Time-Based Capnography to Diagnose Airway Obstruction During Lung Lobectomy in a Dog

A 10-year-old, 7.0 kg, female spayed mixed-breed dog presented for a second opinion regarding lobectomy for a lung mass. Mechanical ventilation was initiated due to hypercapnia (ETCO₂ of 61 mmHg) with PIP of 8 cmH₂O. The PIP was gradually increased to 16 cmH₂O. Six minutes after increasing PIP to 16 cmH₂O, ETCO₂ suddenly dropped to 0 mmHg and the capnography waveform was lost. The endotracheal (ET) tube connection to the ventilator circuit was intact, and no visible abnormalities were noted on the ET tube. Although the ETCO₂ sampling line and water trap, and the monitor were replaced, the ETCO₂ remained at 0 mmHg. Meanwhile, suspecting obstruction within the ET tube or the airway, extubation was performed. A large blood clot in the ET tube was noticed. Reintubation was performed using a new ET tube and mechanical ventilation was restarted with PIP set to 10 cmH₂O. The ETCO₂ showed a reading of 55 mmHg. Five minutes after reintubation, the ETCO₂ waveform disappeared again. The inside of ET tube was suctioned, and a blood clot was again identified. Clinicians should be aware of these risks when performing lung lobectomy without one lung ventilation.