Thoracoscopy in cats

Thoracoscopy in cats presents some unique challenges and is not as frequently performed as it is in dogs but can be a very useful addition to the minimally invasive armamentarium in this species. Most of the challenges in cats are related to the small size of the feline respiratory system and the limited thoracic working space within the chest. A corollary in human medicine exists when thoracoscopic procedures are necessary in pediatric patients who sometimes require lung lobectomy for removal of cystic adenomatoid malformations, pulmonary sequestrations, congenital diaphragmatic hernia, esophageal atresia or tracheoesophageal fistula repairs as well as other lesions. Lung lobectomy in infants as young as 25 days and weighing as little as 3.5kg has been described.

In cats few descriptions of thoracoscopic surgery exist in the literature although investigation of pleural effusion, treatment of persistent right aortic arch and thoracic duct ligation in combination with pericardectomy for treatment of chylothorax have been reported. In addition to these procedures the authors group have also performed thoracoscopic lung biopsy and thymoma resection in cats using a thoracoscopic approach.

Anesthesia – To obtain adequate working space for thoracoscopic interventions in larger patients pneumothorax alone can be used to perform many procedures such as pericardectomy, thoracic duct ligation, ligation of persistent right aortic arch and lung biopsy. While the author has performed lung biopsy with pneumothorax alone in cats there is very limited working space and so other techniques to expand the working space might be necessary. One-lung ventilation (OLV) and carbon dioxide insufflation have been used in dogs to improve working space in the chest and the authors group have investigated these modalities in a feline study. One-lung ventilation can normally be induced in a variety of ways including the use of endobronchial blockers (EBB), double lumen endobronchial intubation or selective intubation. However, the only modality that has been evaluated was the use of the 5Fr Arndt EBB (Cook Medical Inc., Bloomington, IN) as there are no double lumen endobronchial tubes that are small enough to pass down the feline trachea. The technique for passage of the EBB was also modified from the technique used in dogs as the bronchoscope and EBB do not fit concurrently down the lumen of the small endotracheal tubes used in this species. To circumvent this problem jet ventilation was used (set at 180 breaths/minute) to support oxygenation during placement of the EBB. The EBB was preplaced through the lumen of the endotracheal tube and then was advanced down the trachea alongside a 2.5mm flexible bronchoscope while the jet ventilation catheter was functional. The EBB balloon was placed into one of the mainstem bronchi uninflated followed by advancement of the endotracheal tube over the EBB into its normal position as noted previously. Under thoracoscopic visualization the EBB balloon was then inflated and its correct positioning was verified by monitoring lung lobe inflation. In cases where the blocker was placed too deeply within the bronchial tree, the blocker was very slowly pulled out in an attempt to obtain complete blockade of all lung lobes in the right or left hemithorax. This is a challenging technique although once established OLV was well tolerated. The authors also evaluated the cardiorespiratory function of cats with OLV and 3mmHg of carbon dioxide insufflation although this was less well tolerated than OLV alone. In several clinical patients we have also used 3mmHg of CO2 insufflation alone without OLV and this appears to be fairly well tolerated in cats compared to dogs where CO2 insufflation has been associated with a significant drop in cardiac output even at low insufflation pressures.8 However, this is a clinical observation in a few feline cases and we have not evaluated CO2 insufflation critically in cats. Needless to say it should be used with great care in both dogs and cats.  [...]