Supine versus Prone Position during Delayed Cord Clamping in Infants ≥36 Weeks: A Randomized Trial.

OBJECTIVE: There is no recommendation in the literature on optimal positioning of the newborn immediately at birth during delayed cord clamping. To evaluate if prone positioning on the mother's chest at birth during delayed cord clamping leads to a higher hematocrit at 30 hours of life compared to supine positioning. STUDY DESIGN: A randomized unblinded trial comparing prone and supine position of the newborn before umbilical cord clamping. Healthy newborns ≥36 weeks gestational age and born vaginally with cephalic presentation were included. The newborn was randomized to prone or supine position. Umbilical cord clamping was delayed in both groups to 1 minute after birth. The primary outcome was hematocrit at 30 hours of life. As a secondary outcome, cerebral tissue oxygenation (CrSO2) values were compared between both groups by near infrared spectroscopy. RESULTS: There was no difference in hematocrit at 30 hours of life between supine and prone positions with a mean at 52 and 53.1, respectively, mean difference -1.1 (95% confidence interval:-2.7, 0.5), p = 0.17. Newborns in supine and prone positions had comparable level of CrSO2 at 30 hours of life with a mean at 84.1 and 82.2, respectively, mean difference 1.9 (-0.2, 4.0), p = 0.07. There was no correlation between hematocrit and CrSO2 at 30 hours of life (r = 0.14). CONCLUSION: There was no difference between prone and supine positioning immediately after birth during delayed cord clamping on hematocrit at 30 hours of life. In the absence of clear findings, further studies with assessment of the effect of position on breastfeeding success in the case room, on maternal satisfaction and outcome beyond 30 hours are needed to make adequate recommendations on positioning. KEY POINTS: · Delayed cord clamping at 60 seconds is recommended at birth, but optimal positioning is unknown.. · A randomized trial was conducted to compare hematocrit at 36 hours of life of prone versus supine position.. · No difference in hematocrit was found in prone versus supine position during delayed cord clamping..

Hyperbilirubinemia Among Infants Born Preterm: Peak Levels and Association with Neurodevelopmental Outcomes.

OBJECTIVE: To describe the distribution of peak bilirubin levels among infants born before 29 weeks of gestation in the first 14 days of life and to study the association between quartiles of peak bilirubin levels at different gestational ages and neurodevelopmental outcomes. STUDY DESIGN: Multicenter, retrospective, nationwide cohort study of neonatal intensive care units in the Canadian Neonatal Network and Canadian Neonatal Follow-Up Network, including neonates born preterm at 220/7 to 286/7 weeks of gestation born between 2010 and 2018. Peak bilirubin levels were recorded during the first 14 days of age. Main outcome was significant neurodevelopmental impairment, defined as cerebral palsy with Gross Motor Function Classification System ≥3, or Bayley III-IV scores of <70 in any domain, or visual impairment, or bilateral hearing loss requiring hearing aids. RESULTS: Among 12 554 included newborns, median gestational age was 26 weeks (IQR 25-28) and birth weight was 920 g (IQR 750-1105 g). The median peak bilirubin values increased as gestational age increased (112 mmol/L [6.5 mg/dL] at 22 weeks and 156 mmol/L [9.1 mg/dL] at 28 weeks). Significant neurodevelopmental impairment was identified in 1116 of 6638 (16.8%) of children. Multivariable analyses identified an association between peak bilirubin in the highest quartile and neurodevelopmental impairment (aOR 1.27, 95% CI 1.01-1.60) and receipt of hearing aid/cochlear implant (aOR 3.97, 95%CI: 2.01-7.82) compared with the lowest quartile. CONCLUSION: In this multicenter cohort study, peak bilirubin levels in neonates of <29 weeks of gestation increased with gestational age. Peak bilirubin values in the highest gestational age-specific quartile were associated with significant neurodevelopmental and hearing impairments.

Discussing brain magnetic resonance imaging results for neonates with hypoxic-ischemic encephalopathy treated with hypothermia: A challenge for clinicians and parents.

Context: Clinicians use brain magnetic resonance imaging (MRI) to discuss neurodevelopmental prognosis with parents of neonates with hypoxic-ischemic encephalopathy (HIE) treated with therapeutic hypothermia (TH). Purpose: To investigate how clinicians and parents discuss these MRI results in the context of HIE and TH and how these discussions could be facilitated and more meaningful for parents. Procedures: Mixed-methods surveys with open-ended and closed-ended questions were completed by two independent groups. (1) Clinicians responded to clinical vignettes of neonates with HIE treated with TH with various types of clinical features, evolution and extent of brain injury and questions about how they discuss brain MRI results in this context. (2) Parents of children with HIE treated with TH responded to questions about the discussion of MRI that they had while still in the neonatal intensive care unit and were asked to place it in perspective with the outcomes of their child when he/she reached at least 2 years of age. Open-ended responses were analyzed using a thematic analysis approach. Closed-ended responses are presented descriptively. Results: Clinicians reported uncertainty, lack of confidence, and limitations when discussing brain MRI results in the context of HIE and TH. Brain MRI results were "usually" (53%) used in the prognostication discussion. When dealing with day-2 brain MRIs performed during TH, most clinicians (40%) assumed that the results of these early MRIs were only "sometimes" accurate and only used them "sometimes" (33%) to discuss prognosis; a majority of them (66%) would "always" repeat imaging at a later time-point to discuss prognosis. Parents also struggled with this uncertainty, but did not discuss limitations of MRI as often. Parents raised the importance of the setting where the discussion took place and the importance to inform them as quickly as possible. Clinicians identified strategies to improve these discussions, including interdisciplinary approach, formal training, and standardized approach to report brain MRI. Parents highlighted the importance of communication skills, the stress, the hope surrounding their situation, and the need to receive answers as soon as possible. The importance of showing the pictures or making representative drawing of the injury, but also highlighting the not-injured brain, was also highlighted by parents. Conclusions: Discussing brain MRI results for neonates with HIE treated with TH are challenging tasks for clinicians and daunting moments for parents.

Cumulative effect of evidence-based practices on outcomes of preterm infants born at <29 weeks' gestational age.

BACKGROUND: Extremely preterm infants born at <29 weeks' gestational age are at high risk of death or severe neurological injury. Several individual evidence-based practices have been associated with neuroprotection. OBJECTIVE: The objective of the study was to investigate the cumulative effect of 4 evidence-based practices and their association with death and/or severe neurological injury among infants born at <29 weeks' gestational age. STUDY DESIGN: Observational study of infants born at 230-286 weeks gestational age admitted to neonatal intensive care units participating in the Canadian Neonatal Network from 2015 through 2017. We evaluated 4 practices: antenatal corticosteroids, antenatal MgSO4 for neuroprotection, deferred cord clamping ≥30 seconds, and normothermia on admission. The effect of exposure to 1, 2, 3, and all 4 evidence-based practices compared with none on death and/or severe neurological injury was assessed using multivariable logistic regression models adjusted for patient characteristics. RESULTS: Rate of death and/or severe neurological injury was 20% (873 of 4297) and varied based on exposure to evidence-based practices: none, 34% (54 of 157); 1, 27% (171 of 626); 2, 20% (295 of 1448); 3, 18% (263 of 1448); and all 4, 14% (90 of 618). Significantly lower odds of death and/or severe neurological injury were observed with exposure to antenatal corticosteroids (adjusted odds ratio, 0.52, 95% confidence interval, 0.40-0.69) and deferred cord clamping (adjusted odds ratio, 0.81, 95% confidence interval, 0.68-0.96) but not MgSO4 (adjusted odds ratio, 0.88, 95% confidence interval, 0.72-1.08) or normothermia (adjusted odds ratio, 0.96, 95% confidence interval, 0.79-1.16). Infants exposed to ≥2 evidence-based practices had significantly lower odds of death and/or severe neurological injury than those exposed to no evidence-based practices (adjusted odds ratio, 0.61, 95% confidence interval, 0.43-0.88). CONCLUSION: Among infants born at <29 weeks' gestational age, exposure to at least 2 of the evidence-based practices assessed was associated with decreased odds of death and/or severe neurological injury.

Effect of an audience on trainee stress and performance during simulated neonatal intubation: a randomized crossover trial.

BACKGROUND: Neonatal intubation is a stressful procedure taught to trainees. This procedure can attract additional observers. The impact of observers on neonatal intubation performance by trainees has not been studied. Our objective was to evaluate if additional observers present during neonatal mannequin endotracheal intubation (NMEI) by junior trainees, affects their performance and their stress levels. METHODS: A randomized cross over trial was conducted. First year residents with no experience in neonatal intubation were assigned to NMEI condition A or B randomly on day 1. Subjects were crossed over to the other condition on day 2. Condition A: Only one audience member was present Condition B: Presence of an audience of 5 health care providers. Differences in the time to successful NMEI was recorded and compared between conditions. A portable heart rate monitor was used to measure peak heart rate above baseline during NMEI under both conditions. RESULTS: Forty nine residents were recruited. 72% were female with a median age of 25 years (IQR: 24-27). Time to successful intubation was comparable under both conditions with a mean difference of - 3.94 s (95% CI: -8.2,0.4). Peak heart rate was significantly lower under condition A (mean difference - 11.9 beats/min, 95% CI -15.98 to - 7.78). CONCLUSION: Although the time required to NMEI did not increase, our results suggest that presence of observers significantly increases trainee stress. The addition of extraneous observers during simulation training may better equip residents to deal with such stressors. TRIAL REGISTRATION: Date of registration: March 2016, NCT 02726724 .

Temperature Probe Placement during Preterm Infant Resuscitation: A Randomised Trial.

BACKGROUND: Hypothermia on admission to intensive care is associated with poor outcomes in preterm infants. The neonatal resuscitation program recommends the use of servo-control thermoregulation during resuscitation. Very little evidence exists to guide optimal temperature probe placement in the delivery room. OBJECTIVE: The aim of this work was to determine, in moderately preterm infants, if temperature probe placement in the dorsal, thoracic, or axillary area during delivery room resuscitation would result in differing temperatures on admission to the neonatal intensive care unit (NICU). METHODS: A randomised trial with 3 arms was conducted. In total, 122 inborn preterm infants born between 280/7 and 356/7 weeks of gestational age were recruited. The infants were randomly assigned to thermal probe placement in the left lower back, left upper thorax, or left axilla immediately after birth. Temperature was servo-controlled using an infant resuscitation table set to 36.5°C. The primary outcome was axillary temperature at admission to the NICU before transfer to a closed isolette, recorded with a digital thermometer. The secondary outcomes assessed were temperature within the target range (36.5-37.5°C), hypothermia (<36.5°C), and hyperthermia (>37.5°C). RESULTS: All 122 infants were available for outcome analysis. The groups were comparable for birthweight, gestational age, and sex. The mean admission temperature was comparable between the 3 probe positions (mean, 95% CI): dorsum (36.7°C, 36.6-36.8), thorax (36.8°C, 36.7-36.9), and axilla (36.7°C, 36.6-36.9), p = 0.43. The proportion of infants with admission temperatures in the target range was comparable (87.2, 81.4, and 72.5% respectively), p = 0.44. CONCLUSION: Dorsal, thoracic, or axillary temperature probe positioning during resuscitation yield similar admission temperatures in moderately preterm infants. Further studies are required in infants below 28 weeks of gestation to determine the best practice.

Effects of postnatal environmental tobacco smoke on non-nutritive swallowing-breathing coordination in newborn lambs.

While prenatal environmental tobacco smoke (ETS) exposure is a well-known risk factor for sudden infant death syndrome, the effect of postnatal ETS exposure is less clear. The objective of this study was to investigate the effect of postnatal ETS exposure on non-nutritive swallowing (NNS) and NNS-breathing coordination, which are crucial to prevent aspiration related-cardiorespiratory events. Eighteen newborn lambs (6 per group) were randomly exposed to either 10 cigarettes/day, 20 cigarettes/day or room air for 15 days. Lambs were instrumented for recording states of alertness, swallowing, electrocardiogram and breathing; recordings were performed in non-sedated lambs at the end of ETS exposure. Urinary cotinine/creatinine ratio confirmed relevant real-life exposure. Postnatal ETS exposure had no effect on NNS frequency but tended to decrease inspiratory NNS (p=0.07) during quiet sleep. No effect on respiratory or heart rate (p>0.6), apnea index (p=0.2) or sleep states (p=0.3) was observed. In conclusion, postnatal ETS exposure in lambs had only mild effects on NNS-breathing coordination.

PTSD and depression following armed robbery: patterns of appearance and impact on absenteeism and use of health care services.

Armed robbery is a sudden, life-threatening event affecting the victims' mental health. Posttraumatic stress disorder (PTSD) and major depressive disorder (MDD) in this population have rarely been studied. The objectives of the study were to assess the occurrence of PTSD and MDD in victims of armed robbery, and to evaluate occupational functioning and use of health care services. Eighty-six convenience store employees, victims of armed robbery, were evaluated within days after the robbery, and 1 and 3 months after. A validated diagnostic interview (SCID-I) was used. Data about sick leave, absenteeism, and use of health care services were collected. The total number of individuals who had PTSD, MDD, or both at any time during the 3 months following the robbery was 1 (2%), 4 (6%), and 5 (8%), respectively, showing that comorbid PTSD-MDD is as frequent as or even more frequent than either disorder in isolation. Individuals with PTSD (with or without comorbid MDD) reported more absenteeism (η(2) (p) = .25) and more medical visits (η(2) (p) = .12) following the robbery. Clinicians and management resources personnel must be alert to the possibility that both PTSD and MDD, either alone or comorbid, can develop in victims of armed robbery.

Effects of postnatal smoke exposure on laryngeal chemoreflexes in newborn lambs.

Laryngeal chemoreflexes (LCR), which are elicited by the contact of liquids such as gastric refluxate with laryngeal mucosa, may trigger some cases of sudden infant death syndrome. Indeed, while LCR in mature mammals consist of protective responses, previous animal data have shown that LCR in immature newborns can include laryngospasm, apnea, bradycardia, and desaturation. The present study was aimed at testing the hypothesis that postnatal exposure to cigarette smoke is responsible for enhancing cardiorespiratory inhibition observed with LCR. Eight lambs were exposed to cigarette smoke (20 cigarettes/day) over 16 days and compared with seven control lambs. Urinary cotinine/creatinine ratio was measured at a level relevant to previously published levels in infants. On days 15 and 16, 0.5 ml of HCl (pH 2), milk, distilled water, or saline was injected onto the larynx via a chronic supraglottal catheter during sleep. Results showed that exposure to cigarette smoke enhanced respiratory inhibition (P < 0.05) and tended to enhance cardiac inhibition and decrease swallowing and arousal during LCR (P < 0.1). Overall, these results were observed independently of the state of alertness and the experimental solution tested. In conclusion, 16-day postnatal exposure to cigarette smoke increases cardiorespiratory inhibition and decreases protective mechanisms during LCR in nonsedated full-term lambs.

Validation of a new automatic smoking machine to study the effects of cigarette smoke in newborn lambs.

The aim of this study was to describe the characteristics and validate the use of a new, custom-built automatic smoking machine (ASM), primarily designed to study the effects of an environmental tobacco smoke surrogate (ETS surrogate) exposure in animals of various sizes, including large animals. The equipment includes a programmable ASM coupled to a vented whole body chamber, where animals can be exposed to both mainstream and sidestream smoke. The user-friendly interface allows for full programming of puff volume (1-60 mL), time interval between two puffs (1-60 s) and between two cigarettes (1-60 min). Eight newborn lambs were exposed to either 10 (4 lambs, C10 group) or 20 (4 lambs, C20 group) cigarettes, 8 h per day for 15 days. Four additional control, lambs were exposed to air (C0 group). Weight gain was identical in all three groups of lambs. Urinary cotinine/creatinine ratio increased with the number of cigarettes smoked (C0: 11 ± 7 ng/mg; C10: 961 ± 539 ng/mg; C20: 1821 ± 312 ng/mg), with levels in the C10 and C20 groups in keeping with values published in infants exposed to ETS. Overall, results show that our new ASM is especially well suited for ETS surrogate exposure in non-restrained, non-anaesthetized large animals such as sheep.

Postnatal autonomic activity in the preterm lamb.

BACKGROUND: Early postnatal abnormalities of autonomic nervous system (ANS) activity, including at baseline and following cardiorespiratory challenge, are involved in apneas-bradycardias of prematurity, apparent life-threatening events of infancy and sudden infant death syndrome. Literature data suggest that baseline ANS activity does not mature normally after premature birth. OBJECTIVES: This study performed in preterm lambs was aimed at assessing ANS maturation at baseline and following laryngeal chemoreflexes (LCR), a group of reflexes triggered by the contact of liquids with the laryngeal mucosa. METHODS: Heart rate variability (HRV) and baroreflex sensitivity (BRs) were measured at baseline and after LCR during polysomnographic recordings performed in five non-sedated lambs born 15 days prematurely. Laryngeal chemoreflexes were induced by distilled water or acid (pH 2) during sleep and wakefulness on postnatal days 7 (D7) and 14 (D14, full-term equivalence). RESULTS: While the life-threatening cardiorespiratory events of the LCR observed at D7 were no longer present at D14, baseline and post-LCR HRV and BRs indices were significantly lower at D14 compared to D7 (up to p<0.001). These results suggest that an initial autonomic overactivity was present at D7 and normalized at D14. CONCLUSION: The autonomic cardiac and baroreflex control appears to follow a specific evolution in the preterm compared to the full-term newborn lamb, with an important initial autonomic stress, which normalizes at an age equivalent to full-term. Potential relevance of these findings in relation to anomalies of cardiac control in the early postnatal period, such as apneas-bradycardias of prematurity, apparent life-threatening events of infancy and sudden infant death syndrome, awaits further studies.

Laryngeal stimulation by an acid solution in the pre-term lamb.

In a mature organism, the contact between various liquids and the laryngeal mucosa triggers lower airway protective responses (cough, swallowing, arousal). These laryngeal chemoreflexes (LCR) are essential for preventing aspiration. In contrast, previous studies showed that LCR are responsible for apnea and bradycardia in the neonatal mammal. Consequently, LCR, especially when triggered by acid gastrolaryngeal reflux, are deemed responsible for some apneas of prematurity and many life-threatening events of infancy and, probably, for some cases of sudden infant death syndrome. Recently, we have revisited LCR in full-term lambs during quiet sleep. Our results showed that the LCR triggered by HCl (pH 2), mimicking the acid component of an acid gastro-oesophageal reflux, were consistently like the mature LCR reported in adult mammals, without significant apneas and bradycardias (St-Hilaire 2005). These results prompted us to question whether premature birth alters LCR. Results show that LCR triggered in pre-term lambs by both saline and HCl are much more marked and clinically relevant than the ones observed in full-term lambs. Indeed, life-threatening responses to HCl, including repetitive apneas for more than 90 seconds, severe desaturation and bradycardia, were observed in 2 lambs at postnatal day 7 (D7). In addition, LCR were significantly blunted at D14. In conclusion, HCl can trigger potentially dangerous LCR in pre-term lambs at D7, suggesting that LCR in response to acid gastrolaryngeal refluxes are likely involved in some apnea/bradycardia/desaturation in pre-term infants, before they reach a post-conceptional age equivalent to full gestation.

Effects of hypercapnia on non-nutritive swallowing in newborn lambs.

The purpose of this study was to determine the effect of hypercapnia on non-nutritive swallowing (NNS) frequency and on NNS-breathing coordination in newborn lambs. Six lambs were chronically instrumented for recording electroencephalogram, eye movements, diaphragm and thyroarytenoid muscle activity, nasal airflow and electrocardiogram. Each lamb was placed in a Plexiglas chamber and exposed to a hypercapnic gas mixture (21% O2, 5% CO2). Polysomnographic recordings were conducted in non-sedated lambs using a custom-designed radiotelemetry system. Results show that hypercapnia increased NNS frequency in all three states of alertness (p < 0.0001 to 0.03), through a specific increase in ie-type NNS. Causal mechanisms and potential consequences of such observations on aspirations and apneas, as well as on swallowing maturation, will require further studies.

CPAP inhibits non-nutritive swallowing through stimulation of bronchopulmonary receptors.

While swallowing and respiratory problems are among the most frequent disorders encountered in neonates, the interrelationships between both functions are not completely understood. This is especially true for non-nutritive swallowing (NNS), which fulfills the important function of clearing upper airways from both local secretions and liquids refluxed from the stomach. Recently, we showed that nasal CPAP inhibits NNS during quiet sleep in the newborn lamb (Samson, St-Hilaire, Nsegbe, Reix, Moreau-Bussière and Praud 2005). The present study was aimed at testing the hypothesis that NNS inhibition is eliminated when CPAP is directly administered through a tracheostomy, thus eliminating reflexes originating from upper airway receptors. Results show that both nasal and tracheal CPAP 6cm H2O similarly inhibit total NNS during quiet sleep, thus suggesting that the inhibiting effect of nasal CPAP on NNS is mainly mediated through bronchopulmonary mechanical receptors with minimal participation of the upper airways.

Effects of hypoxia and hypercapnia on nonnutritive swallowing in newborn lambs.

The aim of the present study was to investigate the effect of hypercapnia and hypoxia on apnea and nonnutritive swallowing (NNS) frequency, as well as on the coordination between NNS and phases of the respiratory cycle in newborn lambs, while taking into account the potential effects of states of alertness. Six lambs were chronically instrumented for recording electroencephalogram, eye movements, diaphragm and thyroarytenoid muscle (a glottal adductor) activity, nasal airflow, and electrocardiogram. Polysomnographic recordings were performed in nonsedated lambs exposed to air (control), 10% O(2), and 5% CO(2) in a random order at 3, 4, and 5 days of age. Although hypercapnia decreased apnea frequency in wakefulness and active sleep (P = 0.002 vs. air and hypoxia), hypoxia had no significant effect on apnea. In addition, although hypercapnia increased NNS frequency during wakefulness and quiet sleep (P < 0.005 vs. air and hypoxia), hypoxia tended to decrease NNS frequency. Finally, only hypercapnia altered NNS-breathing coordination by increasing NNS at the transition from inspiration to expiration (ie-type NNS; P < 0.001 vs. air and hypoxia). In conclusion, whereas hypercapnia increases overall NNS frequency by specifically increasing ie-type NNS, hypoxia has the inverse tendency. Results were identical in all three states of alertness.

Laryngeal sensitivity in the neonatal period: from bench to bedside.

Laryngeal sensitivity in the newborn has been a subject of great interest for both researchers and clinicians for a number of years. From a clinical standpoint, laryngeal sensitivity is essential for both preventing foreign substances from entering into the lower airway and for finely tuning upper airway resistance. However, heightened reflexes originating from the laryngeal receptors in newborns and infants, due to neural immaturity, can lead to potentially dangerous cardiorespiratory events. The latter have been linked to apneas of prematurity, apparent life-threatening events, and sudden infant death syndrome (SIDS). From a physiological standpoint, many mechanisms pertaining to reflexes originating from laryngeal receptors are yet to be fully understood. This short review is an attempt to summarize current knowledge on laryngeal sensitivity and its potential consequences upon control of breathing abnormalities encountered within the first weeks of life.

Prolonged dynamic changes in autonomic heart rate modulation induced by acid laryngeal stimulation in non-sedated lambs.

BACKGROUND: Exaggerated laryngeal chemoreflexes (LCR) have been implicated in the occurrence and prolongation of apnea in premature and term neonates. OBJECTIVES: To test the hypothesis that the cardiovascular component of the LCR can occur and be prolonged in the absence of apnea. METHODS: Bolus injections of 0.5 ml of citric acid (CitAc) and serum saline were administered onto the larynx in seven non-sedated lambs, aged 4-5 days, during quiet sleep. Blood pressure (BP) and heart rate (HR) variability measurements were taken and compared with results obtained prior to stimulation and with saline. RESULTS: Apneas were rare and occurred consistently in the 32-beat period (10 s) following stimulation. The increase in BP and decrease in HR were consistent after CitAc and saline. All the studied components of HR variability significantly increased after CitAc, but not after saline. The low frequency estimates were significantly increased during a 480-beat period (133 +/- 6.6 s) following CitAc stimulation. Analysis of gains and respiration showed that bradycardia and HR variability changes were neither related to an apnea nor a vagal arterial baroreflex. CONCLUSION: This long-lasting increase in HR variability indicates a prolonged disturbance of the cardiovascular regulatory systems, consisting in increased sympathetic and parasympathetic tones following CitAc stimulation.

Laryngeal response to nasal ventilation in nonsedated newborn lambs.

Although endoscopic studies in adult humans have suggested that laryngeal closure can limit alveolar ventilation during nasal intermittent positive pressure ventilation (nIPPV), there are no available data regarding glottal muscle activity during nIPPV. In addition, laryngeal behavior during nIPPV has not been investigated in neonates. The aim of the present study was to assess laryngeal muscle response to nIPPV in nonsedated newborn lambs. Nine newborn lambs were instrumented for recording states of alertness, electrical activity [electromyograph (EMG)] of glottal constrictor (thyroarytenoid, TA) and dilator (cricothyroid, CT) muscles, EMG of the diaphragm (Dia), and mask and tracheal pressures. nIPPV in pressure support (PS) and volume control (VC) modes was delivered to the lambs via a nasal mask. Results show that increasing nIPPV during wakefulness and quiet sleep led to a progressive disappearance of Dia and CT EMG and to the appearance and subsequent increase in TA EMG during inspiration, together with an increase in trans-upper airway pressure (TUAP). On rare occasions, transmission of nIPPV through the glottis was prevented by complete, active glottal closure, a phenomenon more frequent during active sleep epochs, when irregular bursts of TA EMG were observed. In conclusion, results of the present study suggest that active glottal closure develops with nIPPV in nonsedated lambs, especially in the VC mode. Our observations further suggest that such closure can limit lung ventilation when raising nIPPV in neonates.

Postnatal maturation of laryngeal chemoreflexes in the preterm lamb.

Laryngeal chemoreflexes (LCR) are triggered by the contact of liquids with the laryngeal mucosa. In the mature organism, LCR trigger lower airway protective responses (coughing, effective swallowing, and arousal) to prevent aspiration. General belief holds that LCR are responsible for apnea and bradycardia in the newborn mammal, including humans. Our laboratory has recently shown that LCR in full-term lambs are consistently analogous to the mature LCR reported in adult mammals, without significant apneas and bradycardias (St-Hilaire M, Nsegbe E, Gagnon-Gervais K, Samson N, Moreau-Bussiere F, Fortier PH, and Praud J-P. J Appl Physiol 98: 2197-2203, 2005). The aim of the present study was to assess LCR in nonsedated, newborn preterm lambs born at 132 days of gestation (term = 147 days). The preterm lambs were instrumented for recording glottal adductor electromyogram, electroencephalogram, eye movements, heart rate, respiration, and oximetry. A chronic supraglottal catheter was used for injecting 0.5 ml of saline, distilled water, and HCl (pH 2) during quiet sleep, active sleep, and wakefulness on postnatal days 7 (D7) and 14 (D14). Laryngeal stimulation by water or HCl on D7 induced significant apneas, bradycardia, and desaturation, which, at times, appeared potentially life-threatening. No significant apneas, bradycardias, or desaturation were observed on D14. No consistent effects of sleep state could be shown in the present study. In conclusion, laryngeal stimulation by liquids triggers potentially dangerous LCR in preterm lambs on D7, but not on D14. It is proposed that maturation of the LCR between D7 and D14 is partly involved in the disappearance of apneas/bradycardias of prematurity with postnatal age.