maternal physiology Flashcards
maternal total body water, plasma volume, RBC volume
Increase in TBW from 6.5 to 8.5 L = 2 kg. Expanded plasma volume by 1.2 – 1.3 liters (50%). Expanded RBC volume 0.3 – 0.4 liters (30%). Additional extravascular fluid & intracellular fluid in uterus and breasts. Chronic volume overload with active sodium & water retention
What conditions does increased maternal body water predispose to
Increased TBW can cause weight gain, hemodilution, anemia of pregnancy, elevated cardiac output. Impaired volume expansion has been linked to increased risk of preeclampsia, and impaired fetal growth
maternal changes in osmoregulation
From 10 weeks to 2 weeks postpartum: Placental release of NO and relaxin alters AVP secretion (but plasma AVP is unchanged due to placental inactivation by vasopressinase). Water and sodium retention occurs (water > sodium), plasma osmolality decreases.
Maternal renin-angiotensin-aldosterone system
Marked increases in all components of RAAS. Early pregnancy changes cause decreased MAP which triggers activation of renin-angiotensin (4-5X) and aldosterone (2X). Sodium retention occurs. Deoxycorticosterone and estrogen may contribute to increased tubular Na retention.
Maternal Potassium levels
Potassium is increased, but nost is stored in placenta and fetus. The kidney’s ability to conserve potassium has been attributed to increased progesterone levels.
Maternal ANP/ BNP
Myocardium releases these neuropeptides that maintain vascular hemostasis. ANP/BNP elevated in both physiologic and path states of volume overload; ANP most likely increases but remain within normal range. BNP increases mostly in 3rd trim; highest in pregnancies complicated by preeclampsia but to levels less than used to screen for CHF, so BNP can still be used to screen for CHF in pregnancy.
What causes increased intracellular volume in pregnancy
is increased levels of progesterone which lead to decreased smooth muscle tone and increased volume capacity
maternal BP
•Progressively decreases until 22-24 weeks; returns to baseline at 36 weeks. Diastolic is affected more than systolic. This is due to decreased systemic vascular resistance (progesterone effect on smooth muscle and increased Nitric oxide production)
How to measure maternal BP
take sitting using Korotkoff 5 , when diastolic sound disappears, not Korotkoff 4, when it becomes muffled.
maternal cardiovascular adaptations
- Cardiac output increases 40%: Mainly an increase in stroke volume. HR increases (3rd trimester). 2. Vascular resistance drops (Second trimester): BP > 140/90 mm Hg represents hypertension in pregnancy. Cardiac output is greatest in left lateral position. Uterus compresses the vena cava—avoid supine positioning > 20 weeks.
Changes to the maternal heart
Hypertrophy of ventricular muscle, Increase in preload (end diastolic volume) due to increased venous return, Decrease in afterload due to decreased vascular resistance, increased cardiac compliance, increased myocardial contractility
maternal cardiac output
Increased due to increased HR and stroke volume. Affected by position: Greatest in left lateral position and knee chest position, Uterus compresses the vena cava so lying supine can cause dizziness, nausea, syncope. CO lowest in supine/standing position
Changes in perfusion
No change to brain or liver, but 50% increase in renal perfusion and increased perfusion of breasts, skin, uterus
complications of increased venous presure
Increases in venous pressure & pressure on vena cava contribute to edema, varicose veins, hemorrhoids & increased risk for DVT
maternal cardiac exam
Snus rhythm, BPM < 100, PMI displaced to left, systolic ejection murmur along left sternal border in most (due to increased flow across pulmonary and aortic valves), split S1 (less so with S2), S3 common in third trimester (rapid diastolic filling). S4 rare.
maternal CXR
the apex is displaced laterally and increases in the pulmonary vasculature. Left heart border more straight. Heart more horizontal.
Maternal EKG
mild left axis deviation and nonspecific ST and T wave changes. Small Q wave and negative P wave in lead III. premature atrial and premature ventricular contractions may occur. Almost all women have an arrhythmia during labor.
List the maternal changes in HR, CO, SVR, CVP, PCWP, PAP and MAP
HR increases (20%), CO increases (1.5-2L), SVR decreases, CVP decreases, PCWP unchanged, PAP decreases, MAP decreases
Cardiac output during labor
Increases (most during second stage), highest right after delivery. This is due to Pain: increased sympathetic stimulation. Uterine autotransfusion: 300-500 cc of blood is forced from the uterus into the systemic circulation during each contraction.
physiology of 2nd stage of labor (cardio effects)
Straining phase: increased intrathoracic pressure causes decreased venous return to heart. This combined with elevated SVR causes a transiet reflex bradycardia and decreased CO. Sympathetic discharge causes increased HR and contractility, maintaining cardiac output
Physiology of relaxation phase of valsalva
decreased intrathoracic pressure > rapid increase in preload > increased MAP > reflex bradycardia
postpartum cardiovascular changes
- Acute increase in CO for first hour- Decreased venocaval obstruction, Autotransfusion from uterine circulation, Mobilization of extravascular fluid. 2. Acute loss of up to 500 (vaginal) or 1000 cc (C section) blood with normal delivery. 3. Changes return to prepregnant baseline over a period of wks-mos
