Question 2

A 71-year-old male is transferred to your ICU following a mechanical aortic valve replacement and coronary artery bypass surgery. The anaesthetist reports that he came off bypass readily, has not required any inotropic support, and has epicardial pacing wires in situ. However, shortly after arrival his blood pressure falls to 60/30 mmHg.
a) Outline your differential diagnosis for his hypotension. (20% marks)
b) List four likely causes of excessive post-operative bleeding in this setting. (20% marks)
c) Outline your immediate management. (60% marks)

[Click here to toggle visibility of the answers]

College answer

Not available.

Discussion

This question is basically the same as Question 13 from the first paper of 2012, which demonstrates to exam candidates that they need to reach at least ten years back into historical papers in order to capture all potential repeat SAQs. 

Differential diagnosis for this hypotension can be organised in a number of different ways (see the discussion section of Question 13), but the one which 

  • Preload
    • Inadequate intraoperative fluid
    • Haemorrhage
    • Valve failure (mitral / tricuspid)
  • Rate
    • Bradycardia (or excessive tachycardia!)
  • Rhythm
    • AF or other arrhythmia
  • Contractility
    • Post-bypass myocardial depression
    • Myocardial ischaemia
  • Afterload
    • Artifact: art line is incorrectly zeroed
    • LVOT obstruction
    • Anaphylaxis
    • Vasoplegia
    • Valve failure (aortic or pulmonic)

Considering this was weighted only 20% of the total mark, one should be expected to produce a laconic pointform list rather than a paragraph of text, which means the use of this classification system might be a bit excessive. 

Four likely causes of excessive post-operative bleeding in this setting:

One could pick any from the following list of factors:

  • incomplete surgical haemostasis
  • residual heparin effect after cardiopulmonary bypass
  • platelet abnormalities (platelet dysfunction and thrombocytopenia – from bypass circuit consumption, antiplatelet agents etc)
  • hypothermia 
  • postoperative hypertension
  • clotting factor depletion
  • haemodilution (dilutional thrombocytopenia and coagulopathy)

Immediate management here would have to be structured and detailed to earn full marks. Examples of what that means abound in the past papers, but the best one is probably again in the college answer to Question 13 from the first paper of 2012. A mutant version of that structure is offered here:

  • Maintain  SpO2 ~ 100%
  • Adjust positive pressure, with two goals in mind:
    • Enhancement of preload by controlling the intrathoracic venous flow
    • Enhancement of afterload by increasing LV transmural pressure
    • Perhaps some sort of tamponade effect - the college answer recommends a PEEP of 10, which ( a reader has helpfully pointed out) probably comes from Ilabaca et al (1980).
  • Assess the drains to make sure they are not blocked
  • Maintain satisfactory diastolic pressure with noradrenaline and/or vasopressin
  • Give a fluid bolus
  • Check for a cardiovertable rthythm disturbance
  • Consider increasing pacing rate to 90
  • Organise a TOE or TTE to assess the need for inotropes
  • Check bloods and TEG to see what further factors/platelets the patient might require
  • Alert the surgeons to the deterioration, in case you need to reopen the chest

References

Frederick A. Hensley, Jr., M.D., Donald E. Martin, M.D.,  Glenn P. Gravlee, M.D. A Practical Approach to Cardiac Anaesthesia, 3rd ed. Sibylle A. Ruesch and Jerrold H. Levy. CHAPTER 9. The Postcardiopulmonary Bypass Period: A Systems Approach. 2003 by LIPPINCOTT WILLIAMS & WILKINS

André, Arthur C. St, and Anthony DelRossi. "Hemodynamic management of patients in the first 24 hours after cardiac surgery." Critical care medicine 33.9 (2005): 2082-2093.

Estafanous, Fawzy G., and Robert C. Tarazi. "Systemic arterial hypertension associated with cardiac surgery.The American journal of cardiology 46.4 (1980): 685-694.

Roberts, A. J., et al. "Systemic hypertension associated with coronary artery bypass surgery. Predisposing factors, hemodynamic characteristics, humoral profile, and treatment." The Journal of thoracic and cardiovascular surgery 74.6 (1977): 846-859.

Ilabaca, Patricio A., John L. Ochsner, and Noel L. Mills. "Positive end-expiratory pressure in the management of the patient with a postoperative bleeding heart." The Annals of thoracic surgery 30.3 (1980): 281-284.