New aspects on atelectasis formation and gas exchange impairment during anaesthesia

Perioperative management of patients who have pulmonary disease

The identification of risk factors and optimization of respiratory status are crucial to the successful management of patients who have pulmonary disease and are undergoing a surgical procedure. This article explores the approach to pulmonary patients, from the preoperative assessment to the intraoperative and postoperative periods. The management of specific pulmonary disorders in the perioperative period is discussed.

Kinetics of absorption atelectasis during anesthesia: a mathematical model

Recent computed tomography studies show that inspired gas composition affects the development of anesthesia-related atelectasis. This suggests that gas absorption plays an important role in the genesis of the atelectasis. A mathematical model was developed that combined models of gas exchange from an ideal lung compartment, peripheral gas exchange, and gas uptake from a closed collapsible cavity. It was assumed that, initially, the lung functioned as an ideal lung compartment but that, with induction of anesthesia, the airways to dependent areas of lung closed and these areas of lung behaved as a closed collapsible cavity. The main parameter of interest was the time the unventilated area of lung took to collapse; the effects of preoxygenation and of different inspired gas mixtures during anesthesia were examined. Preoxygenation increased the rate of gas uptake from the unventilated area of lung and was the most important determinant of the time to collapse. Increasing the inspired O2 fraction during anesthesia reduced the time to collapse. Which inert gas (N2 or N2O) was breathed during anesthesia had minimal effect on the time to collapse.

Prevention of postoperative pulmonary complications through respiratory rehabilitation: a controlled clinical study

OBJECTIVE

To investigate the efficacy of respiratory rehabilitation in preventing postoperative pulmonary complications (PPC) and to define which patients can benefit.

DESIGN

A randomized clinical trial.

SETTING

A public hospital.

PATIENTS

Eighty-one patients who had upper abdominal surgery were distributed into two homogeneous groups: control (n = 41) and rehabilitation (n = 40).

INTERVENTION

Breathing exercises in the rehabilitation group.

MAIN OUTCOME MEASURES

Preoperative and postoperative clinical evaluation, spirometry, arterial gasometry, and simple chest X-rays.

RESULTS

The incidence of PPC was 7.5% in the rehabilitation group and 19.5% in the control group; the control group also had more radiologic alterations (p = .01). Stratified PPC analysis did not reveal significant differences between groups. However, high- and moderate-risk patients in the rehabilitation group had fewer PPC. Multivariate analysis showed a greater PPC risk associated with pulmonary history (p = .02) and duration of surgery longer than 120 min (p = .03), while rehabilitation exerted a protective effect (p = .06). Significant postoperative decreases in pulmonary volumes and arterial gas values were recorded in both groups, without significant differences.

CONCLUSIONS

Respiratory rehabilitation protects against PPC and is more effective in moderate- and high-risk patients, but does not affect surgery-induced functional alterations.

What is the role of absorption atelectasis in the genesis of perioperative pulmonary collapse?

During anaesthesia the combination of breathing at low lung volume, the administration of nitrous oxide and high inspired oxygen concentrations produces conditions that favour absorption atelectasis. Measures such as adding nitrogen to the inspired mixture and avoiding high inspired oxygen concentrations would reduce the amount of perioperative atelectasis if gas absorption was important in the genesis of perioperative pulmonary collapse. Experimental results demonstrate that these measures do not protect against atelectasis. This indicates that absorption atelectasis does not play a significant role in the genesis of perioperative pulmonary collapse. Compression atelectasis may be the underlying mechanism.