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  • Anesthetic Implications for the Physiological Changes in Pregnancy & Basic FHR Monitoring J.E. Pellegrini, CRNA, PhD
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  • Changes during the Puerperium zChanges to anatomy & physiology yMost changes to physiology occur during the 1st trimester yMost changes to anatomy occur during the 2nd and 3rd trimester yMany of the changes are beneficial xAs an anesthetist you must have a good understanding of these changes and so that you can determine if they will have an impact on your your anesthetic management
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  • Physiological Changes of Pregnancy Primarily well discuss: zRespiratory Changes zCardiovascular Changes zGI/Hepatic/Renal Changes zChanges in Neural network (metabolism)
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  • Factors influencing the Respiratory System and endotracheal intubation zWeight gain zBreast enlargement zVascularity of the respiratory tract mucosa zPossible edema of the oropharynx, nasopharyx, and vocal cords (**most prevalent in preeclampsia) zProgesterone-beneficial
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  • Respiratory System Changes
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  • Respiratory Changes with Pregnancy
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  • Compensatory Respiratory System Changes zChest Expansion-expands anteroposterior zFRC - decreased yFRC & CC differences underventilated aveoli zAirway closure - ( -a DO2) occurs in 50% of all parturients but hypoxemia extremely rare secondary to increased vent & CO z Residual Volume and ERV tolerance for apnea zABG Changes - reflect chronic hyperventilation xPACO2 32-34 mm Hg by 12 weeks gestation xRespiratory Alkalosis(7.44) HCO3, BE and buffer base xMore prone to metabolic acidosis during prolonged labor secondary to pyruvate & lactic acid accumulation
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  • Compensatory Respiratory System Changes z Ventilation (8-10 wks gestation) yMV 50% at term ( 40% TV and 15% RR) xHelps decrease dead space component x PaCo2 levels (respiratory alkalosis - 7.44) zHypoxia & Hypercarbia - develop rapidly with obstruction, prolonged apnea or hypoxic gas mixture xPO 2 can 80 mm Hg/min faster than non-pregnant Due to O2 consumption, FRC, C.O. & tissue extraction of Oxygen z Airway Resistance xEffects of Progesterone xChest wall but not lung compliance decreases
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  • Compensatory Respiratory System Changes zOxygen Consumption 20% y demands during labor where it is estimated that the avg. labor jogging 12 miles zOxyhemoglobin dissociation curve to the right y(P 50 Values from 26 to 28 mm Hg) z
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  • Clinical Implications of these Respiratory System Changes zEffects on Inhalation Anesthetics yFaster induction rate ( RR and C.O.) yMAC decreased by 30-40% y MAC noted as early as the 8th week gestation zEffects of Maternal Hyperventilation xConstriction of umbilical and uterine vessels x incidence of fetal acidosis zCan attenuate most responses with adequate analgesia yStudies indicate that adequate pain relief (i.e. CLE can normalize oxygenation & MV & O 2 consumption)
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  • Cardiovascular System zBlood Volume y 35% (plasma volume 50% & red cell mass 15%) yBlood loss usually well tolerated at delivery ySee fall in Hct in Postpartum by approximately 5% secondary to diuresis yNormally only have to consider blood after 1500 ml EBL zCardiac Output y 30-40% in 1st trimester and 40-45% during labor and 50-60% in immediate postpartum period yProne to Aortocaval Compression
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  • Changes in Cardiovascular System
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  • Aorto-Caval Syndrome zHypotension y20 weeks gestation yGravid Uterus Weight yCan Decrease C.O. 30% yManagement Plan xPre-induction hydration xLeft Uterine Displacement (or RUD) xEphedrine/Phenylephrine zVenal Caval Compression yDistention of epidural venous plexus yDecrease LA dose 1/3 (>14 wks)
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  • Cardiovascular Changes
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  • Anesthetic Significance of Cardiovascular Changes zVenodilation- increases accidental epidural vein puncture zOxytocin with free H20 volume overload z Hgb levels > 14 indicates low volume status, HTN or diuresis zC.O. high in 4 hrs postpartum zB/P < 90 to 95 torr uterine blood flow zHypotension occurs 75% with T4 level
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  • Gastrointestinal Changes zStomach displaced upward and 45 to the right & displaces the intra-abdominal segment of the esophagus into the thorax decreased tone of the lower esophagus incidence of pyrosis zDelayed gastric emptying incidence of full stomach
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  • Gastrointestinal Changes zObesity - associated 2-20 fold in mortality (PIH, IDDM) zProgesterone y Gastrointestinal motility & esophageal sphincter tone zParturients beyond 18th week of gestation more prone to vomiting and regurgitation yTreat as full stomach at 12th week *put it all together and this spells trouble
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  • Other Compensatory Changes zRenal System - GFR 60% at term y in aldosterone and plasma osmolarity (ADH resetting) y RBF Creatinine clearance & a BUN & Uric Acid levels ( to 2 / 3 that of normal) zHepatic System yUsually no significant changes except slight in level enzymes and 2-4 fold in alkaline phosphatase & cholesterol (from growing placenta) ySlight in plasma cholinesterase & serum albumin yCan see spider angiomata & palmar erythema (from estrogen levels)
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  • Neuromuscular Changes zEndorphins zMAC by 40% zSedative Effect from Progesterone zChanges in SNS ySee down-regulation yAltered Response to Catecholamines
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  • Altered Responses to Anesthesia z sensitivity of neural network yProbably secondary to levels of circulating progesterone xPossible influence from circulating endorphins yApplicable for both neuraxial and peripheral blockades yApplicable for parturients beyond 24th week gestation xDecrease local anesthetic dose by as much as 1/3
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  • Sensitivity of Nerve Fibers with Pregnancy
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  • Summary zMultiple physiological changes in pregnancy have profound impact on your anesthetic management zThe conservative approach is the best approach when dealing with the OB patient zYour principle patient is the parturient
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  • Fetal Monitoring zNo ideal way to assess fetal well-being zFHR one of the better methods yFHR influenced by Para and sympathetic outflow yFHR responds to Baro & Chemo receptors
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  • Maternal & Fetal Monitoring
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  • Fetal Heart Rate zNormal Baseline between 110-160/min ySmall square = 10 seconds yLarge square = 1 minute zBaseline rate determined by rate between contractions z
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  • Three Primary Mechanisms that Uterine Contractions cause FHR Abnormalities
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  • FHR Accelerations zThe FHR will normally remain steady or accelerate with uterine contractions yTypically viewed as a reassuring phenomenon
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  • Early Decelerations zBegins with onset of contraction & ends at the conclusion of contraction (with return to baseline) zTypically caused from Head Compression & routinely not viewed as a sign of fetal distress
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  • Late Decelerations zTransitory Decreases in FHR caused by Utero-Placental deficiency (hypoxia) indicating the fetus is not able to withstand the uterine contractions zPersistent Late Decelerations are considered an ominous sign especially when associated with loss of short term variability
  • Slide 30 160bpm) Decrease in baseline FHR Intermittent late decelerations with good variability zOminous patterns suggest possible fetal compromise.">
  • Nonreassuring Patterns zNonreassuring, or "warning," patterns suggest decreasing fetal capacity to cope with the stress of labor. z zNonreassuring Patterns (Warning Signs) Decrease in baseline variability Progressive tachycardia (>160bpm) Decrease in baseline FHR Intermittent late decelerations with good variability zOminous patterns suggest possible fetal compromise.
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  • Ominous Patterns Persistent late decelerations, especially with z decreasing variability Variable decelerations with loss of variability, z tachycardia, or late return to baseline Absence of variability Severe Bradycardia
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  • Treatment for FHR Abnormalities PatternCauseTreatment Bradycardia, Late Decelerations Hypotension Uterine Hyperstimulation IV fluids, ephedrine (or phenylephrine) change position Decrease Oxytocin Variable Decelerations Umbilical Cord Compression Head Compression Change Position Continue pushing if FHR variability good Late Decelerations Decreased Uterine Bloodflow Change position & apply oxygen Decreased Variability Prolonged Hypoxemia Change position & apply oxygen
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  • So In summary zIf an ominous pattern appears to be present: yHave the mother lie on her left side or in a knee chest position immediately followed by: xIncrease IV fluid. xGive her oxygen @ 10-12L to breathe by mask. xDiscontinue or decrease any CLE infusion xNotify the obstetrical nursing staff & Obstetrician
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