A new laparoscopic model to evaluate device temperatures and cooling times in a surgical setting

Joseph A Paulus, PhD, Xinliang Zheng, PhD, Bruce Dunne, PhD

Covidien, Surgical Solutions

An “in vivo” surgical model to evaluate post-activation cooling times for laparoscopic radiofrequency (RF) vessel sealing devices and assess thermal injury risks is presented; the model provides a more clinically relevant environment (temperature and humidity) than open or bench methods.

Description and Methods:
Surgeons often use laparoscopic RF vessel sealing devices to grasp or manipulate tissues adjacent to the surgical field to expedite procedures and reduce instrument exchanges. When this occurs following device activation, heat retention may result in thermal injury to tissues during the tissue manipulation or contact. Understanding cooling times associated with laparoscopic RF vessel sealing devices and their relation to thermal injury risks may assist surgeons and device makers in minimizing unintended patient injuries.

A laparoscopic porcine model (n=4 animals) was used for “in vivo” device temperature characterization and thermal injury assessment. Thermocouples were attached to the interior seal-plates of 3 identical commercial laparoscopic RF vessel sealing instruments; 68 single and 54 multiple activations on several tissue types (uterine horn, gastric omentum, jejunal mesentery, gastrosplenic A/V bundles) were used to characterize peak temperatures and cool-down rates. Multiple activations were 3 or more immediate sequential activations where a temperature plateau was reached.

Porcine jejunum was used for thermal injury assessment; the proximal jejunum was marked at ~5cm increments with laparoscopic suture. Test devices with attached thermocouples were activated on adjacent, non-target tissues and cooled in the insufflated field to targeted grasping temperatures (10 independent grasp events each at 37, 45, 55, 65, 75 and 85°C); consistent, minimal grasping force was utilized for 5-second intervals on the marked areas. Seal-plate temperatures during the grasp event were recorded electronically. Animals were subsequently maintained under anesthesia for a minimum of 2-hours prior to euthanasia and tissue excision. The jejunum was excised en bloc via open surgery and samples taken for histology. Two cell viability stains were used to assess ‘minor’ (surface epithelial cell death) and ‘significant’ (>50% depth of smooth muscle cell death) damage.

Preliminary Results:
Data indicate that seals on uterine horn resulted in the highest jaw seal plate temperatures for both single and multiple activations (88.8±5.34°C and 97.7±9.9°C, respectively). Gastric omentum seals yielded the lowest device temperatures (77.3±4.3 and 84.5±4.8°C, single and multiple activations). Histological evidence of thermal injury was used to develop a log-logistic model, to correlate initial device grasping temperatures to the probability of a ‘significant’ tissue (jejunal) thermal injury. Assessment of direct thermal injury risks were then computed by simulating n=100,000 sealing event temperatures into the probability model at 5-second cool-down intervals.

This new laparoscopic method for characterizing cooling times for RF vessel sealing devices and assessing risks for thermal injury was successfully demonstrated. Using the thermal injury model for a specific device, thermal injury risk probabilities can be estimated from post-activation seal-plate temperatures, with minimal ”in vivo” animal testing. Porcine jejunum is thinner than in humans and the histological cell viability stains used in this study were highly sensitive; these factors may overestimate clinically relevant risks and require further investigation.

Session: Poster Presentation

Program Number: ETP056

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