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 initiate 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.

Constant Positive Airway Pressure (CPAP)

CPAP works only for patients who are breathing spontaneously. The effect 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.

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.

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

Constant Positive Airway Pressure (CPAP)

Used only with spontaneously breathing patients

Maintains constant positive pressure in airways so resistance is decreased

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

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, VT 700, FIO2 60%. Since 0700, Mr. Hill has been assisting the ventilator with a respiratory rate of 24. (The time is now 1100.)

Question Answer

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.

Question Answer

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).

Question Answer

5. Based on the ABG, the pulmonologist changes the vent settings to SIMV, rate 10, PS 10, FIO2 40%. The VT 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.