Pregnancy-Induced Hypertension (PIH) and Anaesthesia - Complete Guide

1. DEFINITION

Sources: Morgan & Mikhail's Clinical Anesthesiology, p. 1646; Rosen's Emergency Medicine, p. 3355; Goodman & Gilman's Pharmacological Basis of Therapeutics

2. CLASSIFICATION OF HYPERTENSIVE DISORDERS IN PREGNANCY

A. Gestational Hypertension

• New BP ≥ 140/90 mmHg occurring during pregnancy
• Resolves during the postpartum period
• No proteinuria, no evidence of end-organ damage
• Normal mental status, reflexes, LFTs, coagulation

B. Preeclampsia

• Gestational hypertension after 20 weeks WITH:
  • Proteinuria (>300 mg/24 hr), OR
  • Signs of end-organ damage (even without proteinuria per updated criteria)

C. Eclampsia

• Occurrence of tonic-clonic seizures in a patient with signs of preeclampsia
• Progression from preeclampsia to eclampsia is unpredictable and can occur rapidly
• Seizures and coma are the hallmarks

D. Pregnancy-Aggravated Hypertension (Superimposed Preeclampsia)

• Chronic hypertension with superimposed preeclampsia or eclampsia

E. Chronic/Coincidental Hypertension

• Present before pregnancy or persists for more than 6 weeks postpartum
• Often overlaps pathogenetically with essential hypertension
• Risk factor for developing preeclampsia

3. PRE-ECLAMPSIA - DETAILED

Definition

Pathophysiology

1. Endothelial dysfunction - releases vasoactive mediators causing vasoconstriction
2. Thromboxane-prostacyclin imbalance - favoring vasoconstriction and platelet aggregation (antiplatelet agents reduce risk, supporting this mechanism)
3. Hemodynamic progression:
   • Early: elevated cardiac output with higher-than-normal cardiac output
   • Later: cardiac output drops as peripheral resistance rises markedly
4. Intravascular volume is lower than in normal pregnancy despite total body water excess
5. Central venous pressures are normal; capillary wedge pressures are variable

Classification: Mild vs. Severe Pre-eclampsia

• BP: systolic 140-159 / diastolic 90-109 mmHg
• Proteinuria: 300 mg - 2g/24h
• No end-organ symptoms

• Diastolic BP > 110 mmHg
• Severe proteinuria (>5g/24h or 3+ on dipstick)
• CNS effects: headache, visual disturbances (blurring, scotomata)
• Hyperreflexia (precedes seizures)
• Oliguria, elevated creatinine
• Elevated LFTs, liver tenderness
• Pulmonary edema
• Thrombocytopenia

Risk Factors

• Age < 20 years
• Primigravida
• Twin / molar pregnancies (incidence up to 20% in twins, 60% in triplets, 90% in quadruplets)
• Hypercholesterolemia
• Pregestational diabetes
• Obesity
• Family history of PIH
• Assisted reproductive technologies

HELLP Syndrome

• Hemolysis
• Elevated Liver enzymes (ALT and AST > 70 U/L)
• Low Platelet count (< 100,000/mL)

Clinical Features

• Mild BP elevation, no proteinuria, no organ damage, normal reflexes, normal labs

• BP elevation, proteinuria
• Edema (no longer a diagnostic criterion - normal in pregnancy)
• Proteinuria variable in random specimens (24-hour collection required)

• Diastolic > 110 mmHg
• Severe proteinuria
• Headache, visual disturbances (CNS)
• Hyperreflexia before seizures develop
• Thrombocytopenia, elevated LFTs
• Oliguria, elevated creatinine

4. PHARMACOLOGICAL MANAGEMENT OF PRE-ECLAMPSIA

Antihypertensive Drugs

• Hydralazine: 5-10 mg IV/IM, repeat every 20 min (first-line in many settings)
• Labetalol: 20 mg IV; escalate to 40 mg at 10 min if needed; initiate specific treatment only if DBP > 105 mmHg or SBP > 160 mmHg
• Nifedipine (rapid-release): 10 mg PO if IV access unavailable

Magnesium Sulfate (Seizure Prevention + Treatment)

• Loading dose: 4-6 g IV over 15-20 minutes
• Maintenance: 1-3 g/hr IV
• Therapeutic level: 4-6 mEq/L
• Mechanism: not fully clear; has little antihypertensive effect but is the most effective anticonvulsant - prevents recurrent seizures while maintaining uterine and fetal blood flow
• Indicated for: severe preeclampsia, CNS manifestations (headache, visual disturbance, altered mental status), and postpartum women with CNS signs (~20% of eclampsia occurs >48h postpartum)

• Loss of patellar reflexes: ~10 mg/dL (earliest sign)
• Respiratory depression: ~12 mg/dL
• Antidote: Calcium gluconate 1g IV slowly

Corticosteroids

• Given if fetus is viable and ≤ 33 weeks gestation
• Betamethasone 12 mg IM, two doses 24h apart

Definitive Treatment

5. ECLAMPSIA - ACUTE MANAGEMENT

1. Protect airway - lateral decubitus, suction
2. Oxygen supplementation
3. MgSO₄ loading dose (4-6 g IV over 15-20 min) - terminate seizures and prevent recurrence
   • If already on MgSO₄: additional 2 g IV bolus
4. If seizure lasts > 5 min: small dose of propofol or midazolam (avoid polypharmacy)
5. Control hypertension after seizures - only if DBP > 105 or SBP > 160 mmHg
6. Fetal monitoring - HR abnormalities common during seizures, usually resolve after
7. If seizures persist despite MgSO₄: lorazepam 2-4 mg IV; phenytoin/fosphenytoin 15-20 mg/kg IV; levetiracetam 20-60 mg/kg IV
8. Consider CT/MRI if: recurrent/focal seizures, seizures despite therapeutic MgSO₄, decreasing consciousness not postictal
9. Fluid management: intravascular volume is contracted (despite total body water excess) - avoid diuretics and hyperosmotic agents; avoid excessive IV fluids (risk of postpartum pulmonary edema); invasive PA monitoring if needed

6. ANAESTHESIA MANAGEMENT IN PIH/PRE-ECLAMPSIA

Pre-anaesthetic Assessment

• Severity of hypertension and current BP
• Proteinuria, signs of end-organ damage
• Neurological: headache, visual disturbances, hyperreflexia
• Airway: upper airway edema is common and severe - anticipate difficult intubation
• Fluid status: look for pulmonary edema, oliguria

• Full blood count - platelet count (critical for regional decisions)
• Coagulation profile - PT, aPTT, fibrinogen
• LFTs (AST, ALT)
• Renal function - creatinine, urea
• Urine protein
• Thromboelastography (TEG/ROTEM) if available - global coagulation assessment

• Invasive arterial line for severe hypertension, severe disease, or when using IV vasodilator infusions
• Central venous access when vasopressors/inotropes needed or in pulmonary edema and refractory oliguria
• PA catheter rarely needed; noninvasive cardiac output monitors (echocardiography, arterial pulse wave contour analysis) preferred

Haemodynamic Profile (Variable)

• Low-normal cardiac filling pressures
• Increased systemic vascular resistance
• Cardiac output may be reduced, normal, or increased

Regional Anaesthesia (Preferred)

• Best quality pain relief
• Attenuates hypertensive responses to pain and stress
• Reduces circulating catecholamines
• Continuous epidural improves uteroplacental perfusion by up to 75% (provided hypotension is avoided)
• Decreases catecholamine secretion
• Avoids the high risk of failed intubation due to severe upper airway edema

Epidural Anaesthesia (First Choice for Labor)

• Continuous epidural is first choice for most preeclamptic patients during labor and vaginal delivery
• Does not require fluid preload when using dilute local anaesthetic or opioid solutions
• Provides cardiovascular stability through gradual sympatholysis
• Reduces catecholamines, improves uteroplacental flow

Spinal vs. Epidural for Cesarean Section

• Spinal and epidural are associated with similar decreases in arterial BP in mild preeclampsia
• Spinal anesthesia for cesarean: incidence and severity of hypotension does NOT appear to be increased in preeclampsia with severe features vs. normotensive patients (prospective study evidence)
• Both are acceptable; combined spinal-epidural (CSE) is also used

Platelet Threshold for Regional Anaesthesia

• Recommended safe threshold: platelet count ≥ 100,000/μL
• Lower threshold: platelet count as low as 50,000/μL may be acceptable in selected cases when:
  • Count has been stable (not rapidly falling)
  • Global coagulation by TEG is normal
• Main concern: spinal/epidural haematoma → nerve injury/paraplegia
• Many anaesthesiologists are comfortable proceeding if platelets are 70,000-100,000/μL with normal coagulation

General Anaesthesia (Avoid If Possible)

1. Difficult/failed intubation - severe upper airway edema (pharyngeal, glottic, and subglottic edema)
2. Hypertensive crisis at laryngoscopy - exaggerated pressor response (SBP can rise 50-80 mmHg)
3. Risk of cerebral hemorrhage from uncontrolled hypertension during laryngoscopy

• Preoxygenation thoroughly
• Blunt the pressor response to laryngoscopy:
  • Labetalol 10-20 mg IV (2-3 min before induction)
  • Fentanyl 1-2 mcg/kg IV
  • Remifentanil 1 mcg/kg IV
  • Lidocaine 1.5 mg/kg IV
  • Esmolol 1-2 mg/kg IV
  • Hydralazine 5-10 mg IV (longer acting, give 10-15 min before)
• RSI with cricoid pressure (full stomach precautions)
• Suxamethonium 1-1.5 mg/kg for rapid intubation
  • Note: MgSO₄ potentiates neuromuscular blockade - reduce dose of non-depolarizing NMBDs
• Have smaller ETT available (edema may narrow the airway)
• Senior anaesthetist and video laryngoscope at hand
• Extubation: extubate awake, with BP controlled, as re-intubation may be needed

Fluid Management

• Intravascular volume is contracted from vasospasm despite total body water excess
• Endothelial damage + low colloid osmotic pressure (further reduced in proteinuria) = fluids leak out easily
• Crystalloids and colloids readily extravasate → risk of postpartum pulmonary edema
• Aggressive IV fluid loading is NOT recommended
• Judicious fluid boluses only to correct hypovolemia
• Goal-directed therapy using: arterial pulse wave contour analysis, echocardiography
• Avoid diuretics (worsen intravascular hypovolemia, decrease uteroplacental perfusion)
• Invasive pulmonary artery monitoring may be required for accurate fluid management in severe cases

Use of Vasopressors

• Epinephrine in epidural test doses should be avoided or used cautiously (exaggerated hypertensive response due to reduced intravascular volume and endothelial dysfunction)
• Phenylephrine or ephedrine used to treat hypotension from regional anaesthesia - use smaller doses, titrate carefully

Magnesium Interaction with Anaesthesia (Critical!)

• Patellar reflexes (loss indicates toxicity ~10 mg/dL)
• Respiratory rate (depression at ~12 mg/dL)
• Urine output (magnesium is renally excreted; oliguria → toxicity risk)
• Antidote: Calcium gluconate 1g IV

Anaesthetic Plan: Three Scenarios

1. Labor with vaginal delivery → Epidural analgesia (preferred); check platelets first in severe disease
2. Urgent/emergency cesarean → Regional (spinal or epidural) if platelets safe; GA if contraindicated with full airway preparation
3. Planned cesarean → Epidural or spinal (assess coagulation); consider CSE for prolonged surgery

7. POST-DELIVERY CONSIDERATIONS

• Continue MgSO₄ for 24-48 hours postpartum
• ~20% of eclampsia episodes occur >48 hours after delivery - maintain vigilance
• Risk of pulmonary edema in the postpartum period (fluid mobilization)
• Continue antihypertensive therapy postpartum; BP often requires treatment for several weeks
• Preeclampsia increases women's lifetime risk of cardiovascular disease

SUMMARY TABLE: Anaesthesia in PIH

• Morgan & Mikhail's Clinical Anesthesiology, 7e, Chapter 41, pp. 1644-1648
• Rosen's Emergency Medicine, 9e, Chapter on PIH, pp. 3355-3358
• Goodman & Gilman's Pharmacological Basis of Therapeutics, Chapter on Drug Therapy in Obstetrics
• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, Block 19 (Preeclampsia/Eclampsia Anaesthesia)