Module 4.0 - Diagnostic Concepts of Oxygenation & Ventilation/Pulmonary Function Testing Flashcards
(38 cards)
1
Q
What is Pulmonary Perfusion?
A
- It is the movement of mixed venous blood through the pulmonary capillary bed for the purpose of gas exchange between the blood and the alveolar bed.
- The pulmonary vascular system is a high volume system with low capillary resistance.
- Lung bases receive a greater percentage of blood flow than do the apices
2
Q
What is the average pulmonary blood flow?
A
about 6 liters/minute
3
Q
What is the normal mean pulmonary arterial pressure?
A
12-16mmHg
4
Q
What is ventilation?
A
- It is the mechanical movement of air into and out of the alveoli for the purpose of gas exchange between the atmosphere and capillary blood.
- Gas flows from higher atmospheric to lower intrapulmonary pressure during inhalation.
5
Q
What are the two methods by which ventilation is regulated?
A
- Central Nervous System
- Chemical Regulations (PaCO2)
6
Q
Describe the CNS regulation of ventilation
A
- The brain stem centers (medulla and pons) cells fire automatically to trigger inhalation, others fire to halt inhalation and exhalation occurs passively.
- The cerebral cortex allows voluntary control to override brain stem centers in response to chemical stimuli and lung inflation changes.
7
Q
Describe the chemical regulation of ventilation
A
-
Central chemoreceptors in medulla respond to increased partial pressure of carbon dioxide in arterial blood (PaCO2), hypercapnia, and acidosis through medullary stimuli by increasing ventilator depth and rate.
- ↑PaCO2 = AUTOMATIC ↑ depth & rate of ventilations
- Hypercapnia is the major stimulus to alter ventilation. Peripheral chemoreceptors in aortic and carotid bodies respond to decreased PaO2 by stimulating medullary centers to enhance ventilation.
8
Q
What happens to patients with chronically high PaCO2’s?
A
- In these patient’s the hypercapnic ventilatory drive is lost: these patients respond only to changes in PaO2 by stimulation of peripheral receptors to adjust their ventilation.
- Supplemental oxygen should be given carefully to prevent apnea (begin with 1-2 L/minute and assess patient carefully.
- DO NOT withhold oxygen, mechanical ventilation is a backup).
9
Q
What is oxygenation and what are 2 factors that can affect oxygenation?
A
- Oxygenation = Is a measure of the amount of oxygen in the blood and the adequacy of the transport of oxygen through the body
-
2 Factors =
- ↓ Hgb = ↓ Oxygenation
- ↓ Cardiac Output = ↓ Oxygenation
10
Q
What is alveolar diffusion?
A
- This is the exchange of O2 and CO2 across the alveolocapillary membrane.
- Oxygen diffuses down the concentration gradient from higher alveolar pressure (PAO2) to lower pulmonary capillary pressure (PaO2).
- CO2 diffuses at a rate 20 times greater than that of O2 from capillary to the alveolus.
11
Q
What is the normal difference between alveolar and arterial oxygen in young adults?
A
Young adults breathing room air: less than 10 mmHg difference
12
Q
What is the normal difference between alveolar and arterial oxygen in adults >60 years old?
A
Adults >60 on room air: less than 20 mmHg difference
13
Q
What is the normal difference between alveolar and arterial oxygen in patients breathing 100% O2?
A
Patients breathing 100% oxygen: less than 50 mmHg difference
14
Q
What does “work of breathing” mean?
A
The amount of effort required to overcome the elastic and resistive properties of the lungs and chest wall.
15
Q
What is elasticity (elastic recoil)?
A
- It is the tendency of the lungs to return to their original shape. Lungs try to collapse because of tension between the interstitial elastic fibers and the surface of the alveoli.
- Chest wall attempts to resist inward-moving recoil
16
Q
What is compliance?
A
- Compliance is a measure of distensibility or how easily the lungs and thorax can be stretched. It describes resistance as a result of elastic properties.
- Increased compliance means less pressure is needed to stretch the lungs and/or thorax.
- You see higher compliance in COPD, lower compliance in pneumonia (PNA) and acute respiratory distress syndrome (ARDS).
17
Q
How is “resistance” determined when referring to the lung?
A
- Resistance is determined by the radius of the airway through which air is flowing.
- Increased resistance means increased effort for ventilation and increased WOB. PaCO2 is the best indicator for alveolar ventilation.
18
Q
Describe how oxygen is transported in the body
A
O2 carried in the blood:
- 3% of O2 is dissolved in plasma = PaO2 is a measure of this, with a normal range of 80-100 mmHg
-
97% of O2 is bound to hemoglobin = SaO2 or oxygen saturation measures this, with a normal range of 95%-100%.
- O2 that stays bound to Hgb is useless to body cells
- If Hgb decreases, the patient may not be adequately oxygenated
- PaO2 and SaO2 are indirect measurements of O2 available to the tissues
19
Q
What is “affinity” mean as it relates to Hgb & O2?
A
- Affinity is the ability of Hgb to release O2.
- Weak affinity: easily releases O2 to tissues
- Strong affinity: easily accepts and retains O2
20
Q
How do we determine Hgb’s affinity for O2?
A
- Oxyhemoglobin dissociation curve: demonstrates affinity of Hgb for O2
- Flat part of the curve: binding portion in lungs. Increased affinity, binds easily
- Steep part of curve: dissociation portion at the tissue level. Weaker affinity, Hgb readily dissociates O2
21
Q
What does a shift to the left/right in the oxyhemoglobin dissociation curve mean?
A
- Shift to the left: greater affinity. Increased affinity leads to possible tissue hypoxia due to a strong bond between Hgb and O2
- Shift to the right: decreased affinity
22
Q
What is the purpose of a pulmonary function test (PFT)?
A
Purpose is to determine the status of pulmonary function that may then be used for the following :
- Assign a potential diagnosis
- Differentiate between obstructions of airways and decreased pulmonary parenchymal compliance as the source of symptoms
- Evaluate response to treatment
- It is helpful in determining pre-operative surgical risks
Evaluation of pulmonary function is important in many clinical situations both when the patient has known disease and when there are risk factors, such as occupational exposure to agents that are known to cause harm to healthy lung tissue.
23
Q
What are the 3 indications for conducting a pulmonary function test (PFT)?
A
- Evaluate unexplained dyspnea and cough
- Assess the severity of pulmonary dysfunction
- Determine potential reversibility of airway obstruction
24
Q
What are the 4 limitations associated with PFT’ing?
A
- Patient must be able to cooperate with the testing otherwise the value of the testing is negated.
- The person administering the test must be skilled and the person interpreting the test must be knowledgeable of the PFT interpretation
- The patient should be relatively stable with respect to symptoms.
- Temporary worsening of symptoms may invalidate the severity of the dysfunction assessed.
25
What are the 6 types of PFT's?
1. Spirometry
2. Body plethysmography (volume displacement techniques)
3. Measurement of exhaled nitrous oxide
4. Maximal (inspiratory) respiratory pressures
5. Bronchial provocation testing (challenge)
6. High resolution computed tomography
26
What is Spirometry?
* It is an objective measurement of pulmonary function and for the diagnosis and management of respiratory dysfunction.
* Determines forced vital capacity (FVC) and forced expiratory flow rates.
* Forced expiratory volume in one second (FEV1) is considered the gold standard by which obstructive airway disease is measured.
* **The ratio of FEV1/FVC is diagnostic for obstructive lung disease.**
* The patient’s values are compared with predicted values derived from population-based reference groups.
* **Decreased FEV1/FVC (\< 70% normal) indicates the presence of airflow obstruction or an obstructive disorder**. If this abnormal finding is found, a bronchodilator is given and response to therapy measured. **An increase of 12% or greater is an indication for bronchodilator therapy.** If there is severe obstruction at baseline, bronchodilator therapy may be considered for less than 12% improvement for patient management.
27
What are the benefits of using Spirometry?
* It is the most readily available and useful PFT.
* **It is the key diagnostic test for asthma and COPD.**
* The test takes 10-15 minutes and carries minimal risk to patients.
* Graphic display of inspiration and exhalation (flow volume loops) **provides a comprehensive view of respiratory mechanics.**
* Results correlate with morbidity and life expectancy
28
What is Body plethysmography (volume displacement techniques) used for?
* Useful in determining all lung volumes including vital capacity, residual volume in the chest after expiration and total lung capacity (TLC).
* **It more completely differentiates between restrictive and obstructive disorders**. It is decreased with restrictive disorders, normal or increased with obstructive disorders.
29
When and for what is measured exhaled nitrous oxide used?
* **It is a noninvasive marker of airway inflammation.** It appears to reflect lower airway inflammation which is a hallmark of the asthma disease process.
* It is useful in **recognizing inflammation in symptom-free asthmatic patients who have normal lung function.**
* Helps with titration of inhaled steroid therapy in that steroids quickly reduce exhaled nitrous oxide levels indicating a reduction in airway inflammation
30
What is tested when measuring the diffusing capacity of the lung for carbon monoxide (CO2)?
* This test uses CO as a substitute for O2 to assess the gas transfer function of the lungs.
* Decreased diffusion capacity of carbon monoxide in the lung (DLC) **may indicate disorders of pulmonary parenchyma, vascular problems or decreases in alveolar function as seen in lung resection patients or emphysema.**
* **Increased DLCO may indicate asthma, obesity, polycythemia or cardiac left-to-right shunting.**
* Modified techniques to measure DLCO must be used for patients with end stage heart disease or after heart transplant.
31
What is Maximal (inspiratory) respiratory pressures used for?
Helps in the **diagnosis of neuromuscular etiologies of respiratory dysfunction** and in the prognosis of neuromuscular dysfunction:
* **Decreased inspiratory and expiratory pressures** indicate **generalized neuromuscular diseases such as amyotrophic lateral sclerosis**
* **Decreased inspiratory pressures** suggest **dysfunction of the diaphragm**
* **Decreased expiratory pressures are often seen with spinal cord injuries**
32
When is Bronchial provocation testing (challenge) used?
* Aids in **diagnosing** **asthma**, is useful spirometry is normal and cough is unexplained
* Involves the inhalation of methacholine, histamine or other chemical stimulants to induce bronchial smooth muscle constriction.
* **Constriction occurs in asthmatic patients at much lower doses than non-asthmatic patients. _95% accurate._**
33
When is High resolution computed tomography used?
* Used to assesses specific airways and their function.
* May show lesions missed on plain x-ray.
34
What is seen with spirometry with obstructive ventilatory defects?
* Flow rates are reduced
* Lung volumes are within normal range because of air trapping and hyperventilation.
35
What is seen with spirometry with restrictive ventilatory defects?
* Flow rates are normal or increased
* Lung volumes are proportionately reduced
36
How do you determine the severity of defects (lung volumes and flow rates) with spirometry?
* Values **greater than 70% of predicted volumes/flow rates are considered within normal limits**
* **60-70% =** mildly reduced
* **50-60% =** moderately reduced
* **Less than 50% =** severely reduced
* Air trapping and hyperinflation = residual volume and TLC exceed 120% of predicted value
37
How is a Peak expiratory flowmeter used in the management of asthma?
Ideally, patients will measure their peak expiratory flow rate (PEFR) daily and record. This measures the functional airflow limitation. Evaluation of readings can guide management and the potential need for additional medication.
* **PEFR 80-100% of baseline –** Green zone, no change in therapy needed
* **PEFR 50-80% of baseline –** Yellow zone, temporary increase in the intensity of therapy or additional therapy should be considered
* **PEFR below 50% of baseline –** Red zone, urgent/emergency care is advised
38
What are the implications of spirometry readings with geriatric patients?
* Many older adults experience **changes in elastic recoil and MSK changes of the chest wall** - extra time is needed when performing lung function test on this age group
* **Total lung capacity usually remains constant but vital capacity decreases because of residual volume increases**
* Tidal volume may be decreased
* Alveoli collapse more easily
* Number of cilia diminish
* There is a decrease in the cough reflex
