PHYSIOLOGICAL CHANGES IN PREGNANCY

CVS CHANGES
Intravascular volume increases by 35% (about 1000ml) – plasma volume 45%, RBC – 20%. So relative anaemia of pregnancy occurs
Anaemia – Hb < 11 gm/dl, PCV < 33% Blood loss up to 1500 ml need no blood transfusion.
Plasma protein decreases to 5 gm/dl due to dilution and decreased colloid oncotic pressure.

Cardiac output – increases by 40%. Stroke volume 30% and heart rate 15%. Maximum CO at the 32nd week. (Due to steroids). Cardiac output increases by 15% during latent phase, 30% during active phase, 45% during expulsive phase, Post partum – 60% increase of cardiac output

Peripheral circulation -SVR  decreases. Diastolic BP decreases by 15%.
supine hypotension syndrome: on supine position bp decreases by 10 % leading to nausea vomiting and vomiting and changes in cerebration due to compression of IVC by the uterus leading to decreased venous return and decreased CO and decreased BP. Compensated by collateral supply via azygous and paravertebral veins. Increased sympathetic nerve activity leads to increased SVR and increased BP. Aortic compression also occurs which leads to decreased lower blood flow and decreased uterine blood flow and foetal compromise. Treatment is given if systolic BP less than 100 or with Bradycardia with 20 – 30% decreased. Treatment – left lateral position, fluids, wedge, and ephedrine.
RESPIRATORY SYSTEM
Upper airway – oedema, capillary engorgement of the mucosal lining, difficult intubation, small sized tube, increased bleeding.

Minute ventilation – increased by 50%, of that 40% by tidal volume due to progesterone, less by respiratory rate. Due to increased minute ventilation PaCO2 decreases from 40 to 30mm of Hg. PaO2 increases. PH is normal. PaCO2 compensated by decrease in HCO3 from 26 to 22 meq/l. 4 meq/L by renal excretion of sodium HCO3.

Lung volume – decreased ERV plus RV. So decreased FRC. 20% decrease. Other volumes normal. So with increased minute ventilation and decreased FRC, the change in alveolar concentration of anaesthetics occur very fast and so decreased dose is required and fast onset is seen. So make the parturient susceptible to overdose.

Arterial oxygenation – PaO2 falls very fast with apnoea. Decreased FRC and 20% increase in O2 consumption. So pre oxygenation for 6 minutes is given. This also increases umbilical vein O2 concentration. Also contributors are aorto caval compression plus early closure of small arteries leading to V/Q mismatch. So O2 supplemented with all regional anaesthesia technique used.

CNS
-Engorgement of epidural veins (due to IVC compression plus collateral by paravertebral plexus) leads to decreased epidural space. Compress CSF in subarachnoid space – pumping effect by the epidural veins more spread to upper levels.

- Exaggerated lordosis

- High pressure in epidural space

RENAL
renal blod flow is increased gfr increased by 50%
renal glycosuria
proteinuria 300 mg/day
Increased SGOT, LDH, alkaline phosphatase and Cholesterol
decreased total protein and albumin
cholinesterase activity is reduced  but usually immaterial due to large volume of distriubution
GIT
abolition of go angle due to upward displacement of stomach, so the punch coch effect
lost, increased chance of aspiration 
Delayed gastric emptying
COAGULATION SYSTEM
Hypercoagulable state with increased clotting factors mainly VII, VIII, X and fibrinogen

METABOLISM
   BMR – decrease in 3rd and 4th month. Increase by term. 5-40%.Insulinase produced by plasma also cause degradation of insulin. HPL antagonizes insulin at periphery and also increase FFA So in pregnancy a diabetogenic state exists.
Increased FFA, increased cholesterol, increased phospholipids,Increased FFA as in accelerated starvation state could lead to ketonemia, ketonuria in presence of diabetes
Protein content increase with pregnancy (500gm – foetus, 500gm – uterus.) Haemodilution will lead to decrease in albumin concentration. A:G ratio reversed.
ACID BASE
Increase minute ventilation leads to decreased PaCO2 from 40 to 30 mm of Hg (Respiratory alkalosis) and is compensated by increased sodium bicarbonate excretion and decreasee bicarbonate from 26 to 22 meq/l. so this causes shift of ODC to left and decreased release of oxygen. But increased pH leads to increased 2,3 DPG release and shift of ODC to right and increased release of O2. PaCO2 is decreased so that release of CO2 from foetus occurs.
ENDOCRINE
Pituitary – no change,Thyroid – increased thyroid binding globulin. Increased thyroid stimulating factors. increased T3/T4. Adrenal – cortisol level increases.Aldosteone level increases.
OTHERS
calcium, iron, and magnesium content are decreased.