Intra-Aortic Balloon Pump (IABP) - DNB Anesthesia Exam Answer (10 Marks)

IABP arterial waveform: diastolic augmentation and reduced assisted aortic end-diastolic pressure - Fischer's Mastery of Surgery, 8e

Introduction

I. INDICATIONS (3 marks)

A. Established / Class I Indications

B. Contraindications

• Aortic regurgitation (balloon inflation in diastole worsens AR and increases LV end-diastolic pressure)
• Aortic dissection

• Abdominal aortic aneurysm
• Severe peripheral arterial disease (especially at the proposed insertion site)
• Significant coagulopathy
• Uncontrolled sepsis
• Severe tachyarrhythmias (reduces diastolic filling time, impairing efficacy)

II. PHYSIOLOGICAL EFFECTS - Mechanism of Counterpulsation (4 marks)

A. Balloon Inflation (During Diastole)

• Triggered at the dicrotic notch (aortic valve closure) - ECG trigger: middle of T-wave
• Balloon rapidly inflates, displacing blood proximally and distally
• Effect: Raises diastolic aortic pressure (diastolic augmentation)
  • Increases coronary artery perfusion pressure (coronary arteries fill during diastole)
  • Increases cerebral perfusion
  • Increases peripheral organ blood flow

B. Balloon Deflation (Just Before Systole)

• Triggered at the R wave peak on ECG (onset of LV systole)
• Balloon rapidly deflates, creating a "vacuum" effect in the aorta
• Effect: Reduces aortic end-diastolic pressure
  • Decreases LV afterload (the LV ejects against a lower resistance)
  • Decreases LV wall stress
  • Reduces myocardial oxygen consumption (MVO2)

C. Net Hemodynamic Effects (Summary Table)

Important: The IABP does NOT generate cardiac output independently - it requires the heart to have some residual LV function. Any increase in cardiac output depends on the work of the heart itself.

D. Optimal Effect Depends On:

• Correct balloon position in the aorta
• Blood displacement volume (balloon size matched to patient's aortic diameter)
• Balloon diameter relative to aortic diameter (ideally 85-95% of aortic diameter)
• Correct timing of inflation/deflation
• Patient's heart rate, blood pressure, and vascular resistance

III. TECHNIQUE OF INSERTION (3 marks)

A. Equipment

• Double-lumen, 7.5-8.0 Fr catheter with polyethylene balloon
• Balloon size chosen based on patient height (typically 25-50 mL volume)
• Helium gas for inflation
• Pump console (ECG or pressure-triggered)
• Fluoroscopy or bedside X-ray / ultrasound guidance

B. Standard Percutaneous Seldinger Technique (Femoral Approach - most common)

• Patient supine. Access is usually the left femoral artery (can also use right femoral)
• Sterile prep and drape
• Local anesthesia (or GA/sedation if already in theatre)

• Palpate femoral artery at the femoral crease
• Puncture the common femoral artery (above the femoral bifurcation) with a needle at 30-45° angle
• Confirm arterial blood flashback

• Insert a 0.035-inch J-tip guidewire through the needle into the aorta
• Remove the needle; make a small skin incision at the wire entry point

• Pass an introducer sheath (8-9 Fr) over the guidewire using serial dilation
• Remove dilator, leave sheath in situ

• Pre-fold/wrap the balloon catheter
• Advance the balloon catheter over the guidewire through the sheath
• Position the tip of the catheter 2-3 cm distal to the left subclavian artery (around the carina level on X-ray, or 2nd-3rd intercostal space)
• Confirm position with fluoroscopy or chest X-ray (tip at level of carina / aortic knuckle)
• Note: Too high → risk of subclavian/carotid occlusion; Too low → risk of renal/mesenteric artery occlusion

• Connect catheter to the pump console
• Select trigger mode: ECG trigger (R-wave) preferred in sinus rhythm; pressure trigger if ECG unreliable; internal trigger if in asystole/pacing
• Set inflation timing: balloon inflates at dicrotic notch of arterial trace (ECG: middle of T-wave)
• Set deflation timing: balloon deflates just before the R wave (peak of QRS)
• Start at 1:2 ratio (assists every other beat) to check timing and waveform; increase to 1:1 (augments every beat)

• Correct: Diastolic augmentation peak > unassisted systolic peak; assisted aortic end-diastolic pressure lower than unassisted end-diastolic pressure; assisted systolic pressure lower than unassisted
• Early inflation: Augmentation peak merges with systolic upstroke (increases afterload - dangerous)
• Late inflation: Diastolic augmentation begins after dicrotic notch; reduced coronary perfusion benefit
• Early deflation: "V" shape notch before diastole ends; no afterload reduction
• Late deflation: Assisted end-diastolic pressure = unassisted (no afterload reduction)

• Systemic anticoagulation with heparin (ACT 150-180 sec) to prevent thrombosis and limb ischemia

C. Alternative Access Sites

• Axillary / subclavian artery (surgical cut-down) - when bilateral femoral access not possible
• Ascending aorta (intra-operative surgical placement)
• Brachial artery (rarely)

IV. COMPLICATIONS

V. WEANING

• Gradually reduce ratio from 1:1 → 1:2 → 1:3 as hemodynamics improve
• Generally used for a few days; wean as cardiac function recovers
• Remove sheath with direct pressure/compression of femoral artery for 30 minutes post-removal