Apneic Oxygenation in Diagnosis and Treatment of Lung Tumours in an Experimental Porcine Model

Objectives: Respiratory movements may complicate diagnostic and therapeutic procedures such as biopsies and stereotactic irradiation therapy in lung cancer patients. An attempt to avoid respiratory movements, up to 30 minutes, long enough for procedures was performed in an animal study. Methods: Ten anaesthetized minipigs ~30 kg were intubated in the trachea and small NiTi-stents were placed in various parts of the lungs. Using a muscle relaxing drug, the pigs were deprived of the ability to breathe for 30 minutes, a longer time than normally used for positioning and irradiation or for biopsies. No attempt to hyperventilate the animals was made prior to the apneic period. After a lung recruitment manoeuvre, a constant oxygen pressure of 20 cm water was applied to the airways. Using X-ray fluoroscopy, the position of the stents and thereby the movements of the lung, were monitored. Arterial gas analyses were performed every 5 minutes during the apneic period. Results: All animals survived 30 minutes of apneic oxygenation. The median arterial oxygen partial pressure actually rose from 11.8 to 54.3 kPa and there were no changes in oxygen saturation. The median arterial carbon dioxide partial pressure rose from 6.9 to 18.7 kPa and the median pH fell from 7.41 to 7.04 during 30 minutes of apneic oxygenation. Our setup, or our strategy of anaesthesia, did not immobilise the internal parts of the lungs satisfactorily, and must be improved before it can be used in a clinical situation. Conclusion: Physiologically, it is possible to stop respiration using apneic oxygenation for periods long enough to perform biopsies or stereotactic radiation therapy.