Purpose: The hyperthermal liquid, spray and smog caused by energy-based surgical devices (EBDs) may be the potential risk factors for recurrent laryngeal nerve (RLN) thermal injury, but not been reported previously. We aim to demonstrated it both in thyroid surgeries and animal experiments.
Methods: 321 thyroid patients and 32 rats were divided into two groups respectively. A type of endoscopic gauze was implemented in the protected group to prevent nerve from thermal risks. Electromyography and laryngoscope were recorded to determine nerve's conductive ability. Microstructural morphological damage to nerves and muscles were evaluated by light and electron microscopy in the animal experiments.
Results: After thyroid surgeries, the incidence of transient vocal cord (VC) palsy was decreased in the protected group (1.4%) compared with the conventional group (4.7%) (P = 0.037). In animal experiments, the average nerve conductive velocity was significantly decreased in the conventional group (5.8 ± 2.1 vs. 25.5 ± 4.7 m/s, P < 0.01). Typical acute morphological thermal changes of edema, coagulation and homogenization in nerve tissues were recorded by light microscopy in the conventional group. Four weeks later, the average weight of gastrocnemius muscles in the injured limb was significantly decreased (1.3 ± 0.2 vs. 2.2 ± 0.2 g, P < 0.01), while no significant difference was noted in the protected group (2.0 ± 0.3 vs. 2.3 ± 0.4 g, P = 0.61).
Conclusions: Hyperthermal liquid, spray or smog may represent risk factors contributing to RLN thermal injury caused by EBDs. Damage to the nerve's conductive ability and morphological changes in nerves and muscles likely represent typical responses to thermal injury. Implementation of endoscopic gauze may be a promising method to protect the RLN from thermal damage especially in endoscopic thyroid surgeries.
Keywords: Animal experiment; Endoscopic gauze; Recurrent laryngeal nerve; Thermal injury; Thyroid surgery.