Respiratory disturbance index

The respiratory disturbance index (RDI) — or respiratory distress Index — is a formula used in reporting polysomnography (sleep study) findings. Like the apnea-hypopnea index (AHI), it reports on respiratory events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs).[1] RERAs are arousals from sleep that do not technically meet the definitions of apneas or hypopneas, but do disrupt sleep and cause symptoms.

A RERA is characterized by increasing respiratory effort (and thus decreasing esophageal pressures) for 10 seconds or more leading to an arousal from sleep, but one that does not fulfill the criteria for a hypopnea or apnea.[2] The gold standard for measuring RERAs is esophageal manometry, as recommended by the American Academy of Sleep Medicine (AASM). However, esophageal manometry is uncomfortable for patients and impractical to use in most sleep centers.

Some research studies have found that a high RDI was significantly correlated with excessive daytime sleepiness, and that this correlation was stronger than that for the frequency of oxygen saturation decreases below 85%, but other studies have found only a weak correlation.[3] More recent studies have found more impressive outcomes in treating patients with RERA and respiratory events that satisfy the definition of hypopneas in all aspects other than reduction of oxygen saturation levels.[4][5]

The American Academy of Sleep Medicine uses RDI to determine the severity of Obstructive Sleep Apnea according to the following range: 5 - 14.9 for mild, 15 - 29.9 for moderate, and 30+ for severe. [6]

Formula

RDI = (RERAs + Hypopneas + apneas) X 60 / TST (in minutes). That is, RDI means the average number of episodes of apnea, hypopnea, and respiratory event-related arousal per hour of sleep.[7] (TST is "total sleep time".)

See also

References
  1. Richardson, Mark A., & Friedman, Norman R. (Eds.) (2007). Clinician's Guide to Pediatric Sleep Disorders, p. 75. New York: Informa Healthcare USA, Inc.
  2. "Sleep-Disordered Breathing". clevelandclinicmeded.com.
  3. Verster, Joris C., et al. (Eds.) (2008). Sleep and Quality of Life in Clinical Medicine, p. 83. Totowa, New Jersey: Humana Press.
  4. Simmons J., Barlow, S, Sleep, Vol 35S A135, 2012
  5. Jerald H. Simmons, MD and Shaaron Barlow, ANP. "Requiring oxygen desaturation for tabulation of hypopneas lowers the sensitivity of NPSG testing and leaves many patients untreated. In-lab NPSG testing needs to improve if it is to be preserved" (PDF).CS1 maint: uses authors parameter (link) (poster)
  6. https://aasm.org/resources/clinicalguidelines/diagnostic-testing-osa.pdf
  7. Espiritu, Joseph Roland D. (2008). "Sleep-Related Breathing Disorders". In Schmitz, Paul G. (Ed.), Internal Medicine: Just the Facts, p. 663. McGraw-Hill Medical.


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