Comparison of lateral thermal spread using monopolar and bipolar diathermy, the Harmonic Scalpel™ and the Ligasure™

Background: Electrosurgery for dissection and haemostasis should be associated with minimal thermal spread to surrounding tissues. This study investigated lateral thermal spread following ex vivo application of four commonly utilized instruments. Methods: Monopolar and bipolar diathermy (power settings 20, 30 and 40 W), the Harmonic Scalpel (TM) and Ligasure (TM) (power settings 1, 3 and 5) were studied after application to standardized porcine muscle cuts for 5, 10 or 15 s. Temperatures generated at the tips of the instruments, in the tissues adjacent to the tips and I cm away were recorded. Results: Following a 5-s application at the highest power setting, the highest mean(s.d.) temperatures recorded at the tips of monopolar and bipolar diathermy, Harmonic Scalpel (TM) and Ligasure (TM) instruments were 78.9(4.1), 41.9(2.2), 47.6(2.5) and 44.2(2.6)degrees C respectively. Temperatures at the instrument tips after use for 15 s remained above 42 degrees C for 55, 25, 15 and 15 s respectively. Applying monopolar diathermy (10 s at 40 W) resulted in a temperature recording of 59.2(2.2)degrees C in tissues I cm away from the tip of the instrument. Conclusion: The degree of lateral thermal spread varied with instrument type, power setting and application time. Monopolar diathermy resulted in the highest temperatures and the greatest degree of thermal spread in tissues.