Undetected apnea and bradycardia in infants

Very long apnea events in preterm infants

Apnea is nearly universal among very low birth weight (VLBW) infants, and the associated bradycardia and desaturation may have detrimental consequences. We describe here very long (>60 s) central apnea events (VLAs) with bradycardia and desaturation, discovered using a computerized detection system applied to our database of over 100 infant years of electronic signals. Eighty-six VLAs occurred in 29 out of 335 VLBW infants. Eighteen of the 29 infants had a clinical event or condition possibly related to the VLA. Most VLAs occurred while infants were on nasal continuous positive airway pressure, supplemental oxygen, and caffeine. Apnea alarms on the bedside monitor activated in 66% of events, on average 28 s after cessation of breathing. Bradycardia alarms activated late, on average 64 s after cessation of breathing. Before VLAs oxygen saturation was unusually high, and during VLAs oxygen saturation and heart rate fell unusually slowly. We give measures of the relative severity of VLAs and theoretical calculations that describe the rate of decrease of oxygen saturation. A clinical conclusion is that very long apnea (VLA) events with bradycardia and desaturation are not rare. Apnea alarms failed to activate for about one-third of VLAs. It appears that neonatal intensive care unit (NICU) personnel respond quickly to bradycardia alarms but not consistently to apnea alarms. We speculate that more reliable apnea detection systems would improve patient safety in the NICU. A physiological conclusion is that the slow decrease of oxygen saturation is consistent with a physiological model based on assumed high values of initial oxygen saturation.

Accurate automated apnea analysis in preterm infants

OBJECTIVE

In 2006 the apnea of prematurity (AOP) consensus group identified inaccurate counting of apnea episodes as a major barrier to progress in AOP research. We compare nursing records of AOP to events detected by a clinically validated computer algorithm that detects apnea from standard bedside monitors.

STUDY DESIGN

Waveform, vital sign, and alarm data were collected continuously from all very low-birth-weight infants admitted over a 25-month period, analyzed for central apnea, bradycardia, and desaturation (ABD) events, and compared with nursing documentation collected from charts. Our algorithm defined apnea as > 10 seconds if accompanied by bradycardia and desaturation.

RESULTS

Of the 3,019 nurse-recorded events, only 68% had any algorithm-detected ABD event. Of the 5,275 algorithm-detected prolonged apnea events > 30 seconds, only 26% had nurse-recorded documentation within 1 hour. Monitor alarms sounded in only 74% of events of algorithm-detected prolonged apnea events > 10 seconds. There were 8,190,418 monitor alarms of any description throughout the neonatal intensive care unit during the 747 days analyzed, or one alarm every 2 to 3 minutes per nurse.

CONCLUSION

An automated computer algorithm for continuous ABD quantitation is a far more reliable tool than the medical record to address the important research questions identified by the 2006 AOP consensus group.

Under-recognition of alarms in a neonatal intensive care unit

BACKGROUND

Treatment decisions for apnoea of prematurity (AOP) are usually based on nursing staff's documentation of pulse oximeter and heart rate alarms.

OBJECTIVE

In an observational study, to compare the accuracy of oxygen saturation (SpO2) and heart rate alarm documentation, and the resulting interventions by nursing staff, with objectively registered events using polysomnographic and video recording.

METHODS

Data on 21 preterm neonates (12 male) with a diagnosis of AOP were analysed. Nursing staff's desaturation (<80% SpO2) and bradycardia (<80/min) alarm documentation was compared with events registered objectively using simultaneous polysomnography. Interventions by nursing staff were evaluated using 24 h video recordings and compared with their chart documentation. Nursing staff had been unaware that the polygraphic and video recordings would be used subsequently for this purpose.

RESULTS

Median (minimum-maximum) postnatal age was 15.5 (3-65) days. 968 SpO2 desaturation events and  415 bradycardias were documented by polysomnography. Nursing staff registered 23% of these desaturation events, and 60% of bradycardias (n=223, and n=133, respectively). Intraclass correlation coefficient (95% CI) between objectively measured desaturation events and those documented by nursing staff was 0.14 (-0.31 to 0.53); and for bradycardias 0.51 (0.11 to 0.78). 225 nursing staff interventions were registered on video, of which 87 (39%) were documented.

CONCLUSIONS

The alarm documentation by neonatal intensive care unit staff does not appear to be sufficiently accurate to permit further understanding and treatment of AOP. It is unclear if the alarms missed here would have led to clinical consequences had they been documented.

Current definitions for neonatal apnoea: are they evidence based?

Apnoea is defined as cessation of breathing with implicit pathophysiology. This review considers definitions of neonatal apnoea currently available and explores the evidence to support their use. For preterm and term infants, apnoea definitions appear arbitrary, are not supported by guidelines and vary from study to study. Although most alarms on infant breathing monitors are set to alert after a respiratory pause >20s duration is detected, this time period is the equivalent of 17 missed breaths in a preterm infant. Apnoea is likely to be better defined by associated consequence than by pause duration alone in this age group; however, the degree of change in heart rate or oxygen saturation that defines a respiratory pause as pathological is yet to be defined. Further research is required to determine the characteristics that differentiate respiratory events of clinical consequence from normal respiratory variability in term and preterm infants.

Respiratory events in preterm infants prior to discharge: with and without clinically concerning apnoea

PURPOSE

This study aimed to determine the characteristics of respiratory events in preterm infants with clinically concerning apnoea at or beyond 35 weeks postmenstrual age and to compare these findings with a group of preterm infants ready for discharge, without clinically concerning apnoea.

METHODS

Infants born at <32 weeks of gestation and who underwent nap polysomnography at or beyond 35 weeks corrected age prior to discharge were included. Cases were preterm infants with clinically concerning apnoea, and control infants were preterm infants asymptomatic for apnoea. Infants with upper airway obstruction, congenital malformations or apnoea associated with sepsis were excluded. Studies were retrospectively reviewed for length, type and frequency of apnoea. The relationship between sleep state and changes in oxygen saturation was compared between groups. Peri-natal and demographic data were also compared.

RESULTS

Data were complete for 16 case and 18 control infants. Gestational age was similar at birth and at time of study, but cases had a lower birth weight (p = 0.04) and higher weight at study (p = 0.04). There were no group differences in the mean duration, type or numbers of apnoea. The duration of the longest apnoea was greater in case infants (17.4 s vs. 12.3 s, p = 0.02). Lowest oxygen saturation (p < 0.05) and average minimum oxygen saturation (p < 0.05) were lower in case infants.

CONCLUSIONS

Preterm infants with clinically concerning apnoea have similar amounts and types of apnoea but lower oxygen saturation after apnoea compared with controls. The use of oxygen saturation monitoring is more useful than respiratory monitoring alone in recognising these events.

Car seat test for preterm infants: comparison with polysomnography

OBJECTIVES

To monitor preterm infants in a cot and a car seat and compare an observed car seat trial with polysomnography (PSG).

DESIGN

Non-randomised controlled trial.

SETTING

Regional neonatal unit.

PATIENTS

Preterm infants before discharge.

INTERVENTIONS

Nap PSG respiratory and sleep variables were measured including gastro-oesophageal pH. Nurse observations included respiratory distress, apnoea measured by apnoea alarm, oxygen saturation and heart rate. Infants were studied supine in a cot and then in a car seat. Nursing observations were compared with PSG during the car seat trial only. Criteria for failure of the PSG and observed tests were predefined.

MAIN OUTCOME MEASURES

Difference in respiratory instability between cot and car seat. Concurrence regarding failure of the car seat trial between nurse-observed data and PSG.

RESULTS

20 infants (median gestation 33 weeks (range 28-35 weeks; median postmenstrual age (PMA) at study 36.5 weeks (range 35-38 weeks)) were studied. There were sufficient car seat data on 18 infants for comparison. There were fewer central apnoeas and arousals in the cot than the car seat (p = 0.047 and p = 0.024, respectively). Airway obstruction was not more common in the car seat. Younger PMA at time of study predicted failure in both car seat (p = 0.022) and cot (p = 0.022). The nurse-observed test had low sensitivity for predicting PSG failure but more accurately predicted airway obstruction on PSG.

CONCLUSIONS

Immature infants exhibit respiratory instability in cots and car seats. A car seat test does not accurately detect all adverse events during sleep in the seat.

Cardiorespiratory events recorded on home monitors: the effect of prematurity on later serious events

OBJECTIVE

To describe severe alarms on home-documented monitoring in infants born prematurely.

METHODS

In infants born at a post-menstrual age (PMA) less than 35 weeks, a polysomnography was performed before discharge. A heart rate less than 50 beats per minute (bpm) for more than 3 seconds or an apnea lasting for more than 15 seconds with a heart rate less than 60 bpm were defined as abnormal. These babies were given cardiorespiratory home monitoring with memory. Serious alarms on the home monitor were defined as heart rate less than 50 bpm for more than 3 seconds.

RESULTS

Of 1058 infants, 96 infants needed cardiorespiratory home monitoring. Sixty-one infants showed alarms at home. The mean post-conceptional age (PCA) when alarms stopped was 46 weeks. Seventeen patients had serious alarms above the PCA of 50 weeks. There was a significant negative correlation (r = -0.46 and p = 0.0002 by Spearman's rank correlation) between the PMA at birth and the PCA at which the last alarm was noted

CONCLUSION

Prematurely born infants with an abnormal polysomnography at discharge are at high risk for developing acute events at home. A younger PMA at birth correlates with a higher risk of alarms at a later PCA.

Risk of cardio-respiratory abnormalities in preterm infants placed in car seats: a cross-sectional study

BACKGROUND

Little is known about the factors that predispose to the occurrence and severity of cardio-respiratory symptoms during the placement of a prematurely born infant in a car seat. The impact of gestational age, weight at discharge and infant's pre-existing cardio-respiratory status (in the supine position) on cardio-respiratory function during pre-discharge testing in a car seat (semi-upright position) has not been investigated.

METHODS

The cardio-respiratory function of 42 preterm neonates with gestational age 24 to 35 weeks and discharge weight 1790 to 2570 grams were monitored for 45 minutes before, during, and after placement in a car seat. The occurrence of periodic breathing, apnea, bradycardia, or decreased oxygen saturation (SaO2) was analyzed.

RESULTS

Prior to the car seat testing, 15 (35.7%) infants displayed one or more abnormalities of cardio-respiratory function. During the car seat testing, 25 (59.6%) infants had periodic breathing, 33 (78.2%) had oxygen saturation <90%, 14 (33.3%) had bradycardia less than 80 beats per minute, and 35 (83.3%) had a combination of these symptoms. Infants, both with and without pre-existing cardio-respiratory abnormalities, had an almost equal probability (80% vs. 83.3%) for the development of cardio-respiratory symptoms during placement in the car seat. Weight at discharge ([less than or equal to] 2,000 grams) but not the gestational age (<28 weeks or [greater than or equal to] 28<37 weeks), was associated with either increased episodes of oxygen desaturation or the combination of cardio-respiratory symptoms that were seen during the placement of these infants in the car seat. Repositioning from the car seat to the supine position showed normalization of cardio-respiratory function in the majority (83%) of the tested infants. None of the tested clinical factors were associated with the severity of the cardio-respiratory symptoms.

CONCLUSION

Pre-discharge testing of the cardio-respiratory function of preterm infants during placement in a car seat is important for the prevention of cardio-respiratory symptoms during their transportation. However, the high risk for developing cardio-respiratory symptoms will require the consideration of an alternative mode of safe home transportation for preterm infants; especially those with a discharge weight less than 2,000 grams.

Prone or supine for infants with chronic lung disease at neonatal discharge?

OBJECTIVE

To determine whether infants with chronic lung disease (CLD), ready for neonatal unit discharge, maintain cardiorespiratory stability while sleeping supine.

METHODS

Subjects were 15 infants born < 32 weeks gestational age (GA) and ready for discharge from the regional tertiary neonatal intensive care unit. Polysomnography recordings of sleep state, heart rate, arterial oxygen saturation, respiratory effort and nasal/oral airflow were taken prone and supine for up to 3 h post feed with the first position randomly allocated. The main outcome measures were oxygen saturation and apnoea hypopnoea index (AHI).

RESULTS

Seven infants (median GA 27 weeks, birthweight 945 g) had CLD and eight infants (median GA 29 weeks, birthweight 1160 g) did not. CLD infants were more mature at study than non-CLD infants (median 39 vs 36 weeks, P = 0.019). Neither oxygen saturation nor AHI were position dependent and no group differences were noted with respect to CLD status. There was a significant interaction of GA and sleep position with less-mature infants spending less time in quiet sleep (QS) in supine position (P = 0.006). These less-mature infants also had a higher AHI (P = 0.033). As expected, the AHI and arousal index (AI) were higher in active sleep (P < or = 0.001, P = 0.013, respectively) and mean oxygen saturation was lower (P = 0.001).

CONCLUSIONS

The supine position appears appropriate for very preterm infants with CLD going home from the neonatal unit. Respiratory instability on neonatal discharge is more likely to be associated with immaturity than CLD.

Functional magnetic resonance imaging during hypotension in the developing animal

Hypotension in adult animals recruits brain sites extending from cerebellar cortex to the midbrain and forebrain, suggesting a range of motor and endocrine reactions to maintain perfusion. We hypothesized that comparable neural actions during development rely more extensively on localized medullary processes. We used functional MRI to assess neural responses during sodium nitroprusside challenges in 14 isoflurane-anesthetized kittens, aged 14-25 days, and seven adult cats. Baseline arterial pressure increased with age in kittens, and basal heart rates were higher. The magnitude of depressor responses increased with age, while baroreceptor reflex sensitivity initially increased over those of adults. In contrast to a decline in adult cats, functional MRI signal intensity increased significantly in dorsal and ventrolateral medullary regions and the midline raphe in the kittens during the hypotensive challenges. In addition, significant signal intensity differences emerged in cerebellar cortex and deep nuclei, dorsolateral pons, midbrain tectum, hippocampus, thalamus, and insular cortex. The altered neural responses in medullary baroreceptor reflex sites may have resulted from disinhibitory or facilitatory influences from cerebellar and more rostral structures as a result of inadequately developed myelination or other neural processes. A comparable immaturity of blood pressure control mechanisms in humans would have significant clinical implications.

Predischarge monitoring of preterm infants

The objectives of this study were: 1) to perform documented event-monitoring (DEM) for apnea (A, > or = 20 s) and bradycardia (B, < 80 beats per min for > or = 5 s) in premature infants prior to discharge, and 2) to examine the accuracy of nursing documentation (ND) of A and B. Forty-four stable preterm infants, with mean weights and gestational ages at birth (+/- SD) of 1,543 (+/- 365) g, and 30 (+/- 2) weeks, respectively, were studied using DEM for 9 (+/- 2) days prior to discharge. Differences in DEM and ND were analyzed by the z-test for proportions. There were 561 true events recorded by DEM: 56 were As and 505 were Bs. ND revealed 296 events, 190 As and 106 Bs. Of the 56 true As on DEM, only 21 (38%) were correctly reported by ND (P < 0.001, 95% confidence interval (CI) 0.44-0.81). Of the 505 true Bs on DEM, 153 (30%) were correctly reported by ND (P < 0.001, CI 0.63-0.76). When ND was compared with DEM, 174 (59%) of NDs were true events. Of the 106 As on ND, only 21 (20%) were true As on DEM (P < 0.001, CI 0.58-1). Of the 190 Bs on ND, 153 (80%) were true Bs on DEM (P < 0.001, CI 0.13-0.26). ND did not detect 6 of the 33 infants who had significant events on DEM, while 4 of the 11 who had events reported on ND did not have any on DEM. Thus, 10 infants were misclassified by ND (P < 0.01, CI 0.1-0.36). These results indicate that, compared to DEM, ND not only identified significantly fewer true As and Bs, but also misclassified a significant number of infants. We conclude that DEM performed prior to discharge for preterm infants at risk for apnea and bradycardia provides more objective and accurate information than ND.