- In a patient with an acute asthma attack,
a normal or high Paco2 indicates
that the patient can no longer maintain the work of breathing and
is often a sign of impending respiratory failure. A pulsus paradoxus
and electrocardiographic signs of right ventricular strain (ST-segment
changes, right-axis deviation, and right bundle branch block) are
also indicative of severe airway obstruction.
- Asthmatic patients with active bronchospasm presenting
for emergency surgery should be treated aggressively whenever
possible. Supplemental oxygen, aerosolized β2-agonists,
and intravenous glucocorticoids can dramatically improve lung function
in a few hours.
- Intraoperative bronchospasm is usually manifested
as wheezing, increasing peak inflation pressures (plateau pressure
should remain unchanged), decreasing exhaled tidal volumes, or a
slowly rising waveform on the capnograph.
- If the bronchospasm does not resolve after deepening
the anesthetic, less common causes should be considered before administering
more specific drugs. Obstruction of the tracheal tube from kinking,
secretions, or an overinflated balloon; bronchial intubation; active
expiratory efforts (straining); pulmonary edema or embolism; and
pneumothorax can all simulate bronchospasm.
- In patients with chronic obstructive pulmonary
disease (COPD), chronic hypoxemia leads to erythrocytosis, pulmonary
hypertension, and eventually right ventricular failure (cor pulmonale).
- Oxygen therapy can dangerously elevate Paco2 in patients with CO2 retention;
elevating Pao2 above
60 mm Hg can precipitate respiratory failure.
- Preoperative interventions in patients with COPD
aimed at correcting hypoxemia, relieving bronchospasm, mobilizing
and reducing secretions, and treating infections may decrease the
incidence of postoperative pulmonary complications. Patients at
greatest risk for complications are those with preoperative pulmonary
function measurements less than 50% of predicted.
- Patients with pulmonary bullae are at high risk
of developing pneumothoraxes intraoperatively, particularly if ventilated
with positive pressure.
- Restrictive pulmonary diseases are characterized
by decreased lung compliance. Lung volumes are typically reduced,
with preservation of normal expiratory flow rates. Thus, both forced
expiratory volume in 1 s (FEV1) and forced vital capacity
(FVC) are reduced, but the FEV1/FVC ratio is normal.
- Intraoperative pulmonary embolism usually presents
as unexplained sudden hypotension, hypoxemia, or bronchospasm. A
decrease in end-tidal CO2 concentration is also suggestive
of pulmonary embolism but not specific.
The impact of preexisting pulmonary disease on respiratory function
during anesthesia and in the postoperative period is predictable:
Greater degrees of preoperative pulmonary impairment are associated
with more marked intraoperative alterations in respiratory function
(see Chapter 22) and higher rates of postoperative
pulmonary complications. Failure to recognize patients who are at
increased risk is a frequent contributory factor leading to complications,
as patients may not receive appropriate preoperative and intraoperative
care. This chapter examines pulmonary risk in general and then reviews
the anesthetic approach to patients with the most common types of
Six risk factors (Table
23–1) predispose patients to postoperative pulmonary
dysfunction, the most common postoperative complication. The
incidence of atelectasis, pneumonia, pulmonary embolism, and respiratory
failure following surgery is quite ...