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Anesthetic Considerations of Physiological Changes During Pregnancy Presented by: Mona Abdelsamie Assistant lecturer of Anesthesiology Under Supervision.

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Presentation on theme: "Anesthetic Considerations of Physiological Changes During Pregnancy Presented by: Mona Abdelsamie Assistant lecturer of Anesthesiology Under Supervision."— Presentation transcript:

1 Anesthetic Considerations of Physiological Changes During Pregnancy Presented by: Mona Abdelsamie Assistant lecturer of Anesthesiology Under Supervision of: Prof. Dr. Hoda Omar Professor of Anesthesiology & Intensive care Anesthesiology Department Ain Shams University

2 2 OBJECTIVES Maternal physiology during pregnancy. Maternal physiology during pregnancy. Uteroplacental circulation. Uteroplacental circulation. Placental transfer of anesthetic agents. Placental transfer of anesthetic agents. Effect of labor on maternal physiology. Effect of labor on maternal physiology.

3 3 Anaesthesia for parturient What is the difference? Anaesthesia for parturient What is the difference? Physiological changes Alter the usual response to anaesthesia 2 Patients are cared For simultaneously Mother Fetus

4 4 Maternal Physiology during Pregnancy 1) Progressive MAC. 1) Progressive MAC. by 40% at term by 40% at term Returns to normal by 3 rd day Returns to normal by 3 rd day postpartum. postpartum. CNS Progesterone increases 20 times normal level at term β- endorphin surge during labor & delivery

5 5 2) Sensitivity to Local Anesthetics. LA requirements during RA by 30%. Hormonally Mediated Engorged Epidural Venous Plexus CSF Volume Volume of Epidural Space Epidural space Pressure

6 6 ٌ Respiratory system Oxygen consumption 20 – 40% Minute Ventilation 40 – 50% VT & RR & P50 (30 mmHg)PaO 2 PaCo 2 (28-32 mmHg) Compensatory HCo 3 ˉ Progesterone CO 2 Production

7 7 TLC 4550 ml -5%VC 3500 ml No Change IC 2650 ml +15% 2000 ml +5%IRV 650ml+45%VT FRC 1900 ml -20%850ml-25%ERV 1050 ml -15%RV VolumesCapacities Lung volumes & capacities at term gestation in absolute volumes & as the percentage change from non-pregnant Values.

8 8 FRC + O 2 Consumption = Rapid desaturation during periods of apnea. Pre-oxygenation prior to GA is mandatory. Parturient Should not lie flat without supplemental oxygen. FRC & MV Uptake of Inhalational Anesthetics.

9 9 Hormonal Changes Capillary engorgement of respiratory tract mucosa 1) Incidence of difficult intubation. 2) Trauma and bleeding during endotracheal intubation. Use a small ETT (6 – 7 mm) during GA

10 10 Hematological Changes I : 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 viscosity Facilitates maternal & fetal exchange of respiratory gases, nutrients & metabolites Impact of maternal blood loss at delivery

11 11 II : Hypercoagulable state Fibrinogen, factors VII, VIII, IX, X & XII Factor XI III : Other changes: * Leucocytosis up to 21,ooo/µL. * 10-20% in platelet count. * Marked cell mediated immunity susceptibility to viral infection. Risk Of DVT One of the leading causes of maternal mortality

12 12 CVS COP by 40% at term HR 15 – 30% SV 30% Returns to normal 2 weeks postpartum. SVR SBP & DBP, the response to adrenergic and vasoconstrictor agents is decreased. CVP, PAP, PAWP unchanged.

13 13 Supine Hypotension syndrome COP in supine position after 28 th week of gestation. Occurs in 20% of women at term. Compression of IVC Compression of lower aorta Aortocaval compression blood flow to kidneys, uteroplacental circulation & lower extremeties VR COP by 24% at term.

14 14 Compensatory mechanisms in unanaesthetised Women Venous Collaterals Paravertebral Venous plexus Abdominal wall SVR & HR Reduced during general or regional anesthesia. Severe Hypotension Profound Fetal Hypoxia

15 15 No woman in late pregnancy should lie supine without shifting the uterus off the great abdomino-pelvic vessels. Left lateral decubitus Tilting the table Left side down Rigid wedge under The right hip Fluid preloading before neuroaxial anesthesia It does not completely avoid maternal hypotension but it maternal COP preserve uteroplacental blood flow.

16 16 GIT Upward displacement of the stomach by the uterus Incompetence of gastroesophageal sphincter Gastroesophageal reflux & esophagitis. The parturient should be considered a full stomach patient during most of gestation Progesterone tone of gastroesophageal sphincter. Placental Gastrin Hypersecretion of gastric acid. Gastric emptying Delayed with labor.

17 17 Pharmacological prophylaxis against aspiration. No positive pressure ventilation before intubation Rapid sequence induction. Sellicks maneouvre For GA:

18 18 Renal System RBF & GFR by 50% at 1 st trimester but returns to normal in 3 rd trimester. 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 mild glycosuria (1-10g/d) & proteinuria (< 300mg/d). Plasma osmolality by 8 – 10 mosm/Kg.

19 19 Hepatic Effects Hepatic function & hepatic blood flow unchanged. Minor in Sr. Transaminases & LDH in 3 rd trimester. Sr. Alkaline phosphatase (placental). Mild in Sr. albumin (dilutional). 25 – 30% in pseudocholine estrase activity. Progesterone levels inhibit release of cholecystokinin incomplete emptying of gall bladder altered bile acid composition formation of cholesterol stones.

20 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 levelsThyroid gland hypertrohy T 3 & T 4 TBG Free T 3, T 4 & TSH remain normal

21 21 Uteroplacental Circulation At term: uterine blood flow is 10% of COP 600 – 700 ml/min. 80% to placenta

22 22 Maximally dilated uterine vasculature with absent autoregulation. Uterine Blood Flow Directly proportional to difference between uterine arterial and venous pressure. Inversely proportional to uterine vascular 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) have better effects.

23 23 3 major factors uterine blood flow during pregnancy Systemic Hypotension Uterine Vasoconstriction Uterine Contractions Aortocaval compression. Hypovolemia. Sympathetic block with regional anesthesia. stress-induced endogenous Catecholamines during labor. α-adrenergic agonists. Local anesthetic agents. Hypertensive disorders generalized vasoconstriction. Labor. Oxytocin infusions. Extreme hypocapnia PaCO 2 < 20 mmhg. Barbiturates & Propofol.

24 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 given and route of administration. 6: Timing of administration.

25 25 Limited effects if < 1MAC & delivery within 10 min. of induction Cross placenta freely Inhalational Agents Intravenous Agents: Thipental, ketamine & propofol Limited fetal effects in usual induction doses (drug distribution, metabolism & placental uptake) Variable effects.Cross placenta freely Opioids Most significant respiratory depressant effects Morhine Significant respiratory depression peaking 1- 3 h after administration.Meperidine Minimal effect if < 1 µ g/Kg. Fentanyl Minimal effects on fetus. The highly ionized property impedes placental transfer. Muscle Relaxants

26 26 Local anesthetics Placental transfer depends on: 1: pKa. 2: Maternal & fetal pH : Fetal acidosis higher fetal to maternal drug ratios. Binding of hydrogen ions to the nonionized form trapping of local anesthetic in fetal circulation 3: Degree of protein binding : highly protein bound agents diffuse poorly across the placenta. Chloroprocaine has the least placental transfer as it is rapidly broken down by plasma cholinestrase in the maternal circulation.

27 27 Most of anesthetic agents show significant placental transfer Fetal effects of drugs administered to parturient depend on: 1: Maturity of fetal organs, substantial fetal hepatic uptake of many drugs. 2: Dilution of the umbilical venous blood by venous blood from lower half of fetal body modify fetal drug distribution.

28 28 Effect of labor on maternal physiology Stages of labor 1 st stage 2 nd stage 3 rd stage Starts with true labor pains, ends by full cervical dilation. Starts with full cervical dilation, fetal descent occurs, ends with complete delivery of fetus. Extends from birth of the baby to delivery of the placenta. Latent phaseActive phase Progressive cervical effacement & minor dilataton (2 – 4 cm). Progressive cervical dilatation up to 10 cm. 8 – 12 h in nulliparous 5 – 8 h in multiparous. Contractions are min apart, last 1 – 1.5 min 15 – 120 min. 15 – 30 min.

29 29 Intense painful contractions Maternal hyperventilation MV up to 300%. O 2 consumption 60% above 3 rd trimester values PCo 2 < 20 mmHg Uterine VC Fetal acidosis + Periods of hypoventilation transient maternal & fetal hypoxemia in between Contractions.

30 30 Each contraction Displaces 300 – 500ml blood from uterus to central circulation. COP 45% above 3 rd trimesteric value. Maximum strain on the heart occurs immediately after delivery. Uterine intense involution sudden relieve of IVC COP 80% above prelabor values.

31 31 Discussion

32 32 Questions

33 33 Fetal blood concentrations of lidocaine following maternal administration would be higher than expected: If administered during uterine contraction. If administered during uterine contraction. In the presence of umbilical cord compression. In the presence of umbilical cord compression. In the presence of maternal acidosis. In the presence of maternal acidosis. In the presence of fetal acidosis. In the presence of fetal acidosis. In the presence of increased maternal metabolism. In the presence of increased maternal metabolism. X X X X

34 34 Total peripheral resistance decreases. Hb concentration decreases. Plasma cholinestrase concentration increases. Blood glucose concentration increases. Functional residual capacity increases. During pregnancy: X X X

35 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. X X X X

36 36 Maternal arterial pH. Fetal cerebral blood flow. Maternal cerebral blood flow. Maternal uterine artery flow. Fetal arterial PO 2. Maternal hyperventilation produces a decrease in: X X X

37 37 The following substances transfer freely across the placenta: Neostigmine. Neostigmine. Insulin. Insulin. Pancuronium. Pancuronium. Atropine. Atropine. glycopyrolate. glycopyrolate. X X X

38 38 Thank you

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