Hazards of carbon dioxide insufflation during thoracoscopy.

Hazards of carbon dioxide insufflation during thoracoscopy Editor,—I read with interest the review article on the anaesthetic implications of thoracoscopic sympathectomy. 1 When endobronchial anaesthesia is used, carbon dioxide may be insufflated only initially into the ipsilateral pleural space to augment lung collapse. In contrast , when a tracheal tube is used, carbon dioxide is insufflated continuously until the end of surgery. The report assumes that hypoxic pulmonary vasoconstriction (HPV) fails during one-lung ventilation achieved by endobronchial anaesthesia, while it remains intact after tracheal intubation, as the ipsilateral lung is only partially collapsed. 1 This assumption is based on previous reports showing that when more than 70% of the lung is atelectatic, compensation by HPV appears to be ineffective. 2 The authors prefer tracheal intubation during thoracoscopy to endobronchial anaesthesia because of its simplicity, decreased cost, and improved oxygenation. To minimize the risk of inadvertent tension pneumothorax secondary to the continuous insufflation of carbon dioxide during tracheal anaesthesia, a pressure-limited, variable flow of carbon dioxide is recommended. 1 Experimental work in swine has shown that positive pressure insufflation during thoracoscopy results in significant haemody-namic compromise despite the use of selective lung ventilation: cardiac index, mean arterial pressure, and left ventricular stroke work index decreased, whereas pulmonary artery and central venous pressure increased at an insufflation pressure of 5 mm Hg or greater. 3 Thus, carbon dioxide insufflation into the closed chest cavity to a pressure as low as 5 mm Hg may create a physiological response very similar to that of a unilateral tension pneumothorax, 4 with a consequent haemodynamic instability secondary to decreased venous return and/or mediastinal shift. Our anaesthetic technique during video-assisted thoracoscopy depends on double-lumen intubation which provides selective ventilation of the contralateral lung while allowing collapse of the ipsilateral lung without the need for carbon dioxide insufflation. Selective lung ventilation with 100% oxygen ensures adequate oxygenation throughout the procedure, as checked by continuous pulse oximetry. HPV is most active when 30–70% of the lung is hypoxic. 2 The original intrapulmonary shunt secondary to one-lung collapse is about 40–50%, and is decreased to 20–30% by active HPV, 5 as well as by gravity, and collapse of the non-ventilated lung. Partial collapse of the lung on the thoracoscoped side occurs when air enters the pleural cavity. To augment collapse, the lumen of the double-lumen tube on the thoracoscoped side is opened to room air, while suction is intermittently …