respiratory failure - doctor 2016 - ju medicine...respiratory failure and dyspnea are not synonymous...
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RESPIRATORY FAILURE
Nathir Obeidat
University of Jordan
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Definitions
Hypoxemia is reduction in the oxygen
content in the arterial system.
Tissue hypoxia is reduction in the oxygen
delivery to the tissue, caused by reduction
oxygen content and or reduction in cardiac
output.
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Respiratory Failure
TypesType 1 Hypoxemic Respiratory failure
Type 2 Hypercapnic Respiratory failure
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Respiratory failure
Is failure to maintain adequate arterial blood
gas tensions.
1- PaO2 <60 mm Hg
2- PaCO2 >50 mm Hg
Assume 1) breathing room air
2) awake and at rest
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Classification:
1) Lung Failure
2) Pump Failure
3) Defects of respiratory control
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Lung Failure
Hypoxemic respiratory failure due to lung
pathology.
- Affects gas transfer and ventilation /perfusion
relationships.
- Refractory arterial hypoxemia despite O2 therapy.
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2) Respiratory pump failure :
• Is hypercapnic respiratory failure.
• Affects the respiratory pump.
• PCO2 > 50 mm Hg
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3) Defects of respiratory control
- Affects
. Regulation of gas exchange.
. The respiratory pump.
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Pathophysiology of ARF
Mechanisms which cause acute Hypoxemic
respiratory failure
1) Hypoventilation
2) Ventilation/Perfusion mismatch
3) Shunt
4) Diffusion limitation
5) Low FiO2
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BLOOD GAS MEASURMENTS
- Only became available in 1950s
- respiratory failure can only be reliably
diagnosed by measuring arterial blood
gases.
Respiratory failure and dyspnea are not
synonymous .There may be no symptoms
with ARF, or the reverse is true
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Indirect measurment of gas Tension
Oximetry :
Direct measurement of the arterial oxygen saturation from arterialised blood in ear lobe or finger.
The Technique based on differential absorption of red and infra red light by haemoglobin molecule
- Measure only saturation , not partial pressure
- Useful in ICU, Sleep labs and ER.
- Less sensitive in range 94-100%.
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Alveolar Hypoventilation
Causes
1- Neuromuscular diseases
2- Neurological diseases
3- Diseases of respiratory control
4- Drug overdose
5- Sleep apnea
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Continue …Alveolar hypoventilation
Characteristics
• Hypercapnia
• Respiratory acidosis
• PaCO2 = (VCO2/AV) .K
- Associated with hypoxemia due to reduced
PAO2
- If hypoventilation is the only cause for
hypoxia then the PA-a O2 gradient will be
normal (5-15 mmHg)
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What is PA-aO2
• PA-aO2 = PA O2 –PaO2
• PaO2 is taken from ABGs
• PA O2 = FiO2(atmosph pressure –H2O pressure) – PaCO2/k
Room Air FiO2= o.21
Atmosph Pressure = 760 at sea level
680 at JUH.
Water Pressure = 47
PaCO2= is taken from ABG
K is constant value = 0.8
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Ventilation Perfusion mismatch
Characteristics- It is the major mechanism of hypoxia by which lung disease
causes hypoxemia.
- PaCO2 either normal or increased.
- A-a gradient is increased.
- Hypoxia is caused by under ventilated alveoli with respect to their blood flow.
- Within a lung region : decrease PAO2 and increased PACO2 always occurs.
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- Good areas cannot compensate for bad
areas of V/Q mismatch.
- Hypoxemia usually corrected by relatively
small increase in FiO2.
This is because hypoventilated airways are
open and alveolar O2 can be increased
SO Increased PAO2 lead to increased PaO2
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Why in some case PaCO2 is
normal?Because of hyperventilation in other
normal lung region.
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Diseases causes V/Q mismatch
Air Way Diseases
Bronchial Asthma,
COPD,
Bronchiectasis,
Bronchiolitis Obliterans.
Intestitial Lung diseases
Pulmonary embolism
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SHUNT
• It is an extreme of V/Q mismatch
• No ventilation but blood flow continues,
so venous blood reaches arterial
circulation without being oxygenated.
• It causes high A-a gradient
• PaCO2 low because of hyperventilation of
normal well perfused areas.
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- Small increase in FiO2 have no effect on PaO2
- It needs very high FiO2 to improve PaO2
- Usually associated with :
-cardiac shunt
- collapsed or fluid filled the alveoli
- CXR usually shows pulmonary infiltrate.
- PEEP may improves PaO2 by
- opening collapsed lung units
- keeping lung units at higher lung volume and allowing some ventilation
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Diagnosis Of Acute Respiratory Failure
1- Clinical Suspicion that ARF might be
present
2- Confirmation by ABG analysis that ARF is
present.
3- Diagnostic steps to identify specific
etiology of ARF
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Clinical suspicion:
Pre-existing chronic respiratory disease
Acute illness with high incidence of ARF
Symptoms of disease process
- any respiratory symptoms
- Hypoxaemia :cyanosis
Signs : tachypnea, use of accessory
muscles
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Signs of hypoxaemia and acidosis
CNS signs
anxiety,restlessness,confusion,seizures,
coma and cerebral edema
Confirmatiomn CXR ,ABG
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Signs of Hypercapnia
Tachycardia .
Asterixis.
Distension of forearm veins.
Clouding of consciousness.
Pupil edema.
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PRINCIPLES OF MANAGEMENT
1) Maintain an adequate Airway
2) Correct inadequate oxygenation
3) Correct Respiratory acidosis
4) Maintain Cardiac output and Tissue 02
Delivery
5)Treate underlying condition by definitive management .
6) Avoid preventable complications
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Correction of Oxygenation
Goal Of Therapy
Improve PaO2 while avoiding O2 toxicity
In COPD aim for PaO2 60 mmHg or O2 sat
of 90%
In trauma aim for PaO2 80mmHg
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OXYGEN TOXICITY
In COPD, excess O2 may cause:
increase hypercapnia and hypercapnic
acidosis
Parenchymal lung injury due to high levels of o2 ,
it is related to dose and duration
So keep FiO2 to lowest level that achieves
adequate PaO2
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Supplemental O2
Delivery Methods
If slight increase in PaO2 is required
- Nasl canula
- Venturi mask (0.24, 0.28, 0.31,
0.35, 0.40, 0.50)
Always check with repeat ABG
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Measures to Correct Respiratory
Acidosis
GOAL
- Avert life threatening acidosis
- Not to correct PaCO2
- Partial correction usually suffices
PHARMACOLOGY THERAPY
- Bicarbonate administration may lead to
metabolic alkalosis
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MECHANICAL VENTILATION
Non Invasive Ventilation
Non-invasive ventilation refers to the ability
to deliver ventilatory support without
establishing an endotracheal airway.
CPAP
BiPAP
Invasive Ventilation
Needs intubation
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Treatment of Under lying Disease
Bronchodilatation
Removal of Secreations
Antibiotics .