Anesthesia for Thoracoscopy

General anesthesia for thoracoscopy requires adequate analgesia and a balanced plan including local anesthetic. Ventilation is required, either by hand or with a ventilator because the thorax will be open just as with a traditional thoracotomy. Thoracoscopy alone affects blood gasses in normal dogs. Even with bilateral ventilation, PaO2 decreases and PaCO2 increases likely due to V/Q mismatch. Total peripheral vascular resistance decreases, but the affect in normal dogs is not clinically problematic. The changes result in alteration of ventilation based on the patient’s response and blood gas measurements (either direct or indirect measures); however, it is important to remember that research has been reported in normal dogs. Typically, ventilation is altered to allow a viewing space to form. The rigid thorax provides an adequate “room” in which to view, but the lungs and their motion interfere with visualization. A starting guideline to decrease lung volume within the thoracic cavity is to decrease the tidal volume by 1⁄2 and to double the ventilator rate. Monitoring blood gasses or their indirect measures guide further changes required for maintaining adequate ventilation during the procedure.

Rarely is one-lung ventilation required (OLV). OLV increases the working space via atelectasis of the right or left lungs. OLV must be obtained by either selective intubation of one bronchus or bronchial blockade of the desired side. The lung that is not ventilated should be the side undergoing the operative procedure. A flexible endoscope is required to achieve proper OLV, and OLV should be established within the operative suite when the patient is in the position desired for surgery to avoid inadvertent loss of OLV. If OLV is established during thoracoscopy, proper OLV can be verified rather quickly. For selective bronchial intubation, the endotracheal tube is placed over the bronchoscope, which is directed into the desired bronchus under endoscopic visualization. The endotracheal tube is then fed off of the bronchoscope much like catheterization using the Seldinger technique. If bronchial blockade done, the bronchial blocker (an ovoid balloon) is “loaded” on the bronchoscope using its suture loop. The bronchoscope is passed into the bronchus to be blocked (the operative side), and the balloon advanced, inflated, and positioning verified under endoscopic visualization. Specialized endotracheal tubes have a cuff that can be inflated in the trachea and an extension, or bronchial, tube that has a cuff for inflation in a bronchus. Depending on which port is connected to the ventilator system, the tracheal site may be ventilated or the bronchial tube may be used. This allows for alternate OLV, shifting between sides as desired. OLV in normal dogs with closed chest ventilation showed similar changes in PaO2 and PaCO2 as dongs undergoing thoracoscopy, likely the alterations were someone blunted due to the use of normal dogs and normal hypoxemic vasoconstriction, which minimized V/Q mismatch. If alterations in ventilator parameters are significant, PEEP at as little as 5 cmH20 can be used to improve the V/Q mismatch with out significant effects on cardiac output or oxygen delivery.  [...]