Anesthesia for OB
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Cardiovascular changes during pregnancy
- O2 consumption increases 30-40%
- CO increases by 50%
- SV increases 25%
- HR increases 25%
- MAP decreases by 15 mmHg
- SVR decreases by 20%
- PVR decreases by 30%
- Uterine blood flow increases to 10% CO
What are the changes in maternal cardiac output throughout pregnancy?
- CO increases by 50% (plateaus by 28 weeks)
- During labor additional 30-40% increase
- Immediately postpartum 75% increase above pre labor value
- At or below pre labor value by 48 hours postpartum
- 10% above pre-pregnant value by 2 weeks postpartum
Hematologic changes during pregnancy?
- Plasma volume: increased 15% during first trimester, increased 55% during second trimester
- RBC volume increased 30% at term
- Blood volume increased 45%
- Hgb decreased 15% by mid-gestation
- Platelet count unchanged (or decreased)
- PT and PTT decreased
- Fibrinogen increased
- Fibrinolysis increased
- Factors VII, VIII, IX, X, XII increased
Pulmonary and respiratory changes during pregnancy?
- Min Ventilation increased 50%
- Alveolar ventilation increased 70%
- TV increased 40%
- O2 consumption increased 20%
- RR increased 15%
- RV decreased 30%
- FRC decreased 15-20%
- TLC decreased 5%
- No change in dead space, compliance, or FEV1
Normal ABG values in pregnant patient
- pH 7.41-7.44 (7.35-7.45)
- PaO2 85-103 (60-100)
- PCO2 27-33 (35-45)
- HCO3 21-27 (24)
GI changes during pregnancy
- Upward displacement of stomach by uterus
- GE junction shifted upward
- Decreased LES tone
- Increased intragastric pressure
- Possible prolonged gastric emptying time
- **Pt aways considered full stomach**
Renal changes during pregnancy?
- Renal plasma flow, GFR, creatinine clearance all increase
- BUN and creatinine decrease
- Glycosuria up to 10g/dl and proteinuria up to 300mg/dl are not abnormal
- Urinary stasis contributes to increased UTI frequency
CNS changes during pregnancy?
- Progesterone in both plasma and CSF increases 10-20 fold in late pregnancy.
- Progesterone is sedating and potentiates effect of volatile anesthetics
- Pregnant patients more sensitive to local anesthetics
Hepatic changes during pregnancy?
- Liver size, blood flow, morphology unchanged
- Lactate dehydrogenase, serum bili, ALT, AST, Alk Phos increase with pregnancy
- Gallbladder emptying slows and bile concentration increases
Pregnancy-related changes to plasma proteins
- Plasma albumin decreases
- Free fractions of protein-bound drugs increase
- Total protein levels decrease
- Maternal colloid osmotic pressure decreases
- Plasma cholinesterase decreases by about 25% before delivery and 33% by day 3 postpartum
Uterine blood flow pre-pregnancy and at term?
- Pre-pregnant value: 50-190ml/min
- Term value: 600-700ml/min (10% maternal CO)
What is aortocaval compression syndrome? Significance?
- Caused by gravid uterus compressing the IVC and aorta
- Manifests as hypotension and tachycardia
- Aortic compression may lead to decreased uterine and placental blood flow, resulting in non-reassuring FHR changes
- Prevent by left uterine displacement to increase venous return
- Treat symptoms with IVF, supplemental O2, and vasopressors
Physiologic changes during labor?
- CO increases by 40% above pre labor values
- Immediately after delivery CO sharply increases (can reach 75% pre labor values)
- CO increases due to auto transfusion during uterine contractions, particularly after delivery of the placenta
- Hyperventilation common during active labor, may contribute to respiratory alkalosis
- *Resp alkalosis can lead to uterine vasoconstriction, decreased placental perfusion, hypoxemia, and fetal distress
What are the benefits of regional anesthesia during active labor?
- Decreases circulating maternal catecholamine levels
- May attenuate hemodynamic changes, hyperventilation, and stress response
Which parturients are at particular risk immediately after delivery?
Patients with pulmonary hypertension, stenotic valvular lesions, and cardiac disease are at highest risk due to sharp increase in CO (caused by auto transfusion of 500-750ml blood from the uterus)
How long does it take for physiologic alterations of pregnancy to return to normal after delivery?
- CO returns to slightly above pre-pregnant values in 2-4 weeks
- FRC and RV rapidly return to normal
- Alveolar ventilation returns to baseline by 4 weeks postpartum and pCO2 rises as progesterone levels decrease
- Dilutional anemia of pregnancy resolves, Hct returns to normal within 4 weeks (secondary to diuresis)
- Serum creatinine, GFR, and BUN return to normal levels in less than 3 weeks
- Mechanical effects of gravid uterus on the GI system resolve in 2-3 days
- Gastric emptying may be delayed for several weeks as serum progesterone levels decrease slowly
Pain pathways: First stage of labor
- Pain caused by uterine contractions and cervical dilation
- Visceral pain transmitted via sympathetic fibers entering dorsal horn of spinal cord at T10-L1
Pain pathways: Second stage of labor
- Fetal head descends into pelvis
- Pain is transmitted from pelvic floor, lower vagina, and perineum via pudendal nerve, entering the spinal cord at S2-S4
What are the stages of labor?
- Stage 1: cervical dilation and effacement; begins with the onset of regular painful contractions and ends when dilation of the cervix is complete.
- 1st stage has 2 phases. Latent phase - slow cervical dilation and effacement. Active phase - period of progressive cervical dilation, usually begins around 4-5cm
- Stage 2: ends with delivery of the neonate
- Stage 3: ends with delivery of the placenta
Anatomy of the placenta and umbilical cord: placental plates, blood supply
- Basal plate - maternal side of placenta, contains spiral arteries (divisions from the uterine arteries) and veins
- Chorionic plate - fetal side, made up of villi surrounded by chorion
- Intervillous space - space where basal and chorionic plates meet
- Villi contain divisions from 2 umbilical arteries (carry blood to the placenta) and 1 umbilical vein (carries nutrient rich blood back to fetus)
What factors lead to decreased uteroplacental perfusion?
- Aortocaval compression
- Hypotension (>25mmHg decrease in maternal MAP)
- Increased uterine vascular resistance (can be r/t contractions, ketamine doses >1.5mg/kg, oxytocin, and conditions like preeclampsia and abruptio placentae)
- Maternal hypoxia, hypercarbia, hypocarbia
- Increased maternal catecholamines
How are substances transported across the placenta?
- Simple diffusion (*most anesthetics)
- Active transport
- Bulk flow
- Facilitated diffusion
- Breaks in the chorionic membrane
Which anesthetic compounds cross the placenta by simple diffusion? (characteristics of the compounds)
- Low molecular weight
- Small spatial configuration
- Poorly ionized
- Lipid soluble
- *Most anesthetic drugs are highly lipid soluble and have MW <600 so placental transfer is high
What is the normal FHR? Causes of fetal tachycardia/bradycardia?
- Baseline FHR (between contractions) 110-160 bpm
- Tachycardia may indicate fever, hypoxia, use of beta-sympathomimetic agents, maternal hyperthyroidism, fetal hypovolemia
- Bradycardia may indicate hypoxia, complete heart block, beta blockers, local anesthetics, or hypothermia
What is the significance of beat-to-beat variability in the FHR? Causes of changes in variability?
- Thought to represent intact neurologic pathway in the fetus
- Increased variability seen with uterine contractions and maternal activity
- Decreased variability can be due to CNS depression, hypoxia, sleep, narcotic use, vagal blockade, and magnesium therapy
What is the significance of early decelerations in the FHR tracing?
- Early decelerations caused by head compressions (*vagal stimulation*)
- Uniform in shape
- Begin near the onset of uterine contraction with nadir at the same time as peak of contraction
Significance of variable decelerations in FHR?
- Variable decals caused by umbilical cord compression
- Nonuniform in shape
- Abrupt in onset and cessation
- Decrease of >15 bpm, lasting 15 sec - 2 min
- Repetitive variable decals can lead to fetal hypoxia and acidosis
Significance of late decelerations on FHR tracing?
- Late decals caused by uteroplacental insufficiency
- Uniform in shape
- Gradual onset and return to baseline
- Begin after the onset of a contrition, with nadir and recovery after peak and recovery of contraction
- Associated with maternal hypotension, HTN, DM, preeclampsia, or intrauterine growth retardation
- Ominous patterns, indicate fetus is unable to maintain normal oxygenation and pH
- Measured at 1 and 5 minutes (then 10 and 20 min during resuscitative efforts)
- Score of 0-3 indicates severely depressed neonate
- Score of 7-10 is normal
- 0-2 points for each variable
- HR: absent, <100, >100
- Resp effort: apneic, irregular/shallow/weak cry, good/strong cry
- Muscle tone: flaccid, some flexion of extremities, active motion
- Reflex irritability: no response, grimace/weak cry, sneeze/cough/cry
- Color: pale/blue, acrocyanosis, pink
When is the safest time for a pregnant patient to undergo non obstetric surgery?
Second trimester - avoids organogenesis and minimizes risk of preterm labor
Meperidine for labor
- Meperidine 25-50mg IV
- Onset 5-10min
- Duration 2-3 hours
- PCA dosing 15mg q10min
- *Normeperidine is active metabolite that may last for 3 days
- *Neonatal effects most likely if delivery occurs between 1 and 4 hours after dosing
Fentanyl IV for labor
- Dose 1-2mcg/kg IV
- Onset 2-3 min
- Duration 45 min
- PCA dosing 50mcg q10min
- *Short acting, no active metabolites, potent respiratory depression in mother, minimal sedation and nausea
Burtorphanol and Nalbuphine for labor
- Dose: Butorphanol 1-2mg IV; Nalbuphine 10mg IV
- Onset 5 min
- Duration 2-3 hours
- *Sedating for mother
- *Ceiling effect for analgesia and respiratory depression
- *Dysphoric reactions or withdrawal symptoms in opioid dependent patients can occur
Indications for epidural analgesia during labor and delivery?
- Relief of labor-induced pain
- Analgesia can readily be converted to anesthesia
- Benefits for patients with HTN and some types of cardiac disease (e.g. mitral stenosis) due to blunted hemodynamic effects of uterine contractions (increased preload, tachycardia, increased SVR, HTN, hyperventilation)
Contraindications for epidural analgesia during labor and delivery?
- Patient refusal
- Uncontrolled hemorrhage
- Infection at site of needle introduction
- Relative contraindications: systemic maternal infection, elevated ICP, prior spinal instrumentation with hardware, neurologic disease (e.g. MS)
Purpose of epidural test dose?
- Used to detect subarachnoid or IV placement of spinal catheter (preventing total spinal anesthesia or systemic LA toxicity)
- Common test dose: 3cc 1.5% Lido with epi 1:200,000 (45mg Lido, 15mcg epi)
- If subarachnoid, sensory/motor block will appear in 3-5 min
- If IV, tachycardia >30bpm baseline HR will occur within 45 seconds
Bupivacaine for OB epidural analgesia
- Amide LA
- Onset 10 min
- Peak 20 min
- Duration 2 hours
- Dilute solutions - good sensory analgesia, minimal motor blockade
- Early labor - 0.125% or less often adequate
- Active phase - 0.25% may be required
- Highly protein bound (transplacental transfer is limited)
- Addition of epinephrine speeds onset and lengthens duration but also increases intensity of motor blockade (undesirable effect)
Epidural lidocaine for OB
- Amide LA
- Onset within 10 min
- Duration 45-90 min
- Concentrations 0.75%-1.5% for sensory analgesia
- Crosses the placenta more readily than Bupivacaine and produces more motor blockade
- Rarely used outside the OR
2-Chloroprocaine for epidural OB analgesia
- Ester LA
- Rapid onset
- Duration 40 mins (limits use in labor)
- Chloroprocaine 3% frequently used to increase anesthetic level quickly for C/S or vaginal instrumentation delivery
- Very short half-life in maternal and fetal blood due to plasma esterase metabolism (*may be safest of commonly used anesthetics)
Ropivacaine for OB epidural analgesia
- Amide LA
- Slightly less potent than Bupivacaine (onset, duration, sensory block similar)
- Motor blockade slightly less than bupi
- Less cardiotoxicity than bupi (if injected IV) because it minds less avidly to Na channels or cardiac conduction tissue
- More expensive than bupi
Complications of epidural anesthesia
- Hypotension (20-30% baseline) results from sympathetic blockade, peripheral venodilation, decreased venous return; tx volume expansion and vasopressors
- Limited spread/patchy blocks may occur as a result of septa within epidural space or catheter passing into spinal nerve foramina
- IV injection of LA may cause dizziness, restlessness, tinnitus, seizures, loss of consciousness, possible CV collapse
- Unintentional dural puncture (incidence 1-8%)
- Unexpected high block or total spinal
Mechanism of action of intrathecal and epidural opioids?
- Opioids bind to presynaptic and postsynaptic receptor sites in the dorsal horn (Rexed's laminae I, II, and V), altering nociceptive transmission
- Provide analgesia without appreciably affecting sympathetic tone, sensation or voluntary motor function
What opioids are most commonly used for spinal and epidural analgesia during labor? Side effects?
- Spinal: Fentanyl (25mcg) Sufentanyl (5mcg) Morphine (0.25mg) Meperidine (10mg)
- Side effects: pruritis, n/v, delayed respiratory depression
Does epidural anesthesia prolong labor or result in operative delivery?
- Epidural labor analgesia may prolong the second stage of labor by about 30 mins, but there appears to be no harm to mother or fetus
- Epidural analgesia does not increase the risks of cesarean delivery
What are the advantages/disadvantages of spinal anesthesia for c-section?
- + Dense neural blockade, rapid onset, no risk of LA toxicity
- - PDPH (<1% occurrence), hypotension
Which drugs are commonly used for spinal anesthesia for c-section?
- Lidocaine 75mg; duration 45-75 min
- Bupivacaine 11mg; duration 60-120 min
- Tetracaine 7-10mg; duration 90-120 min
- Adjuvant drugs: Epinephrine 200mcg Morphine 0.1-0.3mg Fentanyl 10-25mcg
What are the indications for GA for c-section?
- Extreme fetal distress (in the absence of a functioning epidural catheter)
- Significant coagulopathy
- Inadequate regional anesthesia
- Acute maternal hypovolemia/hemorrhage
- Patient refusal of regional
Concerns for administering GA for c-section
- Goal: minimize maternal risk and neonatal depression
- RSI with cricoid pressure ONLY AFTER pt is prepped and draped and OB's are scrubbed in and ready for incision
- Succ 1-1.5mg/kg
- 50/50 N2O/volatile until delivery (volatile concentrations >0.5 MAC can cause uterine relaxation and excessive bleeding)
- Pitocin administered after delivery
- OG/airway suctioning and awake extubation
What are the classifications of HTN during pregnancy?
What is the pathophysiology of preeclampsia?
- Unknown etiology; maternal, paternal, fetal, and placental factors
- First stage of disease process - abnormal placentation occurs. Spiral arteries fail to dilate with or w/o athetosis
- Results in reduced placental perfusion and release of vasoactive substances
- Principal features: HTN and proteinuria
Complications of preeclampsia?
- Cerebrovascular hemorrhage
- Renal or hepatic failure
- Liver hemorrhage
- Abruptio placentae
- Pulmonary edema
- *Occur more frequently in women who develop preeclampsia before 32 weeks gestation and in those with preexisting medical conditions
What is HELLP syndrome?
- Elevated liver enzymes
- Low platelet count
- *Complication of preeclampsia*
- Microangiopathic hemolytic anemia associated with thrombocytopenia and elevated LFT's
- 10-20% of patients have normal BP
What is the treatment for HELLP?
- Only definite treatment is delivery by immediate c-section
- Patients with lab evidence of DIC are delivered immediately, regardless of gestational age
What is the primary drug used for the management of preeclampsia?
- Mag sulfate - drug of choice for seizure prophylaxis
- Attenuates vascular responses to endogenous and exogenous pressor substances
- Dilates vascular beds
- Not necessarily administered to women with mild disease
- Patients with severe preeclampsia should receive Mag during labor and after delivery
How should BP be managed in preeclampsia?
- Acute severe HTN should be treated to prevent cerebrovascular and CV complications
- BP should not be normalized, but antihypertensives should be used for BP > 160/105
- Hydralazine - arterial vasodilator
- Labetolol - alpha and beta antagonist
- Nifedipine - CCB (smooth muscle relaxation)
- Sodium nitroprusside
Indications for invasive monitoring in preeclampsia
- Refractory HTN
- Pulmonary edema
- Refractory oliguria unresponsive to fluid challenge
- Severe cardiopulmonary disease
Potential complications of mag sulfate treatment?
- Therapeutic range: 4-8mEq/L
- At therapeutic doses, mag sulfate increases sensitivity to muscle relaxants (esp non-depolarizers)
- Increased plasma concentrations may cause EKG changes - widened QRS, prolonged QT
- Deep tendon reflexes absent at level >10mEq/L
- Cardiac arrest occurs at 25mEq/L
- Mag sulfate crosses the placenta - newborn may have decreased muscle tone, respiratory depression, apnea
What is the treatment for magnesium toxicity?
Considerations for neuraxial anesthesia in patients with preeclampsia
- Evaluate coagulation status
- Platelet count (>100,000 ?)
- Spinal anesthesia controversial due to potential for sudden hypotension from rapid onset sympathetic blockade
What is eclampsia?
- Peripartum convulsions and/or coma not R/T coincident neurologic disease.
- Usually preceded by preeclampsia
- S/S headache, visual changes, epigastric pain often precede seizure activity
- Seizures often begin with facial twitching; generalized tonic-clonic seizures develop within seconds
Treatment for eclamptic seizures?
- **Intrauterine resuscitation and maternal airway management**
- Supplemental O2
- Airway support
- Lateral position
- Sodium thiopental 50-100mg (terminates seizure activity)
- Supplemental mag sulfate
- Intrauterine resuscitation
Define preterm labor.
Infants delivered between 20 and 37 weeks after first day of last menstrual period
Treatment of preterm labor?
- CCB's (e.g. nifedipine)
- Magnesium sulfate
- Cyclooxygenase inhibitors
- Beta-mimetic tocolytics
What conditions are associated with preterm labor?
- Placental abruption
- Uterine abnormalities
- Multiple gestations
- Premature rupture of membranes
- Urinary/systemic/gynecologic infection
What are the types of antepartum hemorrhage?
- Placenta previa - placenta implants before the presenting part
- Placental abruption - separation of the placenta most often accompanied by vaginal bleeding, uterine tenderness, and increased uterine activity
- Uterine rupture - defect in the uterine wall that results in fetal distress and/or maternal hemorrhage
- Vasa previa - insertion of umbilical cord where fetal vessels traverse the fetal membranes ahead of presenting part; rupture of these vessels can cause fetal exsanguination (no threat to mother)
What is placenta previa? Associated factors?
- Placenta implants before presenting part
- Classified depending on relationship between cervical os and placenta
- Factors associated: uterine trauma, multiparity, prior c/s or other uterine sx, advanced maternal age, prior hx of placenta previa
- S/S: painless vaginal bleeding in 2nd or 3rd trimester not related to any particular event
- Lack of abdominal pain and no change in uterine activity differentiate it from placental abruption
- First episode of bleeding rarely causes shock or fetal compromise
What is postpartum uterine atony? Associated conditions?
- Failure of contraction and involution of the uterus - can result in severe hemorrhage
- Associated with: multiple gestations, macrosomia, polyhydramnios, high parity, prolonged labor, chorioamnionitis, precipitous labor, augmented labor, tocolytic agents
Management of postpartum uterine atony?
- Bimanual compression, uterine massage
- Oxytocin - 1st line therapy; synthetic hormone that produces vasodilation (can result in hypotension in hypovolemic patients);
- Pitocin Dose: 20-50units/1000ml crystalloid IVF; bolus 5-10units IV
- Methylergonovine - ergot alkaloid preparation; contraindicated in hypertensive disorders, peripheral vascular disease, and ischemic heart disease
- Methergine Dose: 0.2mg IM
- 15-Methylprostaglandin - treatment of refractory uterine atony; side effects include bronchospasm, V/Q mismatch, increased intrapulmonary shunt, hypoxemia
- Dose: 250mcg IM or intramyometrially
What are the anesthetic considerations for diabetes in pregnancy?
- Increased risk for preeclampsia, polyhydramnios, fetal macrosomia, fetal malformations, and cesarean delivery
- Pregestation diabetes associated with preterm labor and delivery
- Glycemia control and tx of hypotension with non-glucose crystalloids + vasopressors to help preserve fetal acid-base status during neuraxial anesthesia for L&D
What causes DIC in obstetric patients?
- Abnormal activation of coagulation cascade with formation of large amounts of thrombin, depletion of coag factors, activation of fibrinolytic system, and hemorrhage
- Frequent causes in OB: preeclampsia, sepsis, fetal demise, abruptio placentae, sepsis, amniotic fluid embolism
What types of renal disease are most frequently seen in obstetric patients?
- Glomerulopathies (nephritic and nephrotic syndromes) and tubulointerstitial diseases
- Nephritic syndromes - involve necrotizing or inflammatory lesions
- Nephrotic syndromes - involve abnormal permeability to proteins
- Tubulointerstitial disease - abnormal tubular function resulting in abnormal urine composition and concentration
Which cardiac disease most commonly complicates pregnancy? Management?
- Congenital heart disease is the most common cardiac disease in pregnant women
- Accounts for 60-80% of cardiac disease during pregnancy
- Intrathecal opioids are good for labor analgesia when patients can't tolerate decreased SVR and decreased venous return
- Slow induction of anesthesia via epidural and prompt treatment of hemodynamic changes
- *Single-injection spinals for c-section contraindicated in many patients with congenital heart disease
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