Presentation on theme: "Anesthetic Considerations of Physiological Changes During Pregnancy"— Presentation transcript:
1 Anesthetic Considerations of Physiological Changes During Pregnancy Presented by:Mona AbdelsamieAssistant lecturer of AnesthesiologyUnder Supervision of:Prof. Dr. Hoda OmarProfessor of Anesthesiology & Intensive careAnesthesiology DepartmentAin Shams University
2 OBJECTIVES Maternal physiology during pregnancy. Uteroplacental circulation.Placental transfer of anesthetic agents.Effect of labor on maternal physiology.
3 Anaesthesia for parturient What is the difference?2 Patients are caredFor simultaneouslyPhysiologicalchangesMotherFetusAlter the usualresponseto anaesthesia
4 Maternal Physiology during Pregnancy 1) Progressive MAC.by 40% at termReturns to normal by 3rd daypostpartum.CNSProgesterone increases20 times normallevel at termβ- endorphin surge duringlabor & delivery
5 2) ↑ Sensitivity to Local Anesthetics. LA requirements Hormonally Mediated2) ↑ Sensitivity toLocal Anesthetics.LA requirementsduring RA ↓ by 30%.↓CSF VolumeEngorged EpiduralVenous Plexus↓Volume ofEpidural Space↑Epidural spacePressure
6 ↑Oxygen consumption 20 – 40% Progesterone ↑ CO2 Production ٌRespiratorysystemProgesterone↑ CO2 Production↑Minute Ventilation40 – 50%↑↑ VT & ↑ RR& ↑P50 (30 mmHg) ↑PaO2↓ PaCo2 (28-32 mmHg)Compensatory ↓ HCo3ˉ
7 TLC VC IC VT FRC ERV RV Volumes Capacities IRV 4550ml -5% 3500ml No ChangeIC2650ml+15%2000ml+5%IRV650ml+45%VTFRC1900ml-20%850ml-25%ERV1050ml-15%RVLung volumes &capacities at termgestation in absolutevolumes & as thepercentage changefrom non-pregnantValues.
8 Rapid desaturation during periods of apnea. ↓ FRC + ↑O2 Consumption=Rapid desaturation duringperiods of apnea.☼Pre-oxygenation prior to GA is mandatory.☼Parturient Should not lie flat withoutsupplemental oxygen.☼ ↑Uptake of InhalationalAnesthetics.↓FRC & ↑MV
9 Capillary engorgement of respiratory tract mucosa Hormonal Changes1) ↑ Incidence of difficult intubation.2) Trauma and bleeding duringendotracheal intubation.☼ Use a small ETT (6 – 7 mm)during GA
10 I : ↑ Blood Volume ( up to 90ml/ Kg) HematologicalChangesI : ↑ Blood Volume ( up to 90ml/ Kg)↑ by 1000 – 1500 ml at term.Returns to normal 1 – 2 weeks postpartum.+↑ Plasma Volume > ↑ RBC mass=Dilutional anemia & ↓ blood viscosityFacilitates maternal & fetalexchange of respiratory gases,nutrients & metabolites↓ Impact of maternal bloodloss at delivery
11 One of the leading causes of maternal mortality II : Hypercoagulable state↑ Fibrinogen, factors VII, VIII, IX, X & XII↓Factor XIRisk Of DVTOne of the leading causes of maternal mortalityIII : Other changes:* Leucocytosis up to 21,ooo/µL.* 10-20% ↓ in platelet count.* Marked ↓ cell mediated immunity→ ↑susceptibilityto viral infection.
12 ↑ COP by 40% at term CVS ↑ HR 15 – 30% ↑ SV 30% Returns to normal 2 weeks postpartum.↓ SVR → ↓ SBP & ↓↓ DBP, the response to adrenergic and vasoconstrictoragents is decreased.CVP, PAP, PAWP → unchanged.
13 Supine Hypotension syndrome COP ↓ in supine position after 28th week of gestation.Occurs in 20% of women at term.Aortocaval compressionCompression of IVCCompression of lower aorta↓ VR → ↓ COP by 24% at term.↓ blood flow to kidneys,uteroplacental circulation &lower extremeties
14 Compensatory mechanisms in unanaesthetised Women Venous Collaterals↑ SVR & HRReduced during generalor regional anesthesia.ParavertebralVenous plexusAbdominalwallSevere HypotensionProfound Fetal Hypoxia
15 Fluid preloading before neuroaxial anesthesia No woman in late pregnancy should lie supine without shiftingthe uterus off the great abdomino-pelvic vessels.Left lateral decubitusRigid wedge underThe right hipTilting the tableLeft side downFluid preloading before neuroaxial anesthesiaIt does not completely avoid maternal hypotension butit↑ maternal COP → preserve uteroplacentalblood flow.
16 GIT The parturient should be considered a full stomach patient during most of gestationGIT☼ Upward displacement of the stomach by theuterus → Incompetence of gastroesophagealsphincter → Gastroesophageal reflux & esophagitis.☼ ↑ Progesterone → ↓ tone of gastroesophageal sphincter.☼ Placental Gastrin → Hypersecretion of gastric acid.☼ Gastric emptying → Delayed with labor.
17 For GA: Pharmacological prophylaxis against aspiration. No positive pressure ventilation before intubationRapid sequence induction.Sellick’s maneouvre
18 ♦ RBF & GFR ↑ by 50% at 1st trimester but returns to normal in 3rd trimester.RenalSystem♦↑ Renin & Aldosterone → Na+ retention.♦ Sr. Creatinine & BUN may ↓ to 0.5 – 0.6mg/dL &8 – 9 mg/dL respectively.♦↓ Renal tubular threshold for glucose & amino acids → mildglycosuria (1-10g/d) & proteinuria (< 300mg/d).♦ Plasma osmolality ↓ by 8 – 10 mosm/Kg.
19 ♦Minor ↑ in Sr. Transaminases & LDH in 3rd trimester. ♦Hepatic function & hepatic blood flow→ unchanged.HepaticEffects♦Minor ↑ in Sr. Transaminases & LDH in 3rd trimester.♦↑ Sr. Alkaline phosphatase (placental).♦ Mild ↓ in Sr. albumin (dilutional).♦ 25 – 30% ↓ in pseudocholine estrase activity.♦↑ Progesterone levels→ inhibit release of cholecystokinin→ incompleteemptying of gall bladder→ altered bile acid composition→ formationof cholesterol stones.
20 Metabolic Effects Pregnancy is Diabetogenic Human Placental lactogen→ relative insulin resistance.Starvation like state↓ Blood Glucose & Amino Acid levels.↑ Free Fatty Acids, Ketones & triglycerides.↑ Estrogen levels→Thyroid gland hypertrohy→ ↑ T3 & T4↑ TBG → Free T3, T4 & TSH remain normal
21 Uteroplacental Circulation At term: uterine bloodflow is 10% of COP≈ 600 – 700 ml/min.80% to placenta
22 Maximally dilated uterine vasculature with absent autoregulation. Directly proportional to difference betweenuterine arterial and venous pressure.Uterine Blood FlowInversely proportional to uterinevascular resistance.Abundant α-adrenergic & some β-adrenergic receptors.Previously , vasoconstrictor agents with predominant β-adrenergic activity(e.g. Ephedrine) were of choice for hypotension during pregnancy.Recent studies show that α-adrenengic drugs (e.g.Phenylephrine) havebetter effects.
24 Placental transfer of anesthetic agents Placental transfer of drugs depends on:1: Molecular weight : < 500 Da cross easily.2: Protein binding.3: Lipid solubility: Highly ionized substances have poor lipid solubility.4: Maternal & fetal pH : affect ionization of the drug.5: Maternal drug concentration: affected by dose givenand route of administration.6: Timing of administration.
25 Thipental, ketamine & propofol Limited effects if < 1MAC & delivery within 10 min. of inductionCross placenta freelyInhalational AgentsIntravenous Agents:Thipental, ketamine & propofolLimited fetal effects in usual induction doses(drug distribution, metabolism & placental uptake)Variable effects.OpioidsMost significant respiratory depressant effectsMorhineSignificant respiratory depression peaking 1- 3 h after administration.MeperidineMinimal effect if < 1µg/Kg.FentanylMinimal effects on fetus.The highly ionized property impedes placental transfer.Muscle Relaxants
26 Local anesthetics → Placental transfer depends on: 1: pKa.2: Maternal & fetal pH : Fetal acidosis → higher fetal to maternaldrug ratios . Binding of hydrogen ions to the nonionized form → trappingof local anesthetic in fetal circulation3: Degree of protein binding : highly protein bound agentsdiffuse poorly across the placenta.Chloroprocaine has the least placental transfer as it is rapidlybroken down by plasma cholinestrase in the maternal circulation.
27 Most of anesthetic agents show significant placental transferFetal effects of drugs administered to parturient depend on:1: Maturity of fetal organs, substantial fetal hepaticuptake of many drugs.2: Dilution of the umbilical venous blood by venous bloodfrom lower half of fetal body → modify fetaldrug distribution.
28 Stages of labor 1st stage 2nd stage 3rd stage Effect of labor on maternal physiologyStages of labor1st stage2nd stage3rd stageStarts with full cervicaldilation, fetal descentoccurs, ends with completedelivery of fetus.Starts with true laborpains, ends by fullcervical dilation.Extends from birth of thebaby to delivery of theplacenta.Latent phaseActive phase8 – 12 h in nulliparous5 – 8 h in multiparous.Contractions are minapart, last 1 – 1.5 min15 – 30 min.Progressive cervical effacement& minor dilataton (2 – 4 cm).Progressive cervical dilatationup to 10 cm.15 – 120 min.
29 Maternal hyperventilation Intense painful contractionsMaternal hyperventilationMV ↑ up to 300%.↑ O2 consumption 60%above 3rd trimester valuesPCo2 < 20 mmHgUterine VC → Fetal acidosis+Periods of hypoventilation → transientmaternal & fetal hypoxemia in betweenContractions.
30 Displaces 300 – 500ml blood from uterus to central circulation. Each contractionDisplaces 300 – 500ml blood fromuterus to central circulation.COP ↑ 45% above 3rd trimesteric value.Maximum strain on the heart occurs immediatelyafter delivery.Uterine intense involution→ sudden relieve of IVC→ ↑ COP 80% above prelabor values.
33 Fetal blood concentrations of lidocaine following maternal administration would be higher than expected:If administered during uterine contraction.In the presence of umbilical cord compression.In the presence of maternal acidosis.In the presence of fetal acidosis.In the presence of increased maternal metabolism.XXX√X
35 The dose of bupivacaine required for spinal anesthesia is reduced in the pregnant patient at term because of decreased :CSF volume.Spinal cord blood flow.Metabolism of bupivacaine.CSF pressure.Turnover of CSF.√XXXX