs of providing incubated preterm infants born before 32 weeks of gestation with homeothermia using either air temperature control (ATC) or skin servocontrol (SSC).

METHODS

We studied 38 incubated preterm infants for the first 11 days of life, calculating the frequency of hypothermia (<36.0°C), hyperthermia (>37.5°C) and thermal challenge, together with energy costs, based on a change in incubator air temperature of 2°C above or below thermoneutrality.

RESULTS

The daily mean incubator air temperature was higher in ATC than SSC (p < 0.05) for the first 6 days, and the mean body temperature was higher in ATC (37.0 ± 0.03°C) than SSC (36.8 ± 0.02; p < 0.01) over the whole study period. The frequency of moderate hyperthermia was higher in ATC (p < 0.001), whereas warm and cold thermal challenges were higher in SSC (p < 0.001). The two groups did not differ in terms of energy costs. The time to recover birthweight was shorter in ATC (p < 0.05).

CONCLUSION

In incubators using ATC, a body temperature of 37°C was associated with lower energy costs and greater weight gain at 11 days of life for preterm infants. Future studies should test SSC shielded abdominal skin temperature set to 37°C.

Impact of nursing care on temperature environment in preterm newborns nursed in closed convective incubators

AIMS

Very-low-birth-weight (VLBW) neonates require regular nursing procedures with frequent opening of the incubator resulting in a decrease in incubator air temperature. This study was designed to assess changes in the thermal status of VLBW neonates according to the type of nursing care and incubator openings.

METHODS

Thirty-one VLBW neonates (mean gestational age: 28.7 ± 0.3 weeks of gestation) were included. Over a 10-day period, each opening of the incubator was recorded together with details about caregiving. Body temperature was recorded continuously, and door opening and closing events were recorded by a video camera.

RESULTS

This study analysed 1,798 caregiving procedures with mean durations ranging from 6.2 ± 2.1 to 88.5 ± 33.4 min. Abdominal skin temperature decreased by up to 1.08°C/h for procedures such as tracheal intubation (p < 0.01). The temperature decrease was strongly correlated with the type of procedure (p < 0.01), incubator opening (p < 0.01) and procedure duration (p < 0.01). The procedure duration accounted for only 10% of the abdominal skin temperature change (p < 0.01).

CONCLUSIONS

For VLBW neonates nursed in skin temperature servo-control incubators, the decrease in abdominal skin temperature during caregiving was correlated with the type of procedure, incubator opening modalities and procedure duration. These parameters should be considered to optimize the thermal management of VLBW neonates.

Hypoxic and hypercapnic events in young infants during bed-sharing

OBJECTIVES

To identify desaturation events (arterial oxygen saturation [Sao(2)] <90%) and rebreathing events (inspired carbon dioxide (CO(2)) >3%), in bed-sharing (BS) versus cot-sleeping (CS) infants.

METHODS

Forty healthy, term infants, aged 0 to 6 months who regularly bed-shared with at least 1 parent >5 hours per night and 40 age-matched CS infants were recruited. Overnight parent and infant behavior (via infrared video), Sao(2), inspired CO(2) around the infant's face, and body temperature were recorded during sleep at home.

RESULTS

Desaturation events were more common in BS infants (risk ratio = 2.17 [95% confidence interval: 1.75 to 2.69]), associated partly with the warmer microenvironment during BS. More than 70% of desaturations in both groups were preceded by central apnea of 5 to 10 seconds with no accompanying bradycardia, usually in active sleep. Apnea >15 seconds was rare (BS infants: 3 events; CS infants: 6 events), as was desaturation <80% (BS infants: 3 events; CS infants: 4 events). Eighty episodes of rebreathing were identified from 22 BS infants and 1 CS infant, almost all preceded by head covering. During rebreathing, Sao(2) was maintained at the baseline of 97.6%.

CONCLUSIONS

BS infants experienced more oxygen desaturations preceded by central apnea, partly related to the warmer microenvironment. Rebreathing occurred mainly during bed-sharing. Infants were at low risk of sudden infant death syndrome and maintained normal oxygenation. The effect of repeated exposure to oxygen desaturation in vulnerable infants is unknown as is the ability of vulnerable infants to respond effectively to rebreathing caused by head covering.

Variations in incubator temperature and humidity management: a survey of current practice

AIM

To describe and assess routine procedures and practices for incubator temperature and humidity management in France in 2009.

METHODS

A questionnaire was sent to all the 186 neonatal care units in France.

RESULTS

The questionnaire return rate was 86%. Seventy-five per cent of the units preferred skin servo-control to air temperature control in routine practice. Air temperature control was mainly used for infants with a gestational age of more than 28 weeks and aged over 7 days of life. In general, thermal management decisions did not depend on the infant's age but were based on a protocol applied specifically by each unit. All units humidified the incubator air, but there was a large difference between the lowest and highest reported humidity values (45% and 100% assumed to be a maximal value, respectively). More than 65% of the units used a fixed humidity value, rather than a variable, protocol-derived value.

CONCLUSION

We observed large variations in incubator temperature and humidity management approaches from one neonatal care unit to another. There is a need for more evidence to better inform practice. A task force should be formed to guide clinical practice.

Assessment of radiant temperature in a closed incubator

In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ (\overline{T}_{r} ) $$\end{document} accounts for 40–60% of the neonate’s total heat loss. In the absence of a benchmark method to calculate \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{T}_{r} $$\end{document}—often considered to be the same as the air incubator temperature—errors could have a considerable impact on the thermal management of neonates. We compared \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{T}_{r} $$\end{document} using two conventional methods (measurement with a black-globe thermometer and a radiative “view factor” approach) and two methods based on nude thermal manikins (a simple, schematic design from Wheldon and a multisegment, anthropometric device developed in our laboratory). By taking the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{T}_{r} $$\end{document} estimations for each method, we calculated metabolic heat production values by partitional calorimetry and then compared them with the values calculated from \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}_{{{\text{O}}_{ 2} }} $$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}_{{{\text{CO}}_{ 2} }} $$\end{document} measured in 13 preterm neonates. Comparisons between the calculated and measured metabolic heat production values showed that the two conventional methods and Wheldon’s manikin underestimated R, whereas when using the anthropomorphic thermal manikin, the simulated versus clinical difference was not statistically significant. In conclusion, there is a need for a safety standard for measuring \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{T}_{r} $$\end{document} in a closed incubator. This standard should also make available estimating equations for all avenues of the neonate’s heat exchange considering the metabolic heat production and the modifying influence of the thermal insulation provided by the diaper and by the mattress. Although thermal manikins appear to be particularly appropriate for measuring \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{T}_{r} $$\end{document}, the current lack of standardized procedures limits their widespread use.

Apnea of prematurity: from cause to treatment

Apnea of prematurity (AOP) is a common problem affecting premature infants, likely secondary to a "physiologic" immaturity of respiratory control that may be exacerbated by neonatal disease. These include altered ventilatory responses to hypoxia, hypercapnia, and altered sleep states, while the roles of gastroesophageal reflux and anemia remain controversial. Standard clinical management of the obstructive subtype of AOP includes prone positioning and continuous positive or nasal intermittent positive pressure ventilation to prevent pharyngeal collapse and alveolar atelectasis, while methylxanthine therapy is a mainstay of treatment of central apnea by stimulating the central nervous system and respiratory muscle function. Other therapies, including kangaroo care, red blood cell transfusions, and CO(2) inhalation, require further study. The physiology and pathophysiology behind AOP are discussed, including the laryngeal chemoreflex and sensitivity to inhibitory neurotransmitters, as are the mechanisms by which different therapies may work and the potential long-term neurodevelopmental consequences of AOP and its treatment.

Interventions for apnoea of prematurity: a personal view

AIM

To review treatments for apnoea of prematurity (AOP).

METHODS

Literature Review and description of personal practice.

RESULTS

Provided that symptomatic apnoea has been ruled out, interventions to improve AOP can be viewed as directed at one of three underlying mechanisms: (i) a reduced work of breathing [e.g. prone positioning, nasal continuous positive airway pressure (CPAP)], (ii) an increased respiratory drive (e.g. caffeine), and (iii) an improved diaphragmatic function (e.g. branched-chain amino acids). Most options currently applied, however, have not yet been shown to be effective and/or safe, except for prone, head-elevated positioning, synchronized nasal ventilation/CPAP, and caffeine.

CONCLUSION

Treatment usually follows an incremental approach, starting with positioning, followed by caffeine (which should be started early, at least in infants <1250 g), and nasal ventilation or CPAP via variable flow systems that reduce work of breathing. From a research point of view, we most urgently need data on the frequency and severity of bradycardia and intermittent hypoxia that can yet be tolerated without putting an infant at risk of impaired development or retinopathy of prematurity.

[Apnea of prematurity: what's new?]

Prematurity apnea remains a major clinical problem that requires treatment choices which are sometimes difficult. Prematurity apnea occurs in most infants of gestational age at birth less than 33 weeks. It is a developmental disorder which usually reflects a "physiological" immaturity of respiratory control. However, neonatal diseases may be associated and play an additive role, resulting in an increased incidence of apnea. Careful screening should therefore be performed in order to make sure that no other factor than immaturity is involved in the occurrence of apnea. Short apnea (less than 10s, without hypoxemia and bradycardia), due to immaturity, are not clinically relevant. More prolonged apnea, that last for more than 15 or 20s, and / or apnea associated with bradycardia or oxygen desaturation, results in short-term disturbances of cerebral haemodynamics and oxygenation, which may negatively impact on neurodevelopmental outcome. Evaluating the immediate severity of apnea and the risks that apnea may affect long-term outcome remains a challenge. The choice of treatments is based on a few evidences. Caffeine citrate, which reduces the incidence of apnea, has been used for decades. However, a thorough evaluation of risks and benefits of this medication has been performed only recently. Caffeine citrate was found to be safe and resulted in unexpected benefits. In treated infants, compared with controls, indeed, a decreased incidence of the following complications was recorded: bronchopulmonary dysplasia at 36 weeks of conceptional age, patent ductus arteriosus, cerebral palsy at 18 months of age. Nasal CPAP can be used in association with caffeine citrate, when the latter is not effective enough.