AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

The respiratory system supplies the body with adequate oxygen for aerobic metabolism and simultaneously removes carbon dioxide, the major metabolic waste. Respiratory failure develops when the rate of gas exchange between the atmosphere and blood is unable to match the body's metabolic demands. It is diagnosed when the patient loses the ability to provide sufficient oxygen to the blood and develops hypoxemia or when the patient is unable to adequately ventilate and develops hypercarbia and hypoxemia.

Pathophysiology

Hypoxemia is caused by one of the following abnormalities:

• Alveolar ventilation (V) and pulmonary perfusion (Q) mismatch
• Intrapulmonary shunt
• Hypoventilation
• Abnormal diffusion of gases at the alveolar-capillary interface
• Reduction in inspired oxygen concentration
• Increased venous desaturation with cardiac dysfunction plus one or more of the above 5 factors

V/Q mismatch, intrapulmonary shunt, and hypoventilation

The 3 most important abnormalities in gas exchange that lead to respiratory failure are V/Q mismatch, intrapulmonary shunt, and hypoventilation.

The V/Q ratio determines the adequacy of gas exchange in the lung. When alveolar ventilation matches pulmonary blood flow, CO₂ is eliminated and the blood becomes fully saturated with oxygen. In the normal lung, gravitational forces affect the V/Q ratio. When a person stands, the V/Q is greater than 1 at the apex of the lung (ventilation exceeds perfusion) and less than 1 at the base (less ventilation with more perfusion). In the overall healthy lung, the V/Q ratio is assumed to be ideal and equals 1.

A mismatch between ventilation and perfusion is the most common cause of hypoxemia. When the V/Q ratio is less than 1 throughout the lung, arterial hypoxemia results. As V/Q mismatch worsens, the minute ventilation increases producing either a low or normal arterial partial pressure of CO₂ (PaCO₂). The hypoxemia caused by low V/Q areas is responsive to supplemental oxygen administration. The more severe the V/Q imbalance, the higher the concentration of inspired oxygen is needed to raise the arterial partial pressure of oxygen (PaO₂).

In the extreme case when the V/Q ratio equals 0, pulmonary blood flow does not participate in gas exchange because the perfused lung unit receives no ventilation. This condition is intrapulmonary shunting and is calculated by comparing the oxygen contents in arterial blood, mixed venous blood, and pulmonary capillary blood (see Other Tests). In healthy people, the percentage of intrapulmonary shunt is less than 10%. When the intrapulmonary shunt is greater than 30%, resultant hypoxemia does not improve with supplemental oxygenation because the shunted blood does not come in contact with the high oxygen content in the alveoli. Instead, treatment consists of recruiting and maximizing lung volume with positive pressure. PaO₂ continues to fall proportionately as the shunt increases.

In contrast, PaCO₂ remains constant because of a compensatory increase in minute ventilation until the shunt fraction exceeds 50%. The protective reflex that reduces the degree of intrapulmonary shunting is hypoxic pulmonary vasoconstriction (HPV); alveolar hypoxia leads to vasoconstriction of the perfusing vessel. This partially corrects the regional V/Q mismatch by improving PaO₂ at the expense of increasing pulmonary vascular resistance.

When ventilation is in excess of capillary blood flow, the V/Q ratio is greater than 1. At the extreme, areas of ventilated lung receive no perfusion, and the V/Q ratio approaches infinity. This extreme condition is referred to as alveolar dead-space ventilation. In addition to alveolar dead space, anatomic dead space represents the volume of air in conducting airways that cannot participate in gas exchange.

Combined, the alveolar and anatomic dead-space volumes are referred to as physiologic dead space, which normally accounts for 30% of total ventilation. Increased dead-space ventilation results in hypoxemia and hypercapnia. This increase can be caused by decreased pulmonary perfusion due to hypotension, pulmonary embolus, or alveolar overdistention during mechanical ventilation. The ratio of dead-space to tidal-gas volume can be calculated on the basis of the difference between CO₂ in arterial blood and in exhaled gas (see Other Tests).

Under steady-state conditions, PaCO₂ is directly proportional to CO₂ production (VCO₂) and inversely proportional to alveolar ventilation (V_A), as follows: PaCO₂ = VCO₂ X (k/V_A), where k is a constant = 0.863.

Therefore, when V_A decreases or VCO₂ increases, PaCO₂ increases. With alveolar hypoventilation, hypoxemia is predicted by using the alveolar gas equation, but the alveolar-arterial gradient remains normal (see Other Tests).

Another way to approach respiratory failure is based on 2 patterns of blood-gas abnormalities. Type I respiratory failure results from poor matching of pulmonary ventilation to perfusion; this leads to noncardiac mixing of venous blood with arterial blood. As a result, type I respiratory failure is characterized by arterial hypoxemia with normal or low arterial CO₂. As an alternative, type II respiratory failure results from inadequate alveolar ventilation in relation to physiologic needs and is characterized by arterial hypercarbia and hypoxemia. Type II respiratory failure occurs when a disease or injury imposes a load on a child's respiratory system that is greater than the power available to do the respiratory work. In this scenario, the hypoxemia is proportional to the hypercarbia.

A wide array of diseases can cause respiratory failure. Therefore, the physician must identify the affected area in the respiratory system that contributes to the respiratory failure. Identification can be achieved by dividing the respiratory system into 3 anatomic parts: (1) the extrathoracic airway, (2) the lungs responsible for gas exchange, and (3) the respiratory pump that ventilates the lung and that includes the nervous system, thorax, and respiratory muscles. In general, diseases that affect the anatomic components of the lung result in regions of low or absent V/Q ratios, initially leading to type I (or hypoxemic) respiratory failure. As an alternative, diseases of the extrathoracic airway and respiratory pump result in a respiratory power-load imbalance and type II respiratory failure. Hypercarbia due to alveolar hypoventilation is the hallmark of diseases involving the respiratory pump.

Pediatric considerations

The frequency of acute respiratory failure is higher in infants and young children than in adults for several reasons. This difference can be explained by defining anatomic compartments and their developmental differences in pediatric patients that influence susceptibility to acute respiratory failure.

The extrathoracic airway comprises the area extending from the nose through the nasopharynx, oropharynx, and larynx to the subglottic region of the trachea. Differences in pediatric versus adult patients include the following:

• Neonates and infants are obligate nasal breathers until the age of 2-6 months because of the proximity of the epiglottis to the nasopharynx. Nasal congestion can lead to clinically significant distress in this age group.
• The small size of the airway is one of the primary differences in infants and children younger than 8 years compared with older patients.
• Infants and young children have a large tongue that fills a small oropharynx.
• Infants and young children have a cephalic larynx. The larynx is opposite vertebrae C3-4 in children versus C6-7 in adults.
• The epiglottis is larger and more horizontal to the pharyngeal wall in children than in adults. The cephalic larynx and large epiglottis can make laryngoscopy challenging.
• Infants and young children have a narrow subglottic area. In children, the subglottic area is cone shaped, with the narrowest area at the cricoid ring. A small amount of subglottic edema can lead to clinically significant narrowing, increased airway resistance, and increased work of breathing. Older patients and adults have a cylindrical airway that is narrowest at the glottic opening.
• In slightly older children, adenoidal and tonsillar lymphoid tissue is prominent and can contribute to airway obstruction.

The intrathoracic airways and lung include the conducting airways and alveoli, the interstitia, the pleura, the lung lymphatics, and the pulmonary circulation. Noteworthy differences among pediatric children include the following:

• Infants and young children have fewer alveoli than do adults. The number dramatically increases during childhood, from approximately 20 million after birth to 300 million by 8 years of age. Therefore, infants and young children have a relatively small area for gas exchange.
• The alveolus is small. Alveolar size increases from 150-180 to 250-300 µm during childhood.
• Collateral ventilation is not fully developed; therefore, atelectasis is more common in children than in adults. During childhood, anatomic channels form to provide collateral ventilation to alveoli. These pathways are between adjacent alveoli (pores of Kohn), bronchiole and alveoli (Lambert channel), and adjacent bronchioles. This important feature allows alveoli to participate in gas exchange even in the presence of an obstructed distal airway.
• Smaller intrathoracic airways are more easily obstructed than larger ones. With age, the airways enlarge in diameter and length.
• Infants and young children have relatively little cartilaginous support of the airways. As cartilaginous support increases, dynamic compression during high expiratory flow rates is prevented.

The respiratory pump includes the nervous system with central control (ie, cerebrum, brainstem, spinal cord, peripheral nerves), respiratory muscles, and chest wall. Features of note in pediatric patients include the following:

• The respiratory center is immature in infants and young children and leads to irregular respirations and an increased risk of apnea.
• The ribs are horizontally oriented. During inspiration, a decreased volume is displaced, and the capacity to increase tidal volume is limited compared with that in older individuals.
• The small surface area for the interaction between the diaphragm and thorax limits displacing volume in the vertical direction.
• The musculature is not fully developed. The slow-twitch fatigue-resistant muscle fibers in the infant are underdeveloped.
• The soft compliant chest wall provides little opposition to the deflating tendency of the lungs. This leads to a lower functional residual capacity in pediatric patients than in adults, a volume that approaches the pediatric alveolus critical closing volume.

Mortality/Morbidity

Acute respiratory failure remains an important cause of morbidity and mortality in children. Cardiac arrests in children frequently result from respiratory failure. In 2000, data from the National Center for Health Statistics listed respiratory illnesses as one of the top 10 causes of pediatric mortality.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• Does the patient have factors that increase the risk for respiratory failure? Factors may include young age; history of prematurity; immunodeficiency; and chronic pulmonary, cardiac, or neuromuscular disease (eg, cystic fibrosis, bronchopulmonary dysplasia, unrepaired congenital heart disease, or spinal muscular atrophy [SMA]).
• Does the patient have a cough, rhinorrhea, or other symptoms of an upper respiratory tract infection to define an etiology?
• Does the patient have a fever or signs of sepsis? Several infections can lead to respiratory failure because of a systemic inflammatory response, pulmonary edema, or acute respiratory distress syndrome (ARDS) or because it can produce a power-load imbalance secondary to increased oxygen consumption.
• How long have the symptoms been present? The natural course of a respiratory illness must be considered. Respiratory syncytial virus (RSV) infections frequently worsen over the initial 3-5 days before improvement occurs.
• Does the patient have any pain? Pain can suggest pleuritis or foreign-body aspiration.
• Does the patient have a possible or known exposure to sedatives (eg, benzodiazepines, tricyclic antidepressants, narcotics) or has he or she recently undergone a procedure that used general anesthesia? This could suggest hypoventilation.
• Does the patient have symptoms of neuromuscular weakness or paralysis? What is the distribution of weakness and duration of symptoms to narrow the differential diagnosis?
• • Bulbar dysfunction suggests myasthenia gravis.
  • Distal weakness that progresses upward suggests Guillain-Barré syndrome.
  • Apnea associated with a traumatic injury suggests a cervical spinal cord injury.
• Does the patient have a history suggestive of a stroke or seizure?
• Does the patient have a history of headaches? With chronic hypercapnia, headaches typically occur at nighttime or upon the patient's awakening in the morning.

Physical

During physical examination, clinicians should avoid interfering with the patient's mechanisms for compensation. Children often find the most advantageous position for breathing. Children with respiratory distress commonly sit up and lean forward to improve leverage for the accessory muscles and to allow for easy diaphragmatic movement. Children with epiglottitis sit upright with their necks extended and heads forward while drooling and breathing through their mouths. Making a child lie down or making him or her cry during an otoscopic examination can precipitate acute respiratory failure.

• General appearance
• • Does the patient appear well or sick?
  • Is the patient cyanotic?
• Respiratory rate, quality, and effort
• • Bradypnea is most often observed in central control abnormalities. Slow and large tidal volume breaths also minimize turbulence and resistance in significant extrathoracic airway obstruction (eg, epiglottitis).
  • The fast and shallow breathing of tachypnea is most efficient in intrathoracic airway obstruction. It decreases dynamic compliance of the lung.
  • Auscultation provides information about the symmetry and quality of air movement. Evaluate the patient for stridor, wheezing, crackles, and decreased breath sounds (eg, alveolar consolidation, pleural effusion).
  • Grunting is an expiratory sound made by infants as they exhale against a closed glottis. It is an attempt to increase functional residual capacity and lung volume. This attempt is made in order to raise functional residual capacity above the critical closing volume and to avoid alveolar collapse. This is a concerning physical finding.
  • Assess for accessory muscle use and nasal flaring. Suprasternal and intercostal retractions are present when highly negative pleural pressures are required to overcome airway obstruction or stiff lungs.
• Chest wall findings: Evaluate for paradoxical movement of the chest wall. In the presence of abnormalities of the pulmonary pump, paradoxical chest-wall movement occurs because of instability of the chest wall associated with absent intercostal muscle use. As the diaphragm contracts and pushes abdominal contents out, the chest wall retracts inward instead of expanding normally.
• Cardiovascular findings
• • Tachycardia and hypertension may occur secondary to increased circulatory catecholamine levels.
  • A gallop is suggestive of myocardial dysfunction leading to respiratory failure.
  • Peripheral vasoconstriction may develop secondary to respiratory acidosis.
• Neurologic findings
• • Patients may be lethargic, irritable, anxious, or unable to concentrate.
  • The inability to breathe comfortably creates anxiety, and superimposed hypoxemia and hypercapnia accentuates any restlessness and agitation. Increased agitation may indicate a general worsening of the patient's condition.

Causes

The most common reasons for respiratory failure in the pediatric population are divided into anatomic compartments, as follows:

• Extrathoracic airway
• • Acquired lesions
  • • Infections (eg, retropharyngeal abscess, Ludwig angina, laryngotracheobronchitis, bacterial tracheitis, peritonsillar abscess)
    • Traumatic causes (eg, postextubation croup, thermal burns, foreign-body aspiration)
    • Other (eg, hypertrophic tonsils and adenoid)
  • Congenital lesions
  • • Subglottic stenosis
    • Subglottic web or cyst
    • Laryngomalacia
    • Tracheomalacia
    • Vascular ring
    • Cystic hygroma
    • Craniofacial anomalies
• Intrathoracic airway and lung
• • Acute respiratory distress syndrome (ARDS)
  • Asthma
  • Aspiration
  • Bronchiolitis
  • Bronchomalacia
  • Left-sided valvular abnormalities
  • Pulmonary contusion
  • Near drowning
  • Pneumonia
  • Pulmonary edema
  • Pulmonary embolus
  • Sepsis
• Respiratory pump
• • Chest wall
  • • Diaphragm eventration
    • Diaphragmatic hernia
    • Flail chest
    • Kyphoscoliosis
  • Respiratory muscles
  • • Duchenne muscular dystrophy
    • Guillain-Barré syndrome
    • Infant botulism
    • Myasthenia gravis
    • Spinal cord trauma
    • SMA
• Central control
• • CNS infection
  • Drug overdose
  • Sleep apnea
  • Stroke
  • Traumatic brain injury

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Foreign bodies, trachea
Guillain-Barré syndrome
Ludwig angina
Neuromuscular disorders (eg, Duchenne muscular dystrophy or SMA type 1)
Pulmonary embolus
Spinal cord injury
Transverse myelitis, cervical or high thoracic
Vascular slings

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• ABG can be used to define acute respiratory failure. Arbitrary definitions include a PaCO₂ greater than 50 mm Hg, a PaO₂ less than 60 mm Hg, or arterial oxygen saturation less than 90%.
• An elevated serum bicarbonate level suggests metabolic compensation for chronic hypercapnia.
• A CBC count may be helpful; polycythemia suggests chronic hypoxemia.
• Electrolyte abnormalities can contribute to weakness; hypokalemia, hypocalcemia, and hypophosphatemia can impair muscle contraction.
• Calculate the alveolar-arterial oxygen difference ([A-a]DO₂), which is the difference between the alveolar partial pressure of oxygen (PAO) and PaO₂.
• • This value is an index of the efficiency of gas exchange by the lungs.
  • The alveolar gas equation is used to calculate the PAO₂ on the basis of the relationship between the pressure of oxygen in inspired gas (PiO₂), the PaCO₂, and the respiratory quotient (RQ), as follows: PAO₂ = FiO₂ (Pb - P_H2O) - (PaCO₂/RQ).
  • • PiO₂ is a function of the fractional concentration of inspired oxygen (FiO₂), the barometric pressure (Pb), and the partial pressure of water vapor (P_H2O) in humidified air.
    • RQ is the ratio of the volume of CO₂ expired to the volume of O₂ consumed by an organism. The body normally produces approximately 200 mL of CO₂ per minute and consumes approximately 250 mL of O₂ per minute; therefore, RQ is 0.8. Different fuel sources produce different RQ values: the RQ for carbohydrates is 1; protein is 0.8; and fat is 0.7.
  • In children, (A-a)DO₂ is normally 5-10 and reflects venous admixture from anatomic right-to-left shunts, which include the bronchial circulation, thesbian veins, and small arteriovenous anastomoses in the lung.
• The PaO₂/FiO₂ ratio is a commonly used indicator of gas exchange.
• • A PaO₂/FiO₂ less than 200 is correlated with a shunt fraction greater than 20%.
  • It is a component used to define ARDS.

Imaging Studies

• Lateral and anteroposterior (AP) radiographs of the neck can depict a radiopaque foreign body or soft-tissue structures encroaching on the lumen of the airway.
• Chest radiographs may yield helpful findings.
• • Evaluate for abnormalities that require immediate intervention (eg, malpositioned endotracheal tube, pneumothorax).
  • Common findings associated with respiratory failure include the following:
  • • Focal or diffuse pulmonary disease (eg, pneumonia, ARDS)
    • Bilateral hyperinflation (eg, asthma)
    • Asymmetric lung expansion suggesting a bronchial obstruction
    • Pleural effusion
    • Cardiomegaly
  • If hypoxemia is present but the chest radiograph is clear, this finding could suggest cyanotic congenital heart disease, pulmonary hypertension, or pulmonary emboli.
• Chest CT scanning can be performed when sophisticated diagnostic images are needed. It can further define radiopacities due to vascular, pleural, interstitial, or airway lesions.
• Airway CT scanning, MRI, and/or angiography can be used to differentiate deep-tissue structures, bone lesions, and vascular abnormalities.
• Fluoroscopy is valuable to evaluate the movement of the diaphragms and dynamic obstructive lesions of both the extrathoracic and intrathoracic airway.
• V/Q scanning can predict a probability of V/Q mismatch secondary to a pulmonary embolism.

Other Tests

• Determination of dead-space volume to tidal gas volume (V_D/V_T)
• • V_D/V_T is based on the difference between PaCO₂ and the CO₂ in exhaled gas (PeCO₂).
  • PeCO₂ is measured by collecting expired gas in a large collection bag and using an infrared CO₂ analyzer to measure the PCO₂ in a sample of gas.
  • In a normal lung, the capillary blood equilibrates fully with alveolar gas; therefore, the PeCO₂ approximates the PaCO₂.
  • As V_D/V_T increases, the PeCO₂ falls below PaCO₂.
  • Reference range V_D/V_T is approximately 0.30.
  • V_D/V_T = (PaCO₂ - PeCO₂)/PaCO₂
• Determination of the intrapulmonary shunt fraction (Q_s/Q_t)
• • Q_s/Q_t is the ratio of shunted flow (Q_s) to the total flow or cardiac output (Q_t). It is derived by the relationship between the oxygen content in arterial blood (CaO₂), mixed venous blood (CvO₂), and pulmonary capillary blood (CcO₂) while breathing FiO₂ that equals 1.
  • Arterial oxygen content (in mL O₂/dL) = [1.34 mL O₂/g hemoglobin X hemoglobin (in g/dL) X SpO₂] + [PaO₂ (in mm Hg) X 0.003 mL O₂/dL/mm Hg].
  • Directly measuring pulmonary capillary blood (CcO₂) is difficult; therefore, CcO₂ is assumed to be 100% when FiO₂ equals 1.
  • The normal intrapulmonary shunt is less than 10%.
  • Q_s/Q_t = (CcO₂ - CaO₂)/(CcO₂ - CvO₂)

Procedures

• Additional diagnostic procedures may be indicated after obtaining the initial history and performing the physical examination, laboratory tests, and radiologic studies.
• • Bronchoalveolar lavage (BAL)
  • • BAL is performed to identify a specific infectious pulmonary pathogen; bacterial, viral, and acid-fast bacillus (AFB) cultures and silver stains can be performed. BAL can also be performed to isolate lipid laden macrophages (suggestive of recurrent aspiration) or pulmonary hemorrhage.
    • In an intubated patient, samples can be obtained blindly or bronchoscopically.
    • BAL is indicated in critically ill children to guide antimicrobial therapy and in children whose conditions have deteriorated during therapy.
  • Lung biopsy
  • • Lung biopsy may be indicated if BAL does not reveal a pathogen, especially in immunocompromised hosts, to identify Aspergillus species or Pneumocystis jiroveci, (previously called Pneumocystis carinii).
    • Lung biopsy is helpful in the diagnosis of sarcoidosis and other granulomatous conditions.
  • Electromyography (EMG) or nerve conduction test: These tests can help determine the etiology for neuromuscular weakness leading to respiratory pump failure.
  • Fiberoptic and rigid bronchoscopy: This can be performed to assess large and small airways for anatomic abnormalities or foreign bodies.
  • Nasal airflow tracings coupled with chest-movement recordings (pneumograms): These have a specific role in identifying sleep-associated extrathoracic airway obstruction and respiratory control abnormalities.
  • Thoracentesis
  • • Check the cell count and protein level to determine whether pleural fluid is an exudate or transudate.
    • Measure triglycerides to determine if the effusion is chylous.
    • Obtain bacterial and AFB cultures.
    • Cytology is used to evaluate for malignant effusions.
  • Test of respiratory mechanics and lung-volume measurements: These are most beneficial in following the progression of disease and the effects of treatment over time.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

Management of acute respiratory failure begins with a determination of the underlying etiology. While supporting the respiratory system and ensuring adequate oxygen delivery to the tissues, initiate an intervention specifically defined to correct the underlying condition. For example, a patient with status asthmaticus is given supplemental oxygen to treat hypoxemia, but corticosteroids and beta-agonist drugs are also given to treat the underlying pathology.

• Extrathoracic airway support
• • For partial upper-airway obstruction, place a nasopharyngeal airway to provide a passageway for air; for example, obstruction caused by anesthesia or acute tonsillitis.
  • An oropharyngeal airway can be used temporarily in the unconscious patient.
  • For extrathoracic airway obstruction, such as croup, the following measures may be helpful:
  • • Inspired humidity to liquefy secretions
    • Heliox (helium and oxygen gas mixture) to decrease work of breathing: A helium concentration of 60-80% has a density lower than that of air and improves breathing by reducing turbulent airflow through a narrowed area. A requirement for inspired oxygen (>0.4) is a limiting factor in the use of Heliox.
    • Racemic epinephrine 2.25%, an aerosolized vasoconstrictor
    • Systemic corticosteroids to decrease airway edema
  • Instrumentation with an endotracheal tube is occasionally needed to maintain its patency in certain cases (eg, epiglottitis, thermal burns to the airway, severe croup).
• Tracheal intubation
• • In general, uncuffed tubes are used in children younger than 8 years because the subglottic trachea surrounded by the cricoid cartilage is the narrowest part of the pediatric airway.
  • • In neonates and infants younger than 6 months, an endotracheal tube with an inner diameter (ID) of 3 or 3.5 mm is appropriate.
    • In infants aged 6-12 months, a tube with a 3.5- or 4-mm ID is appropriate.
    • In children older than 1 year, the following formula can be used: Tube size (ID in millimeters) = (age in years + 16)/4
  • The mnemonic MSOAPP can be used to remember the preparation essential for a safe tracheal intubation procedure.
  • • M = Monitors (heart rate, blood pressure, pulse oximetry, capnography for CO₂ detection)
    • S = Suction and catheters
    • O = Oxygenation with a bag-valve mask
    • A = Apparatus (laryngoscope, endotracheal tubes appropriate for the patient's age and endotracheal tubes 0.5 size smaller and larger, stylets, oral airways)
    • P = Pharmacy (medications for amnesia and paralysis)
    • P = People (respiratory therapist, nurse, a skilled set of hands)
  • Confirming, properly sizing is accomplished by allowing the breathing circuit pressure to rise until air leaking around the tube can be auscultated. Leak pressure should be 15-30 cm H₂O.
• Lung and respiratory pump support
• • Oxygen therapy
  • • The initial treatment for hypoxemia is to provide supplemental oxygen.
    • High-flow (>15 L/min) oxygen delivery systems include a Venturi-type device that places an adjustable aperture lateral to the stream of oxygen. Oxygen is mixed with entrained room air, and the amount of air is adjusted by varying the aperture size. The oxygen hoods and tents also supply high gas flows.
    • Low-flow (<6 L/min) oxygen delivery systems include the nasal cannula and simple face mask.
  • Continuous positive airway pressure (CPAP)
  • • CPAP may be indicated if lung disease results in severe oxygenation abnormalities such that an FiO₂ greater than 0.6 is needed to maintain a PaO₂ greater than 60 mm Hg.
    • CPAP in pressures from 3-10 cm H₂O is applied to increase lung volume and may redistribute pulmonary edema fluid from the alveoli to the interstitium.
    • CPAP enhances ventilation to areas with low V/Q ratios and improves respiratory mechanics.
    • If a high concentration of FiO₂ is needed and if the patient does not tolerate even short periods of discontinued airway pressure, positive-pressure ventilation should be administered.
  • Noninvasive positive-pressure ventilation (NPPV)
  • • Noninvasive mechanical ventilation refers to assisted ventilation provided with nasal prongs or a face mask instead of an endotracheal or tracheostomy tube.
    • This therapy can be administered to decrease the work of breathing and to provide adequate gas exchange.
    • NPPV can be given by using a volume ventilator, a pressure-controlled ventilator, or a device for bilevel positive airway pressure (BIPAP or bilevel ventilator).
    • Inspiratory pressure support is a ventilator modality in which increased circuited pressure during inspiration boosts the patient's effort. However, the patient's effort, as reflected by sensitive measurement of the circuit gas flow, triggers both the beginning and end of the inspiratory phase of the mechanical cycle.
    • The severity of the patient's disease limits the use of this technique if periodic relief from the face mask or nasal prongs is unavailable for days.¹ A tracheal tube is necessary and safer under these circumstances.
  • Conventional mechanical ventilation
  • • Mechanical ventilation increases minute ventilation and decreases dead space. This approach is the mainstay of treatment for acute hypercapnia and severe hypoxemia.
    • A primary strategy for mechanical ventilation should be the avoidance of high peak inspiratory pressures and the optimization of lung recruitment.
    • In adults with ARDS, a strategy to provide low tidal volume (6 mL/kg) with optimized positive end-expiratory pressure (PEEP) offers a substantial survival benefit compared with a strategy for high tidal volume (12 mL/kg).
    • According to the permissive hypercapnia strategy in ARDS, arterial CO₂ is allowed to rise to levels as high as 100 mm Hg while the blood pH is maintained at greater than 7.2 by means of the intravenous administration of buffer solutions. This is done to limit inspiratory airway pressure to values less than 35 cm H₂O.
    • PEEP should be applied to a point above the inflection pressure such that alveolar distention is maintained throughout the ventilatory cycle.
    • Conventional mechanical ventilation optimizes lung recruitment, increases mean airway pressure and functional residual capacity, and reduces atelectasis between breaths.
• Nonconventional modes of ventilation
• • Inverse ratio ventilation
  • • During positive pressure ventilation, the inspiratory phase is prolonged in excess of the expiratory phase.
    • It increases mean airway pressure and improves oxygenation during severe acute lung disease.
    • It is a nonphysiologic pattern for breathing; therefore, these patients are administered heavy sedation and paralysis.
  • Airway pressure release ventilation (APRV)
  • • APRV is a relatively new form of inverse-ratio ventilation in which a continuous gas flow circuit is used. This method allows the patient to breathe spontaneously throughout the ventilatory cycle.
    • In concept, APRV applies a continuous airway pressure (P_high) identical to that of CPAP to maintain lung volume and promote alveolar recruitment. In addition, a time-cycled release phase lowers the set pressure (P_low) to augment ventilation.
    • Clinical and experimental studies with APRV demonstrate improvements in gas exchange, cardiac output, and systemic blood flow.
    • Some data suggest reduced use of sedatives and neuromuscular blockers.²
  • High-frequency oscillatory ventilation (HFOV)
  • • HFOV combines small tidal volumes (smaller than the calculated airway dead space) with frequencies of more than 1 Hz to minimize the effects of elevated peak and mean airway pressures.
    • HFOV has proven benefit in improving the occurrence and treatment of air-leak syndromes associated with neonatal and pediatric acute lung injury.
• Adjunctive therapies for severe hypoxemia
• • Prone positioning
  • • Prone positioning reduces compliance of the thoracoabdominal cage by impeding the compliant rib cage. Gases should distribute toward the sternal and anterior diaphragmatic regions that become dependent on prone positioning. Improved homogeneity of ventilation improves oxygenation.
    • This measure may cause a redistribution of blood flow, improving the V/Q match.
    • Researchers in a multicenter randomized controlled clinical trial concluded that prone positioning did not significantly reduce ventilator-free days, mortality, or time to recovery in pediatric patients with acute lung injury.³
  • Inhaled nitric oxide (NO)
  • • NO is an endogenous free radical that mediates smooth muscle relaxation throughout the body.
    • When delivered by means of inhalation, the potential benefit of NO is to improve ventilation to perfusion matching by enhancing pulmonary blood flow to well-ventilated parts of the lung.
    • This therapy is relatively safe because hemoglobin inactivates it quickly and because does not cause systemic vasodilation leading to hypotension.
    • Methemoglobin and nitrogen dioxide (NO₂) levels should be monitored.
    • Inhaled NO is being studied for use in type I respiratory failure; in 1999, the US Food and Drug Administration (FDA) approved its use in neonates with hypoxic respiratory failure and evidence of pulmonary hypertension.
  • Administration of exogenous surfactant
  • • Surfactant is an endogenous complex of lipids and proteins that lines the walls of alveoli and promotes alveolar stability by reducing surface tension.
    • Relative surfactant deficiency is variably present as a consequence of many lung diseases.
    • Exogenous surfactant replacement is of clear benefit to improve respiratory mechanics and oxygenation in the neonatal respiratory distress syndrome (RDS). Its role in severe lung injury in other pediatric populations or adults is still investigated.
    • Investigators in a multicenter randomized blinded clinical trial concluded that exogenous surfactant replacement in pediatric acute lung injury decreased mortality but that it had no effect on ventilator-free days.⁴
• • Rescue therapy with extracorporeal life support (ECLS)
  • • ECLS: blood is removed from the patient, passed through an artificial membrane where gas exchange occurs, and is returned to the body by either the arterial (venoarterial [VA]) or venous (venovenous [VV]) system.
    • VV ECLS has become the preferred method for patients of all age groups who do not require cardiac support.
    • Data from many studies support the use of ECLS in neonatal respiratory failure when the mortality risk is high. Further studies in pediatric patients are underway.
    • From 1980-1998 at the University of Michigan, 586 neonatal, 132 pediatric, and 146 adult patients were given ECLS for respiratory failure, with survival rates of 88%, 70%, and 56%, respectively.⁵
    • In 2004, the Extracorporeal Life Support Organization (ELSO) Registry reported that the number of pediatric respiratory cases was relatively constant (approximately 200 cases per year), with an overall survival rate of 56%.⁶ Individual centers have various survival rates.

Consultations

• Neurologist for neuromuscular weakness evaluation
• Cardiologist if left-sided valvar obstruction or cardiomyopathy is suspected
• Pulmonologist for chronic pulmonary diseases
• Otorhinolaryngologist for evaluation of foreign-body aspiration or anatomic abnormality

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

The use of medications in the treatment of respiratory failure depends on the underlying disorder. Corticosteroids and beta-agonist medications treat an asthma exacerbation, whereas antibiotics treat bacterial pneumonia. Patients with pulmonary edema from myocardial dysfunction improve with diuretics and inotropic support. See Acute Respiratory Distress Syndrome; Respiratory Distress Syndrome; Pediatrics, Pneumonia; Asthma; and Status Asthmaticus.

Drug Category: Pulmonary vasodilators

Inhaled NO is a pulmonary vasodilator indicated to treat pulmonary hypertension. NO is also being studied for severe hypoxemia in ARDS.

Drug Category: Lung surfactants

Exogenous surfactant can be helpful in the treatment of airspace disease. After inhalation, surface tension is reduced and alveoli are stabilized, decreasing the work of breathing and increasing lung compliance. These drugs are indicated for the prevention and treatment of neonatal RDS. They are also being investigated for the treatment of hypoxemia secondary to ARDS.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• The response to therapy must be continuously assessed.
• Patients with acute respiratory acidosis require admission to the ICU for close monitoring and possible advanced airway management.
• Correct electrolyte abnormalities associated with muscle weakness, such as hypophosphatemia, hypokalemia, hypomagnesemia, and hypocalcemia.
• Narcotics, sedatives, or other respiratory depressants should be cautiously administered when the patient is breathing spontaneously and shows signs of increased respiratory work.
• Maximize nutrition, but avoid overfeeding and high carbohydrate content diet because these can increase CO₂ production and hypercapnia if the patient cannot increase his or her minute ventilation.
• Additional inpatient therapies are discussed in Treatment. These include CPAP, noninvasive mechanical ventilation, conventional and nonconventional mechanical ventilation, prone positioning, and rescue therapy with ECLS.

Further Outpatient Care

• For chronic respiratory insufficiency, frequent follow-up with pulmonary function testing is necessary to provide a reference baseline and to monitor for changes over time and during acute illness.
• Home supplemental oxygen may be indicated in some patients.
• NPPV is an effective home therapy for chronic respiratory failure caused by obstructive sleep apnea, neuromuscular disease, or obesity hypoventilation syndrome. Therapy can be provided nocturnally, intermittently with certain activities, or (in rare cases) continuously.
• Home nursing availability can be helpful to provide additional care.

In/Out Patient Meds

• Prescribed medications depend on the underlying cause that contributed to the respiratory failure.

Transfer

• If the patient has moderate-to-severe oxygenation issues, the decision to transfer him or her to a tertiary care center for potential rescue therapy with ECLS should be made within the first 5 days of acute illness.

Complications

• Noninvasive ventilation poses several risks.
• • It may delay the start of mechanical ventilation by means of an endotracheal tube.
  • Prolonged wearing of the facial interface can lead to nasal congestion, facial reddening, eye irritation, or ulceration of the nasal bridge.
  • Gastric distention can occur, with possible pulmonary aspiration.
• In a spontaneously breathing person with high minute ventilation, care must be taken to maintain that level if tracheal intubation is required. The purpose is to avoid a sudden increase in PaCO₂ that could contribute to hemodynamic instability or cardiopulmonary arrest.
• Tracheal intubation may lead to upper-airway edema and difficult extubation, especially in patients with chronic illness and a limited baseline pulmonary reserve.
• Ventilator-induced lung injury (VILI) may occur secondary to alveoli overdistention (volutrauma).
• Air-leak syndromes, pneumothorax, or pulmonary interstitial emphysema may occur secondary to elevated inspiratory pressures.
• Posthypercapnic alkalosis can occur in patients with chronic hypercapnia if PaCO₂ is rapidly reduced with mechanical ventilation. The kidneys have a relatively slow mechanism to correct the bicarbonate excess. The metabolic alkalosis can be treated by replacing chloride or by increasing renal bicarbonate excretion with acetazolamide.

Prognosis

• The prognosis depends on the underlying etiology leading to acute respiratory failure.
• The prognosis can be good when the respiratory failure is an acute event not associated with prolonged hypoxemia (eg, in the case of a seizure or intoxication).
• The prognosis may be fair when a new process is associated with chronic respiratory failure secondary to a neuromuscular disease or thoracic deformity. This may herald the need for long-term mechanical ventilation.
• The prognosis can vary when respiratory failure is associated with a chronic disease with acute exacerbations.
• Respiratory failure may be the sign of an irreversible progressive disease that leads to death (eg, idiopathic pulmonary hypertension).

Patient Education

• For excellent patient education resources, visit eMedicine's Lung and Airway Center. Also, see eMedicine's patient education article Acute Respiratory Distress Syndrome.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to respond to a child with impending or existing respiratory failure can lead to life-threatening hypoxemia with resultant end-organ perfusion abnormalities, especially hypoxic ischemic encephalopathy.
• Failure to aggressively manage acute respiratory failure with assisted ventilation can lead to an otherwise avoidable respiratory and/or cardiovascular arrest.
• Do not treat alveolar hypoventilation with supplemental oxygen; it must be treated with an augmentation of ventilation.
• Using sedative medications in a nonintubated patient can worsen respiratory acidosis, leading to unrecognized CO₂ narcosis.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

1. Esteban A, Frutos-Vivar F, Ferguson ND, et al. Noninvasive positive-pressure ventilation for respiratory failure after extubation. N Engl J Med. Jun 10 2004;350(24):2452-60. [Medline].
2. Habashi NM. Other approaches to open-lung ventilation: airway pressure release ventilation. Crit Care Med. Mar 2005;33(3 Suppl):S228-40. [Medline].
3. Curley MA, Hibberd PL, Fineman LD, et al. Effect of prone positioning on clinical outcomes in children with acute lung injury: a randomized controlled trial. JAMA. Jul 13 2005;294(2):229-37. [Medline].
4. Willson DF, Thomas NJ, Markovitz BP, et al. Effect of exogenous surfactant (calfactant) in pediatric acute lung injury: a randomized controlled trial. JAMA. Jan 26 2005;293(4):470-6. [Medline]. [Full Text].
5. Bartlett RH, Roloff DW, Custer JR, et al. Extracorporeal life support: the University of Michigan experience. JAMA. Feb 16 2000;283(7):904-8. [Medline].
6. Conrad SA, Rycus PT, Dalton H. Extracorporeal Life Support Registry Report 2004. ASAIO J. Jan-Feb 2005;51(1):4-10. [Medline].
7. Anderson MR. Update on pediatric acute respiratory distress syndrome. Respir Care. 2003;48:261-76. [Medline].
8. Brochard L. Noninvasive ventilation for acute respiratory failure. JAMA. Aug 28 2002;288(8):932-5. [Medline].
9. Priestley MA, Helfaer MA. Approaches in the management of acute respiratory failure in children. Curr Opin Pediatr. Jun 2004;16(3):293-8. [Medline].
10. Schramm CM. Current concepts of respiratory complications of neuromuscular disease in children. Curr Opin Pediatr. Jun 2000;12(3):203-7. [Medline].
11. Sokol J, Jacobs SE, Bohn D. Inhaled nitric oxide for acute hypoxic respiratory failure in children and adults: a meta-analysis. Anesth Analg. Oct 2003;97(4):989-98. [Medline].
12. The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. May 4 2000;342(18):1301-8. [Medline].

Article Last Updated: Feb 12, 2008