Free flap microvascular surgery: pressure, fluid, temperature and the failing flap
Stem
A 62-year-old man, 78 kg, with oral squamous cell carcinoma is having segmental mandibulectomy, neck dissection, tracheostomy and fibula free flap reconstruction, expected to take 10 hours. Six hours in, after the arterial and venous anastomoses, his MAP is 58 mmHg under sevoflurane, he has had 4.5 L of crystalloid, and his temperature is 35.4 °C. The surgeon asks for more fluid and "no pressors, they will spasm the flap."
Question
How do you respond, and what are your physiological goals for the flap?
Ideal answer
HeadlineThe flap needs perfusion pressure, not more crystalloid: I restore his MAP with a judicious vasopressor, stop the fluid creep, and warm him.
- Phenylephrine or norepinephrine to his baseline MAP, because judicious vasopressor use does not increase flap compromise or loss.1
- Stop liberal crystalloid; give fluid only to measured response, because rates over 10 mL/kg/h were associated with more flap complications.2
- Forced-air warming to above 36 °C, because hypothermic vasoconstriction compromises marginally perfused flaps.3
- Lighter anesthetic, check depth and blood loss, because volatile vasodilation is the commonest cause of this hypotension.
- Explain the evidence to the surgeon and agree a target, because we share one goal: flow through the pedicle.
Watch for: flap color and Doppler signal, urine output, lactate and hemoglobin trend.
Breaking down the answer
- The vasopressor dogma — a 10-year review of 5671 flaps showed equal success with vasopressors and less venous congestion;1 evidence is observational but consistent. Changes if: the flap pales after a bolus, then I lower the dose and add volume.
- Fluid overload — complications were 54.8% above 10 mL/kg/h versus 37.1% at 5 mL/kg/h or less; crystalloid over 3000 mL was linked with more flap loss, and pneumonia rose too.2 Edema in the flap and the neck compresses venous outflow.
- Operative time — each extra hour raised the odds of total flap loss by 34%;2 I keep turnover between stages short.
- Temperature — anesthesia widens the thermoregulatory range to about 4 °C and core falls 1.0–1.6 °C in the first hour from redistribution.3 I warm from the start, including fluids.
- Anticoagulation — routine therapeutic heparin or dextran adds bleeding without improving flap survival; standard DVT prophylaxis still applies.1
- Transfusion — red cells were associated with more complications in one cohort;2 I transfuse for physiology, not habit, and keep a restrictive threshold.
Follow-up question
At 2 a.m. in the ICU, the flap skin paddle is purple and swollen, pinprick gives brisk dark blood, and the Doppler signal has changed. The surgeon wants to re-explore now. How do you manage this?
Follow-up answer
HeadlineVenous congestion of the flap, probably venous anastomotic thrombosis; this is a time-critical salvage, and I agree to go now.
His tracheostomy gives a secure airway: I confirm its position and connect him to the anesthesia circuit. I induce gently with an opioid and low-dose propofol or volatile, keep MAP at baseline with a vasopressor, avoid fluid boluses for pressure, and keep him warm. I ask the surgeon whether they want heparin at re-anastomosis or thrombectomy. Most compromise appears within 72 hours, which is why intensive checks focus there.1 Then I review the cause with the team.
Pitfalls that cost points
- Treating every low pressure as hypovolemia; the commonest cause is anesthetic vasodilation in a euvolemic patient.
- A tight neck dressing or tracheostomy ties compressing the flap's venous drainage.
- Withholding NSAIDs for fear of flap hematoma; NSAIDs, including COX-2 inhibitors, did not raise hematoma or thrombosis risk.1
Rapid-fire
Q: When do most flaps fail? A: 82.3% of compromised flaps presented within 24 hours and 95.6% within 72 hours in one series.1
Q: How long should hourly ICU flap checks continue? A: Intensive checks focus on the first 48–72 hours; stepping down after that in stable patients is supported.1
Q: Did noradrenaline predict flap loss in the fluid study? A: No; intraoperative noradrenaline was not independently associated with flap complications or loss.2
Q: What defines hypothermia here? A: Core temperature below 36 °C; even 34–36 °C is linked with cardiac events and bleeding.3
Numbers to know
| Item | Value |
|---|---|
| Crystalloid rate with more flap complications | > 10 mL/kg/h2 |
| Total crystalloid linked to flap loss | > 3000 mL2 |
| Extra odds of flap loss per operative hour | 34%2 |
| Normothermia | ≥ 36 °C3 |
| Compromise presenting by 72 h | 95.6%1 |
Links
- Fluid management: crystalloid, colloid, goal-directed, Vasopressors and inotropes: choosing and titrating, Temperature monitoring and intraoperative hypothermia, Tracheostomy, laser surgery and jet ventilation, Intraoperative hypotension: differential and management
- Microsurgery evidence review (PRS Global Open 2026)
Sources
- 1.Mythbusters in microsurgery: evaluating evidence and debunking dogma, a practical review, part I · Plast Reconstr Surg Glob Open (PMC13105801), 2026 · pmc.ncbi.nlm.nih.gov
- 2.Perioperative predictors of complications and flap loss in microvascular reconstructive surgery: the role of fluid balance, crystalloid administration and operative time · J Clin Med (PMC13411073), 2026 · pmc.ncbi.nlm.nih.govRetrospective single-center cohort, 495 flaps; associations, not causation.
- 3.Perioperative hypothermia in medium- and large-volume plastic surgery: clinical and surgical implications and practical prevention strategies · Cureus (PMC13477116), 2026 · pmc.ncbi.nlm.nih.gov
Facts on this page were checked against these sources on Nov 2, 2026. Guidelines change; confirm doses against current institutional protocols.