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Asthma, a leading cause of respiratory compromise, can be assessed with capnography and effectively treated with BLS and ALS medications
By Bob Sullivan
Asthma is a chronic disease that affects 24 million people in the United States and causes 5,000 to 6,000 deaths each year [1,2]. Prompt recognition and treatment of asthma, a leading cause of respiratory compromise, by EMS providers can quickly relieve symptoms and improve patient outcomes. Here are five things you should know about caring for patients with asthma:
1. Asthma causes more problems with ventilation than oxygenation
Asthma attacks are caused by an exaggerated immune response, which triggers sudden constriction of bronchial smooth muscles, inflammation, and mucus secretion in the lower airways. Asthma attacks can be caused by exposure to an allergen, viral illness, exercise, cold air, or stress, and patients experience shortness of breath, wheezing, coughing, and chest tightness during an attack [1]. Asthma is usually diagnosed in childhood, and patients are prescribed medications, like albuterol, administered by inhaler or nebulizer, as well as oral medications, like Montelukast (Singulair), to manage their symptoms.
Respiratory muscles normally relax during exhalation, but during an asthma attack accessory muscles are needed to push air out. This causes a prolonged expiratory phase, and wheezing from turbulent airflow through constricted airways. During severe asthma attacks, patients cannot fully exhale before taking their next breath in. Carbon dioxide builds up in the lungs as air gets trapped in the alveoli. Unless corrected, patients eventually tire from increased work of breathing and lose the ability to compensate.
2. Patient history and waveform capnography help identify asthma attacks
Asthma attacks can mimic other respiratory conditions. Wheezing from the lower airways can be difficult to distinguish from sounds caused by upper airway inflammation. Anxiety can trigger an asthma attack, but it can also cause hyperventilation with no bronchospasm. The sound of air passing, sometimes referred to as cardiac wheezes, through fluid-filled alveoli from pulmonary edema, can be made worse if misdiagnosed and treated as an asthma attack.
Not all asthma attacks cause wheezing. Cough may be the only sign of an asthma attack, especially in exercise-induced and nocturnal attacks [1]. Breath sounds may be diminished or absent in severe asthma attacks, which an ominous sign of decreased air movement through the lower airways.
Waveform capnography is a valuable tool to differentiate an asthma attack from other causes of respiratory distress. The waveform represents air movement throughout the respiratory cycle, and is normally rectangular shaped. Bronchoconstriction causes air to be released unevenly from the alveoli, which makes the capnography waveform appear rounded, similar to a shark fin [3].
The length of the waveform also represents the exhalation phase, which is prolonged during an asthma attack. The more severe the bronchoconstriction, the more pronounced the shark fin and length of the waveform. This can be seen even if the patient has diminished breath sounds and is not wheezing.
Bronchospasm is the only cause of a rounded, shark-fin capnogram. Respiratory compromise with a rectangular-shaped waveform is caused by something else. This includes wheezing heard in pulmonary edema, because the alveoli still empty evenly and CO2 moves through water at the same rate it moves through air.
Lower airway inflammation from COPD, pneumonia, and bronchiolitis can also cause bronchoconstriction and a shark-fin capnography waveform. A thorough history and physical exam is needed to differentiate asthma from those conditions. Ask the patient about symptom onset, cough, fever and exposure to a trigger. Asthma attacks are usually sudden, with a nonproductive cough and no fever.
3. Assess capnography, work of breathing, lung sounds and pulse-oximetry to determine the severity of an asthma attack
EMS is often called when asthma attacks are worse than ones a patient normally experiences, when a patient is not compliant with their treatment plan, or they do not get better after treatment at home. Ask patients if their current asthma attack is worse than any they have had in the past, if they have ever been intubated for an asthma attack, and if they have used any inhalers or breathing treatments before calling. This helps predict which EMS interventions will be effective and whether assisted ventilation will be needed.
Patients having mild asthma attacks are able to speak in full sentences. Wheezing may be heard at the end of exhalation. In moderate to severe attacks, patients may be seated upright in a tripod position, get winded with speaking, use accessory muscles to breathe, and have supraclavicular and subcostal retractions. Wheezing may be heard throughout exhalation. Also expect the patient to have altered mental status, such as awake and anxious during a moderate attack.
Patients having a severe attack may have difficulty holding their head up from respiratory muscle fatigue and hypoxia, and only speak in short phrases. Wheezing may be heard on inhalation and exhalation, or breath sounds may be diminished or absent. Decreased level of consciousness is another sign of the seriousness of a severe asthma attack.
Capnography also displays real-time feedback on respiratory rate and the amount of CO2 eliminated at the end of exhalation, which helps determine the severity of an asthma attack. End-tidal CO2 (ETCO2) is normally 35-45 mm HG. When an asthma attack begins, bronchoconstriction triggers an increased respiratory rate to compensate and an excess of CO2 to be eliminated.
As the attack progresses, air becomes trapped in the lower airways and the alveoli hyperinflate. Respiratory failure begins when patients are unable to effectively eliminate CO2, and air trapping worsens with each breath the patient takes in [1]. This causes ETCO2 to rises above normal and the shark-fin waveform to be more pronounced [3]. The capnography waveform will appear like a triangle when the patient cannot exhale completely before taking in their next breath
Pulse-oximetry is useful to detect hypoxia in an asthma attack, but this is often a late finding. Hypoxia occurs when patients become too tired to inhale effectively, and the alveoli are so hyperinflated that there is no room for any inspired air. Still, patients with moderate to severe asthma attacks may still inhale enough oxygen to maintain a normal pulse-oximetry reading. Pulse oximetry provides no indication of how hard the patient is working to breathe or if ventilation is effective.
4. Treatment goals: open constricted airways, dry secretions and reduce inflammation
Nebulized albuterol, connected to oxygen at 6-8 LPM, is the first EMS treatment for asthma. Albuterol stimulates beta-2 receptor sites to causes rapid bronchodilation. Ipratropium bromide (Atrovent) can be mixed with albuterol in a nebulizer, which causes bronchodilation and inhibits mucus secretion by inhibiting the vagal response. Both can be administered until the patient’s symptoms improve [1].
Corticosteroids decrease inflammation from an asthma attack. Methylprednisolone (Solu-Medrol) can be administered intravenously or intramuscularly, and prednisone can be administered orally. The onset for both medications is four to six hours, so they should be administered along with bronchodilators and deferred if urgent airway management is needed [2]. Despite the long onset of action, one study found in-hospital delays of steroid administration to asthma patients, and a lower hospital admission rate among patients who received methylprednisolone from EMS [4].
CPAP is a treatment option for moderate to severe asthma attacks. CPAP increases the pressure that the patient exhales against, which pushes open lower airways and improves gas exchange [1]. Nebulized bronchodilators should be administered through CPAP, which provides an air-tight seal to help direct medication into the lower airways.
Magnesium sulfate may help patients with severe asthma attacks in addition to nebulized bronchodilators and CPAP. It works by relaxing smooth bronchial muscles, and is administered as an IV infusion over 20 minutes [2].
Intramuscular or subcutaneous epinephrine may be considered for severe asthma attacks that do not respond to nebulized bronchodilators (a condition known as status asthmaticus), and some services use EpiPens for this [2]. Epinephrine targets beta-1 and beta-2 receptor sites, which causes bronchodilation, but also an increase in heart rate, blood pressure and myocardial oxygen demand.
For patients who are anxious or combative during a severe asthma attack, ketamine is the ideal medication for sedation. This dissociative agent also causes bronchodilation, and ketamine does not carry the risk of respiratory depression and hypotension found in other sedatives [2]. Ketamine can be administered intramuscular or intravenous, and may help patients tolerate having an oxygen mask or CPAP applied.
Monitor the patient’s ETCO2 and reassess their lung sound to assess how well the patient is responding to treatment. A patient is likely improving if their rounded shark-fin capnography waveform shifts to become rectangular, if their ETCO2 returns to normal range, and increased air movement (and possibly louder wheezing) is heard [3]. For a patient whose mentation and respiratory rate decrease, shark-capnography waveform becomes more pronounced, ETCO2 continues to rise above 45 mm HG, and less air movement can be heard on reassessment, prepare to assist ventilation with a bag valve mask.
5. Assist ventilation with caution, and be permissive with hypercapnea
Asthma patients with impending respiratory arrest require assisted ventilation, starting with a bag valve mask and perhaps later with advanced airway device. Although necessary, assisted ventilation comes with a number of risks. Ventilating too fast or too forcefully will worsen air trapping and may cause lung injury. Deliver only enough tidal volume to make the chest rise, and allow the patient to exhale completely before delivering the next breath [2]. Use the length of the capnography waveform as a guide for when the patient exhaled completely. Patients in respiratory failure will have a high ETCO2, even above 100 mm HG. While this is uncomfortable for patients, it is not life-threatening if they are adequately oxygenated with assisted ventilation. Correcting hypercapnea is a complicated process that must be done slowly in the hospital, and hyperventilation can cause great harm.
Asthma attacks are one of most common EMS responses, and timely prehospital care is proven to improve patient outcomes. Use all available tools to accurately diagnose and determine the severity of asthma attacks, to choose the most appropriate treatment, and to assess response to treatment.
References:
- Morris M, Mosenifar Z, Bessman E, et al. Asthma. Retrieved from Medscape website: http://emedicine.medscape.com/article/296301-overview
- Vanden Hoek TL, Morrison LJ, Shuster M, et al. Part 12: cardiac arrest in special situations. 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S829-S861. (ed. note: The 2015 guidelines do not discuss asthma and state that the 2010 guidelines still apply for asthma treatment. http://circ.ahajournals.org/content/132/18_suppl_2/S501.ful
- Kraus B. Advances in the use of capnography for nonintubated patients. Israeli Journal of Emergency Medicine 2008; 8 (3) 3-15.
- Kanpp B, Wood C. The Prehospital Administration of Intravenous Methylprednisolone Lowers Hospital Admission Rates for Moderate or Severe Asthma. Prehospital Emergency Care. 2003;7:423–426
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