Circulatory Support

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Circulatory Support
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Circulatory Failure

• Occurs when cardiac output and/or BP are
  inadequate to maintain tissue blood supply and
  meet metabolic requirements
• Causes
• Heart failure
• Hypovolemia
• Circulatory obstruction
• Inappropriate vasodilation (eg-sepsis)

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Circulatory Assessment

• Cardiac function evaluate CO and exclude heart
  failure
• Determinants of SV
• Preload ventricular end-diastolic volume and
  dependent upon venous return and pressure
• Afterload what the ventricle has to work
  against to pump bloodaortic stenosis, high SVR,
  neg intrathoracic pressure, and LV dilation
  increase LV afterload
• Contractility ability to perform work
  independent of preload and afterload
• Circuit factors hypovolemia, vasodilation,
  obstruction

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Normal distribution of body water

• Total body water is about 42 liters
• ECF accounts for 14 liters
• 11 liters bathes the cells (intersitial)
• 3 liters is plasma
• ICF accounts for 28 liters
• Water distributes throughout the ICF and ECF
• Colloids and colloid-containing fluids pull water
  into the intravascular compartment
• Sodium movement into/out of cells pulls water
  with it

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Circulatory Support

• Diagnosis
• Determines the treatment (fluid administration vs
  fluid restriction)
• Monitoring, supplemental O2, and temp control are
  essential
• ATB are used for infection, thrombolysis for MI,
  and analgesia for pain-induced vasovagal
  hypotension

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Circulatory Support, cont

• Rate and Rhythm
• Both tachycardia and bradycardia can reduce CO
• Restoring sinus rhythm and a normal HR can
  improve BP and CO
• Initially, electrolyte concentrations are
  optimized and arrhythmogenic drugs are withdrawn
• Antiarrhythmic drugs and/or cardioversion may be
  required depending on hemodynamics

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Circulatory Support, cont..

• Fluid therapy
• Goal is to optimize preload
• Fluid challenge
• Give 250 ml over a short time period (lt20 min)
• The response determines the next step
• Increase filling pressure ( ? CVP/PCWP) with
  little to no ? in CO no more fluid
• Transient increase in filling pressure/CO/BP
  need more fluid
• Crystalloid fluids are used first, or the fluid
  that is lost is replaced (eg- blood loss is
  reversed with blood)

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Fluid Replacement

• Crystalloid solutions
• Water to which electrolytes and glucose have been
  added
• Inexpensive and isotonic
• Low sodium fluids (eg-5 dextrose) disperse
  throughout ICF and ECF
• Sodium-containing fluids (eg-NS) only go into the
  ECF as cell membrane pumps remove sodium from the
  ICFthis is preferred since is it has a smaller
  volume of distribution

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Fluid Replacement, cont

• Colloid solutions
• Contain large molecules that cant easily diffuse
  out of blood vessels
• Exert an oncotic pressure, pulling water into the
  intravascular compartment
• Expensive but remain intravascular for long
  periods (it takes 4 times as much crystalloid for
  the same volume expansion)
• Colloids are used when crystalloids cant
  maintain adequate intravascular filling or when
  excessive fluid is contraindicated (eg-pulm
  edema)
• Natural colloids are blood and albumin
• Synthetic colloids include gelatin, dextran, and
  hydroxyethyl starch
• Disadvantages to colloids includes allergic
  reactions, clotting abnormalities, and renal
  impairment
• Blood is usually given if Hb lt8 mg/dl

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Circulatory Support, cont

• Inotropic and vasoactive drugs
• Provide support when optimal HR and preload fail
  to correct circulatory failure
• Hypovolemia, acidosis (pHlt7.1), and electrolyte
  imbalance impair inotropic drug action
• Alpha activation peripheral vasoconstriction
• B1 activation chronotropic and inotropic
• B2 activation vasodilation/bronchodilation

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Inotropic/vasoactive Drugs, cont

• A drug may activate several receptors but the
  balance variesinitially a single drug is used,
  but combinations may be required to correctly
  balance receptor stimulation
• Adrenaline and dopamine have their main effect on
  alpha and beta 1 receptors
• Dobutamine affects beta 1 and beta 1 receptors
• Norepinephrine affects alpha receptors

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Other methods of circulatory support

• Cardiac pacemakers
• Increase CO by regulating the HR
• Ventilatory support
• Reduces cardiorespiratory work and pulmonary
  edema
• Left-ventricular assist devices
• Intra-aortic balloon pumps

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Introduction

• Developed in about 1962
• Consists of a balloon-tipped catheter positioned
  in the descending thoracic aorta via the femoral
  artery
• Catheter is attached to a gas-driving unit that
  alternates inflation of balloon during diastole
  with rapid deflation just before systole

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Equipment

• Single-chambered balloon
• Assembled on a 12 Fr double-lumen catheter
• 1 lumen opens into the balloon and is used to
  deliver gas (CO2 or He)
• Other lumen opens at the catheter tip and is used
  to monitor aortic pressure
• When inflated, it displaces blood volume
  retrograde to the aortic arch and antegrade,
  perfusing areas distal to the balloon

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Equipment, cont

• Dual-chambered balloon
• Small round chamber distal to the larger
  cylindrical balloon
• Smaller balloon inflates slightly before the
  larger oneputs resistance to the antegrade boost
  when the large balloon inflates
• This downstream resistance causes increased
  retrograde flow and increases coronary perfusion

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Equipment, cont

• Triple-segmented balloon
• Middle chamber inflates before the 2 end chambers
• Results in an increased regrograde and antegrade
  blood flow

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Selection of Size

• Balloon capacity varies from 20-40 cc
• The more blood displaced, the better the pump
  functions
• Total occlusion of the aorta can injure it and
  cause hemolysis of RBCs
• The balloon should fill 85 of the diameter of
  the aorta
• Estimating aortic diameter is an uncertain
  process as it varies with individuals and MAP
• You can estimate it from the size of the femoral
  artery and the body surface area

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Insertion Arteriotomy

• Balloon is inserted in femoral artery
• Use the artery with the strongest pulse
• An arterial cutdown is done under a local
• Insert the catheter after attaching a graft the
  graft and catheter are secured with a tie
• Give heparin IV and use it as long as the balloon
  is in place
• Optimal balloon site is just distal to the L
  subclaviandecreases potential for balloon-tip
  perforation of the aortic arch

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Insertion-Percutaneous

• Wrap the balloon around the catheter
• Moisten the tip with saline and flush with
  heparin
• Measure from the femoral to 1cm below the angle
  of Louis to determine the length
• Puncture the femoral with an 18 guage needle
• Advance a guidewire thru the needle into the
  abdominal aorta
• Remove the guidewire and insert a dilator
• Remove the dilator and insert a larger dilator
• Pull out the guidewire and feed the catheter
  through the dilator
• Unwrap the balloon by turning the catheter
• Suture the catheter in place

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Operation

• Uses either He or CO2 to inflate the balloon
• He is lighterweight and has a faster delivery
  timefunctions better with fast HR or arrhythmias
• CO2 is soluble in blood so gas embolism risk is
  low
• Timing is everythingimproper timing can
  compromise the left ventricle
• Premature inflation causes early aortic valve
  closure and decreases the SV
• Late inflation doesnt augment diastole as much
  since aortic blood volume falls rapidly during
  diastole
• Premature deflation causes retrograde blood flow
  from the carotids and coronaries back into the
  aorta
• Late deflation increases resistance to LV
  ejection which increases afterload and O2
  consumption

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Operation, cont

• Requires an EKG, arterial pressure waveform, and
  skilled operator to get the timing right
• The EKG is used by the machine to sense so the
  balloon inflates at the closure of the aortic
  valve and deflates immediately before systole
• Inflation occurs shortly after the T wave
• Deflation occurs at the QRS
• Using the arterial waveform
• Inflation occurs at the dicrotic notch
• Deflation occurs just before the anacrotic rise

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Associated therapy

• Discontinue inotropic and vasopressor drugs
  ASAPthey oppose the pump
• Use fluid to maintain pressures is the
  vasopressor is weaned
• Small doses of vasodilators may be used to
  decrease afterload and increase peripheral
  perfusion because the catheter does take up space
  within the aorta
• IV heparin is used to decrease the risk of
  thrombus formation on the catheter tip
• Prophylactic broad-spectrum antibiotic
• Close monitoring HR, PAP, PCWP, arterial
  pressure, renal function, blood flow to the
  catheterized limb, clotting times

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Complications

• Aortic dissection
• Perforation of the common iliac artery
• Thrombus
• Sepsis
• Vascular insufficiency of the catheterized limb
  (most common)

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Hemodynamics

• Improvement is usually seen within the first hour
  or two
• Increased MAP
• Increased coronary/peripheral perfusion
• Decreased mental confusion
• Increased urinary flow
• Increased CO
• Decreased PAP
• Decreased PCWP
• Optimal duration hasnt been establishedsame say
  no longer than 48 hours use

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Troubleshooting

• If the baseline waveform isnt straight or if the
  plateau isnt good, theres a gas leak
• If the overshoot is very rounded out the balloon
  is too large

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Left Ventricular Assist Device

• A battery operated, mechanical pump thats
  surgically implantedit helps maintain the
  pumping ability of the heart
• A tube pulls blood from the left ventricle into a
  pump which then sends blood into the aorta
• The pump is placed in the upper part of the
  abdomenanother tube attached to the pump is
  brought out of the abdominal wall to the outside
  of the body and attached to the pumps battery
  and control system

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