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Pulmonary Physiology

Pulmonary Physiology

1. Preoperative evaluation and perioperative care of a patient includes

A. Tissue diagnosis of primary disease and decision if an operative procedure is indicated
B. Assessment of patient’s general condition
C. Preoperative preparation and postoperative care
The Evaluation of pulmonary function includes assessment of cardiac function, the oxygen carrying red cells, the lungs, chest wall and ventilatory muscular function

2. Lung physiology

A. Well suited for efficient exchange of O2 and CO2 with a large surface area and low perfusion pressure (300 million alveoli)
B. Gas exchange controlled by two pumps- the right ventricle and the chest cage-diaphragm
C. Elastic recoil of lungs ejects gas and fibrous skeleton maintains airway patency
D. Clinical evaluation of pulmonary function
1) history and physical- exercise tolerance
3) simple spirometry
4) vital capacity (FVC)- total exhaled volume
E. FEV1- forced expiratory volume at one second- indication of flow
1) FEV1 1000-2000 ml adequate for surgery
2) FEV1 800 ml or less preclude surgical resection
D. Restrictive disease- vital capacity, inspiratory and expiratory reserves are diminished- can result from diseases of the lung, pleura, chest cage and muscles -kyphoscoliosis, ARDS, pleural effusions or fibrosis Funcitonal residual volume is decreased limited capacity to expand lungs but no difficulty emptying lungs
E. Obstructive Disease- lung elastic recoil decreases, compromising the force

of exhalation - most common form in clinical practice usually due to smoking, damaged alveoli can lead to pulmonary HTN unsupported airways leads to airway trapping and atelectasis

3. Ventilatory Pump and Work of Breathing

A. Ventilatory pump consist of the thoracic cage and ventilatory muscles
B. The ventilatory pump is a suction pump which expands the chest cage to pull air into the lungs
C. Dyspnea signals that the work required of the ventilatory muscles has reached

a level that exceeds the comfortable capacity of the patient

D. Thoracotomy creates a region of non-contractile muscles which lowers tidal

volume and increases respiratory rate

E. Several disease processes can cause ventilatory pump failure
1) central depression
2) muscle paralysis
3) fatigue
4) mechanical defects in the thoracic cage-trauma, post-surgical
a) failure of ventilatory pump leads to atelectasis and decreased lung compliance
b) functional residual volume decreases with loss of functional alveoli
c) post-operative pain control- epidural can help prevent splinting and therefore atelectasis

4. Work capacity of ventilatory muscles are trainable- sedentary patients will poor muscle function as compared to active patients

A.Fluid Exchange and Lung Water blood circulating through normal lung capillaries at normal rates and pressure causes a net fluid movement from the capillaries into the lung interstitium.The filtered fluid is picked up by the lymphatics and returned to the circulation Management of fluid therapy is critical in post-operative pulmonary resection patients since this fluid balance is disrupted
1) increased filtration post-operatively
2) decreased capillary bed and lymphatic mass
3) increased cardiac output
4) must carefully titrate fluid balance especially in pneumonectomy patients

5. Ventilation -Perfusion Incoordination effective gas transfer relies on the coordination of ventilation and perfusion

A. Ventilation-perfusion mismatch occurs post-operatively
B. V/Q mismatch is the most common form of post-operative hypoxemia
C. Usually secondary to the development of atelectasis

6. Shunt Fraction

A. Determines the fraction of blood ejected by the left ventricle that has no gas exchange in the lungs
1) Patients with a shunt fraction > 0.15 to 0.20 are vulnerable to a low C.O.
2) Tissue oxygen delivery falls
3) Pulmonary artery catheter should be placed to optimize C.O.

7. One Lung Anesthesia

A. Procedure of choice for pulmonary resection
B. Videothoracoscopy has increased demand
C. Unventilated lung is perfused and is a source of an intrapulmonary shunt that can lead to hypoxemia
D. Usually ventilated on 100 % oxygen

8. Pneumonectomy lung reduction surgery

A. Derived from the observation of chest wall adaptation in lung transplant patients
B. Bilateral stapling of peripheral lung tissue to diminish lung volumes
C. Reinforced with bovine pericardial strips to prevent leaks
D. Improvement in symptoms and FEV1
E. Improves diaphragmatic motion

9. Summary of Evaluation of Gas Exchange Function- background facts for assessing pulmonary function are as follows:

A. There is a large reserve in normal individuals
B. Condition of the ventilatory muscles depends on the physical state of the patient
C. As lung volume falls, airways in dependent areas of the lung close
D. With aging and smoking, airways close at higher lung volumes
E. V/Q mismatch occurs with airway closure
F. V/Q mismatch requires increased alveolar ventilation to maintain the same amount of gas exchange
G. Spirometry measures the volumes o flung and the ability to move air
H. PaCO2 is an indicator of adequacy of ventilation
I. PaO2 is an indicator of adequacy of oxygenation

10. Pulmonary Assessing Pre-operative Function

A. History and physical examination
C. Laboratory data
D. Room air arterial blood gas
E. Pulmonary function tests
1) FEV1- 1000- 2000 ml acceptable
2) MVV if > 50 L/min acceptable, if < 28 L/min severely decreased function
3) split-lung function test predicts post-operative FEV1 based on ventilation scan on each lung if post-operative FEV1 > 800 ml then patient will tolerate pneumonectomy e.g. patient with left lower lung tumor, FEV1 1.72
F. Liters with split function of 62 % on right and 38 % on left would predict a post-operative FEV1 of 1.0 liters for left pneumonectomy if PCO2 45 then the patient is not a candidate for resection unless a medical regimen improves gas exchange
1) cessation of smoking
2) bronchodilators
3) appropriate antibiotics for bronchitis
4) exercise