Large airways function during normal pregnancy

[Management of asthma during pregnancy]

Asthma is the most common chronic condition in pregnant women. The risks of complications associated with asthma for the mother, the foetus and the pregnancy are mainly due to uncontrolled asthma and the occurrence of exacerbations. These events are promoted by the patient's difficulty in complying with treatment or by prescription insufficiency for an unjustified fear of teratogenicity. The challenge of the management of asthma during pregnancy is to ensure optimal maternal asthma control in order to prevent foetal hypoxia and thus, reduce the risk of complications. Preventing the occurrence of asthma symptoms and exacerbations, ensuring optimal lung function and managing the risk factors of poor asthma outcomes and comorbidities are the principles necessary to achieve this goal. Because of the low or non-existent risks of the main treatments of asthma for the foetus and the mother, it is widely recommended that all therapies initiated before conception are continued, in particular inhaled corticosteroids, and to adjust the dosage to the minimum effective dose. During the preconception period and throughout pregnancy, coordination of the different healthcare professionals (general practitioner, respiratory specialist and gynecologist) is essential, with the mother-to-be playing a central role in the management of her asthma.

Application of Noninvasive Ventilation in the ObstetricalPatient

Acute respiratory failure in pregnancy is considered a common indication for ICU admissions in the obstetrical population. NIV (i.e., NIPPV and HFNC), although controversial, have been shown to be safe and effective in the treatment of acute respiratory failure and can help prevent invasive mechanical ventilation during pregnancy in a variety of scenarios. However, evidence is limited with mainly case reports and case series reported in the literature, NIV modalities have similar indications and contraindications in the pregnant patient as the general population.

Methodology:

Case reports, prospective RCTs, and meta-analysis involving adult patients with the application of NIPPV as a support strategy for obstetric patients with acute respiratory failure were reviewed. To increase the sensitivity of the search, a combination of terms was utilized such as “high flow nasal canula” with “noninvasive ventilation” and “pregnancy” or “obstetrics” and “acute respiratory failure” or “Acute hypoxic respiratory failure” or “Acute hypercapnic respiratory failure” as keywords. Three electronic databases were searched (Google Scholar, PubMed, and Cochrane Library) from 2017 to 2019. Abstracts and full text publications were screened to fit the search criteria.

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.

Asthma in pregnancy: Physiology, diagnosis, and management

Asthma is a common, potentially serious, medical condition that affects an estimated 8% of pregnant patients, with 4% of all pregnant patients experiencing an exacerbation in the past year. Practitioners must be able to diagnose, educate, and treat such patients as they undergo significant physiological and immunologic change. But staying current can be challenging given over 3000 citations for "asthma and pregnancy" in a recent PubMed search, with 750 described as review articles. Patients have even more difficulty navigating information, with 29 million Google search results for this same query and 1.2 million alone for the question whether asthma medications are safe during pregnancy. This review provides brief answers to important management questions followed by supporting background literature.

Alterations in physiology and anatomy during pregnancy

Pregnant women undergo profound anatomical and physiological changes so that they can cope with the increased physical and metabolic demands of their pregnancies. The cardiovascular, respiratory, haematological, renal, gastrointestinal and endocrine systems all undergo important physiological alterations and adaptations needed to allow development of the fetus and to allow the mother and fetus to survive the demands of childbirth. Such alterations in anatomy and physiology may cause difficulties in interpreting signs, symptoms, and biochemical investigations, making the clinical assessment of a pregnant woman inevitably confusing but challenging. Understanding these changes is important for every practicing obstetrician, as the pathological deviations from the normal physiological alterations may not be clear-cut until an adverse outcome has resulted. Only with a sound knowledge of the physiology and anatomy changes can the care of an obstetric parturient be safely optimized for a better maternal and fetal outcome.

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.

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.

Chemical and mechanical adaptations of the respiratory system at rest and during exercise in human pregnancy

Human pregnancy is characterized by significant increases in ventilatory drive both at rest and during exercise. The increased ventilation and attendant hypocapnia of pregnancy has been attributed primarily to the stimulatory effects of female sex hormones (progesterone and estrogen) on central and peripheral chemoreflex drives to breathe. However, recent research from our laboratory suggests that hormone-mediated increases in neural (or non-chemoreflex) drives to breathe may contribute importantly to the hyperventilation of pregnancy. This review challenges traditional views of ventilatory control, and outlines an alternative hypothesis of the control of breathing during human pregnancy that is currently being tested in our laboratory. Conventional wisdom suggests that pregnancy-induced increases in central respiratory motor output command in combination with progressive thoraco–abdominal distortion may compromise the normal mechanical response of the respiratory system to exercise, increase the perception of exertional breathlessness, and curtail aerobic exercise performance in otherwise healthy pregnant women. The majority of available evidence suggests, however, that neither pregnancy nor advancing gestation are associated with reduced aerobic working capacity or increased breathlessness at any given work rate or ventilation during exhaustive weight-supported exercise.

Effects of human pregnancy and advancing gestation on respiratory discomfort during exercise

This study examined the effects of human pregnancy and advancing gestation on the intensity of respiratory discomfort (dyspnea) during cycle exercise. Fourteen pregnant women (PG) performed a progressive cycle ergometer exercise test involving 20 W/min increases in work rate to symptom limitation and/or a heart rate of 170-175 beats/min at 19.7+/-1.2 weeks (ENTRY), 28.2+/-0.3 weeks (TM2) and 36.3+/-0.3 weeks (TM3) gestation. Eight, age-matched, sedentary non-pregnant women (CG) were also studied for comparison purposes. Measurements included dyspnea intensity (Borg scale), minute ventilation (VE), breathing pattern and other cardiorespiratory parameters. At peak exercise, neither pregnancy nor advancing gestation had an effect on dyspnea, VE, breathing pattern, oxygen uptake or work rate (p>0.05). VE was significantly greater (by 11 L/min at 100 W) in the PG at TM3 versus CG (p<0.05) at all submaximal work rates. VE also increased progressively from ENTRY to TM2 and TM3 during submaximal exercise. Dyspnea was not significantly different at any submaximal work rate in the PG at TM3 versus CG or with advancing gestation in the PG. In addition, dyspnea at a standardized exercise VE of 40 L/min was not different at TM3 versus ENTRY or in the PG at TM3 versus CG. Neither pregnancy nor advancing gestation were associated with increased respiratory discomfort during strenuous non-weight bearing cycle ergometer exercise, despite substantial increases in VE and progressive mechanical adaptations of the respiratory system to accommodate the increasing size of the gravid uterus.

Effect of the oestral cycle on respiratory mechanics in the rat

AIM

To assess the effect of the oestral cycle on the respiratory mechanics of the rat.

METHODS

We measured the main mechanical respiratory parameters, namely respiratory system and lung resistances and compliances, by the end-inflation occlusion method on two populations of female rats, during proestrous-oestrous and metaoestrous-diestrous phases.

RESULTS

Inflation-deflation loops of the lungs were found to be statistically higher in rats during metaoestrous-diestrous phase. No other statistically significant difference was found in the measured mechanical respiratory parameters.

CONCLUSION

Our results suggest that the naturally occurring fluctuations in serum sexual hormone levels during the sexual cycle influence the lung's hysteresis but do not influence the respiratory system and lung resistances or static compliances. A possible effect of female sexual hormones on surfactant activity is also suggested.

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.

Cardiopulmonary complications of pregnancy

OBJECTIVES

To provide an up-to-date review of the literature on the assessment and management of pulmonary and cardiac conditions that may affect women during pregnancy and the postpartum period.

DESIGN

A review of the current literature was performed.

RESULTS

Pregnancy may be complicated by a variety of pregnancy-specific and other cardiopulmonary complications. Management requires knowledge of the cardiopulmonary physiologic changes occurring in pregnancy, the pregnancy-specific conditions that may occur, and the effect of a fetus on maternal care.

CONCLUSIONS

Admission of the pregnant or postpartum woman to the intensive care unit is uncommon but may require specialized knowledge for successful management.

Pulmonary functions in pre-eclamptic women

OBJECTIVE

The purpose of this study was to evaluate certain pulmonary function tests of the pre-eclamptic women in the early postpartum period.

STUDY DESIGN

Forced vital capacity (FVC), forced expiratory volume in 1s (FEV(1)) and peak expiratory flow (PEF) were measured in 13 pre-eclamptic and 15 control subjects undergoing cesarean section (C/S); and 11 pre-eclamptic and 15 control subjects undergoing vaginal delivery (VD) on the postpartum third day.

RESULTS

Pre-eclamptic women had significantly lower FVC, FEV(1) and PEF measurements than the control women (P<0.05). When the subjects were grouped according to the mode of delivery, FVC and FEV(1) values were observed to be significantly different between the pre-eclamptic and control groups undergoing C/S (P<0.05). None of these parameters were significantly different between the pre-eclamptic and control groups who had delivered vaginally (P>0.05).

CONCLUSION

These data indicate that certain pulmonary functions might be impaired in the early postpartum period in pre-eclamptic women undergoing C/S.

Pulmonary function testing in obesity, pregnancy, and extremes of body habitus

Knowing the effect body habitus can have on pulmonary function is important when there is a concern of an underlying respiratory impairment. The pattern of PFT abnormaLities can help distinguish an underlying ventilatory defect as deriving from the body habitus or from a second process. There are limitations, however. Individuals who are obese and have the same weight will likely have different degrees of impairment, for instance. It then becomes difficult to predict the effect body habitus will have in each patient. It therefore is vitally important to evaluate these patients using other clinical data to decide whether the ventilatory defect can be explained by body habitus alone. It also should be noted that some of the more subtle physiologic changes that occur in these conditions are still not fully understood. Hopefully, further insight into these changes can be obtained with further investigation. Certainly, better predictors of the impact of the patient's weight, abdominal girth, and other anthropomorphic data on PFT results would be extremely helpful in the evaluation of these individuals.

Asthma in pregnancy

Contemporary management of the pregnant asthmatic is directed at controlling symptoms and treating the underlying cause of asthma, namely, inflammation. This article discusses the pathophysiology of asthma and the effects of asthma on pregnancy and vice versa and reviews the National Asthma Education Program guidelines for the treatment of asthma in pregnancy.

Pneumonia in pregnancy

Although the advent of broad-spectrum antibiotics has markedly improved the maternal outcomes of pneumonia complicating pregnancy, pneumonia remains a significant condition that may complicate pregnancy. This article has reviewed the inherent physiologic respiratory changes that accompany pregnancy and the common causes of pneumonia in the pregnant woman. The clinical course of bacterial pneumonia seems to be minimally altered by pregnancy, whereas viral pneumonia carries a significantly worse prognosis when encountered during gestation. Prompt diagnosis, the initiation of respiratory support, and appropriate antimicrobial/antiviral therapy are key components of therapy for women in whom pregnancy is complicated by pneumonia. Because preterm labor frequently accompanies pneumonia, women should be monitored closely for the occult onset of preterm labor and appropriate interventions initiated if indicated. Perhaps even more important than interventions to treat acute pneumonia are efforts directed at active immunization or prophylactic therapy to prevent the development of pneumonia in select patient populations. The combination of these efforts is essential to optimize medical care for pregnant women.

Effect of cigarette smoking on maternal airway function during pregnancy

The effects of cigarette smoking on maternal airway function during pregnancy were investigated in a cross-sectional study of 97 smokers and 175 nonsmokers at different gestational ages. The groups were comparable in age, height, and weight. All subjects were healthy. Forced vital capacity, forced expiratory volume in 1 second, their ratio, the forced expiratory flow rates between 0.2 and 1.2 L, 25% and 75%, and 75% and 85%, and instantaneous flows at lung volumes of 25%, 50%, and 75% were measured. All spirometric tests were unaffected by gestational age. However, all parameters of spirometry were significantly less in smokers than in nonsmokers when cumulative data during pregnancy were compared. Forced vital capacity, forced expiratory volume in 1 second, and their ratio were minimally reduced (4%, p less than 0.05; 8%, p less than 0.001; and 4%, p less than 0.001; respectively) in smokers as compared with nonsmokers. Larger reductions were noted in forced expiratory flow rates between 0.2 and 1.2 L (14%, p less than 0.001) and between 25% and 75% (16%, p less than 0.001), and in instantaneous maximum flows at lung volumes of 75% (11%, p less than 0.001) and 50% (13%, p less than 0.001). Maximum reduction of forced expiratory flow rates between 75% and 85% (26%, p less than 0.001) and in instantaneous flows at maximum lung volumes of 25% (23%, p less than 0.001) suggests marked increases in small-airway resistance and early small-airway disease in smokers. The progression of small-airway disease is related to the level of cigarette exposure. The results of our study demonstrate that the bronchodilatory effect expected in pregnancy is not sufficient to overcome the deleterious effects of cigarette smoking.

The respiratory response to pregnancy

The respiratory response to pregnancy appears to be largely mediated by the action of progesterone and, perhaps to a lesser extent, oestrogens, at least in the first and second trimesters. The mechanical effects of the gravid uterus cause relatively little change in pulmonary mechanics, although finer changes in airways function require further investigation. Dyspnoea during pregnancy is also probably hormone-mediated but the exact temporal relationship between hormone status, functional change and the development of symptoms is not yet clearly defined.

Respiratory disease in pregnancy

Respiratory disorders seem to be better tolerated during pregnancy than disorders of the cardiovascular system. Pregnancy seems to have a variable effect on bronchial asthma although respiratory function in general shows little change. Similarly patients with bronchiectasis do not tend to show functional deterioration. Fetal growth, however, may be adversely affected in these conditions if arterial hypoxaemia is present. The problems of drug treatment of respiratory disorders in pregnancy, particularly asthma and tuberculosis, are discussed.

Dyspnoea during normal pregnancy

The incidence, severity and time-course of dyspnoea were assessed in 62 women on eight occasions throughout a normal pregnancy. Fifteen per cent of subjects noticed an increase in dyspnoea in the first trimester compared with the nonpregnant state and in almost half of them dyspnoea was experienced before 19 weeks gestation; 76% complained of this symptom by 31 weeks gestation. After this time, few subjects noticed any increase in their symptoms.

Pregnancy in patients with bronchiectasis

Pulmonary function was monitored at regular intervals throughout pregnancy in three patients with bronchiectasis. They tolerated pregnancy well, and the underlying lung disease did not appear to have any adverse effect on the outcome of the pregnancy.