OSCE 6

This 67-year-old male was admitted to the Intensive Care Unit 6 hours ago following emergency coronary artery bypass grafting.  He has remained hypotensive (mean arterial pressure of 60 mmHg) and oliguric, despite adequate fluid loading to a right atrial pressure of 15 mmHg and an adrenaline infusion at 20 mg/min. A recent transoesophageal echocardiogram demonstrates global severe systolic dysfunction and no evidence of pericardial tamponade.
You have been asked to consider inserting an intra-aortic balloon pump by the attending team.
Consider your approach and preparation for this procedure.

What do you think of the suggestion for inserting a balloon pump in this patient?

Procedure station:   Candidates were expected to provide a systematic approach to the principle of insertion, management and removal of an Intra-Aortic Balloon Pump catheter. Nineteen out of twenty-eight candidates passed this section.

Indications for IABP insertion:

No choice but pump

• Failure to come off bypass
• Severe aortic stenosis, mitral regurgitation or ventricular septal defect
  with haemodynamic compromise, while waiting for repair

Probably harmless, but probably not useful

• High risk CABG patients (pre-op)
• High-risk PCI patients (pre-op)
• Cardiogenic shock while waiting for PCI
• Pulmonary oedema in spite of maximal medical management

Totally experimental

• Takotsubo cardiomyopathy
• Neurogenic stress cardiomyopathy of subarachnoid haemorrhage

What is the evidence for the use of IABP?

• IABP-SHOCK II trial is the only one we can reasonably expect a stressed trainee to remember.
  • Their 30-day mortality was not reduced in their IABP group, suggesting that the IABP is not very useful in this setting
  • This is consistent with the summed data from all previous studies.
  • BUT: their control group did have a high rate of LVAD insertion
  • AHA still recommends IABP: 2013 revision of the AHA guidelines for STEMI still says that it "can be useful" in this setting

Describe the major features of this device.

(Ideally, you'd have an IABP as a prop to hand to the candidate, so they can fiddle with it physically. The picture of my own expired IABP is included here for convenience).

This is an intra-aortic balloon pump catheter.

Its major features are:

• 40ml polyurethane balloon
• Inner tube for insertion (the "blood lumen")
• Outer tube for helium (the "helium lumen")
• A flexible plastic hub to secure the device to the skin with four sutures
• A flexible plastic sheath 
• A hub connector to attach the device to the helium tank

What are the safety features of this device?

• Tear-resistant helium balloon
• Inert biocompatible plastic 
• Radio-opaque markers on either side of the balloon, to assist positioning
• Kink-resistant thin inner tube
• Reinforced extracorporial tubing
• Luer-lock connectors to prevent helium leak
• Flexible plastic hubs allow the device to be secured at six independent pointas on the skin
• A mark on the gas tube indicates when all of the balloon has come out of the introducer sheath
• Volume of the inner tube is clearly documented on the distal hub

How do you size this device? How do you select the appropriate sized balloon?

Generally speaking, the IABPs are sized according to height.

•  Under 152cm = 25ml balloon
• 152-162cm = 34ml balloon
• 162-183cm = 40ml balloon

How would you insert this device?

By Seldinger technique, of course. There is a sheathed and unsheathed version of this procedure

• Prep/drape etc
• Introduce an 18g angiography needle into the common femoral artery
• Introduce the supplied J-tipped 0.6mm wire into the needle
• Keep the wire and discard the needle
• Make a small skin incision
• Dilate the vessel with the supplied sheathed 15cm introducer dilator
• Remove the dilator, keeing the introducer and guide wire in situ
• Slide the balloon catheter over the guidewire
• Advance it to its proper position
• Remove the guidewire
• Flush the inner lumen with saline
• Connect the gas lumen to the pump and start the device

What is the correct position? How would you confirm that it is in the right position?

• Correct position is 2cm distal to the origin of the left subclavian artery
• The distal balloon marker has to be above the origins of the renal arteries

Two main ways of checking the position:

• By measuring: from the level of the 2nd intercostal space in midline, to the umbilicus, to the insertion site in the groin
• By CXR: IABP position should be just below the level of the aortic knuckle
• By TOE
• By fluoroscopy

 What are the contraindications for IABP insertion?

Absolute contraindications

• Aortic regurgitation
• Aortic aneurysm
• Aortic dissection
• Severe sepsis
• Uncontrolled coagulopathy

Relative contraindications

• Atherosclerosis and arterial tortuosity
• Left ventricular outflow tract obstruction
• Contraindications to anticoagulation

Do you need to anticoagulate the patient? If so, then how would you do it?

• Heparin is an appropriate choice
• A pump on 1:1 may not require any anticoagulation, but this is controversial
• A retrospective audit of about 18,000 patients Chin et al (2010):
• anticoagulation in fact did not increase the risk of bleeding complications,
  but the absence of anticoagulation did increase the risk of thrombotic complications. The anticoagulated group also had reduced mortality.
• In summary (own practice) - any well-reasoned answer is appropriate

What are the complications of IABP insertion?

Common complications

• Mild limb ischaemia - 2.9%
• Balloon leak - 1.0%
• Major limb ischaemia - 0.9%
• Haemorrhage - 0.8%
• Leg amputation due to ischaemia - 0.1%

Rare complications

• Atheromatous cholesterol emboli
• Aortic or arterial dissection
• Cerebrovascular accident
• Thrombocytopenia
• Haemolysis
• Helium embolism

What are the different methods of triggering the counterpulsation?

• ECG
  • Inflation of the balloon is triggered by the the beginning of diastole, which correlates with the middle of the T-wave.
  • The balloon is timed to deflate at the very end of diastole. This correlates with the R-wave
• Pressure
• Pacing spikes
• Asynchronous mode (for patients who are asystolic)

The patient undergoes a safe insertion of the IABP, and 1:1 counterpulsation is commenced.  How will you determine that augmentation is effective?

• Turn the pump to 1:2 
• The assisted end-diastolic pressure should be lower than the assisted
• The assisted systolic pressure should be lower than the unassisted systolic
• The balloon inflation should occur at the same time as the aortic valve closes (i.e. at the dicrotic notch

You are called to interpret this waveform while the IBP has been put into 1:2 augmentation mode.

What do you make of the augmentation? Is there a problem here? Explain your answer

There is early balloon inflation and early balloon deflation.

• The assisted systolic pressure is no different to the unassisted
• The assisted diastolic pressure returns to its unassisted level before the next systeole

What are the consequences of this for the effectiveness of the aortic counterpulsation?

Early balloon inflation results in

• Increased LV oxygen demand, due to increased afterload
• Decreased LV oxygen supply, due to decreased diastolic perfusion
• Decreased cardiac output, due to decreased stroke volume

Early balloon deflation results in

• Unimproved left ventricular afterload
• Thus no decrease in LV oxygen demand

Over days, the cardiac output improves gradually. How would you wean the patient off the IABP?

Two main schools of thought:

• gradually decrease balloon volume
• trial 1:2 augmentation, and if well tolerated - remove

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.