Ventilatory response to carbon dioxide of infants following chronic prenatal methadone exposure

SIDS is associated with prenatal drug use: a meta-analysis and systematic review of 4 238 685 infants

OBJECTIVE

To conduct a meta-analysis to determine the association between prenatal drug exposure and risk of sudden infant death syndrome (SIDS).

DESIGN

Studies were searched using PubMed, Medline and Embase and restricted to English, with no publication date limit. Selected studies included published cohort, population or case studies comparing the incidence of SIDS among drug-exposed with drug-free controls. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-Analysis of Observational Studies in Epidemiology guidelines. Data were pooled using a random-effects model to evaluate risk ratios (RR).

SETTING

High-income countries.

PATIENTS

Children with a history of prenatal drug exposure.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

RR of SIDS between drug-exposed and control infants.

RESULTS

Sixteen studies (36 730 infants with any prenatal drug exposure, 21 661 exposed to opioids, 21 571 exposed to cocaine, 5031 exposed to methadone compared with 4 201 955 with no exposure). Any prenatal drug exposure was associated with an increased crude risk of SIDS (RR 7.84, 95% CI 5.21 to 11.81). Prenatal opioid exposure had the highest associative crude risk of SIDS (RR 9.76, 95% CI 5.28 to 18.05), followed by methadone (RR 9.52, 95% CI 4.60 to 19.70) and cocaine (RR 4.40, 95% CI 2.52 to 7.67). Increased crude risk persisted after adjusting for socioeconomic factors (RR 4.24, 95% CI 1.39 to 12.88). The incidence of SIDS for this cohort decreased between 1972 and 2020 but remained significantly higher than controls.

CONCLUSION

Exposure to any drug of dependency during pregnancy is associated with an increased risk of SIDS after controlling for socioeconomic factors. Further study to evaluate mechanisms and contribution of other confounders (eg, smoking) is warranted.

Maternal Methadone Destabilizes Neonatal Breathing and Desensitizes Neonates to Opioid-Induced Respiratory Frequency Depression

Pregnant women and developing infants are understudied populations in the opioid crisis, despite the rise in opioid use during pregnancy. Maternal opioid use results in diverse negative outcomes for the fetus/newborn, including death; however, the effects of perinatal (maternal and neonatal) opioids on developing respiratory circuitry are not well understood. Given the profound depressive effects of opioids on central respiratory networks controlling breathing, we tested the hypothesis that perinatal opioid exposure impairs respiratory neural circuitry, creating breathing instability. Our data demonstrate maternal opioids increase apneas and destabilize neonatal breathing. Maternal opioids also blunted opioid-induced respiratory frequency depression acutely in neonates; a unique finding since adult respiratory circuity does not desensitize to opioids. This desensitization normalized rapidly between postnatal days 1 and 2 (P1 and P2), the same age quantal slowing emerged in respiratory rhythm. These data suggest significant reorganization of respiratory rhythm generating circuits at P1-2, the same time as the preBötzinger Complex (key site of respiratory rhythm generation) becomes the dominant respiratory rhythm generator. Thus, these studies provide critical insight relevant to the normal developmental trajectory of respiratory circuits and suggest changes to mutual coupling between respiratory oscillators, while also highlighting how maternal opioids alter these developing circuits. In conclusion, the results presented demonstrate neurorespiratory disruption by maternal opioids and blunted opioid-induced respiratory frequency depression with neonatal opioids, which will be important for understanding and treating the increasing population of neonates exposed to gestational opioids.

Characteristics and causes of death in children with neonatal abstinence syndrome

AIM

To determine characteristics of death in children with neonatal abstinence syndrome (NAS).

METHODS

A population-based linkage study of children from birth to 13 years of age in New South Wales (NSW), Australia, born 1 July 2000 to 31 December 2011. Infants with an International Statistical Classification of Diseases and Related Problems, Australian modification coding of NAS (P96.1, n = 3842) were compared to infants (n = 1 018 421) without NAS by birth, hospitalisation and death records linkage.

RESULTS

Forty-five (1.2%) children with NAS died, compared to 3665 (0.4%) other children. Most deaths (n = 30, 66%) in NAS children occurred between 1 month and 1 year. Risk of death was independently increased in full-term children (hazard ratio 2.34, 95% confidence interval 1.63-3.35; P < 0.001) from lower socio-economic groups (1.23, 1.12-1.35; P < 0.001), most commonly from ill-defined or external causes, including assault and accidents (P < 0.001).

CONCLUSIONS

Children with NAS, especially those of term gestation and from lower socio-economic groups, are more likely to die, especially from external causes.

Retrospective study found that outpatient care for infants exposed to drugs during pregnancy was sustainable and safe

AIM

We determined the safety, feasibility and sustainability of an outpatient model of care for infants exposed to intra-uterine drugs.

METHODS

This was a retrospective chart review of 774 drug-exposed infants born between 1998 and 2016 at the Royal Hospital for Women, Sydney, Australia.

RESULTS

Most (86%) of the mothers used multiple drugs, including opioids (58%). More than three-quarters (78%) of the infants were born full term at a mean gestation of 38 weeks and hospitalised for a median of seven days. This rose to 14 days if they were medicated for neonatal abstinence syndrome (NAS). Most of the NAS patients (83%) were discharged on medication, namely morphine, and the median duration of NAS treatment was 76 (interquartile range 35-120). Three medication errors occurred: two extra doses of phenobarbitone and one infant weaned off morphine faster than prescribed. No infants were rehospitalised for NAS. Four died from sudden infant death syndrome at 2.2-5.8 months after discharge and one drowned at 15 months. None were medicated at the time of death.

CONCLUSION

Outpatient care for drug-exposed infants was sustainable and had low complication rates, even for those with NAS. The optimum duration of follow-up and impact on hospital costs should be examined.

Prenatal Opioid Exposure and Intermittent Hypoxemia in Preterm Infants: A Retrospective Assessment

INTRODUCTION

Intermittent hypoxemia (IH) is defined as episodic drops in oxygen saturation (SpO₂). Preterm infants are at increased risk for IH due to their immature respiratory control/apnea of prematurity. The clinical relevance of IH is a relatively new observation with rising evidence linking IH to neonatal morbidities and long-term impairment. Hence, assessing factors that influence IH in preterm infants is imperative. Given the epidemic of opioid misuse in the USA, there is an urgent need to understand the impact of prenatal opioid exposure on neonatal outcomes. Hence, we wanted to assess the relationship between isolated prenatal opioid exposure and IH in preterm infants.

METHODS

In order to accurately calculate IH, SpO₂ data were prospectively collected using high-resolution pulse oximeters during the first 8 weeks of life in preterm infants less than 30 weeks gestational age. Data related to prenatal opioid misuse were retrospectively collected from medical charts. Infants with tobacco or poly-drug exposure were excluded. The primary outcome measure is percent time spent with SpO₂ below 80% (%time-SpO₂ < 80). The secondary outcome measure is the number of severe IH events/week with SpO₂ less than 80% (IH-SpO₂ < 80).

RESULTS

A total of 82 infants with isolated opioid exposure (n = 14) or who were unexposed (n = 68) were included. There were no significant differences in baseline characteristics between opioid exposed and unexposed groups. There was a statistically significant increase of 0.23 (95% CI: 0.03, 0.43, p = 0.03) in mean of the square root of %time-SpO₂ < 80. The number of IH-SpO₂ < 80 events was higher in the opioid exposed group (mean difference = 2.95, 95% CI: -0.35, 6.25, p-value = 0.08), although statistical significance was not quite attained.

CONCLUSION

This study shows that preterm infants prenatally exposed to opioids have increased IH measures compared to unexposed infants. Interestingly, the increased IH in the opioid exposed group persists beyond the immediate postnatal period.

Ventilatory response to hypercarbia in newborns of smoking and substance-misusing mothers

RATIONALE

Infants of mothers who smoked (S) or substance misused (SM) during pregnancy have an increased risk of sudden infant death syndrome (SIDS).

OBJECTIVES

To test the hypothesis that infants of S and SM mothers compared with infants of non-substance-misusing, nonsmoking mothers (control subjects) would have a reduced ventilatory response to hypercarbia and that any reduction would be greater in the SM infants.

METHODS

Infants were assessed before maternity/neonatal unit discharge. Maternal and infant urine samples were obtained and tested for cotinine, cannabinoids, opiates, amphetamines, methadone, cocaine, and benzodiazepines.

MEASUREMENTS AND MAIN RESULTS

Respiratory flow and Vt were measured using a pneumotachograph inserted into a face mask placed over the infant's mouth and nose. The ventilatory responses to three levels of inspired carbon dioxide (0 [baseline], 2, and 4% CO2) were assessed. Twenty-three SM, 34 S, and 22 control infants were assessed. The birth weight of the control subjects was higher than the SM and S infants (P = 0.017). At baseline, SM infants had a higher respiratory rate (P = 0.003) and minute volume (P = 0.007) compared with control subjects and S infants. Both the SM and S infants had a lower ventilatory response to 2% (P < 0.001) and 4% (P < 0.001) CO2 than the control subjects. The ventilatory response to CO2 was lower in the SM infants compared with the S infants (P = 0.009).

CONCLUSIONS

These results are consistent with infants of smoking mothers and substance misuse/smoking mothers having a dampened ventilatory response to hypercarbia, which is particularly marked in the latter group.

Management of neonatal abstinence syndrome from opioids

Most infants at risk for neonatal abstinence syndrome have opioid plus another drug exposure; polypharmacy is the rule rather than the exception. Scales for evaluation of neonatal abstinence syndrome are primarily based for opioid withdrawal. A standard protocol to treat neonatal abstinence syndrome has not been developed. Institute nonpharmacologic strategies for all neonates at risk. The American Academy of Pediatrics recommends mechanism-directed therapy (treat opioid withdrawal with an opioid) as the first-line therapy. Second-line medications are currently under evaluation.

S-Methadone augments R-methadone induced respiratory depression in the neonatal guinea pig

Methadone is administered as a racemic mixture, although its analgesic and respiratory effects are attributed to R-isomer activity at the mu opioid receptor (MOP). Recently, we observed a four-fold increase in inspiratory time in 3-day-old guinea pigs following an injection of racemic methadone. We hypothesized that this effect was due to augmentation of R-methadone induced respiratory depression by the S-methadone isomer. In the current longitudinal study, we injected 3-, 7-, and 14-day-old neonatal guinea pigs with saline, R-methadone, S-methadone, or R- plus S-methadone in order to characterize the roles of the individual isomers, as well as the synergistic effects of co-administration. Using plethysmography, we measured respiratory parameters while breathing room air and during a 5% CO(2) challenge. S-Methadone alone had no respiratory effects. However, the R- plus S-methadone group showed greater respiratory depression and increased inspiratory time than the R-methadone group in the youngest animals, suggesting that the respiratory effects of R-methadone are augmented by S-methadone in early development.

Respiratory effects of chronic in utero methadone or morphine exposure in the neonatal guinea pig

This study uses a neonatal guinea pig model to compare the effects of in utero methadone or morphine exposure upon breathing control. We hypothesize that in utero methadone exposure will result in similar respiratory disturbances to those seen in morphine exposed neonates, but that the onset will be slower and the duration longer, due to methadone's longer elimination half-life. Pregnant Dunkin-Hartley guinea pigs received once-daily injections of methadone, morphine, or vehicle (saline) during the last half of gestation and pups were studied 3, 7, or 14 days after birth. In utero methadone or morphine exposure resulted in decreased birth weight compared to vehicle, and pups experienced a withdrawal syndrome which included increased locomotor activity and respiratory disturbances but no change in rectal temperature. Both opioid exposures increased inspiratory minute ventilation during CO(2) challenge at 3 days after birth, but only in morphine exposed pups was this withdrawal effect still present on day 7. Surprisingly, only morphine exposure increased inspiratory minute ventilation during room air breathing. We conclude that in utero methadone exposure is not equivalent to in utero morphine exposure. With respect to neonatal respiratory control, methadone-induced changes in respiration are only apparent during hypercapnia.

Methadone-induced respiratory depression in the neonatal guinea pig

Respiratory depression, the most serious side-effect of opioid treatment, is well documented for morphine, the most commonly used opioid in neonatal care. Less is known about methadone, a clinically relevant opioid analgesic, especially during neonatal development. This study was undertaken to determine the neonatal respiratory effects of methadone. We hypothesize that methadone is equipotent to morphine, compared to our previous morphine results in the same animal model, but has a much longer duration of action, due to its longer elimination half-life. Neonatal guinea pigs (3-14 days old) randomly received a single subcutaneous dose of methadone or saline. Using a non-invasive plethysmographic method, we measured ventilatory and metabolic parameters before injection and at intervals for 32 hr after injection while pups breathed "room air" or 5% CO(2) gas mixtures. Methadone-induced depression of ventilation was most evident during 5% CO(2) challenge. The onset of drug effects was within 15 min for all ages and doses, but the duration of action decreased with age. While the depth of methadone-induced respiratory depression did not depend on pup age, the control of breathing was different in 3-day-old pups, where inspiratory time increased fourfold; twice that of older pups. We conclude that methadone induces a naloxone reversible respiratory depression in guinea pig neonates and, in the very young, causes an abnormal breathing pattern due to changes in respiratory timing. Methadone is more potent than morphine with respect to neonatal respiratory depression, but surprisingly, the duration of methadone action was not longer than morphine.

Management of the newborn infant affected by maternal opiates and other drugs of dependency

Illicit drug use during pregnancy is common and probably underestimated in the majority of published studies. The infant exposed to opiates or other drugs of dependency during intrauterine development is at risk for post-natal withdrawal as well as to long-term problems that are associated with drug-effects and often, adverse social circumstances. This article examines the early management of the infant and mother for detection and monitoring of drug-exposure, pharmacological intervention for withdrawal and the management of associated, particularly infective and psychosocial, problems. Practical concerns surrounding these issues are discussed and further research on psychosocial intervention to improve long-term outcome are much needed.

Central sleep apnea in stable methadone maintenance treatment patients

STUDY OBJECTIVES

Methadone, a long-acting mu-opioid agonist, is an effective treatment for heroin addiction. Our previous data show that 6 of 10 methadone maintenance treatment (MMT) patients had central sleep apnea (CSA). This study aims to confirm these results and to investigate the pathogenesis of the CSA.

METHODS

Twenty-five male and 25 female MMT patients and 20 age-, sex-, and body mass index (BMI)-matched normal subjects were tested with polysomnography, blood toxicology, and ventilatory responses to hypoxia and hypercapnia. Resting cardiorespiratory tests were performed in the MMT group

RESULTS

MMT patients and normal subjects were 35 +/- 9 years old (mean +/- SD), and BMI values were 27 +/- 6 kg/m2 and 27 +/- 5 kg/m2, respectively. Thirty percent of MMT patients had a central apnea index (CAI) > 5, and 20% had a CAI > 10. All normal subjects had a CAI < 1, and no difference was found in obstructive apnea-hypopnea index between the two groups. Methadone blood concentration was the only significant variable (t = 2.33, p = 0.025) associated with CAI and explains 12% of the variance. Awake Pa(CO2), antidepressant use, reduced ventilatory response to hypercapnia, and widened awake alveolar-arterial oxygen pressure gradient together explain a further 17% of the CAI variance.

CONCLUSIONS

Thirty percent of stable MMT patients have CSA, a minority of which can be explained by blood methadone concentration. Other physiologic variables may also play a role in the pathogenesis of CSA in MMT patients, and further research is indicated in this area.

Effects of opioid dependence and tobacco use on ventilatory response to progressive hypercapnia

Respiratory depression is a serious medical risk of opioid use. Most opioid abusers also smoke cigarettes, perhaps further compromising breathing. Differences in ventilatory response to nonhypoxic hypercapnia were studied in healthy volunteers with limited substance use (LU), tobacco smokers (SM), and opioid-dependent, methadone-maintained smokers (OD). The last two groups had similar current cigarette use and all groups were similar in gender and body mass index. Because previous data suggest that SM are sensitive to hypoxia but not hypercapnia, it was predicted that only the OD group would exhibit decreased carbon dioxide (CO(2)) sensitivity. All subjects rebreathed CO(2) during three identical sessions (four trials per session). Fractional end-tidal (Fet) CO(2) levels during repeated 4-min exposures to progressive hypercapnia (6% to 10%) were similar across groups. Ventilatory response (breathing rate, tidal volume and minute volume) linearly increased with FetCO(2) concentration and did not differ significantly across sessions. Relative to the LU and SM groups (which did not significantly differ), the CO(2)-minute volume and CO(2)-breathing rate functions were significantly shifted rightward (decrease in intercept but not slope) for OD subjects. These data are consistent with the hypothesis that chronic opioid exposure and/or short-term methadone maintenance (but not tobacco or nicotine use) produces a specific decrease in CO(2) sensitivity, primarily through an inhibitory effect on respiratory frequency.

Substance abuse and parenthood: biological mechanisms--bioethical challenges

This review catalogues the long-term health effects of parental recreational drug abuse on the fetus and the subsequent well-being of the child. It is hard to conceive that parents would knowingly harm the health of their children, yet toxic effects resulting from ignorance, addiction or any of a number of socioeconomic factors are still responsible for handicapping countless potentially healthy offspring. The negative effects of female recreational drug and alcohol abuse during pregnancy are well documented, but exposure prior to conception and male-mediated effects are less well publicized. Abnormalities in the sperm are prevalent among men who consume recreational drugs, and birth defects are more often linked with paternal than with maternal DNA damage. This review is divided into three parts. Part I describes the biology and potential mechanisms of adverse alterations in reproductive potential, Part II explores the socioeconomic determinants of substance use, and raises the question of poverty. Drug-induced disability is not evenly distributed among the population as there are ethnic and socioeconomic disparities of infant mortality, childhood morbidity and reproductive dysfunction. Part III describes the author's conclusion that fundamental social change is needed to protect future children without threatening parents' basic freedom, and real change requires new beliefs and prioritics that must evolve from the ground up. An ecological model of care concentrating on health issues is described. Such an ecological model of care is in tune with the fundamental principles of bioscience ethics and emphasises that high quality education, health and good preconceptional/prenatal care are essentials in the search for greater equity in standard of living across a population.

Epidural and intravenous bolus morphine for postoperative analgesia in infants

PURPOSE

To compare two doses of bolus epidural morphine with bolus iv morphine for postoperative pain after abdominal or genitourinary surgery in infants.

METHODS

Eighteen infants were randomly assigned to bolus epidural morphine (0.025 mg.kg-1 or 0.050 mg.kg-1) or bolus iv morphine (0.050-0.150 mg.kg-1). Postoperative pain was assessed and analgesia provided, using a modified infant pain scale. Monitoring included continuous ECG, pulse oximetry, impedance and nasal thermistor pneumography. The CO2 response curves and serum morphine concentrations were measured postoperatively.

RESULTS

Postoperative analgesia was provided within five minutes by all treatment methods. Epidural groups required fewer morphine doses (3.8 +/- 0.8 for low dose [LE], 3.5 +/- 0.8 for high dose epidural [HE] vs. 6.7 +/- 1.6 for iv, P < 0.05) and less total morphine (0.11 +/- 0.04 mg.kg-1 for LE, 0.16 +/- 0.04 for HE vs 0.67 +/- 0.34 for iv, P < 0.05) on POD1. Dose changes were necessary in all groups for satisfactory pain scores. Pruritus, apnoea, and haemoglobin desaturation occurred in all groups. CO2 response curve slopes, similar preoperatively (range 36-41 ml.min-1.mmHg ETCO2-1.kg-1) were generally depressed (range, 16-27 ml.min-1.mmHg ETCO2-1.kg-1) on POD1. Serum morphine concentrations, negligible in LE (< 2 ng.ml-1), were similar in the HE and iv groups (peak 8.5 +/- 12.5 and 8.6 +/- 2.4 ng.ml-1, respectively).

CONCLUSION

Epidural and iv morphine provide infants effective postoperative analgesia, although side effects are common. Epidural morphine gives satisfactory analgesia with fewer doses (less total morphine); epidural morphine 0.025 mg.kg-1 is appropriate initially. Infants receiving epidural or iv morphine analgesia postoperatively need close observation in hospital with continuous pulse oximetry.

Relationship of maternal substance abuse to subsequent sudden infant death syndrome in offspring

To assess the possible relationship between maternal drug use during pregnancy and subsequent sudden infant death syndrome (SIDS), we identified 1760 cases of SIDS from a population of more than 1.2 million infants (1.45/1000) born in New York City between 1979 and 1989. The SIDS rate in drug-exposed infants was 5.83 per 1000 infants, compared with 1.39 per 1000 infants who were not drug exposed. With control for known associated high-risk variables, the risk ratio for SIDS in each individual drug group (methadone, 3.6; heroin, 2.3; methadone and heroin, 3.2; cocaine, 1.6; cocaine and methadone or heroin, 1.1) was higher than in the non-drug-exposed group. Higher rates of SIDS were found in infants exposed to opiates alone than in cocaine-exposed infants, but increasing rates of SIDS in cocaine-exposed infants toward the end of the decade suggested that "crack" cocaine may be linked to these increasing rates. Declines in the overall rate of SIDS during the decade were observed for both the drug-exposed (11.28 to 4.09 per 1000) and the nonexposed groups (1.70 to 1.05 per 1000). Differences in rates of SIDS between major racial-ethnic groups in nonexposed infants were not apparent if the mothers used drugs during pregnancy. Seasonal variation and distribution of ages at time of SIDS death did not differ between the drug-exposed group and the nonexposed group, suggesting that drug-associated SIDS may provide clues as to the cause or causes of SIDS.

Responses to hypoxia and hypercapnia in infants of substance-abusing mothers

Because infants of substance-abusing mothers (ISAM) have an increased risk of sudden infant death syndrome and have abnormal sleeping ventilatory patterns, we studied the effects of mild hypoxia during quiet sleep on ventilatory pattern, heart rate, and arousal in 23 healthy ISAM (mean +/- SEM: 9.0 +/- 0.49 weeks of age) and 15 healthy, similarly aged, control infants. Hypercapnic challenges were performed in six ISAM and eight control subjects. Hypoxic arousal responses were elicited by rapidly decreasing inspired oxygen tension to 80 mm Hg for 3 minutes or until arousal occurred. Failure to arouse to hypoxia occurred in the majority of infants in both groups. All infants had a fall in end-tidal carbon dioxide tension during hypoxia, suggesting that each had a hypoxic ventilatory response. However, the fall in end-tidal carbon dioxide tension was significantly less in the ISAM (mean +/- SEM: -4.0 +/- 0.3 vs -8.0 +/- 1.0 mm Hg), suggesting blunted ventilatory responses to hypoxia. Periodic breathing occurred during 9.5% of hypoxic challenges in control infants compared with 37% in ISAM (p = 0.056). Heart rates were significantly higher in the ISAM before, during, and after hypoxic challenges. Hypercapnic challenges (inspired carbon dioxide tension of 60 mm Hg for a maximum of 3 minutes) resulted in arousal in all infants; however, ISAM required a significantly longer exposure to hypercapnia before arousal (mean +/- SEM; 116 +/- 7.8 vs 79 +/- 13.9 seconds; p < 0.02). We conclude that ISAM have an impaired repertoire of protective responses to hypoxia and hypercapnia during sleep, and that this may play a role in their increased risk for sudden infant death syndrome.

Control of breathing in babies of narcotic- and cocaine-abusing mothers

To learn if chemoreceptor control of breathing is abnormal in babies whose mothers took narcotics, cocaine, or both drugs during pregnancy, we performed hypoxia and hypercapnia challenges on 28 babies (greater than or equal to 36 weeks gestation). Six babies were exposed to narcotics, six to cocaine, nine to both drugs, and seven babies were controls. Studies were done at 3 and 8 weeks and 3 and 5 months of age. Gestational ages were similar, but birth weight was lower in the cocaine group. Respiratory rate was higher in both groups of cocaine-exposed babies at 3 weeks. End-tidal partial pressure of CO2 (PCO2) was decreased and partial pressure of O2 (PO2) increased at 3 and 8 weeks in babies exposed to narcotics plus cocaine. At 3 weeks, babies exposed to narcotics plus cocaine had a shift to the left in CO2 response with a normal slope; at 8 weeks, both intercept and slope were decreased. Responses to hypoxia were similar among the four groups. Babies exposed to narcotics plus cocaine before birth have abnormalities in control of breathing in the first months after birth.

Maternal substance use and subsequent sudden infant death syndrome (SIDS) in offspring

Over 400,000 babies may be born annually following intrauterine exposure to opiates, stimulants and other illicit drugs. In addition, fetal exposure to alcohol and nicotine is common: of the 56 million women in the childbearing age range, 34 million are drinkers and 18 million are smokers. Published epidemiologic data suggest a strong association between Sudden Infant Death Syndrome (SIDS) and maternal smoking, a weaker association between SIDS and maternal opiate use, a still weaker association between SIDS and maternal cocaine use, and no association of SIDS and maternal alcohol use. Direct scientific links, however, between SIDS and exposure to any of these substances are still lacking. Because of reports in the medical literature and lay press linking maternal substance use to subsequent SIDS, specific drug-related counseling issues must be recognized by health professionals to provide effective intervention in the event of a SIDS death.

Sudden infant death syndrome in infants of substance-abusing mothers

A population-based study was performed to determine whether substance abuse during the perinatal period may be a risk factor for sudden infant death syndrome (SIDS). The incidence of SIDS was studied in 2143 infants of substance-abusing mothers (ISAM) born in Los Angeles County during 1986 and 1987 who were reported to the Los Angeles County Department of Health Services because of a history of drug exposure or positive urine test results in the mother, infant, or both. By comparing the ISAM birth reports with records of autopsy-proven SIDS in Los Angeles County, we found 19 SIDS cases in the population of 2143 ISAM, a SIDS rate of 8.87 cases per 1000 ISAM (95% confidence interval 5.3 to 13.8). This was significantly higher than the SIDS rate for the non-ISAM general population: 396 SIDS deaths among 325,372 live births, an incidence rate of 1.22 cases per 1000 births, p less than 0.00001. The age of ISAM at death was 99 +/- 63 (mean +/- SD) days compared with 91 +/- 52 days for the non-ISAM population (not significant). The incidence of SIDS was significantly greater in male infants, during the winter months, in black infants, and in non-Hispanic white infants in the non-ISAM population. Such differences were not observed in the ISAM group. A greater incidence of symptomatic apnea was reported before SIDS for the ISAM than for the non-ISAM population (22% vs 5.4%, p = 0.022). We conclude that ISAM have a higher incidence of SIDS than the non-ISAM general population. However, it was not possible to separate maternal substance abuse from other confounding variables that may also have had an impact on SIDS risk in the ISAM group.

Candidate cell populations for respiratory chemosensitive fields in the human infant medulla

The histology and location of human respiratory chemosensitive fields are not known. In contrast, the physiology of respiratory chemosensory areas in the ventral medulla of cats has been studied extensively, and their anatomy has been partially described. Using basic principles of comparative cytoarchitecture and computer-aided reconstructions of serial-sectioned medullae, we describe the histology and three-dimensional distribution of putative respiratory chemosensors in the feline and human infant medulla. We found that ventrolateral neurons of the human nucleus conterminalis are homologous to neurons identified in the feline L chemosensitive field by Trouth and others, and that ventrolaterally situated neurons in the human arcuate nucleus correspond to neurons predominating in the feline S and M fields. In addition, there are foci of thickened marginal glia along the feline ventral medullary surface that colocalize with chemosensitive fields identified by physiologic studies reported by others; we identify similar foci in the infant medulla. Thickened marginal glia are intermixed with neuronal fibers, often adjacent to neurons of the feline chemosensitive fields and their human counterparts, suggesting that they constitute a chemosensory neuropil at the medullary surface. Computer-aided reconstructions provide insight into the three-dimensional topography of putative respiratory chemosensors and their relationships to other brainstem structures in ways not obvious in single or even multiple sections. This delineation of candidate human respiratory chemosensors is a first step toward their postmortem analysis in patients with central ventilatory control disorders where finding histological abnormalities in these sites would support their role in human ventilation.

Three-dimensional distribution of 3H-naloxone binding to opiate receptors in the human fetal and infant brainstem

Despite the putative role of opioids in disorders of the developing human brainstem, little is known about the distribution and ontogeny of opioid-specific perikarya, fibers, terminals, and/or receptors in human fetuses and infants. This study provides baseline information about the quantitative distribution of opiate receptors in the human fetal and infant brainstem. Brainstem sections were analyzed from three fetuses, 19-21 weeks gestation, and seven infants, 45-68 postconceptional weeks, in whom the postmortem interval was less than or equal to 12 hours. Opiate receptors were localized by autoradiographic methods with the radiolabelled antagonist 3H-naloxone. Computer-based methods permitted quantitation of 3H-naloxone binding in specific nuclei, as well as three-dimensional reconstructions of binding patterns. High 3H-naloxone binding corresponds primarily to sensory and limbic nuclei, and to nuclei whose functions are known to be influenced by opioids, e.g., trigeminal nucleus (pain), nucleus tractus solitarii and nucleus parabrachialis medialis (cardio-respiration), and locus coeruleus (arousal). The regional distribution of opiate receptors as determined by 3H-naloxone binding is similar in human infants to that reported in human adults and animals and corresponds most closely to that of mu receptors. We found, however, that opiate receptor binding is high in the fetal and infant inferior olive, in comparison to low binding reported in this site in adult humans, primates, and rodents. In addition, opiate receptors are sparse in the fetal and infant substantia nigra, as in reports of the adult human substantia nigra, compared to moderate densities reported in primates and rodents. By midgestation, the regional distribution of 3H-naloxone binding in human fetuses is similar, but not identical, to that in infants. Highest 3H-naloxone binding occurs in the inferior olive in fetuses at midgestation, compared to the interpeduncular nucleus in infants. Tritiated naloxone binding quantitatively decreases in virtually all nuclei sampled over the last trimester, but not to the same degree. The most substantial binding decrease (two- to fourfold) occurs in the inferior olive and may reflect programmed regressive events, e.g., neuronal loss, during its development. Definitive developmental trends in 3H-naloxone binding are not observed in the postnatal period studied. The heterogeneous distribution of opiate binding in individual brainstem nuclei underscores the need for volumetric sampling in quantitative studies.

Ventilatory response to inspired carbon dioxide in premature infants recovering from intraventricular hemorrhage

We examined the ventilatory response to inhaled carbon dioxide with a computerized waveform analyzer in two groups of premature infants. Twenty-seven infants suffered from periventricular-intraventricular hemorrhage (IVH) during the first week of life and comprised the study group (birth weight 1.2 +/- 0.2 kg, gestational age 29 +/- 2 weeks). The control group consisted of 15 infants without IVH (birth weight 1.4 +/- 0.3 kg, gestational age 30 +/- 2 weeks). Study infants were evaluated at a postnatal age of 9 +/- 2 weeks and control infants at 7 +/- 3 weeks. No differences were found in the slope or position of the ventilatory response curve, baseline PACO2, increase in minute ventilation, VT/Ttot, and Ti/Ttot between the two groups. Subgroups with unresolved apnea (10 IVH and eight control infants) demonstrated a rightward shift of the ventilatory response curve compared to those infants without apnea. A previous IVH did not reduce the ventilatory response to CO2 in this group of infants.

Fetal breathing movements and the response to carbon dioxide in patients on methadone maintenance

Fetal breathing movements were monitored on six methadone maintenance patients and ten healthy control patients, studied while breathing room air and while breathing a prepared gas mixture with 5% carbon dioxide, both before and 2 hours after either the usual daily dose of methadone or a diet drink. There was no difference before and after the diet drink in control patients, who showed a significant increase in the incidence of fetal breathing movements from 37.1% +/- 5.9% (SEM) on room air to 69.4% +/- 2.8% while breathing 5% carbon dioxide (p less than 0.01). In the patients studied on room air before receiving methadone, fetal breathing movements were significantly decreased from those of the control group, 4.7% +/- 1.2% (p less than 0.01), with a further decrease when studied after receiving methadone, 1.3% +/- 0.7%. Fetal breathing movements did increase significantly in response to 5% carbon dioxide both before and after receiving methadone; however, in both instances the incidence was significantly less that that of the control group. The findings of the present study on methadone subjects demonstrate that abnormal function of the respiratory control network is evident in utero, which may be predictive of subsequent neonatal respiratory development.

Altered respiratory control in newborn puppies after chronic prenatal exposure to alpha-1-acetylmethadol (LAAM)

Respiratory studies were conducted on newborn puppies chronically exposed to alpha-l-acetylmethadol . HCl (LAAM) during portions of gestation. Bitches received daily oral doses of LAAM from the second week through the sixth week of pregnancy (LAAM-6) or through the end of a 9-week pregnancy (LAAM-9), but not after parturition. LAAM-9 pups displayed narcotic abstinence signs during the first week after birth, while LAAM-6 pups did not. LAAM-9 pups had increased tidal volume, respiratory frequency, alveolar ventilation and O2-consumption and decreased alveolar CO2-tension during the first week of life compared to placebo-treated controls. The LAAM-9 CO2-response curve was significantly displaced to the left of control. These data are consistent with relative hyperventilation during neonatal withdrawal from LAAM. LAAM-6 pups had decreased tidal volume and alveolar ventilation during 4 of the 6 weeks studied. These changes in ventilation were associated with a decrease in O2 consumption. By 6 weeks after birth CO2-response curves of both LAAM-9 and LAAM-6 pups were shifted to the right of control. These changes in CO2-responsiveness suggest the possibility of prolonged disturbances of respiratory control which may continue beyond the sixth week of life.

Accelerated respiratory response to moderate exercise in late pregnancy

We studied the rates of change of expired ventilation (VE, BTPS), O2 consumption (VO2, STPD) and CO2 production (VCO2, STPD) at the start and stop of 6 min of 50-W bicycle exercise, comparing 20 healthy young women at 38 weeks of pregnancy (G) and 3 months postpartum (NG). VO2, VCO2 and VE were significantly greater at rest for G than for NG. The absolute increases of VO2 and VCO2 from steady-state rest (SSR) to steady-state exercise (SSE) were the same for G and NG. The absolute increase of VE from SSR to SSE was significantly greater for G than NG. VCO2 and VE increased more rapidly in G than NG, but only during the first 90 sec of exercise. Recovery rates after exercise were equal for G and NG. We believe that lower extremity muscles of G contract on more distended veins at the onset of exercise, forcing increased volumes of venous blood through the lungs, increasing VO2 and VCO2. VE follows VCO2 closely.

Respiratory and hemodynamic effects of methadone in pregnant women

Minute ventilation, end-tidal PCO2, O2 and CO2 concentrations in expired air, pulse rate and arterial blood pressure were measured in the last half of pregnancy in eight women taking methadone daily. Measurements were made with the subjects seated at rest, during the steady state of 50-watt bicycle exercise, and during recovery. Calculations of O2 consumption. CO2 production, alveolar ventilation and oxygen debt were made. Studies were repeated in five subjects postpartum. Methadone diminishes the normal hyperventilation of pregnancy and its effect persists for more than 24 h. When comparisons are made of pregnant and postpartum values, some respiratory stimulation during pregnancy is apparent. Maternal oxygen debt following standard exercise during pregnancy is diminished after the daily dose of methadone and the maternal heart rate response to exercise is diminished concurrently. The maternal hypoventilation induced by methadone and maintained during exercise may be relevant to the low birth weights and high incidence of sudden infant death syndrome observed by others in the offspring of methadone-dependent women.