Disorders in Pregnancy

(1)

Professor of Medicine, Department of Medicine, Chief, Division of Nephrology and Hypertension, Rutgers New Jersey Medical School, Newark, NJ, USA

Keywords

Metabolic acidosisMetabolic alkalosisRespiratory alkalosisRespiratory acidosis

During pregnancy , several anatomic and physiologic changes occur in pulmonary system. Pertinent lung volume changes in pregnancy are summarized in Table 19.1.

Table 19.1

Lung volume changes in pregnancy

O₂ consumption	↑ (20%). Further increase during labor and delivery
Minute ventilation	↑ (30–50%)
Tidal volume	↑ (40–50%)
Functional residual capacity	↓ (20%)
Total lung capacity	↓ (4–5%) or no change
Vital capacity	No change
Respiratory rate	No change, but hyperventilation is common

Acid-Base Disorders

Acid-base values in the mother and fetus are important to assess fetal oxygenation and fetal well-being in utero. Respiratory alkalosis is commonly observed in pregnancy, whereas metabolic alkalosis is rather uncommon. Metabolic acidosis and respiratory acidosis are also uncommon. Let us discuss each of these disturbances in detail.

Respiratory Alkalosis

Among the four primary acid-base disorders, the most common acid-base disorder is respiratory alkalosis. As early as 1912, investigators observed hyperventilation, low pCO₂, and HCO₃ ⁻ concentrations in pregnancy. In subsequent years, similar values were reported in several studies. In these later studies, blood pH was reported to be >7.40. Based on alkaline pH, low pCO₂, and low HCO₃ ⁻, the primary acid-base disturbance was found to be respiratory alkalosis. Table 19.2 shows various arterial blood gas (ABG) values in early and late pregnancy and at high altitude. It takes at least 1 week after delivery to return these abnormal ABG values to nonpregnant values.

Table 19.2

Acid-base values in pregnancy at sea level and high altitude

Measurement	Nonpregnant	1st trimester	3rd trimester	1388 meters	4200 meters
pH	7.35–7.45 (7.40)	7.40–7.44 (7.42)	7.41–7.45 (7.43)	7.43–7.49 (7.46)	7.39–7.52 (7.43)
pO₂ (mmHg)	80–100 (90)	99–111 (105)	100–112 (106)	84–98 (91)	48–76 (61)
pCO₂ (mmHg)	35–45 (40)	27–32 (28)	23–29 (26)	24–28 (26)	14–32 (24)
HCO₃ ⁻ (mEq/L)	22–26 (24)	17–19 (18)	15–19 (17)	17–18 (18)	12–20 (16)
O₂ saturation (%)	94–100 (98)	98	98	96	90