Page 679 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

498 PART 4: Pulmonary Disorders

β-adrenoreceptors, the severity of asthma, and its response to therapy. DHI or tension pneumothorax limit venous return to the right heart.
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Survivors of near-fatal asthma attacks may also have diminished ven- Asthma can also cause acute coronary syndrome in at-risk patients.
tilatory drive in the face of hypoxemic or mechanical stimuli (ie, poor Large drops in intrathoracic pressure increase LV afterload and decrease
perceivers of airflow obstruction). Other concerning features include coronary blood flow, which can cause an imbalance between myocardial
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symptoms of long duration (which suggest a substantial component of oxygen supply and demand. β-agonists, theophylline, and hypoxemia
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inflammation and slow recovery), late arrival for care, fatigue, altered may further disrupt this balance.
mental status, and sleep deprivation. Deterioration despite optimal
treatment, including the concurrent use of oral steroids, further identi- ■ MEASUREMENT OF AIRFLOW OBSTRUCTION
fies patients at risk. The degree of airflow obstruction can be determined by measuring
“All that wheezes is not asthma” is a valid clinical saw to consider. The PEFR or FEV . A PEFR or FEV <40% of predicted or the patient’s
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absence of a history of asthma should alert the physician to other diag- personal best characterizes severe exacerbation. Objective measure-
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noses (although asthma can first occur at any age). A history of smoking ments are generally safe to obtain except in the sickest patients, and may
suggests chronic obstructive pulmonary disease (COPD), which may be provide important information because physician estimates are often
associated with fixed airflow obstruction and chronic respiratory acidosis. wrong. In critically ill patients, it is wise to defer measurements, which
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Cardiac asthma refers to the airway hyperreactivity that occurs in may worsen bronchospasm and even precipitate an arrest. 57
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congestive heart failure. Heart failure is generally discernible by Measurement of the change in PEFR or FEV helps in the assessment
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examination, but the distinction between LV dysfunction and airway of treatment response. Several studies have demonstrated that failure of
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obstruction can occasionally be difficult. As discussed above, severe initial therapy to improve expiratory flow after 30 minutes predicts a
airflow obstruction is a rare cause of pulmonary edema, and broncho- refractory course and need for hospitalization or continued treatment
dilators may improve airflow obstruction in LV failure. Foreign body in an ED. 37,58-60 Changes in PEFR before 30 minutes of treatment have
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aspiration must be considered in children and at-risk adults. Upper elapsed do not predict outcome. 61
airway obstruction from granulation tissue, tumor, laryngeal edema,
or vocal cord dysfunction is in the differential, but classic extrathoracic ■ PULSE OXIMETRY AND ARTERIAL BLOOD GASES
obstructions cause inspiratory phase (not expiratory phase) prolonga-
tion and stridor. In these cases, fiberoptic laryngoscopy may be indi- Pulse oximetry should be performed at the time of arrival to the ED
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cated to confirm a laryngeal level process. For patients with tracheal and monitored until there is a clear response to therapy. Supplemental
stenosis (eg, from prior intubation), CT imaging and fiberoptic bron- oxygen is recommended to maintain arterial oxygen saturation at greater
choscopy establishes the diagnosis. Important clues to focal obstruction than 90% (>95% in pregnant women and patients with coronary artery
include localized wheeze, and rarely, asymmetric hyperinflation on disease). 62
the chest radiograph. Pneumonia complicating asthma is unusual but When FEV is less than 25% predicted or of the patient’s personal best,
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should be considered when there is fever, purulent sputum, localizing an arterial blood gas should be considered. In early (mild) acute asthma,
signs, and refractory hypoxemia. In large series of patients with pulmo- hypoxemia and respiratory alkalosis are common. Hypercapnia signals
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nary embolus, wheezing was not a reported sign. However, wheezing a severe attack, but in and of itself is not an indication for intubation.
has been described anecdotally, and dyspnea out of proportion to Conversely, hypercapnia is not always present in cases of severe obstruc-
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measures of airflow obstruction should prompt the consideration of tion and impending respiratory arrest. 22
Metabolic acidosis with a normal anion gap occurs when there
pulmonary embolus. has been bicarbonate wasting in response to respiratory alkalosis. An
■ PHYSICAL EXAMINATION elevated anion gap suggests excess serum lactate, possibly secondary to
The general appearance of the patient (ie, posture, speech pattern, increased work of breathing, tissue hypoxia, intracellular alkalosis, or
decreased lactate clearance by the liver. Lactic acidosis correlates with
positioning, and mental status) allows for quick assessment of severity, the severity of airflow obstruction, is more common in men, and occurs
response to therapy, and need for intubation. Adults with acute asthma more frequently when β-agonists are administered parenterally. 64
who assume the upright position have a higher heart rate (HR), respira- Serial blood gases are usually not necessary to determine clinical course.
tory rate (RR), and PP and a significantly lower partial pressure of arte- Physical examinations and peak flows allow for valid clinical assessments
) and PEFR than patients who are able to lie supine.
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rial oxygen (Pa O 2 in most cases. Patients who deteriorate on clinical grounds should be con-
Diaphoresis is associated with an even lower PEFR. Accessory muscle . Conversely, improving patients
use and PP indicate severe airflow obstruction, but the absence of either sidered for intubation regardless of Pa CO 2
should not be intubated despite hypercapnia. Serial blood gases are help-
does not rule out severe obstruction. 34 ful in intubated patients to guide ventilator management.
Examination of the head and neck should focus on identifying baro-
trauma and upper airway obstruction. Tracheal deviation, asymmetric ■ RADIOGRAPHIC STUDIES
breath sounds, a “mediastinal crunch,” and subcutaneous emphysema
suggest pneumothorax or pneumomediastinum. The mouth and neck Chest radiography plays little role in the assessment or management of
should be inspected for mass lesions or signs of previous surgery routine patients. Even in hospitalized patients, radiographic findings
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including tracheostomy. The lip and tongue should be inspected for influence treatment in 1% to 5% of cases. 65-68 In one study that reported
angioedema. major radiographic abnormalities in 34% of cases (which the authors felt
Wheezing correlates poorly with the degree of airflow limitation. impacted management), the majority of findings were classified as focal
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Severe airflow obstruction may present with poor air movement and parenchymal opacities or increased interstitial markings, common indi-
a silent chest; in this situation the emergence of wheezing signals cators of atelectasis in asthma. Chest radiography should be reserved for
improved air entry and clinical improvement. Localized wheezing or patients suspected of having heart failure, pneumothorax, pneumonia,
crackles should prompt consideration of atelectasis, pneumonia, pneu- or atelectasis. In mechanically ventilated patients, chest radiography
mothorax, endobronchial lesions, or foreign body. further identifies endotracheal tube position.
arrhythmias occur. Bradycardia is an ominous sign of impending arrest. ■ ADMISSION CRITERIA
Sinus tachycardia is common, but supraventricular and ventricular
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Clinical signs of right-sided and left-sided heart failure suggest pri- Patients demonstrating a good response to initial therapy in the ED may
mary cardiac disease. Yet, acute asthma alone can cause examination be discharged home with close follow-up. There should be significant
and electrocardiographic findings of transient right-sided strain and improvement in breathlessness, improved air movement on physical
rarely pulmonary edema. 52,53 Jugular venous distention also occurs when examination, and a FEV or PEFR ≥70% of predicted or personal best.
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