Life With ALS.com
+ Diagnosed Aug 2005
+ Bipap March 2007
+ PEG July 2007
+ Trache and Vent July 2008
Still Living, Loving & Laughing
You might find the following information helpful:
Patients with neuromuscular diseases
who are developing progressive respiratory failure due to respiratory muscle weakness
will die unless mechanical ventilation is used. The rate of progression is often
hard to predict. Some patients seem suddenly to experience life-threatening hypercapnic
respiratory failure. They may not have been aware of gradually increasing symptoms
and signs, particularly since they are often not physically active and are often
not being regularly monitored with simple pulmonary function tests.
Administering
oxygen does not provide assistance to the weakening respiratory muscles, but gives
both the patient and the doctor the false impression that appropriate treatment is
being provided. While in fact hypoventilation is mistaken for an oxygen transfer
problem. Indeed, administering oxygen can mask the problem. Also there is a danger
of causing respiratory depression by giving oxygen (see reference to the article
by Dr. Peter Gay - Mayo Clinic - below). Oxygen is NOT the treatment for hypoventilation.
It will improve the SaO2, but not the hypoventilation and may increase the danger
of dying of sudden respiratory failure.
In hypercapnic respiratory failure due to
hypoventilation, the SaO2 falls due to the rise of the CO2. The alveoli in the lungs
(tiny gas exchange units) should clear most of the CO2 out with each breath. Instead,
with hypoventilation, CO2 accumulates and thus there is decreased room in the alveoli
for oxygen. When mechanical ventilation using room air is provided, it lowers the
CO2 in the alveoli, corrects the SaO2, and rests the respiratory muscles. The ventilator
should be adjusted to achieve a normal SaO2, on room air. If oxygen is being administered,
one cannot use noninvasive oximetry to tell whether enough assisted ventilation is
being provided; repeated arterial blood gas specimens (ABGs) would be needed.
When
there is respiratory failure in neuromuscular patients (ALS, post-polio, SMA, muscular
dystrophy, etc.) who have no additional pulmonary disease that impairs oxygen transfer,
the ventilator set-up is adjusted to:
be comfortable for the patient;
achieve SaO2
of 95% or higher on room air (this can be measured with a finger-sensor oximeter);
assist
the patient to effectively cough and clear secretions;
provide improved oral communication
(if vocal communication is possible).
It has been common for people using noninvasive
nasal ventilation (NPPV) with a bi-level positive pressure unit to use inadequate
settings; frequently, they are not monitored with clinical evaluation and oximetry.
The EPAP is often set too high – usually it should not be higher than 3-4 cm H2O;
the IPAP is set too low – usually it needs to be 12-16 cm H2O and adjusted to achieve
an oxygen saturation of 95% or higher.
Some situations may require administering oxygen
temporarily, such as pneumonia due to infection or aspiration. If this occurs in
patients with respiratory muscle weakness and hypoventilation, then it is important
to provide both assisted ventilation and supple-mental oxygen, and use ABGs to monitor
them.
(The late Dr. Oppenheimer, former head of pulmonary medicine at UCLA, sent me
that article a few years back. He went on to tell me that when PALS are given oxygen
it tricks the brain into thinking the body doesn't need to put forth the effort to
breathe.)
__________________