Intra-Aortic Balloon Pump (IABP)

Overview and History

• Fischer's Mastery of Surgery, 8th ed.
• Braunwald's Heart Disease

Device Construction

• A 7- to 8-French double-lumen catheter with a 25-50 mL, 25-cm long sausage-shaped polyurethane balloon at its distal end
• One lumen connects to the pump console to inflate/deflate the balloon
• Helium gas is used exclusively because:
  • Its low viscosity allows rapid transfer in and out of the balloon
  • If rupture occurs, helium absorbs very rapidly in blood (safety advantage)
• The pump console controls timing via ECG or pressure triggers

Placement

• Inserted percutaneously via the femoral artery (most common) using fluoroscopic or ultrasound guidance
• Optimal position: descending aorta, just distal to the left subclavian artery, proximal to the renal arteries
• Operative placement in the ascending aorta or via the axillary artery is an alternative

Mechanism of Action - Counterpulsation

• Triggered at aortic valve closure - corresponds to the dicrotic notch on arterial waveform or mid-T wave on ECG
• Balloon inflates, displacing blood from the descending aorta
• Elevates aortic diastolic pressure (diastolic augmentation)
• Increases coronary artery perfusion pressure
• Augments cerebral perfusion

• Triggered at the R wave on ECG
• Rapid deflation creates a void in the aorta
• Reduces LV afterload (lower systemic vascular resistance)
• Lowers LV end-diastolic pressure
• Facilitates LV ejection, decreasing myocardial oxygen consumption (MVO2)

Timing and Trigger Modes

• Inflation: mid-T wave (aortic valve closure)
• Deflation: peak R wave (onset of systole)

• Inflation: dicrotic notch of aortic pressure tracing
• Deflation: just before systolic upstroke

• Early inflation - increases afterload (inflates before aortic valve closes)
• Late inflation - reduces diastolic augmentation benefit
• Early deflation - reduces coronary perfusion benefit
• Late deflation - increases afterload (balloon still inflated when LV starts ejecting)

• 1:1 - full support (inflates with every beat)
• 1:2 - inflates every other beat (used during weaning)
• 1:3 - minimal support (used during weaning)

Indications

Contraindications

• Severe aortic regurgitation (inflation worsens AR by increasing diastolic pressure back into LV)
• Aortic dissection (risk of propagation)

• Aortic aneurysm
• Significant coagulopathy
• Severe peripheral arterial disease (especially at insertion site)

IABP vs. Other MCS Devices

Clinical Evidence - IABP-SHOCK II Trial

• At 30 days: 39.7% mortality in IABP group vs. 41.3% in control (RR 0.96; 95% CI 0.79-1.17; p = 0.69) - no significant difference
• No significant difference in secondary endpoints or time to hemodynamic stabilization
• Outside of patients receiving reperfusion, long-term benefits of IABP are not clearly established

Complications

• Major complications: 2.6%
• All complications: 8.1%

• Limb ischemia (major vascular complication - most common)
• Bleeding at insertion site
• Thrombotic complications (IV heparin given for prevention)
• Stroke
• Balloon rupture (helium gas embolism - rare but catastrophic)
• Infection
• Death

Weaning the IABP

• Gradually decrease counterpulsation ratio: 1:1 → 1:2 → 1:3
• Monitor hemodynamics at each step
• Remove when patient tolerates minimal support without hemodynamic deterioration

Key Points Summary

1. Mechanism: Diastolic inflation augments coronary perfusion; systolic deflation reduces afterload
2. Gas: Helium only (low viscosity, rapid absorption if rupture)
3. Position: Descending aorta, distal to left subclavian, proximal to renal arteries
4. Timing: ECG-triggered (R wave for deflation, T wave for inflation)
5. Absolute contraindications: Aortic regurgitation and aortic dissection
6. IABP-SHOCK II: No mortality benefit in cardiogenic shock complicating AMI
7. Partial support only: Requires residual cardiac function to be effective
8. Declining use: Impella and VA-ECMO now preferred for higher-acuity cardiogenic shock

Anaesthetic Management of a Patient Posted for TURP

1. Preoperative Assessment

History and Examination

• Cardiovascular: Assess for IHD, hypertension, heart failure, valvular disease - cardiac events are the leading cause of perioperative morbidity
• Respiratory: COPD, chronic bronchitis (common in elderly male smokers)
• Renal: Obstructive uropathy may cause chronic renal impairment; check baseline creatinine and eGFR
• Medications: Note anticoagulants, antiplatelets, alpha-blockers (tamsulosin), diuretics
• Coagulation: Previous catheterizations may have caused prostatic inflammation; assess for coagulopathy
• Exercise tolerance: Functional capacity estimate

Investigations

Anticoagulation Decision

• Patients on anticoagulant therapy require careful consideration before spinal anaesthesia
• Decision made jointly with the surgeon, weighing risk of stopping anticoagulation vs. benefit of regional technique
• May require bridging with short-acting anticoagulants (heparin)
• TURP itself carries significant postoperative bleeding risk, mandating normal coagulation perioperatively

2. Choice of Anaesthetic Technique

Why Spinal is Preferred

1. Early detection of TURP syndrome: Patient remains awake - restlessness, confusion, and agitation are early warning signs of hyponatremia that would be masked under general anaesthesia
2. Early detection of bladder/capsule perforation: Awake patient complains of new lower abdominal/back pain
3. Lower mortality: A large ACS-NSQIP analysis (2010-2016, 28,486 TURP patients) showed neuraxial anaesthesia associated with lower 30-day mortality vs. general anaesthesia
4. Reduced VTE risk: Regional anaesthesia reduces postoperative venous thrombosis
5. Technically feasible: Adequate muscle relaxation of pelvic floor and perineum for surgeon

Spinal Anaesthesia - Key Points

• Target level: T10 - interrupts sensory transmission from prostate and bladder neck; also eliminates uncomfortable sensation of bladder distension
• Avoid levels above T10: Higher levels mask symptoms of bladder perforation (shoulder/abdominal pain, nausea/vomiting)
• Spinal preferred over epidural for TURP because:
  • Technically easier in elderly patients
  • Epidural may incompletely block sacral nerves (S2-S4) innervating prostate, bladder neck, and penis
  • Spinal provides more reliable sacral coverage

When General Anaesthesia is Used

• Patient refusal of regional technique
• Technical difficulty performing neuraxial block
• Coagulopathy or anticoagulation
• Concerns about sacral nerve coverage
• Unpredictable operative duration (consider GA or CSE)

Caution: Under general anaesthesia, acute hyponatremia from TURP syndrome may delay or prevent emergence from anaesthesia. Restlessness in a sedated/GA patient must never be automatically attributed to inadequate anaesthesia and treated with more sedation/anaesthetic agents - this can be fatal.

3. Irrigating Fluids - Understanding the Problem

• Electrolyte solutions cannot be used with monopolar TURP (they disperse electrocautery current)
• Bipolar TURP uses saline - eliminates hyponatraemia risk but volume overload still possible
• Bag/bottle height determines intravesical pressure and rate of fluid absorption - keep height low

4. Positioning

• Decreased pulmonary compliance
• Cephalad shift of diaphragm
• Reduced lung volumes (RV, FRC, TV, VC)
• Increased cardiac preload
• Risk of lower limb compartment syndrome with prolonged positioning

5. Intraoperative Monitoring

• Halt surgery and assess Na⁺ if >750-1000 mL absorbed
• Terminate surgery if >1000-1500 mL absorbed (females) or >2000 mL (males)
• With saline irrigant (bipolar): terminate after >2500 mL absorbed

6. TURP Syndrome - The Central Complication

Definition

1. Circulatory fluid overload
2. Dilutional hyponatraemia and hypo-osmolality
3. Solute toxicity (glycine, sorbitol, mannitol)

Risk Factors

• Large prostate gland, prolonged resection (>1 hour)
• High intravesical irrigation pressure
• Open venous sinuses
• Hypotonic irrigants
• Low bag height vs. long resection time

Clinical Features

Treatment

7. Blood Loss Management

• Average blood loss: 3-5 mL/min of resection time (~200-300 mL total)
• Difficult to assess due to dilution with irrigating fluid
• Blood type and screen adequate for most; cross-match for large glands or anaemic patients
• ~2.5% patients require intraoperative transfusion
• Transfusion threshold guided by clinical signs of hypovolaemia + serial Hb for prolonged procedures
• Post-TURP haemorrhage: caused by release of prostatic tissue plasminogen activators causing fibrinolysis
  • Treatment: ε-aminocaproic acid 4-5 g IV loading dose, then 1 g/h infusion; or tranexamic acid

8. Other Intraoperative Complications

9. Postoperative Management

• Analgesia: Simple analgesics (paracetamol, NSAIDs if renal function permits); bladder spasm from catheter may require antispasmodics (oxybutynin)
• Monitoring for delayed TURP syndrome: Symptoms can appear hours after surgery
• Haematuria: Continuous bladder irrigation; haemorrhage in <1% requires surgical revision
• Fluid balance: Monitor for continued absorption of residual irrigation fluid
• Anticoagulation resumption: Discuss timing with surgeon given bleeding risk
• Temperature: Actively warm the patient if hypothermic
• DVT prophylaxis: Early mobilisation; consider LMWH given reduced VTE risk was a benefit of regional anaesthesia

10. Bipolar vs. Monopolar TURP - Anaesthetic Implications

Summary - Key Teaching Points

1. Spinal to T10 is the anaesthetic of choice - allows early detection of TURP syndrome
2. Never dismiss restlessness under sedation/GA as inadequate anaesthesia without excluding hyponatraemia
3. Irrigating fluid monitoring is mandatory - track input vs. output throughout
4. Treat TURP syndrome: mild - furosemide; severe - hypertonic saline (slow correction)
5. Prophylactic antibiotics essential (prostate colonization + open venous sinuses)
6. Warmed irrigation fluids prevent hypothermia
7. Elderly patient with cardiac/renal comorbidity requires careful preop assessment
8. Bipolar TURP with saline irrigant has reduced but not eliminated fluid-related complications