Fetal Heart Rate Response to Maternal Hypocapnia and Hypercapnia in Late Gestation

Severe tachypnoea and dyspnoea due to physiological hyperventilation in pregnancy

Physiological hyperventilation and dyspnoea in pregnancy are well-established phenomena and commonly lead to a chronic respiratory alkalosis with compensatory renal excretion of bicarbonate. However, the underlying mechanism of dyspnoea during normal pregnancy remains largely undefined. Increasing progesterone levels are a primary factor leading to increased respiratory drive to ensure the rising metabolic demands of the pregnancy are met. Dyspnoea symptoms typically begin in the first or second trimester, are mild, and do not interfere with activities of daily living. We report the case of a 35-year-old female with severe physiological hyperventilation of pregnancy presenting with profound dyspnoea, tachypnoea, and presyncope from 18 weeks of gestation until delivery. Subsequent investigations revealed no identifiable underlying pathology. There remain limited reports of such severe physiological hyperventilation of pregnancy. This case highlights interesting questions regarding the respiratory physiology of pregnancy and underlying mechanisms.

A Detailed Review of Critical Care Considerations for the Pregnant Cardiac Patient

Maternal cardiovascular disease is a leading cause of maternal death worldwide and recently, maternal mortality has increased secondary to cardiovascular causes. Maternal admissions to critical care encompass 1%-2% of all critical care admissions, and although not common, the management of the critically ill pregnant patient is complex. Caring for the critically ill pregnant cardiac patient requires integration of pregnancy-associated physiologic changes, understanding pathophysiologic disease states unique to pregnancy, and a multidisciplinary approach to timing around delivery as well as antenatal and postpartum care. Herein we describe cardiorespiratory changes that occur during pregnancy and the differential diagnosis for cardiorespiratory failure in pregnancy. Cardiorespiratory diseases that are either associated or exacerbated by pregnancy are highlighted with emphasis on perturbations secondary to pregnancy and appropriate management strategies. Finally, we describe general management of the pregnant cardiac patient admitted to critical care.

Chronic hypoxia in pregnant mice impairs the placental and fetal vascular response to acute hypercapnia in BOLD-MRI hemodynamic response imaging

INTRODUCTION

Brief hypercapnic challenge causes acute placental hypoperfusion with fetal brain sparing on BOLD-MRI. We hypothesize that this non-invasive imaging strategy can distinguish between normal pregnancy and chronic placental hypoperfusion (using the maternal hypoxia model).

METHODS

Eighteen pregnant female ICR mice were randomized to three groups: normoxia, late-onset hypoxia (12%O₂;E13.5-17.5) and early-onset hypoxia (12%O₂;E10.5-17.5). On E17.5, animals were imaged in a 4.7-T Bruker-Biospec MRI scanner. Fast coronal True-FISP was performed to identify organs of interest (placenta and fetal heart, liver and brain). BOLD-MRI was performed at baseline and during a 4-min hypercapnic challenge (5%CO₂). %-change in placental and fetal signal was analyzed from T2*-weighted gradient echo MR images. Following MRI, fetuses and placentas were harvested, weighed and immuno-stained.

RESULTS

In normoxic mice, hypercapnia caused reduction in BOLD-MRI signal in placenta (-44% ± 7%; p < 0.0001), fetal liver (-32% ± 7%; p < 0.0001) and fetal heart (-54% ± 12%; p < 0.002), with relative fetal brain sparing (-12% ± 5%; p < 0.0001). These changes were markedly attenuated in both hypoxia groups. Baseline fetal brain/placenta SI ratio was highest in normoxic mice (1.14 ± 0.017) and reduced with increasing duration of hypoxia (late-onset hypoxia: 1.00 ± 0.026; early-onset hypoxia: 0.91 ± 0.016; p = 0.02). Both hypoxic groups exhibited fetal growth restriction with prominent placental glycogen-containing cells, particularly in early-onset hypoxia. There was increased fetal neuro- and intestinal-apoptosis in early-onset hypoxia only.

CONCLUSIONS

BOLD-MRI with brief hypercapnic challenge distinguished between normoxia and both hypoxia groups, while fetal neuroapoptosis was only observed after early-onset hypoxia. This suggests that BOLD-MRI with hypercapnic challenge can identify chronic fetal asphyxia before the onset of irreversible brain injury.

The Effect of Maternal Pulmonary Function Test Parameters on Umbilical Cord Blood Gas and the Duration of Labor

OBJECTIVE

To evaluate the relationship between the maternal pulmonary function test (PFT) and the Apgar score of the newborn, umbilical cord blood (UCB) gas values and the duration of delivery.

MATERIAL AND METHODS

The present study included 41 volunteer nulliparous pregnant women who presented to our obstetrics clinic and PFTs were performed by using spirometry.

RESULTS

A significant positive correlation was observed between 5^th-minute Apgar scores and maternal FEV1 (forced expiratory volume in the first second) (lt), FEV1%, FVC (lt), FVC% (r=0.509, p=0.003; r=0.47, p=0.007; r=0.434, p=0.013; r=0.417, p=0.017; respectively). A significant positive correlation was observed between UCB pH value and maternal FEV1 (lt), FVC (lt) (r=0.515, p=0.003; r=0.351, p=0.049; respectively).

CONCLUSION

Our results showed that FEV1 and FVC values, which indicate maternal respiratory functions, may affect Apgar scores of the newborn and UCB gas values.

Maternal Sepsis and Septic Shock

The year 2015 marked the 200th anniversary of the birth of Ignaz Semmelweis, the Hungarian physician who identified unhygienic practices of physicians as a major cause of childbed fever or puerperal sepsis. Although such practices have largely disappeared as a factor in the development of chorioamnionitis and postpartum or puerperal endometritis, it is appropriate that this article on sepsis in pregnancy acknowledges his contributions to maternal health. This review describes the incidence and mortality of sepsis in pregnancy, methods to identify and define sepsis in this population, including scoring systems, causes, and sites of infection during pregnancy and parturition and management guidelines.

Restrictive lung disease in pregnancy

Restrictive lung disease is uncommon in pregnancy. We reviewed 15 pregnancies in 12 women with restrictive disease due to kyphoscoliosis, neuromuscular disease, or parenchymal lung disease. Median FVC was 40% predicted, and six women (50%) had an FVC &lt; 1.0 L. In the 14 pregnancies in which at least two spirometry readings were available, FVC increased in three pregnancies, decreased in three, and remained stable in eight, with maximal changes of 0.4 L. Three women required supplemental oxygen, and one woman with neuromuscular disease required noninvasive ventilation. Premature delivery occurred in nine pregnancies (60%), and 10 deliveries (67%) were by cesarean section. Neuraxial anesthesia was used in 10 of 15 deliveries but was limited in the others by difficult spinal anatomy. There was no maternal or neonatal mortality. Women with restrictive lung disease tolerate pregnancy reasonably well, but many have premature delivery. A multidisciplinary approach is essential, with monitoring of spirometry and oxygenation and planning for labor and delivery.

Influence of hypoxia and hypercapnia on sleep state-dependent heart rate variability behavior in newborn lambs

STUDY OBJECTIVES

Although hypercapnia and/or hypoxia are frequently present during chronic lung disease of infancy and have also been implicated in sudden infant death syndrome (SIDS), their effect on cardiac autonomic regulation remains unclear. The authors' goal is to test that hypercapnia and hypoxia alter sleep-wake cycle-dependent heart rate variability (HRV) in the neonatal period.

DESIGN

Experimental study measuring HRV during sleep states in lambs randomly exposed to hypercapnia, hypoxia, or air.

SETTING

University center for perinatal research in ovines (Sherbrooke, Canada). INSERM-university research unit for signal processing (Rennes, France).

PARTICIPANTS

Six nonsedated, full-term lambs.

INTERVENTIONS

Each lamb underwent polysomnographic recordings while in a chamber flowed with either air or 21% O(2) + 5% CO(2) (hypercapnia) or 10% O(2) + 0% CO(2) (hypoxia) on day 3, 4, and 5 of postnatal age.

MEASUREMENTS AND RESULTS

Hypercapnia increased the time spent in wakefulness and hypoxia the time spent in quiet sleep (QS). The state of alertness was the major determinant of HRV characterized with linear or nonlinear methods. Compared with QS, active sleep (AS) was associated with an overall increase in HRV magnitude and short-term self-similarity and a decrease in entropy of cardiac cycle length in air. This AS-related HRV pattern persisted in hypercapnia and was even more pronounced in hypoxia.

CONCLUSION

Enhancement of AS-related sympathovagal coactivation in hypoxia, together with increased heart rate regularity, may be evidence that AS + hypoxia represent a particularly vulnerable state in early life. This should be kept in mind when deciding the optimal arterial oxygenation target in newborns and when investigating the potential involvement of hypoxia in SIDS pathogenesis.

Newborn ventilatory response to maternal chronic hypercapnia

This is a case of a neonate born with a respiratory acidosis with a compensatory metabolic alkalosis. This case demonstrates placental physiology of gas exchange as well as the blunted ventilatory response in the neonate from chronic hypercapnia.

The management of the critically ill obstetric patient

Hypertensive disorders, postpartum hemorrhage, and sepsis are the most common indications for intensive care unit admission among obstetric patients. In general, ICU mortality is low, and better than would be predicted using available mortality prediction tools. Provision of care to this special population requires an intimate understanding of physiologic changes that occur during pregnancy. Clinicians must be aware of the way various diagnostic and treatment choices can affect the mother and fetus. Most clinically necessary radiographic tests can be safely performed and fall under the maternal radiation exposure limit of less than 0.05 Gray (Gy). Careful attention must be paid to acid-base status, oxygenation, and ventilation when faced with respiratory failure necessitating intubation. Cesarean delivery can be justified after 4 minutes of cardiac arrest and may improve fetal and maternal outcomes. The treatment of obstetric patients in the ICU introduces complexities and challenges that may be unfamiliar to many critical care physicians; teamwork and communication with obstetricians is crucial.