Home event recordings of oxygenation, breathing movements, and heart rate and rhythm in infants with recurrent life-threatening events

Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS

Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK₁R, IL1RI and 5-HT₃R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.

Home Cardiorespiratory Monitoring in Infants at Risk for Sudden Infant Death Syndrome (SIDS), Apparent Life-Threatening Event (ALTE) or Brief Resolved Unexplained Event (BRUE)

Sudden infant death syndrome (SIDS) is defined as the sudden death of an infant younger than one year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. About 90% of SIDS occur before six months of age, the peak incidence is between two and four months, and the median age for death is elven weeks. The clinical, social, and economic relevance of SIDS, together with the evidence that prevention of this syndrome was possible, has significantly stimulated research into risk factors for the development of SIDS in the hope of being able to introduce new effective preventive measures. This narrative review discusses the potential relationships between apparent life-threatening events (ALTE) or brief resolved unexplained events (BRUE) and SIDS development, and when a home cardiorespiratory monitor is useful for prevention of these conditions. A literature analysis showed that home cardiorespiratory monitoring has been considered a potential method to identify not only ALTE and BRUE but SIDS also. ALTE and BRUE are generally due to underlying conditions that are not detectable in SIDS infants. A true relationship between these conditions has never been demonstrated. Use of home cardiorespiratory monitor is not recommended for SIDS, whereas it could be suggested for children with previous ALTE or severe BRUE or who are at risk of the development of these conditions. However, use of home cardiorespiratory monitors assumes that family members know the advantages and limitations of these devices after adequate education and instruction in their use.

The Science (or Nonscience) of Research Into Sudden Infant Death Syndrome (SIDS)

This Viewpoint paper presents a timely and constructive critique of mainstream SIDS research. It is concerning that twenty-first century medical science has not provided an answer to the tragic enigma of SIDS. The paper helps explain why this is so and illustrates possible shortcomings in the investigation of Sudden Infant Death Syndrome/Sudden Unexplained Infant Death (SIDS/SUID) by mainstream researchers. Mainstream findings are often based on questionable and dogmatic assumptions that return to founding notions such as the Triple Risk Hypothesis and the contention that the mechanisms underlying SIDS/SUID are heterogeneous in nature. The paper illustrates how the pathological findings in SIDS have been under-investigated (or ignored) and that key epidemiological risk factors have slipped from memory. This apparent amnesia has resulted in failure to use these established SIDS facts to substantiate the significance of various neuropathological, neurochemical, or other research findings. These unsupported findings and their derivative hypotheses are therefore ill-founded and lack scientific rigor.

CONCLUSION

The deficits of SIDS "science" revealed in this paper explain why the SIDS enigma has not yet been solved. To make progress in understanding SIDS, it is important that researchers, as scientists, uphold standards of research. Encouragement for new directions of research is offered.

A mouse zoonotic virus (LCMV): A possible candidate in the causation of SIDS

Lymphocytic choriomeningitis virus (LCMV) is a ubiquitous virus carried by rodents. It causes human disease through contact with infectious mouse faeces, urine or secretions. The virus initially infects the human respiratory tract and lungs and produces typical viral symptoms and signs. The infection is usually self-limiting and recovery is the norm. A small proportion of individuals may develop aseptic meningitis. It is hypothesised that in infancy the virus may cause respiratory tract infection through contact with mouse excreta. The infection could activate production of staphylococcal enterotoxin in babies who are colonised by Staphylococcus aureus. Indeed, a mouse animal model has shown that the combination of LCMV infection and introduction of enterotoxin B produces fatal haematogenous shock. Neither agent alone is lethal. Pathological (and physiological) evidence indicates shock could be the underlying terminal event in SIDS (the observed tissue damage seen in the heart and diaphragmatic muscles, and apoptosis observed in the brain and brainstem of SIDS cases). These features are consistent with a haematogenous shock event. The epidemiology of SIDS is entirely consistent with a mouse-related viral zoonosis. Moreover, rural cases of SIDS tend to feature more often than urban cases and their occurrence would be consistent with the dynamics of mouse populations. Low socioeconomic living conditions (a major risk factor for SIDS) is consistent with prevalence of mouse populations and poor hygienic conditions, with overcrowding. Prone sleeping would facilitate aspiration or ingestion of infectious material from contaminated surfaces. and poor hygienic conditions, with overcrowding, and prone sleeping would facilitate aspiration or ingestion of infectious material from contaminated surfaces. The epidemiology and pathology of SIDS and the dynamics and ubiquity of mouse populations together with human serological data would support the hypothesis that LCMV is a potential candidate as a key factor in the causation of SIDS.

Infection, Celestial Influences, and Sudden Infant Death Syndrome: A New Paradigm

The etiology of sudden infant death syndrome (SIDS) still remains unclear. This situation would seem unprecedented for 21st-century medical science. This article explores scientific fields that have not been largely considered in investigating the etiology of SIDS so far. In this study, we examined previously ignored studies on heliobiology, celestial influences, and SIDS in the non-medical literature in an attempt to answer the following questions: is there a relationship between sunspot/solar activity and the occurrence of SIDS? Could there be alternative reasons for the decline in SIDS incidences in the 1990s that were originally attributed to the “Back-to-Sleep” campaign? We note that the decline coincided with the ~11-year cyclical diminution in sunspot numbers (SSNs). The SSN/SIDS relationship does not necessarily imply causality; however, it supports published data regarding sunspots, Schumann resonance, and geomagnetic effects. How solar energy could adversely influence a baby’s existence remains conjectural. Observations in this respect suggest pathways involving melatonin and/or infection/inflammation.

Take a deep breath and wake up: The protean role of serotonin preventing sudden death in infancy

Recordings from infants who died suddenly and unexpectedly demonstrate the occurrence of recurring apneas, ineffective gasping, and finally, failure to restore eupnea and arouse prior to death. Immunohistochemical and autoradiographic data demonstrate a constellation of serotonergic defects in the caudal raphe nuclei in infants who died of Sudden Infant Death Syndrome (SIDS). The purpose of this review is to synthesize what is known about adaptive responses of the infant to severely hypoxic conditions, which unleash a flood of neuromodulators that inhibit cardiorespiratory function, thermogenesis, and arousal and the emerging role of serotonin, which combats this cardiorespiratory inhibition to foster autoresuscitation, eupnea, and arousal to ensure survival following an hypoxic episode. The laryngeal and carotid body chemoreflexes are potent in newborns and infants, and both reflexes can induce apnea and bradycardia, which may be adaptive initially, but must be terminated if an infant is to survive. Serotonin has a unique ability to touch on each of the processes that may be required to recover from hypoxic reflex apnea: gasping, the restoration of heart rate and blood pressure, termination of apneas and, eventually, stimulation of eupnea and arousal. Recurrent apneic events, bradycardia, ineffective gasping and a failure to terminate apneas and restore eupnea are observed in animals harboring defects in the caudal serotonergic system models - all of these phenotypes are reminiscent of and compatible with the cardiorespiratory recordings made in infants who subsequently died of SIDS. The caudal serotonergic system provides an organized, multi-pronged defense against reflex cardiorespiratory inhibition and the hypoxia that accompanies prolonged apnea, bradycardia and hypotension, and any deficiency of caudal serotonergic function will increase the propensity for sudden unexplained infant death.

Prenatal intermittent hypoxia sensitizes the laryngeal chemoreflex, blocks serotoninergic shortening of the reflex, and reduces 5-HT3 receptor binding in the NTS in anesthetized rat pups

We tested the hypothesis that exposure to intermittent hypoxia (IH) during pregnancy would prolong the laryngeal chemoreflex (LCR) and diminish the capacity of serotonin (5-hydroxytryptamine; 5-HT) to terminate the LCR. Prenatal exposure to IH was associated with significant prolongation of the LCR in younger, anesthetized, postnatal day (P) rat pups age P8 to P16 compared to control, room air (RA)-exposed rat pups of the same age. Serotonin microinjected into the NTS shortened the LCR in rat pups exposed to RA during gestation, but 5-HT failed to shorten the LCR in rat pups exposed to prenatal IH. Given these observations, we tested the hypothesis that prenatal hypoxia would decrease binding to 5-HT3 receptors in the nucleus of the solitary tract (NTS) where 5-HT acts to shorten the LCR. Serotonin 3 receptor binding was reduced in younger rat pups exposed to IH compared to control, RA-exposed rat pups in the age range P8 to P12. Serotonin 3 receptor binding was similar in older animals (P18-P24) regardless of gas exposure during gestation. The failure of the 5-HT injected into the NTS to shorten the LCR was correlated with a developmental decrease in 5-HT3 receptor binding in the NTS associated with exposure to prenatal IH. In summary, prenatal IH sensitized reflex apnea and blunted processes that terminate reflex apneas in neonatal rat pups, processes that are essential to prevent death following apneas such as those seen in babies who died of SIDS.

The Sudden Infant Death Syndrome mechanism of death may be a non-septic hyper-dynamic shock

BACKGROUND

Sudden Infant Death Syndrome (SIDS) mechanisms of death remains obscured. SIDS' Triple Risk Model assumed coexistence of individual subtle vulnerability, critical developmental period and stressors. Prone sleeping is a major risk factor but provide no clues regarding the mechanism of death. The leading assumed mechanisms of death are either an acute respiratory crisis or arrhythmias but neither one is supported with evidence, hence both are eventually speculations. Postmortem findings do exist but are inconclusive to identify the mechanism of death. WHAT DOES THE PROPOSED HYPOTHESIS BASED ON?: 1. The stressors (suggested by the triple risk model) share a unified compensatory physiological response of decrease in systemic vascular resistant (SVR) to facilitate a compensatory increase in cardiac output (CO). 2. The cardiovascular/cardiorespiratory control of the vulnerable infant during a critical developmental period may be impaired. 3. A severe decrease in SVR is associated with hyper-dynamic state, high output failure and distributive shock.

THE HYPOTHESIS

Infant who is exposed to one or more stressors responds normally by decrease in SVR which increases CO. In normal circumstances once the needs are met both SVR and CO are stabilized on a new steady state. The incompetent cardiovascular control of the vulnerable infant fails to stabilize SVR which decreases in an uncontrolled manner. Accordingly CO increases above the needs to hyper-dynamic state, high output heart failure and hyper-dynamic shock.

CONCLUSIONS

The proposed hypothesis provides an appropriate alternative to either respiratory crises or arrhythmia though both speculations cannot be entirely excluded.

Apparent Life-Threatening Events (ALTE): Italian guidelines

Five years after the first edition, we have revised and updated the guidelines, re-examining the queries and relative recommendations, expanding the issues addressed with the introduction of a new entity, recently proposed by the American Academy of Pediatrics: BRUE, an acronym for Brief Resolved Unexplained Events. In this manuscript we will use the term BRUE only to refer to mild, idiopathic cases rather than simply replace the acronym ALTE per se.In our guidelines the acronym ALTE is used for severe cases that are unexplainable after the first and second level examinations.Although the term ALTE can be used to describe the common symptoms at the onset, whenever the aetiology is ascertained, the final diagnosis may be better specified as seizures, gastroesophageal reflux, infection, arrhythmia, etc. Lastly, we have addressed the emerging problem of the so-called Sudden Unexpected Postnatal Collapse (SUPC), that might be considered as a severe ALTE occurring in the first week of life.

Infection: the neglected paradigm in SIDS research

Despite decades of investigation and millions of dollars spent, the cause of sudden infant death syndrome (SIDS) eludes researchers. It is timely therefore to reconsider the reasons for this failure and to explore how research might go forward with better prospects. This review assesses SIDS research in the context of clinicopathological and epidemiological features and determines that only infection attains congruence.

Apparent life-threatening events: assessment, risks, reality

Apparent life-threatening events (ALTEs), because of their prevalence as well as their potential to hide serious diseases and consume significant medical resources, remain a challenge for physicians caring for infants. In this review, we focused on the assessment of the well-appearing infant for the most serious diagnoses, namely serious bacterial infections, seizure disorders, child abuse, metabolic disorders and severe apnoea with hypoxemia. Our extensive review of the literature has highlighted the difficulties physicians are facing in this evaluation, especially for the youngest infants (aged less than 2 months). Large-scale prospective studies are needed to identify risk factors and to guide physicians as to who should be investigated and the minimal investigation needed to avoid missing such conditions as serious bacterial infection, abusive head injury or repeated severe cardiorespiratory events. While infants with severe forms of metabolic disorders typically present with evident signs and symptoms, less severe forms of metabolic disorders, seizure disorders, and some forms of child abuse will often be diagnosed only when recurrent events are investigated.

A perspective on SIDS pathogenesis. the hypotheses: plausibility and evidence

Several theories of the underlying mechanisms of Sudden Infant Death Syndrome (SIDS) have been proposed. These theories have born relatively narrow beach-head research programs attracting generous research funding sustained for many years at expense to the public purse. This perspective endeavors to critically examine the evidence and bases of these theories and determine their plausibility; and questions whether or not a safe and reasoned hypothesis lies at their foundation. The Opinion sets specific criteria by asking the following questions: 1. Does the hypothesis take into account the key pathological findings in SIDS? 2. Is the hypothesis congruent with the key epidemiological risk factors? 3. Does it link 1 and 2? Falling short of any one of these answers, by inference, would imply insufficient grounds for a sustainable hypothesis. Some of the hypotheses overlap, for instance, notional respiratory failure may encompass apnea, prone sleep position, and asphyxia which may be seen to be linked to co-sleeping. For the purposes of this paper, each element will be assessed on the above criteria.

Indications for home apnea monitoring (or not)

Although there is a large body of literature describing infants who experience apnea of prematurity and apparent life-threatening events, there is no consensus regarding the use of home monitoring. This article focuses on issues that affect decision making regarding the use of home monitors in these two groups of infants and reviews existing data to guide a decision to discontinue monitoring at hospital discharge or to prescribe monitoring in the home.

Transient bacteraemia: A possible cause of sudden life threatening events

The concept proposed is that transient bacteraemia occurring in otherwise healthy individuals can cause acute life threatening events due to bacterial toxaemia even though the bacteraemia is rapidly cleared (<20 min). This is most likely to occur in infancy at around two to three months of age when anti-toxin IgG reaches its nadir. Sudden unexpected death in infancy, acute life threatening events, haemorrhagic shock and encephalopathy, and the triad of retinal haemorrhage, encephalopathy and bilateral thin film subdural haematomata are conditions which could be caused by this mechanism. Investigations need to be directed to measuring bacterial toxins in blood, CSF and urine; anti-toxin IgG in blood; and bacterial specific nucleic acid sequences in blood, CSF and urine using polymerase chain reaction in order to confirm recent bacteraemia. Furthermore the upper respiratory tract bacterial flora should be mapped in cases and appropriately matched live healthy community controls. Sudden onset, profound life threatening physiological dysfunction occurring in later life could also be caused by a similar mechanism and should be investigated in a similar way; candidate conditions include epilepsy, migraine, stroke and cardiac arrhythmias.

Home and hospital monitoring for ALTE

Apparent life-threatening events (ALTE) results from various causes. Documented monitoring of cardiorespiratory parameters and Hb-O(2) saturation by pulse oximetry (SpO(2)) has proven useful in the identification of significant events both in hospital and at home. Home monitoring might be especially helpful for infants with recurrent but infrequent clinical events not captured during a hospital admission.

Apparent life-threatening events and sudden infant death on a monitor

This review summarises recent data on mechanisms for apparent life-threatening events (ALTE) and sudden infant death (SID) which show that (i). recordings obtained during ALTE allow the detection of previously unrecognised but preventable mechanisms in a significant proportion of infants and should thus be performed routinely in infants with such a history, (ii). in recordings obtained during SID and idiopathic ALTE, prolonged apnoea was found in only a minority, while severe hypoxaemia appeared to the common mechanism, (iii). it remains yet unclear by which mechanism this hypoxaemia develops, with upper and/or lower airway obstruction, rebreathing of expired air and intrapulmonary shunting being potential candidates, (iv). there is evidence that arousal fails during SID, which could be related to known risk factors such as tobacco smoke exposure, whereas (v). gasping occurred during the majority of SID cases where respiratory patterns have been analysed, but it remains unclear why gasping remains ineffective in resuscitating the infant from hypoxaemia.

Fetal hemoglobin synthesis determined by gamma-mRNA/gamma-mRNA + beta-mRNA quantitation in infants at risk for sudden infant death syndrome being monitored at home for apnea

OBJECTIVE

Fetal hemoglobin (HbF) levels in the hemolysates obtained from infants who died from sudden infant death syndrome (SIDS) are reported to be markedly increased compared with controls. This finding could have been explained by increased HbF synthesis caused by episodes of hypoxemia in the SIDS infants. A prospective study in a group of infants being monitored at home after an apparent life-threatening event (ALTE) and considered at increased risk for SIDS was conducted with an improved ribonuclease protection assay. The ribonuclease protection assay allowed for the quantitation of [gamma/(gamma+beta)]-globin mRNAs, which has a highly significant correlation with the levels of HbF synthesis.

METHODS

Thirty-five infants who were admitted for an ALTE were included in the study. All infants were at home under surveillance with a cardiorespiratory monitor and followed in an apnea clinic with monthly appointments. Seventy-three blood samples were obtained between 38 and 61 weeks of postconceptional age. For control purposes, a similar group of 37 normal infants (99 samples) whose HbF synthesis was previously determined were included.

RESULTS

Mean [gamma/(gamma+beta)]-globin mRNAs were increased in the ALTE group at 42 to 45 and 46 to 49 weeks of postconceptional age (mean: 55.2 +/- 17.4% and 33.9 +/- 14%) in comparison with HbF synthesis in controls (mean: 42.6 +/- 13.7% and 23.6 +/- 9.8%).

CONCLUSIONS

The data obtained in this report from infants who were considered at risk for SIDS show that HbF synthesis is increased between 42 and 49 weeks of postconceptional age. Determining HbF synthesis as described in this study may have value as a marker for episodes of hypoxemia for certain infants who are at risk for SIDS.

Short-term event recording as a measure to rule out false alarms and to shorten the duration of home monitoring in infants

Apnea and cardiorespiratory home monitors are commonly used for electronic surveillance of infants. Frequent alarms can be very stressful for parents and lead to unnecessarily prolonged home monitoring. The aims of this study were to determine the frequency and type of significant events by using short-term home event recordings of respiratory, electrocardiogram and oxygenation patterns, to consider the pros and cons of oxygenation recording, to correlate the findings with observations made by parents and to find out whether parents could be reassured by the use of these monitors. We investigated recordings from 26 healthy symptomless infants (14 male, 12 female) whose parents experienced anxiety and stress owing to frequent alarms on their apnea (n = 2) or cardiorespiratory home monitors (n = 24). 770 events were analyzed and compared with the parents' interpretation. Median duration of monitoring was 10 days. Only 39/770 alarms (5.1%) were classified as true alarms. Of these, 30 alarms (76.9%) were misinterpreted as false alarms by parents. In contrast, of 218 alarms regarded as true by parents only 15 (6.9%) were in fact true, alarms. The comparison of monitor data and the parents' reports showed no correlation in interpretation of alarms, for both true (r = 0.06) and false alarms (r = -0.09). Of 283 oxygenation alarms, only two were due to real desaturation. Following short-term monitoring, 21/26 parents (80.7%) declared they were reassured. Monitoring could immediately be discontinued in 17/26 infants (65.4%). Short-term event recording can clarify the significance of frequent alarms, reassure parents and shorten the duration of home monitoring.

Heart rate changes in response to mild mechanical irritation of the high cervical spinal cord region in infants

Alterations in the heart rate were monitored before, during and after the application of a unilateral mechanical impulse to the high cervical spinal cord region which was administered strictly in connection with the so called manual therapy (diagnosis= KISS). The investigation is based on a survey of 695 infants between the ages of 1 and 12 months. A notable change in the heart rate was evident in 47.2% of all examined infants (n= 695). In 40.1% of these infants, the change in heart rate was characterized by heart rate decrease of 15-83% compared to control conditions. Infants in their first 3 months of life responded more often with a severe bradycardia (50-83% decrease), older infants (7-12 months) more often with a mild bradycardia (15-49.9% decrease). This comparison revealed a significantly increased occurrence of severe bradycardia in the younger age group compared to the group of children >3 months (significance 0.0017). In 12.1% (n= 84) of the infants, the bradycardia was accompanied by an apnea. We discuss the hypothesis that mechanical irritation of the high-cervical region serves as a trigger that may be involved in sudden infant death (SID).

Apparent life threatening events in infants presenting to an emergency department

OBJECTIVE

To describe the aetiology and outcome of apparent life threatening events (ALTE) presenting to an emergency department (ED), and to assess the value of an initial investigation protocol.

DESIGN

A 12 month prospective study of infants under 1 year of age who presented to a children's hospital ED after an ALTE. A standardised history sheet and initial investigation protocol were used. All infants were admitted to hospital and followed up at six months.

RESULTS

There were 65 infants recruited, median age 7 weeks. None had died at the time of writing. Diagnoses included gastro-oesophageal reflux n=17 (26%), pertussis, n=6 (9%), seizures, n=6 (9%), urinary tract infection (5), factitious illness (2), brain tumour, atrial tachycardia, persistent ductus arteriosus and opioid related apnoea. No diagnosis was reached in 15 cases (23%). Fifty seven (88%) had only one admission to hospital for ALTE. More serious diagnoses were associated with a presentation age over 2 months, abnormal initial clinical examination, and recurrent ALTE.

CONCLUSIONS

ALTEs presenting to the ED may remain as a single, unexplained event or be attributable to numerous causes, ranging from minor to serious. Knowledge of the commoner causes and factors associated with higher risk could result in a more targeted approach, improving the decision making process and benefiting both infants and parents.

Computerised audiovisual event recording for infant apnoea and bradycardia

Event recording, by differentiating between true and false events, has advanced the diagnosis and management of infants on home cardiorespiratory monitors; however, the pathogenesis of many events remains obscure. To clarify infant behaviours around the time of apnoea/bradycardia alarms, a computerised audiovisual event recording system (CAVERS) triggered by the apnoea/bradycardia recorder, has been developed. The audiovisual recording can begin up to 3 min before the alarm and can continue for up to 3 min after the alarm. CAVERS information is recorded for a total of 65 events in 13 infants. The CAVERS proves most helpful in documenting infant position and the wide variety of behaviours associated with bradycardic events. These behaviours range from sleep or quiet wakefulness to crying and generalised movements. Post-event activity is also highly variable. Interestingly, 20 of 65 events appear to terminate when the infant wakes to the audible monitor alarm. Nursing intervention is documented for 14 of 42 bradycardic events but only one of 23 apnoeic events. The CAVERS, by elucidating infant behaviours, provides information complementary to that given by cardiorespiratory event recording. It is suggested that infant monitors of the future should incorporate both audiovisual and cardiorespiratory data to elucidate optimally apparent life-threatening events, apnoeas and bradycardias.

Age-dependent metabolic effects of repeated hypoxemia in piglets

The aim of this study was to determine whether repeated exposure to hypoxemia would modify the response to hypoxemia during maturation. We exposed piglets to three 1-h cycles of hypoxemia (PaO2 = 30 to 35 mmHg; 1 mmHg = 133.3 Pa) at 1 week (n = 9), 2-3 weeks (n = 10), and 4-5 weeks of age (n = 10). O2 consumption (VO2) and CO2 production (VCO2) were measured, and alveolar ventilation (VA) was derived from VCO2 and PaCO2. Levels of lactic acid (lactate) and serum catecholamines were also measured. With hypoxemia, time had a significant effect on VO2 and body temperature in an age-dependent fashion: that is, whereas the 1 week group and the 4-5 week group showed both variables decreasing over time, the 2-3 week group showed no drop in VO2 and a small increase in body temperature over time. Lactate levels increased with hypoxemia in all animals during the first exposure. However, with repeated exposures to hypoxemia, only the 2-3 week group continued to increase its lactate levels. Furthermore, the changes in lactate levels paralleled the changes in epinephrine levels with hypoxemia. We found, too, that although VA increased significantly with hypoxemia in all animals, this change was not modified by age or repeated exposures. No significant effects of age or repeated exposures were found in the cardiovascular response to hypoxemia. We concluded that, from a metabolic viewpoint, after repeated exposures to hypoxemia the 2-3 week animals responded differently.Key words: metabolic rate, lactic acid, maturation, catecholamines.

Neuronal apoptosis in sudden infant death syndrome

Although evidence shows that victims of sudden infant death syndrome (SIDS) suffer repetitive episodes of hypoxemia, only subtle abnormalities have been found in their brains by light microscopy. The aim of the present study was to determine whether apoptosis, a form of cell death that can be triggered by hypoxemia and that leaves no scarring detectable by light microscopy, would be present in hypoxia-sensitive brain regions of SIDS victims. We looked for the presence of apoptosis with an in situ end-labeling method that detects DNA fragmentation. We studied 29 SIDS victims who were age-matched to nine control cases. We found significant neuronal apoptosis in 79% of the SIDS cases: 55% of the cases positive in the hippocampus and 96% positive in the brainstem. Whereas the distribution of apoptosis in the hippocampus was in hypoxia-sensitive subregions, the distribution in the brainstem was mostly in dorsal nuclei, including those involved with sensation in the face and position of the head (nucleus of the spinal trigeminal tract and vestibular nuclei). The control cases showed no significant apoptosis in the hippocampus and a mild degree in the brainstem in three cases. Our results indicate the occurrence of an acute insult at least several hours before death, an insult from which the infants had apparently recuperated. This suggests that SIDS victims suffered repeated apoptosis resulting in significant neuronal damage and, thus, functional loss in key brain regions. The involvement of specific nuclei in the brainstem may be linked to the fact that prone sleeping is a significant risk factor for SIDS. Enhanced neuronal death by apoptosis may thus have major implications for understanding the sequence of events leading to SIDS.

High cervical stress and apnoea

The aim of this study was to investigate vegetative reactions in infants after mechanical irritation of the suboccipital region. The investigation is based on 199 infants who were observed while being treated with a suboccipital impulse (manual therapy). The results revealed vegetative reactions in more than half of all cases (52.8%, n = 105). The frequency of such vegetative reactions observed was at follows: flush 48.7% (n = 97), apnoea 22.1% (n = 44), hyperextension 13% (n = 26), and sweating 7.5% (n = 15). It is pointed out that approximately 25% of all the infants examined reacted by apnoea due to a mechanical irritation of the suboccipital region. This symptom was part of an extensive vegetative reaction. This method of inducing an apnoea has not yet been described; from this it follows that there are close relations to sudden infant death.

Frequency and timing of recurrent events in infants using home cardiorespiratory monitors

OBJECTIVE

To determine the incidence, type, timing, and factors predictive of recurrent significant events in infants with home cardiorespiratory monitors.

STUDY DESIGN

We reviewed data accumulated for 147 patients with an event-recorder type of monitor. The infants were allocated to one of four diagnostic categories: apparent life-threatening events (ALTE, n = 73), former premature infants with persistent apnea and bradycardia (n = 29), siblings of victims of sudden infant death syndrome (SIDS) (n = 24), and parental anxiety after a nonsignificant event (n = 21).

RESULTS

Compliance with monitoring was excellent; the monitors were used on 94% of the prescribed days. Fifty-three (36%) of 147 infants had significant events; of those, 46 (87%) experienced their first event during the first month of monitoring, and 69% of the events occurred during that first month. The most prevalent event type was a bradycardic event. Among infants in the ALTE group, events during the initial investigation period predicted the likelihood of events at home; 2 of the 47 infants (4%) with negative results for an investigation and no events recorded in hospital had apnea, and 4 had a bradycardic event (9%). In contrast, when significant events were recorded in hospital, the events were likely to recur at home (69% and 35% of the infants had apnea or bradycardia, respectively; p < 0.001).

CONCLUSION

Because most apnea, bradycardia, and recurrent clinical events began during the first month of monitoring, we emphasize the need for vigilant follow-up care of infants immediately after institution of home monitoring. Readmission for investigation is warranted in infants with severe or multiple recurrent events.

Clinical characteristics of an apparent life-threatening event (ALTE) and the subsequent occurrence of prolonged apnea or prolonged bradycardia

The objective of this study was to test the hypothesis that the characteristics of an apparent life-threatening event (ALTE) influence the risk for a subsequent episode of prolonged apnea or bradycardia. Data were obtained from 182 infants referred because of an apparent life-threatening event who were followed up at home for 2 lunar months on an apnea/bradycardia monitor with recording capability. A prolonged episode was defined as apnea > or = 20 sec long or an episode of bradycardia > or = 10 sec in duration as validated and measured from the event recordings. Seventeen percent of infants had at least one episode of prolonged apnea or prolonged bradycardia. Change in skin color, degree of resuscitative intervention, and behavioral state were not statistically significant factors influencing the risk of a subsequent prolonged episode. Contrary to clinical expectation, a significantly greater percentage of infants subsequently had a prolonged episode whose muscle tone was described as normal during the ALTE (24.0%), when compared with those infants whose ALTE was associated with limpness or increased muscle tone (9.3%). The coexistence of gastroesophageal reflux did not influence the overall results. The observations in this study place in question the clinical approach of relying on the detailed characteristics of an ALTE in determining the need for follow-up studies and/or home monitoring.

Intra-alveolar pulmonary siderophages in sudden infant death: a marker for previous imposed suffocation

Staining for iron showed previously overlooked intra-alveolar siderophages widely distributed in the lungs of two pairs of siblings, all of whom had hospital admissions for apparent life-threatening events (ALTEs) before dying suddenly at home. A mother and babysitter were convicted of their murder and manslaughter respectively. There were no siderophages in the lungs of a fifth infant whose death was included in the murder charge but who had no ALTEs. Bleeding from mouth or nose was observed during six of ten previous ALTEs suffered by these children and three unrelated infants in the same care. Such external hemorrhage is well described in imposed infant suffocation which may be one aspect of "Munchausen syndrome by proxy" child abuse. Our findings imply that there may also be intrapulmonary hemorrhage and that intra-alveolar siderophages can be a marker for previous abuse. Retrospectively we found diffusely distributed intra-alveolar siderophages in the lungs of seven of 158 infants with diagnoses of SIDS. Siderophages in such numbers demand an explanation and if this is not provided by clinical history or other necropsy findings should cause suspicion of previous imposed suffocation and infanticide and require further enquiry. The lungs should be stained for iron in all cases of sudden infant death.

Abnormal hypoxemia after life-threatening events in infants born before term

This study aimed to determine whether preterm infants who have a history of apparent life-threatening events (ALTE) have abnormalities in oxygenation and, if so, whether the ALTE would stop with oxygen therapy. We assessed 92 patients (median gestational age at birth, 32 weeks (range, 24 to 36 weeks); median birth weight, 1840 gm (650 to 3500 gm)) who had had a single (n = 20) or recurrent ALTE. Median postnatal age at referral was 3.2 months (0.5 to 44.7 months). All had been considered otherwise free of symptoms and adequately oxygenated in air at the time of discharge from their neonatal unit, before the ALTE. Fifty-two patients had received mouth-to-mouth resuscitation, and 40 vigorous stimulation. Ninety-one patients underwent 8- to 12-hour recordings of arterial oxygen saturation, the plethysmographic waveforms from the oximeter, breathing movements, and electrocardiograms. These recordings were compared with previously published data from 110 "healthy" preterm infants made at around 6 weeks after discharge from hospital. Compared with these data, 49 recordings (54%) were normal, 19 showed abnormal hypoxemic episodes, 6 had abnormally low baseline arterial oxygen saturation (< 95%), and 17 had both. In 31 of 33 patients, ALTE stopped or were reduced in frequency or severity after additional inspired oxygen (0.1 to 1.0 L/min via nasal cannulas) was given. Oxygen was given for a median duration of 3.9 months (range, 0.8 to 17.2 months). Persistent events in the remaining two patients were subsequently found to be due to intentional suffocation in one and epileptic seizures in the other. Monitoring of transcutaneous oxygen tension at home was undertaken in 84 patients. To date, this has been discontinued in 81 after a median duration of 7.3 months (0.3 to 18.9 months). We conclude that recognition and treatment of abnormalities in episodic or baseline hypoxemia may reduce the risk of further ALTE in previously preterm infants.