Obstructive sleep apnea (OSA), sleep study and continuous positive airway pressure (CPAP) machine settings

Author: V. Dimov, M.D.
Reviewer: S. Randhawa, M.D.

A 27-year-old Caucasian male (CM), morbidly obese is seen for preoperative evaluation for Roux-en-Y gastric bypass surgery. He has suffered from obesity for many years and has tried numerous weight-reduction programs with no success. His current weight is 395 pounds, and his height is 5 feet, 11 inches. He denies any symptoms of chest pain, palpitations, heart murmurs or irregular pulse. No history of orthopnea. He has exertional dyspnea. No history of asthma, emphysema or chronic cough. No history of smoking.

Past medical history (PMH)

Obesity, sbstructive sleep apnea (a sleep study was ordered), degenerative joint disease (DJD).

Social history (SH)

Denies any history of alcohol, tobacco or illicit drugs.

Family medical history (FH)

His father has OSA.


Ibuprofen (Motrin) PRN, Hydrochlorothiazide (HCTZ) daily.

Physical examination

VS 36.8-16-84-133/85.
Morbidly obese, in non apparent distress (NAD).
The rest of the examination is unremarkable.

EKG: NSR, HR 79, left axis.

What happened?

He had a sleep study which conformed the clinical suspicion of OSA. The recommended setting was CPAP 10 cm H2O QHS. The first step in treating OSA is to find the right CPAP setting. The second is to find the device that fits the patient and is tolerated. Nasal trumpets are tolerated best but they cannot deliver pressure higher than 10 cm H2O. The full face mask is the most effective device, delivering pressure up to 20 cm H20, but many patients experience claustrophobia, find it very uncomfortable, and for these reasons, do not use it.

Sleep Study Report

Weight (lbs) = 406
Height = 70


Indications: Loud snoring, excessive daytime sleepiness.
ESS = 6

PMH: morbid obesity

Medications: Ambien given for the test

He is undergoing preop evaluation for bariatric surgery

An overnight/daytime full montage split night polysomnography was performed, recording EEG, EOG, chin and leg EMG, EKG airflow, thoracic and abdominal effort, snoring via a microphone, pulse oximetry, body positioning and CPAP pressure.

Total recording time=395
sleep efficiency was=increased
Sleep efficiency (normal about 85%)=96
Sleep latency was=reduced
Sleep Latency in minutes (normal 15-20 min)=3
Sleep architecture revealed=reduced amounts of REM sleep
REM % of TST (normal=20% of TST)=0.5
REM latency was=REM was absent
(Normal REM latency 70-120 min)=66
REM rebound was seen on CPAP

At (cmH20) =0
L/min O2 =0
Baseline SpO2 %=97
Min SpO2 %=87
Overall RDI=112

Overall AHI=110

Respiratory Index=2
Obstructive apneas=38
Central Apneas=0
Respiratory Effort Related Arousals (RERAS)=4

Snoring without CPAP (% of sleep time)=49
Snoring was reported as=loud

CPAP titration was started at=5
CPAP/BiPAP final pressure=13
In this study the most adequate pressure was=10
Higher pressures =no significant benefit

Obstructive Sleep Apnea with hypersomnia

Avoid sedatives, hypnotics and narcotics=unless sleep apnea treated.
CPAP/BIPAP cm H20=10.
Do not operate heavy machinery or drive=unless OSA/other sleep disorder treated
Weight reduction=to IBW
Heated humidifier=with CPAP

What happened next?

He has been on CPAP for 2 weeks and today he had a Roux-en-Y gastric bypass surgery 2 hours ago.

He has been on CPAP for more than one week, VS are stable and he can be transferred to RMF.

What did we learn from this case?

The most important parameter for diagnosing OSA is AHI (Apnea-Hypopnea Index). In healthy people AHI is less than 10.

If you have to choose just one number to diagnose OSA, choose AHI. As a single measurement AHI is comparable to the importance of RSBI in weaning and extubation. RSBI of less than 100 predicts the successful extubation of a ventilated patient in 85 percent of the cases.

This is a simple bedside evaluation for OSA:

Physical exam - just check two things:

- Neck size

The risk size for OSA is 17' for men, and 16' for women

- Look inside the patient's mouth: "Open your mouth please" and check the the Mallampati Score (MS)

Mallampati Score (source: med.univ-rennes1.fr) (click to enlarge the images).


- Epworth Sleepiness Scale (ESS), if more than 12, the patient is at high risk for OSA


Obstructive Sleep Apnea-Hypopnea Syndrome - eMedicine.
Snoring and Obstructive Sleep Apnea, Upper Airway Evaluation - eMedicine.
Epworth Sleepiness Scale - University of Maryland, SMMC.com.
Treatment of Obstructive Sleep Apnea in Primary Care - AFP 02/04.
Obstructive Sleep Apnea - AFP 11/99.
Dr. Magboul Anesthesia page - MSN.
Obstructive Sleep Apnea as a Risk Factor for Stroke and Death - NEJM 11/05.
Continuous Positive Airway Pressure for Central Sleep Apnea and Heart Failure - NEJM 11/05.
Sleep — A New Cardiovascular Frontier - NEJM Editorial 11/05.

9% of men and 5% of women have sleep apnea, some patients "choke" up to 500 times per night. The first paper on positive airway pressure for sleep apnea (PAP) was published in The Lancet 30 years ago. Lancet, 2011.

Related reading

Mavs Fan at the Finals - Photos - SI.com http://goo.gl/tIdL3
Sleepiness and sleep-disordered breathing may be found in 19-29% of children with positive allergy test (http://goo.gl/AfCWZ).

Understanding PAP Therapy for your Sleep Apnea - video from Cleveland Clinic (2013):

Published: 02/01/2004
Updated: 02/05/2012

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