Intra-Aortic Balloon Pump (IABP): Mechanism, Principles & Anaesthetic Implications

1. Overview and History

• Braunwald's Heart Disease, 15e - Fischer's Mastery of Surgery, 8e

2. Positioning

3. Mechanism of Action: Counterpulsation

• Increased diastolic blood pressure (coronary augmentation)
• Decreased systolic pressure and end-diastolic pressure (afterload reduction)
• Modest increase in cardiac output (~0.5-1.0 L/min)
• Reduced myocardial oxygen consumption
• Requires the patient to have some residual LV function - the IABP amplifies, not replaces, LV work
• Braunwald's Heart Disease | Tintinalli's Emergency Medicine

4. Triggering Modes

1. ECG trigger - Inflation timed to middle of T-wave (dicrotic notch equivalent); deflation timed to R-wave peak
2. Arterial pressure waveform trigger - Inflation just after the dicrotic notch; deflation just before the next systolic upstroke
3. Pacer mode - When the patient is paced; uses pacer spike rather than R-wave
4. Internal (asynchronous) trigger - Used in cardiac arrest, used at a fixed rate

• Early inflation - Balloon inflates before aortic valve closes -> increases afterload (dangerous)
• Late inflation - Diastolic augmentation reduced
• Early deflation - Loses afterload reduction benefit
• Late deflation - Balloon still inflated when LV ejects -> increased afterload
• Fuster & Hurst's The Heart, 15e

5. Indications

• Braunwald's Heart Disease | Washington Manual of Medical Therapeutics

6. Contraindications

• Fischer's Mastery of Surgery, 8e

7. Anaesthetic Implications

7.1 Preoperative Considerations

• Identify the presence of IABP before any anaesthetic - review trigger mode, support ratio (1:1, 1:2, 1:3), console alarms
• Patients presenting for CABG or cardiac surgery with critical left main CAD or unstable angina should have IABP placed for stabilisation before induction of anaesthesia, to prevent haemodynamic collapse at induction
• Understand the underlying indication - the degree of LV impairment guides induction agent selection, monitoring strategy, and vasoactive drug planning
• Check anticoagulation status - IABP requires systemic anticoagulation (usually heparin); this impacts neuraxial anaesthesia, invasive line placement, and surgical bleeding
• Washington Manual of Medical Therapeutics | Sabiston Textbook of Surgery, 20e

7.2 Intraoperative Monitoring

• Invasive arterial monitoring is mandatory - the arterial waveform is used to assess IABP timing and effects; it also demonstrates the augmented diastolic waveform (diastolic pressure > systolic on assisted beats at 1:2)
• Central venous access - for vasoactive drugs; PAC may be used in complex cases
• Pulse oximetry: SpO2 accuracy is reduced in the presence of IABP - accuracy depends on the brand of pulse oximeter and the support ratio, with accuracy generally reduced at higher support ratios (1:1). In patients with continuous-flow VADs, pulse oximetry may be entirely unreliable due to non-pulsatile flow; cerebral oximetry is then advocated
• Echocardiography (TOE/TEE) - essential to assess LV function, valvular pathology (especially AR), check balloon position, and guide haemodynamic management
• ECG monitoring must be high quality - artefact from IABP can interfere with the trigger signal
• Miller's Anesthesia, 10e

7.3 Induction and Maintenance

• Avoid tachycardia - at high heart rates (>120-130 bpm), diastole shortens and the IABP loses effectiveness; there is inadequate time for diastolic augmentation
• Avoid bradycardia/arrhythmias - atrial fibrillation and frequent ectopics cause irregular triggering and poor counterpulsation; an irregular rhythm impairs IABP efficacy significantly
• Induction agents - choose those with minimal myocardial depression; high-dose opioid-based induction (fentanyl/sufentanil) is commonly used in cardiac cases; ketamine may be considered to maintain SVR, but may increase myocardial O2 demand
• Avoid large increases in SVR - while the IABP reduces afterload, addition of vasoconstrictors that markedly increase SVR can negate this benefit
• IABP should ideally remain ON during induction - particularly in haemodynamically unstable patients; do not pause without a clear indication
• The placement of IABP is usually performed under conscious sedation, but the anaesthesiologist is often involved when the patient is compromised haemodynamically or from a respiratory standpoint
• Miller's Anesthesia, 10e | Barash's Clinical Anesthesia, 9e

7.4 Specific Intraoperative Scenarios

• IABP is paused during CPB (aortic cross-clamp) - no cardiac cycle to trigger
• Restart in asynchronous mode when coming off CPB, then switch to synchronised mode once cardiac rhythm is established
• Particularly useful for failure to wean from CPB - significant low cardiac output state post-CABG/valve surgery

• IABP must remain functional throughout - ensure the console is available in the operating room and that biomedical/perfusion staff are present
• Patient positioning is limited - femoral insertion restricts hip flexion; axillary insertion restricts arm positioning
• Surgical field prep must avoid the insertion site
• Radiolucency matters - fluoroscopy may be needed intraoperatively to check position

• Frequent PVCs cause alternating trigger signals
• AF requires switching to pressure trigger mode
• In VF/pulseless VT, switch to internal trigger mode
• During defibrillation - the IABP console should be capable of withstanding defibrillation shock, but confirm with the device manufacturer

7.5 Postoperative and ICU Management

• Weaning the IABP: reduce the counterpulsation ratio progressively: 1:1 -> 1:2 -> 1:3, while monitoring haemodynamic parameters (cardiac output, MAP, heart rate, urine output). Do not wean too early in haemodynamically unstable patients
• Haemodynamic targets during IABP support: maintain adequate preload; the IABP does not replace volume; avoid vasodilators that may excessively drop diastolic pressure and negate diastolic augmentation
• Immobility: patients with femoral IABP must remain immobilised with the affected limb straight - neuraxial anaesthesia, epidural management, and physiotherapy are constrained
• Postoperative pain management: consider that morphine and opioids may cause bradycardia which can impair IABP triggering
• Limb ischaemia monitoring: hourly checks of the limb distal to insertion; document neurovascular observations
• Fischer's Mastery of Surgery, 8e

8. Complications

• Fischer's Mastery of Surgery, 8e | Braunwald's Heart Disease

9. Comparison with Other MCS Devices (Anaesthetic Perspective)

• Miller's Anesthesia, 10e

Key Anaesthetic Summary Points

1. Always identify IABP before starting any anaesthetic - trigger mode, ratio, console availability, anticoagulation status
2. Maintain regular cardiac rhythm - arrhythmias severely impair IABP efficacy
3. Avoid tachycardia - shortens diastolic augmentation time
4. Invasive arterial line is mandatory - enables real-time assessment of IABP timing and haemodynamic effect
5. SpO2 accuracy is reduced with IABP - validate with ABG
6. ECG trigger artefact is common - use pressure trigger as alternative
7. IABP does not replace volume - adequate preload must be maintained
8. Aortic regurgitation is an absolute contraindication - inflation worsens AR
9. Keep the device running during induction in haemodynamically unstable patients
10. Wean gradually after stabilisation - not before haemodynamic goals are met