Asthma: Clinical sciences

Asthma is an episodic, chronic respiratory disorder characterized by airway obstruction caused by inflammation and hyperresponsiveness of the bronchial smooth muscle. Asthma is reversible, which means the obstruction can virtually disappear with medications like bronchodilators, and inducible, which means the obstruction can occur in response to a variety of stimuli; including allergens, irritants, and respiratory tract infections.

Clinical manifestations are highly variable, ranging from infrequent and mild symptoms that have minimal functional limitations, to frequent acute asthma exacerbations causing significant impairment in functional capacity, and even life-threatening respiratory failure that’s often referred to as status asthmaticus.

Now, if you suspect asthma, you should first perform an ABCDE assessment to determine whether your patient is stable or unstable. If they’re unstable, stabilize their airway, breathing and circulation, obtain IV access, and begin continuous vital sign monitoring including heart rate and blood pressure.

Next, obtain focused history and physical, order labs, including ABG, and perform spirometry to assess the patient’s peak expiratory flow, or PEF, for short. Finally, don’t forget to place your patient on pulse oximetry. History typically reveals shortness of breath, cough, and chest tightness. On the flip side, physical exam is likely to show tachypnea and use of accessory inspiratory muscles. In addition, auscultation can reveal bilateral wheezing due to inflamed and narrowed airways, and if the condition worsens, you may find decreased or even absent breath sounds, since less air is reaching alveoli.

Next ABG might reveal arterial pH of 7.35 or less and pCO2 above 45 mmHg, indicating respiratory acidosis and hypercapnia; while spirometry usually shows PEF less than 40%. Finally, pulse oximetry might demonstrate saturation below 90%.

If this is the case, suspect acute asthma exacerbation, or even status asthmaticus, and immediately administer supplemental oxygen at 100% FiO2, inhaled bronchodilators including a short-acting muscarinic antagonist like ipratropium and a short-acting beta agonist or SABA like albuterol, as well as systemic corticosteroids, either oral or IV. If the patient doesn’t respond to treatment, you can also give a single dose of IV magnesium. Lastly, in severe cases, you may even proceed with endotracheal intubation and mechanical ventilation, especially if your patient has altered mental status, cyanosis, or inability to maintain respiratory effort, as well as worsening hypercapnia and respiratory acidosis.

Now let's go back to the ABCDE assessment and discuss stable patients. First, perform a focused history and physical. Your patient is likely to report shortness of breath, coughing, and chest tightness, often triggered by allergens and exercise, and they may even have an existing diagnosis of asthma. On the other hand, physical examination often reveals tachypnea and wheezing. If this is the case, suspect asthma, or if your patient has already been diagnosed with asthma, suspect worsening of its severity.

You’ll want to monitor the patient's vital signs, including heart rate, blood pressure, respirations, and oxygen saturation. Finally, provide supplemental oxygen to maintain an oxygen saturation above 90%. The next step in patient management is to obtain spirometry, including FVC and FEV1 to confirm the diagnosis. FVC, or forced vital capacity, is the maximum amount of air a person can forcibly exhale from their lungs after a maximum inhalation, while FEV1 is the volume of air exhaled during the first second of this forced exhalation.

Now, here’s a clinical pearl to keep in mind! Spirometry can be performed with a simple handheld spirometer. First, have your patient take a maximal breath in, then forcibly exhale into the spirometer until all of the air is emptied from their lungs. This will generate a flow-volume loop, which will differentiate between obstructive and restrictive patterns of lung disease.

Now that you’ve completed spirometry, calculate the patient’s FEV1 to FVC ratio. If the ratio is within normal range, or even elevated, for the patient’s age, consider an alternative diagnosis. On the other hand, if the ratio is below normal range, suspect an obstructive lung disease, which includes asthma. But this is not enough to confirm the diagnosis so your next step is to perform bronchodilator reversibility, or BDR testing. BDR testing consists of giving an inhaled dose of a SABA, followed by repeat spirometry, paying particular attention to the FEV1.