Influence of retractor type and position on thoracoscopic-assisted pulmonary surgery in dogs

Abstract

Thoracotomy is performed frequently in dogs for the purposes of exploration of the thorax, lung lobectomy, correction of vascular ring anomalies and patent ductus arteriosus, pericardiectomy, thoracic duct ligation, biopsy and resection of mediastinal and pleural masses and removal of foreign bodies from within the pleural space, intrathoracic oesophagus and the lower respiratory tract. Persistent post-thoracotomy pain is reported frequently by human patients characterised by discomfort and altered sensation in the skin adjacent to the surgical site. Multiple surgical techniques have been developed in an attempt to reduce the morbidity of these procedures. Minimally invasive surgical techniques have been a significant step towards this goal. A significant limitation of minimally invasive surgery is the loss of tactile feedback and video-assisted techniques which utilise smaller incision, permitting the introduction of the surgeon’s hand or fingers to the thorax have been developed to overcome these limitations. These techniques have recently been introduced for veterinary patients (Chambers and others 2012, Gower and Mayhew 2011a, Laksito and others 2010b, 2011, Wormser and others 2014). Both traditional and video or thoracoscopic-assisted techniques require the use of tissue retractors, typically placed in an intercostal position. Access is afforded by the forceful retraction of soft tissues such as the intercostal muscles and ribs. Studies in both animals and humans have demonstrated detrimental soft tissue changes associated with such retraction including direct and ischaemic damage to the soft tissues adjacent to the retraction device. The present study examines several aspects of thoracoscopic-assisted pulmonary surgery in dogs including the effect on blood flow in the intercostal musculature and nerve conduction in the intercostal nerves associated with two different retraction modalities. Additionally, the influence of assisted port location and thoracic conformation on access to and delivery of pulmonary tissues for the purposes of complete or partial lung lobectomy was assessed.

Force, contact area and pressure were compared and related to intramuscular pressure, perfusion, oxygen indices, nerve conduction and histologic change in dogs undergoing simultaneous controlled thoracotomy incisions. The novel retractor resulted in lower pressure and improved oxygenation in adjacent tissues compared to mechanical retraction which may translate clinically into reduced post-operative morbidity. For all lobes except the accessory lung lobe, the exposure provided by the reported thoracoscopic-assisted approach was considered adequate for complete or partial lung lobectomy. The cranial and caudal portions of the left cranial lung lobe and the right middle lung lobe were best exposed with the assisted portal in the middle dorso-ventral third of the thoracic wall at the fourth intercostal space of the ipsilateral side in both breeds. The right cranial lung lobe was best exposed with the assisted portal positioned in the middle third of the fourth intercostal space in kelpies but the sixth intercostal space in greyhounds. The right caudal lung lobe was best exposed when the assisted portal was positioned in the ventral third of the fourth intercostal space in the kelpie but in the middle third of the sixth intercostal space in the greyhound. The described thoracoscopic-assisted technique is a practical method for exposure of the lobes of the lung, other than the accessory lobe, for partial lung lobectomy in the dog. The portals described also allow the introduction of a linear stapler for the purpose of complete lung lobectomy.