Toke Hoppenbrouwers

Cardiopulmonary and intracranial pressure changes related to endotracheal suctioning in preterm infants

Although endotracheal (ET) suctioning is performed frequently in sick newborn infants, its effects on cardiorespiratory variables and intracranial pressure (ICP) have not been thoroughly documented in neonates greater than 24 h who were not paralyzed while receiving mechanical ventilation. This study evaluates these changes in preterm infants who required ventilatory assistance. We measured transcutaneous PO2 and PCO2 (PtcO2 and PtcCO2, respectively), intra-arterial BP, heart rate, ICP, and cerebral perfusion pressure (CPP) before, during, and for at least 5 min after ET suctioning in 15 low birth weight infants less than 1500 g and less than or equal to 30 days of age. One infant was studied twice. A suction adaptor was used to avoid disconnecting the patient from the ventilator and to attempt to minimize hypoxemia and hypercapnia during suctioning. The patients were studied in the supine position and muscle relaxants were not used. PtcO2 decreased 12.1% while PtcCO2 increased 4.7% 1 min after suctioning; however, greater increases in mean BP (33%) and ICP (117%) were observed during suctioning. CPP also increased during the procedure. ICP returned to baseline almost immediately, whereas BP remained slightly elevated 1 min after suctioning. Our findings demonstrate that ET suctioning significantly increases BP, ICP, and CPP in preterm infants on assisted ventilation in the first month of life. These changes appear to be independent of changes observed in oxygenation and ventilation.

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.

The Emergence of a Circadian Pattern in Respiratory Rates: Comparison between Control Infants and Subsequent Siblings of SIDS

Summary: The objective of the present study is to compare the emergence of a circadian respiratory pattern in subsequent siblings of SIDS and control infants to see whether the unique time and age of SIDS is correlated with altered circadian manifestations. During the first three months of life, a pattern in respiratory rates emerged which appeared to be the nightly portion of a circadian rhythm. Subsequent siblings of SIDS exhibited transient accelerated maturation of this circadian pattern. During the first month of life, minima in respiratory rates in quiet sleep occurred during the second and third intervals of the night in subsequent siblings, a pattern not seen until three months of age in control infants.Speculation: Two recent reports suggest a developmental model in which a physiological deficit can bring about a transient acceleration in maturation. Glück et al. (9) demonstrated an accelerated pattern of lung development as measured by the appearance of phosphatidylglycerol in amniotic fluid as much as eight wk early in intrauterine growth-retarded fetuses. Minkowsky (23) presented preliminary data of increased levels of neurotransmitters such as serotonin and precursors in fetal rats with experimentally induced intrauterine malnutrition. It is tempting to speculate that accelerated maturation in electroencephalographic sleep frequencies and respiratory circadian patterns in subsequent siblings of sudden infant death syndrome are manifestations of a compensatory response to an oxygen deficit.

Transcutaneous Oxygen and Carbon Dioxide during the First Half Year of Life in Premature and Normal Term Infants

ABSTRACT: Repetitive polysomnograms were recorded from a total of 33 infants, 19 healthy preterm infants, and 14 term controls between 40 wk postconceptional age and 6 mo of age. These nighttime recordings lasted 2—4 h, except at 52 wk in preterm infants and at 3 mo of age in term infants when an overnight 12-h recording was performed. Minute by minute values of transcutaneous Po. (Ptco2) and transcutaneous PCO2 (PtcCO2) levels and variability during the awake state, active sleep, and quiet sleep were obtained through computer analyses of the polygraphic data. The results from preterm infants at corrected postconceptional age could not be differentiated from those of control infants. PtcO2 levels rose between 40 wk and 3 mo, and PtcCO2 levels declined. Sleep states modulated only the variability of PtcO2, not the level; in contrast, state modulation was seen in both variability and level of PtcCO2 throughout the age span studied. During sleep the number of transient declines in PtcO2 > 2.03 kPa (15 mm Hg) decreased with advancing age. Hypercapnic PtcCO2 values decreased with age as well, but their prevalence in healthy, young infants suggests the need for revaluation of criteria for hypercapnia based on transcutaneous measurements. The data demonstrate that ventilatory regulation continues to undergo changes between 1 and 3 mo, the age of highest risk for sudden infant death syndrome.

Respiration during the First Six Months of Life in Normal Infants. III. Computer Identification of Breathing Pauses

Summary: The first objective of this study was to quantify computer-identified breathing pauses in excess of two sec duration in relation to sleep states. The second objective was to examine which respiratory variables at one wk and one month of age predicted total apnea at 2 and 3 months of age.Short apnea (2 to 5 sec) were abundant in recordings of normal infants during the first one-half year of life. Apnea between 6 and 9 sec should be considered normal, whereas apnea in excess of 9 sec occurred most frequently in the first wk of life and declined sharply thereafter. Recording duration substantially affected apnea counts. Apnea at later ages could not be reliably predicted from recordings during the first wk of life.Speculation: Short breathing pauses in QS during the age span under investigation are probably inversely related to breathing rate and caused by the same mechanism responsible for the decline in rate. The change in breathing pauses over age in AS can probably be accounted for by two sources of variance, first, the decline in rate and second, rate-independent developmental changes in control of ventilation during AS.

Respiration during the first six months of life in normal infants: IV. Gender differences

Respiratory rates and breathing pauses of various durations were examined in 19 normal infants, 12 male and 7 female, during the first 6 months of life. Twelve-hour all-night polygraphic recordings were obtained during the first week of life and at 1, 2, 3, 4 and 6 months. A computer program and visual analysis were used to score sleep state and calculate respiratory rates and apnea densities. In the newborn period there were no gender differences. Males breathed faster and exhibited fewer breathing pauses between 2 and 5 sec from one month of age on. The close correlation between respiratory rate and short breathing pauses suggests that the latter are an integral part of normal respiratory regulation. These findings can be explained by gender-related differences in metabolic rate or maturation of the central nervous system.

Factors affecting nursery survival of very low birth weight infants

398 infants with birthweight (BW) 500-1500 g born from January 2 1982 to December 1983 were studied to determine incidence and survival rate by BW and gestational age (GA) categories and to determine causes of death and factors influencing mortality. 58% of the group survived. Factors other than those in the perinatal and postnatal period did not significantly influence survival. Infants with BW below 1000 g delivered by elective C-section had better survival than those delivered vaginally. Survival increased progressively with increasing BW and GA categories with GA more than BW being the limiting factor. Eleven (6.6%) of the deaths in the very low birth weight infants occurred during the nursery period after 28 days of age. These deaths would not have been addressed in the neonatal mortality.

EFFECT OF BREATHING PATTERN ON OXYGENATION DURING SLEEP IN PREMATURES

Periodic breathing (PB) occurs commonly in ostensibly healthy preterm infants, yet its significance is unknown. To elucidate the effect of PB on oxygenation, we studied 13 AGA 32 wk infants with a mean BW of 1744 gms at a postnatal age of 7 days. Infants in good condition were selected and morbid conditions such as asphyxia at birth were specifically excluded. Impedance pneumography, R-R interval, PtcO2 and PtcCO2 were continuously recorded for up to 8 hrs. The O2 and CO2 electrodes were calibrated at a temperature of 43.5 and 44°C, respectively. Sleep state was determined using the behavioral criteria of Prechtl. Periods of regular breathing (RB) and PB were identified for both active (AS) and quiet sleep (QS). PB was defined as repetitive pauses of 3-5 sec. duration separated by 10-15 sec. of RB. After stabilization in each sleep state, the first 2 min. of RB and PB were selected for determination of PtcO2 and PtcCO2 levels. For analysis, samples were taken every 10 sec. and averaged over the 2 min. period. No difference in mean PtcCO2 levels occurred in either breathing pattern or sleep state. PtcCO2 was lower during PB than RB in both sleep states. Marked variability of levels occurred during AS with only occasional fluctuations during QS, but there were no differences in the mean levels between AS and QS. Since respiratory rate was reduced in PB, the relative hypoxia during PB under normal conditions is determined by respiratory rate and not by sleep state.

1413 PHYSIOLOGIC FOLLOW UP OF PRETERM INFANTS WITH APNEA

Otherwise healthy preterm infants may continue to exhibit prolonged apnea beyond the first week of life, a condition some consider leading to an increased risk for SIDS. To elucidate the significance of these apnea, we studied 17 AGA infants between 32-36 weeks post conceptual age. Eight of these (A) exhibited 2 or more central apnea ≥20 sec. during an 8 hour period after the first week of life.Polygraphic records were obtained between 6-10 pm at 40 weeks, 1 month and 3 months adjusted age, from which Quiet Sleep (QS) and Active Sleep (AS) were derived. Minute by minute values for heart rate (HR), respiratory rate (RR), transcutaneous O2 (PtcO2) and CO2 (PtcCO2) were determined during AS and QS with a computer. Representative results at 40 wks are presented as mean and (sd).Apneic preterms were not different from non-apneic infants (N) at this either of the other follow up ages. While preterm infants are statistically at increased risk for SIDS, these data do not warrant singling out the apneic prcterm as at greater risk for abnormal autonomic sequelae.

The development of the circadian heart rate rhythm (CHR) in Asian infants

OBJECTIVEnTo test the hypothesis that term-born Asian infants, at reduced risk to die of Sudden Infant Death Syndrome (SIDS) exhibit a circadian heart rate rhythm (CHR) at a later age than non-Asian term infants.nnnMETHODnRepeated overnight heart rate (HR) traces obtained with a battery-operated Polar S810i heart-rate monitor at home in 17 Asian Torajan infants in Indonesia, were compared with those of 52 non-Asian infants monitored as part of the Collaborative Home Infant Monitoring Evaluation (CHIME). HR was determined using a moving window averaging technique. A comparison of median HR during quiet sleep (QS) episodes (identified by minimum HR variability), established the presence of CHR.nnnRESULTSnSeventy three percent of non-Asian CHIME infants ≤7 weeks exhibited CHR compared to 45% of Asian Torajan infants. Between 8 and 12 weeks, 94% of non-Asian CHIME infants exhibited CHR, compared to 33% of Asian Torajan infants (p<0.001). Forty seven and 56% of Asian Torajan infants exhibited the CHR at the age intervals of 16-20 weeks and 21-25 weeks respectively. Active wakefulness percentages as a function of the entire recording and median QS HR were not significantly different in the two groups.nnnCONCLUSIONnDespite the fact that Asian Torajan infants were on average a week older than non-Asian CHIME babies, between two and three months of age only one in three exhibited the CHR, compared to virtually all non-Asian CHIME infants. We speculate that the cause of this difference rests in the infants environment rather than their genetic origin.