Thoracic Anesthesia

Surgical interventions which involve thoracotomy and lateral positioning of the patient generally require that the ipsilateral lung remain deflated to optimize exposure. One lung ventilation is accomplished by the use of a double lumen tube (DLT) which consists of an endobronchial tube as well as a tube which remains in the trachea. Each tube is cuffed. Right and left DLTs are designed so that the endobronchial tube enters the right or left bronchus, respectively.

It is essential that the endobronchial tube be placed correctly in the bronchus. Confirmation of correct placement is accomplished by auscultation, direct visualization and observation of ventilatory parameters.

Auscultation

One of the tubes is clamped. Breath sounds should then be heard upon auscultation only on the side corresponding to the patent tube. Moreover, only the corresponding hemithorax should rise upon positive pressure ventilation.

Direct Visualization

Fiberoptic bronchoscopy is used to visualize placement of the DLT. The bronschoscope is introduced through the tracheal tube and is advanced to its outlet. At this level the carina should be clearly visible. In addition, the cuff of the endobronchial tube should be visible in the bronchus. Chest radiography is not as precise as fiberoptic bronchoscopy for confirmation of tube placement.

Ventilatory Parameters

Adequate one lung ventilation can be confirmed after placement of the DLT. The tube which is ventilating the lung that will ultimately be deflated during the surgical procedure is clamped. After establishment of one lung ventilation the end-tidal carbon dioxide, peak inspiratory pressure and oxygen saturation should not change significantly. Any significant decrease in end-tidal C02 and increase in peak inspiratory pressure indicate airway obstruction and require repositioning of the DLT. A decrease in 02 saturation may indicate airway obstruction or severe atelectasis. An arterial blood gas should be analyzed 10 minutes after one lung ventilation has been initiated.

The DLT can be dislodged from its correct position during positioning of the patient or during surgical manipulation, leading to airway obstruction and desaturation. Repositioning of the DLT with the aid of a fiberoptic bronchoscope should be attempted. Efforts to improve oxygenation include providing continuous positive airway pressure to the deflated lung or, if the end-tidal C02 remains within normal limits, applying positive end expiratory pressure to the lung being ventilated. The DLT should be periodically suctioned to avoid obstruction by secretions or blood.

Left DLTs are used for procedures necessitating a right thoracotomy. Many anesthesiologists, concerned that a right DLT may not provide adequate ventilation to the right upper lobe (because of the possibility of occlusion of the takeoff of the right superior lobe bronchus by the endobronchial tube), advocate the use of a left DLT for procedures requiring a left thoracotomy as well. However, DLTs designed for right endobronchial intubation contain a large side opening which easily opposes this takeoff. Patency of the right superior lobe bronchus, therefore, is generally maintained with right dlts. Ventilation of the right upper lobe can be confirmed by fiberoptic bronchoscopy and by auscultation of the axilla.

Intubation of the left bronchus for procedures involving the left hemithorax (and thus requiring deflation of the left lung) may also lead to complications in certain situations. A bronchus rendered stiff by an endobronchial tube can be injured during surgical manipulation. Moreover, ventilation to the right lung may be compromised as mediastinal contents may compress the unintubated right bronchus when the patient is placed in the right lateral decubitus position. Left DLTs must be inserted with caution in the presence of a thoracic aneurysm; abrupt intubation of the left bronchus can rupture an overriding aneurysm.

An alternative to the double lumen tube is the wire guided endobronchial blocker. The wire guided endobronchial blocker is particularly useful in a patient with a difficult airway, which would make insertion of a double lumen tube extremely difficult, or in a patient requiring nasal intubation, which would preclude the use of a double lumen tube.

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