The respiratory response to pregnancy

The role of maternal hormones in regulating autonomic functions during pregnancy

Offspring development relies on numerous physiological changes that occur in a mother's body, with hormones driving many of these adaptations. Amongst these, the physiological functions controlled by the autonomic nervous system are required for the mother to survive and are adjusted to meet the demands of the growing foetus and to ensure a successful birth. The hormones oestrogen, progesterone, and lactogenic hormones rise significantly during pregnancy, suggesting they may also play a role in regulating the maternal adaptations linked to autonomic nervous system functions, including respiratory, cardiovascular, and thermoregulatory functions. Indeed, expression of pregnancy hormone receptors spans multiple brain regions known to regulate these physiological functions. This review examines how respiratory, cardiovascular, and thermoregulatory functions are controlled by these pregnancy hormones by focusing on their action on central nervous system circuits. Inadequate adaptations in these systems during pregnancy can give rise to several pregnancy complications, highlighting the importance in understanding the mechanistic underpinnings of these changes and potentially identifying ways to treat pregnancy-associated afflictions using hormones.

An update on the physiologic changes during pregnancy and their impact on drug pharmacokinetics and pharmacogenomics

For many years, the medical community has relied in clinical practice on historic data about the physiological changes that occur during pregnancy. However, some newer studies have disputed a number of assumptions in these data for not being evidence-based or derived from large prospective cohort-studies. Accurate knowledge of these physiological changes is important for three reasons: Firstly, it facilitates correct diagnosis of diseases during pregnancy; secondly, it enables us to answer questions about the effects of medication during pregnancy and the ways in which pregnancy alters pharmacokinetic and drug-effects; and thirdly, it allows for proper modeling of physiologically-based pharmacokinetic models, which are increasingly used to predict gestation-specific changes and drug-drug interactions, as well as develop new knowledge on the mode-of-action of drugs, the mechanisms underlying their interactions, and any adverse effects following drug exposure. This paper reviews new evidence regarding the physiologic changes during pregnancy in relation to existing knowledge.

Asthma in pregnancy: An update

AIM

To update obstetric care providers about asthma management.

SUMMARY

Asthma is the most frequent comorbid chronic illness in pregnancy. Convincing evidence shows that uncontrolled asthma magnifies the risk of maternal, fetal and neonate complications. Unfortunately, one in four women take no inhaler during pregnancy, and it is likely that decreased adherence, rather than changes in pathology, explains uncontrolled maternal asthma. Patient surveys reveal a need for information and reassurance. Although some molecules are preferred in pregnancy, there is currently no basis to withhold any asthma medication - old or new. Biomarkers such as blood eosinophils and fractional exhaled nitric oxide are an effective way to assess the risk of asthma attacks and the likelihood of responding to inhaled steroids. Furthermore, practice-changing trials in mild asthma show that switching reliever-only regimens to as-needed 'controller-and-reliever' therapy is effective. We suggest that applying these changes can alleviate women's concerns and improve outcomes.

Dyspnea in pregnancy

Dyspnea in pregnancy is common. It can result from adaption to body changes in pregnancy and also from complications therein. Understanding the mechanisms of change in the respiratory system during pregnancy helps with the differential diagnosis of dyspnea in normal pregnancy as opposed to pathological dyspnea.

Statement on pregnancy in pulmonary hypertension from the Pulmonary Vascular Research Institute

Pregnancy outcomes in patients with pulmonary hypertension remain poor despite advanced therapies. Although consensus guidelines recommend against pregnancy in pulmonary hypertension, it may nonetheless occasionally occur. This guideline document sought to discuss the state of knowledge of pregnancy effects on pulmonary vascular disease and to define usual practice in avoidance of pregnancy and pregnancy management. This guideline is based on systematic review of peer-reviewed, published literature identified with MEDLINE. The strength of the literature was graded, and when it was inadequate to support high-level recommendations, consensus-based recommendations were formed according to prespecified criteria. There was no literature that met standards for high-level recommendations for pregnancy management in pulmonary hypertension. We drafted 38 consensus-based recommendations on pregnancy avoidance and management. Further, we identified the current state of knowledge on the effects of sex hormones during pregnancy on the pulmonary vasculature and right heart and suggested areas for future study. There is currently limited evidence-based knowledge about both the basic molecular effects of sex hormones and pregnancy on the pulmonary vasculature and the best practices in contraception and pregnancy management in pulmonary hypertension. We have drafted 38 consensus-based recommendations to guide clinicians in these challenging topics, but further research is needed in this area to define best practices and improve patient outcomes.

Pulmonary complications in pregnancy: considerations for care

Anatomic and physiologic changes of pregnancy predispose the mother to increased morbidity and mortality whereas increasing risks of a less than optimal outcome for the fetus. The frequency and significance of acute and chronic respiratory conditions in pregnant women have increased in recent years. Clinicians must have an understanding of cardiopulmonary physiology to promptly recognize and treat pregnant women with respiratory conditions ranging from asthma to adult respiratory distress syndrome. Hospitals must establish systems to assure timely assessment, multidisciplinary care, and possibly a plan for transfer to a higher level of care to provide highest quality care to the perinatal patient presenting with a severe respiratory condition to promote optimal outcomes for the woman and the fetus.

High altitude during pregnancy

One of the greatest physiologic challenges during pregnancy is to maintain an adequate supply of oxygenated blood to the uteroplacental circulation for fetal development. This challenge is magnified under conditions of limited oxygen availability. High altitude impairs fetal growth, increases the incidence of preeclampsia, and, as a result, significantly increases the risk of perinatal and/or maternal morbidity and mortality. This review summarizes the clinical consequences and physiologic challenges that emerge when pregnancy and high altitude coincide and highlights the adaptations that serve to protect oxygenation and fetal growth under conditions of chronic hypoxia.

CO and NO pulmonary diffusing capacity during pregnancy: Safety and diagnostic potential

This paper reviews the scientific evidence for the safety of carbon monoxide (CO) and nitric oxide (NO) inhalation to measure pulmonary diffusing capacity (DL(CO) and DL(NO)) in pregnant women and their fetuses. In eight earlier studies, 650 pregnant women had DL(CO) measurements performed at various times during pregnancy, with a minimum of two to four tests per session. Both pregnant subjects that were healthy and those with medical complications were tested. No study reported adverse maternal, fetal, or neonatal outcomes from the CO inhalation in association with measuring DL(CO). Eleven pregnant women, chiefly with pulmonary hypertension, and 1105 pre-term neonates, mostly with respiratory failure, were administered various dosages of NO (5-80ppm for 4 weeks continuously in pregnant women, and 1-20ppm for 15min to 3 weeks for the neonates). NO treatment was found to be an effective therapy for pregnant women with pulmonary hypertension. In neonates with respiratory failure and pulmonary hypertension, NO therapy improved oxygenation and survival and has been associated with only minor, transient adverse effects. In conclusion, maternal carboxyhemoglobin ([Hb(CO)]) levels can safely increase to 5% per testing session when the dose-exposure limit is 0.3% CO inhalation for <or=3min, and for NO, 80ppm for <or=3min. The risk of late fetal or neonatal death from increased Hb(CO) from diffusion testing is considerably less than the risk of death from all causes reported by the Centers for Disease Control, and is therefore considered "minimal risk".

Perioperative management of the female and gravid patient

Care of female and gravid patients requires a detailed understanding of the unique issues inherent to quality treatment. Increasingly important data continue to accumulate about significant differences in the physiology of men and women and the way they express disease. Furthermore, the gravid patient requires specific alterations and considerations in clinical care that not only affect the mother but also the fetus. This article focuses on key elements that the treating surgeon should consider.

Physiological changes of pregnancy and monitoring

Advances in medical care have led to increasing numbers of complex, high-risk obstetric patients. Specialist training and a sound knowledge of normal maternal physiology are essential to optimize outcomes. One of the earliest observed changes is peripheral vasodilatation; this causes a fall in systemic vascular resistance and triggers physiological changes in the cardiovascular and renal systems, with 40-50% increases in cardiac output and glomerular filtration rates. Safety concerns over Swan Ganz catheters have driven the increasing interest in alternative techniques, such as echocardiography, thoracic bioimpedance and pulse contour analysis, although their exact roles in future obstetric high-dependency care have yet to be established. Analysis of arterial blood gases is fundamental to the management of sick patients, and correct interpretation can be aided by a systematic approach. Observation charts are almost ubiquitous in all aspects of medicine, but little evidence exists to support their use in the high-dependency setting.

Physiologic changes in pregnancy

Pregnancy is associated with physiologic changes that affect virtually every organ system in the mother. These physiologic changes allow the parturient to support the growing uterus and fetus and to withstand labor and the postpartum course. Because the gravida may require surgery while pregnant, it is important to have an appreciation of these physiologic changes. These maternal adaptive responses have significant implications for anesthetic, operative, and perioperative management.

Respiratory physiologic changes in pregnancy

In summary, the major physiologic changes that occur in pregnancy are the increased minute ventilation, which is caused by increased respiratory center sensitivity and drive; a compensated respiratory alkalosis; and a low expiratory reserve volume. The vital capacity and measures of forced expiration are well preserved. Patients who have many lung diseases tolerate pregnancy well, with the exception of those who have pulmonary hypertension or chronic respiratory insufficiency from parenchymal or neuromuscular disease.

Lung function and breathing regulation parameters during pregnancy

AIM

The aim of this study was to evaluate the changes in lung function and breathing regulation parameters measured in women who did not suffer from any respiratory system disorders (in comparison with body mass index values obtained before pregnancy) in any particular trimester of pregnancy.

METHODS

The study was carried out on 51 pregnant women aged 26.6 +/- 4.9 years and 40 healthy women (control group). Spirometry, flow-volume loop, respiratory resistance (RRS), and respiratory pattern were evaluated using computerized spirometer "Lungtest," Poland. The examinations were performed in the first, second, and third trimesters of pregnancy.

RESULTS

The statistically significant differences during pregnancy were stated in cases of tidal volume (VT) and minute ventilation (MV) (whereas breath frequency was nearly on the same level), inspiratory drive (VT/TI) and also occlusion pressure (P0.1), RRS, and peak expiratory flow (PEF). We observed a correlation between BMI at the baseline with P0.1, MV, and VT/TI.

CONCLUSIONS

We conclude that BMI at the baseline seems to predict the increase in MV, occlusion pressure, and inspiratory drive. The fact that RRS values increase during pregnancy and both forced expiratory volume (FEV1) and FEV1% forced vital capacity (FVC) values remain at the same level may reflect the effect of the autonomous nervous system on the respiratory tract.

Pulmonary complications of pregnancy

Pregnancy induces significant physiologic stresses on the pulmonary and cardiovascular systems that may precipitate respiratory compromise. In addition, certain disease states that are unique to the pregnant woman, such as amniotic fluid emboli syndrome, may be associated with respiratory failure. The physiologic changes that affect the pregnant woman are reviewed. Pregnancy-related conditions are discussed as well as how common diseases, such as the acute respiratory distress syndrome, asthma, pneumonia, and AIDS,have to be approached when balancing the needs of the fetus with maternal well-being.

Basal metabolic rate in hyperemesis gravidarum: comparison to normal pregnancy and response to treatment

OBJECTIVE

The aim of the study was to measure resting minute ventilation and oxygen consumption in patients with hyperemesis gravidarum before and after treatment and to compare the results with those of normal pregnant women.

STUDY DESIGN

Baseline evaluation was performed with the use of an open-circuit ventilatory system in 17 hospitalized patients with hyperemesis gravidarum and was repeated 1 week after treatment. Thirty-seven normal pregnant women served as control subjects.

RESULTS

Resting minute ventilation and oxygen consumption were decreased by 20% and 15% (P <.001), respectively, in patients with hyperemesis compared with control subjects. The decrease occurred despite a measurable increase of free thyroxine compared with normal pregnancy. Treatment resulted in a 10% increase in oxygen consumption in those patients with increased thyroid stimulation, but not otherwise.

CONCLUSION

Resting oxygen consumption is reduced significantly in patients with hyperemesis gravidarum that is consistent with a state of partial starvation rather than increased in parallel with increases of thyroid axis activity.

The distribution of progestin receptor mRNA in rat brainstem

Hypothalamic sites wherein P4, through progestin receptor, (Pgr; commonly abbreviated PR), maximizes the expression of female sexual behaviors and gonadotropin surge release have been studied intensively. However, little is known regarding PR expression in brainstem regions likely to regulate changes in autonomic functions observed when P4 levels are elevated (i.e. pregnancy). Using in situ hybridization, we found PR mRNA-containing cells widely distributed throughout the brainstem of ovariectomized, estradiol-treated Sprague-Dawley rats, with high expression in regions including the medial vestibular nucleus, nucleus of the solitary tract, substantia nigra (compact part), ventral tegmental area, hypoglossal nucleus, locus coeruleus, Purkinje cell layer of the cerebellum and inferior olivary complex. We also detected moderate to high levels of PR gene expression in several regions, such as the trapezoid nucleus, facial nucleus, periaqueductal gray regions, and rostral ventrolateral medulla. These results demonstrate that PR expression is widespread in the brainstem and identify nuclei wherein P4 may act to influence a number of physiological functions during pregnancy.

Anaesthesia for caesarean delivery: low-dose epidural bupivacaine plus fentanyl

To determine the acceptability of epidural bupivacaine-induced sixth thoracic (T6) sensory blockade and the analgesic efficacy of epidural fentanyl 50 microg, 24 parturients undergoing elective caesarean section were given a test dose of lidocaine 60 mg plus epinephrine followed by 10 ml of either 0.5 % bupivacaine (control group) or 0.5 % bupivacaine plus 50 microg fentanyl (fentanyl group) in a randomized double-blind manner. Fifteen minutes later loss of pinprick sensation was determined. Additional local anaesthetic was titrated to achieve T6 sensory blockade. Intraoperative pain intensity was assessed using a 10 cm visual analogue scale (VAS); total dose of bupivacaine and need for i.v. rescue fentanyl were recorded. The incidence of intraoperative respiratory depression, nausea, vomiting and pruritus were documented. Mean (+/- SD) volume of bupivacaine was 14.1 +/- 3.05 ml versus 13 +/- 1.48 ml for the control and fentanyl groups respectively. The most severe intraoperative VAS for pain was significantly (P=0.023) lower in the fentanyl group (0.4 +/- 0.08 cm) than in the control group (3.1 +/- 0.3 cm). Rescue fentanyl was administered in 40% and 0% of patients in the control and fentanyl groups respectively. The incidence of side-effects was unaffected by treatment group. Apgar scores were similar in the two groups. We conclude that following administration of 10-15 ml 0.5% bupivacaine plus fentanyl 50 microg, T6 sensory blockade is associated with good intraoperative analgesia without obvious maternal or neonatal respiratory depression.

Regulation of breathing and perception of dyspnea in healthy pregnant women

STUDY OBJECTIVE

To examine if the perception of dyspnea during normal pregnancy may be related to an inappropriate ventilatory response to the increased metabolic rate, due to a higher chemosensitivity.

PATIENTS AND INTERVENTIONS

At weeks 12, 24, and 36 of gestation and 4 months after delivery, 11 healthy pregnant women with dyspnea and 12 asymptomatic pregnant women were studied. Progesterone plasma levels, lung volumes, diffusion capacity, maximal respiratory pressures, rest oxygen uptake, breathing pattern, and mouth occlusion pressure (P0.1) were measured. Progressive isocapnic hypoxic stimulation and progressive hyperoxic hypercapnic stimulation were performed.

RESULTS

Oxygen ventilation equivalent during pregnancy was significantly higher for the dyspneic group than for nondyspneic pregnant women. Dyspneic patients exhibited greater minute ventilation, tidal volume, and P0.1 than the nondyspneic group. The mean values of ventilatory and P0.1 slopes to hypoxia and CO2 during pregnancy were significantly greater in the patients with dyspnea than in asymptomatic subjects. These changes were not due to differences in progesterone plasma levels. A significant relation among the Borg score, inspiratory drive, and chemosensitivity was found.

CONCLUSIONS

In some pregnant women, a higher sensitivity to CO2 and hypoxia may induce excessive ventilation to metabolic demand, which would contribute to dyspnea.

Epidural morphine for analgesia after caesarean section: a report of 4880 patients

This retrospective study was undertaken to assess the efficacy and safety of epidural morphine in providing analgesia following Caesarean section under epidural anaesthesia. The morphine was administered as a single bolus, following delivery, in doses ranging from 2 to 5 mg. The charts of 4880 Caesarean sections, performed on 4500 patients, were reviewed. The duration of analgesia and the occurrence of any symptoms which might be side-effects of the epidural morphine were recorded. The duration of analgesia was 22.9 +/- 10.1 hr and was not correlated with the dose of epidural morphine. Eleven per cent of the patients required no supplemental analgesia during the first 48 hr. Twelve patients (0.25 per cent) had respiratory rates less than 10 breaths per minute, on at least one occasion. No serious sequelae resulted from these periods of bradypnoea. Pruritus occurred in 58 per cent of patients, nausea and vomiting in 39.9 per cent and dizziness in ten per cent. Herpes simplex labialis was recorded in 3.5 per cent of patients. Epidural morphine is thus confirmed as an effective analgesic technique post-Caesarean section with 3 mg being the optimal dose. Even in this young healthy patient population, clinically detectable respiratory depression occurs so clinical respiratory monitoring is indicated.

Use of oral contraceptives in women with cystic fibrosis

Oral contraceptive pills (OCP) represent the most common contraceptive method among teenagers and young adults. Because many women with cystic fibrosis (CF) are now surviving into childbearing age and are at risk for the complications of pregnancy in CF, oral contraceptive use may be indicated. However, it has been suggested that OCP use by CF patients may be associated with deterioration in pulmonary function. Ten adolescent and young adult women with CF and moderate-to-severe obstructive lung disease were studied while taking a combination oral contraceptive pill (Ovral 28). No significant deterioration was found in clinical status or pulmonary function. Careful follow-up should nevertheless be continued to monitor for other adverse effects of oral contraceptive use in CF, such as cholelithiasis.

Changes of ventilation and ventilatory response to hypoxia during the menstrual cycle

The relationship between change in hypoxic sensitivity in respiration, defined as increment in ventilation per drop of arterial O2 saturation (delta VE/delta SaO2), with the phase change from follicular to luteal and those in resting pulmonary ventilation (VE), mean inspiratory flow (VT/TI), alveolar partial pressures of CO2 and O2 (PACO2 and PAO2, respectively) and body temperature was studied in 10 women. There was a significant relationship between % increase in hypoxic sensitivity and decrement of resting PACO2 that occurred in the luteal phase. However, no significant relationships were observed between change in hypoxic sensitivity and those in the remaining parameters studied. The intersubject variation in % increase in resting VE during the luteal phase was not associated with that in % increase in hypoxic sensitivity. The results indicate that the contribution of increased hypoxic sensitivity to increasing VE during the luteal phase is variable among subjects. Reasons for the increase in hypoxic sensitivity with hypocapnia are discussed.