Overnight Oximetry Flashcards
(27 cards)
What’s the difference between type 1 and type 2 polysomnography?
Type 1 = attended sleep study
Type 2 = unattended sleep study
What’s the difference between type 3 and type 4 limited sleep studies?
Type 3 = at least 4 channels monitored
Type 4 = Only 1 or 2 monitored parameters
What is the clinical use of overnight oximetry?
A continuous overnight measurement during sleep, measuring oxygen saturation (SpO2) & pulse rate
Give 3 uses of OO?
1 –> Determine Frequency of O2 desaturations and SpO2
2–> Give information on pulse rate (marker for sleep arousal)
3–> Evaluation of treatments e.g. CPAP
How do you perform OO?
- Performed at home (commonly)
- Need correct size probe and correct placement
- Aware of limitations like varnish etc
- Use Instruction sheet
- Set up Oximeter with date/time/battery/clean
- Cover probe with opaque material elimination environmental light
- Taping lead to back of hand helping securing device in place
- DO NOT TAPE OVER PROBE
- Sleep Questionnaire
Which patients wouldn’t be suitable for OO?
- Severe Intellectual Disabilities
- Communication difficulties
- Physical difficulties
- Unstable home
- Discretionary (serious medico-legal)
- More extensive studies needed
Advantages of OO?
- Easy to perform
- Can be done at home
- Cheaper
Disadvantages of OO?
- Normal Study cannot exclude Sleep Apnoea
- Cannot distinguish between OSA and CSA
- Patient Co-operation
What is the ODI?
Oxygen Desaturation Index (ODI)
Define ODI?
- The number of 4% desaturations per hour of sleep
- Sometimes called RDI (Respiratory Disturbance Index)
How do we calculate ODI?
ODI =
Total no. of desaturations) / (sleep duration in hours
A worked example of ODI?
So the patient had 35 desats
and slept for 7 hours
so ODI = 35/7 = 5
units are events per hour
so 5 events per hour
What is a normal ODI?
Mild –> 5-14 events per hour
Moderate –> 15-20 events per hour
Severe–> 30+ events per hour
What are the essential features for screening equipment for OSAHS?
- Sampling Frequencies for each signal must be appt
- Portable
- Battery Powered or Rechargeable
- Data must be downloadable and editable
- Easy to clean/decontaminate
- Comply with Intl/EU standards
What is the minimal sampling frequency?
4Hz
Why can inappropriate sampling frequency lead to?
underestimate of desaturation events
What is Sample Frequency?
The number of samples per second in a sound
What is Sample Frequency measured in?
Measured in Hertz (Hz) – a unit of frequency
What does minimal Samp frequency actually mean in terms of per second?
–> minimum sample frequency for SpO2 (4Hz)
–>1 Hz = 1 sample per second
–>4 Hz = 4 samples per second
–>Sample time therefore is reduced to 0.25 sec
Relationship between SF and time?
↑sample freq = ↓ time
as in a higher frequency means there is less time between every sample
What is data averaging?
- the average of repeated SpO2 readings over a specific time interval
What is the maximum averaging times?
-3s
What is the protocol for negative studies?
- must be investigated further using a multi-channel screening system”
What is the 4 steps to interpret Interpretation and Pulse Oximetry traces?
- Quality of data (artefact/length)
- Interpretation (Look at traces/data)
- Link report to patient/referral
- Recommendations/Further actions
–> Services should have SOP’s for reporting
