Anesthetic Management of Intraoperative Hypertensive Crisis in a Patient Posted for Strangulated Hernia Repair

Overview of the Clinical Scenario

1. Emergency induction in a potentially full-stomach patient with limited time for optimization
2. Management of intraoperative hypertensive crisis — a sudden, severe rise in blood pressure that threatens end-organ damage (stroke, myocardial infarction, acute heart failure)

Preoperative Assessment

Identification of Hypertension

• Record blood pressure in both arms; identify baseline and chronic antihypertensive medications
• Assess for secondary hypertension: pheochromocytoma (paroxysmal hypertension + palpitations + diaphoresis), hyperthyroidism, illicit drug use (cocaine), or coarctation of aorta
• Evaluate end-organ damage: ECG (LVH, ischemic changes), serum creatinine, electrolytes (especially if on diuretics)
• For patients with systolic BP >180 mmHg or diastolic >110 mmHg, weigh the risk of delaying surgery against the emergency nature of strangulation — in most cases, surgery cannot be delayed, so optimization must occur intraoperatively (Miller's Anesthesia, p. 3867–3868)

Medication Considerations

• Continue antihypertensives up to the day of surgery except ACE inhibitors and ARBs, which should ideally be withheld 24 hours preoperatively (associated with intraoperative hypotension). However, in true emergencies, this may not be feasible (Miller's Anesthesia, p. 3868)
• If pheochromocytoma is suspected preoperatively, α-blockade must precede surgery to prevent a catastrophic hypertensive crisis on induction (Comprehensive Clinical Nephrology, p. 1649; Sabiston Textbook of Surgery)

Causes of Intraoperative Hypertensive Crisis

Preoperative Preparation

Full Stomach Precautions (Rapid Sequence Induction — RSI)

• NPO status cannot be ensured — RSI is mandatory
• Preoxygenation: 3–5 minutes of 100% O₂ or 4 vital capacity breaths
• Sellick's maneuver (cricoid pressure) during induction
• Agents: Propofol (or ketamine if hemodynamically unstable) + Succinylcholine (1.5 mg/kg) or Rocuronium (1.2 mg/kg) for rapid intubation
• Have vasopressors (phenylephrine, ephedrine, norepinephrine) and antihypertensives immediately available

Pre-induction Antihypertensive Strategy

• IV labetalol 5–20 mg IV (α + β blockade) — reduces tachycardia and hypertension of laryngoscopy
• IV esmolol bolus 0.5–1 mg/kg — short-acting β-blocker for blunting intubation response
• IV fentanyl 2–3 µg/kg — attenuates sympathetic response to laryngoscopy
• Lidocaine 1.5 mg/kg IV 90 seconds before intubation — blunts hypertensive and ICP response

Intraoperative Anesthetic Management

Monitoring (Minimum)

• Invasive arterial line (radial artery preferred) — beat-to-beat BP monitoring; mandatory when hypertensive crisis is anticipated
• ECG (5-lead with ST analysis)
• Pulse oximetry, capnography (EtCO₂)
• Urine output (Foley catheter)
• Consider CVP line if hemodynamically unstable or large fluid shifts expected

General Anesthesia — Agent Selection

• Propofol (1.5–2.5 mg/kg) — causes vasodilation, reduces BP; preferred in hypertensive patients
• Ketamine — avoid as first choice if hypertension is a concern (stimulates sympathetic nervous system); use only if profound hemodynamic instability/shock
• Etomidate (0.3 mg/kg) — hemodynamically most stable induction agent; suitable if there is concern about hypotension immediately post-induction alternating with hypertensive crisis

• Volatile agents (isoflurane, sevoflurane, desflurane): dose-dependent vasodilation and myocardial depression — concentration must be titrated carefully. Excessive concentrations → hypotension; inadequate concentration → hypertension from light anesthesia (Morgan & Mikhail's Clinical Anesthesiology, p. 2703)
• Total IV Anesthesia (TIVA) with propofol infusion + remifentanil is an excellent option — provides tight hemodynamic control and rapid titration
• Depth of anesthesia monitoring (BIS or entropy) helps prevent under/over dosing

Managing the Hypertensive Crisis Intraoperatively

• Is anesthesia too light? → Increase volatile agent concentration or propofol infusion
• Is there hypercapnia? → Check and correct ventilation
• Is there hypoxia? → Check airway, FiO₂
• Inadvertent vasopressor given? → Stop immediately

• Aim for a 20–25% reduction from baseline MAP — not a precipitous drop
• Abrupt normalization risks cerebral/coronary ischemia in chronically hypertensive patients (rightward shift of autoregulation curve)
• Maintain MAP >65 mmHg to ensure organ perfusion

Special Considerations in Emergency Surgery

Sepsis / Peritonitis

• Sepsis-induced vasodilation can cause sudden hypotension after controlling hypertension — vigilant titration essential
• Adequate volume resuscitation with crystalloids (Ringer's lactate/PlasmaLyte) guided by dynamic parameters (pulse pressure variation, stroke volume variation)
• May require vasopressors (norepinephrine) if vasodilatory shock supervenes after hypertensive episode

Aspiration Risk and RSI

• Avoid bag-mask ventilation during RSI to prevent gastric insufflation
• Have suction immediately available (Yankauer)
• Confirm tube placement with capnography immediately

Pain and Opioids

• Adequate intraoperative opioid dosing (fentanyl, morphine) blunts surgical stimulation and reduces hypertensive responses
• Neuraxial adjuncts (spinal or epidural, if not contraindicated by sepsis/coagulopathy) can provide excellent intraoperative hemodynamic stability and reduce general anesthetic requirements

Postoperative Considerations

• Continue invasive BP monitoring in recovery
• Resume oral/IV antihypertensives as soon as hemodynamically stable
• Do NOT withhold ACEI/ARB postoperatively — failure to resume is associated with adverse outcomes (Miller's Anesthesia, p. 3868)
• Manage pain adequately — postoperative pain is a major driver of hypertensive crises
• Watch for end-organ complications: troponin for myocardial injury, neurological assessment for cerebrovascular events, urine output for renal perfusion

Summary Algorithm

Intraoperative Hypertensive Crisis
            ↓
Exclude correctable causes:
  • Light anesthesia → ↑ depth
  • Hypercapnia → ↑ ventilation
  • Hypoxia → ↑ FiO₂
  • Bladder distension → Foley
            ↓
Pharmacologic Treatment:
  • Acute / short-lived → Esmolol or Labetalol IV
  • Severe / sustained → Sodium nitroprusside or Nicardipine infusion
  • Ischemia associated → IV Nitroglycerine
  • Pheo suspected → Phentolamine
            ↓
Target: 20–25% MAP reduction
Maintain MAP > 65 mmHg
            ↓
Postoperative monitoring & BP optimization

Key References

• Miller's Anesthesia, 10e — Hypertension: Preoperative Evaluation and Perioperative Management, pp. 3867–3868
• Morgan & Mikhail's Clinical Anesthesiology, 7e — Anesthetic Management: Choice of Agents, p. 2703
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e — Perioperative cardiovascular management
• Schwartz's Principles of Surgery, 11e — Strangulated/Incarcerated hernia repair: anesthetic considerations
• Comprehensive Clinical Nephrology, 7e — Intraoperative hypertensive crisis: pheochromocytoma management, p. 1649

Physiological Changes During Pregnancy

Summary of Key Quantitative Changes

1. Central Nervous System

• MAC decreases by ~40% at term for all volatile anesthetic agents. Progesterone (which rises 20× above normal at term) is sedating and is partly responsible. A surge in β-endorphins during labor and delivery also contributes. MAC returns to normal by the third day postpartum.
• Sensitivity to local anesthetics is enhanced: neural blockade occurs at reduced concentrations during regional anesthesia. Epidural dose requirements may be reduced by as much as 30%.
• Epidural venous plexus engorgement: Inferior vena cava obstruction by the gravid uterus distends epidural veins and increases epidural blood volume, producing three key effects:
  1. Decreased spinal CSF volume
  2. Decreased potential volume of the epidural space
  3. Increased epidural pressure (may become positive rather than negative)
  • These effects enhance cephalad spread of local anesthetics and increase the risk of inadvertent intravascular injection when placing epidural needles/catheters.

2. Respiratory System

Ventilatory Changes

• Oxygen consumption rises up to 50% by term (increased fetal + maternal metabolic demand)
• Minute ventilation increases up to 50%, mainly through a 40% rise in tidal volume and a smaller 15% rise in respiratory rate — a state of physiological hyperventilation
• PaCO₂ falls to 28–32 mmHg; compensated by renal bicarbonate excretion (HCO₃⁻ ↓ to ~20 mEq/L) → mildly alkalotic pH ~7.44
• PaO₂ rises slightly (~103 mmHg); 2,3-DPG increases, shifting the O₂-Hb dissociation curve rightward (P₅₀ increases from 27 → 30 mmHg), facilitating O₂ delivery to fetal and maternal tissues
• Dead space decreases but intrapulmonary shunting increases toward term

Lung Volumes

• Enlarging uterus elevates the diaphragm, but diaphragmatic motion is not restricted
• FRC decreases by 20% at term (due to reduced expiratory reserve volume); returns to normal within 48 h postpartum
• Vital capacity and closing capacity are minimally affected
• Flow-volume loops are unaffected; airway resistance decreases

Airway

• Capillary engorgement of respiratory mucosa → edema of nose, oropharynx, larynx, and trachea → predisposes to trauma, bleeding, and obstruction during airway manipulation
• Smaller endotracheal tubes (6.0–6.5 mm) should be used; gentle laryngoscopy is essential

Clinical Consequence

3. Cardiovascular System

Blood Volume and Composition

• Blood volume increases by 1000–1500 mL at term (total ~90 mL/kg)
• Plasma volume increases 55% vs. red cell mass 25–45% → physiological dilutional anaemia (Hb normally ≥11 g/dL at term; ~11.6 g/dL)
• The dilutional anemia is offset by increased cardiac output and the rightward shift of the O₂-Hb curve — overall oxygen delivery is maintained
• This expanded volume provides a buffer for blood loss at delivery: average blood loss ~200–500 mL (vaginal), ~800–1000 mL (caesarean)

Cardiac Output

• CO increases 40% at term via ↑ heart rate (20%) and ↑ stroke volume (30%)
• Greatest increases during first and second trimesters; relatively stable in third trimester, but rises further during labor and immediately after delivery
• Cardiac chambers enlarge; mild myocardial hypertrophy on echocardiography
• CVP, PAP, and PAWP remain unchanged
• CO returns to normal ~2 weeks postpartum

Blood Pressure and Vascular Resistance

• Peripheral vascular resistance falls (~15%), lowest in mid-second trimester
• Systolic BP decreases slightly (~5%); diastolic BP decreases more (~15%)
• Pulmonary vascular resistance also decreases (~30%); prevents pulmonary hypertension despite increased flow
• Estrogen and progesterone-mediated vasodilation + placental arteriovenous shunting contribute

Aortocaval Compression

• After week 20, the gravid uterus compresses the inferior vena cava in the supine position → decreased venous return → decreased CO
• ~5% of term women develop supine hypotension syndrome (pallor, sweating, nausea, hypotension)
• The aorta is also compressed → reduced uteroplacental blood flow
• Treatment: tilt patient left lateral (>15° right hip wedge)
• Combined with regional/general anesthesia → risk of fetal asphyxia
• Chronic partial caval obstruction → venous stasis, phlebitis, oedema in lower limbs; distension of epidural and paravertebral venous plexus

Cardiac Examination Findings

• Displaced, enlarged cardiac shadow on CXR (elevated diaphragm)
• Left axis deviation and T-wave changes on ECG
• Grade I–II systolic ejection murmur (flow murmur)
• Exaggerated splitting of S1; S3 gallop may be heard
• Small asymptomatic pericardial effusion possible

4. Haematological System

Anaemia and Blood Cells

• Physiological dilutional anaemia (plasma ↑55% vs. RBC ↑25%) — Hb ~11.6 g/dL at term
• Leukocytosis: normal WBC may reach 13,000/mm³ in pregnancy (up to 21,000/mm³ during labor) — unrelated to infection
• Platelets: decrease ~10%; gestational thrombocytopenia (not <70,000/mm³) is a diagnosis of exclusion; PT and PTT decrease ~20%

Coagulation — Hypercoagulable State

• Pregnancy is a prothrombotic state, beneficial to limit blood loss at delivery
• Increased: fibrinogen (factor I), factors VII, VIII, IX, X, XII (increases of 30–250%)
• Decreased: factors XI and XIII; antithrombin III; protein S
• Unchanged: factors II and V; protein C
• TEG/ROTEM at term: decreased R-time, decreased K-time, increased α-angle, increased MA → confirms hypercoagulability
• Accelerated fibrinolysis in late third trimester
• Risk of VTE is increased throughout pregnancy and especially postpartum

5. Gastrointestinal System

• Gastroesophageal reflux and heartburn are common and worsen with gestational age
• Progesterone and estrogen reduce lower oesophageal sphincter (LOS) tone
• Gravid uterus displaces stomach cephalad, converting intra-abdominal oesophagus to intrathoracic — further reduces LOS competence
• Gastrin (secreted by placenta) increases gastric acid secretion → lower gastric pH
• Gastric emptying is not prolonged in uncomplicated pregnancy, but is significantly delayed by labor, pain, anxiety, and opioids
• All laboring patients are considered to have a full stomach → aspiration prophylaxis + rapid sequence induction is standard

6. Hepatic System

• Hepatic blood flow unchanged
• Minor elevations in AST, ALT, LDH in the third trimester (remain within normal limits)
• Alkaline phosphatase doubles (placental production — not indicative of liver pathology)
• Serum albumin decreases (dilutional) → reduced colloid oncotic pressure → increased free fraction of highly protein-bound drugs
• Plasma cholinesterase (pseudocholinesterase) decreases 25–30% from 10th week of gestation to 6 weeks postpartum → theoretical prolongation of succinylcholine action (rarely clinically significant)
• Incomplete gallbladder emptying (progesterone inhibits cholecystokinin) → risk of cholesterol gallstone formation

7. Renal System

• Renal blood flow increases 60–80% by mid-pregnancy
• GFR increases 50% above baseline by the third month (remains elevated until 3 months postpartum)
• Serum creatinine and BUN decrease (~50% lower upper limit of normal): creatinine may fall to 0.5 mg/dL; BUN to ~9 mg/dL — a "normal" creatinine of 1.0 mg/dL may indicate significant renal impairment in pregnancy
• Glycosuria and proteinuria (up to 300 mg/day) are physiological due to reduced tubular reabsorption threshold
• Plasma osmolality decreases 8–10 mOsm/kg

8. Musculoskeletal System

• Relaxin (elevated throughout pregnancy) loosens pelvic ligaments and joint capsules in preparation for delivery
• Lumbar lordosis increases as the uterus enlarges → low back pain
• Symphysis pubis and sacroiliac joints widen

9. Metabolic and Endocrine System

• Diabetogenic state: insulin levels rise progressively; human placental lactogen (hPL) causes relative insulin resistance → gestational diabetes in susceptible individuals
• Pancreatic β-cell hyperplasia (compensatory)
• Altered carbohydrate, fat, and protein metabolism favours fetal growth — biochemically resembles starvation (low glucose/amino acids, high ketones/FFAs/triglycerides)
• Thyroid: gland hypertrophies; thyroid-binding globulin increases; total T3 and T4 rise, but free T3, free T4, and TSH remain normal
• Calcium: serum calcium decreases, but ionized calcium remains normal

10. Uteroplacental Circulation

• At term, uterine blood flow = ~10% of cardiac output (600–700 mL/min) vs. 50 mL/min in the non-pregnant state
• 80% supplies the placenta; 20% goes to the myometrium
• Uterine vasculature is maximally vasodilated (autoregulation absent) but retains α-adrenergic sensitivity
• Three major causes of reduced uterine blood flow: (1) systemic hypotension, (2) uterine vasoconstriction, (3) uterine contractions
• Extreme hypocapnia (PaCO₂ <20 mmHg) can reduce uterine blood flow → fetal hypoxemia and acidosis
• Vasopressor of choice for hypotension in pregnancy: phenylephrine (less fetal acidosis than ephedrine in clinical studies)

Clinical Summary: Anesthetic Implications

• Morgan & Mikhail's Clinical Anesthesiology, 7e — Chapter 40: Obstetric Physiology, pp. 1572–1581
• Miller's Anesthesia, 10e — Chapter 58: Obstetric Anesthesia, pp. 8813–8820