What is monitoring?
Monitoring is the continuous observation of measures of the body’s functions, for example breathing and heart rate. Some devices not only monitor, but also record the measurements for later study. In CHS, the usual type of monitoring used is pulse oximetry (also known as oxygen saturation monitoring, SpO2).
Why monitor the oxygen levels?
Oxygen is critical for the body to function. It is taken in through the lungs from the air we breathe in and circulated around the body in the blood stream. Keeping adequate levels of blood oxygenation (SpO2), is crucial for survival, adequate growth and learning. In CHS, the breathing is insufficient to keep the oxygen levels normal. Monitoring will inform us what levels are being achieved at any moment in time.
Monitoring is performed using devices that can continuously monitor the levels of oxygen in the blood, but without taking blood samples. Monitoring oxygen tells us about adequacy of ventilation and alerts carers if a life-threatening event occurs. The monitor emits an audible alarm that allows carers to take appropriate steps to restore normal ventilation and oxygen levels.
Monitoring oxygen levels is recommended during ventilation and whenever the child is left alone and likely to fall asleep. Sometimes monitoring is done during wakefulness in the day time. This will be decided by your physician.
How do pulse oximeters work?
Pulse oximeters use the colour of blood to tell us about the amount of oxygen being carried. Blood rich in oxygen is a brighter red colour, while blood depleted in oxygen is dark in colour. The sensor on a pulse oximeter shines red light through the skin and this is variably transmitted to a sensor (probe) depending on the oxygen levels. The measurement is dependent on having a good pulse in the way of the light path and this is usually shown on the front of the oximeter by a bouncing light bar or wave.
What are normal oxygen levels?
These are 95-100%.
When are low oxygen levels dangerous?
Short-lived drops in oxygen may occur in children without CHS when they have short pauses in breathing during sleep. These do not usually cause harm. There is evidence that the more time children spend with lower oxygen levels (<92%), the more likely they are to have effects on their growth and learning. Exact cut-offs cannot be easily defined. Low alarm settings on your pulse oximeter will be decided with your physician.
What may affect the oxygen measurement?
The probe may not detect a pulse if:
· there is a lot of movement
· the foot or hand is too cold
· the probe is too loose or too tight
· there is very bright light
· the probe is too old
· the probe is displaced (the LED is not opposite the sensor)
You need to be taught how to apply the probe correctly and how to obtain and read proper measurements.
What do we do when the monitor sounds an alarm?
Monitors may produce true alarms, when the oxygen level is low, or they may sound false alarms, which identify that the oxygen level is not being measured correctly. It is helpful to learn how to distinguish these, for example, by examining whether there is adequate pulse detection.
If the alarm is due to poor pulse detection, check the probe or re-site it. If the alarm stops and the values shown on the monitor return to normal, it means that this was a false alarm.
If you are not sure, or the individual looks unwell in any way, you should respond as if the oxygen level is truly low. Check whether the chest is moving and whether he/she is responsive. These may indicate either a breathing problem or cardio-respiratory arrest:
Are there any risks from the oxygen monitoring?
You need to know how to look after the skin to avoid harm. A too tightly attached probe can affect the blood supply or burn the skin.
What else can be monitored?
Another sign of inadequate breathing is a high level of carbon dioxide (CO2), the waste gas we normally breathe out. When breathing is inadequate, the carbon dioxide may rise and cause sleepiness or coma. It is possible to measure CO2. There are two ways:
1. this measures carbon dioxide in the exhaled air from the nose or tracheostomy (end-tidal CO2), or
2. by a heated probe placed on the skin (transcutaneous CO2)
Patients will usually have carbon dioxide measured in the hospital or during a sleep study. Some patients have their own carbon dioxide monitors for use at home. Sometimes this may be used to guide changes in the settings on the ventilator.
Pulse oximeters and other devices also measure the heart rate. There is a wide range of normal heart rates, which vary with age. Usually low alarms will be decided with your physician.
In patients suffering from CHS, the minimum home monitoring is the pulse oximeter. Monitoring must be carried out during sleep and every time the baby is left alone.