Critical Review Form Diagnostic Test

Transcription

1 Critical Review Form Diagnostic Test Diagnosis and Initial Management of Obstructive Sleep Apnea without Polysomnography A Randomized Validation Study Annals of Internal Medicine 2007; 146: Objectives: To determine whether the conventional PSG (polysomnography approach was superior to the ambulatory approach in terms of controlling obstructive sleep apnea as measured by the apnea hypopnea index (AHI) on CPAP after 3 months of treatment and to determine whether there was any difference between the 2 management strategies in terms of sleepiness, quality of life, treatment adherence, and CPAP after 3 months of treatment. (p. 158) Methods: Industry-sponsored, randomized, controlled, open-label clinical trial at the University of British Columbia Sleep Disorders Clinic from May 2004 Nov Eligible subjects had a high pretest probability of obstructive sleep apnea (OSA) as defined by the constellation of an Epworth Sleepiness Scale score 10, Sleep Apnea Clinical Score (see PGY-I paper) 15, and respiratory disturbance index (RDI, measured by the Remmers Sleep Recorder, a home oxymeter which also assesses respiratory effort, airflow, snoring, and leg movements) 15 per hour. Based upon preliminary data, this constellation of findings was felt to identify a subset with 98% probability of OSA. Exclusion criteria included pregnancy, FEV 1 < 70%, known cause of daytime sleepiness, major psychiatric disorder, life-threatening co-morbid illness, MVA attributable to hypersomnolence in the preceding 5-years, previous treatment for OSA, or contraindication to nasal CPAP. Using a stratified block randomization (stratified by ESS score and RDI oximetry) in blocks of 20, each patient picked one allocation card from an envelope based upon their block assignment. Allocation was noted by the CPAP coordinator prior to all subjects receiving one-on-one instruction from this coordinator on OSA, CPAP, and mask fitting. Subjects were allocated into PSG group (immediate regularly scheduled overnight sleep study by a trained technologist) or ambulatory group. In the latter group, the Autoset Spirit (ResMed Inc, Sydney, Australia) was used to autotitrate CPAP pressures between 4-20 cm H 2 0. Data from the ResMed

2 Autoscan was evaluated at 1- and 2-weeks with CPAP adjustments made accordingly. CPAP pressures at Day 14 were maintained for the duration of the trial. Baseline PSG was only obtained in the PSG group, although all ambulatory and PSG subjects had overnight PSG at 3-months to ascertain AHI on CPAP (the primary outcome). Secondary 3 months included post-treatment ESS and a quality-of-life assessment (SAQLI), CPAP adherence and final CPAP settings. The study had 95% power to detect AHI between group difference of 5 episodes/hour with 2-sided p=0.05 with 30 patients in both groups. Because of the floor-ceiling effects of most outcome measures used, a Wilcoxon rank-sum test was used to compare groups for these measures. Additionally the authors used a sensitivity analysis for worst-case and best-case scenarios to address the impact of missing data. Guide Comments I. Are the results valid? A. Did clinicians face diagnostic uncertainty? Somewhat. Although these were sleep specialists evaluating patients referred to a sleep clinic for primary care suspected sleep disorders (OSA or other), none had an established diagnosis of OSA. Nonetheless, applying the baseline risk and content-expertise of clinicians to general ED settings is questionable. B. Was there a blind comparison with an independent gold standard applied similarly to the treatment group and to the control group? No at baseline only the PSG group had PSG testing. The very point of this study is to identify an acceptable more readily available diagnostic pathway. Still lacking gold-standard testing at baseline the study may (Confirmation Bias) C. Did the results of the test being evaluated influence the decision to perform the gold standard? (Ascertainment Bias) suffer confirmation bias. The patients in the ambulatory group did not have a diagnostic PSG. However, because the oximetry RPI was similar in both groups and because patients were randomly assigned, it is likely that the baseline AHI was comparable.

3 II. What are the results? A. What likelihood ratios were associated with the range of possible test results? Among 79 screened patients, 68 were eligible for randomization with 35 to PSG and 33 to ambulatory group (Fig 2, p. 161). There was no significant difference between the 2 groups though the ambulatory group was non-significantly older with more men (Table 1, p. 162). If the ESS 10, SACS 15, and RDI 15/hour then 94% (95% CI 81-99%) had AHI > 15/night (moderate to severe OSA) in the PSG group. Three-month ESS, SAQLI did not differ between groups at 3- months. CPAP compliance was better in the ambulatory group (difference 1.2/hour/night). 62% of PSG group would have preferred to be in ambulatory group. Only 6% of ambulatory group would have preferred PSG group. Findings were robust to sensitivity analysis. Worst-case scenario: if all subjects with incomplete data in PSG had 25 th percentile AHI while ambulatory had 75 th percentile, overall results group difference would be AHI 0.3/h. Similarly, CPAP compliance would have favored the ambulatory approach 0.97h/night. Vice-versa best case scenario would be AHI 1.2/h and CPAP adherence 1.5 hour/night favoring the ambulatory group.

4 III. How can I apply the results to patient care? A. Will the reproducibility of the test result and its interpretation be satisfactory in my clinical setting? B. Are the results applicable to the patients in my practice? C. Will the results change my management strategy? D. Will patients be better off as a result of the test? Uncertain, sleep physicians evaluating selected patients referred to British Columbia Sleep Clinic. Uncertain different patients in different settings. This is the key question for EM. Is it the responsibility of EM to identify high-risk OSA patients? Would ED identification of a high-risk OSA subset alter short-term outcomes (OSA-related morbidity)? What would be the ergonomic cost to ED thoroughfare by screening patients using these tools? Is there a medial malpractice risk of not identifying OSA in those who pass through our ED? Is there a modifiable safety risk in high-risk OSA patients who we discharge on narcotics, benzodiazepines, muscle relaxants or sedating anti-emetics? Before OSA screening tools are employed in ED s everywhere these questions should be answered. Unknown see above. Limitations 1) Ambulatory group did not have baseline polysomnography. 2) No assessment of concomitant sedating medication use or ED utilization to permit extrapolation of these results to our populations, though the results were robust to lower prevalence rates of OSA. 3) ESS, SACS, and RDI not validated in ED populations.

5 4) Remmers Sleep Recorder and outpatient CPAP not readily available to largely uninsured ED populations. 5) Superiority trial under-powered to detect equivalence. Bottom Line In one British Columbia Sleep Clinic population, high-risk OSA patients can immediately begin CPAP therapy following brief screening without definitive polysomnography without impairing 3-month sleep apnea events, quality of life or adverse events. In fact, the non-psg approach appears to improve compliance and is favored by patients. The authors offer a feasible alternative to PSG in the form of risk-stratification with ESS, SACS, and RDI with 94% pre-test probability of OSA. If validated in ED populations, such an approach could identify high-risk OSA patients allowing immediate institution of CPAP while waiting criterion standard PSG testing. In already over-crowded ED s such interventions would need to demonstrate reduced short-term morbidity and not compromise the care of other ED patients.