Introduction:
The presented study is an attempt to comprehensively analyze the lateral spread of heat during thyroidectomy. Obtained results may be valuable in other surgical disciplines in which thermal analysis is difficult or impossible.

Objective:
The aim of the study was to evaluate the temperature distribution in the operating field during thyroidectomy performed with the use of modern haemostatic instruments, and to define the safety margin for the investigated devices.

Material and Methods:
Ninety-three patients were thyroidectomised due to thyroid neoplasm. During all the operations the thermovisual measurements were carried out along with continuous intraoperative neuromonitoring of the recurrent laryngeal nerve (CIONM). Investigated patients were divided into 5 groups, named according to the applied haemostatic technique: LigaSure (N=17); ThermoStapler (N=20); Focus (N=19); SonoSurg (N=17) and Monopolar (N=20).

Results:
At maximal performance settings, the highest working temperature was observed for the ThermoStapler, while the lowest temperature was recorded for the Monopolar. Safety margin and working time were increased in Focus and SonoSurg, compared to LigaSure and ThermoStapler. The differences in the necrosis thickness were negligible. The largest distance of the midline of the active blade from isotherm of 42ºC observed in the study was 5.51 mm; none of investigated devices used at a bigger distance had influence on the morphology of the electric signal of CIONM.

Conclusions:
The thermo-visual camera allows non-invasive, safe, and real-time monitoring and analysis of temperature distribution in the operation area during thyroidectomy. Proposed minimal safety margin for the analysed devices is 5.51 mm.