00:00
So the subject of this lecture are respiratory
physiology disorders. What we're going to
talk about in this lecture is type I and type
II respiratory failure, the differences between
them and how they should be treated. A little
bit about respiratory acid-based disorders,
and then we are going to move on to talk about
a specific cause of type I respiratory failure,
the acute respiratory distressed syndrome,ARDS
and also type II, causes of type II respiratory
failure which affect lung ventilation but
actually the lungs are normal and that's mainly
obstructive sleep apnea with some discussion
of obesity hypoventilation and chest wall
and muscle disease. An important point is
that ventilatory diseases,
which cause chronic respiratory failure, are
usually worse at night with worse physiological
parameters overnight and first thing in the
morning. Right, so type I respiratory failure,
this is respiratory failure with hypoxia alone,
normal PaCO2, but a PaO2, which is, less than
8 no matter what the inspired oxygen concentration
is. Now this is often an acute one-off event
but it can also be a complication of chronic
lung diseases.
01:15
What's the treatment? Well it depends on the
cause, somebody comes in with pneumonia and
hypoxia as a consequence of type I respiratory
failure, you clearly treat that pneumonia,
But the discussion that we are going to have
today is really about oxygen, and how we use
oxygen in patients with type I respiratory
failure. And, essentially, the problem is
how to correct the hypoxia, and we can use
as much oxygen as much as it is necessary in
these circumstances.
01:47
In general, we follow a progression of oxygen delivery devices based on the patients needs.
01:52
This progression starts with a nasal cannula,
then progresses to a simple facemask,
then a non-rebreather mask,
then a high-flow nasal cannula,
then non-invasive positive pressure such as CPAP or BiPAP, and finally with intubation.
02:07
And what we're trying to do
is we're trying to aim for saturations above
90%, correct the hypoxia completely but not
only that we would like to make the patient
able to breathe at a comfortable respiratory
rate. Because if they're maintaining a saturation
of 95%, but they're breathing at 40 per minute,
that is not a good situation, that means they're
struggling very hard, they will tire, and it's
quite likely that they will fail to maintain
their oxygenation if they have to keep persisting
with a respiratory rate of 40 per minute.
02:36
So what we do if the patient is remaining
hypoxic or has a very high respiratory rate
despite breathing oxygen from a mask or a
non-rebreathing bag? Well there is a non-invasive
form of ventilatory support the called the
continuous positive airway pressure, CPAC.
02:53
Now, this is a facemask that provides a small
amount of additional pressure on the inhaled
air, oxygen mix, 5 to 15 cm of water, and it
maintains that through the whole respiration,
both inspiration and expiration, and what
this does is actually recruits more alveolar
units that the patient can use during their
respiration. It splints open and recruits
more alveolar units during inspiration and
that allows the inhaled oxygen concentration
to maintain a better arterial oxygen level.
And this is a good treatment for isolated
type I respiratory failure. Somebody presenting
with say for example, community acquired pneumonia
or pulmonary oedema where they have type I
respiratory failure, but no other major organ
damage. If this is not adequate, if this starts
to work, or starts to fail to work, or the
patient becomes tired despite CPAP therapy,
then the next step will be intubation and
artificial ventilation in the intensive
care department.
04:03
So what are the common causes of type I respiratory
failure? Well acutely, pneumonia, pulmonary
aspiration, pulmonary oedema
a large pulmonary embolus and
ARDS which I'll discuss in the later slides.
04:16
Chronically, patients can have type I respiratory
failure due to interstitial lung disease,
if it's severe enough, if they have had chronic
pulmonary emboli leading to significant pulmonary
artery damage, then they'll have type I respiratory
failure, as will patients with severe pulmonary
hypertension.
04:33
And the phenotype of COPD that tends to get type I respiratory
failure are those of the emphysematous
pink puffer type phenotype.