EVALUATION OF THE PATIENT FOR LUNG RESECTION
Indications and Criteria
Resection of lung disease results in a greater impairment in postoperative
lung function than does most other types of surgery (see Chapter
49
). Lung resection in patients with pulmonary dysfunction is associated
with a high risk of postoperative complications, even the possibility of death.
These patients require a more extensive pulmonary evaluation, particularly if removal
of an entire lung is anticipated. A major aim of the evaluation
is to decide whether the removal of lung tissue can be tolerated without compromising
pulmonary function to a degree that the patient dies from pulmonary insufficiency
or is severely disabled. The long-term ability to withstand such lung resection
is related to the amount and functional status of the lung parenchyma removed and,
more importantly, to the function of the remaining lung tissue. Removal of lung
from an already compromised patient may be followed by inadequate gas exchange, pulmonary
hypertension, and incapacitating dyspnea. The role of the anesthesiologist is to
be aware of these risks, but the decision about whether a patient can tolerate the
proposed resection with acceptable risk rests with the surgeon and pulmonologist.
Although much of the literature in this area emphasizes long-term
disability of the pneumonectomy patient, the immediate impact on pulmonary function
may be as great in patients undergoing lobectomy because of surgical trauma to the
remaining tissue of the same lung. Results of pulmonary function studies must be
viewed in light of the patient's age, the status of the cardiovascular system, and
the patient's cooperation and motivation. Data on pneumonectomy patients collectively
indicate that removal of the entire lung is likely to be tolerated if the preoperative
pulmonary function meets the following criteria: (1) FEV1
greater than
2 L and FEV1
/FVC ratio of at least 50%, (2) MVV greater than 50% of predicted,
and (3) RV/TLC ratio less than 50%.
If any of these criteria is not met, more sophisticated split-function
pulmonary testing is indicated to estimate the relative functional contribution of
each lung. If, for example, the lung to be removed contributes less to ventilatory
function than the other lung does, low spirometric values are not as ominous. Usually,
split-function pulmonary testing consists of xenon radiospirometry to assess ventilation
and macroaggregates of iodine or technetium to scan perfusion. The relative contribution
of each lung to total ventilation or perfusion can be used to predict postoperative
pulmonary function. A predicted postoperative FEV1
of at least 800 mL
should be required before pneumonectomy is performed. The risk of significant resting
carbon dioxide retention and resting dyspnea appears to be high with FEV1
values less than this. If surgery is still contemplated in the face of a low predicted
FEV1
value, an invasive study is recommended. The pulmonary artery of
the lung to be removed can be subjected to occlusion by a balloon. If pulmonary
hypertension (mean pulmonary arterial pressure >35 mm Hg) and arterial hypoxemia
(PaO2
<45 mm Hg) do not occur, it can
be assumed that the remaining lung may be able to accommodate the entire cardiac
output. Such a patient may be allowed to undergo surgery despite failure to fulfill
the mechanical ventilatory criterion. The indications for performing this invasive
procedure are not agreed on universally, but many physicians still heed the advice
of Olsen and colleagues that balloon occlusion, if feasible, should be performed
when the less invasive studies are inconclusive.
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