Respiratory

The pregnant patient has a compensated respiratory alkalosis (PCO₂ = 32-34), ↑ minute ventilation (MV; ↑ 50%), and ↓ FRC (↓ 20%). ↑ O₂ consumption (↑ 20%) with ↓ FRC results in rapid onset of hypoxemia if ventilation is compromised. Small airway closure due to elevation of diaphragm (exaggerated by obesity and supine position) can → VQ mismatch and ↓ PaO₂. ↑ MV and ↓ FRC enhance uptake of inhalational anesthetics. Mucosal capillary engorgement in upper airways may necessitate a smaller ETT and mandates careful airway suctioning to avoid bleeding. Avoid any nasal airways. Airway changes can occur in labor and necessitate an airway evaluation just prior to administration of anesthesia.

Tests: As indicated from H&P

Cardiovascular

Typically, there is a ↓ SVR (↓ 15%), ↓ diastolic pressure and ↓ MAP (↓ 15%) with ↑ HR (↑ 20%) and ↑ CO (↑ 30-40%, higher in multifetal pregnancy, higher in labor). Use left uterine tilt (15°) to minimize aortocaval compression and supine hypotension. Immediately postpartum, 600-800 mL blood enters the central circulation, due to placental autotransfusion, with further ↑ in CO.

Tests: As indicated from H&P

Hematologic

These patients have ↑ red cell mass (↑ 300-400 mL), ↑ plasma volume (↑ 1200-1300 mL), ↑ blood volume (↑ 1500-1600 mL), ↑ more with multifetal pregnancy. WBC count may ↑ to 15,000/mm³. Iron deficiency anemia often is superimposed on the dilutional anemia of pregnancy (Hct 33%). The typical blood loss of 700-1000 mL is usually well tolerated. Excessive blood loss is possible with uterine atony, multiple gestation, previous C-section, PIH, placenta previa, abruptio placenta, and prolonged labor. Repeat C-section associated with placenta previa poses high risk for hemorrhage because of increased risk for associated placenta accreta.

Tests: Hgb/Hct

Gastrointestinal

Abnormalities, including ↑ intragastric pressure, ↓ esopageal spinchter tone, and ↓ gastric motility (after onset of labor), predisposes to aspiration pneumonitis. All parturients should be considered to have full stomachs and should receive nonparticulate antacid (e.g., 0.3 M Na citrate 30 mL) immediately prior to general or regional anesthesia. Administer iv metoclopramide 10 mg and ranitidine 150 mg or famotidine 20 mg before all C-sections.

Hepatic

Liver enzymes can be mildly elevated, alkaline phosphatase is elevated from placental source, and plasma protein concentration is diminished (↑ unbound drug levels).

Tests: As indicated from H&P

Renal

These patients have ↑ renal blood flow (↑ 50%), ↑ GFR, and ↑ creatinine clearance, and ↓ serum creatinine and ↓ BUN. Dependent edema results from increased water and Na⁺ retention 2° resetting of the osmotic threshold for thirst and vasopressin secretions.

Tests: As indicated from H&P

Laboratory

T&S maternal blood if risk factors for blood loss are present (e.g., third C-section). Routine cross-match unnecessary unless significant blood loss is anticipated. Routine autologous blood donation is not recommended. Coagulation studies and Plt count recommended with PIH, abnormal placentation, heavy maternal bleeding. BUN, Cr, UA, and fasting blood glucose; others as indicated from H&P.

Premedication

Agents to decrease risk of aspiration pneumonitis include a nonparticulate antacid (e.g., Na citrate 30 mL po), ranitidine 150 mg iv and metoclopramide 10 mg iv. Sedatives are not routinely administered. In extremely anxious patients, however, 0.5-1.0 mg midazolam iv is an excellent anxiolytic, without apparent effect on maternal memory or alertness or neonatal condition.

Pregnancy-induced hypertension (PIH)

PIH is characterized by generalized vasoconstriction with relative intravascular volume depletion and, occasionally, diffuse capillary leak. There may be ↑ risk of hypotension with regional anesthesia. Cautious hydration prior to regional anesthesia is necessary to prevent hypotension or pulmonary edema. Hepatic dysfunction may be present (HELLP syndrome). Epidural, spinal, and combined spinal-epidural (CSE) are all considered safe techniques in PIH assuming normal Plt count. Cardiovascular stability is better with regional than GA, provided intravascular volume is adequate. Abnormal coagulation (↓ Plt count or dysfunctional Plt) contraindicates regional anesthesia. If GA is necessary, it is vital that precautions are taken to ↓ laryngoscopic hypertensive response. Use supplementation along with RSI technique; lidocaine (1 mg/kg), emolol (1-2 mg/kg), and/or remifentanyl (0.5-1 mg/kg). Labetalol (20 mg) or hydrolazine (5-10 mg) can be used, but beware of onset times (< 5 min and 5-15 min, respectively), so choose drugs appropriate to urgency. There is a potential for difficult intubation in PIH due to airway edema; therefore, a small ETT (6.0 mm) should be available. MgSO₄ potentiates neuromuscular blocking agents; avoid defasciculating dose of muscle relaxant before induction, use smaller than normal doses of nondepolarizing agents, and monitor neuromuscular function. MgSO₄ may potentiate hypotension and increase vasopressor requirements.

Tests: PT; PTT; Plt; TEG or bleeding time; LFTs

Eclampsia

Treat eclamptic Sz with adequate oxygenation and a small dose of either midazolam (2 mg) or propofol (20-40 mg). Intubate if necessary to protect airway. Initiate MgSO₄ therapy (loading dose: 4-6 g iv over 20 min; then infuse @ 1-2 g/h). If 2nd seizure occurs during maintenance dose (rare); can administer 2nd bolus dose of 2 g over 5 min.

Massive maternal hemorrhage:

• Placenta previa

• Abruptio placenta

• Ruptured uterus

Administer massive transfusion protocol (MTP) available at institution. Insert 2 large-bore iv catheters (14-16 ga) and consider sending Hg/HCT and coagulation studies. Ensure immediate availability of cross-matched blood and if unavailable consider uncross-matched or O-negative blood. Rapidly restore intravascular volume with crystalloid, colloid, or both until blood is available. If bleeding continues, administer MTP, consisting of a transfusion of PRBC, plasma, and platelets. Induction with either ketamine (1-1.5 mg/kg) or etomidate (0.2-0.6 mg/kg) is preferred in hypovolemic or unstable patients. DIC and dilutional coagulopathy may follow abruptio placenta, amniotic fluid embolism, massive blood loss, and resuscitation. A ratio of RBC:FFP:PLT of 6:4:1 or RCB:FFP of 1:1 is currently recommended during massive transfusion.

Uterine atony is treated with oxytocin 20-40 U/L in NS @ rate sufficient to control atony (250-500 mL/h). Small boluses 1-2 U are appropriate, but avoid larger doses (risk of ↓ BP); alternatively, methylergonovine, 0.2 mg im (risk of HTN), Carboprost Tromethamine (Hemabate®; a synthetic analog of PGF2x), 0.25 mg im or intramyometrially (risk of pulmonary HTN, bronchospasm) or misoprostol (600 mg buccal or 1000 mg PR). Uterine artery embolization may be effective in controlling continued postpartum bleeding and may be considered before surgical artery ligation or hysterectomy. Emergency hysterectomy, however, may be the only solution to continued bleeding. Induction of GA may be necessary if massive bleeding occurs during regional anesthesia.

Diabetes

Diabetic patients have an increased propensity to ↓ BP following regional anesthesia. Determine blood glucose hourly and maintain at 80-100 mg/dL. Insulin requirements decrease drastically after delivery, and insulin dosage must be reduced to prevent maternal hypoglycemia.

Tests: Fasting blood glucose; UA

Response to anesthetic drugs

In pregnant patients, MAC is ↓ 30% for inhaled agents; combined with more rapid uptake, this predisposes to anesthetic overdose. Sensitivity to local anesthetics also is increased. Epidural space capacity is decreased 2° engorgement of epidural veins; this decreases requirements for local anesthetics and increases possibility of intravascular injection of drugs. Increased sensitivity to nondepolarizing muscle relaxants (especially in patients receiving MgSO₄) mandates careful monitoring and use of reduced doses. Decreased protein binding may increase toxicity of highly protein-bound drugs such as bupivacaine.

Epidural

Apply monitors, fluid load, and place the patient in the sitting or lateral decubitus position. Locate the epidural space with a 17-18 ga Tuohy needle and LOR to saline (preferable) or air technique. A 3 mL test dose of 1.5-2% lidocaine (45-60 mg) with 1:200,000 epinephrine (15-20 mcg) is given through the epidural needle or catheter to exclude intravascular injection (Sx: tachycardia, palpitations, dizziness, tinnitus, new taste in mouth) or subarachnoid placement (motor/sensory block in lower extremities, rapid onset of pain relief). After 3-5 min, inject 15-20 mL 2% (300-400 mg) lidocaine with 1:200,000 epinephrine (75-100 mcg) incrementally over 5-10 min. Sodium bicarbonate, 1 mEq/10 mL lidocaine, hastens onset of block and improves the block quality, but increases risk of ↓ BP. Bupivacaine, levobupivacaine, or ropivacaine 0.5%, 15-20 mL (75-100 mg), with or without epinephrine 1:200,000 and/or fentanyl (50-100 mcg), or 2-chloroprocaine (450-600 mg) or 2% lidocaine with epinephrine should produce adequate surgical anesthesia within 5-10 min.

Left uterine displacement is best achieved by evaluating the right hip with a wedge or towel. Administer O2 by mask or nasal cannula, and continue to monitor FHR prior to abdominal prep. Monitor BP every min until stable, then every 3-5 min. Treat ↓ in BP with further uterine displacement, additional fluids, and vasopressors as outlined earlier. Maintain BP at baseline levels to optimize placental perfusion. For inadequate anesthesia, give additional epidural local anesthetic, 50-100 mcg fentanyl iv or epidurally, 50% N₂O/O₂, ketamine 10-20 mg iv, midazolam 1-2 mg iv, and/or infiltrate with local anesthetic. The patient must remain conscious to avoid risk of aspiration. If anesthesia is still inadequate, induce GA (see below).

After delivery of infant and placenta, rapidly infuse oxytocin 10-20 U/hr. Monitor for excessive blood loss, recognizing that significant blood loss can occur quickly and outside of direct observation, and is often underestimated. Chest pain, mild oxyhemoglobin desaturation, and SOB after delivery may be due to irritation of diaphragm by blood or packs, too high or inadequate level of anesthesia, or venous air or amniotic fluid embolization. Transient S-T segment changes on ECG may occur, but do not usually signify myocardial ischemia.

Spinal

Apply monitors, administer fluid, and position as for epidural anesthesia. Metoclopramide 10 mg iv, 5-10 min prior to block decreases intraop N/V. Insert 25-27-ga pencil-point needle and verify free flow of CSF. If technical difficulties or urgent situations are encountered, a larger pencil-point needle (e.g., 22-ga Sprotte) may be considered. Inject hyperbaric 0.75% spinal bupivacaine 11.25-12.0 mg (1.5-1.6 mL) ± fentanyl 10-20 mcg and preservative-free morphine 0.1-0.2 mg, and position the patient with left uterine displacement. Monitor and treat ↓ BP as for epidural. Adjust operating table position to insure a T4 level of anesthesia. If anesthesia is inadequate and time permits, consider repeating block with CSE, spinal (caution with dosing), or epidural catheter. Treat persistent inadequate anesthesia as for epidural. Induce GA if other measures fail.

Combined spinal-epidural (CSE)

An alternative technique combining the rapid onset and density of spinal anesthesia with the flexibility of continuous epidural anesthesia (e.g., if necessary to extend the duration or intensity of the block). Apply monitors, administer fluid, and position as for spinal/ epidural. The most common technique is the needle-through-needle. When the epidural space is located with a standard 17-18 ga Tuohy needle, insert a 25-27 ga pencil-point spinal needle through it and administer either a standard C-section spinal dose of bupivacaine and narcotics as described for spinal or reduced dose if indicated (e.g., repeated block after failed spinal or epidural; maternal cardiac disease or short stature). Secure the epidural catheter and use if needed. Appreciate that the epidural catheter is untested and an epidural test dose is advisable prior to dosing.

Induction

Elevate the right hip (wedge or towel) to provide left uterine displacement. Preoxygenation for 3-5 min is optimal; however, 4-8 maximal inspiratory breaths in 30 sec is a satisfactory substitute in an emergency. Head up and CPAP may improve oxygenation in obese parturients. Place patient in maximal “sniff” position (ramp patient if necessary), to optimize position for intubation. After patient is prepped and draped and obstetric team is ready to begin, perform rapid-sequence induction with cricoid pressure. Administer propofol 2-3 mg/kg (or ketamine 1-1.5 mg/kg or etomidate 0.2-0.6 mg/kg in hypovolemic or cardiovascularly unstable patients) and succinylcholine 1-1.5 mg/kg to induce GA and facilitate intubation. Inflate cuff of ETT and verify tracheal placement by ETCO2 waveform and auscultation of bilateral breath sounds.

Failed intubation

If tracheal intubation is unsuccessful, oxygenation and mask ventilation must become a priority, and numerous attempts to intubate should be avoided. Summon experienced help and quickly decide whether surgery must proceed. The risks of continuing with mask GA and cricoid pressure must be weighed against the risk of allowing the mother to awaken. If mask ventilation is impossible, quickly attempt ventilation with an LMA. If this succeeds, either continue to use throughout the case or place an ETT (6 mm ID) through LMA blindly or with FOL; alternatively, use an intubating LMA. A Pro-seal LMA has been used successfully as a rescue supraglottic airway device in this situation and may negate the necessity for ET intubation. Cricoid pressure may interfere with mask ventilation or LMA placement and should be released if necessary. If LMA fails to allow ventilation, attempt emergency transtracheal ventilation using a 12-14 ga iv catheter (or specific cricothyroid airway device) and appropriate tubing to connect to a high-pressure O₂ source (e.g., jet ventilator). If these measures are unsuccessful, an emergency cricothyrotomy or tracheostomy should be performed by experienced personnel. Planning for a failed intubation must occur before it actually happens. A difficult-intubation tray, including video laryngoscopes, supraglottic airways, and equipment for emergency jet ventilation, must be immediately accessible in or very near the delivery room.

Maintenance

50% N₂O/O₂ with isoflurane, sevoflurane, or desflurane (limit MAC < 1.5 to prevent uterine atony). Propofol infusion for maintenance negates the uterine relaxant effect of the halogenated agents but may lead to more neonatal depression. Avoid hypocapnia during controlled ventilation which may ↓ umbilical blood flow. After delivery, NDMR rarely required, additional opioid (e.g., fentanyl 150-250 mcg) and increase volatile and N₂O concentrations if necessary. Administer small doses of muscle relaxants (e.g., vecuronium 2-3 mg or rocuronium 10-20 mg) if needed. Reverse with neostigmine 0.05 mg/kg and glycopyrrolate 0.01 mg/kg or atropine 0.02 mg/kg. Consider titrating longer-acting opioids (e.g., hydromorphone 1-2 mg) for postpartum analgesia. Midazolam (1-2 mg), given after delivery, helps avoid maternal awareness, which occasionally occurs with this anesthetic technique. Consider TAP (transversus abdominus plane) blocks preemergence.

Emergence

Delay extubation until patient is fully awake and muscle strength has returned to normal.

Blood and fluid requirements

Moderate blood loss

IV: 16-18 ga × 1 (additional larger

IV access if hemorrhage)

NS/LR 1-3 L typical replacement

Infuse 1-2 L dextrose-free crystalloid (± colloid 500 mL) immediately prior to regional anesthesia. Typical blood loss = 700-1000 mL. A rapid-fluid infuser and blood warmer should be available in the event that large-volume blood transfusion is required.

Monitoring

Standard monitors (see p. B-1)

FHR monitor

±CVP

±arterial line

Arterial BP monitoring via automated BP device, or arterial line for severe or labile HTN. CVP useful in PIH for oliguric patients unresponsive to fluid challenges. Occasionally, a PA catheter is indicated (e.g., for pulmonary edema, unresponsive oliguria).

Positioning

Left uterine displacement (blanket under right hip and/or table tilt)

Minimizes aortocaval compression.

Complications

Amniotic fluid embolism

Rare cause of hemodynamic instability, hypoxemia, and DIC. Often fatal. Rx: supportive: 100% O₂, PEEP, and vasopressors. Correct Plt, clotting factors, and metabolic disturbances. CPB has been used successfully.

Complications

VTE

Postpartum hemorrhage

Pregnancy and C-section increases risk of venous thromboembolism. DX: pleuritic chest pain, cough, hypoxemia, ↑ RR, ↑ HR, ↑ A-a gradient. Rx: supportive: 100% O₂, volume expansion, and vasopressors. See p. B-8.

See Anesthetic Considerations for Removal of Retained Placenta, p. 855.

Pain management

Epidural: 2-4 mg (preservativefree) morphine after delivery.

Intrathecal: Morphine (preservative-free) 0.1-0.2 mg given with spinal local anesthetic.

Chloroprocaine may interfere with analgesia from epidural opioids

Common side effects include: pruritus 70%, nausea 30-40%, and, rarely, respiratory depression. Nalbuphine (5-10 mg) and naloxone (0.1-0.4 mg) are used for reversal of these side effects. Metoclopramide (10 mg iv) and/or ondansetron (4 mg iv) may be needed for persistent nausea. Risk of delayed respiratory depression in healthy patients is small; however, adequately trained nursing staff and a protocol for treatment of complications are mandatory if neuraxial opioids are used. These patients should not routinely receive sedatives or other systemic opioids for 12 h, and close monitoring of RR and level of consciousness every hour is necessary for 12 h then every 2 h for the next 12 h. Pulse oximetry and monitors of ventilation (e.g., ETCO2) should be considered in high-risk patients, including those with obstructive sleep apnea, morbid obesity, and patients receiving additional sedatives.

Parenteral opioids: iv opioids (e.g., fentanyl 50-100 mcg, hydromorphone 0.1-0.2 mg) boluses prn or PCA instituted in recovery room. NSAIDS (e.g., ketorolac): iv either in OR at end of case or in PACU or if unable to take orally post surgery. Acetaminophen: iv 1000 mg in OR or in PACU.

Oral analgesics: NSAIDs (e.g., ibuprofen) and acetaminophen around-the-clock dosing for 48-72 postcesarean. Oxycodone or Hydromorphone (or equivalent oral opioid), for breakthrough pain management. TAP block is a beneficial rescue analgesic option in select patients.

Tests

As indicated