Chapter 181
Respiratory System
 Minute ventilation during labor 75–150% increase in the first stage Oxygen consumption may increase by 45% Epidural anesthesia prevents changes in the first stage 150–300% increase in the second stage Oxygen consumption may increase by 75%Paco2 may fall to 10–15 mm HgSerum lactate rises Epidural anesthesia does not prevent changes in minute ventilation, oxygen consumption and serum lactate in the second stage Postpartum FRC increases after birth but remains below normal for 1–2 weeks O2 consumption, minute ventilation, and tidal volume remain elevated till at least 6–8 weeks postpartum
Cardiovascular System
 Cardiac output in labor (between uterine contractions) 10% increase in early first stage Increase in SV (HR unchanged) Epidural analgesia reduces but does not fully eliminate the increases in cardiac output 25% increase in late first stage 40% increase in second stage Systolic and diastolic blood pressures Elevated from the late first stage Progressive activation of the sympathetic nervous system during labor Labor epidural analgesia attenuates these changes Aortocaval compression (in the supine position) 20% reduction in uterine blood flow50% decrease in lower extremity blood flow About 8% of women may develop bradycardia and significant hypotension when lying supine (supine hypotensive syndrome) Uterine blood flow and uterine contractions during labor Increases to 600–900 mL/min on average (50–190 mL/min preconception) Uterine contractions augment CO and SV by an additional 15–25% (300–500 mL of blood displaced with each contraction) Compression of the aorta by the uterus increases with contractions Reduces uterine filling and increases afterload Immediate postpartum hemodynamics CVP rises and cardiac output increases up to 75% of predelivery values Relative hypervolemia and increased venous return in this period is a result of relief of caval compression and reduction of vascular capacitance, which exceeds the blood loss of labor (autotransfusion) Further postpartum hemodynamics During the first hour postpartum term, CO decreases to 30% above the prelabor value; it reaches the prelabor value about 48 h postpartumCO 10% above prepregnant value at 2 weeks, returns to baseline at 12–24 weeks postpartumHR normalizes in 2 weeksStroke volume takes much longer and is still 10% above baseline at 24 weeksLV hypertrophy regresses gradually and is still appreciable at 24 weeks
Blood Volume
 Blood volume 94 mL/kg (prepregnant value is 76 mL/kg) Average blood loss during vaginal delivery is about 600 mLAverage blood loss during Cesarean section is 1,000 mL General anesthesia using volatile anesthetics results in a somewhat larger blood loss than regional anesthesia Plasma volume 69 mL/kg (prepregnant value is 49 mL/kg) Postpartum changes Blood volume falls to 125% of prepregnant value by the end of the first postpartum week and declines to 110% at 6–9 weeksHb and hematocrit fall in the first 3 days, and then rise rapidly (plasma ...

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

## Subscription Options

### AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more