Clinical manifestations of acute respiratory failure. Respiratory failure: causes and development, clinic, help and treatment. Chest deformity

Respiratory failure is a pathology that complicates the course of most diseases of internal organs, as well as conditions caused by structural and functional changes in the chest. To maintain gas homeostasis, the respiratory section of the lungs, airways and chest must work in a stressful mode.

External respiration provides oxygen to the body and removal of carbon dioxide. When this function is disturbed, the heart begins to beat hard, the number of red blood cells in the blood increases, and the level of hemoglobin rises. Strengthened work of the heart is the most important element of compensation for insufficiency of external respiration.

In the later stages of respiratory failure, compensatory mechanisms fail, the functional capabilities of the body decrease, and decompensation develops.

Etiology

Pulmonary causes include a disorder in the processes of gas exchange, ventilation and perfusion in the lungs. They develop with lobar, lung abscesses, cystic fibrosis, alveolitis, hemothorax, hydrothorax, water aspiration during drowning, traumatic chest injury, silicosis, anthracosis, congenital malformations of the lungs, chest deformities.

Extrapulmonary causes include:

Alveolar hypoventilation and bronchial obstruction are the main pathological processes of respiratory failure.

At the initial stages of the disease, compensation reactions are activated, which eliminate hypoxia and the patient feels satisfactory. With severe disorders and changes in the gas composition of the blood, these mechanisms do not cope, which leads to the development of characteristic clinical signs, and in the future - severe complications.

Symptoms

Respiratory failure is acute and chronic. The acute form of pathology occurs suddenly, develops rapidly and poses a threat to the life of the patient.

In primary insufficiency, the structures of the respiratory tract and the respiratory organs are directly affected. Its reasons are:

Pain with fractures and other injuries of the sternum and ribs,
Bronchial obstruction with inflammation of the small bronchi, compression of the respiratory tract by a neoplasm,
Hypoventilation and lung dysfunction
Damage to the respiratory centers in the cerebral cortex - TBI, drug or drug poisoning,
Respiratory muscle damage.

Secondary respiratory failure is characterized by damage to organs and systems that are not part of the respiratory complex:

blood loss
Thrombosis of large arteries,
Traumatic shock,
intestinal obstruction,
Accumulation of purulent discharge or exudate in the pleural cavity.

Acute respiratory failure is manifested by rather vivid symptoms. Patients complain of a feeling of lack of air, shortness of breath, difficulty inhaling and exhaling. These symptoms appear before the others. Tachypnea usually develops - rapid breathing, which is almost always accompanied by respiratory discomfort. The respiratory muscles are overstrained, it requires a lot of energy and oxygen to work.

With an increase in respiratory failure, patients become excited, restless, euphoric. They cease to critically assess their condition and the environment. Symptoms of "respiratory discomfort" appear - whistling, remote wheezing, breathing is weakened, tympanitis in the lungs. The skin becomes pale, tachycardia and diffuse cyanosis develop, the wings of the nose swell.

In severe cases, the skin turns grayish and becomes sticky and moist. As the disease develops, arterial hypertension is replaced by hypotension, consciousness is depressed, coma and multiple organ failure develop: anuria, stomach ulcer, intestinal paresis, kidney and liver dysfunction.

The main symptoms of the chronic form of the disease:

Shortness of breath of various origins;
Increased breathing - tachypnea;
Cyanosis of the skin - cyanosis;
Strengthened work of the respiratory muscles;
compensatory tachycardia,
Secondary erythrocytosis;
Edema and arterial hypertension in the later stages.

Palpation is determined by the tension of the muscles of the neck, contraction of the abdominal muscles on exhalation. In severe cases, paradoxical breathing is revealed: on inspiration, the stomach is pulled inward, and on exhalation it moves outward.

In children, pathology develops much faster than in adults due to a number of anatomical and physiological features of the child's body. Babies are more prone to swelling of the mucous membrane, the lumen of their bronchi is rather narrow, the process of secretion is accelerated, the respiratory muscles are weak, the diaphragm is high, breathing is more shallow, and the metabolism is very intense.

These factors contribute to the violation of respiratory patency and pulmonary ventilation.

Children usually develop an upper obstructive type of respiratory failure, which complicates the course, paratonsillar abscess, false croup, acute epiglotitis, pharyngitis, and. The timbre of the voice changes in the child, and "stenotic" breathing appears.

The degree of development of respiratory failure:

First- difficult breathing and restlessness of the child, hoarse, "cock" voice, tachycardia, perioral, intermittent cyanosis, aggravated by anxiety and disappearing when breathing oxygen.
Second- noisy breathing that can be heard from a distance, sweating, constant cyanosis on a pale background, disappearing in an oxygen tent, coughing, hoarseness, retraction of the intercostal spaces, pallor of the nail beds, lethargic, adynamic behavior.
Third- severe shortness of breath, total cyanosis, acrocyanosis, marbling, pallor of the skin, drop in blood pressure, suppressed reaction to pain, noisy, paradoxical breathing, weakness, weakening of heart sounds, acidosis, muscle hypotension.
Fourth the stage is terminal and is manifested by the development of encephalopathy, asystole, asphyxia, bradycardia, seizures, coma.

The development of pulmonary insufficiency in newborns is due to an incompletely mature surfactant system of the lungs, vascular spasms, aspiration of amniotic fluid with primordial feces, and congenital anomalies in the development of the respiratory system.

Complications

Respiratory failure is a severe pathology requiring urgent therapy. The acute form of the disease is difficult to treat, leads to the development of dangerous complications and even death.

Acute respiratory failure is a life-threatening pathology that leads to the death of the patient without timely medical care.

Diagnostics

Diagnosis of respiratory failure begins with the study of the patient's complaints, the collection of an anamnesis of life and illness, and the clarification of comorbidities. Then the specialist proceeds to examine the patient, paying attention to the cyanosis of the skin, rapid breathing, retraction of the intercostal spaces, listens to the lungs with a phonendoscope.

To assess the ventilation capacity of the lungs and the function of external respiration, functional tests are carried out, during which the vital capacity of the lungs, the peak volumetric forced expiratory flow rate, and the minute respiratory volume are measured. To assess the work of the respiratory muscles, measure the inspiratory and expiratory pressure in the oral cavity.

Laboratory diagnostics includes the study of acid-base balance and blood gases.

Additional research methods include radiography and magnetic resonance imaging.

Treatment

Acute respiratory failure develops suddenly and rapidly, therefore you need to know how to provide emergency first aid.

The patient is laid on the right side, the chest is freed from tight clothing. To prevent the tongue from sinking, the head is thrown back, and the lower jaw is pushed forward. Then foreign bodies and sputum are removed from the pharynx using a gauze pad at home or an aspirator in a hospital.

It is necessary to call an ambulance team, since further treatment is possible only in the intensive care unit.

Video: first aid for acute respiratory failure

Treatment of chronic pathology is aimed at restoring pulmonary ventilation and gas exchange in the lungs, delivering oxygen to organs and tissues, pain relief, and eliminating the diseases that caused this emergency.

The following therapeutic methods will help restore pulmonary ventilation and airway patency:

After the restoration of respiratory patency, they proceed to symptomatic therapy.

In the absence of the effect of the therapy, they proceed to surgical treatment - lung transplantation.

Video: lecture on respiratory failure

When a person has acute respiratory failure, the organs cannot get enough oxygen to function properly. Acute tissue oxygen deprivation can develop if the lungs cannot eliminate carbon dioxide from the blood on their own. This is one of the emergencies that occurs against the background of a violation of external respiration. The main reasons for this complication are various mechanical obstacles that impair breathing, allergic or inflammatory edema, spasms in the bronchi and pharynx. Since this process interferes with normal breathing, it is necessary to know the rules of first aid in order to preserve the health and life of a person.

What is acute respiratory failure?

Respiratory failure is a condition in which gas exchange in the lungs is impaired, resulting in low blood oxygen levels and high carbon dioxide levels. There are two types of respiratory failure. In the first case, the oxygen that enters the lungs to be delivered to the rest of the body is not enough. This can lead to further problems because the heart, brain, and other organs need an adequate supply of oxygen-rich blood. This is called hypoxemic respiratory failure because respiratory failure is caused by low oxygen levels in the blood. Another type is hypercapnic respiratory failure, which results from high levels of carbon dioxide in the blood. Both types can be present at the same time.

To understand the process of respiration, one must know how gas exchange occurs. Air initially enters through the nose or mouth into the trachea, then passes through the bronchi, bronchioles, and enters the alveoli, the air sacs, where gas exchange occurs. Capillaries pass through the walls of the alveoli. It is here that oxygen is efficiently passed through the walls of the alveoli and enters the blood, while simultaneously moving carbon dioxide from the blood to the air sacs. If acute respiratory failure occurs, then oxygen does not enter the body in sufficient quantities. Accordingly, the state of health worsens, the organs and the brain do not receive oxygen, the consequences appear immediately after the onset of the attack. If it is not stopped in time, then the person will most likely die.

Symptoms of respiratory failure

Acute respiratory failure can occur in various pathological conditions in the body.. Any form of injury that compromises the airways can significantly affect blood gases. Respiratory failure depends on the amount of carbon dioxide and oxygen present in the blood. If carbon dioxide levels are elevated and blood oxygen levels are low, the following symptoms may occur:

cyanosis of the fingertips, tip of the nose, lips;
increased anxiety;
confusion;
drowsiness;
increase in heart rate;
change in the rhythm of breathing;
extrasystole or arrhythmia;
profuse sweating.

Causes of acute respiratory failure

One of the most common causes of respiratory failure is the occlusion of the lumen of the respiratory tract after vomiting, bleeding, or ingestion of small foreign objects. Cases of acute respiratory failure can be in medicine. For example, in dentistry, practitioners often encounter forms of insufficiency such as stenotic or obstructive. Stenotic asphyxia is the result of allergic edema. Obstructive asphyxia can be caused by entry into the respiratory tract of various objects used in the treatment, such as a tooth, gauze sponges or impression materials. From this, a person begins to suffocate and, again, oxygen in sufficient quantities does not enter the body.

In the case of acute asphyxia, the patient's breathing becomes frequent with a further stop. The patient may have convulsions, tachycardia. Against the background of asphyxia, the patient's skin becomes gray, the pulse is weak, consciousness is disturbed. It is important that the medical staff act immediately and accurately if this happened in the hospital, if not, first aid must be provided so that the person survives before the arrival of the SP team. The danger is that there is no time to think. The lack of oxygen begins to destroy cells. At any moment, either the brain or one of the vital organs can fail, and the loss of consciousness will only aggravate the situation.

There are various other causes of acute respiratory failure that you should be familiar with. The most important factor in the health of any person is his lifestyle. Since medical intervention rarely leads to shortness of breath and asthma attacks. The reasons for the development of this condition should be sought precisely in your usual way of life. In addition, if an attack begins due to surgical intervention, the doctors will quickly orient themselves and provide the necessary assistance. As for other situations, no one guarantees that a person with a medical education will be nearby. Therefore, doctors themselves advise avoiding factors that are a potential cause of acute respiratory failure.

Main reasons:

medical intervention in the nasopharynx or oral cavity;
trauma;
acute respiratory distress syndrome;
chemical inhalation;
alcohol abuse;
stroke;
infection.

Any form of injury that compromises the airways can significantly affect the amount of oxygen in the blood. Try not to injure your body. Acute respiratory distress syndrome is a serious disease that occurs against the background of an inflammatory process in the lungs, determined by a violation of the diffusion of gases in the alveoli and a low oxygen content in the blood. Also, the attack leads to the so-called "chemical inhalation" - the inhalation of toxic chemicals, vapors or smoke, which can lead to acute respiratory failure.

Alcohol or drug abuse is not the last cause of an attack. An overdose of them can disrupt the brain and stop the ability to inhale or exhale. A stroke in itself causes disruptions in the body, not only the brain and heart suffer, but also the respiratory system. Infection is the most common cause of respiratory distress syndrome.

First aid for acute respiratory failure

The goal of treatment and prevention of respiratory failure is to saturate the body with oxygen and reduce the level of carbon dioxide in the body. Treating an attack may include eradicating the underlying causes. If you notice a person has acute respiratory failure, then the following steps should be taken. First, immediately seek emergency medical attention - call an ambulance. Then, the victim needs to be given first aid.

Check circulation, airways and breathing. To check for a pulse, place two fingers on your neck to check for breathing, tilt your cheek between the victim's nose and lips, and feel the breath. Watch for chest movements. Do all the necessary manipulations within 5-10 seconds. If the person has stopped breathing, give artificial respiration. With your mouth open, pinch your nose and press your lips to the victim's mouth. Breathe in. If necessary, repeat the manipulation several times. Continue mouth-to-mouth resuscitation until medical personnel arrive.

Acute respiratory failure (ARF) is a condition in which the body is not able to maintain the normal maintenance of the gas composition of the blood. For some time it can be achieved due to the increased work of the respiratory apparatus, but its capabilities are quickly depleted.

Causes and mechanisms of development

Atelectasis can cause acute respiratory failure.

ARF is the result of various diseases or injuries in which pulmonary ventilation or blood flow disorders occur suddenly or progress rapidly.

According to the mechanism of development, there are:

hypoxemic;
hypercapnic variant of respiratory failure.

With hypoxemic respiratory failure, sufficient oxygenation of arterial blood does not occur due to a violation of the gas exchange function of the lungs. The following problems can cause its development:

hypoventilation of any etiology (asphyxia, aspiration of foreign bodies, retraction of the tongue,);
decrease in the concentration of oxygen in the inhaled air;
pulmonary embolism;
atelectasis of the lung tissue;
airway obstruction;
non-cardiogenic pulmonary edema.

Hypercapnic respiratory failure is characterized by an increase in the concentration of carbon dioxide in the blood. It develops with a significant decrease in pulmonary ventilation or with increased production of carbon dioxide. This can be observed in such cases:

with diseases of a neuromuscular nature (myasthenia gravis, poliomyelitis, viral encephalitis, polyradiculoneuritis, rabies, tetanus) or the introduction of muscle relaxants;
with damage to the central nervous system (traumatic brain injury, acute cerebrovascular accident, poisoning with narcotic analgesics and barbiturates);
at or massive ;
with a chest injury with its immobilization or damage to the diaphragm;
with seizures.

Symptoms of ARF

Acute respiratory failure occurs within a few hours or minutes after the onset of exposure to a pathological factor (acute disease or injury, as well as exacerbation of a chronic pathology). It is characterized by impaired breathing, consciousness, circulation and kidney function.

Respiratory disorders are very diverse, they include:

tachypnea (breathing at a frequency above 30 per minute), irregular polypnea and apnea (stopping breathing);
expiratory dyspnea (with difficulty exhaling, often accompanies hypercapnic DN);
stridor breathing with retraction of the supraclavicular spaces (occurs with obstructive airway diseases);
pathological types of breathing - Cheyne-Stokes, Biot (occur with brain damage and drug poisoning).

The severity of disorders in the functioning of the central nervous system directly depends on the degree of hypoxia and hypercapnia. Its initial manifestations can be:

lethargy;
confusion;
slow speech;
motor anxiety.

An increase in hypoxia leads to stupor, loss of consciousness, and then to the development of coma with cyanosis.

Circulatory disorders are also caused by hypoxia and depend on its severity. It could be:

severe pallor;
marbling of the skin;
cold extremities;
tachycardia.

As the pathological process progresses, the latter is replaced by bradycardia, a sharp drop in blood pressure and various rhythm disturbances.

Kidney dysfunctions appear in the late stages of ARF and are caused by prolonged hypercapnia.

Another manifestation of the disease is cyanosis (cyanosis) of the skin. Its appearance indicates pronounced disturbances in the oxygen transport system.

Degrees of ODN

From a practical point of view, on the basis of clinical manifestations during ARF, 3 degrees are distinguished:

The first of them is characterized by general anxiety, complaints of lack of air. In this case, the skin becomes pale in color, sometimes with acrocyanosis and covered with cold sweat. The respiratory rate increases to 30 per minute. Tachycardia appears, unexpressed arterial hypertension, partial pressure of oxygen drops to 70 mm Hg. Art. During this period, DN is easily amenable to intensive care, but in its absence it quickly passes into the second degree.
The second degree of ARF is characterized by the excitation of patients, sometimes with delusions and hallucinations. The skin is cyanotic. The respiratory rate reaches 40 per minute. The heart rate increases sharply (more than 120 per minute) and blood pressure continues to rise. In this case, the partial pressure of oxygen drops to 60 mm Hg. Art. and lower, and the concentration of carbon dioxide in the blood increases. At this stage, immediate medical attention is necessary, since delay leads to the progression of the disease in a very short period of time.
The third degree of ODN is the limit. A coma with convulsive activity sets in, spotty cyanosis of the skin appears. Breathing is frequent (more than 40 per minute), superficial, may be replaced by bradypoea, which threatens with cardiac arrest. Blood pressure is low, the pulse is frequent, arrhythmic. In the blood, limiting violations of the gas composition are revealed: the partial pressure of oxygen is less than 50, carbon dioxide is more than 100 mm Hg. Art. Patients in this condition need urgent medical care and resuscitation. Otherwise, ODN has an unfavorable outcome.

Diagnostics

Diagnosis of ARF in the practical work of a doctor is based on a combination of clinical symptoms:

complaints;
medical history;
objective examination data.

Auxiliary methods in this case are the determination of the gas composition of the blood and.

Urgent care

All patients with ARF must receive oxygen therapy.

The therapy of ARF is based on dynamic monitoring of the parameters of external respiration, the composition of blood gases and the acid-base state.

First of all, it is necessary to eliminate the cause of the disease (if possible) and ensure the patency of the airways.

All patients with acute arterial hypoxemia are shown oxygen therapy, which is carried out through a mask or nasal cannulas. The goal of this therapy is to increase the partial pressure of oxygen in the blood to 60-70 mm Hg. Art. Oxygen therapy with an oxygen concentration of more than 60% is used with extreme caution. It is carried out with the obligatory consideration of the possibility of the toxic effect of oxygen on the patient's body. With the ineffectiveness of this type of exposure, patients are transferred to mechanical ventilation.

Additionally, such patients are assigned:

bronchodilators;
drugs that thin sputum;
antioxidants;
antihypoxants;
corticosteroids (as indicated).

With depression of the respiratory center caused by the use of narcotic drugs, the use of respiratory stimulants is indicated.

If acute respiratory failure occurs, emergency care can save a person's life. Acute respiratory failure is a critical condition in which a person feels a clear lack of oxygen, such a condition is life-threatening and can lead to death. In such a situation, medical attention is urgently needed.

Emergency care for acute respiratory failure

There are three degrees of this critical condition:

A person complains of suffocation, lack of oxygen, low blood pressure, normal heartbeat.
It is characterized by obvious anxiety and arousal of a person, the patient may become delirious, there is a violation of respiratory breathing, the pressure drops, the skin becomes moist, covered with sweat, the heartbeat is increased.
Limiting, the patient is in a coma, the pulse is weak, poorly palpable, the pressure is very low.

The most common causes of acute respiratory failure are respiratory injuries, chest injuries, and broken ribs. Lack of oxygen is possible with pneumonia, pulmonary edema, brain diseases, etc. It can also be caused by a drug overdose. What is the first aid for this disease?

First aid

How is emergency care provided for acute respiratory failure?

A person must be hospitalized, and before the arrival of an ambulance, he needs to be given emergency care.

What is the algorithm for providing first aid to a patient? Be sure to inspect the oral cavity and, if foreign bodies are found, ensure the patency of the respiratory tract.

In case of tongue sticking, this problem must be eliminated. If the person is unconscious and lying on their back, their tongue may sink and block their airways. The patient begins to make a sound similar to wheezing, after which a complete cessation of breathing is possible.

To eliminate the retraction of the tongue, it is necessary to push the lower jaw forward and at the same time make a bend in the occipital-cervical region. That is, with your thumbs you need to press the chin down, and then push the jaw forward, tilting the patient's head back.

If you have time to carry out these actions in time, the retraction of the tongue is eliminated and the airway patency is restored.

The simplest thing that can be done to keep the tongue of an unconscious person from sinking is to lay the patient on his side with his head thrown back. In this position, the tongue cannot fall and the vomit will not enter the respiratory tract. It is preferable to turn the patient on the right side - so there will be no disturbance of gas exchange and blood circulation.

In order for the tongue not to sink, there are special devices - oral rubber or plastic air ducts. The air duct must be of the right size so that it can be freely installed in the patient's oral cavity. The air duct helps to eliminate the problem of a stuck tongue, and the patient's breathing becomes quiet and calm.

The air duct can be nasal, it is placed at the level of the oropharynx and provides calm breathing. Before installing the air duct, the patient needs to clean the oral cavity with a napkin or suck out the foreign contents of the mouth with an aspirator.

When aspiration, you need to remember about asepsis, especially when cleaning the trachea and bronchi. It is not necessary to clean the mouth and trachea with the same catheter. Catheters must be sterile. Aspiration is done carefully to avoid injury to the airway mucosa.

Tracheal intubation is an important medical procedure, which is carried out both immediately with an attack of acute respiratory failure, and during the transportation of the patient. Tracheal intubation should be able to be done by any emergency physician, especially doctors of specialized emergency teams.

After tracheal intubation, patients receive intensive care, and then they are transferred to a hospital ward, if possible in an intensive care unit. During transportation, the patient is provided with free airway patency, and also improves alveolar ventilation.

With a respiratory rate of over 40 times per minute, you need to do an indirect heart massage, constantly, until the ambulance arrives.

First aid video for respiratory failure:

If the patient has acute respiratory failure of the first degree, then it may be sufficient to eliminate the attack by installing an oxygen mask with 35-40% oxygen. The effect will be even stronger if nasal catheters are used to supply oxygen to the patient. In acute respiratory failure of the second and third degree, the patient is transferred to artificial lung ventilation.

The term acute respiratory failure defines a pathological condition in which the function of external respiration is sharply impaired. This leads to a decrease in the supply of oxygen to the blood with the development of hypoxia (a state of insufficient supply of oxygen to all cells and tissues of the body, followed by a violation of energy metabolic processes occurring with its participation). Respiratory failure is a life-threatening condition for a child, so it requires prompt assistance to restore the function of external respiration.

Development mechanism

External respiration is provided by the structures of the respiratory system, namely the respiratory tract, through which the inhaled air enters the alveoli of the lungs, where gas exchange occurs between the blood (oxygen binds to hemoglobin, and carbon dioxide from the blood enters back into the alveoli). Violation of the function of external respiration most often in its development has several pathogenetic mechanisms leading to a violation of the passage of air through the respiratory tract:

Various mechanisms of development of acute respiratory failure require appropriate approaches in emergency therapy. The provision of care at the prehospital stage is almost the same.

The reasons

Acute respiratory failure is a polyetiological pathological condition, the development of which can be caused by a significant number of causes. The most common of these in children are:

Under the influence of these causes, various mechanisms for the development of a pathological condition are realized, which require appropriate therapeutic approaches aimed at eliminating their impact.

Clinical symptoms

Against the background of acute respiratory failure, hypoxia develops, from which neurocytes (cells of the nervous system) of the brain primarily suffer. As a result, the clinical picture is dominated by manifestations of impaired functional activity of the central nervous system, these include:

Euphoria is a state of unmotivated joy and elation, which is the first manifestation of insufficient oxygen supply to the brain cells.
Decreased concentration of attention (ability to concentrate), increased speech arousal, accompanied by talkativeness.
Emotional disorders, accompanied by increased resentment, irritability, tearfulness, an uncritical assessment of the child's own condition.
Decreased motor activity (pronounced hypodynamia).
Inhibition of various types of reflexes (skin, tendon, periosteal).
The state of decortication is a critical decrease in the functional activity of the cerebral cortex with the preserved activity of subcortical structures. This condition is accompanied by loss of consciousness, motor excitation, moderate dilation of the pupils with their sluggish reaction to light, the absence of skin reflexes with an increase in tendon and periosteal reflexes.
The development of hypoxic coma is an extreme degree of hypoxia of the structures of the nervous system, manifested by a lack of consciousness, reactions to various types of stimuli, a significant expansion of the pupils with their absence of reaction to light, dry eyes with a decrease in luster, and movement of the eyeballs in different directions.

In addition to manifestations of inhibition of the activity of the structures of the central nervous system, acute respiratory failure is also accompanied by various respiratory disorders in the form of shortness of breath, difficulty inhaling or exhaling, remote wheezing, dry or wet cough. The color of the skin becomes bluish (cyanosis).

Help

First of all, with the appearance of even minimal signs of the development of acute respiratory failure, an ambulance should be called. Prior to her arrival, it is necessary to perform a number of measures aimed at improving blood oxygen saturation and reducing signs of hypoxia:

After the arrival of medical specialists, the hospital stage of care begins. After assessing the child's condition, the severity of hypoxia, the possible causes of its development, various drugs are administered, inhalations with oxygen are carried out. If it is impossible to restore patency for air in the larynx, a tracheostomy is performed.