Anesthetic Management of Preeclampsia
DEFINITIONS
Pre-eclampsia:
Hypertension, proteinuria, and edema during pregnancy, with usual onset after twenty weeks gestational age.
Incidence: 2.6% of all pregnancies; recurs in 20%. Risk factors include: Age between 25-34, Primip:multip 6.8:1, Twin:single 5:1.
Severe if: Systolic BP > 160, Diastolic BP > 110, proteinuria > 2 g/D, oliguria < 400 cc/D, creatinine > 1.2, headache or visual disturbances, pulmonary edema, intrauterine growth retardation, RUQ or epigastric pain, increased liver function tests, or thrombocytopenia.
Eclampsia:
Pre-eclampsia with addition of seizures. Incidence: 0.056% of all pregnancies.
H.E.L.L.P. Syndrome:
Hemolysis (on peripheral smear, or inc. haptoglobin), Elevated Liver function tests (T.Bil>1.2, LDH>600 SGOT>70) and Low Platelets (< 100K). Incidence: 4-12% of all preeclamptics.
FINDINGS
Brain MRI:
Bright T1 weighted and dark T2 weighted images are consistent with cerebral edema. Lesions are most common in the distribution of the posterior cerebral artery and are associated with visual disturbances. Lesions in the basal ganglia and deep white matter are less common and are associated with mental status changes.
Renal Lesions:
Subendothelial fibrin deposits, electron dense droplets in glomerular epithelial cells that contain: albumin, immunoglobulin, fibrinogen, and complement. These deposits usually disappear in the postpartum period.
Hepatic Lesions:
Periportal or focal parenchymal necrosis with large hyaline deposits of fibrin like material in sinusoids. Decreased synthesis of pseudocholinesterase may prolong sux, chloroprocaine or tetracaine.1 Differential diagnosis is preeclampsia vs. Acute Fatty Liver of Pregnancy.
PT/PTT Glucose Ammonia Fibrinogen AFLP Inc. Dec. Inc. Dec. Preeclampsia Nml. Nml. Nml. Nml or inc.
Hemodynamics:
Pre-eclamptic patients are typically volume depleted, with low cardiac output, low pulmonary capillary wedge pressure, high systemic vascular resistance. Central venous and pulmonary capillary wedge pressure are usually only poorly correlated. Left ventricular dysfunction due to chronic hypertension or peripartum cardiomyopathy may produce pulmonary edema. Plasma volume is 30-40% less than normal peripartum patients. One study using a pulmonary artery catheter found decreased left ventricular performance with normal contractility, consistent with changes secondary to increased afterload.
MANAGEMENT
Fluid Status:
Management of fluids is sometimes complicated due to poor CVP-PCWP correlation, decreased urine output, and wide variability of hemodynamic profile. Pre-eclamptic patients are especially sensitive to the sympathetic blockade that occurs as a result of regional anesthesia and poorly tolerate pre-hydration before regional anesthesia. A pulmonary artery catheter may be needed to guide hydration in the severely pre-eclamptic patient, or if a massive fluid resuscitation is required.
Seizure Prophylaxis:
MgSO4 – 6 g I.V. loading dose (slowly), then 2-3 g/Hr infusion. Therapeutic range: 5-7 mEq/L. Toxicity: 5-9 meq/L – prolonged PR & Wide QRS. >9 meq/L – Loss of tendon reflexes, respiratory arrest and cardiovascular collapse. Mechanism of action: Generalized CNS depression. MgSO4 also interferes with impulse transmission at myoneural junction by decreasing calcium conductance, decreasing release of acetylcholine, and decreasing the excitability of postsynaptic and muscle membranes. Vasodilation of small-diameter intracranial vessels may decrease cerebral ischemia.
Side Effects: MgSO4 potentiates and prolongs non-depolarizing neuromuscular blocking drugs. MgSO4 may exaggerate the decrease in blood pressure that occurs with regional anesth. After prolonged administration fetal, levels approach maternal levels and may result in neonatal hypotonia and respiratory depression.
Alterations in pulmonary function tests: Decreased Maximal Expiratory Pressure (30->25), decreased FEV1 (2.6->2.3), decreased forced vital capacity (3.4->3.2). These effects start after approximately two hours of therapy.
Hypertension:
1st line: Hydralazine, 5-10 mg increments to decrease mean arterial pressure 20% or diastolic BP < 100. Decreases maternal mean arterial pressure and uterine vascular resistance. Uterine blood flow is increased. Hydralazine crosses the placenta and can cause neonatal hypotension.
Labetelol: 1 mg/kg blocks the response to endotracheal intubation without producing neonatal effects. Rapid onset, with gradual decrease in blood pressure. SVR is decreased, with no change in cardiac output.
Nitroprusside: 0.25-0.5 ug/kg/Min. Animal/human studies: if used in a low dose, nitroprusside is effective; there is no evidence of fetal cyanide accumulation.
Nifedipine: 18 40-120 mg PO QD. More effective than hydralazine, less fetal distress, fewer NICU days.
Nitroglycerine: Decreased mean arterial pressure, but did NOT prevent response to intubation. Patients receiving volume expansion are markedly resistant.
Trimethaphan: Not always effective. Causes tachycardia, tachyphylaxis, histamine release, prolongs the duration of action of succinylcholine.
Labor Analgesia:
I.M. narcotics, if regional is contraindicated:
Epidural: Preferred because: Can increase placental blood flow by up to 75%, decreases and stabilizes maternal blood pressure, does not cause respiratory depression, and provides excellent analgesia. Careful management of fluid status by appropriately managed pre- hydration prevents decrease in blood pressure and in uterine BF.
Contraindications to regional analgesia/anesthesia: clotting abnormality, local skin infection, severe hypotension.
General Management:
Resuscitation equipment handy, fetal heart rate and contraction monitors, physiologic monitors as indicated.
Monitoring:
Mild Pre-eclampsia:
Routine monitors (i.e., ECG, noninvasive blood pressure, pulse oximeter, capnography, stethoscope)
Severe Pre-eclampsia:
Routine monitors plus an arterial line, central venous or pulmonary artery catheter (indications: Pulmonary edema, refractory oliguria, intractable HTN, hemorrhagic hypovolemia requiring massive fluid resuscitation)
Goal: CVP 4-6 and PCWP 8-10 — “colloid use is controversial” 1
Pressors: Use caution: Pre-eclamptic patients are more sensitive to these drugs than are normal parturients. The use of smaller doses is recommended. E.g., try 2.5 mg increments of ephedrine.
Cesarean Section:
Considerations:
Control hemodynamic and fluid status, seizure prophylaxis, monitoring as above.
Epidural anesthesia:
Epidural anesthesia is suitable for caesarian section, provided there are no contraindications. Epidural anesthesia has been shown to produce significantly lower levels of stress hormones (corticotropin, beta-endorphin, catecholamines) than general anesthesia.
Low concentrations of local anesthetics should be used. Small, incremental doses produce a gradual change in blood pressure. Add fentanyl 1 to 2 u/cc. A typical infusion rate is 10-15 cc/Hr.
General anesthesia:
Used for emergencies, or when epidural anesthesia is contraindicated.
Anticipate:
1) A pronounced hemodynamic response to intubation. Use anti- hypertensives to decrease MAP 20% or diastolic BP < 100.
2) Airway edema may result in a possibly difficult intubation. Repeated attempts at endotracheal intubation may cause hypertension, or pulmonary edema or make subsequent attempts more difficult.
3) MgSO4 prolongs and intensifies action of neuromuscular blocking agents.
4) Aspiration risk: Use clear antacids pre-op, rapid sequence, suction stomach after induction.
Preparation for Anesthesia: Clear antacid, metoclopramide IV, 15% left uterine displacement, pre-oxygenate at least 3-4 min, or 3-4 very deep breaths, tight mask fit to fully de-nitrogenate.
Induction: Rapid sequence: Thiopental 4 mg/kg using cricoid pressure, Succinylcholine 1 mg/kg.
Maintenance: 50% N2O until delivery, then add fentanyl, isoflurane, and/or increase N2O percentage.
Emergence: Consider labetalol, or other anti-hypertensive to control inc. B/P with extubation.
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