Monitoring Asthma Outcomes

Respiratory therapists deal with asthma every day: in caring for patients in the hospital, in the emergency department, in the clinic, and in schools; seeing to our personal health (many RTs have asthma); and, for many of us who are parents, caring for our children. According to the 2008 figures from the Centers for Disease Control and Prevention (CDC), more than 38 million patients have been diagnosed with asthma during their lifetime. Of these patients, some 23.3 million currently have asthma (one out of every 14 people), and 12.7 million had had an asthma attack within the previous year. Asthma costs average out to more than $19.7 billion a year; and, according to the figures from 2006, we had 10.6 million doctor visits, 1.6 million emergency department visits, and 440,000 hospitalizations.¹

Control of asthma has become the key feature in the latest guidelines for care and management.² According to the Expert Panel Report-3 (EPR-3) guidelines, control of asthma has two goals: reducing impairment and reducing risk. Reducing impairment includes maintaining (near) normal lung function and normal activities, preventing chronic symptoms, and infrequent use of short-acting ß2-agonists (SABA). Reducing risk includes preventing exacerbations, minimizing the need for ED visits or hospitalization, preventing loss of lung function (or preventing reduced lung growth in children), and having few or no adverse effects from therapy. When we talk of monitoring asthma outcomes, these particulars are included. This article will examine several issues related to monitoring the outcomes of asthma care and discuss what the future may bring as research uncovers new ways of treatment as well as new ways of assessing control.

Pulmonary Function

Pulmonary function testing (PFT)—in particular measurement of spirometry and the patient’s response to a bronchodilator—is a major tool in the diagnosis of asthma. The FEV₁% predicted (this is the measured FEV₁ compared to the predicted FEV₁) and FEV₁/FVC (often called the FEV₁%) are used in the EPR-3 guidelines to classify patients with untreated asthma into four categories: intermittent, mild persistent, moderate persistent, and severe persistent. Beyond the initial diagnosis, subsequent spirometry testing to examine FEV₁ (or measuring peak expiratory flow) is a major part of monitoring asthma outcomes and control. The EPR-3 recommends spirometry for all patients >5 years of age to assess reversibility. Reversibility is defined as a 12% change plus a 200 ml increase in FEV₁ (this is the preferred marker; a 12% change plus a 200 ml increase in FVC is also an acceptable marker according to the American Thoracic Society’s guidelines for interpreting pre/post-bronchodilator studies).

After the diagnosis is made and treatment begins, follow-up spirometry should be done after a short time (as soon as 2 weeks to a month). Once control is achieved, spirometry should be performed at least every 1 to 2 years to monitor changes over time. If peak expiratory flow (PEF) is used, the patient can use this daily as a self-monitoring tool to assess control and get an early warning of possible exacerbation. Note that the EPR-3 suggests that the FEV₁ is better used for predicting exacerbations than in determining severity. In the ED, the FEV₁ (or PEF) can be used to guide treatment accurately; and, as the patient responds to therapy, these measurements help guide the decision to discharge the patient.

Impulse oscillometry (IOS) is a relatively new measurement in pulmonary function testing and may be useful in testing children less than 5 years of age (even as young as 2).³ Preschool children often have a difficult time performing acceptable forced expiratory maneuvers, but IOS obtains measurements during tidal volume breathing to get information on respiratory impedance, which can then be used to derive resistance and reactance. The IOS measurement uses a loudspeaker that sends sound waves through a mouthpiece and down into the tracheobronchial tree to obtain the information during tidal volume breathing. The test is quick—it usually takes 15 to 30 seconds to perform a measurement, and three acceptable measurements are needed—so total test time for IOS is often about 2 minutes. Research suggests that IOS may be useful in assessing the initial condition of and subsequent response to SABA in the peripheral airways as well as in the central airways.³ The usefulness and applications of IOS are still being assessed, but many centers are including this measurement as part of the complete PFT. As of the time of writing this article, IOS has not been included in any of the asthma guidelines as a recommended test to assess asthma. In a recently published article in Current Opinion in Allergy and Clinical Immunology concerning IOS, the authors conclude:

Although this procedure has been used for several years and shows promise in identifying the very young asthmatic child, there is still much to be learned about what it actually measures. Additional information is also needed regarding confounding factors, reproducibility, relationship to clinical manifestations, and what constitutes normal values, before it can become a standard procedure.³

Quality of Life

According to the EPR-3 guidelines, quality of life should be assessed periodically (from 1-month to 6-month intervals). Items included in this assessment are: missed days of school or work, reduction in usual activities (such as home, work, or school activities or recreation/exercise), sleep disturbances, and changes in activities of a caregiver of a child who has asthma. Quality of life correlates in the low to moderate range with symptoms of asthma (in contrast to the poor correlation between pulmonary function measurements and symptoms).

A patient’s perceptions and experiences should be examined directly with questions such as “Since your last visit, how many days of school have you missed?” The EPR-3 mentions several validated surveys that are useful tools to assess quality of life. Overall or generic assessment can be measured with questionnaires such as the Medical Outcome Study Short-Form Health Survey (often called the SF-36) or the SF-12 Health Survey (a shortened version of the SF-36).⁴ These tools are useful in researching asthma’s impact on a population.

Asthma-specific questionnaires that give more sensitive assessment of the impact of asthma on the individual are also available. The EPR-3 guidelines mention several, including the Mini Asthma Quality of Life Questionnaire (Juniper et al, 1999a), Asthma Quality of Life for Children (Juniper et al, 1996), and the Asthma Quality of Life Questionnaire (Katz et al, 1999; Marks et al, 1993).²

Asthma Control Questionnaires

Asthma control falls into three classifications in the EPR-3 guidelines: well-controlled, not well-controlled, and very poorly controlled. For youths and adults (>12 years of age), these classifications are determined by examining six areas:

1. Symptoms (such as cough, wheezing, chest tightness, and dyspnea);
2. Nighttime awakenings;
3. Interference with normal activities;
4. Use of relief medications (short-acting ß-agonists);
5. Pulmonary function (either FEV₁ or PEF); and
6. Scoring on a validated questionnaire.

There are many validated questionnaires mentioned in the published research on asthma. See the Table for a sample of these tests, along with some comments. The EPR-3 mentions three asthma control questionnaires in particular: the Asthma Therapy Assessment Questionnaire (ATAQ), Asthma Control Questionnaire (ACQ), and Asthma Control Test (ACT). Control of asthma has an impact on quality of life, and as the scores on these questionnaires improve, the asthma patients find their quality of life also improving.

Biomarkers

Biomarkers have become a hot topic for assessing lung function, response to therapy, and assessment of outcomes. Researchers are actively pursuing a good, reliable biomarker; and studies are beginning to show promise for the future.

There are many biomarkers being examined; those that are getting most attention are linked to allergic airway inflammation and include blood and sputum eosinophil counts, fractional exhaled nitric oxide concentration (FeNO), and serum immunoglobulin E (IgE). In examining these biomarkers as possible key measurements for predicting adverse events or use in monitoring a decline in lung function over time, the evidence has been rated as low. The EPR-3 guidelines use a rating scale of A, B, C, or D when making recommendations, with A being the strongest—characterized as randomized controlled trials and having a rich body of data—and D being the weakest—characterized as panel consensus judgement. The EPR-3 discussion of assessment of control (risk and impairment) states that biomarkers, “such as sputum eosinophils and FeNO, may also be useful, but they require further evaluation in both children and adults before they can be recommended as clinical tools for routine asthma management (Evidence D).”² Many studies are looking at combining the results of a biomarker measurement with an established tool (such as FeNO combined with spirometry results ) or a combination of two of these biomarkers (such as FeNO and sputum eosinophils) to assess the usefulness of the combination in managing asthma, titrating corticosteroid therapy, or predicting adverse events.^5-7

Exhaled carbon dioxide (CO₂) has been used as a biomarker for many years to assess ventilation. Capnography measurement of end-tidal CO₂ (Etco₂) is often used as a continuous noninvasive monitor for this parameter. Researchers examined the concordance between Etco₂ and Paco₂ in adult asthmatics in a study published in October 2005. Over an 18-month period, 39 adults were enrolled in the study. The median age of the group was 40 years (interquartile range of 32–48 years), and 44% were males; 37 of the 39 patients were in the severe category based on the EPR-2 guidelines, which were in effect at the time of the study…the classification has not changed with the EPR-3 guidelines. ABG results for Paco₂ were compared to Etco₂ and the results showed a mean difference between the two of 1.0 mm Hg (95% confidence interval, 0.1-2.0 mm Hg) with a median difference of 0 mm Hg.⁸ In the detailed results comparing each of the pairs of CO₂ measurements, the authors included the peak expiratory flow rate (PEFR) and %predicted PEFR. It was interesting to note that 12 of the 39 patients had a Paco₂ that was above 40 mm Hg and all 12 had a %predicted PEFR below 28. The Paco₂ averaged 51 mm Hg with a median of 48.5 mm Hg and range from 43 to 64 mm Hg. The %predicted PEFR averaged 22 with a median of 22 and range from 15 to 28.

Another study published in 2007 examined the association of Etco₂ with disease severity in children in the emergency department (ages ranged from 3 to 17 years).⁹ This was a blinded prospective observational study where treatment was given according to a standardized asthma pathway and the treating physician was blinded to Etco₂ measurements. The Etco₂ measurements were obtained before and after the initial treatment and before and after each subsequent treatment up to a total of three treatments. The results showed that the Etco₂ measurements did not distinguish between those with mild disease and those with more severe disease. There was also overlap in the Etco₂ results and the association with other objective measures such as the PEFR and the Pediatric Asthma Severity Score (PASS). This issue with overlap was enough that the authors concluded that the Etco₂ measurement would not be useful in classifying the severity of childhood asthma in the emergency department.⁹

Conclusion

As we have seen, controlling asthma has become the focus of caring for people with asthma. Teaching them self-management empowers them to have direct input on control of their disease, by reducing both impairment and risk. We can better understand the disease and measure success in gaining control of asthma by examining the outcomes of therapy. Using pulmonary function and IOS, assessing quality of life, gathering objective measures of asthma control, and moving forward with biomarkers such as FeNO and sputum eosinophils, we gain insight into finding effective therapy, reducing impairment and risk, and improving both self-management and professional-directed care. Etco₂ results may be useful in a severe exacerbation when there is concern that the patient may slip into acute respiratory failure, but it does not appear to be useful in assessing the levels of severity as established by the EPR-3 guidelines. The final message to take home is that more research is on the way to establish the best evidence-based approaches, and as the body of knowledge grows, we need to stay abreast of the changes.

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Bill Pruitt, MBA, RRT, CPFT, AE-C, is a senior instructor and director of clinical education in the department of cardiorespiratory sciences, College of Allied Health Sciences, at the University of South Alabama in Mobile, and a PRN therapist at Springhill Medical Center and Mobile Infirmary Medical Center in Mobile. For further information, contact [email protected].

References

1. Centers for Disease Control and Prevention. Asthma. Available at: www.cdc.gov/asthma/aag/2010/overview.html. Accessed November 3, 2010.
2. Guidelines for the Diagnosis and Management of Asthma (EPR-3). Available at: www.nhlbi.nih.gov/guidelines/asthma. Accessed November 1, 2010.
3. Galant SP, Nickerson B. Lung function measurement in the assessment of childhood asthma: recent important developments. Curr Opin Allergy Clin Immunol. 2010;10:149-54.
4. SF-36 Health Survey. Available at: www.sf-36.org. Accessed November 6, 2010.
5. Bush A, Saglani S. Management of severe asthma in children. Lancet. 2010;376:814-25.
6. Szefler SJ, Phillips BR, Martinez FD, et al. Characterization of within-subject responses to fluticasone and montelukast in childhood asthma. J Allergy Clin Immunol. 2005;115:233–42.
7. Smith AD, Cowan JO, Brassett KP, Herbison GP, Taylor DR. Use of exhaled nitric oxide measurements to guide treatment in chronic asthma. N Engl J Med. 2005;352(21):2163–73.
8. Corbo J, Bijur P, Lahn M, Gallagher EJ. Concordance between capnography and arterial blood gas measurements of carbon dioxide in acute asthma. Ann Emerg Med. 2005;46:323-7.
9. Guthrie BD, Adler MD, Powell EC. End-tidal carbon dioxide measurements in children with acute asthma. Acad Emerg Med. 2007;14:1135-40.