Balloon Pumps

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    Source: Webb et al 2015 Seminars in Cardiothoracic and Vascular Anesthesia (see attached paper)

    Introduction

    • Intra-Aortic Balloon Pump (IABP) is a myocardial assist device
    • Introduced in 1968
    • Components:
      • 8-9.6 French catheter with a 20-50mL balloon and IABP consoleIABP diagram.png
    • Uses Counterpulsation
      • Transfers gas (CO2 or helium) between the console and balloon according to the timing of the cardiac cycle. 
      • The inner catheter lumen is used for BP measurements
      • Helium is used more commonly, due to low density (can move quickly), easily dissolve in blood if there is a leak.
    • Unlike other cardiac assist devices, IABP indirect affects LV function by maximizing myocardial oxygen supply and minimizing oxygen demand.
      • In comparison to LVADs act as a pump to support the heart and promote forward flow. 

     

    Important Concepts

    • Creatinine should improve following initiation of counterpulsation
      • If creatinine worsens, check to rule out juxta-renal balloon position (occluding renal arteries)
    • Positioning:
      • Must be positioned (on Xray)
        • 2-3cm distal to subclavian artery
        • At the level of carina
          OR
        • Between 2nd and 3rd intercostal spaces
      • (TEE can confirm position)
      • Position too high = subclavian and vertebral artery occlusion.
      • Position too low = mesenteric and renal artery occlusion
    • Thrombosis Risk:
      • Augmentation rates 1:4 and lower carry a very high risk of thrombosis
        • (only use for less than 30min, unless anticoagulating)
      • NEVER leave it in standby mode except when removing
        • (thrombosis occurs quickly in animal models could embolize causing limb ischemia.  The cannula itself also  reduces aorta flow)

     

    Sizing

    • Should not exceed 80-90% of aorta when inflated.
    • Inflation volumes = 50-60% of stroke volume. 
    • sizing.png

     

    Hemodynamics

    • Counterpulsation is a technique that synchronizes pumping with the heart cycle
      • Assists in circulation
      • Decreases work of heart
    • IABPs inflate on closure of Ao valve during diastole
      • This increases diastolic pressure, and helps back-perfuse coronary arteries (which rely on diastolic pressures to perfuse)
      • NOTE: CPP (Coronary Perfusion Pressure) = DBP - LVEDP
    • Deflate immediately before the aortic valve reopens during systole
      • This decreases afterload of the ventricle, which has a number of effects:
        • Improves ventricular emptying (lowers LVEDP)
        • Decreases myocardial oxygen demand (minimizes wall stress)
      • Anothe way to put it, deflation during systole creates a "suction effect", which assists ventricular empying.

     

    Beneficial Effects:

    • Coronary Blood Flow
      • Increases flow to coronaries by raising diastolic pressure 
      • However, studies show no increase in flow past occluded lesions.  (Help ischemia through improved collateral flow!!)
      • Studies studying an increase in coronary flow are conflicting.  (may be due to autoregulation of coronary flow)
        • However, counterpulsation did increase coronary flow in cases with decreased cardiac output (autoregulation is lost)
    • Cerebral Blood Flow
      • Early animal studies = controversial.
      • Unclear
    • Renal Blood Flow
      • Increases by up to 25% (studies with doppler ultrasound)
    • Hematologic
      • Mild hemolytic anemia and thrombocytopenia (shearing)

     

    Indications / Contraindications

    • Guideline-Based Recommendations:
      • 2011 ACCF/AHA/SCAI Guideline for Percutaneous
        Coronary Intervention: Executive Summary
    • AHA Class Indication

      Class I

      Level B

      A hemodynamic support device is

      recommended for patients with cardiogenic shock after

      STEMI who do not quickly stabilize with pharmacological therapy

      Class IIb

      Level C

      High-Risk Patients undergoing Coronary Intervention

      Elective insertion of an appropriate hemodynamic support device

      as an adjunct to PCI may be reasonable in carefully selected

      high-risk patients. (Level of Evidence: C)

       

      High Risk =

        - Unprotected left main or last-remaining-conduit PC

        - Severely depressed EF undergoing PCI of a vessel supplying a large territory

        - Cardiogenic shock

       

      Patient risk, hemodynamic support, ease of application/removal, and operator and

      laboratory expertise are all factors involved in consideration of use of these devices.

      With devices that require large cannula insertion, the risk of vascular injury and related

      complications are important considerations regarding necessity and choice of device

       

     

    • Other Indications:
    • Indications

      - Cardiogenic Shock

       

      - Acute MI

       

      - Preoperative Stabilization

        (For CABG)

       

      - Acute MR + VSD

       

      - Weaning from cardiopulmonary bypass

       

      - Hemodynamic instability during PCI

     

    Contraindications

     

    • - Aortic Regurgitation

      (will worsen regurgitation!! worsen  myocardial stress, decrease CPP and DPTI)

       

      - Aortic Dissection/aneurysm

        (placing in false lumen = rupture/progression)

       

      - Multiple organ failure + no anticipated

        recovery

      - Aortic stents or graft

      - Septic Shock

      - Severe PVD or stents at cannulation

      - Patient refusal or DNR

       

     

     

    Evidence Base:

    • Acute MI Without Cardiogenic Shock
      • Limited benefit, unless patients are high risk. 
      • CRISP Trial - does counterpulsation reduce infarct size pre-PCI?  (decided to use for high-risk pts)
    • Acute MI With Cardiogenic Shock
      • IABP-Shock-II Trial --> Does not reduce 12-mo mortality (but many problems with the study)
        • Some argue benefit only if placed prior to reperfusion
    • High-Risk Patients Undergoing Coronary Intervention (CABG or PCI)
      • Prophylactic use of IABP (vs rescue IABP or conservative therapy) in high-risk patients undergoing PCI = lower mortality and fewer complications. 
      • BCIS-I follow-up study = no difference in MACCE
        • But long-term all-cause mortality data 51mo later = 34% reduction of death
    • RV Failure
    • Pts Undergoing CABG  (mortality benefit in high-risk patients based on Cochrane review)

    Management of IABPs


    • Settings:

    • Parameter Options Notes
      Augmentation Ratio

      1:1 (augments each beat)

      1:2 (augments every other)

      1:3 

      1:4

      (1:8 in some devices)

      - Useful for weaning

      - Also useful to check if augmentation

        is effective. (compare augmented/non-

         augmented beats.

       

      - 1:4 and 1:8 rarely used

        because they carry a high risk of thrombosis

      if operated >30min. (unless anticoagulated)

       

      Trigger Source

      (how does the device

      know when Aortic valve

      opens and closes)


       

      ECG Trigger

         (Systole = peak of R-wave=deflate)

         (Diastole = middle of T-wave = inflate)

       

      - Sensing R-wave can be difficult

      - Manufacturers use different algorithms

      - Poor ECG quality & arrhythmias can make

        this unreliable method

      Pressure Trigger

         Arterial pressure mode is used to 

         sense systole and diastole

         Aortic valve closure = dicrotic notch

         Aortic valve opening = systolic upstroke

      - Good if ECG is unreliable

      Internal Trigger (Operator Mode)

        - Asynchronous trigger mode that 

      augments a HR of 80 bpm.

       

      - Only used if there is no cardiac output

       and no ECG 

      - Used during arrest and cardiopulmonary

        bypass.

        (literature to suggest pulsatile flow improves

         perfusion in bypass)

      Pacer Triggers

        - Uses ventricular pacing spike

        - Can use V pacing and AV pacing

      - MUST be 100% paced

      - Should not be used for demand pacing

      Atrial Fibrillation Trigger

        - rejects pacer spikes and artifact

        - Analyzes height and slope of 

          positive or negative QRS complex

       
      Modes of Operation

      Automatic

        - Computer determines optimal trigger

           source and inflation/deflation timing

       

      Semi-Automatic

        - Operator selects appropriate trigger

          and initial inflation/deflation timing.

        - Then device will determine timing

           based on HR and rhythm changes

       

      Manual

        - Operator sets trigger and timing

        - Operator must adjust if change in 

           HR or rhythm occurs

        - Modern machines use fiber optic

          sensors with fluid transducers that 

          constantly calibrate and recalibrate

         the balloon inflation/deflation.

         (most match within 12ms of aortic valve)

     

     

    Weaning from IABP

    • Consider weaning when hemodynamic status improves.
    • Weaning must be done over hours by gradually decreasing augmentation ratio
    • Inotropic support may be added or increased during weaning.
    • This is done by slowly decreasing the augmentation ratio
      • Assess response via: (compare to pre-weaning)
        • SvO2
        • Echo
        • Cardiac index
        • Wedge pressure
        • Lactate
        • Urine output
      • BP may go up (due to lack of afterload reduction by IABP)
      • If indices worsen, consider putting back to 1:1
    • Failure to wean = consider other LV assist devices
    • IABP Removal
      • Check coagulation (INR, PTT, platelets)
      • Vascular injury can occur during removal.
        • Hematomas at the site
        • Pseudoaneurysm formation
        • Retroperitoneal Bleed
      • Must apply pressure to the insertion site with a "NO PEEK" technique for 45min. 
        • Some centers have stabilizing pressure devices after manual holding
        • MUST monitor lower extremity pulses.

     

    Anticoagulation

    • No standardized recommendations as of 2014 (assuming not left in 1:3 or less augmentation mode for more than 30min)
    • Must consider patient-to-patient
      • If risk of thrombosis is high and bleeding risk is low--> anticoagulate. 
    • Should never be left on standby (except just prior to removal)
      • Thrombosis could occur, and embolize to cause limb ischemia
      • The cannula in the aortia occludes some flow as well!

     

    Complications

    • Vasopressors/inotropes must be available when troubleshooting
    • Two groups of complications:
      • Vascular
      • IABP related
    • Types of complications:
      • Vascular Injury (embolism, dissection, occlusion during balloon inflation)
        • Monitor organ ischemia & limb pulses.
        • Cannula can kink, or dislodged+ migrate with pt movement (may need to sedate patient)
      • Infection
      • Balloon Malfunction
    • Keeping balloon >2 days = increased risk of complications (vascular injury, bleeding, GI bleeding), but no difference in mortality.
      • In the study average duration was 21 days.
      • No recommendation as to optimal duration of use.

     

    Special Scenarios

    Dysrhythmias

    • Augmentation can be hindered by reduced balloon filling time. 
    • Try to control arrhythmias (esp afib)
    • If patient has atrial fibrillation - ensure using AFib triggered mode. 

     

    Cardiac Arrest

    • Put IABP to pressure trigger mode, and reduce threshold
    • This will synchronize it to make chest compressions more effective. 
    • ECG trigger can be used if pt has QRS complexes
    • Can also use internal trigger mode. 
    • Can be continued during defibrillation
      • Ensure that NO ONE TOUCHES the console or cables. 

     

    ECMO

    • Has been used successfully in ecmo --> possible synergistic effect.
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