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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2664_Библиотеки_им_академика_М_И_Перельмана
.pdf
USMLE Step 2 CK
l Internal Medicine
Major Side Effects. Bronchospasm, heart block, bradycardia, Raynaud phenomenon, depression, impotence, fatigue, decreased HDL, increased triglycerides, hyperglycemia.
Relative Contraindications. Asthma or COPD, atrioventricular conduction defects, CHF from
systolic dysfunction, diabetes because of masking signs of hypoglycemia.
Central-acting sympatholytics
Clonidine Guanabenz
Guanfacine Methyldopa
Specific Indications. Clonidine can be useful in opiate detoxification.
Major Side Effects. Depression, fatigue, dry mouth, impotence, bradycardia, heart block,
memory loss. Methyldopa gives hepatitis and Coombs-positive hemolytic anemia.
Relative Contraindications. Elderly or depressed patients.
Direct vasodilators
Hydralazine Minoxidil
Specific Indications
• Hydralazine is used in eclampsia
• Minoxidil is used locally to treat baldness
Major Side Effects
• Minoxidil gives marked fluid retention, pericardial effusion, and hirsutism
• Hydralazine gives a lupus-like syndrome
Relative Contraindications. Angina pectoris.
Alpha-adrenergic blockers
Doxazosin Prazosin Terazosin
Specific Indications. Patients with lipid disorders (they reduce LDL and increase HDL), prostatic hypertrophy (to reduce obstructive symptoms).
300
Major Side Effects. Syncope after the first dose, dizziness, headache.
Relative Contraindications. None.
Practice Questions
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1. What acid-base disorders are represented by the following sets of arterial blood tests?
Chapter 8
l Nephrology
pH Pco2, mm Hg HCO
–
, mEq/L
3
(A) 7.32 28 14
(B) 7.47 20 14
(C) 7.08 49 14
(D) 7.51 49 38
Answers:
(A) Metabolic acidosis (low pH, low HCO
(B) Respiratory alkalosis (high pH, low Pco2, compensatory reduction in HCO
tion). Note that a low HCO
–
concentration does not necessarily imply a primary meta-
3
–
concentration, compensatory reduction in Pco2).
3
3
bolic acidosis.
(C) Combined respiratory and metabolic acidosis (low pH, high Pco2, low HCO
tration).
(D) Metabolic alkalosis (high pH, high HCO
–
concentration, compensatory increase in Pco2).
3
2. Match the clinical histories with the appropriate arterial blood values.
pH Pco2, mm Hg HCO
–
, mEq/L
3
(A) 7.37 65 37
–
concentra-
–
concen-
3
(B) 7.22 60 26
(C) 7.35 60 32
1. A 60-year-old man with chronic bronchitis develops persistent diarrhea
2. A markedly obese 24-year-old man
3. A 14-year-old girl with a severe acute asthmatic attack
4. A 56-year-old woman with chronic bronchitis is started on diuretic therapy for peripheral
edema, resulting in a 3-kg weight loss
Answers:
It is easiest to answer this problem by first determining the acid-base disorders represented by
the 3 sets of blood values.
The low pH and high Pco2 indicate respiratory acidosis. In chronic respiratory acidosis, a
(A)
Pco2 of 65 mm Hg (25 mm Hg greater than normal) should be associated with a plasma
–
HCO
concentration of approximately 33 mEq/L (3.5 mEq/L increase in the plasma
3
–
HCO
concentration for each 10 mm Hg elevation in the Pco2). Thus, the HCO
3
–
3
con-
centration of 37 mEq/L represents a superimposed metabolic alkalosis.
301
USMLE Step 2 CK
l Internal Medicine
(B) At a Pco2 of 60 mm Hg, the HCO
–
concentration should be roughly 26 mEq/L in acute
3
respiratory acidosis (1 mEq/L increase per 10 mm Hg elevation in the Pco2) and 31 mEq/L
in chronic respiratory acidosis. Therefore, these values may represent acute respiratory
acidosis or metabolic acidosis (lower the HCO
–
concentration from 31 to 26 mEq/L)
3
superimposed on chronic respiratory acidosis.
(C) Chronic respiratory acidosis or metabolic acidosis (raising the HCO
–
concentration
3
from 26 to 32 mEq/L) superimposed on acute respiratory acidosis.
From the history:
1. Chronic bronchitis plus diarrhea suggests combined chronic respiratory acidosis and
metabolic acidosis, or B.
2. Marked obesity suggests chronic hypercapnia, or C.
3. Severe acute asthma suggests acute respiratory acidosis, or B.
4. Chronic bronchitis plus diuretics suggests chronic hypercapnia with superimposed
metabolic alkalosis, or A. The metabolic alkalosis in this case is on the basis of volume
contraction from the use of the diuretic.
302
Pulmonology
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Learning Objectives
❏ Interpret results of pulmonary function testing and chest radiography
❏ Diagnose disturbances of gas exchange
❏ Describe the presentation and management of obstructive lung disease, atelectasis,
interstitial lung disease, and acute respiratory distress syndrome
❏ Outline the presentation, diagnosis, and management of sleep apnea
❏ List the types of lung cancer and their epidemiologic associations and prognosis
❏ Present risk factors, diagnosis, and treatment plan for pulmonary thromboembolism
9
DIAGNOSTIC TESTS
Pulmonary Function Tests
Pulmonary function tests (PFTs) are non-invasive tests used mainly to do the following:
• Categorize of different types of lung processes (restrictive versus obstructive)
• Assess disease severity (in overall prognosis and preoperative evaluation)
• Evaluate post-treatment lung function
Spirometry can be done in the office setting and allows the determination of most lung volumes and capacities, as well as expiratory flows and bronchodilator response. Complete PFTs
are done in the pulmonary lab and allow the measurement of TLC, DLco, and methacholine
challenge testing.
PFTs consist of different tests:
• Static lung compartments are measured by lung volumes , such as total lung capacity
(TLC), residual volume (RV) and vital capacity (VC) .
• Airflow or air movement is measured by the expiratory flow rate (ratio of forced expiratory volume in 1 second to forced vital capacity [FEV1/FVC] and forced expiratory
flow 25−75% of expiration [FEF25–75, also called midmaximal flow rate MMFR]) .
• Alveolar membrane permeability is measured by the diffusing capacity of a gas (DLco) .
• The methacholine challenge test is an adjunct test used for evaluat ing bronchial
hyperactivity in asthma patients who have normal PFTs .
Clinical Pearl
Perform PFTs in all patients
before they undergo lung
resection surgery.
303
USMLE Step 2 CK
Figure 9-1. Determination of Lung Volumes
l Internal Medicine
Generally, <80% of predicted in any lung volume or flow rate is considered abnormal, while
>120% of predicted is consistent with air trapping.
Table 9-1. Pulmonary Function Tests
PFT Normal Range
TLC 80–120% predicted
RV 75–120%
FEV1/FVC Ratio 80%
DLco 75–120%
Lung volumes
Ventilatory function is measured under static conditions for the determination of lung volumes (see Figure 9-1) and thus allows for the diagnosis of restrictive lung disease.
IC: inspiratory capacity
FRC: functional residual
capacity
: tidal volume
V
T
FEV
IC
FRC
1
80–120%
VC
TLC
VC
V
T
R
V
RV
304
Table 9-2. Pulmonary Indices
Figure 9-2. Forced Expiratory Volumes
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Index Description
Total lung capacity (TLC) Volume of gas in the lungs after maximal inspiration
Residual volume (RV) Volume of gas remaining in the lungs after forced
maximal expiration (unused space)
Vital capacity (VC) Volume of gas exhaled with maximal forced expiration
TLC = RV + VC or VC = TLC – RV
Forced expiratory volumes (FEVs)
Forced expiratory volumes measure air movement in and out of the lungs (airflow measurement under dynamic conditions). FEVs can determine the degree of obstruction by comparing the forced volume expired at 1 second (FEV1) to the forced vital capacity (FVC). In
patients with no obstruction, the ratio is 0.80 (80% of predicted). It is decreased in patients
with chronic obstructive disease (emphysema and chronic bronchitis) and asthma.
The FEVs are normal or elevated in patients who have restrictive disease because there is no
problem with airflow. Also, asthmatic patients may have a normal FEV1/FVC because they
may have normal airflow (no bronchoconstriction) when asymptomatic.
Chapter 9
l Pulmonology
Forced expiratory flow (FEF
and is another way to express airflow. Generally consider the FEF
FEV1/FVC, but the FEF
25–75
) is another measurement that can be done during the FEVs
25-75
equivalent to the
25-75
usually detects obstructive disease earlier.
FEVs can be determined during spirometry or full pulmonary function testing.
6
5
4
3
2
1
Normal
FEV
1
sec
10 2
Seconds
FEV
FVC = 5.0
1
FVC
3 4
= 4.0
1
6
5
4
3
2
1
Obstructive
1
sec
10 2
FEV1 = 1.3
FVC = 3.1
FEV
1
Seconds
FVC
3 4
6
5
4
3
2
1
10 2
Restrictive
sec
Seconds
FEV1 = 2.8
FVC = 3.1
FEV
1
1
FVC
3 4
305
USMLE Step 2 CK
Figure 9-3. Alveolar Diffusing Capacity
● Internal Medicine
Carbon monoxide diffusing capacity (DLco)
Lung diffusion testing is used to determine how well oxygen passes from the alveolar space
of the lungs into the blood. Whereas spirometry measures the mechanical properties of the
lungs, the lung diffusing capacity test (DLco) measures the ability of the lungs to perform gas
exchange. The single-breath DLco test requires the patient to inhale DLco gas consisting of
helium, carbon monoxide, and room air. Generally, diffusing capacity is reduced when alveolar walls are destroyed and pulmonary capillaries are obliterated by emphysema, or when the
alveolar-capillary membrane is thickened by edema, consolidation, or fibrosis (as in interstitial
lung disease).
PFTs with an obstructive pattern and decreased DL
emphysema. PFTs with a restrictive pattern and decreased DLco are likely to be some type of
interstitial lung disease (intrapulmonary restriction) or mild left heart failure.
Increased DLco may be seen in pulmonary hemorrhage, e.g., Goodpasture syndrome.
Disintegration
of alveolar
septum
Emphysema
Normal Interstitial Lung
co should prompt the consideration of
Inflammation and
formation of
scar tissue
Disease
Clinical Pearl
Patients with asthma may have
normal PFTs. In these patients,
methacholine challenge will
provoke an asthmatic crisis
and allow the diagnosis of
asthma to be made by PFTs.
Thus, perform methacholine
challenge only for patients
with normal PFTs and for
whom you are considering a
diagnosis of asthma.
306
Methacholine challenge test
Bronchoprovocation with methacholine is done to evaluate patients with cough or wheezing
and who have a normal PFT, for possible asthma (bronchial reactivity).
During the test, the patient inhales an aerosol of methacholine. Results of PFTs (e.g., spirometry) performed before and after the inhalations are used to quantitate the response. A positive
test is defined as a decrease from the baseline FEV1 of 20% or more.
Bronchodilator reversibility
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Nonreversible obstructive lung disease and reversible obstructive lung disease can be distinguished by giving the patient an inhalation of a beta-agonist (albuterol). Consider asthma as
the likely diagnosis when PFTs show evidence of an obstructive pattern, but then reverse by
more than 12% and 7,200 mL after using the bronchodilator.
Table 9-3. PFT Questions
PFT Indices Patient 1 Patient 2
TLC 110% 55%
RV 120% 50%
VC 90% 50%
Chapter 9
l Pulmonology
FEV1/FVC 80% 90%
FEF
Dlco Patient 1a: 90%
What is your diagnosis?
(MMFR) 50% 90%
25–75
Patient 1b: 40%
Patient 2a: 90%
Patient 2b: 40%
Flow Volume Loops
Flow volume loop diagrams also express airflow in different lung diseases and give the relationship between flow rates compared with lung volumes. On the y-axis is flow rate and on
the x-axis is volume. Lung volumes increase to the left on the abscissa. The shape of the loop
can characterize the type and distribution of airway obstruction.
When comparing a normal flow volume loop with one of restrictive lung disease, the restrictive lung disease alters the size of the loop (a shift to the right of the x-axis), which is related
to a reduction in lung volumes.
On the other hand, obstructive lung disease alters the shape of the loop by causing a reduction of airflow (alterations on the y-axis).
In the case of a fixed airway-obstruction (tracheal stenosis after prolonged intubation), the
flow volume loop is flattened on the top and bottom.
With dynamic extrathoracic airway obstruction (vocal cord paralysis), the obstruction occurs
mostly with inspiration while expiration is mostly normal. This effect causes the flow volume
loop to be flattened only on bottom.
Note
Diagnoses for Patients 1
and 2 are revealed at the end
of this chapter.
307
USMLE Step 2 CK
Figure 9-4. Flow Volume Loops
Figure 9-5. Flow Volume Loops
l Internal Medicine
flow
Expiratory
0
flow
capacity
Inspiratory
Total
lung
N
O
FO
N: normal
O: obstructive
FO: fixed obstruction
Volume
123456
0
Residual
volume
Clinical Pearl
FEO may occur in the setting
of a tracheal tumor or foreign
object aspiration or tracheal
stenosis after prolonged
intubation.
8
flow
Expiratory
0
(Liters/sec)
TLC
flow
Inspiratory
-6
N
R
O
N: normal
R: restrictive
O: obstructive
123456
0
Volume
308
DISTURBANCES IN GAS EXCHANGE
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The most important factor in gas exchange is oxygen delivery (Do2) to the vital organs.
Remember, Do2 is not Pao2 (Pao2 is calculated in the arterial blood gases). We can calculate
Do2 from the following equation:
Chapter 9
l Pulmonology
Do2 = Cardiac Output × (1.34 × Hb × HbSat) + 0.0031 × Pao
where Do2 represents oxygen delivery, HbSat is hemoglobin saturation, and Pao2 represents
partial pressure of oxygen in the blood (oxygen dissolved in plasma).
Don’t memorize the above formula, just know the concept.
Notice that the amount of oxygen delivered to the tissues accounted for by the Pa
dissolved in blood) is minimal. The two most important factors in the delivery of oxygen to
the vital organs are the cardiac output and hemoglobin.
In a critically ill patient, it is most important (the next step) to keep the hemoglobin and cardiac output near normal. There will be minimal change in Do2 if you increase the Pao2 from
60 to 100 mm Hg by giving the patient 100% oxygen.
The alveolar–arterial gradient (PAo2–Pao2 gradient) is useful in the assessment of oxygenation and is calculated by the following formula:
PAo2–Pao2 gradient = (150 – 1.25) × Pco2 – Pao
or
A – a = [150 – (1.25 × PaCO2) – PaO2]
2
o
(oxygen
2
2
Know this formula and how to calculate the PAo2–Pao2 gradient.
The above formula is valid only in patients who are breathing room air. This gradient is
5–15 mm Hg in normal young patients. It increases with all causes of hypoxemia except
hypoventilation and high altitude. The gradient also increases with age.
Clinical Problem. Can you think of any clinical condition in which the patient would have severe
hypoxemia but a normal gradient? Hint: You will commonly see this in the emergency room.
CHEST RADIOGRAPHY
Chest radiography is often the initial diagnostic study performed to evaluate patients with
respiratory symptoms. It may also be the initial evidence of pulmonary disease in a patient
without symptoms, e.g., the pulmonary nodule found on an incidental x-ray.
Note
The answer to this
clinical problem can be
found at the end of this
chapter.
309
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