CONTENTS

• Basic use and monitoring
  • Correct position on chest radiograph
  • Waveform troubleshooting
    • Evaluating IABP efficacy
    • Evaluating IABP timing
  • BP monitoring with IABP in place
  • Anticoagulation for IABP
  • Weaning off the IABP
• Complications
• Physiologic effects of IABP
• Indications & contraindications
• Questions & discussion

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correct IABP position on chest radiograph

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ideal location

• Chest radiograph:
  • ~2 cm below the superior aspect of the aortic arch. (Shepard 2019)
  • At the level of the carina.
  • Slightly above the left main bronchus.
• Anatomically, the IABP should be ~2 cm distal to the origin of the left subclavian artery.

risks of intra-aortic balloon pump malpositioning

• Too proximal:
  • It may promote ischemia to the brain and left arm.
  • Increases risk of aortic injury (e.g., dissection or pseudoaneurysm).
• Too distal:
  • Occlusion of renal and mesenteric arteries.
  • Ineffective counterpulsation.

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troubleshooting IABP waveforms

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evaluating IABP efficacy (in 1:2 or 1:3)

To evaluate the efficacy of IABP counterpulsation, consider two factors: 

effective diastolic augmentation

• [1] Peak diastolic augmentation should be the highest pressure (higher than the unassisted systolic pressure).
  • If the systolic pressure approaches or exceeds the augmented diastolic pressure, it suggests that systolic function is adequate, so the IABP may not be needed to support cardiac output. (Bojar 2021)
  • Alternatively, low augmented diastolic pressure may indicate late inflation of the IABP (discussed below).
• [2] Assisted MAP may increase compared to unassisted MAP.
  • MAP elevation is especially likely in patients with acute mitral regurgitation or ventricular septal defect. A more significant MAP increase might imply that the IABP is more beneficial.

effective systolic unloading

• Reduced augmented BP indicates effective afterload reduction.
• [1] Assisted diastolic BP should be ~15-20 mm lower than the unassisted diastolic BP. (39132456)
• [2] Assisted systolic pressure should be ~5 mm lower than the unassisted systolic pressure. (39132456)
• (Further discussion of the ideal physiological effects of IABP below: ⚡️)

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evaluating the timing of IABP inflation

inflation should occur at the dichroic notch

• Inflation should begin during early diastole, immediately after aortic valve closure. The upstroke of inflation should occur slightly after the systolic waveform, obscuring the dichrotic notch. On the ECG, this is roughly the middle of the T-wave.
• Early inflation (during systole) will block systolic blood flow through the aorta, which is extremely problematic.
  • 🔎 Inflation begins before the dichroic notch.
  • 🔎 Assisted systolic BP may rise (rather than fall, as it should).
  • 🔎 There may be a loss of the curve's desired “V” shape between native systole and augmented diastole. (39132456)
• Late inflation (during late diastole) will limit the efficacy of the IABP.
  • 🔎 Inflation is seen significantly after the dicrotic notch.
  • 🔎 Augmented diastolic Bp may be equal to or lower than the unassisted SBP.

deflation timing

• Deflation should occur during early systole. Deflation should cause the diastolic pressure to dip ~10-15 mm below the patient's unassisted diastolic pressure. Deflation coincides with the peak of the R-wave on the ECG.
• Early deflation (during diastole) causes the IABP to be ineffective. This might even induce transient retrograde blood flow in the carotid or coronary arteries. (16635618)
  • 🔎 Deflation is seen as a sharp drop in pressure. This pressure drop occurs too far ahead of the end-diastolic pressure.
  • 🔎 Early deflation may lead to a lack of reduction in the assisted diastolic and systolic BP.
• Late deflation (during mid-systole) will impede systolic blood flow through the aorta (increasing afterload).
  • 🔎 Assisted diastolic waveform fuses with the systolic waveform.
  • 🔎 Assisted diastolic pressure will increase (potentially higher than unassisted diastolic BP).
  • 🔎 Systolic Bp rise may be blunted with a shallow slope.

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blood pressure monitoring with IABP in place

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Bottom line: the IABP console MAP is the reference standard. (32404615)

blood pressure from the IABP

• The central lumen of the IABP allows monitoring of central aortic pressure. This is generally considered the gold standard for blood pressure measurement.
• If this pressure signal is transmitted to the bedside monitor, the bedside monitor will be confused by this BP tracing:
  • The bedside monitor will call the highest Bp the SBP and the lowest Bp the DBP. However, the highest and lowest BP reflect balloon inflation and deflation (figure below).
  • Some bedside monitors may calculate the MAP based on the highest and lowest BP measurements, which is likewise incorrect. However, this will be more accurate if the monitor calculates the MAP based on the integrated blood pressure over time. (30936134)
  • If the IABP is in 1:3 or 1:4, the monitor may flip and flop between augmented and native BP measurements.
• The IABP console may be designed to interpret BP waveforms better. If there is a significant disagreement between the bedside monitor and the IABP console, the IABP console will generally be more accurate. (30936134)

noninvasive oscillometric BP cuff

• Oscillometric cuffs weren't designed to measure BP for patients receiving IABP therapy.
• Oscillometric cuffs may be inaccurate among patients on an IABP. (32404615)

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anticoagulation for IABP

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• Some practitioners prefer therapeutic heparin anticoagulation due to concern that clots could form on the IABP, resulting in subsequent embolization. However, there is no high-quality evidence that anticoagulation is required for an IABP, especially when functioning at 1:1 (rapid inflation and deflation may theoretically deter clot formation). Indeed, anticoagulation could potentially increase the risk of atheroembolization from the aortic wall. Available data indicate that heparin doesn't reduce the risk of ischemic events but does increase the risk of bleeding. (12958723, 19031189)
• Cardiologists often use anticoagulation for IABP, whereas cardiac surgeons don't. The degree of practice variation across different units within the same institution is frequently dramatic.
• If you don't believe a general intensivist on this matter, the following excerpt is from an article coauthored by nine cardiologists from illustrious institutions: (37209795)

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weaning off the IABP

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determining when to remove the IABP involves various factors 

• [1] Clinical improvement, e.g.:
  • There is minimal need for inotropic support (e.g., a single inotrope at low doses such as dobutamine <10 ug/kg/min, miorinone <0.5 ug/kg/min, or epinephrine at 1 ug/min). (Bojar 2021)
  • Cardiac index >2 L/min/m2.
  • SvO2 >65%.
• [2] Is the IABP helping? Consider augmented vs. unaugmented BP, as discussed above. ⚡️
• [3] Complications may hasten the need to remove the IABP:
  • Leg ischemia.
  • Balloon malfunction.
  • Thrombocytopenia.
  • Infection or concern for line infection.

technique of weaning IABP

• There is little clear evidence regarding IABP weaning.
• The IABP may be changed to a lower ratio (1:3 or 1:4) to observe the physiological effect this has on the patient.
  • The duration of a low inflation ratio should be limited for patients who aren't anticoagulated. (Bojar 2021)
  • After at least 30 minutes at a lower setting, cardiac function and perfusion data may be evaluated (e.g., mixed venous oxygen saturation) to determine whether this is tolerated. (Salim 2018)
• Less frequently, another option for weaning may be to reduce the amount of augmentation.

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complications of IABP

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risk factors for major (vascular) complications

• Female gender.
• Age >75 years old.
• Body surface area <1.8 m2.
• Peripheral arterial disease.
• Prolonged support.
• Larger catheter size (>9.5 French); sheathed catheter.
• Use longer than roughly two days. (25348545)

vascular complications (major risk)

• Limb ischemia.
  • This is the most common complication (~14% of patients).
  • Limb ischemia can reflect arterial thrombosis, plaque rupture, or distal embolization. Thrombosis at the insertion site may become more likely if the IABP remains in place for more than a few days. (Bojar 2021)
• Visceral ischemia (including renal ischemia).
  • Visceral artery obstruction by the balloon itself is surprisingly common, but it usually only occludes the artery during diastole, so the results are generally not severe.
  • Embolization of atherosclerotic debris may cause occlusion of visceral arteries.
• Spinal cord ischemia may result from the embolization of atherosclerotic debris or a periadventitial aortic hematoma. (Bojar 2021)
• Vascular laceration, hemorrhage.
  • Retroperitoneal hemorrhage.
• Hematoma.
• Pseudoaneurysm formation.

other complications

• Thrombocytopenia:
  • Mild-moderate thrombocytopenia may occur due to platelet destruction, but platelet count rarely falls <50,000-100,000/ml.  Platelet count should rapidly improve following IABP removal. (Moscucci 2013)
• Hemolysis may occur, but less than other mechanical support devices.
• Line infection, sepsis.
• Peripheral neuropathy.
• Cholesterol embolization.
• Ischemic stroke (may result from vigorous flushing of the IABP to dislodge a thrombus).

balloon rupture

• Rupture may result from inflation against calcified aortic plaque.
• Clinical signs:
  • Blood or serosanguinous fluid may be seen in the extracorporeal tubing.
  • Sudden change in diastolic augmentation pressure.
  • IABP alarms (autofill failure or gas loss).
• Management:
  • Put the IABP on standby.
  • Placing the patient's head down to reduce the risk of cerebral embolization.
  • Disconnect the catheter extender tubing from the IABP console.
  • Clamp the extracorporeal tubing distal to the white y-fitting.
  • IABP should be removed immediately. Thrombus formation may occur rapidly, trapping gas within the balloon and making it difficult to remove the IABP safely. (Bojar 2021) If there is difficulty removing the IABP, it must be taken out in the operating room with the use of a surgical cutdown to control any subsequent hemorrhage. (Sundt 2022)
  • IABP replacement may be considered if clinically required.

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IABP and arrhythmias

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IABP & tachyarrhythmias 

• In AF, the IABP may be timed to deflate at the peak of the R-wave (atrial fibrillation trigger mode). (39132456)
• IABP may be unable to function at rates over ~150/min. Consider switching to 1:2 mode. (Bojar 2021)
• For patients who are dependent on IABP, a new arrhythmia (e.g., atrial fibrillation) may cause the IABP to stop synchronizing correctly, leading to hemodynamic collapse. Immediate cardioversion may be required (note that defibrillation or cardioversion are safe in the context of an IABP).

IABP & pacemakers

• Pacemaker spikes may sometimes be misinterpreted as R-waves; this may be managed as follows:
  • Timing the IABP off the arterial pressure contour.
  • Changing to a lead that isn't confused by the pacemaker spikes.
  • Setting the console to discriminate between pacemaker spikes and R-waves. (Moscucci 2013)
• Pacer trigger: This is a triggering mode wherein ventricular pacing spikes trigger IABP inflation. (39132456) It shouldn't be used for demand pacing but it may be helpful for patients who are 100% paced. (25348545)

IABP management during cardiac arrest

• [1] Switch to semi-autonomous mode.
• [2] Switch to pressure trigger mode (this will sync with compressions or any endogenous beats).
• The pressure threshold may need to be reduced. (25348545)
• If the IABP is not persistently inflated (not deflating), it might need to be temporarily switched to standby mode. However, the IABP should not be left in standby mode for long since this may promote thrombosis. (25348545)

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physiologic effects of IABP

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general physiological effects of IABP

• Effects on diastolic BP, systolic BP, and MAP are discussed above: ⚡️
• Pulmonary capillary wedge pressure may decrease (~20%).
• Cardiac output might increase (~20% or roughly 0.5-1 L/min). (37209795) However, RCTs have not shown an improvement in cardiac output as compared to a medical therapy arm. (22266974) 
• Right ventricular function may be improved by supporting right ventricular myocardium perfusion and reducing LV filling pressures (thereby reducing right ventricular afterload). However, IABP is inadequate for severe RV failure. (Bojar 2021)

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IABP indications & contraindications

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Indications for IABP are controversial since IABP insertion has never been shown to improve outcomes in RCTs (despite numerous attempts to show benefit).  

indications

• Refractory ischemia.
• Cardiogenic shock (although no mortality benefit was shown in the IABP-Shock II trial), especially in the context of:
  • Severe mitral regurgitation.
  • Ventricular septal defect.
• Inability to wean off cardiopulmonary bypass following cardiac surgery.

contraindications

• Unlikely to be effective:
  • Aortic regurgitation (more than mild AR is an absolute contraindication).
  • LV outflow tract obstruction.
  • Difficulty timing IABP inflation due to tachycardia or arrhythmia (e.g., atrial fibrillation, frequent ventricular ectopy).
  • Profound shock or cardiac arrest (IABP is unlikely to provide sufficient mechanical support).
  • Chronic end-stage heart disease without recoverability or destination therapy. (Brown 2023)
• Aortic & vascular issues:
  • Aortic dissection.
  • Significant aortic aneurysm.
  • Recent aortic surgery.
  • Known aortic atheroma.
  • Severe stenosis of the distal aorta.
  • Severe peripheral artery disease.
• Uncontrolled bleeding disorder.
• Uncontrolled bacteremia.

patient factors that may suggest more significant benefits from IABP

• Regurgitant lesions that are sensitive to afterload reduction:
  • Mitral regurgitation.
  • Ventricular septal defect.
• Excessive preload (e.g., cardiogenic pulmonary edema).
• Excessive afterload.
• Absence of tachycardia (which makes IABP less effective, ideally HR<~90 b/m). (37209795)
• Active coronary artery ischemia.
• Cardiac output is only mildly reduced (i.e., IABP will provide enough support).
• Acutely decompensated heart failure may benefit more than patients with acute cardiogenic shock. (39132456)

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questions & discussion

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