Obstetrical Anesthesia Dr Lindsey Patterson

Objectives Overview of maternal physiology Analgesia for labor and delivery Regional anesthesia Anesthesia concerns in the parturient Study MCQs with explanations

Physiological Changes-CVS Almost all the changes seen are due to high levels of progesterone and include: 35%  Total Blood Volume  heart rate 15 beats/min 40%  CO 30%  SV 15%  SVR 500ml/min  blood flow to uterus  venous return from legs AORTOCAVAL COMPRESSION (mechanical)

Impact of CVS changes Patients with pre-existing cardiac disease may decompensate either during labor or immediately post delivery. This corresponds to the time of maximal CO Approx 400 – 600ml blood loss occurs at delivery Supine 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 faster Decreased FRC and increased oxygen consumption increase the risk of hyoxia with apnea Preoxygenation prior to GA less effective

Physiological Changes- Airway Venous engorgement of airway mucosa Edema of airway mucosa Worsening of Mallampati score in labor

Impact of Airway Changes Trauma to upper airway with suctioning, intubation Increased incidence of difficult/failed intubation x10 Require smaller ETT

Physiological Changes-CNS Decrease in MAC by 25 – 40% Decreased dose of Local Anesthetic requirement for regional techniques More rapid onset of neural blockade

Impact of CNS Changes Decreased inhalation anesthetic agent requirements Decreased dose of local anesthetic for same effect Increased risk of local anesthetic toxicity

Physiological Changes - GIT Increased gastric fluid volume Increased gastric fluid acidity Decreased competency of lower esophageal sphincter

Impact of GIT Changes Increased risk of aspiration All parturients are a “full stomach” Aspiration prophylaxis recommended for C/S 0.3M Sodium citrate 30 mls po Ranitidine 50mg iv Metoclopramide 10mg iv

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

Pain of childbirth Nociceptive pathways involved T10 – L1 during labor plus S2-S4 for delivery

Is pain bad in labor? Psychological stress can cause: increased levels of catecholamines hyperventilation These may result in decreased uterine blood flow leading to hypoxia and acidosis in the fetus

Factors affecting pain perception in labor Mental preparation Family support Medical support Cultural expectations Underlying mental status Parity Size and presentation of the fetus Maternal pelvic anatomy Duration of labor Medications

Analgesia for labor and delivery Non-medication Inhalational Parenteral Regional

Analgesia- Non medication options Breathing exercises Autohypnosis Acupuncture White Noise/ Music Massage/ walking TENS Water bath

Inhalation Medications Nitronox: 50:50 mixture of oxygen and nitrous oxide Low dose Isoflurane in oxygen Advantages: on demand delivery, relatively safe Disadvantages: variable efficacy, nausea, drowsiness, neonatal depression

Parenteral Medications Narcotics: meperidine, morphine fentanyl Advantages: relatively good analgesia Disadvantages: nausea, vomiting, sedation, neonatal depression (max. 2 hours after meperidine dose), short duration of action

Regional techniques Epidural, 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 parturient General considerations of the parturient undergoing surgery Obstetric surgery

General considerations Altered physiology as mentioned Risks to the fetus: Effect of the disease process/therapies Possible teratogenicity of anesthetic agents Intraoperative effects on uteroplacental blood flow Increased risk of preterm labor/ risk of abortion

Maternal considerations Altered physiology Altered response to anesthesia Decrease in MAC Increased sensitivity to neuraxial agents Decreased plasma cholinesterase Decreased protein binding (more free drug) Limited drug information in parturients

Fetal Considerations Teratogenicity: Limited information due to impracticality of conducting trials with sufficient power Guidelines 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 trimester No anesthetic agent is a proven teratogen in humans Anesthetic agents deemed safe include: thiopental,morphine, meperidine,fentanyl, succinylcholine, NDMRs Limiting nitrous oxide use but only if hypotension secondary to volatiles can be avoided

Anesthetic management in the parturient should be directed to: Avoidance of hypoxemia Avoidance of hypotension Avoidance of acidosis Maintain PaCO2 in the normal range for the parturient Minimize effects of aortocaval compression

Anesthesia for Caesarean Section Preparation Preventing complications Choice of Anesthetic technique Effects on the fetus

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

Preventing complications Aspiration prophylaxis Detailed airway assessment Fluid resuscitation/left lateral tilt to prevent hypotension Safe practice for placement of neuraxial blocks

Anesthetic techniques Local infiltration by surgeon Regional anesthesia: spinal, epidural, combined spinal-epidural General anesthesia

Local Infiltration Rarely performed Patient usually in extremis Surgery must be done via midline incision, gentle retraction, no exteriorization of the uterus Usually done to supplement a regional technique if local anesthetic toxicity not a concern

Regional: Spinal Anesthesia Simple to perform Rapid onset Single shot technique Profound neural block Technique of choice for uncomplicated elective caesarean sections and in many emergency caesarean sections

Spinal Anesthesia Potential Complications: Hypotension Headache (rare ~1:100) Backache (temporary ~24hrs) Nausea/vomiting (secondary to BP, narcotics) Neurological damage (very rare) Anaphylaxis (very rare)

Regional: Epidural Anesthesia More technically challenging Slower onset Used when already placed for labor analgesia Useful in parturient where a slow, controlled onset of block is needed Allows prolongation of block should surgery be complicated

Epidural Anesthesia Potential Complications: Hypotension Headache (approx 1:100) Transient backache ~24hrs Urinary retention Unintentional spinal injection Intravascular injection of local anesthetic Neurological damage Infection

Regional: Combined spinal-epidural Used 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 catheter Complications: as mentioned for spinals and epidurals

General Anesthesia Used when Patient refuses regional technique Regional technique is contraindicated Emergency C/S when there is inadequate/absent regional analgesia and to delay will cause undue risk to the fetus / mother

General Anesthesia Complications: Failed intubation Failed ventilation causing death or neurological injury Awareness Aspiration pneumonia

Anesthesia: Effects on the fetus Avoid hypotension, hypoxia, acidosis, hyperventilation Limit time between uterine incision and delivery to less than 3 minutes Infants exposed to GA have lower Apgar at one minute but no difference at 5 mins No significant alteration in neurobehavioral scores with regional techniques

MCQ 1. Epidural Anesthesia in Obstetric Practice MCQ 1. Epidural Anesthesia in Obstetric Practice. Which of the following is false. A. Commonly causes itching B. Can be used to control blood pressure in pre-eclampsia C. Causes uterine relaxation D. Causes urinary retention E. Contributes to the effects of aortocaval compression

MCQ 1. Epidural Anesthesia in Obstetric Practice… A. Commonly causes itching B. Can be used to control blood pressure in pre-eclampsia C. Causes uterine relaxation D. Causes urinary retention E. 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 pH B. MAC is decreased C. It is contra-indicated in patients with a bleeding diathesis D. Is a major cause of overall maternal mortality E. Succinylcholine crosses the placenta

MCQ 2. All of the following are false concerning general anesthesia in the parturient, EXCEPT: A. General anesthesia reduces gastric pH B. MAC is decreased C. It is contra-indicated in patients with a bleeding diathesis D. Is a major cause of overall maternal mortality E. 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-T12 B. Sensation from the birth canal is via the pudendal nerve C. Lower segment innervation is via S2-4 D. Motor function occurs via sympathetic and parasympathetic nerves E. 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-T12 B. Sensation from the birth canal is via the pudendal nerve C. Lower segment innervation is via S2-4 D. Motor function occurs via sympathetic and parasympathetic nerves E. 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 EXCEPT A. Resting PaCO2 is decreased B. Hematocrit is decreased C. Blood volume is increased D. Gastric secretion is increased E. Total peripheral resistance is decreased

MCQ 4: Physiological changes seen in the last trimester include all EXCEPT A. Resting PaCO2 is decreased B. Hematocrit is decreased C. Blood volume is increased D. Gastric secretion is increased E. Total peripheral resistance is decreased

Gastric acid production does not increase 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. Metoclopramide B. Glycopyrollate C. Sodium citrate D. Clear fluids 4 hours pre-op E. Ranitidine

MCQ 5: All of the following are suitable for aspiration prophylaxis prior to caesarean section, EXCEPT: A. Metoclopramide B. Glycopyrollate C. Sodium citrate D. Clear fluids 4 hours pre-op E. 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 stimulation B. White noise C. Epidural bupivacaine D. Intrathecal narcotics E. 70% Nitrous oxide in Oxygen

MCQ 6: All are suitable techniques for pain relief in labor EXCEPT: A. Transcutaneous electrical nerve stimulation B. White noise C. Epidural bupivacaine D. Intrathecal narcotics E. 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 section B. Fetal distress C. INR 1.6 D. Maternal exhaustion E. Maternal multiple sclerosis

MCQ 7: Which of the following is a contraindication to epidural analgesia in labor: A. Previous caesarean section B. Fetal distress C. INR 1.6 D. Maternal exhaustion E. 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 avoided Maternal 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 reduced Coagulopathy is an absolute contraindication to epidural analgesia

MCQ 8 : Likely complications of epidural opioids include all of the following, EXCEPT: A. Itching B. Urinary retention C. Hypotension D. Respiratory depression E. Nausea

MCQ 8 : Likely complications of epidural opioids include all of the following, EXCEPT: A. Itching B. Urinary retention C. Hypotension D. Respiratory depression E. Nausea