OPERATIVE OBSTETRICSANESTHESIA ppsx

ANESTHESIA*

Anesthesia management is markedly influenced by pregnancy.

Pregnancy-induced physiologic alterations may be compounded by

labor, pregnancy-associated conditions (e.g., pregnancy-induced

hypertension), or intercurrent disease states of the mother or fetus

(e.g., heart disease, pulmonary hypertension, diabetes, or isoimmu￾nization). The pregnancy alterations most influencing anesthesia

are those of the cardiovascular, pulmonary, and gastrointestinal

systems.

At term, cardiac output is increased by 30%–40% above non￾pregnant levels in the absence of aortocaval compression. Increased

cardiac output speeds the onset of inhalation anesthetics. Uterine

involution leads to an autotransfusion of
500 mL. Thus, there is

potential for fluid overload with volume loading.

Parturients have a diminished functional residual capacity de￾spite increased total lung capacity, increased oxygen consumption,

and diminished oxygen saturation. Little apnea may produce sig￾nificant hypoxia. Therefore, supplemental O2 is recommended with

either regional or general anesthesia. There is a decrease in physi￾ologic dead space and a decreased gradient between arterial and

end-tidal CO2 tensions. Thus, with general anesthesia, the end-tidal

CO2 levels should be maintained several torr higher than in the non￾pregnant patient.

Term parturients have increased intragastric volumes, decreased

gastric pH, accentuated intragastric pressure, and delay in gastric

emptying. Thus, there is enhanced risk of gastric aspiration. Aspi￾ration of gastric contents may cause maternal death.

16

OPERATIVE OBSTETRICS

CHAPTER

483

*

Modified from M.L. Pernoll and J. Mandel, Cesarean section. In: J.S.

McDonald, ed. Bonica’s Text of Obstetrical Anesthesia. 1994.

483

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BENSON & PERNOLL’S

484 HANDBOOK OF OBSTETRICS AND GYNECOLOGY

PREOPERATIVE PREPARATION

LABORATORY DETERMINATIONS

For the normal patient undergoing anesthesia, determination of Hct

or Hgb is necessary, but a differential count contributes little to

management. The history and physical examination are generally

sufficient predictors of derangements of electrolytes and the coag￾ulation profile. In the majority of patients, a preoperative ECG is

unnecessary, and although chest x-ray carries little fetal risk, it

should be obtained only if the history and physical examination

suggest its necessity.

The population of patients requiring cesarean section includes

a higher proportion of high-risk pregnancies than those delivered

vaginally. For operative patients, individualized studies are re￾quired. For example, diabetic women will need a serum glucose de￾termination. Preeclamptic women may exhibit coagulation defects

in the coagulation cascade and platelet function, and assessment

may require the usual platelet count, fibrinogen, prothrombin, and

partial thromboplastin times as well as more specialized testing.

For the anticipated cesarean section patient, blood is usually

typed for ABO/Rh and screened for unexpected significant anti￾bodies. Patients who have active bleeding (e.g., placenta previa or

abruptio placentae), preeclampsia, overdistention of the uterus, co￾agulopathy, or prolonged labor or who required oxytocin stimula￾tion are at risk of hemorrhage and should have at least 2 units of

packed red cells available. In response to concerns about HIV, many

obstetricians advise gravidas to have 1–2 units of blood drawn dur￾ing pregnancy, usually in the late second or early third trimester and

stored for autotransfusion if necessary.

FASTING

The practice of maintaining patients NPO past midnight before

elective cesarean section or major anesthesia should lower in￾tragastric volume and raise pH, thus reducing the risk of gastric

aspiration.

INTRAVENOUS HYDRATION

Fasting, emesis, or insensible loss may directly diminish intravas￾cular volume, aortocaval compression may cause inadequate venous

return in parturients, and complications (e.g., toxemia and hemor￾rhage) may be present. Therefore, volume repletion is an important