Preoperative evaluation and perioperative care of a patient includes
1. tissue diagnosis of primary disease and decision if an operative
procedure is indicated
2. assessment of patients general condition
3. 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
Lung physiology
1. well suited for efficient exchange of O2 and CO2 with a large
surface area and low
perfusion pressure (300 million alveoli)
2. gas exchange controlled by two pumps- the right ventricle
and the chest cage-diaphragm
3. elastic recoil of lungs ejects gas and fibrous skeleton maintains
airway patency
4. Clinical evaluation of pulmonary function
a. history and physical- exercise tolerance
b. CXR, ABG
c. simple spirometry
d. vital capacity (FVC)- total exhaled volume
FEV1- forced expiratory volume at
one second- indication of flow
FEV1 1000-2000 ml adequate for surgery
FEV1 800 ml or less preclude surgical resection
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
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
Ventilatory Pump and Work of Breathing
1. Ventilatory pump consist of the thoracic cage and ventilatory
muscles
2. the ventilatory pump is a suction pump which expands
the chest cage to pull air into the
lungs
3. dyspnea signals that the work required of the ventilatory
muscles has reached
a level that exceeds the comfortable
capacity of the patient
4. thoracotomy creates a region of non-contractile muscles which
lowers tidal
volume and increases respiratory rate
5. several disease processes can cause ventilatory pump failure
e. central depression
f. muscle paralysis
g. fatigue
h. mechanical defects in the thoracic cage-trauma, post-surgical
1. failure of ventilatory pump leads to atelectasis and
decreased lung compliance
2. functional residual volume decreases with loss of functional
alveoli
3. post-operative pain control- epidural can help prevent splinting
and therefore atelectasis
9. work capacity of ventilatory muscles are trainable- sedentary
patients will
poor muscle function as compared
to active patients
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
Ventilation -Perfusion Incoordination effective gas transfer relies
on the coordination of ventilation and perfusion
1. ventilation-perfusion mismatch occurs post-operatively
2. V/Q mismatch is the most common form of post-operative hypoxemia
3. usually secondary to the development of atelectasis
Shunt Fraction
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.
One Lung Anesthesia
1. procedure of choice for pulmonary resection
2. videothoracoscopy has increased demand
3. unventilated lung is perfused and is a source of an intrapulmonary
shunt that can lead to
hypoxemia
4. usually ventilated on 100 % oxygen
Pneumonectomy lung reduction surgery
1. derived from the observation of chest wall adaptation in lung
transplant patients
2. bilateral stapling of peripheral lung tissue to diminish lung
volumes
3. reinforced with bovine pericardial strips to prevent leaks
4. improvement in symptoms and FEV1
5. improves diaphragmatic motion
Summary of Evaluation of Gas Exchange Function- background facts
for assessing
pulmonary function are as follows:
1. there is a large reserve in normal individuals
2. condition of the ventilatory muscles depends on the physical
state of the patient
3. as lung volume falls, airways in dependent areas of the lung
close
4. with aging and smoking, airways close at higher lung volumes
5. V/Q mismatch occurs with airway closure
6. V/Q mismatch requires increased alveolar ventilation to maintain
the same amount of gas
exchange
7. spirometry measures the volumes o flung and the ability to
move air
8. PaCO2 is an indicator of adequacy of ventilation
9. PaO2 is an indicator of adequacy of oxygenation
Pulmonary Assessing Pre-operative Function
1. History and physical examination
2. CXR
3. laboratory data
4. Room air arterial blood gas
5. pulmonary function tests
a. FEV1- 1000- 2000 ml acceptable
b. MVV if > 50 L/min acceptable, if < 28 L/min severely decreased
function
c. 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
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
a. cessation of smoking
b. bronchodilators
c. appropriate antibiotics for bronchitis
d. exercise |
