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`Hypoxia, Cyanosis, Dyspnea
Dr. R. Zotomayor November 10, 2010
HYPOXIA Signs and Symptoms of Acute Hypoxia
MAIN FUNCTION OF RESPIRATORY SYSTEM: Respiratory: Tachypnea, breathlessness,
Obtain oxygen from external environment & dyspnea, cyanosis
supply it to cells Cardiovascular: Increased cardiac output,
Remove from the body the carbon dioxide
palpitations, tachycardia, arrhythmias,
produced by cellular metabolism
The main function of the respiratory system hypotension, angina, vasodilatation, diaphoresis,
is the exchange of oxygen from the and shock
atmosphere for carbon dioxide produced by Central nervous: Headache, impaired judgment,
the cells of the body. inappropriate behavior, confusion, euphoria,
Other functions for the respiratory system delirium, restlessness, papilledema, seizures,
include participation in the acid-base balance obtundation, coma
of the body, phonation, pulmonary defense, Neuromuscular: Weakness, tremor, asterixis,
and metabolism. hyper-reflexia, incoordination
An abnormality in chain of gas and/or Metabolic: Sodium and water retention, lactic
blood flow results in impaired acidosis
oxygenation/ventilation
Severe Hypoxia
decrease ATP
cell membrane depolarization
Ca2+ influx
activation of Ca2+ dependent phospholipase and
protease
cell swelling
cell necrosis
EFFECTS:
Systemic Arterioles
Hypoxia ↓ ATP opening of K channels in vascular
smooth ms cells systemic arterioles dilate
Pulmonary Arterioles
Hypoxia dec ATP inhibition of K channels
depolarization activation of voltage gated channels
inc cytosolic Ca2+ pulmonary vasculature smooth ms
HYPOXIA cell contraction pulmonary arterial constriction
blood shunts toward better ventilated portions of the
Reduction in oxygen level lungs
↓ O2 availability to cells/ tissues results in CNS
inhibition of the respiratory chain and Hypoxia causes: impaired judgment, motor in-
↑anaerobic glycolysis coordination, clinical picture resembling acute alcoholism
Pasteur’s Effect – switch from aerobic to High altitude illness – cerebral vasodilation HA,
anaerobic metabolism w/c results into dec ATP dizziness, fatigue, insomnia, GI sx, somnolence
production (drop in O2 level)
NON-PULMONARY HYPOXIA
Respiratory: tachypnea
Vascular: compensatory mechanism inc SV, inc CO,
Respiratory Hypoxia:
inc HR, vasodilatation, diaphoresis,papiledema,
- most common cause is ventilation-perfusion
hypocapnia in the brain
mismatch (V/Q mismatch) resulting perfusion of
Neuro: weakness, tremor, hypereflexia,
poorly ventilated alveoli
Metabolic: Na and H2O retention
- may also be caused by hypoventilation associated
with an elevation of PaCO2
- may also be caused by shunting of blood across
the lung from the pulmonary arterial to the
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venous bed (intrapulmonary R-L shunting) by CAUSES OF HYPOXEMIA:
perfusion of non-ventilated portions of the lung
dec PaO2 1. HYPOVENTILATION
o The volume of fresh gas going to the
O2 alveoli per unit time (alveolar
Alveolar Ventilation = --------- ventilation) is reduced.
CO2 o If the resting oxygen consumption is
not correspondingly reduced,
hypoxemia inevitably result.
o Commonly caused by diseases outside
the lungs; very often the lungs are
normal.
- Hypoventilation always causes a rise in PC02
o Relationship between arterial PC02
and level of alveolar ventilation
PC02 = VCO2 + K
VA
o VC02 = CO2 output
o VA = alveolar ventilation
Figure: Gas exchange o K = constant
-
Hypoxia secondary to High Altitude If alveolar ventilation is halved, the PC02 is doubled.
- as one ascends to 3000m, the reduction of the O2
content of inspired air leads to a dec in alveolar Disorders where hypoventilation can be seen:
PO2 to about 60mmHg (High Altitude Illness) o Sleep apnea
Central sleep apnea
Hypoxia secondary to R-L extrapulmonary Obstructive sleep apnea
shunting o Sudden infant Death Syndrome
- caused by congenital cardiac malformation
(Tetralogy of Fallot, transposition of great
vessels) CAUSES OF HYPOVENTILATION:
Anemia Hypoxia Depression of the respiratory center by drugs
- ↓ Hb dec O2 carrying capacity dec O2 Barbiturates, morphine derivatives
transported to the tissues hypoxia Diseases of the medulla
Encephalitis, hemorrhage, neoplasm
Carbon Monoxide Intoxication Abnormalities of the spinal cord
- Carboxy Hb is unavailable for O2 transport dec Following dislocation
O2 transported to tissues hypoxia
Anterior horn cell disease
poliomyelitis
Circulatory Hypoxia
- venous and tissue PO2 values are reduced as a Diseases of the nerves to the respiratory
consequence of reduced tissue perfusion and muscles
greater tissue extraction Guillain-Barre Syndrome
ex. Strangulating one another. Diseases of the myoneural junction
Mechanism: compressing blood vessels both Myasthenia gravis or
artery and vein, no circulation occurs anticholinesterase poisoning
Diseases of the respiratory muscles
Specific Organ Hypoxia Progressive muscular dystrophy
- Atherosclerosis arterial obstruction dec Thoracic cage abnormalities
perfusion hypoxia
Crushed chest
- Raynaud’s disease vasoconstriction dec
Upper airway obstruction
perfusion hypoxia
Tracheal compression
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2. DIFFUSION IMPAIRMENT CAUSES OF VQ ABNORMALITIES:
o Means that equilibrium is not reached - Low compliance (pulmonary fibrosis, lack of
between the P02 in the pulmonary surfactant)
capillary blood and alveolar gas - High airway resistance (asthma, COPD)
- Extrinsic Compression of Alveoli
(Compression atelectasis due to hydrothorax
or pneumothorax)
Other causes:
- venous obstruction
- expansion of interstitial fluid / edema arterial
compression dec perfusion hypoxia
- ↓ cardiac output & Hypovolemic shock
compensatory mechanism: vasoconstriction
dec perfusion hypoxia
- ↑ O2 requirements
- ↑ metabolic rate
- ↑ O2 consumption w/o inc in perfusion
hypoxia e.g. fever, thyrotoxicosis, exercise
Changes in P02 along the Pulmonary Capillary - Improper O2 utilization
- Cyanides and other poisons bind to tissues
3. SHUNT
making them unable to utilize O2
o Means that some blood reaches the
arterial system without passing MIXED CAUSES OF HYPOXEMIA:
through ventilated regions of the Frequently occurs
lungs. Often impossible to accurately define the
o Pulmonary mechanism of hypoxemia
Intrapulmonary shunts like AV
Oxygen delivery to tissues
malformations
Oxygen carrying capacity of the blood
Consolidated Pneumonia
Cardiac output
where the area is perfused but
Distribution of blood flow to the
unventilated.
periphery
ARDS
o Extrapulmonary
Congenital heart Diseases
(ASD/VSD/PDA)
4. VENTILATION- PERFUSION INEQUALITY
o Ventilation and blood flow are
mismatched in various regions of the
lung resulting to inefficient gas
transfer
o Very common
o Responsible for most of the
hypoxemia of COPD, interstitial lung
disease and vascular disorders like
pulmonary embolism
o Usually identified after the other 3
causes of hypoxemia are excluded.
ADAPTATION TO HYPOXIA:
o All lungs have VQ inequality
o Normal upright lung: regional pattern
1. Hypoxia stimulation of chemoreceptors in the
with VQ ratio decreasing from apex to carotid and aortic bodies and in the medulla
base ↑ventilation loss of CO2 may lead to respiratory
o Factors that can exaggerate the alkalosis
hypoxemia of VQ inequality
o Concomitant hypoventilation 2. Hypoxia ↓PaO2 dec cerebrovascular resistance
o Reduction in cardiac output cerebral blood flow ↑ O2 delivery to the brain is
maintained
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Dyspnea
3. Hypoxia ↑erythropoietin ↑erythropoiesis - sensation of breathlessness or inadequate
↑RBC/polycythemia ↑Hb breathing is the most common complaint of
patients with cardiopulmonary diseases.
ASSESMENT OF SEVERITY: Evaluation of the complaint is complicated by
• Arterial P02 can be used but may be the fact that in many circumstances,
misleading shortness of breath is a normal consequence
• Alveolar-arterial difference for P02 of exertion. Furthermore, perception of
• PA02 = PI02 – PaC02 + F shortness of breath varies considerably
among individuals at the same level of fitness
R
and work and even in the same individual
performing comparable work at different
ALVEOLAR GAS EQUATION: times. In disease states, perception of
PAO2 = (PIO2) – (PaCO2/R) dyspnea can vary greatly among individuals.
PIO2 = (Barometric pressure-Water vapor pressure) x
FIO2 According to ATS/ERS 2000, Dyspnea is
Thus: • Breathing discomfort
In a normal individual breathing room air: • Qualitatively distinct sensations
PAO2 = (760 – 47) x 0.21 – 40/0.8 • Physiologic, psychological, social & environmental
= 150 – 50 factors
= 100 • Induce secondary physiological & behavioral
changes
A-a O2 gradient ROOTWORDS = Greek
o difference between alveolar and • Dys – painful, difficult
arterial PO2 • Pneuma – breath
o result of imperfect diffusion, low V/Q
areas at the lung bases, and MECHANISM OF DYSPNEA
physiological shunts
Normal A-aO2 gradient < 20 mmHg
A-a Gradient: PAO2 – PO2
N Less than 15 mmHg ≤ 30
Age ***
Inc ≈ 3 mmHg per decade
DYSPNEA
• Unpleasant awareness of breathing
• Subjective
• Commonly accompanies cardiac or
bronchopulmonary diseases
• May accompany anxiety
• Labored
• Sensation of dyspnea is often poorly or vaguely
described by patient.
• Most common complaint of patients with
cardiopulmonary diseases.
• Evaluation of the complaint is complicated by the
fact that in many circumstances, shortness of
breath is a normal consequence of exertion.
• Perception of shortness of breath varies
considerably among individuals at the same level of
fitness and work and even in the same individual
performing comparable work at different times.
• In disease states, perception of dyspnea can vary
greatly among individuals.
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DIFFERENTIAL DIAGNOSIS
DIFFERENTIATE RESPIRATORY VS. CARDIAC PULMONARY EDEMA
RESPIRATORY CARDIO
Usually more
gradual in onset Nocturnal
History
Nocturnal exacerbations
exacerbations
Usually obvious evidence of cardiac or
pulmonary disease. Findings may be
Examinations
absent at rest when symptoms are present
only at exertion
Rarely causes
dyspnea unless tests
of obstructive
disease (FEV1,
Pulmonary
FEV1/FVC) or
function test
restrictive disease
(total lung capacity)
are reduced (<80%
predicted).
LV ejection fraction
at rest and/or
Ventricular
during exercise
performance
usually depressed in
cardiac dyspnea.
TIME COURSE: DEVELOPMENT OF BREATHLESSNESS
POSSIBLE MECHANISMS OF DYSPNEA Pneumothorax
o
Condition Mechanism Immediate Pulmonary edema 2 to cardiac arrhythmia
Inc sense of effort Inhalation of foreign body
Asthma Stimulation of irritant receptors in Left heart failure
airways Asthma
Hours
Pneumonia
Neuromuscular
Inc sense of effort Laryngeal edema
Disc
Pneumonia
Hypoxia, Hypercapnia, Dynamic
COPD Days ARDS
Airway Compression
Left heart failure
Afferent Mismatch
Mechanical Pleural effusion
Factors Assoc with the underlying Weeks Anemia
Ventilation
condition Muscle weakness
Pulmonary Stimulation of pressure receptors in Tumors
Embolism pulmonary vasculature of R. Atrium Pulmonary fibrosis
Months
Thyrotoxicosis
Muscle weakness
Muscle weakness
Years COPD
Chest wall disorders
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DIFFERENTIATION BETWEEN CARDIAC AND - Decreased Cardiac Output
PULMONARY DYSPNEA - Elevated Pulmonary Venous Pressure
1. Careful history: Dyspnea of lung disease usually - Right to Left Shunt
more gradual in onset than that of heart disease; MISCELLANEOUS
nocturnal exacerbations common with each. Pink - Anemia
frothy sputum- Congestive Heart Failure; relief - Anxiety/Psychological
after coughing up thick sputum- COPD - Deconditioning
2. Examination: Usually obvious evidence of cardiac
or pulmonary disease. Findings may be absent at CYANOSIS
rest when symptoms are present only at exertion.
3. Pulmonary function tests: Pulmonary disease
Bluish color of skin/mucous membranes due to
rarely causes dyspnea unless tests of obstructive
increased amount of reduced hemoglobin
disease (FEV1, FEV1/FVC) or restrictive disease
(total lung capacity) are reduced (<80% Detected when O saturation is:
predicted). o <85% - white-skinned
4. Ventricular performance: LV ejection fraction at o <75% -dark-skinned
rest and/or during exercise usually depressed in Reduced Hb > 50 g/L (5 g/dL) – it is the absolute
cardiac dyspnea. rather than the relative quantity of reduced hb
which is important in producing cyanosis
Causes of ACUTE Dyspnea:
• Anxiety/Hyperventilation Usually most marked in the lips nail beds, ears
• Asthma and malar eminences
• Chest trauma Degree of cyanosis is modified by the quality of
• Pneumothorax cutaneous pigment, thickness of the skin, state of
• Fractured Ribs the cutaneous capillaries.
• Pulmonary Edema
• Pulmonary Embolism Causes of cyanosis
• Spontaneous Pneumothorax A. Central Cyanosis
o arterial disaturation or abnormal Hb
Causes of CHRONIC Dyspnea:
RESPIRATORY o mucous/skin both affected
Airway Disease B. Peripheral Cyanosis
- Upper Airway Obstruction o slow blood flow with greater O2
- Asthma extraction
- Chronic Bronchitis o results from vasoconstriction and
- Emphysema diminished peripheral blood
- Cystic Fibrosis flow/disease.
Parenchymal Lung Disease
- Interstitial Lung Disease
- Malignancy CENTRAL CYANOSIS
- Primary A. Decreased pO2
- Metastatic i. Decreased atmospheric pressure (high altitude)
- Pneumonia ii. Pulmonary disease – common cause of
Pulmonary Vascular Disease central cyanosis
- A-V Malformation a. Alveolar hypoventilation
- Intravascular Obstruction
b. V/Q mismatch diffusion impairment
- Vasculitis
- Veno-occlusive disease c. Impaired O2 diffusion
Pleural Disease iii. Anatomic Shunts
- Effusion a. Congenital Heart Disease
- Fibrosis b. Pulmonary A-V fistulas
- Malignancy
congenital/acquired;
Chest Wall Disease
- Deformities (e.g. Kyphoscoliosis) solitary/multiple;
- Abdominal “Loading”(ascites, pregnancy, microscopic/massive
obesity) c. Multiple small intrapulmonary shunts
Respiratory Muscle Disease most common congenital cardiac lesion
- Neuromuscular Disorder (Myasthenia Gravis, associated with cyanosis in the adult is
Polio) the combination of ventricular septal
- Phrenic Nerve Dysfunction defect and pulmonary outflow tract
- Weakness obstruction
CARDIOVASCULAR
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more severe the obstruction, greater the Problem Acute
Associated
degree of R-L shunting Cough and sputum symptoms and
inflammation
settings
iv. Hb with low O2 affinity Dry cough
B. Hemoglobin Abnormalities (without sputum), Acute, fairly minor
may become illness with
a. Methemoglobinemia - hereditary, acquired Laryngitis productive of hoarseness.
b. Sulfhemoglobinemia - acquired variable amounts Often assoc. With
of sputum viral nasopharyngitis
c. Carboxihemoglobinemia - not true cyanosis
PERIPHERAL CYANOSIS Acute, often viral
Dry cough,
Common etiology: vasoconstriction and Tracheobronchitis may become
illness with burning
decreased peripheral blood flow (cold exposure, retrosternal
productive
discomfort
shock, CHF, peripheral vascular disease)
Dry hacking cough, Acute, febrile illness,
Mucous membranes (oral cavity and beneath Mycoplasma and often becoming often with malaise,
tongue) are spared viral pneumonia productive of headache, and
mucoid sputum possibly dyspnea
1. Decreased cardiac output Pneumococcal:
2. Cold exposure sputum mucoid Pneumococcal:
3. Blood flow redistribution from extremities or purulent; Acute illness with
may be blood- chills, high fever,
4. Arterial obstruction streaked, dyspnea and chest
5. Venous obstruction Bacterial pneumonia diffusely pinkish, or pain; Often preceded
rusty by acute URTI
Klebsiella: similar; Klebsiella: occurs in
APPROACH TO PATIENTS WITH CYANOSIS or sticky red, and older alcoholic men,
jellylike typically
1. HISTORY
duration (congenital heart disease) Repeated attempts to
exposure to drugs/chemicals clear the throat.
2. DIFFERENTIATE CENTRAL VS PERIPHERAL Postnasal discharge
CYANOSIS Chronic cough; sputum may be sensed by
Postnasal drip mucoid or patient or seen in
Use of lab tests, chest x-ray (heart and lung mucopurulent posterior pharynx.
diseases) Associated with
Response of extremities to warming chronic rhinitis, with or
3. PRESENCE OR ABSENCE OF CLUBBING OF without sinusitis
FINGERS (bulbous soft tissues enlargement) Often long-standing
cigarette smoking.
(+) may indicate heart and/or lung Chronic cough; sputum
Recurrent
disease; chronic mucoid to purulent,
Chronic Bronchitis superimposed
(+) not found in peripheral and acute maybe blood-streaked
infections. Wheezing
central type of cyanosis or even bloody
and dyspnea may
o Clubbing w/o cyanosis – ineffective develop
endocarditis, ulcerative colitis Chronic cough; sputum
Recurrent
o Slight cyanosis – lips, cheeks – (-)clubbing purulent, often
bronchopulmonary
of fingers – common in px with mitral copious and foul-
Bronchiectasis infections common;
stenosis smelling; may be
sinusitis may coexist.
blood-streaked or
o Combination of clubbing and cyanosis – bloody
congenital cardiac disease, pulmonary
Cough dry or sputum Early, no symptoms.
disease
that is mucoid or Later, anorexia, weight
o Peripheral cyanosis is not associated with Pulmonary
purulent; may be loss, fatigue, fever, and
clubbed fingers Tuberculosis
blood streaked or night sweats
4. ABG’s DETERMINATION bloody
o spectroscopic and other examinations for Sputum purulent and A febrile illness. Often
abnormal hemoglobin Lung abscess
foul-smelling; may be poor dental hygiene
bloody and a prior episode of
impaired consciousness
Cough, with thick
Episodic wheezing and
mucoid sputum,
dyspnea, but cough
Asthma especially near end of
may occur alone. Often
an attack
a history of allergy
7 of 8 |Page
Associated
Problem Cough and sputum symptoms and Clinical Questions
settings
1. A 16 Y/O female complains of difficulty of breathing
Cough dry to Usually a long
Neoplasm productive; sputum history of cigarette after an argument with her mother. She was previously
Cancer of the Lung may be blood- smoking. Associated well, active member of the volleyball team. She describes
streaked or bloody manifesta tions are a heavy compressive pain at the center of the chest. PE is
numerous.
unremarkable, with occasional sighing breaths. The most
Often dry, likely condition to explain her symptoms is:
Cardiovascular especially on
Dyspnea,
Disorders exertion or at night;
orthopnea,
Left Ventricular may progress to the A. angina C. asthma
paroxysmal
Failure or Mitral pink frothy sputum B. anxiety D. pulmonary embolism
nocturnal dyspnea
Stenosis of pulmonary edema
or to frank
hemoptysis 2. A 60 y/o, heavy smoker male complains of progressive
Dry to produc tive; Dyspnea, anxiety, difficulty of breathing of 4 months duration associated
Pulmo Emboli
may be dark, bright chest pain, fever; with occasional dry cough. There is no chest pain nor
red, or mixed with factors that predis fever. The chest is resonant with distant breath sounds
blood pose to deep venous
and occasional rhonchi /wheezing. He most likely has:
thrombosis
Exposure to
Variable. There may A. chronic bronchitis C. asthma
Irritating Particles, irritants. Eyes, nose,
be a latent period
Chemicals, or Gases and throat may be B. emphysema D. coronary disease
between exposure
affected.
and symptoms
3. A 65 y/o, ex- heavy smoker is seen at the ER because of
Wheezing, especially
at night (often difficulty of breathing of 2 months duration associated
mistaken for with cough and recent onset of bloody sputum. There is a
Chronic cough, asthma), early 20-lbs weight loss in the past 6 months but denies fever.
Gastroesophageal especially at night or morning hoarseness,
On examination, there is a persistent rhonchi over the
reflux early in the morning and repeated
attempts to clear the
right-mid lung. The condition that needs to be strongly
throat. Often a considered is:
history of heartburn
and regurgitation
A. chronic bronchitis C. asthma
B. lung cancer D. tuberculosis
Patient
History ABG
Physical Examination CBC
Exclude Anemia
Chest X ray
Inapparent Pulmonary
Disease or possible Obvious Pulmonary Dx
Heart disease
Exclude Infx, Neoplasm
ECHOCARDIOGRAPHY
Normal
AbNormal
Pulmonary Function Test
Diffusing Capacity
Work Up
Cardial Dx 8 of 8 |Page
