V˙/Q˙ distribution and correlation to atelectasis in anesthetized paralyzed humans

Abstract

Regional ventilation and perfusion were studied in 10 anesthetized paralyzed supine patients by single-photon emission computerized tomography. Atelectasis was estimated from two transaxial computerized tomography scans. The ventilation-perfusion (V/Q) distribution was also evaluated by multiple inert gas elimination. While the patients were awake, inert gas V/Q ration was normal, and shunt did not exceed 1% in any patient. Computerized tomography showed no atelectasis. During anesthesia, shunt ranged from 0.4 to 12.2. Nine patients displayed atelectasis (0.6-7.2% of the intrathoracic area), and shunt correlated with the atelectasis (r = 0.91, P < 0.001). Shunt was located in dependent lung regions corresponding to the atelectatic area. There was considerable V/Q mismatch, with ventilation mainly of ventral lung regions and perfusion of dorsal regions. Little perfusion was seen in the most ventral parts (zone 1) of caudal (diaphragmatic) lung regions. In summary, shunt during anesthesia is due to atelectasis in dependent lung regions. The V/Q distributions differ from those shown earlier in awake subjects.

Feasibility and Results of Awake Thoracoscopic Resection of Solitary Pulmonary Nodules

“…This type of injury include airway pressureinduced injury, lung inflation-induced injury, injury due to cyclic opening and closing of small airways/lung units, and release of a variety of proinflammatory mediators [7]. Yet, atelectasis in the dependent lung is a regular finding during one-lung ventilation with muscle paralysis [11]. Moreover, prolonged collapse of the nondependent lung during one-lung ventilation can delay its complete reexpansion after weaning leading to the development of further atelectasic areas in the nondependent lung.…”

Evaluation of Differences between PaCO2 and ETCO2 by Age as Measured during General Anesthesia with Patients in a Supine Position

“…Increased intrapulmonary shunting and decreased functional residual capacity with ventilation-perfusion inhomogeneity have been recognized as part of the associated pathophysiology [9,10]. It is recognized that V/Q mismatch can occur in patients given general anesthesia or in those with lung disease [11]. Herr et al [12] reported that an increased F I O 2 was associated with increases in venous admixture and might result in slightly increased P(a-ET)CO 2 .…”

Respiratory Management of Perioperative Obese Patients

“…Atelectasis impairs gas exchange and increases physiological shunt, ventilation-perfusion mismatch, and work of breathing. 24 Lung mechanics are also impaired in the atelectatic lung, because the lung is less compliant at lower volumes. 22 In normal-weight anesthetized subjects, Rothen et al 25 showed by chest CT imaging that atelectasis is enhanced by the use of 1.0 F IO 2 during preoperative induction compared with the use of 0.3 F IO 2 as a result of absorption atelectasis.…”