Cardiopulmonary bypass: conduct and separation
Stem
A 66-year-old man, 92 kg, is having three-vessel coronary bypass grafting on cardiopulmonary bypass. His preoperative ejection fraction was 35%, and he took lisinopril the morning of surgery. The distal and proximal anastomoses are done, the cross-clamp has been off for 15 minutes, his nasopharyngeal temperature is 36.4 °C, and he is in sinus rhythm at 52 with epicardial pacing wires placed. The surgeon says, "We're ready to come off."
Question
How do you prepare this patient for separation from bypass, and how do you take him off?
Ideal answer
HeadlineA weak, just-ischemic ventricle: I separate deliberately, running the checklist out loud before anyone touches the venous line, because errors of omission happen here.1
- Temperature: no rewarming overshoot above 37 °C, because cerebral hyperthermia worsens brain injury.1
- Rhythm and labs: atrial pacing at a normal rate, not 52 with a stiff ventricle; potassium, calcium, hemoglobin, glucose, blood gas.
- Lungs and monitors: re-expand under vision, ventilate 100% oxygen, alarms on; re-zero transducers; TEE for de-airing, regional wall motion and both ventricles.
- Inotrope running or drawn up, vasopressor ready, given his ejection fraction and the vasoplegia his ACE inhibitor predicts.1
- Partial venous occlusion, filling on TEE, flow down stepwise, then off; when the surgeon agrees, protamine slowly, cardiotomy suction off as it starts.1
Watch for: pressure, filling, ventricular function and graft territories after separation.
Breaking down the answer
- Checklist first — weaning is a multidisciplinary step where a cognitive aid reduces omissions; the forgotten ventilator is the classic one.1
- Predict a hard wean — low ejection fraction, valve regurgitation, urgency and long bypass time predict difficult separation: escalating support, a failed first attempt, or a mechanical device.1 I start the inotrope before I need it.
- Name vasoplegia — low pressure with normal or high output, 5–25% of cardiac surgery, linked to ACE inhibitors; vasopressin, norepinephrine and methylene blue are the tools.1
- Anticoagulation logic — a weight-based heparin bolus with ACT above about 480 s (above 400 s for maximally activated devices) kept the circuit open; reversal is the mirror image.2 Heparin resistance before bypass: more heparin, then antithrombin concentrate or plasma.1
- Protamine is dosed, not guessed — titrate to residual heparin, ratio below 2.6 mg per 100 units; the European guideline favors below 1:1, because excess protamine is itself an anticoagulant.2 1
- TEE drives decisions — an empty ventricle (volume), a failing one (inotrope, balloon pump), a regional defect (graft problem the surgeon must fix).
Follow-up question
He comes off on low-dose epinephrine. Two minutes into the protamine infusion, his pressure falls to 62/35, the PA pressure doubles, and TEE shows a dilated, hypokinetic right ventricle with the septum bowing left. What do you do?
Follow-up answer
HeadlineCatastrophic protamine reaction: acute pulmonary vasoconstriction and RV failure. I stop the protamine and tell the team we may go back on bypass.
The pump stays primed and the circuit ready. I give 100% oxygen, bolus epinephrine, add a vasopressor to restore right coronary perfusion pressure, and start an inhaled pulmonary vasodilator. If the ventricle does not recover in a minute or two, we re-heparinize with a full weight-based dose, confirm an adequate ACT and go back on bypass to rest the heart.2 Once stable, I reassess on TEE, separate again and give protamine much more slowly, documenting the reaction for future anesthetics.
Pitfalls that cost points
- Giving protamine before the surgeon is done with the cannulas.
- Treating every low pressure as hypovolemia instead of letting TEE separate volume, contractility and vasoplegia.
- More protamine to "fix" ongoing oozing.
Rapid-fire
Q: What pump flow do perfusionists target? A: About 2.2–2.8 L/min/m² at moderate hypothermia to normothermia, increasingly guided by oxygen delivery.1
Q: How do you anticoagulate a patient with HIT who needs urgent bypass? A: Bivalirudin is a reasonable option; elective cases wait for a negative functional assay, and heparin is then acceptable for bypass even if the immunoassay is still positive.2,3
Q: What limits cooling and rewarming speed? A: The gradient between heat exchanger and arterial inflow should not exceed 10 °C.1
Q: What is heparin rebound and how is it treated? A: Residual heparin reappearing after reversal; a low-dose protamine infusion of 25 mg/h for up to 6 hours may be considered.2
Numbers to know
| Item | Value |
|---|---|
| ACT on bypass | >480 s; >400 s with maximally activated devices2 |
| Protamine ratio | <2.6 mg/100 U (STS); <1:1 (EACTS)2 1 |
| Pump flow | 2.2–2.8 L/min/m²1 |
| Vasoplegia incidence | 5–25%1 |
| Rewarming ceiling | Avoid >37 °C1 |
| Heparin rebound | Protamine 25 mg/h up to 6 h2 |
Links
- Heart failure and reduced ejection fraction, Vasopressors and inotropes: choosing and titrating, Pulmonary artery catheter: indications, waveforms, complications, Perioperative hypothermia and coagulopathy, Pulmonary hypertension and right ventricular failure
- Atlas: The 11 TEE views; Ventricular function and wall motion
- STS/SCA/AmSECT anticoagulation during CPB (2018); EACTS/EACTAIC/EBCP CPB guideline (2024)
Sources
- 1.2024 EACTS/EACTAIC/EBCP Guidelines on cardiopulmonary bypass in adult cardiac surgery · EACTS/EACTAIC/EBCP, 2024 · ebi.ac.ukInteract Cardiovasc Thorac Surg 2025;40:ivaf002; sections 9.3 (anticoagulation), 9.4–9.5 (MAP, flow), 11 (separation).
- 2.STS/SCA/AmSECT Clinical Practice Guidelines: Anticoagulation during Cardiopulmonary Bypass · STS/SCA/AmSECT, 2018 · pmc.ncbi.nlm.nih.gov
- 3.From general guidance to surgical reality: adapting the heparin-induced thrombocytopenia algorithm for cardiac surgery · JTCVS Open (PMC13711180), 2026 · pmc.ncbi.nlm.nih.govCommentary on the AATS expert consensus document on HIT.
Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.