Introduction
Almost everyone who has a critically ill friend or relative
may expect to hear the term, respiratory failure. Although
failure to breathe normally was recognized even in ancient
times as an ominous sign, the term, "respiratory failure,"
did not appear in the medical literature until the 1960s.
Doctors now understand that respiratory failure is a serious
disorder caused by a variety of different medical problems
that may or may not start in the lung. Healthy people as
well as patients with either pulmonary (lung) or
nonpulmonary diseases can develop respiratory failure.
The recognition of respiratory failure as a life-threatening
problem led to the development of the concept of the
intensive care unit (ICU) in modern hospitals. ICU personnel
and equipment support vital functions to give patients their
best chance for recovery. Today's sophisticated ICU
facilities with their novel mechanical life support devices
evolved as doctors and scientists learned more and more
about the causes of respiratory failure and how to treat it.
This fact book is a brief overview of the unique changes in
lung function that are typical of respiratory failure and
the widely different medical conditions that can cause those
changes. It also discusses the methods that are used to
restore normal respiration and prolong life, and the related
dilemma of deciding if and when to withdraw or withhold life
support from a hopelessly sick patient.
Who Can Get Respiratory Failure
Many different medical conditions can lead to respiratory
failure. Listed below are a few examples of people who may
develop respiratory failure.
- A patient with a long history of asthma, emphysema, or
chronic obstructive lung disease
- A patient who is undergoing major surgery in the abdomen,
heart, or lung
- A person who has taken an overdose of sleeping pills or
certain depressant drugs
- A premature baby who weighs less than 3 pounds
- A baby with bronchopulmonary dysplasia
- A patient suffering from AIDS
- A person who has received multiple physical injuries
- A person who has suffered extensive burns
- A person who has bled extensively from a gunshot wound
- A person who has almost drowned
- A patient with severe heart failure
- A patient with severe infections
- A person who is extremely obese
Breathing and Respiratory Failure
The term, "respiratory failure," is used when the lungs are
unable to perform their basic task - gas exchange. This
process involves transfer of oxygen from inhaled air into
the blood and of carbon dioxide from the blood into the
lungs, with the result that the arterial blood, blood
circulating through the body from the heart, has enough
oxygen to nourish the tissues.
Gas exchange occurs in tiny air sacs in the lung, called
alveoli. When a person breathes in (inspiration), air is
brought into the alveoli by the action of the respiratory
muscles - the diaphragm, the muscles between the ribs, and
the accessory muscles (those between the neck and the chest
wall). These are collectively called "the ventilatory
apparatus." The activity of the respiratory muscles is
controlled by respiratory centers in the brain. The brain's
respiratory centers in turn are controlled by
chemoreceptors, special cells that are sensitive to the
amounts of carbon dioxide or oxygen in the blood. The
chemoreceptors that are sensitive to oxygen concentration
are located in the large arteries in the neck in the carotid
bodies. When they sense a fall in the level of oxygen in the
blood, they send messages that stimulate the respiratory
center in the brain so that there will be an increase in the
rate or depth of breathing.
Whenever any part of the ventilatory apparatus and/or the
respiratory centers fails to work properly, the result can
be respiratory failure. Both adults and babies can develop
respiratory failure. In infants, however, respiratory
failure occurs mostly in premature babies whose lungs have
not yet fully developed.
Transfer of oxygen of inhaled air into the blood and of
waste carbon dioxide of blood into the lungs occurs in the
alveolus.
What Happens During Respiratory Failure
When the process of gas exchange is faulty, there is not
enough oxygen in the blood (hypoxemia) to fuel the body's
metabolic activity. In addition, sometimes there is also an
accumulation of carbon dioxide, a waste product of
metabolism, in the blood and tissues (hypercapnia).
Hypercapnia makes blood more acidic; this condition is
called acidemia. Eventually the body tissues become acidic.
This condition, called acidosis, injures the body's cells
and interferes with the functions of the heart and central
nervous system. Ultimately, lack of oxygen in the blood
causes death of the cells in the brain and other tissues. If
not adequately treated, respiratory failure is fatal.
Hypoxemic Respiratory Failure
When a lung disease causes respiratory failure, gas exchange
is reduced because of changes in ventilation (the exchange
of air between the lungs and the atmosphere), perfusion
(blood flow), or both. Activity of the respiratory muscles
is normal. This type of respiratory failure which results
from a mismatch between ventilation and perfusion is called
hypoxemic respiratory failure. Some of the alveoli get less
fresh air than they need for the amount of blood flow, with
the net result of a fall in oxygen in the blood. These
patients tend to have more difficulty with the transport of
oxygen than with removing carbon dioxide. They often
overbreathe (hyperventilate) to make up for the low oxygen,
and this results in a low CO2 level in the blood
(hypocapnia). Hypocapnia makes the blood more basic or
alkaline which is also injurious to the cells.
If not adequately treated, respiratory failure is fatal.
Hypercapnic Respiratory Failure
Respiratory failure due to a disease of the muscles used for
breathing ("pump or ventilatory apparatus failure") is
called hypercapnic respiratory failure. The lungs of these
patients are normal. This type of respiratory failure occurs
in patients with neuromuscular diseases such as myasthenia
gravis, stroke, cerebral palsy, poliomyelitis, amyotrophic
lateral sclerosis, muscular dystrophy, postoperative
situations limiting ability to take deep breaths, and in
depressant drug overdoses. Each of these disorders involves
a loss or decrease in neuromuscular function, inefficient
breathing and limitation to the flow of air into the lungs.
Blood oxygen falls and the carbon dioxide increases because
fresh air is not brought into the alveoli in needed amounts.
In general, mechanical devices that help move the chest wall
help these patients.
Conditions That May Progress To Respiratory Failure
Almost all lung diseases including asthma, chronic
obstructive pulmonary disease (COPD), AIDS-related
pneumonia, other pneumonias and lung infections, and cystic
fibrosis may eventually lead to respiratory failure
particularly if the diseases are inadequately treated. These
patients find it very hard to breathe and the result is low
oxygen and high carbon dioxide blood levels.
People whose normal lungs have been injured, such as from
exposure to noxious gases, steam, or heat during a fire, can
subsequently go into respiratory failure. Adult respiratory
distress syndrome (ARDS), also referred to as acute
respiratory distress syndrome, is a form of acute
respiratory failure caused by extensive lung injury
following a variety of catastrophic events such as shock,
severe infection, and burns. ARDS can occur in individuals
with or without previous lung disease.
Hyaline membrane disease or respiratory distress syndrome of
the newborn (RDS), the most common respiratory illness
affecting premature babies, is another kind of respiratory
failure. In this condition, the baby's lungs do not have
enough surfactant, a substance that makes it possible for
air to pass into the alveoli by lowering surface tension and
preventing their collapse.
Symptoms Of Respiratory Failure
The clinical features of respiratory failure vary widely in
individual patients because so many different conditions can
lead to this disorder. There are no physical signs unique to
respiratory failure. At extremely low arterial oxygen (PaO2)
levels, patients have rapid heart rates, rapid breathing
rates, and they are confused, sweaty, and cyanotic (blue).
Chronically low arterial oxygen makes patients irritable,
and elevated carbon dioxide produces headaches and
sleepiness. Difficult, rapid, or labored breathing (dyspnea)
is a consistent symptom in the awake patient.
The functions of the heart and blood vessels are often
severely impaired in patients with respiratory failure. In
some cases, chronic hypoxemia produces narrowing of the
blood vessels in the lung which, along with the lung damage
or the associated treatments, may weaken the heart and the
circulatory system. Some of the signs of inadequate
circulation are constriction of blood vessels in the skin,
cold extremities, and low urine output.
Diagnosis Of Respiratory Failure
It is impossible to estimate the extent of hypoxemia and
hypercapnia by observing a patient's signs and symptoms, and
mild hypoxemia and hypercapnia may go entirely unnoticed.
Blood oxygen must fall markedly before changes in breathing
and heart rate occur.
The clinical features of respiratory failure vary widely
in individual patients.
The way to diagnose respiratory failure, therefore, is to
measure oxygen (PaO2) and carbon dioxide (PaCO2) in the
arterial blood. However the levels that indicate respiratory
failure are somewhat arbitrary. Depending on age, a PaO2
less than 60 mm Hg or PaCO2 greater than 45 mm Hg generally
mean that the patient is in respiratory failure.
Management Of Respiratory Failure
The patient with respiratory failure cannot be adequately
treated in the general care areas of the hospital.
Therefore, patients in severe respiratory failure are
usually treated in the intensive care unit. Current therapy
for all forms of respiratory failure attempts, first, to
provide support for the heart, lungs, and other affected
vital organs; and second, to identify and treat the
underlying cause.
Since the immediate threat to patients with respiratory
failure is due to the inadequate level of oxygen delivered
to the tissues, oxygenation is the basic therapy for acute
respiratory failure due to lung disease. Oxygen-enriched air
is usually given to the patient by nasal prongs, oxygen
mask, or by placing an airtube into the trachea (windpipe).
Since prolonged high oxygen levels can be toxic, the
concentration of oxygen must be carefully controlled for
both short- and long-term treatment. Assisted ventilation
with mechanical devices may be the first priority for
neuromuscular disease patients going into respiratory
failure. Additional treatments employ ventilation which
helps to keep the lungs inflated at low lung volumes
(positive end-expiratory pressure, PEEP), and fluid and
nutritional management.
Endotracheal Intubation
Endotracheal intubation involves insertion of a tube into
the trachea. It permits delivery of precisely determined
amounts of oxygen to the lungs and removal of secretions,
and ensures adequate ventilation. Combined with mechanical
ventilation, endotracheal intubation is the cornerstone of
therapy for respiratory failure.
Mechanical Ventilation
If the patient is tiring despite ongoing therapy, a
mechanical ventilator, also called a respirator, is used.
The ventilator assists or controls the patient's breathing.
Positive End-Expiratory Pressure (PEEP)
Positive end-expiratory pressure is used with mechanical
ventilation to keep the air pressure in the trachea at a
level that increases the volume of gas remaining in the lung
after breathing out (expiration). This keeps the alveoli
open, reduces the shunting of blood through the lungs, and
improves gas exchange. Most ventilators have a PEEP
adjustment.
Extracorporeal Membrane Oxygenator (ECMO)
The extracorporeal membrane oxygenator (ECMO) is essentially
an artificial lung. It is an appropriately cased artificial
membrane which is attached to the patient externally
(extracorporeally), through a vein or artery. Although the
best substitute for a diseased lung that cannot handle gas
exchange adequately is a healthy human lung, such
substitution is often not possible. Circulating the
patient's blood through the ECMO offers another approach.
Gas exchange using ECMO keeps the patient alive while the
damaged lungs have a chance to heal.
In 1974, the National Heart, Lung, and Blood Institute
(NHLBI) organized a carefully designed clinical trial, to
determine the effectiveness of ECMO for patients with acute
respiratory distress syndrome. In this study, ECMO appeared
to be no more useful than conventional therapy. On the other
hand, ECMO seems to be an effective option in some infants
with respiratory failure when treatment with mechanical
ventilation fails. However ECMO is expensive, is associated
with nonrespiratory complications, and is available only in
a few specialized centers.
Management of Fluids and Electrolytes
Pulmonary edema, the buildup of abnormal amounts of fluid in
the lung tissues, often occurs in respiratory failure.
Therefore fluids are carefully managed and monitored to
maintain fluid balance and avoid fluid overload which may
further worsen gas exchange.
Pharmacologic Therapy
Because respiratory failure may be the end result of several
different diseases, no single drug therapy is effective in
all situations.
- Antibiotics help when infections (sepsis) as well as
pneumonia are involved in respiratory failure.
- Bronchodilators, for example, theophylline compounds,
sympathomimetic agents (albuterol, metaproterenol,
isoproterenol), anticholinergics (ipratropium bromide),
and corticosteroids, reverse bronchoconstriction and
reduce tissue inflammation.
- Other drugs, such as digitalis, improve cardiac output,
and drugs which increase blood pressure in shock can
improve blood flow to the tissues.
No single drug therapy is effective in all situations.
Bronchoscopy
Patients with respiratory failure who have excessive lung
secretions are sometimes helped by fiberoptic bronchoscopy,
a technique for accessing the interior of the bronchi, the
larger air passages of the lungs. The bronchoscope is a
flexible tube with a light at the end that is passed through
the nose or mouth into the trachea and bronchi. Fluid or
tissue can be removed from the bronchi (aspiration), and
cells for microscopic examination can be obtained by washing
the interior of the larger breathing tubes (lavage).
Bronchoscopy is useful for placing or removing endotracheal
tubes, removing foreign bodies from the lung, and collecting
tissue samples for diagnosis.
Intravenous Nutritional Support
Nutritional supplementation is essential to maintain or
restore strength when weakness and loss of muscle mass
prevent patients from breathing adequately without
ventilatory support. Appropriate nutrients (fats,
carbohydrates, and predigested proteins) are fed
intravenously for this purpose.
Physiotherapy
Physiotherapy includes chest percussion (repeated sharp
blows to the chest and back to loosen secretions), suction
of airways, and regular changes of body position. It helps
drain secretions, maintains alveolar inflation and prevents
atelectasis, incomplete expansion of the lung.
X-ray Monitoring
X-ray images of the chest help the doctor monitor the
progress of lung and heart disease in respiratory failure.
The portable chest radiograph taken with an x-ray machine
brought to the bedside is often used for this purpose in the
intensive care unit.
Lung Transplantation
Lung transplantation currently offers the only hope for
certain patients with end-stage pulmonary disease. The
shortage of suitable donors and the high cost of the
procedure continue to be major obstacles that limit its use.
Complications of Treatment
Oxygen toxicity, pulmonary embolism (closure of the
pulmonary artery or one of its branches by a blood clot or a
fat globule), cardiovascular problems, barotrauma (injury to
the lung tissue from excessive ventilatory pressure),
pneumothorax (air in the pleural space), and
gastrointestinal bleeding are some of the complications of
treatment. They result from fluid overload, mechanical
ventilation, PEEP, and other procedures used in the
management of respiratory failure.
Weaning the Patients From Ventilators
The process of returning the patient to unassisted and
spontaneous breathing is called weaning. Weaning is a
complex process that requires the understanding and
cooperation of the patient. It can cause great fatigue and
depression in patients because of the slow- and long-term
nature of the treatment procedures.
Weaning a patient too rapidly or prematurely can be
dangerous. Some patients, particularly those who had severe
underlying cardiac disease and prolonged episodes of acute
illnesses, may require weeks to months to wean. The doctor
considers weaning only when the patient is awake, has good
nutrition, and is able to cough and breathe deeply.
Discontinuation of Ventilatory Support
The difficult question of whether and when to discontinue
life-sustaining mechanical ventilation to the patient who is
not responding to any treatment is sometimes faced by the
doctor and the family. The legal, ethical, and financial
implications of continuing or withholding treatment to the
patient in terminal respiratory failure are important issues
addressed at family, professional, and government levels.
Respecting the rights and wishes of the patient and helping
the patient achieve a dignified and peaceful end while
continuing to assure care and comfort is a responsibility
shared by both the caregivers and the family. The family
with a good understanding of respiratory failure in all its
dimensions is best equipped to play its part in sharing this
responsibility.
More About Some Common Lung Diseases Leading to Or
Characterized by Respiratory Failure
Asthma
The hallmarks of asthma are obstruction to air flow and
bronchoconstriction, tightening of the muscles in the walls
of the bronchi, that is usually relieved by drugs called
bronchodilators. Acute asthma attacks that persist, do not
respond to bronchodilator therapy, and threaten life are
referred to as status asthmaticus. Due to the heavy work of
breathing, patients eventually tire and decrease their
respiratory efforts. Patients in this condition are prone to
develop respiratory failure. Respiratory failure is more
common in women with asthma, in patients over 40 years of
age, and in patients in whom treatment is delayed, or oral
corticosteroid therapy is stopped suddenly.
During an attack of asthma, airways obstruction from mucus
secretions and thickened bronchial tissue can lead to severe
hypoxemia, hypercapnia, and acidosis. Other potential
complications are pneumonia and accumulation of air in
pleural spaces. Patients with hypercapnia are at increased
risk of death.
In children with asthma, respiratory muscle fatigue and
interrupted breathing (apnea) are indications of existing or
developing respiratory failure.
Chronic Obstructive Pulmonary Disease (COPD)
COPD patients may develop acute respiratory failure when
their chronic airway obstruction is complicated by
infections, pulmonary emboli, heart failure, and drug-
induced respiratory depression. Influenza often precipitates
respiratory failure even without evidence of pneumonia in
COPD patients. The hallmark of respiratory failure in COPD
is increasing dyspnea and worsening blood gas abnormalities.
Depending on the triggering event, various other clinical
features may appear. The most dire sign is a decline in the
patient's condition associated with PaO2 of less than 50 mm
Hg and a PaCO2 greater than 50 mm Hg during air breathing.
Uncontrolled administration of oxygen to patients with COPD
and acute respiratory failure without therapy directed at
reducing the work of breathing can result in further
hypercapnia, acidosis, stupor, and coma.
Pneumonia
Patients with very severe pneumonia go into respiratory
failure because of lung inflammation and accumulation of
fluid that interferes with gas exchange. They breathe hard
and become exhausted; their respiratory muscles are unable
to keep up the pace. Blood carbon dioxide rises and oxygen
in the blood falls further. Sedation, at the time of
respiratory stress, may worsen the situation by depression
of the brain activity which is needed to keep respiratory
muscles working at high levels. This, in turn, decreases the
amount of breathing and may promote the development of
respiratory failure.
Respiratory Distress Syndrome of the Newborn
One type of respiratory failure in the newborn infant,
especially those born prematurely, is commonly referred to
as "respiratory distress syndrome." It is also called
hyaline membrane disease because of the formation of an
abnormal, hyaline (glassy and transparent under the
microscope), protein-containing membrane in alveoli. RDS may
also occur in full-term babies born to diabetic mothers.
The causes of RDS are complex, but it is believed that the
major problem is a poorly developed lung. Surfactant, a
unique fat-containing protein necessary to reduce the
surface tension in the alveoli of the lung to prevent their
collapse, is deficient in RDS babies. The most effective
treatment for RDS is the administration of surfactant.
Surfactant replacement therapy for RDS, available since
1989, has brought about a 30 percent reduction in death rate
for neonatal RDS in the United States (from 89.9 deaths per
100,000 live births in 1989 to 58.3 deaths per 100,000 in
1992). The National Heart, Lung, and Blood Institute (NHLBI)
is supporting the development and testing of several
different surfactant preparations useful in replacement
therapy for RDS.
Adult or Acute Respiratory Distress Syndrome
Acute respiratory failure in adults as a clinical entity was
first reported in 1967. Respiratory failure usually occurred
following a catastrophic event in individuals with no
previous lung disease and who did not respond to ordinary
methods of respiratory support. Regardless of the event
causing the lung injury, the patients exhibited common signs
and symptoms, x-ray findings, and tissue changes. Because
many of its features resembled the respiratory distress
syndrome of the newborn, RDS, the adult disease was called
"ARDS." As with RDS, there is increasing evidence that loss
of surfactant function may also be associated with ARDS.
Inhalation of gastric contents (aspiration), pulmonary
infections, shock, trauma, burns, extrapulmonary sepsis,
inhalation of toxic gases, drug overdose, and near-drowning
are some of the different situations that can cause ARDS. An
estimated 150,000 cases of ARDS occur yearly in the United
States. The estimated mortality rate of ARDS is 50-70
percent.
ARDS is often associated with multiple organ failure (heart,
liver, kidneys, and lungs). Patient survival usually depends
on the number of organs which fail, the degree and nature of
damage, and the age and previous health status of the
patient. The incidence of multiple organ failure is
particularly high when sepsis or hypotension from loss of
blood are the underlying causes of ARDS.
Keeping on Top of Your Condition
Keeping in tune with your disease or condition not only makes treatment less intimidating but also increases its chance of success, and has been shown to lower a patients risk of complications. As well, as an informed patient, you are better able to discuss your condition and treatment options with your physician.
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