Physiologic changes in pregnancy Nikolai Kolotiniuk, PGY-2

Cardiovascular System CO increases 30-50%, with half occurring in the first 8wks

Increase in preload (BV) increase SV and Increase HR (15-20bpm)Reduced afterload (decrease in SVR) 1st-2nd trimester - ?decreased responsiveness to vasopressin and NE (also ?increase NO, PGI2)

Dependence on sympathetic system for HD stability increases progressively throughout pregnancy, reaching peak at term pharmacologic sympathectomy could significantly drop BPs

Respiratory System Mechanical - thoracic cage circumference enlarges by 5-7cm. (relaxation of ligamentous

attachment) Inspiration – almost total attributable to diaphragmatic excursion (chest wall already

expanded, diaphragm sits higher) FRC – decrease by 20% 2/2 upward movement in diaphragm, decrease in RV, ERV. TV

goes up by 45%. Dead space up by 45% Rightward shift of oxyhemoglobin curve (P50 = 30 mmHg) Capillary engorgement in larynx/NP/OP --> increased risk for epistaxis O2 consumption increases by almost 20% to meet metabolic demands. CO2 production

increases by 30% to 300ml/mino O2 consumption continues to increase throughout pregnancy and CO increases to a

lesser extent ==> decreased mixed venous O2 Minute ventilation (50%)

o Progesterone increases sensitivity of resp center to CO2 +/- direct stim of respiratory center, normally would cause resp. alkalosis but renal excretion of bicarbonate is in pregnant

TV (40%) & RR (10-15%) Chronic Resp alkalosis: PCO2 40-->27-32…?helps the fetus to eliminate CO2. Renal

compensation by HCO3 excretion Hypoxic ventilator response doubles despite an already present alkalosis in CSF/blood Rate of uptake & elimination of inhaled anesthetics due to MV & FRC

Hematology Rightward shift in oxygen-Hgb dissociation curve + 2,3 DPG (favor offloading of O2 at

tissues) Plasma volume increases by 50% by 34 weeks (starts at 6wks), RBC volume up by 30%

(physiologic anemia) Estrogens --> stimulate RAAS --> NaCl/H2O retention Reduction of PT/PTT by 20%, increased resistance to aPC, decrease Prot S, increase in F I, II,

V, VII, VII, X, XII. Decrease in antithrombin III. Enhanced platelet turnover. Increase in PF-4 and B-thromboglobulin signal elevated

platelet activation, and the progressive increase in platelet distribution width and platelet volume are consistent with greater platelet consumption during pregnancy. Platelet aggregation is increased in response to collagen, epi, ADP, arachidonic acid. Bleeding time not altered

Leukocytosis with bandemia, PMN function is depressed however --> increase incidence of infections and lower incidence of Sx in patients with autoimmune diseases

GI GERD --> stomach pushed up, rotated 45 degrees to the right, LES relaxes

Physiologic changes in pregnancy Nikolai Kolotiniuk, PGY-2

Constipation 2/2 decreased peristalsis and intestinal transit Biliary stasis,higher cholesterol content in bile secretion, hypomotility increased

gallbladder dz

Renal/Endocrine GFR increases 50%

o avg proteinuria ~ 200mg Thyroid follicular hyperplasia (increase by 50-70%), estrogen raises TBGincrease total

T3/T4 by 50% Exaggerated starvation ketosis, insulin resistant Increase in corticosteroid binding globulin by 100% by 2nd trimester to 200% by third

trimester Neuro

MAC , (50% at term) sensitivity to local anesthetics