Nomogram predicts vascular crisis after free flap surgery

A retrospective study of 568 patients undergoing free flap surgery found that a four-factor nomogram estimated the risk of postoperative vascular crisis with an area under the receiver operating characteristic curve of 0.817 in the development cohort and 0.852 in a later internal validation cohort. The model combined serum albumin concentration, smoking status, hemoglobin concentration and intraoperative packed red blood cell transfusion. Vascular crisis occurred in 63 patients, or 11.1% of the cohort, and involved thrombosis or spasm in vessels connected to a transplanted flap. The findings suggest that routinely available clinical and perioperative measures could help identify patients who may warrant closer postoperative monitoring, although the model has not been externally tested in other hospitals or populations.

Free flap transplantation transfers living tissue, together with its own blood supply, to repair severe soft-tissue defects or reconstruct limb and external-organ functions. Although advances in microsurgical anastomosis, instruments and robotic surgery have improved the quality of vascular connections, postoperative vascular crises remain a major perioperative complication. Such events can compromise flap viability, require emergency salvage surgery, prolong hospitalization and contribute to permanent impairment of limb function. The study was conducted at No. 971 Hospital of the People’s Liberation Army Navy in China using clinical records from January 2012 through August 2023. Among 1,084 records screened, investigators included 568 patients aged 6 years or older who completed free flap surgery. They excluded non-free flap procedures, operations converted to another procedure, patients younger than 6 and patients classified as American Society of Anesthesiologists Physical Status class IV or V.

To separate model development from later validation, the researchers divided the patients chronologically, using December 31, 2020 as the cutoff. Records from 402 earlier patients formed the training cohort, while 166 later patients formed the validation cohort. The training group included 42 vascular crises, or 10.4% of its patients, and the validation group included 21, or 12.7%. The overall median age was 44 years, with an interquartile range of 31–51 years, and the median operative duration was seven hours, with an interquartile range of 5.5–8.5 hours. Most participants were men. Common flap types included anterolateral thigh, forearm and thoracoumbilical flaps. Anterolateral thigh flaps had the greatest absolute number of crises and necroses, but the study did not establish flap type as an independent predictor or demonstrate that the observed counts represented higher within-type risks.

Vascular crisis was diagnosed through bedside assessment of flap color, temperature, capillary refill time, tension and bleeding after pinprick. A pale or gray flap with reduced temperature, prolonged or absent capillary refill and little or no bleeding was considered suspicious for arterial compromise. A dark-red or cyanotic flap with swelling, increased tension and profuse dark-red bleeding suggested venous compromise. Two senior microsurgeons independently assessed and confirmed all cases, resolving discrepancies through discussion or consultation with another senior microsurgeon. Of the 63 crises, 37 patients underwent surgical exploration; arterial crisis was confirmed in 22 and venous crisis in 15. Another 26 patients had findings consistent with mild venous crisis and improved with conservative measures, including removal of sutures to relieve tension, incision and bloodletting for decompression, and volume expansion. Seventeen flaps were lost overall, producing a flap survival rate of 97.0%.

Univariate screening in the training cohort identified 13 variables for inclusion in multivariable modeling. Stepwise multivariable logistic regression then identified four independent statistical associations with vascular crisis. Each 1 g/L increase in serum albumin was associated with an odds ratio of 0.927, with a 95% confidence interval of 0.868–0.991, indicating that higher albumin was associated with lower odds of crisis. Smoking had an odds ratio of 4.713 compared with non-smoking, with a 95% confidence interval of 2.184–10.171. Each 1 g/L increase in hemoglobin had an odds ratio of 0.971, with a 95% confidence interval of 0.952–0.990. Each additional unit of packed red blood cell transfusion had an odds ratio of 1.170, but its 95% confidence interval of 0.993–1.377 included 1 and its P value was 0.060. The authors nevertheless retained transfusion as one of the four variables in the nomogram. These retrospective associations do not show that changing any factor would prevent a crisis.

The nomogram translates the four inputs into points that are summed and converted into a predicted probability. The researchers also created a dynamic online calculator that returns a risk estimate and 95% confidence interval. In the training cohort, the area under the receiver operating characteristic curve was 0.817, with a 95% confidence interval of 0.747–0.887. In the later validation cohort, it was 0.852, with a 95% confidence interval of 0.774–0.929. Calibration analysis showed agreement between predicted and observed risk, with a mean absolute error of 0.019, corresponding to an average prediction error of 1.9%. Decision curve analysis indicated clinical utility across a modeled risk-threshold range of 1% to 51%. A complete-case sensitivity analysis produced results consistent with the primary analysis. The online tool and transparent point system make the model accessible without specialized computing equipment, but its usefulness still depends on accurate inputs and validation in the intended clinical setting.

Several biological pathways could connect the selected variables with flap failure, although the retrospective data cannot determine which mechanisms were responsible. The authors interpreted lower albumin as a marker of poorer perioperative nutritional or physiological condition, noting that low albumin can alter colloid osmotic pressure, promote edema and contribute to impaired microcirculation. Smoking was associated with the largest odds ratio in the model and has a plausible vascular relationship because tobacco constituents can affect endothelial function, vasoconstriction, inflammation and thrombosis. Hemoglobin was included because it determines oxygen-carrying capacity, although the relationship is complex: anemia may reduce oxygen delivery to a flap, while moderate to severe blood loss can trigger redistribution of blood flow away from peripheral tissues. The model measured these relationships statistically rather than testing them experimentally or establishing a causal pathway.

Packed red blood cell transfusion requires particular caution because the model cannot distinguish a direct transfusion effect from confounding by anemia, blood loss or hemodynamic instability. Transfusion may be administered after substantial blood loss or in response to high-risk anemia, so it can also act as an indicator of compromised circulatory status. The authors discussed possible effects of transfused blood, including reduced nitric oxide availability, enhanced endogenous coagulation and inflammatory and endothelial activation. Their mechanistic discussion also relied partly on previous animal research, which cannot establish clinical benefit or harm in patients. The retrospective association between transfusion and vascular crisis should therefore not be interpreted as evidence that transfusion causes the complication, nor does the model establish a safe or unsafe transfusion threshold for free flap surgery.

The model is notable for combining preoperative laboratory measures with smoking and a perioperative transfusion variable in a transparent logistic-regression framework, while its simplicity also defines its limitations. The retrospective, single-center design leaves room for selection, measurement and unmeasured-confounding biases. Seventy patients, or 12.3% of the cohort, had at least one missing value, principally unavailable preoperative liver or kidney test results and missing intraoperative urine-output data. The investigators imputed missing continuous values with means or medians according to distribution and categorical values with modes, then conducted a complete-case sensitivity analysis. The four-variable model did not explicitly include surgical site, flap type, number of anastomosed vessels or other measures of surgical quality. It also included only 63 endpoint events across the full dataset, so some coefficient estimates, particularly for transfusion, carry substantial uncertainty.

Validation was limited to a chronologically later subset from the same hospital rather than an independent external cohort. The validation sample was modest, containing only 21 vascular crises, and the confidence intervals around discrimination were correspondingly broad. Prospective, multicenter studies would be needed to determine whether the nomogram retains its performance across different institutions, flap procedures and patient populations, and whether using it to guide perioperative care improves outcomes. The findings do not show that the model can prevent thrombosis or reduce flap loss. Instead, they provide a calibrated risk estimate for postoperative vascular crisis based on four routinely available factors, offering a potential screening aid for closer observation while leaving real-world clinical value and generalizability for further study.

Subject of Research: Development and internal validation of a four-factor nomogram for predicting vascular crisis after free flap surgery.

Article Title: Construction and validation of a predictive nomogram for vascular crisis risk following free flap surgery

Article References: Qu, Y.-L., Xue, J., Du, X.-Y., Zhang, D.-D., Wang, Y., Zhu, Y.-L., & Wang, J.-F. (2026). Construction and validation of a predictive nomogram for vascular crisis risk following free flap surgery. Frontiers in Medicine, 13, Article 1930369. https://doi.org/10.3389/fmed.2026.1930369

Image Credits: AI Generated

DOI: 10.3389/fmed.2026.1930369

Keywords: free flap surgery, vascular crisis, risk prediction, clinical nomogram, flap thrombosis, serum albumin, smoking, hemoglobin, blood transfusion, internal validation, Construction, validation