Internal Medicine Correlations and Clinical Scenarios (CCS) USMLE Step 3

CASE 2: Chronic Obstructive Pulmonary Disease

Setting: office

CC: “I get short of breath when I walk up a flight of stairs.”

VS: BP: 110/70 mm Hg; P: 64 beats/minute; T: 98°F; R:12 breaths/minute

HPI: A 75-year-old long-term male smoker comes to the office with increasing dyspnea when walking, especially upstairs. The patient had been a smoker of one pack/day for 50 years. He quit 2 years ago. This is the first time he has had a decrease in exercise tolerance as he could walk two to three blocks before becoming short of breath.

ROS:

No cough, no sputum, no fever

No weight loss

PMHX:

Diabetes: well controlled

Medications:

Metformin, glyburide

PE:

Chest: no wheezing, no rales, no rhonchi

Cardiovascular: no murmurs

Extremities: some clubbing, no edema

Initial Orders:

Oximeter

Chest x-ray

PFTs

There are no unique physical findings in chronic obstructive pulmonary disease (COPD).

At very late stages of the disease, patients can develop a barrel chest.

What is the physiologic basis of a barrel chest?

a. Increased fibrosis of lungs

b. Increased residual volume

c. Decreased compliance

d. Decreased FEV₁

Answer b. Increased residual volume

As air becomes trapped in the lungs, the diaphragm flattens and the chest enlarges. These increased volumes are all residual volume, or the part of the air that cannot be exhaled. This is all a sign of increased total lung capacity, but not usable lung. The usable part of lung volume, the FEV₁ and FVC, both diminish (Figure 7-2).

Figure 7-2. Cellular mechanisms in chronic obstructive pulmonary disease. Cigarette smoke and other irritants activate epithelial cells and macrophages in the lung to release mediators that attract circulating inflammatory cells, including monocytes (which differentiate to macrophages within the lung), neutrophils, and T lymphocytes (T helper [TH1] and TC1 cells). Fibrogenic factors released from epithelial cells and macrophages lead to fibrosis of small airways. Release of proteases results in alveolar wall destruction (emphysema) and mucus hypersecretion (chronic bronchitis). (Reproduced with permission from Brunton LL, et al. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 12th ed. New York: McGraw-Hill; 2011.)

FEV₁/FVC Down + Residual Volume Up = COPD

Report:

Oximeter: 94% room air saturation

Chest x-ray: clear lung fields, hyperaeration, some flattening of diaphragm

Which of these becomes abnormal first in COPD?

a. TLC

b. FEV₁

c. Forced expiratory flow 25% to 75% (FEF25–75%) or peak mid-maximal flow

d. Forced vital capacity (FVC)

Answer c. Forced expiratory flow 25% to 75% (FEF25–75%) or peak mid-maximal flow

The FEF25–75% will become abnormal first in COPD. This is the middle part of the breath. FEF25–75% decrease will precede a decrease in the FEV₁.

FEF25–75% indicates a small airway.

Small airways collapse first.

As radius decreases, the pressure of collapse increases.

Law of Laplace

P = T/R

Where P is pressure, T is wall tension, and R is radius

Move the clock forward 1 week. The patient still reports decreased exercise tolerance. The patient’s PFTs show:

Decrease in FEF25–75%

FEV₁ 65% of predicted

FVC 80% of predicted

What is the best therapy to use first?

a. Tiotropium

b. Terbutaline

c. Inhaled fluticasone (steroid)

d. Theophylline

Answer a. Tiotropium

Tiotropium and ipratropium are the best initial inhalers for COPD. It is not clear whether albuterol should be used first as well. The other answers are clearly wrong. Terbutaline is a beta-2-specific agonist with very little efficacy. Theophylline is an add-on drug as fourth or fifth line to try to keep patients off oral steroids.

Terbutaline is a beta-2-specific agonist.

Tiotropium

• Antimuscarinic drug

• Dilates bronchi

• Decreases secretions

You advance the clock 1 week. The patient reports dry mouth and constipation. Tiotropium inhibits the muscarinic receptors in the

Bowel (constipation)

Bladder (urinary retention)

Eye (worsens glaucoma by dilating the pupil)

Salivary glands (dry mouth)

The neuromuscular junction has nicotinic receptors for acetylcholine.

It is not affected by tiotropium.

Stop the tiotropium. However, not all patients with COPD will respond to albuterol. Only half have asthma-like “reactive airways” disease. Do PFTs before and after the use of albuterol and see if there is an improvement.

Pre- and post-bronchodilation PFTs

• Do FEV₁ before and after albuterol administration.

• If there is a 12% increase in FEV₁, it indicates reversible airway disease.

There is a 20% rise in FEV₁ with albuterol. You start the medication and advance the clock. The patient is still not controlled and you add an inhaled steroid to therapy.

Inhaled steroids are all identical in efficacy

• Fluticasone

• Beclomethasone

• Triamcinolone

The patient returns in 1 week much improved with greater exercise tolerance. He is then lost to follow-up for a year during which time he does not return. The next time you see the patient he is much more short of breath with dyspnea starting at half-a-block exertion.

In severe COPD, which of these is most likely to be found on this patient’s PFTs?

Answer b. FEV₁ and FVC both down

With severe COPD, FEV₁ and FVC go down, but FEV₁ decreases even more. TLC goes up, but it is not useful. It is all unusable residual volume.

COPD is from the loss of elastin fibers (Figure 7-3).

Figure 7-3. A computed tomography (CT) scan of a patient (at the level of the pulmonary veins) showing multiple large peripheral bullae; the patient was diagnosed with severe paraseptal emphysema. (Reproduced with permission from Miller WT, Jr. Diagnostic Thoracic Imaging. New York: McGraw-Hill; 2006.)

Orders:

ABG

Restart albuterol, tiotropium, and inhaled steroids

Basic metabolic panel (CHEM-7)

Complete blood count (CBC)

Which of the following is a feature of this patient’s disorder?

a. Decreased lung compliance

b. Increased lung compliance

c. Hypersensitivity of central chemoreceptors

Answer b. Increased lung compliance

COPD is an increase in lung compliance. Patients can inhale, but cannot exhale. This is why they retain carbon dioxide (CO₂). They cannot move the air. There is an insensitivity of central chemoreceptors to CO₂ and acid. This is part of why there is a blunted respiratory drive.

Three drives for respiration

• Increased CO₂

• Acid (hydrogen ion)

• Decreased PO₂

Because of shortness of breath, have the patient return in just 1 to 2 days to see if there is improvement. He is somewhat improved, but exercise intolerance makes it impossible for him to walk the two flights of stairs in his own house.

ABG Report: pH 7.37; PCO₂ 60 mm Hg; PO₂ 59 mm Hg; saturation 89%

Central chemoreceptors are stronger than peripheral chemoreceptors.

• Central CO₂ and acid

• Peripheral oxygen

Report:

CBC: hematocrit (Hct) 55%; mean corpuscular volume (MCV) 78 fL

CHEM-7: bicarbonate 36 mEq/L (elevated)

Chronic Hypoxia = Increased Erythropoietin = High Hematocrit (Polycythemia)

Polycythemia from hypoxia gives small cells (low MCV).

The patient meets criteria for chronic home oxygen. Low-flow oxygen (1–2 L/minute) lowers mortality. Low-flow oxygen in hypoxic COPD lowers mortality. Criteria for home oxygen use are:

PO₂ <55 mm Hg or saturation <88%

PO₂ <60 mm Hg or saturation <90% with polycythemia or pulmonary hypertension

Peripheral chemoreceptors for oxygen

Detect PO₂ <60 mm Hg

The patient is started on oxygen and continued on tiotropium, albuterol, and inhaled steroids. Bicarbonate level is elevated in the kidney by carbonic anhydrase in response to the chronic elevation of PCO₂.

When CCS says, “Case will end in 5 minutes of real time,” it does not mean you made a mistake. It does give you an opportunity to do any health maintenance you may have forgotten.

Final Orders:

Flu vaccine yearly

Pneumococcal vaccination for anyone with COPD

Chronic Respiratory Acidosis = Metabolic Alkalosis

Oxygen prevents fatal pulmonary hypertension.