FRCA Notes

Complications of Cardiopulmonary Bypass

Resources

  • Complications following CPB can be fatal and require prompt recognition & management
  • There is a fair degree of overlap with the complications following cardiac surgery in general, be it using CPB or not
  • Atelectasis (70%)

  • Pleural effusion (~10%)

  • Acute lung injury ± respiratory failure is a common complication (9%)
    • It is associated with a 6x increase in mortality rate vs. those without respiratory failure
    • Circuit-associated activation of inflammatory (complement) and oxidative stress pathways leads to a pulmonary ischaemia-reperfusion injury

  • Decreased chest wall compliance from sternotomy closure and pain

  • Left lower lobe collapse from phrenic nerve neuropraxia due to cold slush cardioplegia/retraction ± poor re-expansion following one-lung ventilation

  • Pulmonary hypertension ± right heart failure
    • From the effects of protamine (↑PVR), CPB-induced TXA2 release, atelectasis and HPV

  • Pulmonary effects of hypothermia

  • Vasoplegia and prolonged hypotension

  • Myocardial injuries
    • Stunning from cardiotomy and/or cardioplegia
    • Myocardial infarction from coronary graft ischaemia or air embolus

  • Arrhythmias
    • Up to 40% will experience AF
    • As a consequence of hypothermia
    • Due to direct trauma
    • Secondary to electrolyte disturbance

  • Cardiac tamponade (1.5%)

  • CABG graft ischaemia (4 - 5%)

  • Aortic dissection during cannulation of the aorta (0.06-0.23%)

  • A systemic multi-organ dysfunction syndrome can occur due to end-organ hypoperfusion and ischaemia

  • Neurocognitive impairments

  • Choreoathetosis (appearing 2-6 days in those who experienced DHCA to below 15°C)

  • Spinal cord ischaemia (1-4%)

  • Watershed infarcts and stroke (1.2%), either due to sluggish blood flow post-bypass and/or micro-emboli

  • Awareness
    • Historically higher than general surgical population
    • Reduced incidence following routine use of TIVA, depth-of-anaesthesia monitoring or addition of volatile to the oxygenator

  • Effects of hypothermia during CPB
    • Reduced GFR and associated acidosis
    • 'Cold diuresis'

  • AKI from low-flow states and/or thromboembolic events
    • Increased preoperative NT-proBNP concentrations are associated with postoperative AKI (BJA, 2021)
    • A degree of renal dysfunction occurs in 30-40%
    • Patients may develop stage 1 (7%), stage 2 (3.4%) or stage 3 (1.3%) AKI
    • 0.7-1.3% require dialysis, which if required is associated with a large increase in mortality to ∽60%

  • Hypothermia, either delayed re-warming or rebound hypothermia

  • Hyperglycaemia from hypothermia-induced insulin resistance and the effect of endogenous catecholamines

  • Haemodilution can cause derangement of most electrolytes

  • Acidosis, often multifactorial
    • Global perfusion changes
    • Effects of anaemia and hypothermia
    • Hepatic or renal failure
    • Limb or gastrointestinal ischaemia from embolism

  • Hepatic dysfunction
    • Manifests as increased lactate intra-operatively
    • Manifests as raised ALT post-operatively
    • Can be due to venous cannula being advanced into hepatic circulation, or partial drainage of the hepatic venous system causing congestion in undrained veins

  • Splanchnic ischaemia from low-flow states and/or thromboembolic events

  • Pancreatitis

Anaemia

  • Haemodilution is the main cause for anaemia and requirement for blood transfusion
  • Reduced by:
    • Minimising the circuit & circuit-prime volumes, or using autologous priming
    • Use of haemofilters to remove water from blood

  • Other causes of anaemia include:
    • Haemolysis; roller-pump induced haemolysis may be obviated by using a centrifugal pump
    • Blood loss (occult or otherwise)

Coagulopathy

  • Clotting factor dilution from the crystalloid prime

  • Clotting factor consumption
    • Can be reduced by coating circuits with heparin and phosphorylcholine
    • This improves post-CPB platelet count, reduces blood loss and reduces inflammatory mediator release

  • Platelet dysfunction, usually arising from:
    • Mechanical stress from old roller-pumps, now obsolete and replaced by either centrifugal pumps or more modern roller-pumps
    • Effect of pre-operative antiplatelet medications

  • Clotting within the CPB circuit is rare, although is associated with poor outcome especially if open-heart surgery

Embolic phenomena

  • Micro and macro air embolism can occur

  • Fat embolism is also possible; risk can be reduced by using cell salvage (85% reduction) and avoiding cardiotomy suction

  • Use of safety devices, automatic clamps and vented blood filters can help reduce risk of embolism

  • Activation of complement by the bypass circuit can trigger a SIRS response
    • Use of a leucocyte-depleting filter or use of haemofilters can mitigate the inflammatory response
    • The REMOVE study aims to assess use of cytokine absorbed in the circuit to reduce the SIRS response

  • Anaphylaxis e.g. to protamine

  • Infection
    • Mediastinitis (1-4%)
    • Saphenous vein harvesting site infection (up to 24%)