Obstetrical Anesthesia Clerks2007

Obstetrical AnesthesiaDr Lindsey Patterson

ObjectivesOverview of maternal physiologyAnalgesia for labor and deliveryRegional anesthesia Anesthesia concerns in the parturientStudy MCQs with explanations

Physiological Changes-CVSAlmost all the changes seen are due to high levels of progesterone and include:

35% Total Blood Volume heart rate 15 beats/min40% CO30% SV 15% SVR500ml/min blood flow to uterus venous return from legsAORTOCAVAL COMPRESSION (mechanical)

Impact of CVS changesPatients with pre-existing cardiac disease may decompensate either during labor or immediately post delivery. This corresponds to the time of maximal COApprox 400 600ml blood loss occurs at deliverySupine hypotensive syndrome

Aortocaval Compression

Physiological Changes - Resp oxygen consumption ~ 20% (100% in labor) due to increased metabolic rate minute ventilation ~ 50% (due to increased tidal volume) arterial pCO2 FRC causing a decrease in oxygen reserves

Impact of Resp. changes Uptake of inhalational agents is fasterDecreased FRC and increased oxygen consumption increase the risk of hyoxia with apneaPreoxygenation prior to GA less effective

Physiological Changes- AirwayVenous engorgement of airway mucosaEdema of airway mucosaWorsening of Mallampati score in labor

Impact of Airway ChangesTrauma to upper airway with suctioning, intubationIncreased incidence of difficult/failed intubation x10Require smaller ETT

Physiological Changes-CNSDecrease in MAC by 25 40%Decreased dose of Local Anesthetic requirement for regional techniquesMore rapid onset of neural blockade

Impact of CNS ChangesDecreased inhalation anesthetic agent requirements Decreased dose of local anesthetic for same effectIncreased risk of local anesthetic toxicity

Physiological Changes - GITIncreased gastric fluid volumeIncreased gastric fluid acidityDecreased competency of lower esophageal sphincter

Impact of GIT ChangesIncreased risk of aspirationAll parturients are a full stomachAspiration prophylaxis recommended for C/S0.3M Sodium citrate 30 mls poRanitidine 50mg ivMetoclopramide 10mg iv

Analgesia for labor and deliveryWhere is the pain coming from?Is pain bad in labor?Analgesic options

Pain of childbirthNociceptive pathways involved

T10 L1 during laborplusS2-S4 for delivery

Is pain bad in labor?Psychological stress can cause:increased levels of catecholamineshyperventilation

These may result in decreased uterine blood flow leading to hypoxia and acidosis in the fetus

Factors affecting pain perception in laborMental preparationFamily supportMedical supportCultural expectationsUnderlying mental statusParity Size and presentation of the fetusMaternal pelvic anatomyDuration of laborMedications

Analgesia for labor and deliveryNon-medicationInhalationalParenteralRegional

Analgesia- Non medication optionsBreathing exercisesAutohypnosisAcupunctureWhite Noise/ MusicMassage/ walkingTENSWater bath

Inhalation MedicationsNitronox: 50:50 mixture of oxygen and nitrous oxideLow dose Isoflurane in oxygen

Advantages: on demand delivery, relatively safeDisadvantages: variable efficacy, nausea, drowsiness, neonatal depression

Parenteral MedicationsNarcotics: meperidine, morphine fentanyl

Advantages: relatively good analgesia

Disadvantages: nausea, vomiting, sedation, neonatal depression (max. 2 hours after meperidine dose), short duration of action

Regional techniquesEpidural, spinal, combined spinal-epidural

Advantages: excellent pain control, minimal impact on progress of labor with low doses, less drug transfer to fetus, improved uterine blood flow, decrease in birth trauma e.g. use of forceps, minimal neonatal depression

Disadvantages: invasive technique, side effects (hypotension, headache, itching, nausea, urinary retention, limited mobility), nerve damage, infection

Anesthesia in the parturientGeneral considerations of the parturient undergoing surgeryObstetric surgery

General considerationsAltered physiology as mentionedRisks to the fetus:Effect of the disease process/therapiesPossible teratogenicity of anesthetic agentsIntraoperative effects on uteroplacental blood flowIncreased risk of preterm labor/ risk of abortion

Maternal considerationsAltered physiologyAltered response to anesthesiaDecrease in MACIncreased sensitivity to neuraxial agentsDecreased plasma cholinesteraseDecreased protein binding (more free drug)Limited drug information in parturients

Fetal ConsiderationsTeratogenicity:Limited information due to impracticality of conducting trials with sufficient powerGuidelines based on a) effects on reproduction in animals; b) epidemiological surveys of OR personnel; c) studies of pregnancy outcomes in parturient undergoing ante partum surgery

Nitrous oxide has been shown to have a teratogenic effect in rats during the first trimesterNo anesthetic agent is a proven teratogen in humansAnesthetic agents deemed safe include: thiopental,morphine, meperidine,fentanyl, succinylcholine, NDMRsLimiting nitrous oxide use but only if hypotension secondary to volatiles can be avoided

Anesthetic management in the parturient should be directed to:Avoidance of hypoxemiaAvoidance of hypotensionAvoidance of acidosisMaintain PaCO2 in the normal range for the parturientMinimize effects of aortocaval compression

Anesthesia for Caesarean SectionPreparationPreventing complicationsChoice of Anesthetic techniqueEffects on the fetus

PreparationPremeds: antacid (sodium citrate)IV access and fluid bolus within 30 minutes of operating (avoid glucose containing fluids)Left lateral tilt with wedge under right pelvisRoutine Monitors: ECG, NIBP, pulse oximeter, fetal monitoring Additional monitors for GAs: ETCO2, nerve stimulator, temp probe

Preventing complicationsAspiration prophylaxisDetailed airway assessmentFluid resuscitation/left lateral tilt to prevent hypotensionSafe practice for placement of neuraxial blocks

Anesthetic techniquesLocal infiltration by surgeonRegional anesthesia: spinal, epidural, combined spinal-epiduralGeneral anesthesia

Local InfiltrationRarely performedPatient usually in extremisSurgery must be done via midline incision, gentle retraction, no exteriorization of the uterusUsually done to supplement a regional technique if local anesthetic toxicity not a concern

Regional: Spinal AnesthesiaSimple to performRapid onsetSingle shot techniqueProfound neural blockTechnique of choice for uncomplicated elective caesarean sections and in many emergency caesarean sections

Spinal AnesthesiaPotential Complications:HypotensionHeadache (rare ~1:100)Backache (temporary ~24hrs)Nausea/vomiting (secondary to BP, narcotics)Neurological damage (very rare)Anaphylaxis (very rare)

Regional: Epidural AnesthesiaMore technically challengingSlower onsetUsed when already placed for labor analgesiaUseful in parturient where a slow, controlled onset of block is neededAllows prolongation of block should surgery be complicated

Epidural AnesthesiaPotential Complications:HypotensionHeadache (approx 1:100)Transient backache ~24hrsUrinary retentionUnintentional spinal injectionIntravascular injection of local anestheticNeurological damageInfection

Regional: Combined spinal-epiduralUsed when require the speed and density of a spinal anesthetic with the flexibility of prolonging the block by supplemental increments of local anesthesia via the epidural catheterComplications: as mentioned for spinals and epidurals

General AnesthesiaUsed when Patient refuses regional techniqueRegional technique is contraindicatedEmergency C/S when there is inadequate/absent regional analgesia and to delay will cause undue risk to the fetus / mother

General AnesthesiaComplications:Failed intubationFailed ventilation causing death or neurological injuryAwarenessAspiration pneumonia

Anesthesia: Effects on the fetusAvoid hypotension, hypoxia, acidosis, hyperventilationLimit time between uterine incision and delivery to less than 3 minutesInfants exposed to GA have lower Apgar at one minute but no difference at 5 minsNo significant alteration in neurobehavioral scores with regional techniques

MCQ 1. Epidural Anesthesia in Obstetric Practice. Which of the following is false.A. Commonly causes itchingB. Can be used to control blood pressure in pre-eclampsiaC. Causes uterine relaxationD. Causes urinary retentionE. Contributes to the effects of aortocaval compression

MCQ 1. Epidural Anesthesia in Obstetric PracticeA. Commonly causes itchingB. Can be used to control blood pressure in pre-eclampsiaC. Causes uterine relaxationD. Causes urinary retentionE. Contributes to the effects of aortocaval compression

Itching is one of the most common side-effects of opioids when delivered in the epidural space. Their use allows for a decreased concentration of local anesthetic whilst maintaining excellent analgesia. Patients have better motor function and retain the ability to push.

MCQ 2. All of the following are false concerning general anesthesia in the parturient, EXCEPT:A. General anesthesia reduces gastric pHB. MAC is decreasedC. It is contra-indicated in patients with a bleeding diathesisD. Is a major cause of overall maternal mortalityE. Succinylcholine crosses the placenta

General anesthetics have no effect on gastric pH. It is the method of choice in patients with a bleeding diathesis since regional anesthesia is contra-indicated. Although of concern to Anesthesiologists general anesthesia is not a major cause of maternal mortality. Succinylcholine is unable to cross the placenta and effect the fetus.

MCQ 3. The following are all true concerning the nerve supply of the uterus , EXCEPT:A. Sensation from the upper segment travels with the sympathetic nerves to T11-T12B. Sensation from the birth canal is via the pudendal nerveC. Lower segment innervation is via S2-4D. Motor function occurs via sympathetic and parasympathetic nervesE. An intact nerve supply is essential to initiate normal labor

Normal labor occurs in patients with a transected spinal cord.

MCQ 4: Physiological changes seen in the last trimester include all EXCEPTA. Resting PaCO2 is decreasedB. Hematocrit is decreasedC. Blood volume is increasedD. Gastric secretion is increasedE. Total peripheral resistance is decreased

Gastric acid production does not increase. There is an increased risk of aspiration due to delayed gastric emptying and a decrease in lower esophageal sphincter tone.

MCQ 5: All of the following are suitable for aspiration prophylaxis prior to caesarean section, EXCEPT:A. MetoclopramideB. GlycopyrollateC. Sodium citrateD. Clear fluids 4 hours pre-opE. Ranitidine

Metoclopramide acts as a pro-kinetic to empty the stomach of any gastric contents.Sodium citrate is a non-particulate antacid used to neutralize gastric contents.Ranitidine is an H2 antagonist used to prevent gastric acid secretion.Allowing clear fluids up to 4 hours prior to suregry has been shown to decrease the gastric content volume so decreasing the risk of aspiration.Glycopyrollate is an anti-sialogogue used for preoperative preparation when an awake intubation is anticipated.

MCQ 6: All are suitable techniques for pain relief in labor EXCEPT:A. Transcutaneous electrical nerve stimulationB. White noiseC. Epidural bupivacaineD. Intrathecal narcoticsE. 70% Nitrous oxide in Oxygen

The concentration of nitrous oxide in oxygen when used for analgesia is 50%. Higher concentrations can result in loss of consciousness.

MCQ 7: Which of the following is a contraindication to epidural analgesia in labor:A. Previous caesarean sectionB. Fetal distressC. INR 1.6D. Maternal exhaustionE. Maternal multiple sclerosis

Epidural analgesia is not contraindicated in patients who have had a prior C/S. The pain caused as a result of uterine rupture is not effectively masked by epidural analgesia.Fetal distress can be reduced by epidural analgesia so long as hypotension is avoidedMaternal exhaustion is an indication for epidural analgesia. Maternal multiple sclerosis is not a contraindication to epidural analgesia as long as the concentration of local anesthetic is reducedCoagulopathy is an absolute contraindication to epidural analgesia

MCQ 8 : Likely complications of epidural opioids include all of the following, EXCEPT:A. ItchingB. Urinary retentionC. HypotensionD. Respiratory depressionE. Nausea

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Obstetrical Anesthesia Clerks2007