What is expiratory valve?

The main tasks of the expiratory valve sets are to control the respiratory phases and the positive end-expiratory pressure (PEEP). Their design also prevents internal ventilator components from coming into contact with the patient’s exhaled gas.

What causes rebreathing?

[1] It could result from hypoventilation due to leaks, exhausted soda lime, bypassing the absorber inadvertently, or due to a malfunction of unidirectional valves (UDVs). Incompetence of expiratory UDV, caused by a damaged disc or a disc stuck in an open position, has been reported earlier.

What is an inspiratory valve?

The inspiratory valve prevents backflow through the inspiratory limb during expiration and the expiratory valve prevents backflow through the expiratory limb during inspiration.

How does an expiratory valve work?

The exhalation valve is controlled by a pressure signal from the ventilator, conveyed through small-bore tubing. This signal determines the timing of flow into and out of the patient for mandatory inflations and also may control the PEEP level.

What is PEEP exhalation valve?

Positive End Expiratory Pressure (PEEP) is used to maintain pressure on the lower airways at the end of the breathing cycle which prevents the alveoli from collapsing during expiration.

What increases ETCO2?

In severe cases of respiratory distress, increased effort to breathe does not effectively eliminate CO2. This causes CO2 to accumulate in the lungs and more of it to be excreted with each breath (hypercapnea), which would cause the ETCO2 level to rise.

When is APL valve used?

The APL (Adjustable Pressure Limiting) valve is only used during manual (or spontaneous) ventilation in the Modulus II machines. As its name indicates, the APL valve limits the amount of pressure buildup that can occur during manual ventilation.

How do you test an APL valve?

With the end of the breathing system still covered with your thumb, squeeze the reservoir bag. Listen to ensure there are no leaks. You should not hear any gas escaping. With the end of the tube still covered, open the APL valve by turning it anti-clockwise.

What are unidirectional valves?

The unidirectional valves allow the air flow in the only direction indicated by the arrow, and prevent it on the opposite way. Available with ball or piston shutter. The ball shutter closing avoids the friction between the components.

What happens when the inspiratory valve malfunctions?

An incompetent inspiratory valve will allow exhaled CO 2 – containing gas to enter the inspiratory limb of the circuit during expiration. During the next inspiration, the CO 2 -containing gas in the inspiratory limb enters the patient, extending the expiratory alveolar plateau (phase III) of the time capnogram (Fig. above).

What’s the difference between a stuck expiratory valve and an open valve?

Unlike a stuck, open expiratory valve, an inspiratory valve that remains open during expiration shows the end-tidal carbon dioxide baseline returning to zero. The best way to understand this is to consider taking the circle system breathing circuit and removing the inspiratory valve entirely from the circuit.

Can a capnograph detect an incompetent expiratory valve?

The capnograph may show a prolonged expiratory upstroke (similar to in COPD) An expiratory valve stuck in the open position may be detected by failure of capnogram to return to zero. Dorsch JA and Dorsch SE. Understanding Anesthesia Equipment, 5th edition, LWW: p 414-5, 715. 2008

Is the expiratory valve part of the anesthesia circuit?

Dorsch JA and Dorsch SE. Understanding Anesthesia Equipment, 5th edition, LWW: p 414-5, 715. 2008 S T Pyles, L S Berman, J H Modell Expiratory valve dysfunction in a semiclosed circle anesthesia circuit–verification by analysis of carbon dioxide waveform. Anesth.