Going to High Altitude with a Newborn Infant

What altitude is safe for infants? An expert panel survey

AIM

To assess advice given to parents who wish to travel to high altitudes with an infant and to provide guidance on this topic.

METHOD

Using an anonymous self-report survey online, we collected information on the advice provided by practitioners, who practice in mountain environments, to parents who wish to travel to altitude with an infant. General practitioners and pediatricians working in the French Alps were asked about the maximum allowable altitude for different ages and the specific recommendations given.

RESULTS

A total of 104 practitioners (39% general practitioners) responded to the study. Overall, to spend 1 day at altitude, practitioners recommended a median altitude of 1200, 1500, 1600, and 2000 m for infants under 1, 3, 12, and 24 months, respectively. Their main recommendations for infant protection focused on cold protection, increased hydration, and increased humidity level in the ambient air. Prevention of sudden infant death syndrome was essential according to the respondents. For infants with upper airway infection, most of the participants (90%, n = 94) recommended against traveling to altitude.

CONCLUSION

This survey revealed a certain consensus about the maximum travel altitude to be recommended for infants.

Surfactant Therapy for Respiratory Distress Syndrome in High- and Ultra-High-Altitude Settings

OBJECTIVE

The objective of this study is to investigate the therapeutic effect of surfactant replacement therapy (SRT) on respiratory distress syndrome (RDS) in premature infants in the Qinghai-Tibet Plateau.

MATERIALS AND METHODS

This multi-center retrospective cohort study collected and screened reasonable clinical data of 337 premature infants with RDS from 10 hospitals in the Qinghai-Tibet Plateau from 2015 to 2017. We grouped the cases by rationally analyzing their baseline characteristics, using logistic analysis to evaluate each factor's effect on the prognosis of the infants, and comparing the short-term improvement in blood gas and mortality after SRT treatment at different altitudes, in high-altitude (1,500-3,500 m) and ultra-high-altitude (3,500-5,500 m) groups.

RESULTS

Independent of altitude, the mortality rate of children with RDS in the SRT group was significantly lower than that of children in the non-SRT group (both P < 0.05). The effect of SRT on preterm infants with RDS in the high-altitude group [odds ratio (OR) = 0.44, 95% confidence interval (CI) = 0.22-0.87, P = 0.02] was better than that in the infants in the ultra-high-altitude group (OR = 0.26, 95% CI = 0.13-0.58, P < 0.01), with death rates of 34.34 and 49.71%, respectively. Similarly, after SRT, the improvement of PaO₂/FiO₂ and pH of children at high altitude was significantly better than those of children at ultra-high altitude (all P < 0.01).

CONCLUSIONS

SRT plays a prominent role in curing infants with RDS in both high- and ultra-high-altitude regions, although with better effects at high rather than ultra-high altitude. This study provides a basis for further large-scale studies on SRT for RDS treatment at high altitudes.

Hypoxia in utero increases the risk of pulmonary hypertension in rat offspring and is associated with vasopressin type‑2 receptor upregulation

Pulmonary hypertension (PH) in newborns and adults is a disease that can lead to right heart failure and result in a shorter lifespan. PH was induced by maintaining pregnant rats in a hypoxic chamber for 4 h twice a day, from days 7–21 of pregnancy. Hypoxia was confirmed by a decrease in the partial pressure of oxygen (PaO₂) and the oxygen saturation (SaO₂) of arterial blood in the aorta. The body weight of newborns from hypoxic rats was ~20% decreased compared with the control newborns of normoxic rats. The vascular wall thickness/vascular diameter values of hypoxia treated pubs were increased compared with that of control newborns 7 days after birth; however, it decreased to similar levels than in the control group after 3 months, and then further decreased to significantly lower levels than in the control group at 6 months after birth. At birth, the lung tissues of newborns from hypoxic rats exhibited an increase in the levels of mRNA and proteins associated with PH such as HIF-1α, HIF-2α, V2R, TGF-β, TNF-α, Ang-2 and α-SMA. At 3 and 6 months after birth, the levels of both V2R mRNA and protein in offspring from hypoxic rats were at least 2-fold higher, whereas the expression of all other factors decreased compared with the control offspring. By contrast, HIF-2α and Ang-2 expression levels were significantly increased in the 6-month-old control offspring from normoxic rats. V2R overexpression in pups induced by hypoxia in maternal rats was sustained until their adulthood. V2R may be a marker for detecting PH.

Long-Term High-Altitude Hypoxia and Alpha Adrenoceptor-Dependent Pulmonary Arterial Contractions in Fetal and Adult Sheep

Autonomic innervation of the pulmonary vasculature triggers vasomotor contractility predominately through activation of alpha-adrenergic receptors (α-ARs) in the fetal circulation. Long-term hypoxia (LTH) modulates pulmonary vasoconstriction potentially through upregulation of α₁-AR in the vasculature. Our study aimed to elucidate the role of α-AR in phenylephrine (PE)-induced pulmonary vascular contractility, comparing the effects of LTH in the fetal and adult periods on α-AR subtypes and PE-mediated Ca²⁺ responses and contractions. To address this, we performed wire myography, Ca²⁺ imaging, and mRNA analysis of pulmonary arteries from ewes and fetuses exposed to LTH or normoxia. Postnatal maturation depressed PE-mediated contractile responses. α₂-AR activation contracted fetal vessels; however, this was suppressed by LTH. α_1A- and α_1B-AR subtypes contributed to arterial contractions in all groups. The α_1D-AR was also important to contractility in fetal normoxic vessels and LTH mitigated its function. Postnatal maturity increased the number of myocytes with PE-triggered Ca²⁺ responses while LTH decreased the percentage of fetal myocytes reacting to PE. The difference between myocyte Ca²⁺ responsiveness and vessel contractility suggests that fetal arteries are sensitized to changes in Ca²⁺. The results illustrate that α-adrenergic signaling and vascular function change during development and that LTH modifies adrenergic signaling. These changes may represent components in the etiology of pulmonary vascular disease and foretell the therapeutic potential of adrenergic receptor antagonists in the treatment of pulmonary hypertension.

Pediatric High Altitude Cerebral Edema in the Nepal Himalayas

High altitude cerebral edema (HACE) is a rare complication of ascent to altitudes of over 2500 m (8200 ft). We are not aware of a previously published case report of HACE in a patient under the age of 18 y. We report on 2 cases of suspected HACE in 2 patients, aged 12 and 16 y, who presented to the Manang Himalayan Rescue Association clinic at 3500 m. The 16-y-old patient presented with severe headache, vomiting, and ataxia after rapid ascent to 3800 m. The 12-y-old patient presented with severe headache, vomiting, visual disturbances, and ataxia at 4500 m, which began to resolve with descent to the clinic at 3500 m. Our cases suggest that HACE can occur in children and adolescents. Because there are no specific guidelines for treatment of acute mountain sickness or HACE in patients under the age of 18 y, we recommend treatment as for adults: oxygen, immediate descent, and dexamethasone. Simulated descent in a portable hyperbaric chamber can be used if oxygen is not available and if actual descent is not possible.

Athletes at High Altitude

CONTEXT

Athletes at different skill levels perform strenuous physical activity at high altitude for a variety of reasons. Multiple team and endurance events are held at high altitude and may place athletes at increased risk for developing acute high altitude illness (AHAI). Training at high altitude has been a routine part of preparation for some of the high level athletes for a long time. There is a general belief that altitude training improves athletic performance for competitive and recreational athletes.

EVIDENCE ACQUISITION

A review of relevant publications between 1980 and 2015 was completed using PubMed and Google Scholar.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 3.

RESULTS

AHAI is a relatively uncommon and potentially serious condition among travelers to altitudes above 2500 m. The broad term AHAI includes several syndromes such as acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). Athletes may be at higher risk for developing AHAI due to faster ascent and more vigorous exertion compared with nonathletes. Evidence regarding the effects of altitude training on athletic performance is weak. The natural live high, train low altitude training strategy may provide the best protocol for enhancing endurance performance in elite and subelite athletes. High altitude sports are generally safe for recreational athletes, but they should be aware of their individual risks.

CONCLUSION

Individualized and appropriate acclimatization is an essential component of injury and illness prevention.

Wilderness Preparticipation Evaluation and Considerations for Special Populations

Children, older adults, disabled and special needs athletes, and female athletes who participate in outdoor and wilderness sports and activities each face unique risks. For children and adolescents traveling to high altitude, the preparticipation physical evaluation should focus on risk assessment, prevention strategies, early recognition of altitude-related symptoms, management plans, and appropriate follow-up. As the risk and prevalence of chronic disease increases with age, both older patients and providers need to be aware of disease and medication-specific risks relative to wilderness sport and activity participation. Disabled and special needs athletes benefit from careful pre-event planning for the potential medical issues and equipment modifications that may affect their health in wilderness environments. Issues that demand special consideration for female adventurers include pregnancy, contraceptive use, menses, and ferritin levels at altitude. A careful preparticipation evaluation that factors in unique, population- specific risks will help special populations stay healthy and safe on wilderness adventures. The PubMed and SportDiscus databases were searched in 2014 using both MeSH terms and text words and include peer-reviewed English language articles from 1977 to 2014. Additional information was accessed from Web-based sources to produce this narrative review on preparticipation evaluation for special populations undertaking wilderness adventures. Key words include children, adolescent, pediatric, seniors, elderly, disabled, special needs, female, athlete, preparticipiation examination, wilderness medicine, and sports.

Wilderness Preparticipation Evaluation and Considerations for Special Populations

Children, older adults, disabled and special needs athletes, and female athletes who participate in outdoor and wilderness sports and activities each face unique risks. For children and adolescents traveling to high altitude, the preparticipation physical evaluation should focus on risk assessment, prevention strategies, early recognition of altitude-related symptoms, management plans, and appropriate follow-up. As the risk and prevalence of chronic disease increases with age, both older patients and providers need to be aware of disease and medication-specific risks relative to wilderness sport and activity participation. Disabled and special needs athletes benefit from careful pre-event planning for the potential medical issues and equipment modifications that may affect their health in wilderness environments. Issues that demand special consideration for female adventurers include pregnancy, contraceptive use, menses, and ferritin levels at altitude. A careful preparticipation evaluation that factors in unique, population-specific risks will help special populations stay healthy and safe on wilderness adventures. The PubMed and SportDiscus databases were searched in 2014 using both MeSH terms and text words and include peer-reviewed English language articles from 1977 to 2014. Additional information was accessed from Web-based sources to produce this narrative review on preparticipation evaluation for special populations undertaking wilderness adventures. Key words include children, adolescent, pediatric, seniors, elderly, disabled, special needs, female, athlete, preparticipiation examination, wilderness medicine, and sports.

Prenatal programming of pulmonary hypertension induced by chronic hypoxia or ductal ligation in sheep

Pulmonary hypertension of the newborn is caused by a spectrum of functional and structural abnormalities of the cardiopulmonary circuit. The existence of multiple etiologies and an incomplete understanding of the mechanisms of disease progression have hindered the development of effective therapies. Animal models offer a means of gaining a better understanding of the fundamental basis of the disease. To that effect, a number of experimental animal models are being used to generate pulmonary hypertension in the fetus and newborn. In this review, we compare the mechanisms associated with pulmonary hypertension caused by two such models: in utero ligation of the ductus arteriosus and chronic perinatal hypoxia in sheep fetuses and newborns. In this manner, we make direct comparisons between ductal ligation and chronic hypoxia with respect to the associated mechanisms of disease, since multiple studies have been performed with both models in a single species. We present evidence that the mechanisms associated with pulmonary hypertension are dependent on the type of stress to which the fetus is subjected. Such an analysis allows for a more thorough evaluation of the disease etiology, which can help focus clinical treatments. The final part of the review provides a clinical appraisal of current treatment strategies and lays the foundation for developing individualized therapies that depend on the causative factors.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Arterial blood gas parameters of normal foals born at 1500 metres elevation

REASONS FOR PERFORMING STUDY

Arterial blood gas analysis is widely accepted as a diagnostic tool to assess respiratory function in neonates. To the authors' knowledge, there are no published reports of arterial blood gas parameters in normal neonatal foals at altitude.

OBJECTIVE

To provide information on arterial blood gas parameters of normal foals born at 1500 m elevation (Fort Collins, Colorado) in the first 48 h post partum.

HYPOTHESIS

Foals born at 1500 m will have lower PaO2 and PaCO2 than foals born at sea level due to low inspired oxygen and compensatory hyperventilation occurring at altitude.

METHODS

Sixteen foals were studied. Arterial blood gas analysis was performed within 1 h of foaling and subsequent samples were evaluated at 3, 6, 12, 24 and 48 h post partum. Data were compared to those previously reported in healthy foals born near sea level.

RESULTS

Mean PaO2 was 53.0 mmHg (7.06 kPa) within 1 h of foaling, rising to 67.5 mmHg (9.00 kPa) at 48 h post partum. PaCO2 was 44.1 mmHg (5.88 kPa) within one hour of foaling, falling to 38.3 mmHg (5.11 kPa) at 48 h. Both PaO2 and PaCO2 were significantly lower in foals born at 1500 m elevation than those near sea level at several time points during the first 48 h.

CONCLUSIONS AND POTENTIAL RELEVANCE

Foals at 1500 m elevation undergo hypobaric hypoxia and compensatory hyperventilation in the first 48 h. Altitude specific normal arterial blood values are an important reference for veterinarians providing critical care to equine neonates.

Bubble continuous positive airway pressure, a potentially better practice, reduces the use of mechanical ventilation among very low birth weight infants with respiratory distress syndrome

OBJECTIVE

The purpose of this work was to assess a quality improvement initiative to implement a potentially better practice, bubble continuous positive airway pressure, to reduce bronchopulmonary dysplasia and improve other pulmonary outcomes among very low birth weight infants with respiratory distress syndrome.

METHODS

An initiative to implement the use of bubble continuous positive airway pressure is described that was based on the adoption of habits for change, collaborative learning, evidence-based practice, and process development. To assess the efficacy of this intervention, very low birth weight infants with respiratory distress syndrome born after implementation of bubble continuous positive airway pressure use (period 2: March 1, 2005, to October 4, 2007; N = 126) were compared with historical controls born during a previous period of ventilator use (period 1: January 1, 2003, to February 28, 2005; N = 88). Infants at both time periods were similar with respect to characteristics and aspects of perinatal care. Pulmonary outcomes compared for the 2 time periods included receipt of mechanical ventilation, duration of mechanical ventilation, pneumothoraces, and incidence of bronchopulmonary dysplasia. Nonpulmonary outcomes were also compared.

RESULTS

The use of mechanical ventilation declined during period 2. The mean duration (+ SD) of conventional ventilation during period 2 was shorter than during period 1 (3.08 + 6.17 vs 5.25 + 8.16 days), and fewer infants during period 2 required conventional ventilation for >6 days compared with those in period 1 (13.6% vs 26.3%). In regression models, the effect of period 2 persisted after controlling for other predictors of duration of conventional ventilation. There were no significant differences in other pulmonary or nonpulmonary outcomes, with the exception of mild retinopathy of prematurity (stage I or II), which was more common during period 2. The enhanced odds of retinopathy of prematurity persisted after controlling for other known predictors of this condition.

CONCLUSION

Among very low birth weight infants with respiratory distress syndrome, the use of bubble continuous positive airway pressure is a potentially better practice that may reduce the use of mechanical ventilation. Although an increase in retinopathy of prematurity was observed in our population, carefully designed randomized, controlled trials will be required to more accurately address the potential risks and benefits of this therapy.

Effect of long-term high-altitude hypoxia on fetal pulmonary vascular contractility

Hypoxia in the fetus and/or newborn is associated with an increased risk of pulmonary hypertension. The present study tested the hypothesis that long-term high-altitude hypoxemia differentially regulates contractility of fetal pulmonary arteries (PA) and veins (PV) mediated by differences in endothelial NO synthase (eNOS). PA and PV were isolated from near-term fetuses of pregnant ewes maintained at sea level (300 m) or high altitude of 3,801 m for 110 days (arterial Po(2) of 60 Torr). Hypoxia had no effect on the medial wall thickness of pulmonary vessels and did not alter KCl-induced contractions. In PA, hypoxia significantly increased norepinephrine (NE)-induced contractions, which were not affected by eNOS inhibitor N(G)-nitro-l-arginine (l-NNA). In PV, hypoxia had no effect on NE-induced contractions in the absence of l-NNA. l-NNA significantly increased NE-induced contractions in both control and hypoxic PV. In the presence of l-NNA, NE-induced contractions of PV were significantly decreased in hypoxic lambs compared with normoxic animals. Acetylcholine caused relaxations of PV but not PA, and hypoxia significantly decreased both pD(2) and the maximal response of acetylcholine-induced relaxation in PV. Additionally, hypoxia significantly decreased the maximal response of sodium nitroprusside-induced relaxations of both PA and PV. eNOS was detected in the endothelium of both PA and PV, and eNOS protein levels were significantly higher in PV than in PA in normoxic lambs. Hypoxia had no significant effect on eNOS levels in either PA or PV. The results demonstrate heterogeneity of fetal pulmonary arteries and veins in response to long-term high-altitude hypoxia and suggest a likely common mechanism downstream of NO in fetal pulmonary vessel response to chronic hypoxia in utero.