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Physiological changes-in-pregnancy 1

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Physiological changes-in-pregnancy 1

  1. 1. Physiological changes in pregnancy Dr Megha Aggarwal University College of Medical Sciences & GTB Hospital, Delhi www.anaesthesia.co.in
  2. 2. Today’s seminar 1. 2. 3. 4. 5. 6. Introduction Why to know the changes during pegnancy Systems affected Anaesthetic implications Changes during labour Changes during puerperium
  3. 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. 4. Why study these changes? 1. 2. 3. 4. 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. 5. Systems affected Body wt & metabolism Respiratory Cardiovascular Hematopoietic Gastrointestinal CNS Hepatobiliary Renal Endocrine Pharmacological
  6. 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. 7. Respiratory 1. 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, S relaxin) →↓pulmonary resistance (-50%)
  8. 8. Changes in lung vol and capacities PARAMETER CHANGE 1. TV +45% 2. FRC -20% 3. ERV -25% 4. Dead space +45% 5. RR No change/+ 6. MV +45% 7. Alveolar ventilation +45% Note: change in MV is solely due to ↑in TV and not RR
  9. 9. Continued…
  10. 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. Breathing diaphragmatic > thoracic - advantage during high regional blockade www.anaesthesia.co.in
  11. 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) ↑ PaO2 to 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. 12. Anaesthetic implications PARAMETER CONSEQUENCE 1. MV ↑ Faster denitrogenation 2. ↓FRC + ↑O2 consumption Rapid hypoxia during apnoea 3. ↑MV + ↓FRC 4. Mucosal engorgement Faster inhalational induction Faster emergence Faster changes in depth Difficult airway 5. Predominant diaphragmatic breathing High spinal does not affect MV & PaCO2 much
  13. 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. 14. Continued… 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 ↑EF Chest X Ray – 1. Apparent cardiomegaly 2. ↑ LA (lateral view) 3. ↑ vascular markings 4. Straightening of left heart border 5. Pleural effusion
  15. 15. Continued… PARAMETER CHANGE 1.CO +40% 2. SV +30% 3. HR +15% 4. SBP No change 5. DBP -15% 6. SVR -15% 7. Femoral venous P +15% Note: fall in DBP while SBP is unaffected
  16. 16. Continued…
  17. 17. Continued… Blood pressure Position max. in supine min. in lateral Age ↑with age Parity nullipara> multipara SV(↑) SBP SBP unaffected vsl distensibility(↑compliance) BP ↓PP DBP SVR(↓) DBP ↓
  18. 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. Why no fall in blood pressure ? 1.Reflex vasoconstriction 2.Diversion of blood through paravertebral & epidural venous plexus, ovarian veins – maintains VR
  19. 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. Oxford position
  20. 20. Compression of aorta & IVC in supine & lateral tilt position www.anaesthesia.co.in
  21. 21. Anaesthetic implications PARAMETER 1. ↓RA filling CONSEQUENCE ↓SV & CO (25%) 2. Chronic partial IVC Venous stasis, phlebitis, obstruction edema in lower limbs Note: Adverse hemodynamic ↓ed spinal LA requirement 3. Epidural plexus engorged effects ↓ed after engagement of fetal head. 4. Systemic hypotension + Compromised uteroplacental blood flow ↑ Uterine venous P
  22. 22. Hematology & Coagulation PARAMETER 1. BV CHANGE +45% 2. Plasma volume + 55% 3. RBC volume +33% 4. Hemoglobin -17% 5. Hematocrit 35.5%
  23. 23. BV (%∆ from prepregnancy) Table showing % change in RBC and plasma volume Plasma RBC 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. 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. 25. Continued… Coagulation Hypercoagulable, ↓AT III ↑coagulation factors ↑fibrinopeptide A TEG ↓PT/PTTK ↑ fibrinolysis, ↑FDP ↑Plasminogen ↑platelet turnover BT unaltered
  26. 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. 27. Anaesthetic implications Risk of aspiration pneumonitis 1. Ph < 2.5 (nearly all) 2. Gastric vol > 25 ml ( 60%) 3. ↓ LES tone + ↑ intragastric P + ↓ gastric emptying 4. Recent food intake prior to labour/ surgery 1. Consider gravida as FULL STOMACH beyond 1st trimester 2. Give aspiration prophylaxis 3. Regional anaesthesia / inhalational analgesia preferred 4. Plan RSI
  28. 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. 29. Continued… 1. ↑ pain threshold at term & ↑ endogenous neuropeptides labour 2. ↓ MAC / ED95 1.Sedative effect of progesterone 2. ↑ CNS serotonergic activity 3.+ of endorphin system 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. 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. 31. Pelvic widening & resultant head down tilt
  32. 32. Anaesthetic implications SPINAL EPIDURAL 1. ↓ Segmental dose S 1. ↑ Dural puncture 2. Rapid onset & longer duration 2.↓Sensitivity of hanging drop technique (+epidural P) 3. Requirement normalise at 3.Unintentional i.v. injection 3. 24-48 hr PP 4. ↑ Rostral spread (esp. during uterine contraction) 4. ↓Segmental dose (small doses) (↑neural sensitivity) 5. Same spread with large doses (unaltered extravascular epidural vol)
  33. 33. Hepatobiliary system Progesterone →↓ cholecystokinin→↓GB emptying Altered bile composition  Serum bilirubin & liver enzymes ↑upto upper limit of normal range Gall stones
  34. 34. Renal Progesterone + estrogen → +RAAS → Na & H2O retention CHANGE CONSEQUENCE 1. Renal plasma flow↑(70%) GFR ↑ + Plasma expansion Renal indices < normal (creatinine ↓0.5-0.6) BUN ↓ 8-9) 2. ↑GFR + ↓absorption threshold Mild glycosuria(1-10g/dl) Proteinuria(<300mg/d) 3. Ureter & renal pelvis dilate Pyelonephritis
  35. 35. Continued…  ↑ Kidney size → normal at 6 wk postpartum  ↑ creatinine clearance →normal at 8-12 wk postpartum  ↑ frequency of micturition6-8wk → resetting of osmoregulation (polyuria + polydipsia) late pregnancy → P on bladder by presenting part
  36. 36. Endocrine ensure continuous GLUCOSE METABOLISM Estrogen, progesterone Hpl, prolactin, cortisol, FFA glucose supply to foetus 4 contrainsulin factors hyperinsulinemia (resistance) lipogenesis, hyperlipidemia, hyperketonemia Fasting hypoglycemia (foetal consumption) PP hyperglycemia& hyperinsulinemia
  37. 37. Continued… LIPID METABOLISM ↑HDL, LDL, TG Hyperlipidemia of pregnancy is not atherogenic PROTEIN METABOLISM + nitrogen balance
  38. 38. Continued… THYROID Thyromegaly due to ↑ placental HCG (↓TSH ) ↑ T3 + T 4 ↑TBG (estrogen) Free T3/T4 unchanged Euthyroid
  39. 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. 40. Changes during labour RESPIRATORY SYSTEM Stage I MV Stage II +75-150% +150-300% O2 need +40% +75% O2 requirement > consumption → Anaerobic metabolism
  41. 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. 42. Changes in puerperium Cardiovascular Relative hypervolemia (autotransfusion) + TIME ↑VR (↑CVP) CO Immediate PP +75% D-2 Just below predelivery 2 wk +10% 12-24 wk = Prepregnant Nervous system Spinal LA dose requirement reaches prepregnant level at 24-48 hr
  43. 43. www.anaesthesia.co.in Continued… Respiratory PARAMETER PREPREGNANT LEVEL AT FRC 1-2 wk O2 consumption 6-8 wk TV 6-8 wk MV 6-8 wk Alveolar PCO2 6-8 wk Mixed venous PCO2 6-8 wk
  44. 44. www.anaesthesia.co.in Continued… 600 ml –vaginal delivery 1L – caesarean section Same for RA/GA 1st wk = 25% 6-9 wk = +10% Hb 6 wk Protein Blood loss PREPREGNANT AT BV Hematological PARAMETER 6 wk TLC D-1 = 15000 6 wk >prepreg. Fibrinolysis Immediate postpartum Clotting + at placental separation Fibrinogen & platelet count ↑ D3 – D5 Thrombosis
  45. 45. www.anaesthesia.co.in References 1. Obstetric anaesthesia – principles and practiceDavid 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. 46. www.anaesthesia.co.in

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