# Drain Fluid Amylase as an Early Negative Predictor of Salivary Fistula Following Free Flap Reconstruction

## TL;DR

This study shows that measuring amylase in surgical drain fluid can help predict if a patient will develop a salivary fistula after head and neck surgery.

## Contribution

The study identifies a 15% threshold change in drain amylase as a novel early predictor of salivary fistula risk.

## Key findings

- A 15% increase in drain amylase from day 1 to 2 predicted salivary fistula with 58.3% sensitivity and 80.6% specificity.
- A 15% threshold had a 91.5% negative predictive value for identifying low-risk patients.
- The amylase threshold remained significant after adjusting for prior radiation, transfusion, and laryngectomy.

## Abstract

Salivary fistula is a known complication following head and neck free flap reconstruction involving the aerodigestive tract. We sought to examine the association between surgical drain fluid amylase and salivary fistula formation during postoperative hospitalization.

Eighty patients who underwent head and neck reconstruction involving the aerodigestive tract at our institution between 2019 and 2023 were included. Amylase concentration (IU/L) was measured from a Jackson‐Pratt drain located along the mucosal closure line on postoperative days 1–5.

Twelve patients (15%) developed salivary fistulas. The change in drain amylase concentration between postoperative day 1 and day 2 was found to be significantly higher in those who developed a fistula during postoperative hospitalization. A receiver operating characteristic curve found that a threshold of 15% provided a sensitivity of 58.3% and specificity of 80.6% (area under the curve 0.767) to predict salivary fistula. This threshold remained significant on multivariate analysis (odds ratio 5.35, 95% confidence interval 1.79–24.3) when controlling for prior radiation, perioperative transfusion, and total laryngectomy. When retrospectively applied to our cohort, a cutoff of 15% resulted in a positive predictive value of 35% and a negative predictive value of 91.5%.

Change in surgical drain fluid amylase from postoperative day 1 to 2 was associated with fistula formation following free flap reconstruction of the aerodigestive tract. Importantly, a change in amylase of < 15% from postoperative day 1 to 2 was best at identifying patients who are at low risk of developing salivary fistula during postoperative hospitalization, with a negative predictive value of 91.5%.