Ventilator Modes

Mode refers to how the machine will ventilate the patient in relation to the patient’s own respiratory efforts. There is a mode for nearly every patient situation, plus many can be used in conjunction with each other.

Control Ventilation (CV)

CV delivers the preset volume or pressure regardless of the patient’s own 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 synchrony with the ventilator.

Assist-Control Ventilation (A/C)

A/C delivers the preset volume or pressure in response to the patient’s own 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 inititate a breath but who have weakened respiratory muscles.

Synchronous Intermittent Mandatory Ventilation (SIMV)

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 in 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)

PEEP is 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 the 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 reexpanding 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.

 

Ventilator Modes
Mode	Function	Clinical Use
Control Ventilation (CV)	Delivers preset volume or pressure regardless of patient’s own inspiratory efforts	Usually used for patients who are apneic
Assist-Control Ventilation (A/C)	Delivers breath in response to patient effort and if patient fails to do so within preset amount of time	Usually used for spontaneously breathing patients with weakened respiratory muscles
Synchronous Intermittent Mandatory Ventilation (SIMV)	Ventilator breaths are synchronized with patient’s respiratory effort	Usually used to wean patients from mechanical ventilation
Pressure Support Ventilation (PSV)	Preset pressure that augments the patient’s inspiratory effort and decreases the work of breathing	Often used with SIMV during weaning
Positive End Expiratory Pressure (PEEP)	Positive pressure applied at the end of expiration	Used with CV, A/C, and SIMV to improve oxygenation by opening collapsed alveoli
Constant Positive Airway Pressure (CPAP)	Similar to PEEP but used only with spontaneously breathing patients	Maintains constant positive pressure in airways so resistance is decreased
Independent Lung Ventilation (ILV)	Ventilates each lung separately; requires two ventilators and sedation/paralysis	Used for patients with unilateral lung disease or different disease process in each lung
High Frequency Ventilation (HFV)	Delivers small amounts of gas at a rapid rate (60-100 breaths/minute); requires sedation/paralysis	Used for hemodynamic instability, during short-term procedures, or if patient is at risk for pneumothorax
Inverse Ratio Ventilation (IRV)	I:E ratio is reversed to allow longer inspiration; requires sedation/ paralysis	Improves oxygenation in patients who are still hypoxic even with PEEP; keeps alveoli from collapsing

 

Alarms and Common Causes

As mentioned earlier, the ventilator is designed to monitor many aspects of the patient’s respiratory status, and there are many different alarms that 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.

High Pressure Limit	Low Pressure	High Respiratory Rate	Low Exhaled Volume
Secretions in ETT/airway or condensation in tubing   Kink in vent tubing   Patient biting on ETT   Patient coughing, gagging, or trying to talk   Increased airway pressure from bronchospasm or pneumothorax	Vent tubing not connected   Displaced ETT or trach tube	Patient anxiety or pain   Secretions in ETT/airway   Hypoxia   Hypercapnia	Vent tubing not connected   Leak in cuff or inadequate cuff seal   Occurrence of another alarm preventing full delivery of breath

 

Case Study

Mr. Hill has been on the ventilator for 24 hours. You volunteered to care for him today, since you know him from the intubation yesterday. The settings ordered by the pulmonologist after intubation were as follows: A/C, rate 14, V_T 700, FIO₂ 60%. Since 0700, Mr. Hill has been assisting the ventilator with a respiratory rate of 24 (The time is now 1100).

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1. Describe the ventilator settings.

The ventilator delivers 14 breaths per minute, each with a tidal volume of 700 ml. The A/C mode delivers the breaths in response to Mr. Hill’s own respiratory effort, but will initiate the breath if he doesn’t within the set amount of time. (He’s currently breathing above the vent setting.) The oxygen concentration is 60%.

You notice that Mr. Hill’s pulse oximetry has been consistently documented as 100% since intubation. You also notice that his respiratory rate is quite high and that he’s fidgety, doesn’t follow commands, and doesn’t maintain eye contact when you talk to him. He hasn’t had any sedation since he was intubated.

2. Which lab test should you check to find out what his true ventilatory status is?

Arterial blood gas (ABG) - which he should have had done with his morning labs. If not, check with the pulmonologist about getting one.

3. Which two parameters on the ABG will give you a quick overview of Mr. Hill’s status?

PaCO2 (which affects the pH) and PaO2. With his high respiratory rate, Mr. Hill is at risk for hypocapnia from “blowing off CO2.”  If the PaO2 is adequate, the FIO2 could be decreased, since his oxygen saturation has been consistently 100%.

4.  What are some possible causes of Mr. Hill’s increased respiratory rate? (Give the corresponding nursing interventions as well.)

Secretions - suction through the ETT, as well as his mouth. Anxiety or pain - Mr. Hill hasn’t received any sedation since he was intubated. At this point, he should at least have a prn order for sedation, if not a continuous IV infusion. The vent settings may not be appropriate – check the ABGs and notify the pulmonologist.

Mr. Hill didn’t have an ABG done this morning, so you obtain an order from the pulmonologist to get one now (1130). When it comes back, the PaCO₂ is 28, the pH is 7.48, and the PaO₂ is 120 (normals: PaCO₂ 35-45 mm Hg, pH 7.35-7.45 mm Hg, PaO₂ 80-100 mm Hg).

5. Based on the ABG, the pulmonologist changes the vent settings to SIMV, rate 10, PS 10, FIO₂ 40%. The V_T remains 700. How will these new settings help Mr. Hill?

SIMV will deliver 10 breaths with the full tidal volume each minute, but in synchrony with Mr. Hill’s spontaneous breaths. This mode is not triggered to deliver a breath each time Mr. Hill inhales, and the tidal volume of his spontaneous breaths is under his control. Pressure support decreases the work of breathing that results from breathing through the ventilator circuits and tubing. The PaO2 was higher than desired, indicating that the FIO2 could be decreased. We need to be careful to prevent oxygen toxicity.

The pulmonologist also orders midazolam (Versed) 1-2 mg every hour prn for sedation.

 

     

 

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