850 likes | 2.28k Views
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
E N D
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 • Changes during puerperium
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
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
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
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%)
Changes in lung vol and capacities Note: change in MV is solely due to ↑in TV and not RR
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
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
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)
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
Continued… Note: fall in DBP while SBP is unaffected
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
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
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
Compression of aorta & IVC in supine & lateral tilt position www.anaesthesia.co.in
Anaesthetic implications Note: Adverse hemodynamic effects ↓ed after engagement of fetal head.
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
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
Continued… Coagulation Hypercoagulable, ↑ fibrinolysis, ↑platelet turnover ↑FDP ↑Plasminogen ↓AT III ↑coagulation factors ↑fibrinopeptide A BT unaltered TEG ↓PT/PTTK
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)
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
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)
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
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
Hepatobiliary system Progesterone →↓ cholecystokinin→↓GB emptying Altered bile composition • Serum bilirubin & liver enzymes ↑upto upper limit of normal range Gall stones
Renal Progesterone + estrogen → +RAAS → Na & H2O retention
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
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
Continued… LIPID METABOLISM ↑HDL, LDL, TG Hyperlipidemia of pregnancy is not atherogenic PROTEIN METABOLISM + nitrogen balance
Continued… THYROIDThyromegaly due to ↑ placental HCG (↓TSH ) ↑ T3 + T4 Free T3/T4 unchanged Euthyroid ↑TBG (estrogen)
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
Changes during labour RESPIRATORY SYSTEM O2 requirement > consumption →Anaerobic metabolism
Continued… CARDIOVASCULAR SYSTEM ↑sympathetic activity ↑cardiac contractility, SVR, VR(↑CVP) ↑CO (+10,+25,+40 in stage I,II,III) (+15-25% during each contraction)
Changes in puerperium Cardiovascular Relative hypervolemia + ↑VR (↑CVP) (autotransfusion) Nervous system Spinal LA dose requirement reaches prepregnant level at 24-48 hr
www.anaesthesia.co.in Continued… Respiratory
www.anaesthesia.co.in Continued… Hematological Blood loss 600 ml –vaginal delivery 1L – caesarean section Same for RA/GA
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