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Physiological changes in pregnancy

Physiological changes in pregnancy. Dr Megha Aggarwal. University College of Medical Sciences & GTB Hospital, Delhi. www.anaesthesia.co.in. Today’s seminar. Introduction Why to know the changes during pegnancy Systems affected Anaesthetic implications Changes during labour

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Physiological changes in pregnancy

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  1. Physiological changes in pregnancy Dr Megha Aggarwal University College of Medical Sciences & GTB Hospital, Delhi www.anaesthesia.co.in

  2. Today’s seminar • Introduction • Why to know the changes during pegnancy • Systems affected • Anaesthetic implications • Changes during labour • Changes during puerperium

  3. www.anaesthesia.co.in Introduction Changes occur in pregnancy to 1. Support the foetus 2. Prepare mother for delivery Changes are due to 1. Hormonal changes 2. Increasing size of uterus and foetus 3. Anatomical changes

  4. Why study these changes? • To differentiate normal from abnormal • To understand its anaesthetic implications • To make the process of delivery smooth • To anticipate and manage complications www.anaesthesia.co.in

  5. Systems affected

  6. Body wt. & metabolism Wt GAIN = 17% = 12 kg T1 = 1-2 kg T2 = 5-6 kg T3 = 5-6 kg BMR +15% at term O2 consumption+35% (↑needs of fetus, uterus, placenta) + 40% in stage I of labour + 75% in stage II of labour

  7. Respiratory • Anatomical a) Rib cage and breast enlargement- laryngoscopy difficult b) Diaphragm pushed cranially- changes in lung vol c) ↑ mucosal engorgement nasal – epistaxis nasal intubation difficult oropharyngeal – smaller ETT ↑mallampatti score d) ↓Chest wall compliance (lung compliance unaffected) e) Subglottic airway dilatation (progesterone, cortisone, relaxin) →↓pulmonary resistance (-50%)

  8. Changes in lung vol and capacities Note: change in MV is solely due to ↑in TV and not RR

  9. Continued…

  10. Continued… 2. Physiological changes 1. ↑MV → ↑ TV (RR unchanged) 1. Progesterone (↑CNS sensitivity to CO2) 2.↑CO2 production alkalosis (compensatory but incomplete↓HCO3- →↑pH . by 0.02-0.06) 2. Breathingdiaphragmatic > thoracic - advantage during high regional blockade www.anaesthesia.co.in

  11. Continued… 3.Blood gases a) Paco2_- ↓to 30 mm Hg by 30 wk, no further change b) ∆ Paco2_- ETco2= 0 (because no. of unperfused alveoli i.e. DS ↓ due to ↑CO) c) ↑ PaO2to 107 mmHg but ↓when supine d) ∆ AV O2 early gestation: ↑CO> ↑O2 consumption → ↑ ∆ AV O2 late gestation: ↑CO< ↑O2 consumption → ↓ ∆ AV O2 e) FRC < closing capacity → small airways close during normal tidal ventilation → predisposes to hypoxia

  12. Anaesthetic implications

  13. Circulatory changes Examination- 1.Apical impulse in 4th ICS & laterally 2.Loud S1 3.A2P2 changes less with respiration 4.S3 in 16% cases 5.Grade I - II early mid-diastolic murmur at left sternal border. 6. Asymptomatic pericardial effusion ECG – 1.Sinus tachycardia ( ↓PR & QT interval) 2.ST depression & T inversion in left precordial leads 3.Left axis deviation (false)

  14. ECHO – 1. Enlargement of chambers 2. LVH 3. Annular dilatation of all valves except Aortic (regurgitation) 4. ↑ LVEDV but no change in filling P(PCWP/CVP) (because of cardiac dilatation & hypertrophy) 5. LVESV-unchanged Chest X Ray – 1. Apparent cardiomegaly 2. ↑ LA (lateral view) 3. ↑ vascular markings 4. Straightening of left heart border 5. Pleural effusion Continued… ↑EF

  15. Continued… Note: fall in DBP while SBP is unaffected

  16. Continued…

  17. Continued… Blood pressure Position Age Parity max. in supine ↑with age nullipara> multipara min. in lateral SV(↑) SBP SBP unaffected vsl distensibility(↑compliance) BP DBP SVR(↓) DBP ↓ ↓PP

  18. Continued… Aortocaval compression : starts at 13-16 wk 1.Concealed caval compression. In supine position gravid uterus compresses IVC & ↓CO without fall in the blood pressure. Whyno fall inbloodpressure? 1.Reflex vasoconstriction 2.Diversion of blood through paravertebral & epidural venous plexus, ovarian veins – maintains VR

  19. Continued… 2.Overt caval compression (supine hypotensive syndrome) • Hypotension, sweating, bradycardia, pallor, nausea, vomiting. • Due to uncompensated ↓VR Prevention of SHS: (aim is to displace the uterus) 1.Providing left lateral tilt 15 degrees beyond 28wk 2.Placing wedge under the right buttock 3. Oxfordposition

  20. Compression of aorta & IVC in supine & lateral tilt position www.anaesthesia.co.in

  21. Anaesthetic implications Note: Adverse hemodynamic effects ↓ed after engagement of fetal head.

  22. Hematology & Coagulation

  23. Table showing % change in RBC and plasma volume Plasma RBC BV (%∆ from prepregnancy) T1 T2 T3 1hr 1wk 6wk Note: 1. Hemodilution - patency of uteroplacental vascular bed 2. Facilitates exchange of resp. gases, nutrients & metabolites 3. Reduces impact of maternal blood loss at delivery

  24. Continued… Plasma proteins: 1. ↓Total proteins - ↑unbound ( active) drug 2. ↓cholinesterase conc. (25%) but no change in duration of action of Sch. Immunity: 1. Leukocytosis – mainly PMN but function is impaired (↓chemotaxis & adherence) a) ↑ Infection b) diagnosis difficult c) ↓ s/s of autoimmune disorders 2. ↓Antibody titers to HSV, Measles, Influenza A

  25. Continued… Coagulation Hypercoagulable, ↑ fibrinolysis, ↑platelet turnover ↑FDP ↑Plasminogen ↓AT III ↑coagulation factors ↑fibrinopeptide A BT unaltered TEG ↓PT/PTTK

  26. Gastrointestinal system Anatomical 1. ↑Angle of GE junction 2. Cephalad displacement of stomach & intestine 3. Vertical rather than horizontal stomach Physiological 1. Relaxed LES (progesterone) ↓barrier P. 2. Delayed gastric emptying (narcotics, anticholinergics, pain of labour)

  27. Anaesthetic implications • Risk of aspiration pneumonitis • Ph < 2.5 (nearly all) • Gastric vol > 25 ml ( 60%) • ↓ LES tone + ↑ intragastric P + ↓ gastric emptying • Recent food intake prior to labour/ surgery

  28. Nervous system Vertebral column 1. ↑ Lumbar lordosis - ↓vertebral interspinous distance 2. Distended epidural veins & ↓ CSF volume 3. Positive Lumbar epidural P (difficult identification) 4. CSF P unaffected (↑ during uterine contraction)

  29. Continued… Dependence on sympathetic nervous system ↑ progressively a) counteracts adverse effects of aortocaval compresion b) greater preloading during neuraxial blockade c) pharmacological sympathectomy can cause marked ↓ in BP

  30. Continued… ↓Spinal anaesthetic dose requirement (25%) 1.↑ Neural suseptibility to LA 2. Epidural plexus engorgement 3. CSF changes a)↓CSF protein (↑unbound drug) b)↑ CSF pH (↑ unionised drug) 4. Pelvic widening & resultant head down tilt in lateral position 5. Apex of thoracic kyphosis higher

  31. Pelvic widening & resultant head down tilt

  32. Anaesthetic implications

  33. Hepatobiliary system Progesterone →↓ cholecystokinin→↓GB emptying Altered bile composition • Serum bilirubin & liver enzymes ↑upto upper limit of normal range Gall stones

  34. Renal Progesterone + estrogen → +RAAS → Na & H2O retention

  35. Continued… • ↑ Kidney size → normal at 6 wk postpartum • ↑ creatinine clearance →normal at 8-12 wk postpartum • ↑ frequency of micturition- 6-8wk → resetting of osmoregulation (polyuria + polydipsia) late pregnancy → P on bladder by presenting part

  36. Endocrine ensure continuous glucose supply to foetus GLUCOSE METABOLISM 4 Estrogen, progesterone Hpl, prolactin, contrainsulinfactors cortisol, FFA hyperinsulinemia (resistance) lipogenesis, hyperlipidemia, hyperketonemia Fasting hypoglycemia (foetal consumption) PP hyperglycemia& hyperinsulinemia

  37. Continued… LIPID METABOLISM ↑HDL, LDL, TG Hyperlipidemia of pregnancy is not atherogenic PROTEIN METABOLISM + nitrogen balance

  38. Continued… THYROIDThyromegaly due to ↑ placental HCG (↓TSH ) ↑ T3 + T4 Free T3/T4 unchanged Euthyroid ↑TBG (estrogen)

  39. Pharmacological 1. Sch. - ↓pseudocholinesterase (-25%) but no effect on duration of action 2. NDMR - Rapid & prolonged effect 3. ↓Chronotropic response to isoproterenol & epinephrine (downregulation of β rec. ) 4. Pressor response – inconsistent refractory 5. LA toxicity – unaffected

  40. Changes during labour RESPIRATORY SYSTEM O2 requirement > consumption →Anaerobic metabolism

  41. Continued… CARDIOVASCULAR SYSTEM ↑sympathetic activity ↑cardiac contractility, SVR, VR(↑CVP) ↑CO (+10,+25,+40 in stage I,II,III) (+15-25% during each contraction)

  42. Changes in puerperium Cardiovascular Relative hypervolemia + ↑VR (↑CVP) (autotransfusion) Nervous system Spinal LA dose requirement reaches prepregnant level at 24-48 hr

  43. www.anaesthesia.co.in Continued… Respiratory

  44. www.anaesthesia.co.in Continued… Hematological Blood loss 600 ml –vaginal delivery 1L – caesarean section Same for RA/GA

  45. References www.anaesthesia.co.in 1. Obstetric anaesthesia – principles and practice- David H Chestnut 2. Anaesthesia & Co-existing diseases-Stoelting 3. Millers anaesthesia 4. Short Practice of Anaesthesia – Churchill Davidson 5. Textbook of obstetrics- DC Dutta

  46. www.anaesthesia.co.in

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