Ex vivo ovine model for head and neck surgical simulation

OBJECTIVE

To evaluate a fresh, ovine/sheep head and neck tissue model to teach otolaryngology-head and neck surgical techniques.

STUDY DESIGN

Observational animal study.

SETTING

A university animal resource facility.

METHODS

Tissue was collected from pre-pubescent sheep (n=10; mean age: 4months; mean mass: 28kg) following humane euthanasia at the end of an in vivo protocol. No live animals were used in this study. The head and neck of the sheep were disarticulated and stored at 5°C for 1-5days. The tissues were tested in a variety of simulated procedures by a medical student and four fellowship-trained otolaryngology faculty. Practicality and similarity to human surgeries were assessed.

RESULTS

While ovine head and neck structures are proportionally different, the consistencies of skin, subcutaneous tissues and bone are remarkably similar to that seen in human dissection. Particularly useful were the eyelids and orbits, facial nerve and parotid gland, mandible, anterior neck and submandibular triangle. Surgeries performed included blepharoplasty, ptosis repair, orbital floor exploration, facial nerve dissection and repair, mandibular plating, tracheotomy, laryngofissure, tracheal resection and laryngectomy. The model was also useful for flexible and microsuspension laryngoscopy.

CONCLUSION

Fresh, ovine tissue provides a readily available, anatomically compatible, affordable, model for training in otolaryngology-head and neck surgery. The use of sheep tissues carries a low risk for disease transmission and is ethically defensible. Structural variations in the sheep temporal bone, paranasal sinuses and skull base anatomy limit the usefulness of the model for surgical training in these areas.

Heat dissipation after nonanatomical lung resection using a laser is mainly due to emission to the environment: an experimental ex vivo study

Laser-directed resection of lung metastases is performed more frequently in recent years. The energy-loaded laser rays heat up the lung tissue, considerably. It is still unclear which mechanism is more important for tissue heat dissipation: the lung perfusion or the tissue emission. Therefore, we created a special experimental model to investigate the spontaneous heat dissipation after nonanatomical lung resection using a diode-pumped laser with a high output power. Experiments were conducted on paracardiac pig lung lobes (n = 12) freshly dissected at the slaughterhouse. Nonanatomical resection of lung parenchyma was performed without lobe perfusion in group 1 (n = 6), while group 2 (n = 6) was perfused at a physiological pressure of 25 cm H2O at 37 °C with saline via the pulmonary artery. For this, we used a diode-pumped neodymium-doped yttrium aluminum garnet (Nd:YAG) LIMAX® 120 laser (Gebrüder Martin GmbH & Co. KG, Tuttlingen, Germany) with a wavelength of 1,318 nm and a power output of 100 W. Immediately after completing laser resection, the lungs were monitored with an infrared camera (Type IC 120LV; Trotec, Heinsberg, Germany) while allowed to cool down. The resection surface temperature was taken at 10-s intervals and documented in a freeze-frame until a temperature of 37 °C had been reached. The temperature drop per time unit was analyzed in both groups. Immediately after laser resection, the temperature at the lung surface was 84.33 ± 8.08 °C in group 1 and 76.75 ± 5.33 °C in group 2 (p = 0.29). Group 1 attained the final temperature of 37 °C after 182.95 ± 53.76 s, and group 2 after 121.70 ± 16.02 s (p = 0.01). The temperature drop occurred exponentially in both groups. We calculated both groups' decays using nonlinear regression, which revealed nearly identical courses. The mean time of tissue temperature of >42 °C, as a surrogate marker for tissue damage, was 97.14 ± 26.90 s in group 1 and 65.00 ± 13.78 s in group 2 (p = 0.02). Heat emission to the environment surpasses heat reduction via perfusion in nonanatomically laser-resected lung lobes. In developing a cooling strategy, a topical cooling method would be promising.