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12: Anesthesia for Surgery During Pregnancy

Yaakov Beilin

INTRODUCTION

The incidence of surgery during pregnancy is between 0.3% and 2.0%.1,2 There are approximately 4,000,000 deliveries per year in the United States; this translates to approximately 80,000 anesthetics per year administered to pregnant women for intercurrent surgical procedures. In actuality, this may be an underestimate due to surgery performed prior to clinical recognition of the pregnancy. Surgery may be required at any time during pregnancy, and appendectomy is the most frequently performed nonobstetric operation.3

Anesthesia for the pregnant woman is one of the rare situations where the anesthesiologist contends with two patients—the mother and the unborn fetus. Therefore, providing a safe anesthetic requires an understanding of the physiologic changes of pregnancy and the impact of anesthesia and surgery on the developing fetus.

PHYSIOLOGIC CHANGES OF PREGNANCY

The pregnant woman undergoes significant physiologic changes to allow adaptation for the developing fetus. These changes are discussed in Chapter 1 and summarized in Table 12-1.

Table 12-1.Physiologic Changes of Pregnancy
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Table 12-1.Physiologic Changes of Pregnancy
Organ System Nature of Change
Respiratory
 Minute ventilation Increases by 50%
 Tidal volume Increases by 40%
 Respiratory rate Increases by 10%
 Oxygen consumption Increases by 20%
 PaO2 Increases by 10 mm Hg
 Dead space No change
 Alveolar ventilation Increases by 70%
 PaCO2 Decreases by 10 mm Hg
 Arterial pH No change
 Serum HCO3– Decreases by 4 mEq/L
 Functional residual capacity Decreases by 20%
 Expiratory reserve volume Decreases by 20%
 Residual volume Decreases by 20%
 Vital capacity No change
Cardiovascular
 Cardiac output Increases by 30%-40%
 Heart rate Increases by 15%
 Stroke volume Increases by 30%
 Total peripheral resistance Decreases by 15%
 Femoral venous pressure Increases by 15%
 Central venous pressure No change
 Systolic blood pressure Decreases by 0%-15%
 Diastolic blood pressure Decreases by 10%-20%
 Intravascular volume Increases by 35%
 Plasma volume Increases by 45%
 Red blood cell volume Increases by 20%
Gastrointestinal
 Motility Decreases
 Stomach position More cephalad and horizontal
 Transaminases Increases
 Alkaline phosphatase Increases
 Pseudocholinesterase Decreases by 20%
Hematologic
 Hemoglobin Decreases
 Coagulation factors Increases
 Platelet count Decreases by 20%
 Lymphocyte function Decreases
Renal
 Renal blood flow Increases
 Glomerular filtration rate Increases
 Serum creatinine and blood urea nitrogen Decreases
 Creatinine clearance Increases
 Glucosuria 1-10 g/d
 Proteinuria 300 mg/d
Nervous system
 Minimum alveolar concentration Decreases by 40%
 Endorphin levels Increases

FETAL CONSIDERATIONS

Drug Teratogenicity

A teratogen is a substance that produces an increase in the incidence of a defect that cannot be attributed to chance. To produce a defect, the teratogen must be administered in a sufficient dose at a critical point in development. In humans, this critical point is during organogenesis, which extends from 15 to approximately 60 days gestational age. Each organ system has its own unique period of susceptibility depending on ...

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