Question 13 and Question 14 both relate to the following clinical scenario:

A 71-year-old man is transferred to your intensive care unit 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.

a) Outline your differential diagnosis for his hypotension

His blood pressure improves rapidly with a fluid bolus, and examination is otherwise unremarkable. However, he is noted to lose 250ml of blood from his mediastinal drains over the next 30 minutes.

b) List 4 likely causes of, or contributors to, excessive post-operative bleeding in this setting, and outline your immediate management.

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College Answer

a) Differential diagnosis for hypotension

  • Artefactual 
  • Preload – intravascular volume depletion (eg blood loss, rewarming), medication effect (eg 
    propofol), anaphylaxis, vasoplegia 
  • Contractility – arrhythmia, myocardial ischaemia, valvular dysfunction, hypoxia, pacing wire 
    problem 
  • Afterload – pericardial tamponade, tension pneumothorax, elevated intrathoracic pressure 
  • Outflow tract obstruction

b) Causes of post-operative bleeding and management

  • Excessive bleeding is usually due to one or more of the following factors:
    • incomplete surgical hemostasis
    • residual heparin effect after cardiopulmonary bypass
    • platelet abnormalities (platelet dysfunction and thrombocytopenia – from bypass, antiplatelet agents etc)
    • hypothermia
    • postoperative hypertension
    • clotting factor depletion
    • hemodilution (dilutional thrombocytopenia and coagulopathy)
  • Initial management
    • Assess airway, breathing, circulation.
    • PEEP 10
    • Look for potential underlying causes (as above).
    • Measure ACT and formal coagulation profile. If ACT/APTT raised, consider Protamine. 
    • Consider platelet transfusion early if antiplatelet agent in days prior to surgery or platelet dysfunction considered likely contributor. 
    • Manage hypertension with titratable agent (eg GTN, SNIP) 
    • Correct hypothermia 
    • FFP if INR and/or APTT raised. Platelet transfusion if thrombocytopenia.
    • Transfusion of packed red blood cells may also be necessary to replace blood loss. Optimal transfusion strategy, including the level below which RBC transfusion clearly improves outcomes, is uncertain (eg TRACS trial).
    • Notify cardiothoracic surgeon early if concerned. Pre-existing protocol (including guidelines for notification) useful.
    • If haemodynamically unstable from blood loss, or if bleeding persists despite above measures, consider re-thoracotomy.
    • Use of DDAVP and Factor 7 controversial. 

Discussion

This question revisits the topic of post-cardiothoracic surgery complications. Ruesch and Levy, in their chapter from Practical Approach to Cardiac Anaesthesia have nice point-form guides which calmly deal with the stressful situation of haemodynamic instability after bypass. (in general, that book is awesome). I have made my own notes on this subject, but I claim no special expertise in it. There I categorise the differential diagnosis for hypotension in the post-bypass patient, as well as the various steps one needs to take in assessing the medical and surgical causes of bleeding.

In general, it is good to organise the answer to these in the system of "measurement error, preload, contractility, afterload, rate and rhythm"; or any other system (any is better than none).

Thus:

Causes of post-cardiotomy instability, organised by alphabetical mnemonic order

A - Artifactual; art line is incorrectly zeroed

B - Tension pneumothorax

C - Cardiac tamponade

   - Myocardial ischaemia

   - Acute valvular failure (eg. of grafted valve)

   - LVOT obstruction

   - Post-bypass myocardial depression

   - Arrhythmia (eg. AF)

D - Excess sedative (eg propofol)

E - Post-bypass hypocalcemia

F - Inadequate preload - need more fluid

...Or: excessive preload in the failing left heart - causing diastolic dysfunction of the left heart

G - Arterial embolism of the mesenteric vessels (chaos ensues)

H - Haemorrhage - inadequately reversed heparinisation or DIC

   - could be into pericardial sack or pleural space

I - Anaphylaxis; reaction to anaesthetic agents

   - Vasoplegia due to circuit-induced SIRS

Causes of post-cardiotomy instability, organised by affected hemodynamic variable

  • 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)

Post-cardiothoracic surgical bleeding complications

Excessive bleeding is usually due to one or more of the following factors:

  • incomplete surgical hemostasis
  • 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
  • hemodilution (dilutional thrombocytopenia and coagulopathy)

References

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.