Normal cardiopulmonary physiology during pregnancy

Physiology of normal pregnancy

The pregnant patient in the intensive care unit (ICU) poses many challenges. Physicians and nurses need to understand the basic concepts of maternal physiology and fetal physiology. The physicians must care for the mother and consider the potential adverse effects that diagnostic and therapeutic interventions might have on the fetus. This article focuses primarily on the normal pregnant state with appropriate references to how pregnancy may affect the patient in specific circumstances relating to the ICU. The physiologic adaptation of the major organs to the pregnant state should be familiar to ICU physicians.

Acute lung injury and acute respiratory distress syndrome in pregnancy

Acute respiratory failure can be the result of a variety of clinical conditions, such as congestive heart failure, pneumonia, pulmonary embolism, exacerbation of obstructive lung diseases, and acute respiratory distress syndrome (ARDS). This article focuses on developments related to acute lung injury and ARDS and reviews epidemiology, pathogenesis and therapeutic advances with an emphasis on the obstetric population. A brief discussion of tocolytic-induced pulmonary edema, preeclampsia, venous air embolism, and aspiration-related ARDS is included. Management of pregnant women with ARDS is outlined.

Pregnancy-Related Maternal Deaths

Pregnancy is a normal biologic process, but because of a variety of physiologic factors, it increases a woman's risk for death. Maternal deaths in pregnancy may be due to conditions unique to pregnancy, conditions associated with pregnancy, or conditions unrelated to but exacerbated by pregnancy. Death may occur during any trimester, during labor/birth, or postpartum. In this report, we present 45 cases of pregnancy-related maternal deaths that were investigated and autopsied at the Dallas County Medical Examiners office between 1977 and 1999, and we review the topic of pregnancy-related maternal death.

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.

Treatment of community-acquired lower respiratory tract infections during pregnancy

The incidence of lower respiratory tract infection (LRTI) in women of child-bearing age is approximately 64 per 1000 population. The spectrum of illness ranges from acute bronchitis, which is very common, through influenza virus infection and exacerbations of underlying lung disease, to pneumonia, which, fortunately is uncommon (<1.5% LRTI), but can be severe.

Acute bronchitis is generally mild, self-limiting and usually does not require antibacterial therapy. Influenza virus infection in pregnant women has been recently related to increased hospitalization for acute cardiorespiratory conditions. At present, the safety of the newer neuraminidase inhibitors for the treatment of influenza virus infection has not been established in pregnancy and they are not routinely recommended. In influenza virus infection complicated by pneumonia, antibacterial agents active against Staphylococcus aureus and Streptococcus pneumoniae superinfection should be used.

There are few data on infective complications of asthma or COPD in pregnancy. The latter is rare, as patients with COPD are usually male and aged over 45 years. Management is the same as for nonpregnant patients.

The incidence and mortality of pneumonia in pregnancy is similar to that in nonpregnant patients. Infants born to pregnant patients with pneumonia have been found to be born earlier and weigh less than controls. Risk factors for the development of pneumonia include anemia, asthma and use of antepartum corticosteroids and tocolytic agents. Based on the few available studies, the main pathogens causing pneumonia are S. pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae and viruses. β-Lactam and macrolide antibiotics therefore remain the antibiotics of choice in terms of both pathogen coverage and safety in pregnancy. In HIV-infected pregnant patients, recurrent bacterial pneumonia, but not Pneumocystis carinii pneumonia (PCP), is more common than in nonpregnant patients. Trimethoprim/sulfamethoxazole (cotrimoxazole) has not definitely been associated with adverse clinical outcomes despite theoretical risks. Currently it is still the treatment of choice in PCP, where mortality remains high.

In conclusion, there are few data specifically related to pregnant women with different types of LRTI. Where data are available, no significant differences compared with nonpregnant patients have been identified. In considering the use of any therapeutic agent or investigation in pregnant patients with LRTI, safety aspects must be carefully weighed against potential benefit. Otherwise, management strategies should not differ from those for nonpregnant patients. Further research in this area is warranted.

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.

Single-breath carbon monoxide diffusing capacity

Measurement of DL(CO) remains a clinically useful way to assess transfer of gases across the lung. It is important, however, to be vigilant in controlling the sources of variation and to be aware of those that remain when interpreting the measured values.

Pneumonia in pregnancy

Pneumonia occurs in the pregnant population with a frequency equal to that in the general population. However, its course is often more virulent, and mortality rates from certain pathogens may be high. The pregnant woman is more susceptible to injury to the respiratory tract due to a number of factors. These include alterations in the immune system which involve cell-mediated immunity and mechanical and anatomical changes involving the chest and abdominal cavities. The cumulative effect is decreased tolerance of hypoxia and acute changes in pulmonary mechanics. The spectrum of pathogens is similar to that for nonpregnant individuals, and the management of pneumonia in pregnancy does not differ in general from the nonpregnant state. However, careful attention should be paid to the fetoplacental unit with delivery generally indicated for obstetric purposes only. Issues that also need to be addressed include effects of certain infections, medications, fever, and hypoxia on the developing fetus.