Anesthetics, key point, Respiratory System, Uncategorized

VENTILATOR MODES || VCV, A/PCV, PSV, SIMV, CPAP etc || Alarms and common causes



A medical ventilator or Ventilator Modes is a machine that supports breathing, the mechanical ventilator machine is designed to move breathable air into and out of the lungs. It is mainly used in critical care units in hospital & rehabilitation centers. To provide breathing for a patient who is physically unable to breathe, or breathing insufficiently.


Ventilator Modes refers to the machine will ventilate the patient concerning the patient’s respiratory efforts. there is a mode for nearly every patient situation, plus many can be used in conjunction with each other.

Volume Control Ventilation ( VCV / CV )

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V delivers the preset volume or pressure regardless of the patient’s inspiratory efforts. This mode is used for patients who are unable to initiate a breath. If it is used with spontaneously breathing patients, they must be sedated and/or pharmacologically paralyzed so they don’t breathe out of synchronizing with the ventilator.

Assist Control Ventilation (A/PCV )

A/C delivers the preset volume or pressure in response to the patient’s inspiratory effort but will initiate the breath if the patient does not do so within the set amount of time. This means that any inspiratory attempt by the patient triggers a ventilator breath. The patient may need to be sedated to limit the number of spontaneous breaths since hyperventilation can occur. This mode is used for patients who can initiate a breath but who have weakened respiratory muscles.

Synchronous Intermittent Mandatory Ventilation (SIMV)

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SIMV was developed as a result of the problem of high respiratory rates associated with A/C. SIMV delivers the preset volume or pressure and rate while allowing the patient to breathe spontaneously between ventilator breaths. Each ventilator breath is delivered in synchrony with the patient’s breaths, yet the patient is allowed to completely control the spontaneous breaths. SIMV is used as a primary mode of ventilation, as well as a weaning mode. (During weaning, the preset rate is gradually reduced, allowing the patient to slowly regain breathing on his or her own.) The disadvantage of this mode is that it may increase the work of breathing and respiratory muscle fatigue.

Pressure Support Ventilation (PSV)

PSV is Preset pressure that augments the patient’s spontaneous inspiratory effort and decreases the work of breathing. The patient completely controls the respiratory rate and tidal volume. PSV is used for patients with a stable respiratory status and is often used with SIMV to overcome the resistance of breathing through ventilator circuits and tubing.

Positive End Expiratory Pressure (PEEP)

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PEEP is a positive pressure that is applied by the ventilator at the end of expiration. This mode does not deliver breaths but is used as an adjunct to CV, A/C, and SIMV to improve oxygenation by opening collapsed alveoli at the end of expiration. Complications from increased pressure can include decreased cardiac output, pneumothorax, and increased intracranial pressure.

Constant Positive Airway Pressure (CPAP)

CPAP is similar to PEEP except that it works only for patients who are breathing spontaneously. The effect of both is comparable to inflating a balloon and not letting it completely deflate before inflating it again. The second inflation is easier to perform because resistance is decreased. CPAP can also be administered using a mask and CPAP machine for patients who do not require mechanical ventilation, but who need respiratory support; for example, patients with sleep apnea.

Independent Lung Ventilation (ILV)

This method is used to ventilate each lung separately in patients with unilateral lung disease or with a different disease process in each lung. It requires a double-lumen endotracheal tube and two ventilators. Sedation and pharmacological paralysis are used to facilitate optimal ventilation and increased comfort for the patient.

High-Frequency Ventilation (HFV)

HFV delivers a small amount of gas at a rapid rate (as much as 60-100 breaths per minute.) This is used when conventional mechanical ventilation would compromise hemodynamic stability, during short-term procedures, or for patients who are at high risk for pneumothorax. Sedation and pharmacological paralysis are required.

Inverse Ratio Ventilation (IRV)

The normal inspiratory: expiratory ratio is 1:2 but this is reversed during IRV to 2:1 or greater (the maximum is 4:1). This mode is used for patients who are still hypoxic even with the use of PEEP. The longer inspiratory time increases the amount of air in the lungs at the end of expiration (the functional residual capacity) and improves oxygenation by re-expanding collapsed alveoli. The shorter expiratory time prevents the alveoli from collapsing again. Sedation and pharmacological paralysis are required since it’s very uncomfortable for the patient.


Alarms and common causes

As mentioned earlier, the ventilator is designed to monitor many aspects of the patient’s respiratory status, and many different alarms can be set to warn healthcare providers that the patient isn’t tolerating the mode or settings. The following are common ventilator alarms and their most frequent causes.

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