Anesthesia Student Survival Guide.pdf - Index of

PhysiOlOGy And AnesthesiA fOr CArdiAC And thOrACiC surGery ● 279
Often during surgery, one-lung ventilation (OLV) is required. During anesthesia,
with the chest open, OLV creates an obligatory right-to-left transpulmonary
shunt through the nonventilated, nondependent lung because the V/Q
ratio of that lung is zero.
One-Lung Ventilation
Absolute indications for OLV include: (1) Isolation to prevent contamination
of a healthy lung in abcess, infected cyst, or massive hemorrhage, (2) Control
of distribution of ventilation to one lung as in bronchopleural fistula, bronchopleural
cutaneous fistula, unilateral cyst or bullae, and major bronchial
disruption of trauma, (3) Unilateral lung lavage, or (4) Video-assisted thoracoscopic
surgery (VATS). Other indications are surgical exposure such as thoracic
aortic aneurysm, pneumonectomy, upper lobectomy, esophageal surgery,
middle and lower lobectomy, and thoracoscopy under general anesthesia.
OLV is accomplished by isolating one lung using a double-lumen endotracheal
tube, or a bronchial blocker. The bronchial blocker can be used either
in the form of a prefabricated tube with blocker attached (Univent tube®) or
as a separate blocker inserted through a T-piece adapter at the top of the tube
(Arndt blocker®, Cohen blocker®, Fogarty® catheter).
During OLV, the non-dependent lung is not ventilated, and thus becomes
atelectatic. Without ventilation, hypoxic pulmonary vasconstriction occurs
in that lung and diverts blood flow to the ventilated lung. This results in an
improvement in oxygenation by reducing the shunt fraction. OLV creates a
physiological shunt where the non-dependent lung is perfused but not ventilated.
The shunt fraction typically increases from 10% (in the two-lung ventilated
anesthetized patient) to 27.5% (in the one lung ventilated patient).
During OLV, if the patient is hypoxic, first apply CPAP (continuous positive
airway pressure) to the non-ventilated lung. If no improvement occurs, apply
PEEP (positive end-expiratory pressure) to the ventilated lung. If the patient
still cannot tolerate OLV, two-lung ventilation must be reinstituted.
Double Lumen Endotracheal Tube
Double lumen tubes (DLT) come in two varieties: left- and right-sided (see
Fig. 17.6). Although many feel that left-sided tubes are easier to manage clinically,
this has been recently refuted in the literature (Ehrenfeld et al.) and a tube
should be selected based on the surgical site (typically placed contralateral to
the surgical procedure). All double lumen tubes have both cuffed endobronchial
portions and tracheal cuffs. The endobronchial portions are curved either