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