**2. Perioperative pulmonary physiology**

The major cardiopulmonary complications that alter normal lung function occur as a result of surgery (thoracotomy and resection of lung parenchyma) and anaesthesia (table 1). The thoracic surgery causes restrictive changes in the lung function characterized by moderate to severe reductions (50%) in vital capacity and up to 70% decrease of functional residual capacity (FRC). As a result of the FRC decrease, the volume of airway closure is shifted, so

Perioperative Pulmonary Functional Assessment 373

Table 2. Postoperative pulmonary complications in patients with thoracic surgery (Swenson,

In the preoperative thoracic surgery the functional assessment schemes have varied over the past 50 years. Most respirotary function tests which were utilized in order to minimize morbidity and postoperative mortality (table 3) are no longer used today, being replaced by simpler techniques that provide similar or better information. Today the process of lung function assessment is spread out over several phases comprising a series of breathing tests that the patients scheduled for thoracic surgery will be given according to their baseline pulmonary function and the amount of lung tissue for resection. These steps complement each other, so that the degree of severity of impairment of lung function is the fact that

> FVC, FEV1, ppo-FEV1 TLC, RV, TLC/RV% DLCO, ppo-DLCO PaO2, PaCO2 PAP, PVR

% Perfusion en each lung % Ventilation in each lung

Distance walked

VO2 peak

Table 3. Pulmonary function test used in the preoperative assessment. FVC: Forced vital capacity. FEV1: Forced expiratory volume in 1 second. ppo: postoperative. TLC: Total lung capacity. RV: Residual volumen. DLCO: Diffusion capacity of the lung for carbon monoxide. PaO2: Oxygen partial pressure of artery. PaCO2: Carbon dioxide partial pressure of artery. PAP: Pulmonary artery pressure. PVR: Pulmonary vascular resistance. VO2: Oxygen uptake.

**Postoperative pulmonary complications**

Infection (Pneumonia or bronchitis)

Prolonged mechanical ventilation Exacerbation of chronic lung disease

**Specific thoracic surgical complications**

Bronchopleural fistula and empyema

determines whether or not to go a step higher.

Exercise test (6-min walking, shuttle walk and

Diffusing capacity of the lung for CO

Cardiopulmonary exercise test

**Pulmonary function test Parameter**

Gastroesophafeal anastomotic leak

**General complications**

Pulmonary embolism Obstructive sleep apnea

Sternal wound infection

**3. Lung function tests** 

Atelectasis

Bronchospam Respiratory failure

Pleural effusion Phrenic nerve injury

1999).

Spirometry Lung volumes

Arterial gasometry Pulmonary hemodynamic Perfusion scintigraphy Ventilation scintigraphy

stair climbing)

in the areas of pulmonary decline the end point of exhalation is below the closure volume, which causes an early closure of the airway and, therefore, of the areas of atelectasis. The factors that reduce FRC include supine position, pain, general anaesthesia and obesity. These functional changes occur without apparent obstruction of the airway, so that the ratio of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) does not decrease.

The action of the anaesthetic and the muscle relaxant used in the surgical procedure, involves a decrease in lung volumes. In addition, the effects of these drugs on the diaphragm and the bulbar center responsible for regenerating respiratory impulses are the main reasons that justify changes in lung volumes.

The cause of the diaphragm muscle dysfunction is not clear yet. Direct damage to the muscles during the surgical intervention has been proposed as one of possible mechanisms, but transdiaphragmatic pressure measurements during maximal phrenic nerve stimulation suggest that the depression of the central nervous system efferent traffic on the diaphragm occurs as a result of inhibitory reflexes associated with pain and other stimuli to sympathetic or vagal receptors.

Hypoxemia and arterial hypercapnia that appear, especially in the postoperative period, are mainly due to the effects of anaesthesia used during the surgery and cause a decrease in the interrelation ventilation/perfusion (V/Q), and besides lead to deterioration of hypoxic pulmonary vasoconstriction, alveolar hypoventilation or low cardiac output. The gas exchange disorder is intensified with combination of hypoventilation, increase in dead space ventilation, rapid shallow breathing and a decrease in mixed venous oxygen saturation due to low cardiac output, anemia and arterial desaturation and increased peripheral oxygen consumption with pain, fever or stress (Beckles et al., 2003).


Table 1. Mechanism of lung function changes with anesthesia and surgery (Swenson, 1999).

Ventilatory depression is also typical of the postoperative period and is marked by the residual effects of anaesthesia that inhibit normal response to hypoxia and hypercapnia. Analgesics and other sedatives may enhance these effects, and impede the implementation of pulmonary rehabilitation. They can rarely lead to episodes of sleep apnea.

The lung defends itself from attacks of infectious and environmental agents with cough and mucociliary clearance. The former is suppressed both with excessive and poor pain treatment. The latter can be altered by an ineffective cough, limited by restrictive changes and weakened respiratory muscles and also by atelectasis and dysfunction and ciliary damage caused by anaesthetic gases (Swenson, 1999).

Finally, it should be noted that many of these functional alterations may come as a result of postoperative complications such as atelectasis, infections, respiratory failure or exacerbations of chronic obstructive lung disease (table 2).

in the areas of pulmonary decline the end point of exhalation is below the closure volume, which causes an early closure of the airway and, therefore, of the areas of atelectasis. The factors that reduce FRC include supine position, pain, general anaesthesia and obesity. These functional changes occur without apparent obstruction of the airway, so that the ratio of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) does not

The action of the anaesthetic and the muscle relaxant used in the surgical procedure, involves a decrease in lung volumes. In addition, the effects of these drugs on the diaphragm and the bulbar center responsible for regenerating respiratory impulses are the

The cause of the diaphragm muscle dysfunction is not clear yet. Direct damage to the muscles during the surgical intervention has been proposed as one of possible mechanisms, but transdiaphragmatic pressure measurements during maximal phrenic nerve stimulation suggest that the depression of the central nervous system efferent traffic on the diaphragm occurs as a result of inhibitory reflexes associated with pain and other stimuli to

Hypoxemia and arterial hypercapnia that appear, especially in the postoperative period, are mainly due to the effects of anaesthesia used during the surgery and cause a decrease in the interrelation ventilation/perfusion (V/Q), and besides lead to deterioration of hypoxic pulmonary vasoconstriction, alveolar hypoventilation or low cardiac output. The gas exchange disorder is intensified with combination of hypoventilation, increase in dead space ventilation, rapid shallow breathing and a decrease in mixed venous oxygen saturation due to low cardiac output, anemia and arterial desaturation and increased peripheral oxygen

Table 1. Mechanism of lung function changes with anesthesia and surgery (Swenson, 1999). Ventilatory depression is also typical of the postoperative period and is marked by the residual effects of anaesthesia that inhibit normal response to hypoxia and hypercapnia. Analgesics and other sedatives may enhance these effects, and impede the implementation

The lung defends itself from attacks of infectious and environmental agents with cough and mucociliary clearance. The former is suppressed both with excessive and poor pain treatment. The latter can be altered by an ineffective cough, limited by restrictive changes and weakened respiratory muscles and also by atelectasis and dysfunction and ciliary

Finally, it should be noted that many of these functional alterations may come as a result of postoperative complications such as atelectasis, infections, respiratory failure or

of pulmonary rehabilitation. They can rarely lead to episodes of sleep apnea.

main reasons that justify changes in lung volumes.

consumption with pain, fever or stress (Beckles et al., 2003).

**Lung function changes with anesthesia and surgery** 

damage caused by anaesthetic gases (Swenson, 1999).

exacerbations of chronic obstructive lung disease (table 2).

Inhibition of cough and mucociliary system

sympathetic or vagal receptors.

Impairment of gas exchange Reduction in lung volumes Dysfunction of the diaphragm Depression of ventilatory control

decrease.


Table 2. Postoperative pulmonary complications in patients with thoracic surgery (Swenson, 1999).
