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Cardiopulmonary bypass and cardiac surgery
Before cardiopulmonary bypass a high dose of heparin is given and a long ACT is confirmed; at the end it is reversed with protamine, and on the way cold, haemodilution, potassium cardioplegia and an orderly separation from the machine are managed.
Why it matters in the exam
The exam asks about the heparin dose and the ACT target, the protamine calculation and the reactions to it (hypotension, anaphylaxis, pulmonary hypertension), heparin resistance (antithrombin deficiency) and the alternative in HIT (bivalirudin). It also asks what is needed before separation from bypass, what causes bleeding after cardiac surgery, and what "vasoplegia" after bypass is.
The machine replaces the heart and lungs: blood is drained from the veins, oxygenated and returned to the aorta. The heart is arrested in diastole with a potassium-rich cardioplegia solution, and the body is sometimes cooled to protect organs. During bypass haemoglobin falls because of dilution, and the clotting and inflammatory systems are activated by contact with the circuit. Transoesophageal echo is used to monitor function and valves.
After separation the common complications are bleeding (surgical or from coagulopathy), tamponade, vasoplegia with hypotension despite good output, kidney injury, stroke and delirium. In bleeding, viscoelastic tests are used to tell residual heparin, fibrinogen deficiency, dysfunctional platelets and surgical bleeding apart. A patient with recent HIT receives bivalirudin instead of heparin. At the end of surgery the patient is moved ventilated to intensive care, where drain output, urine output, glucose, electrolytes and rhythm are followed — because atrial fibrillation and late bleeding are common in the first days.
Key points
- Heparin 300–400 U/kg, ACT above 400–480 seconds.
- Potassium cardioplegia arrests the heart in diastole.
- Separation: temperature, electrolytes, ventilation, rhythm.
- Protamine 1 mg per 100 U of heparin, slowly.
- HIT — bivalirudin.
Summary table
| Stage | What is done | Exam point |
|---|---|---|
| Before bypass | Heparin 300–400 U/kg; ACT above 400–480 seconds | Resistance: antithrombin deficiency — antithrombin concentrate or plasma |
| During bypass | Potassium cardioplegia, cooling as needed, dilution monitored | The heart stops in diastole |
| Separation | Rewarming, correct potassium, calcium and acidosis, ventilate the lungs, rhythm or pacing, inotropes as needed | Do not separate a cold or unventilated patient |
| Reversal | Protamine 1 mg per 100 U of heparin | Hypotension, anaphylaxis, pulmonary hypertension |
| HIT | Bivalirudin instead of heparin | No heparin at all |
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Sources
- Miller's Anesthesia, 9th edition (2020) — Anesthesia for Cardiac Surgical Procedures; Cardiopulmonary Bypass
- STS/SCA/AmSECT/SABM Clinical Practice Guidelines: Patient Blood Management in Cardiac Surgery, 2021 — Anticoagulation and reversal
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.