RESPIRATORY FAILURE
DR. Mohamed Seyam PhD. PT.
Assistant Professor of Physical Therapy
RESPIRATORY FAILURE
Failure of the respiratory system to provide adequate gas
exchange for metabolic requirements is known as
respiratory failure (RF). This is divided into the following:
I. Type I Respiratory Failure
II. Type II Respiratory Failure
RESPIRATORY FAILURE
The process of respiration includes more than gas exchange in
the lung, but the term respiratory failure is reserved for disorders
that result in a disturbance of arterial blood gases only.
Respiratory insufficiency occurs when adequate gas exchange is
maintained but at great cost to the breathing mechanism. It is
sometimes a sign of impending respiratory failure
ventilation/perfusion ratio (or V/Q ratio)
The ventilation/perfusion ratio (or V/Q ratio) is a measurement used to
assess the efficiency and adequacy of the matching of two variables:
"V" – ventilation – the air that reaches the alveoli
"Q" – perfusion – the blood that reaches the alveoli
VQ Ratio can defined as: the ratio of the amount of air reaching the alveoli
to the amount of blood reaching the alveoli.
These two variables, V & Q, constitute the main determinants of the blood
oxygen (O2) and carbon dioxide (CO2) concentration.
The V/Q ratio can be measured with a ventilation/perfusion scan.
Extreme alterations of V/Q
An area with perfusion but no ventilation (and thus a V/Q of
zero) is termed "shunt."
An area with ventilation but no perfusion (and thus a V/Q
undefined though approaching infinity) is termed dead
Pathophysiology
A lower V/Q ratio impairs pulmonary gas exchange and is a cause of low
arterial partial pressure of oxygen (paO2).
Excretion of carbon dioxide is also impaired, but a rise in the arterial
partial pressure of carbon dioxide (paCO2) is very uncommon because this
leads to respiratory stimulation and the resultant increase in alveolar
ventilation returns paCO2 to within the normal range.
These abnormal phenomena are usually seen in:
chronic bronchitis, asthma, hepatopulmonary syndrome, and acute
pulmonary edema.
A high V/Q ratio decreases PACO2 and increases PAO2.
This finding is typically associated with pulmonary embolism
(where blood circulation is impaired by an embolus).
Ventilation is wasted, as it fails to oxygenate any blood.
A high V/Q can also be observed in emphysema as a maladaptive
ventilatory overwork of the undamaged lung parenchyma.
Arterial pO2 will decrease as a result due to lack of reoxygenation.
Classification of Respiratory Failure
Type I
Type II
Type I Respiratory Failure
RESPIRATORY FAILURE Type I (hypoxemic) is
failed oxygenation, represented by Pa02 below 60 mmHg.
It is caused by failure of the gas exchanging function of the
respiratory system.
It can be acute (e.g. pneumonia) or
chronic (e.g. pink puffer type of COPD).
Type II Respiratory Failure
Respiratory failure type II (hypercapnic) is
failed ventilation, represented by PaC02 over 45 mmHg and hypoxemia.
It is caused by
1. failure of the respiratory pump
2. can be acute (e.g. severe acute asthma)
3. chronic (severe restrictive disease).
Type II RF is also known as ventilatory failure.
It is a clinical manifestation of impaired central respiratory control, muscle
weakness or fatigue, reflected by respiratory muscle strength falling below
30% of normal.