A reply

Abstract

The letter of Drs Latter and Mulvey touches upon several interesting issues. Yes, the four clamps do look cumbersome, but not so in use [1]. Clamp 1 initiates and maintains single lung ventilation, as is standard practice. Clamp 2 enables the double-lumen tube on the side of the nonventilated lung to be occluded for the short time it takes to connect the ambient pressure oxygen reservoir. Clamp 3 serves to contain the oxygen in the reservoir until such time as it is connected to the nonventilated lung. Clamp 4 can be omitted, if desired, as described in a separate correspondence [2]. The use of Clamp 2 is a simple, practical method of excluding nitrogen from the nonventilated lung, which is after all the object of the exercise [1]. If the airway of the nonventilated lung is momentarily left open to air as the reservoir is being connected, it is possible for more than 250 ml of ambient air to enter the nonventilated lung in the course of a single ventilation to the dependent, ventilated lung [3]. Drs Latter and Mulvey report that, once single-lung ventilation to the dependent lung is initiated, they separately ventilate the nondependent lung with 100% oxygen presumably by hand ‘shortly before the pleura is opened’. This practice will progressively wash out any nitrogen that may have entered the nondependent lung at the time their C-breathing system was connected. With nitrogen successfully excluded or eliminated, I suggest they try connecting an oxygen reservoir at ambient pressure rather than oxygen CPAP. The former practice offers several additional practical advantages [1], while the latter is contraindicated or counterproductive in many thoracoscopic procedures. I apply Clamp 1 at end-expiration to minimise the increase in inflation pressure in the ventilated lung over the short period before the nonventilated lung is opened to the oxygen reservoir. Whilst this is not of any importance in most cases, it may well be of relevance in patients with respiratory disease and high levels of intrinsic PEEP. Of greater importance, however, is the need to ensure that Clamp 2 is not left inadvertently applied for longer than is necessary [1]. As regards the apparent concern about ‘early atelectasis’, I hold the view that prompt passive and then absorptive collapse of the nonventilated lung does not prejudice patient wellbeing either intra-operatively or postoperatively. It does, on the other hand, serve to improve surgical access and operative conditions in many thoracic operations, especially those performed thoracoscopically.