Introduction

This concept describes the methods in selecting diagnosed obstructive sleep apnea (OSA) patients and a matched general population group in a thesis titled Serious postoperative cardiovascular and respiratory complications in obstructive sleep apnea patients: Matched cohort analysis of clinical and administrative data by Thomas Mutter (2012). This study compares serious postoperative complications for patients diagnosed with OSA to a non-OSA general population cohort.

For a definition of obstructive sleep apnea (OSA) used in Mutter (2012), please see the obstructive sleep apnea (OSA) glossary term.

Thomas Mutter's thesis is available through the University of Manitoba (U of M) on-line library system at: http://mspace.lib.umanitoba.ca/jspui/bitstream/1993/8114/1/mutter_thomas.pdf . NOTE: Access to this thesis and to the links provided in this concept to corresponding tables in the thesis is restricted to those with access to the U of M on-line library system.

Obstructive Sleep Apnea (OSA) Group

Patients with diagnosed OSA were identified in the Saint Boniface General Hospital (SBGH) Sleep Disorder Centre Research and Teaching database. This database contains data on more than 4000 patients referred to the St. Boniface laboratory for sleep assessment, having had an in-lab polysomnography (PSG) and given informed consent for participation in the database. For each patient up to four diagnoses were recorded in the database.

Patients from the SBGH sleep lab were included in the OSA group if they had a diagnosis of OSA or upper airway resistance syndrome. Co-diagnosis of Central Sleep Apnea (CSA) was considered if patients had OSA, as well as CSA, Cheyne Stokes respiration, or sleep hypoventilation. Obesity Hypoventilation Syndrome (OHS) was considered as a comorbidity for patients with both an OSA and OHS diagnosis.

Non-OSA Matched Group

Patients with no evidence of OSA and having had a surgery during the period of 1985-2006 were identified in the Medical Services database and matched to an OSA diagnosed patient. Up to four non-OSA control patients were matched by surgical tariff, diagnosis, and approximate date of surgery. Patients having an OSA diagnosis or high risk of sleep apnea were excluded.

To avoid high risk undiagnosed OSA or OSA patients, records were not included if they:


1. were ever included in the SBGH database;
   
   
2. had surgery that is used to treat OSA or OSA symptoms, identified by the following surgical tariff codes in the Medical Services data:
   
   
   • 583 - Lefort II maxillary osteotomy and advancement
     
   • 616 - Mandibular osteoplasty
     
   • 1928 - Nasal septoplasty
     
   • 1929 - Nasal septoplasty with repair of septal perforation
     
   • 1935 - Turbinectomy
     
   • 1949 - Rhinoplasty with septoplasty
     
   • 1966 - Nasal turbinate cautery
     
   • 2021 - Septoplasty and ethmoidectomy, unilateral
     
   • 2022 - Septoplasty and ethmoidectomy bilateral
     
   • 2023 - Septoplasty and polypectomy, unilateral
     
   • 2024 - Septoplasty and polypectomy, bilateral
     
   • 2026 - Septoplasty and polypectomy and ethmoidectomy, bilateral
     
   • 2028 - Septoplasty, polypectomy, ethmoidectomy, antrostomy, bilateral
     
   • 2883 - Uvulopalatopharyngoplasty
     
   • 2885 - Palate lesion resection
     
   • 2887 - Uvulectomy
     
   • 2898 - Pharyngoplasty
     
   • 2899 - Palate resection unlisted or unusually complicated
     
   • 2992 - Tonsillectomy, < 13 years old
     
   • 2993 - Tonsillectomy, adult
     
   • 2994 - Hemorrhage post-tonsillectomy
     
   • 2996 - Adenoidectomy without tonsillectomy
     
   • 3011 - Pharyngoplasty
     
     NOTE: This list is produced from Table 1. OSA patient surgeries excluded from matching to non-OSA controls in Mutter, 2012.
   
   
3. had a tariff submitted for sleep study interpretation in the Medical Services data, using the following tariff codes:
   
   
   • 77921 - Neurophysiology screening sleep disorder study: interpretation
     
   • 77922 - Neurophysiology screening sleep disorder: technical
     
   • 8872 - Diagnostic polysomnography
     
   • 8873 - Therapeutic polysomnography
     
   • 8874 - Multiple sleep latency testing
     
     NOTE: This list is produced from Table 2. Medical service tariffs used to exclude members of the general population at high risk of sleep apnea from the pool of potential matches in Mutter, 2012.
   
   
4. had a diagnosis of sleep apnea in the Hospital Abstracts data, using the following ICD codes:
   
   
   ICD-9-CM Codes:
   
   
   • 327.2 - Organic sleep apnea
     
   • 327.2 - Organic sleep apnea, unspecified
     
   • 327.21 - Primary central sleep apnea
     
   • 327.22 - High altitude periodic breathing
     
   • 327.23 - Obstructive sleep apnea (adult) (pediatric)
     
   • 327.24 - Idiopathic sleep related non-obstructive alveolar hypoventilation
     
   • 327.25 - Congenital central alveolar hypoventilation syndrome
     
   • 327.26 - Sleep related hypoventilation/ hypoxemia in conditions classifiable elsewhere
     
   • 327.27 - Central sleep apnea in conditions classified elsewhere
     
   • 327.29 - Other organic sleep apnea
     
   • 780.51 - Insomnia with sleep apnea, unspecified
     
   • 780.53 - Hypersomnia, unspecified
     
   • 780.57 - Unspecified sleep apnea
     
   • 786.04 - Cheyne-Stokes respiration
   
   ICD10-CA Codes:
   
   
   • G47.3 - Sleep apnoea
     
   • G47.30 - Sleep apnoea, obstructed
     
   • G47.31 - Sleep apnoea, central
     
   • G47.38 - Other sleep apnoea
     
   • E66.2 - Extreme obesity with alveolar hypoventilation
     
   • R06.3 - Periodic breathing
   
   NOTE: This list is produced from Table 3. ICD codes used to exclude patients at high risk of sleep apnea from the pool of potential matches in Mutter, 2012.

Cautions:

This method does not exclude patients with undiagnosed OSA who never seek treatment and fails to capture patients privately paying for diagnosis or treatment, and where a sleep apnea diagnosis was not recorded in hospital discharge abstract. Only Hospital Discharge Abstracts were examined for non-OSA diagnoses codes as Medical Services does not capture enough specificity.

NOTE: In December 2018, a 5-digit diagnosis code variable was added to the Medical Services data. If recorded, the first 3-digits of both the 3-digit and 5-digit diagnosis code variables will match exactly. The 5-digit diagnosis code variable applies to records from 2015/16 forward.

Matching Process

After applying the exclusions, the remaining potential control patient surgeries were matched to OSA patient surgeries with the same anesthetic tariff and diagnosis submitted with that tariff, within +/- 3 years of the OSA patient’s date of surgery. Anesthetic tariffs were used to identify surgeries because unlike surgical tariffs which can have multiple tariffs submitted for a single surgical event, an anesthetic tariff is only submitted once for the most complex aspect of the operation. Additionally if more than four potential matches were made, those closest to surgery date were chosen. Matches were also based on the ICD-9-CM 3-digit code for particular surgery that went with the anesthesia tariff.

For more information on the process that was used to match OSA patient exposures to surgery to non-OSA control exposures to surgery from the general population, please see Figure 4 in Mutter, 2012.