CPAP: working mechanism, applications, drawbacks, handling


CPAP stands for Continuous Positive Airway Pressure. It is a type of non-invasive positive pressure ventilation) in which a single positive pressure is applied to the patient and can be changed as per the requirement.

CPAP for obstructive sleep apnea

Sleep Apnea is a condition where the tissues of the respiratory tract get relaxed while sleeping. This relaxation causes the airway path to be narrowed or blocked due to which patients show different symptoms such as:

  • Suffocation
  • Tiredness
  • Snoring

CPAP  aids patients from having the problem of sleep apnea. A constant pressure of 5 cm H2O to 18 cm H2O is applied to the patient while sleeping. This pressure allows the airway to widen for the air to flow into the lungs.


  • Continuous high airflow might cause patients, difficult sleep
  • High air pressure might cause patients, difficult to expire
  • Chance of air leakage from the CPAP masks
  • Dry nose and mouth
  • Headache to some patients


  • Connect the AC cord to the machine and the power supply
  • Connect connecting tube, mask, and humidification tank (if needed)
  • Turn on the machine
  • Pre-heat the water of the humidifier before use (30 mins earlier)
  • The pressure value can range from 5 to 25 cm H2O. Set the value as per the direction of the doctor.
  • Set Ramp time to 30 or 45 mins (if needed). Ramp time is the time period for the positive pressure to reach the set value. Patients often set the starting pressure to  5 cm H2O.


  • Use soap water to clean mask and humidification tank
  • Do not use alcohol to clean the CPAP machine. You can use Collins.
  • Always use distilled water in the humidification tank
  • An ultra-fine filter is disposable
  • Film filter is washable (life span: 6 months)
  • Check for any leakage in the tubing system.

The working mechanism of CPAP


Atmospheric air goes to the blower of the machine through the filters. The blower compresses the air and sends high-pressure air to the connecting tube. Then the air goes to the patient through the nasal mask.

The pressure sensor senses the air pressure in the connecting tube. This sensed pressure signal goes to the microprocessor. Then, the microprocessor analyzes the variation among the set and obtained pressure value. In case of any variation, it either increases or decreases the voltage signal of the driver motor. This, in turn, controls the speed of the blower. Based on the companies there can be some variations in the above block diagram.

Breathing cycle under CPAP

The graph shows that the breathing cycle under CPAP is almost the same as the normal breathing cycle.  Also, CPAP pressure is nearly equal to PEEP pressure.



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