Respiratory Failure – lower airway obstruction: bronchiolitis/asthma

1. Description of the problem

Asthma

Asthma is a chronic disease that affects people of all ages. An acute exacerbation triggers a triad of symptoms that result in diminished airflow and airway obstruction. It is a disease of the lower airways marked by a triad of airway swelling, hyperreactivity and increased mucus production, which results in obstruction of the lower airways causing hyperinflation and ventilation perfusion mismatch.

These physiologic changes lead to coughing, wheezing, shortness of breath, and chest tightness. An asthma exacerbation can be brought on by many factors; for example, changes in weather, allergens, exercise, or an infectious process. The triggers may vary for a given individual.

Bronchiolitis

Bronchiolitis is a disease that most commonly affects young children. It tends to be infectious in nature, typically viral. In bronchiolitis there is also airway edema and obstruction to airflow, which can lead to wheezing and respiratory distress. The younger the infant the more severely affected they tend to be.

Clinical features

The clinical feature of asthma are:

• Wheezing and/or coughing

• Shortness of breath or difficulty in breathing

• Respiratory distress (tachypnea and possibly retractions)

• Post-tussive emesis

• Chest pain

• Depending on the severity of the attack, patients can be hypoxic and in severe cases hypercarbic.

The clinical features of bronchiolitis are:

• Respiratory distress (tachypnea, retractions, nasal flaring, grunting)

• Coughing

• Rhinorrhea (often copious)

• Wheezing

• Fever

• Apnea in infants

Key management points

In both asthma and bronchiolitis the initial management will depend on the severity of the presentation The patient should be placed on a pulse oximeter and supplemental oxygen provided if the saturations are below normal. Management should then be provided to ensure adequate oxygenation and ventilation. For mild cases of asthma this may mean simply giving an inhaled beta agonist and perhaps steroids; however, in the patient in extremis this may require subcutaneous epinephrine (or terbutaline) and possible emergent intubation This approach is also true for the infant with bronchiolitis.

The mild cases often improve significantly simply with deep nasal suctioning. If this does not help, then a trial of bronchodilators can be tried. About one third of the cases will respond to traditional beta agonists such as albuterol; in those who do not respond a subset will respond to nebulized racemic epinephrine. However, there are a subset who do not respond to either, in which case the treatment is generally supportive care. Additionally, small infants can often have significant distress or even apnea with bronchiolitis and may require noninvasive positive pressure ventilation (NIPPV) or even intubation.

In either type of patient if there is severe distress, the child should be made NPO (nothing by mouth) and an intravenous (IV) line started for fluid administration and possibly for medication administration.

2. Emergency Management

In any case of respiratory distress, the first priority is to ensure an adequate airway. Most children who present with asthma will come in some degree of distress; however, most are able to be treated without intubation. A good physical examination and a brief history are essential. One should assess work of breathing to include respiratory rate, evidence of retractions, ability to speak and limitations (ie, can they speak in full sentences or just one to two words), and the quality of the breath sounds (end-expiratory wheeze, continual wheeze, or absence of breath sounds).

One should assess the child’s mental status as signs of confusion or excessive sleepiness may be an indication of hypercarbia. If the child is experiencing significant distress, a blood gas may be warranted. One should anticipate a relatively low PCO2 from the tachypnea. If the CO2 is normal or high this may suggest respiratory insufficiency and potentially impending failure.

The child with bronchiolitis can present often with simply signs of cough and congestion. The case may be mild and all that is required is nasal suctioning and reassurance to the parents. However, some children with bronchiolitis will present with severe distress and or apnea. In this case along with deep nasal suctioning the children may require increasing support with either NIPPV (ie, cpap or hi-flow nasal cannulae) or intubation. The decision to intubate will be made based on clinical appearance, blood gas results and capabilities of your institution.

Asthma

• Place patient on monitor and pulse oximeter.

• Oxygen to maintain saturations greater than 90 to 92

• If severe distress or unable to take medicines by mouth, establish IV access.

• If in extremis give subcutaneous epinephrine and prepare to intubate.

• If in severe distress or altered mental status, check blood gas and consider intubation.

• If not in extremis, give inhaled beta agonist.

• Consider addition of atrovent if moderate to severe exacerbation.

• If not vomiting and able to take PO give steroids by mouth; if unable and more than mild exacerbation give IV steroids.

• If persistent distress or hypoxia, admission for continued treatment and observation is warranted.

• Continually monitor progression. If not improving consider adjunctive therapies such as ipratropium bromide, magnesium sulfate, Heliox and NIPPV.

• If in extremis or impending respiratory failure, intubation is warranted.

Bronchiolitis

• Place patient on monitor and pulse oximeter.

• Oxygen to maintain saturations greater than 90-92.

• If severe distress or unable to take medicines by mouth, establish IV access; if unable, consider Intraosseous.

• If in extremis prepare to intubate.

• If in severe distress or altered mental status, check blood gas and consider intubation.

• If not in extremis, deep nasal suctioning. Infants are obligate nasal breathers and will often improve with good suctioning.

• If not significantly improved, give an inhaled beta agonist such as albuterol.

• If does not improve, consider nebulized racemic epinephrine.

• If persistent distress or hypoxia, admission for further treatment and observation is warranted.

• Continually monitor progression. If not improving, consider adjunctive therapies such as NIPPV and heliox.

• If in extremis or impending respiratory failure, intubation is warranted.

3. Diagnosis

Diagnostic criteria and tests

Asthma is a chronic disease hallmarked by airway inflammation, airway hyperactivity and increased secretions, which lead to obstruction of flow. The diagnosis is often made based on a history of recurrent symptoms. Pulmonary function test may be done to help establish the diagnosis; however, often the diagnosis is made by pediatricians based on repeated episodes of wheezing.

The diagnosis of bronchiolitis is likewise often made based on history and physical examination. In a young infant who presents with cough, wheeze, and rhinorrhea one must entertain the diagnosis of bronchiolitis. The vast majority are viral. The most common virus is respiratory syncytial virus (RSV). This virus most commonly occurs in late fall and winter but the season varies depending on where the patient lives.

Normal lab values

The asthmatic child may have a chest radiograph that shows hyperinflation and flattening of the diaphragm. Other laboratory tests are often unremarkable. If the child has an allergic component to their asthma they may have an eosinophilia on the differential of their complete blood count. During an exacerbation (or in periods of poor control), children will often have decreased peak expiratory flows or low forced expiratory volumes.

The most common diagnostic test performed for bronchiolitis is a test for RSV or a respiratory viral panel or culture. A chest radiograph is often performed and can show hyperinflation, perihylar cuffing and areas of atelectasis.

Establishing the diagnosis

The diagnosis of both asthma and bronchiolitis are made generally from the history and physical examination. The child with asthma will have history of recurrent cough and wheeze and may have identifiable triggers. Unless an infection is the cause of the exacerbation, they are generally afebrile.

The diagnosis of bronchiolitis is also often based on history and physical examination. In older children and adults it generally mimics an upper respiratory tract infection with cough and congestion. In younger children it is much more likely to be symptomatic. They present with fever, cough, wheeze and distress. There may be a history of other family members or friends being ill with “colds.”

Differential diagnosis

The differential diagnosis for asthma and bronchiolitis includes other entities that can present with wheeze or respiratory distress. This includes aspiration pneumonia, gastroesophageal reflux, congestive heart failure, foreign body and other airway disorders such as vocal cord paralysis or tracheomalacia. A good history and physical examination can often help one differentiate.

Confirmatory tests

In the acute setting the diagnosis of asthma is based primarily on history and physical examination. For the child with bronchiolitis a test for RSV, or a viral panel, may be helpful in confirming the diagnosis and for cohorting patients who are admitted.

4. Specific Treatment

Asthma

The first-line treatment of asthma in the child includes bronchodilator therapy. One generally starts with a beta agonist such as albuterol to help relax the bronchial smooth muscle. Beta agonist can be administered either as intermittent inhaled treatments or in the more moderate-to-severe case as a continuous treatment over about an hour. In the child in extremis one would administer epinephrine or terbutaline subcutaneously. Additionally, steroids such as prednisone or methylprednisolone are also given fairly early in the course. Steroids will help reduce airway inflammation; however, in the acute phase steroids promote upregulation of the beta receptors, thus making the beta agonist more effective.

If the child is having more than a mild attack one should add anticholenergics such as ipratroprium bromide to the inhalational treatment. Ipratropium also causes airway relaxation; however, this is accomplished through action on the muscarinic receptor.

The next line of therapy to be considered either in the child with a severe attack or the child with a moderate attack who is not improving is magnesium sulfate. This therapy will also promote smooth muscle relaxation. Magnesium will be administered intravenously over 20 minutes. One must monitor the blood pressure in a child receiving magnesium therapy as it may cause hypotension.

If the child is still having difficulty one can proceed with more aggressive beta agonist therapy in the form of IV infusion. Typically terbutaline is used. Generally the child is given a loading dose and then maintained on an infusion. IV terbutaline has more systemic side effects than inhaled beta agonists. If giving an infusion one should monitor for signs of ischemia such as ST segment depression.

If the child is having moderate to severe distress but is not experiencing significant hypoxia (requiring less than 50% FIO₂) one can consider the addition of heliox. Heliox is a blend of helium and oxygen. Because helium is a lighter, or less dense gas, it reduces turbulent flow. The theory is that it will improve delivery of both oxygen and nebulized particles to more distal airways.

If the child continues to have severe distress one can consider the use of NIPPV. This may help with decreasing the work of breathing. However, in small children NIPPV may cause agitation and may require the addition of sedation to tolerate. Giving sedation may alter the ability to monitor the child’s neurologic status and therefore must be done cautiously in a closely monitored setting. In a small child generally cpap is started at 5 and titrated up as needed to a level of 8 to 10. In the older child bipap may be more beneficial. Generally starting at settings of 12/6 and titrating upwards to 16/8.

If the child presents in extremis or progresses to respiratory failure, intubation is necessary. Intubation of an asthmatic child must not be taken lightly. Introduction of an endotracheal tube can cause severe bronchospasm. The intubation should be done by the person who has the most airway experience. If possible, a round of code drugs should be readily available as well as normal saline or lactated ringers. As long as no contraindication exists the intubation drug of choice is ketamine along with a short-acting paralyzing agent such as rocuronium or succinylcholine. Intubation will alter intrathoraxic pressure and can lead to hypotension. If time permits many recommend bolusing the patient with crystalloid prior to intubation.

Once intubated the ventilator needs to be set cautiously. Patients with asthma tend to be intubated for hypercarbic respiratory failure related to the inability to exhale fully. The knee jerk response is to set the ventilator to a high rate to increase minute ventilation. However, in the asthmatic because they are air trapping the rate actually needs to be set relatively low, often as low as 8 to 12 breaths per minute. Likewise, because of the poor chest wall compliance they may take relatively high peak pressure (in the 40s) to ensure adequate delivery of tidal volume.

One must remember, however, that not all that pressure is being seen by the distal airways and measuring a plateau pressure may be helpful and reassuring. If possible maintain a plateau pressure less than 30cm H₂O. Furthermore, to allow adequate exhalation the inspiratory time should be set relatively low to maintain an I:E ratio of around 1:4 or 1:5. Finally the positive end expiratory pressure (PEEP) should also be set relatively low (generally 5 or less to start).

Also it is important to note the goal for the intubated asthmatic is not normalization of the blood gas.

To minimize barotrauma we accept relatively higher PCO₂ and a relatively lower pH. A strategy of permissive hypercapnea. Most would argue a pH above 7.20 is an acceptable target as long as there is no significant hemodynamic instability.

Finally, the patient with severe asthma is at risk of developing a pneumothorax. If there are sudden changes in oxygen saturation or severity of dyspnea one should explore the potential of a pneumothorax.

Bronchiolitis

Infants are obligate nasal breathers and bronchiolitis is often accompanied by copious thick nasal secretions. Often deep nasal suctioning provides significant relief and improvement. Once suctioning is complete one can institute a trial of bronchodilator therapy if the child is still having distress and wheezing is heard on examination. Start with a beta agonist and reassess for improvement. If there is positive improvement continue treatments as necessary. If there is no improvement institute a trial of inhaled racemic epinephrine. If there is a positive response to this then continue to utilize as necessary up to every 2 hours.

If there is no response then discontinue inhalational therapy and continue supportive care. Steroids are generally not indicated in the child with pure bronchiolitis. If there is a strong family history of asthma, a short trial of steroids can be considered.

Additionally, If the child is having significant distress, one can consider the use of NIPPV (either in the form of hi-flow nasal cannulae or cpap or bipap). Keep in mind that normal oxygen saturations do not ensure adequate ventilation. If the child is having significant distress, a blood gas may be warranted. Initial NIPPV settings are often determined by age and severity of the distress. Hi-flow nasal cannulae is often started at 5 liters per minute and titrated up, CPAP or Bipap as described above for asthma.

If the distress continues to be significant, a trial of heliox may be initiated. If the child is having apnea, high oxygen requirements or high PCO₂ the child may require intubation. If the infant is less than a year, atropine should be used along with whatever sedative and paralytic chosen. Once on the ventilator, settings should be chosen according to age. The goal is to achieve a TV of around 6 to 8cc/kg and to maintain a peak inspiratory pressure (PIP) greater than 30cm H₂O. The rate is adjusted as needed to maintain a PCO₂ within acceptable range. Allowing some degree of permissive hypercapnea will generally allow lower pressures to be used and help avoid barotrauma.

If high pressures are an issue, adding a paralytic drip may help to improve compliance.

If a child is requiring a PIP greater than 30, peep greater than 10 or an FIO₂ persistently greater than 60% to 70% one should consider transition to high frequency of ventilation. Moreover, infants with bronchiolitis who require mechanical ventilation often have a secondary bacterial superinfection. Respiratory cultures should be obtained and one should consider coverage for bacterial pneumonia.

Additionally, new research reports some success with hypertonic saline nebulization. It is thought to help promote mucociliary clearance and reduce airway edema by absorbing water from the mucosa and submucosa.

Drugs and dosages

Asthma

• Albuterol intermittent nebulization: 2.5 mg for the infant or 5 mg per nebulization for the child

• Albuterol continuous nebulization: 7.5 mg/h for the infant, 5 mg/h for the child and 15 mg/h for the adolescent

• Ipratropium bromide 0.25 to 0.5 mg added to the first 3 nebs and then every 4 to 6 hours given with the albuterol for the first 24 hours.

• Methylprednisolone 2 to 4 mg/kg/day in divided doses with a maximum single dose of 60 mg

• Magnesium sulfate 25 to 75 mg/kg to a max of 2g given IV over 20 minutes. May repeat every 4 to 6 hours as necessary.

• Terbutaline: loading dose of 5 to 10mcg/kg and then an infusion of 0.4 to 10mcg/kg/min

• Subcutaneous epinephrine: 0.3 to 0.5 mg of the 1:1000 solution

• Ketamine 1 to 2 mg/kg

Bronchiolitis

• Albuterol intermittent nebulization: 2.5 mg for the infant or 5 mg per nebulization for the child

• Racemic epinephrine 0.25 to 0.5mL in 3cc normal saline

Refractory cases

Refractory Asthma

In particularly refractory cases of intubated asthma one should consider a trial of inhaled anesthesia, and if this fails extracorporeal life support (ELSO). Given that ELSO is not offered at all institutions, if an intubated asthmatic is not improving after intubation, one should consider transfer to an ELSO center.

Refractory Bronchiolitis

In the child who is failing conventional ventilation with bronchiolitis, one should consider high-frequency ventilation and if this too fails one should consider ELSO.

5. Disease monitoring, follow-up and disposition

Expected response to treatment

The overall prognosis for patients with asthma or bronchiolitis is very good. Patients who fail to improve in the emergency room or urgent care setting should be admitted to the hospital for further observation and management. Those patients requiring greater than 40% FIO₂, heliox or NIPPV should be admitted to an intensive care unit for further management. Once a child is able to be maintained on room air and nebulized treatments no more frequently than every 4 hours, discharge home can be considered with follow-up by the patient’s primary care physician.

It is important to inform parents of infants with bronchiolitis that the children can have cough, congestion and wheeze for a few weeks after the initial presentation.

Incorrect diagnosis

The diagnosis of asthma and bronchiolitis is generally based on history and physical examination. If the child is not improving as expected, one should consider alternative diagnosis or confounding issues. In small children, foreign body aspiration must be entertained. Additionally in the very ill bronchiolitic, one must consider a secondary bacterial infection.

Follow-up

Patients who are admitted for asthma or bronchiolitis should follow up with their primary physician within a few days of discharge. Those with recurrent or poorly controlled asthma should be referred to a pulmonologist or allergist for further work-up and long-term management.

Pathophysiology

Asthma

Asthma is a chronic condition caused by inflammation of the airways. The inflammatory response involves many cell types including lymphocytes, mast cells and macrophages; and involves the release of histamine, leukotrienes and other mediators of the inflammatory response. The inciting factor for the inflammation is multifaceted. There can be underlying genetic components as well as environmental factors. The inflammation leads to increased mucus production and hyperreactivity, or bronchospasm, of the airway.

The inflammation, bronchoconstriction and increased secretions all contribute to airflow obstruction. The airflow obstruction in turn leads to hyperinflation and ventilation perfusion mismatching. Over time if not corrected there can be a resultant hypoxia and in the more severe cases hypercarbia.

Bronchiolitis

Bronchiolitis is most often caused by a viral infection. In the majority of cases the causative agent is RSV, but it can be caused by parainfluenza, rhinovirus, metapneumovirus as well as others. The virus infiltrates epithelium of the small airways and causes necrosis and sloughing of the airway. There is then release of inflammatory mediators, which further promote airway edema. The combination of edema, sloughing and secretions in turn leads to obstruction of the small airways, which results in hyperinflation, atelectasis and respiratory distress.

Epidemiology

Asthma

Asthma is one of the most common diseases in children. It accounts for millions of emergency room visits and hospitalizations per year. Furthermore it has a high economic and social burden. The direct and indirect cost (treatment, missed days of work, etc) are estimated to be in the billions of dollars per year. There is higher incidence in industrialized countries. Some believe this is secondary to environmental triggers such as pollution. However, others believe the disparities in prevalence may not be as drastic as they appear; rather the incidence is significantly underreported in underdeveloped countries as in Africa and India.

In childhood, boys are more likely to be diagnosed with asthma than girls. This difference evens out in adolescence and then shifts in adulthood to females having a higher incidence than males. There also appears to be a racial disparity. African Americans have a higher incidence of asthma and asthma-related hospitalizations than do Caucasians.

Bronchiolitis

Bronchiolitis is a disease that mainly affects children under the age of 2 years. The vast majority of children who require hospital admission are under 1 year of age and more than half of these are children less than 6 months of age; premature infants or those with congenital heart disease tend to be more severely affected.

There is a seasonal pattern with infections seen predominantly in the late fall and winter. In warmer countries there is a shift to earlier in the year and the season may also extend into early spring.

Transmission occurs through contact with secretions; therefore contact isolation is recommended for hospitalized children.

Prognosis

Asthma

The prognosis for children with asthma is generally very good. In fact many children with childhood onset asthma will have decreasing symptoms with age. However, not all children do well. Each year several thousand individuals can die from asthma. Unlike in adults in whom death is often related to poor control and a slow deterioration, death in children tends to occur suddenly with a very rapid onset of symptoms. Both in adults and children death generally occurs in the prehospital setting. Any child who has had multiple admissions or an admission to an intensive care unit should be referred to a pulmonologist or allergist for further monitoring and treatment.

Bronchiolitis

Overall the prognosis of infants with bronchiolitis is very good. Only a small percentage of infected children (about 2%) actually require hospitalization and of those hospitalized the mortality rate is approximately 1%; many of the infants who die from bronchiolitis are higher risk infants with a history of congenital heart disease or those with a history of bronchopulmonary dysplasia.

Special considerations for nursing and allied health professionals.

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What's the evidence?

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