EMERGENCY OXYGENATOR CHANGEOUT Predisposing Factors and Resulting Incidence

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EMERGENCY OXYGENATOR CHANGEOUTPredisposing
Factors and Resulting Incidence

• Tony Fisher
• Harefield Hospital
• U.K.

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OXYGENATOR PROBLEMS

• Leaks in
• Membranes
• Housing
• Heat Exchanger
• Grossly contaminated circuit
• Clots in Oxygenator / Reservoir
• Oxygenator Failure
• Raised trans - oxygenator pressure

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LEAKING OXYGENATORS

• INCIDENCE
• Stoney I in 23,426 cases
• Kurusz 2,371
• Jenkins 1,932
• Fisher 20,781 Housing leaks
  resulting in EOC
• Stensved 1,635
• Mejak 37,294 Water to blood
  leaks

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CONTAMINATED OXYGENATORS

• INCIDENCE
• Stoney 1 in 374,819 cases
• Kurusz 3,260
• Jenkins 6,762
• Mejak 23,148

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CLOTS IN OXYGENATOR and D.I.C.

• INCIDENCE
• Stoney 1979 1 in 787 cases
• Wheeldon 1981 3,667
• Kurusz 1986 1,479
• Svenmarker 1991 400
• Jenkins 1997 3,005
• Mejak 2000 2,283

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CLOTS IN OXYGENATOR

• 1990 - 92 1994 - 96
• n
  68,937 97,313
• Oxy clotted going
• back on bypass
• aprotinin 6 0
• Oxy clotted going
• back on bypass 0 1
• Oxy clotted
• aprotinin
  3 1
• Oxy clotted
  1 2

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FAILED OXYGENATORS

• INCIDENCE
• Stoney 1 in 3,022 cases
• Wheeldon 2,063
• Kurusz 1,134
• Mejak 2,458

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POSSIBLE CAUSES OF FAILED MEMBRANE OXYGENATORS

• Clot formation
• Plasma or blood leak
• Raised trans-oxygenator pressure gradient (R.T.P.)

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CONTRIBUTING FACTORS FOR FAILED OXYGENATORS

• Gas supply problems
• Metabolic requirements
• State of anaesthesia,
• Poor oxygenator design
• Large patients

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CHARACTERISTICS OFR.T.P. GRADIENT

• A.C.T. is greater than 480 secs
• Starts to occur immediately upon going on bypass
• Pressure drop across oxygenator increases rapidly
• Reaches a plateau
• Reduces rapidly back to base line after about 30
  minutes or on rewarming

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CHARACTERISTICS OF R.T.P. GRADIENT

• Effect may be reduced by rewarming
• Oxygenation may become inadequate
• If the oxygenator is changed out it does not
  recur

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SUGGESTED CAUSES OF RAISED T.O.P. GRADIENT

• The blockage is caused by the development of a
  fibrin - platelet thrombus
• This appears to start in the heat exchanger but
  grows into, or breaks away into the oxygenator
  fibre bundle

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RAISED TRANS-OXYGENATOR PRESSURE GRADIENT

• INCIDENCE
• Study Incidence Requiring
• Size E.O.C.
• Stensved 11,451 1 in 89 1 in 954
• Blomback 1,800 164
  600
• Wahba 1,959 42 490
• Fisher 3,684 228
  1,228

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MEASUREMENT of TRANS-OXYGENATOR PRESSURE

• Reasonably linear relationship between Pressure
  Gradient and Flow
• Therefore can be based on Poiseuilles Formula
• Flow ? x p x r4
• 8 x ? x l

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MEASUREMENT of TRANS-OXYGENATOR PRESSURE

• Variations in measurements due to
• Viscosity changes
• Haematocrit
• Prime constituents
• Flow
• Temperature
• Site of measurement
• OVERALL Variation about 10

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INCIDENCE by HOSPITAL

• Hospital 1 2 3 4 5 6 7 8
• No. cases 602 730 982 498 400 144 87
  241
• No incidents 1 4 1 2 1 2 2 3
• No. of cases
• per incidence 602 183 982 249 400 72 44 80

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INCIDENCE by OXYGENATOR

• Oxygenator No. Used No.Incidents
• Terumo SX18 25 0
• Terumo SX25 300 1
• Medos Hilite 264 0
• Affinity 341 0
• Sorin Monolyth 128 2
• Cobe Duo 986 8
• Cobe Optima 208 0
• Dideco Avant 982 1
• Bard Quantum 371 4
• Gish Vision 87 0

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• Raised Trans-Oxygenator Pressure Gradient can
  only be seen if it is monitored
• Greater awareness of the problem results in more
  monitoring
• If monitoring is not done then the problem
  presents as a Failed Oxygenator

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FAILED OXYGENATORS

• INCIDENCE YEAR
• Stoney 1 in 3,022 cases 1979
• Wheeldon 2,063 1981
• Kurusz 1,134 1986
• Mejak 2,458 2000

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SUMMARY

• Happens immediately upon going on bypass
• Eventually disappears
• Does not recur upon emergency changeout
• Incidence varies between different units
• At least two different possibly unrelated
  initiating factors
• These factors may always have been present

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CONCLUSION

• Oxygenators may need emergency replacing due to
  mechanical failures
• A rare event - maybe 1 in 20,000 cases
• This can only be improved by better quality
  control by the manufacturers

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CONCLUSION

• Oxygenators may need emergency replacing due to
  clotting problems
• Incidence 1 in 3,000 cases
• This problem needs to be addressed by improving
  anticoagulation monitoring

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CONCLUSION

• Oxygenators may need emergency replacing due to a
  fibrin - platelet thrombus which may be
  demonstrated by a raised trans-oxygenator
  pressure gradient.
• Incidence 1 in 1,000 cases
• This problem may always have been with us, and
  needs to be addressed by continuing research into
  its aetiology.