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Anesthetic Implications for the Physiological Changes in Pregnancy & Basic FHR Monitoring. J.E. Pellegrini, CRNA, PhD. Changes during the Puerperium. Changes to anatomy & physiology Most changes to physiology occur during the 1st trimester

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Anesthetic Implications for the Physiological Changes in Pregnancy & Basic FHR Monitoring

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Anesthetic implications for the physiological changes in pregnancy basic fhr monitoring

Anesthetic Implications for the Physiological Changes in Pregnancy & Basic FHR Monitoring

J.E. Pellegrini, CRNA, PhD

Changes during the puerperium

Changes during the Puerperium

  • Changes to anatomy & physiology

    • Most changes to physiology occur during the 1st trimester

    • Most changes to anatomy occur during the 2nd and 3rd trimester

    • Many of the changes are beneficial

      • As 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

Physiological changes of pregnancy

Physiological Changes of Pregnancy

Primarily we’ll discuss:

  • Respiratory Changes

  • Cardiovascular Changes

  • GI/Hepatic/Renal Changes

  • Changes in Neural network (metabolism)

Factors influencing the respiratory system and endotracheal intubation

Factors influencing the Respiratory Systemand endotracheal intubation

  • Weight gain

  • Breast enlargement

  • Vascularity of the respiratory tract mucosa

  • Possible edema of the oropharynx, nasopharyx, and vocal cords (**most prevalent in preeclampsia)

  • Progesterone-beneficial

Respiratory system changes

Respiratory System Changes

Respiratory changes with pregnancy

Respiratory Changes with Pregnancy

Compensatory respiratory system changes

Compensatory Respiratory SystemChanges

  • Chest Expansion-expands anteroposterior

  • FRC - decreased

    • FRC & CC differences  underventilated aveoli

  • Airway closure - (-a DO2)occurs in 50% of all parturients but hypoxemia extremely rare secondary to increased vent & CO

  •  Residual Volume and ERV   tolerance for apnea

  • ABG Changes- reflect chronic hyperventilation

    • PACO2 32-34 mm Hg by 12 weeks gestation

    • Respiratory Alkalosis(7.44) HCO3, BE and buffer base 

    • More prone to metabolic acidosis during prolonged labor secondary to pyruvate & lactic acid accumulation

Compensatory respiratory system changes1

Compensatory Respiratory SystemChanges

  • Ventilation (8-10 wks gestation)

    • MV  50% at term ( 40% TV and 15% RR)

      • Helps decrease dead space component

      •  PaCo2 levels (respiratory alkalosis - 7.44)

  • Hypoxia & Hypercarbia -develop rapidly with obstruction, prolonged apnea or hypoxic gas mixture

    • PO2 can  80 mm Hg/min faster than non-pregnant 

      • Due to  O2 consumption,  FRC,  C.O. &  tissue extraction of Oxygen

  •  Airway Resistance

    • Effects of Progesterone

    • Chest wall but not lung compliance decreases

  • Compensatory respiratory system changes2

    Compensatory Respiratory SystemChanges

    • Oxygen Consumption  20%

      • demands during labor where it is estimated that the avg. labor  jogging 12 miles

    • Oxyhemoglobin dissociation curve to the right

      • (P50 Values  from 26 to 28 mm Hg)

    Clinical implications of these respiratory system changes

    Clinical Implications of these Respiratory System Changes

    • Effects on Inhalation Anesthetics

      • Faster induction rate ( RR and C.O.)

      • MAC decreased by 30-40%

      •  MAC noted as early as the 8th week gestation

    • Effects of Maternal Hyperventilation

      • Constriction of umbilical and uterine vessels

      •  incidence of fetal acidosis

  • Can attenuate most responses with adequate analgesia

    • Studies indicate that adequate pain relief (i.e. CLE can normalize oxygenation &  MV & O2 consumption)

  • Cardiovascular system

    Cardiovascular System

    • Blood Volume

      •  35% (plasma volume  50% & red cell mass  15%)

      • Blood loss usually well tolerated at delivery

      • See fall in Hct in Postpartum by approximately 5% secondary to diuresis

      • Normally only have to consider blood after 1500 ml EBL

    • Cardiac Output

      •  30-40% in 1st trimester and 40-45% during labor and 50-60% in immediate postpartum period

      • Prone to Aortocaval Compression

    Changes in cardiovascular system

    Changes in Cardiovascular System

    Aorto caval syndrome

    Aorto-Caval Syndrome

    • Hypotension

      • 20 weeks gestation

      • Gravid Uterus Weight

      • Can Decrease C.O. 30%

      • Management Plan

        • Pre-induction hydration

        • Left Uterine Displacement (or RUD)

        • Ephedrine/Phenylephrine

    • Venal Caval Compression

      • Distention of epidural venous plexus

      • Decrease LA dose 1/3 (>14 wks)

    Cardiovascular changes

    Cardiovascular Changes

    Anesthetic significance of cardiovascular changes

    Anesthetic Significance of Cardiovascular Changes

    • Venodilation- increases accidental epidural vein puncture

    • Oxytocin with free H20  volume overload

    •  Hgb levels > 14 indicates low volume status, HTN or diuresis

    • C.O. high in 4 hrs postpartum

    • B/P < 90 to 95 torr   uterine blood flow

    • Hypotension occurs 75% with T4 level

    Gastrointestinal changes

    Gastrointestinal Changes

    • Stomach 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

    • Delayed gastric emptying   incidence of full stomach

    Gastrointestinal changes1

    Gastrointestinal Changes

    • Obesity - associated 2-20 fold  in mortality (PIH, IDDM)

    • Progesterone

      •  Gastrointestinal motility & esophageal sphincter tone

    • Parturients beyond 18th week of gestation more prone to vomiting and regurgitation

      • Treat as full stomach at 12th week

        *put it all together and this spells trouble

    Other compensatory changes

    Other Compensatory Changes

    • Renal System - GFR  60% at term

      •  in aldosterone and  plasma osmolarity (ADH resetting)

      •  RBF   Creatinine clearance & a  BUN & Uric Acid levels (½ to 2/3 that of normal)

    • Hepatic System

      • Usually no significant changes except slight in level enzymes and 2-4 fold  in alkaline phosphatase & cholesterol (from growing placenta)

      • Slight  in plasma cholinesterase & serum albumin

      • Can see spider angiomata & palmar erythema (from  estrogen levels)

    Neuromuscular changes

    Neuromuscular Changes

    • Endorphins

    • MAC  by 40%

    • Sedative Effect from Progesterone

    • Changes in SNS

      • See down-regulation

      • Altered Response to Catecholamines

    Altered responses to anesthesia

    Altered Responses to Anesthesia

    •  sensitivity of neural network

      • Probably secondary to  levels of circulating progesterone

        • Possible influence from circulating endorphins

      • Applicable for both neuraxial and peripheral blockades

      • Applicable for parturients beyond 24th week gestation

        • Decrease local anesthetic dose by as much as 1/3

    Sensitivity of nerve fibers with pregnancy

    Sensitivity of Nerve Fibers with Pregnancy



    • Multiple physiological changes in pregnancy have profound impact on your anesthetic management

    • The conservative approach is the best approach when dealing with the OB patient

    • Your principle patient is the parturient

    Fetal monitoring

    Fetal Monitoring

    • No ideal way to assess fetal well-being

    • FHR one of the better methods

      • FHR influenced by Para and sympathetic outflow

      • FHR responds to Baro & Chemo receptors

    Maternal fetal monitoring

    Maternal & Fetal Monitoring

    Fetal heart rate

    Fetal Heart Rate

    • Normal Baseline between 110-160/min

      • Small square = 10 seconds

      • Large square = 1 minute

    • Baseline rate determined by rate between contractions

    Three primary mechanisms that uterine contractions cause fhr abnormalities

    Three Primary Mechanisms that Uterine Contractions cause FHR Abnormalities

    Fhr accelerations

    FHR Accelerations

    • The FHR will normally remain steady or accelerate with uterine contractions

      • Typically viewed as a reassuring phenomenon

    Early decelerations

    Early Decelerations

    • Begins with onset of contraction & ends at the conclusion of contraction (with return to baseline)

    • Typically caused from Head Compression & routinely not viewed as a sign of fetal distress

    Late decelerations

    Late Decelerations

    • Transitory Decreases in FHR caused by Utero-Placental deficiency (hypoxia) indicating the fetus is not able to withstand the uterine contractions

    • Persistent Late Decelerations are considered an ominous sign especially when associated with loss of short term variability

    Nonreassuring patterns

    Nonreassuring Patterns

    • Nonreassuring, or "warning," patterns suggest decreasing fetal capacity to cope with the stress of labor.

    • Nonreassuring Patterns (Warning Signs)

    • ·Decrease in baseline variability

    • ·Progressive tachycardia (>160bpm)

    • ·Decrease in baseline FHR

    • ·Intermittent late decelerations with good variability

    • Ominouspatterns suggest possible fetal compromise.

    Ominous patterns

    Ominous Patterns

    • ·Persistent late decelerations, especially with

    • decreasing variability

    • ·Variable decelerations with loss of variability,

    • tachycardia, or late return to baseline

    • ·Absence of variability

    • ·Severe Bradycardia

    Treatment for fhr abnormalities

    Treatment for FHR Abnormalities

    So in summary

    So – In summary

    • If an ominous pattern appears to be present:

      • Have the mother lie on her left side or in a knee chest position immediately followed by:

        • Increase IV fluid.

        • Give her oxygen @ 10-12L to breathe by mask.

        • Discontinue or decrease any CLE infusion

        • Notify the obstetrical nursing staff & Obstetrician

    Anesthetic implications for the physiological changes in pregnancy basic fhr monitoring

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