Terry M. Baird

Longitudinal assessment of hemoglobin oxygen saturation in healthy infants during the first 6 months of age

Limitations in home monitoring technology have precluded longitudinal studies of hemoglobin oxygen saturation during unperturbed sleep. The memory monitor used in the Collaborative Home Infant Monitoring Evaluation addresses these limitations. We studied 64 healthy term infants at 2 to 25 weeks of age. We analyzed hemoglobin oxygen saturation by pulse oximetry (SpO(2)), respiratory inductance plethysmography, heart rate, and sleep position during 35, 127 epochs automatically recorded during the first 3 minutes of each hour. For each epoch baseline SpO(2) was determined during >/=10 s of quiet breathing. Acute decreases of at least 10 saturation points and <90% for >/=5 s were identified, and the lowest SpO(2) was noted. The median baseline SpO(2) was 97.9% and did not change with age or sleep position. The baseline SpO(2) was <90% in at least 1 epoch in 59% of infants and in 0.51% of all epochs. Acute decreases in SpO(2) occurred in 59% of infants; among these, the median number of episodes was 4. The median lowest SpO(2) during an acute decrease was 83% (10th, 90th percentiles 78%, 87%); 79% of acute decreases were associated with periodic breathing, and >/=16% were associated with isolated apnea. With the use of multivariate analyses, the odds of having an acute decrease increased as the number of epochs with periodic breathing increased, and they lessened significantly with age. We conclude that healthy infants generally have baseline SpO(2) levels >95%. The transient acute decreases are correlated with younger age, periodic breathing, and apnea and appear to be part of normal breathing and oxygenation behavior.

Apnoea of prematurity

Idiopathic apnoea of prematurity is a common and troublesome disorder which requires therapeutic intervention to avoid potential morbidity in premature infants who require neonatal intensive care. Although the definition of apnoea is inconsistent, this condition has been defined most widely as cessation of breathing in excess of 15 seconds duration, typically accompanied by desaturation and bradycardia. Shorter episodes of apnoea, and even periodic breathing, may be accompanied by bradycardia or hypoxemia, with an incidence approaching 100% in the most immature preterm infants.1 Resolution of apnoea of prematurity runs a very variable time course, and the persistence of such episodes is of uncertain pathophysiologic consequence. Apnoea is traditionally classified into three categories based on the presence or absence of obstruction of the upper airways. Central apnoea is characterised by total cessation of inspiratory efforts with no evidence of obstruction. In obstructed apnoea, the infant tries to breathe against an obstructed upper airway resulting in chest wall motion without airflow throughout the entire apnoea. Mixed apnoea consists of obstructed respiratory efforts usually following central pauses, and is probably the most common type of apnoea.2,3 The site of obstruction in the upper airways is mostly in the pharynx, however, it may also occur at the larynx, and possibly both sites. Mixed apnoea typically accounts for more than half of all long apnoeic episodes, followed in decreasing frequency by

Cardiopulmonary monitoring at home: The CHIME monitor

A new physiologic monitor for use in the home has been developed and used for the Collaborative Home Infant Monitor Evaluation (CHIME). This monitor measures infant breathing by respiratory inductance plethysmography and transthoracic impedance; infant electrocardiogram, heart rate and R-R interval; haemoglobin O2 saturation of arterial blood at the periphery and sleep position. Monitor signals from a representative sample of 24 subjects from the CHIME database were of sufficient quality to be clinically interpreted 91.7% of the time for the respiratory inductance plethysmograph, 100% for the ECG, 99.7% for the heart rate and 87% for the 16 subjects of the 24 who used the pulse oximeter. The monitor detected breaths with a sensitivity of 96% and a specificity of 65% compared to human scorers. It detected all clinically significant bradycardias but identified an additional 737 events where a human scorer did not detect bradycardia. The monitor was considered to be superior to conventional monitors and, therefore, suitable for the successful conduct of the CHIME study.

Asystole and Severe Bradycardia in Preterm Infants

Transient episodes of apnea and bradycardia are common in preterm infants. Pronounced asystole or sinus arrest, however, is relatively rare and the clinical significance of such events is unknown. Objective: The purpose of our study was to: (1) evaluate the prevalence of severe bradycardic and asystolic events in infants studied with polygraphic cardiorespiratory monitoring, (2) characterize these events, and (3) correlate the events with other clinical findings. Methods: A total of 583 studies were performed in 454 preterm infants at a post-conceptional age 37.4 ± 2.5 (range 34–42 weeks). Asystolic pauses were defined as no QRS complex for ≧3 s consistent with a heart rate <20 beats per minute (bpm). Severe bradycardia was defined as no QRS for ≧2 s consistent with a heart rate of 21–30 bpm. Results: Eight infants (29.5 ± 3.9 weeks’ gestational age, birth weight 1,283 ± 445 g) met the criteria of having had at least 1 asystolic event (heart rate ≤20 bpm). These infants had a total of 32 episodes of bradycardia ≤30 bpm, of which 22 episodes were classified as asystole. During the asystolic episodes, the P-R interval remained unchanged in 21 of 22 episodes and prolonged in 1. One patient had non-sustained ventricular tachycardia before resumption of normal sinus rhythm. All asystolic events were associated with apnea (mean duration of 17.7 ± 9.4 s) and O2 saturations fell by 10 ± 6%. A pH probe study was available in 9 of 22 asystolic events and 6 of 10 severe bradycardic events. Gastroesophageal reflux was temporally related to only one asystolic and two bradycardic events. Clinical follow-up of these infants at a mean age of 14 months (range 1–46) reveals no symptomatic sequelae; although 1 infant died from multisystem failure associated with multiple congenital anomalies. Conclusions: Asystolic pauses occur in 1.8% of a selected population of preterm infants who have been experiencing cardiorespiratory events, are related to respiratory pauses, and appear to have a benign long-term outcome, although future study should incorporate long-term neurodevelopmental outcome.

Multivariable cardiorespiratory monitoring at home: collaborative home infant monitoring evaluation (CHIME)

Infants at low and increased risk for sudden infant death syndrome (SIDS) from five clinical centers in the United States are being studied at home using a cardiorespiratory monitor that stores physiologic data surrounding detected events and normative data unrelated to events. The monitor records breathing waveforms by inductance plethysmography (IP), and transthoracic impedance (TTT), ECG, beat-beat heart rate, hemoglobin oxygen saturation, and times of monitor use. Comparisons with simultaneously recorded overnight polysomnograms (PSG) in hospital validated the ability of this device to detect cardiorespiratory events including upper airway obstruction. Parental compliance in using this complicated instrument is slightly lower than that reported for conventional home cardiorespiratory monitors.

Weekly telephone contact does not enhance the compliance of home apnea monitoring

OBJECTIVE:To evaluate the effect of weekly telephone contact with families in enhancing the use of home apnea monitors.STUDY DESIGN:This was a prospective, randomized, single-blinded study of 65 infants who were prescribed home apnea monitoring at the time of initial discharge from the hospital. Exclusion criteria included participation in any other study involving home monitoring or nonavailability of home telephone. Infants were randomized either to the “standard” or “telephone” group by a stratified balanced block technique. All families were instructed to use the monitor during the first 4-week period at all times except during bathing and during the second 4-week period at all unattended times and at night. The families in the telephone group were contacted weekly for 8 weeks. The telephone interview reviewed the events of the previous week but did not include specific encouragement to use the monitor. Both groups received routine pediatric care and follow-up at our high-risk premature clinic. The primary outcome measure was compliance measured as the percentage of time as well as the hours per day that the infant spent on the monitor as recorded by the documented monitor.RESULTS:The telephone (n = 30) and standard (n = 32) groups were similar (p > 0.10) with respect to birth weight (1567 ± 778 versus 1710 ± 777 gm), gestational age (30.9 ± 4.2 versus 31.1 ± 4.6 weeks), maternal age (24.9 ± 6.0 versus 25.3 ± 5.4 years), and commercial insurance (46.7% versus 46.9%), a marker of higher socioeconomic status. Compliance of the telephone versus the standard group was similar during thefirst 4-week period (74.7 ± 24.9 versus 75 ± 27.8%, p = 0.85) (17.9 ± 5.9 versus 18.2 ± 6.6 hours/day), the second 4 week period (63.4 ± 29.1 versus 58.9 ± 30.9%, p = 0.59) (15.2 ± 7.0 versus 14.1 ± 7.4 hours/day) and the entire 8-week period (69.3 ± 24.7 versus 67.7 ± 26.2%, p = 0.82, Mann-Whitney U-test) (16.7 ± 6.0 versus 16.1 ± 6.5 hours/day), respectively. An abnormal pneumocardiogram at the time of discharge was the only identified factor that improved the compliance for the entire 8-week period (73.1 ± 22 versus 52.1 ± 28.5%, p = 0.02) (17.5 ± 5.2 versus 12.5 ± 6.8 hours/day) and the first 4-week period of monitoring (81.7 ± 22.9 versus 59.5 ± 31.3%, p = 0.01) (19.6 ± 5.5 versus 14.2 ± 7.5 hours/day).CONCLUSION: Weekly telephone contact, without specific encouragement to use the monitor, did not improve compliance. Compliance was greater in subjects who had abnormal pneumocardiogram results at the time of discharge from hospital regardless of their telephone/standard group assignment. We speculate that in this already compliant population, more targeted advice is necessary to increase compliance.

Assessment of Sleep Position Over Time Among Infants At Risk of Sudden Infant Death Syndrom (SIDS) and Healthy Term Infants. |[dagger]| 462

The AAP continues to recommend avoidance of the prone sleep position to reduce the risk of SIDS. To evaluate compliance with this recommendation over time among families of at-risk and healthy term (HT) infants, we determined sleep position by interview among 630 enrollees in the Collaborative Home Infant Monitoring Evaluation (CHIME) at 5 sites across the USA from 5/1/94-4/30/96. Of these, 503 (89 SIDS siblings (SS), 88 apnea of infancy(AOI), 264 preterm (PT) infants ≤ 34 wks, 62 HT) completed the first follow up visit (≈30 days after enrollment). To determine adherence over time, we examined a subset of 208 infants (51 SS, 28 AOI, and 99 PT, 30 HT) who completed a minimum of 4 follow-up visits at the following postconceptional ages (mean wks ± SD): 44 ± 4, 49 ± 4, 56 ± 5, 71± 15. Table

A thin film temperature sensor for measuring nasal and oral breathing in neonates

A nasal-oral air temperature sensor for measuring breathing in infants has been developed using microelectronic technology. Preliminary studies with this sensor on eight infants showed that six of them demonstrated periods of oral, along with nasal, breathing.

Monitoring infant respiration using an Eight-channel transthoracic impedance monitor

A special transthoracic electrical impedance infant respiration monitor that can sample eight pairs of electrodes has been used to measure breathing patterns in newborn infants. Quasi-simultaneous recordings have been made and used to determine the breath amplitude and duration of spontaneously occurring apneas during two-hour sessions. Preliminary results from eight infants have shown that breath amplitudes usually vary by factors of six to ten, cardiogenic artifact varies from 6 to 27% of mean breath amplitude for different electrode placements, and the apparent duration of apnea is often different for different electrode pairs.

Ability to Predict a Family's Use of a Home Respiratory Inductance Plethysmography (RIP) Monitor † 687

Ability to Predict a Familys Use of a Home Respiratory Inductance Plethysmography (RIP) Monitor † 687