Mechanical Ventilation Explained with Modes and Sample Settings

 

MECHANICAL VENTILATION

Patients can be ventilated in various ways.

In mandatory breathing methods, the equipment fully or partially controls the breathing.

In spontaneous breathing methods, the patient either breathes independently at the PEEP level or receives support from the equipment.

FORMS OF BREATHING/VENTILATION

During ventilation treatment, patients experience different phases with varying support requirements:

Figure 1. Forms of Breathing/Ventilation 

(The light shaded portion of the circle is how much respiratory effort the patient does.)

THREE GROUPS OF VENTILATION MODES

Ventilation modes can be categorized into three groups: volume-controlled modes, pressure-controlled modes, and spontaneous/assisted modes.

1. Support of spontaneous breathing:

For example, SPN/CPAP

2. Volume-controlled ventilation:

For example, VC-SIMV

VC-AC

3. Pressure-controlled ventilation:

For example, PC-BIPAP

APRV

PC-AC

PC-SIMV

Key Concepts Before Exploring Ventilation Modes

PATIENT-TRIGGERED BREATHING

In patient-triggered mandatory breathing, the patient breathes independently. The equipment detects this attempt and initiates inspiration.

MECHANICALLY TRIGGERED BREATHING

Mechanically triggered mandatory breaths occur without patient activity and are always timed. The patient has no control over the timing of inspiration, which is determined by set parameters (Respiratory rate, Inpiratory ratio IR, or inspiratory time Ti).

FLOW TRIGGER

A flow trigger detects if the patient initiates inspiration. The trigger threshold is set based on patient needs, ensuring a consistent frequency of mandatory breaths. Setting alarm limits prevents barotrauma or inadequate ventilation and prompts ventilator adjustments when necessary.

CONTROL VARIABLES FOR EXPIRATION

Expiration can be triggered by flow or time cycling.

FLOW-CYCLED: Expiration starts when inspiratory flow drops to a set proportion of the maximum flow, allowing the patient to control the start of expiration.

TIME-CYCLED: Expiration starts based on the set inspiratory time (Ti), making it ventilator-controlled with little patient influence.

MODES OF VENTILATION

SUPPORT OF SPONTANEOUS BREATHING

SPN-CPAP/PS: Can involve spontaneous or assisted spontaneous breathing with continuous positive pressure. The patient initiates most of the breathing effort, and this mode is ideal before extubation. Pressure support can be added to assist spontaneous breaths.

Figure 2. Sample setting for SPN-CPAP

VOLUME-CONTROLLED VENTILATION

VC-SIMV: Combines controlled and assisted spontaneous breathing, delivering a set tidal volume (VT) with synchronized mandatory breaths. The patient can breathe spontaneously during expiration, supported by pressure as needed.

Figure 3. Sample setting for VC-SIMV

VC-AC: Ensures the patient receives at least the set VT, with each detected breathing effort triggering an additional mandatory breath. If no breath is detected within the set time, the ventilator initiates a mandatory breath, maintaining a minimum ventilation frequency.

Figure 4. Sample setting for VC-AC

PRESSURE-CONTROLLED VENTILATION

PC-AC: Allows controlled or mixed ventilation, where every detected breath attempt triggers a mandatory breath. The patient controls the number of additional breaths.

Figure 5. Sample setting for PC-AC

PC-SIMV: Combines controlled ventilation with spontaneous breathing, synchronizing mandatory breaths with the patient’s efforts. Spontaneous breathing can be supported with pressure throughout the breathing cycle.

Figure 6. Sample setting for PC-SIMV

PC-BIPAP: Allows spontaneous breathing at any time, with mandatory breaths synchronized for both inspiration and expiration.

Figure 7. Sample setting for PC-BIPAP

PC-APRV: Used for hypoxemic respiratory failure (including ARDS). Spontaneous breathing occurs at the upper pressure level (P high) with brief pressure relief times (P low) to support CO2 elimination.

Figure 8. Sample setting for PC-APRV

RISKS AND COMPLICATIONS OF MECHANICAL VENTILATION

1. Barotrauma: Alveoli rupture due to overinflation, causing lung collapse. Keep PIP below 40.

2. Volutrauma: Alveoli fill with fluid due to high tidal volumes, common in ARDS and post-blood transfusion.

3. Ventilator-Associated Pneumonia (VAP): Lung infection developing 48 hours or more after intubation.

4. Oxygen Toxicity: Occurs from prolonged exposure to high oxygen levels (FiO2 > 60%).

 

TABLE COMPARING MECHANICAL VENTILATOR MODES

DEFINITION OF TERMS

		Abbreviation	Normal values	Things to consider
Compliance	The lung's ability to stretch and expand	C	50-100ml/cmH2O	Low compliance indicates stiff lung High indicated a pliable lung
Automatic tube compensation	Compensate for the non-linearly flow-dependent pressure drop across an ETT during inspiration	ATC	N/A	ATC enables the precise compensation of this increased work of breathing, with easy setting options
Minute volume	The volume of gas inhaled/exhaled from a person's lungs per minute.	MV	MV= VT X RR
Positive End Expiratory Pressure	The maintenance of positive pressure (above atmospheric) at the airway opening at the end of expiration.	PEEP	Continuous pressure (generally from 5 to 8 cmH2O) is added to the airway- to increase the effectiveness of oxygenation
Peek Inspiratory Pressure	The highest level of pressure applied to the lungs during inhalation	PIP	Approx. 20cmH20 Resp failure 30-40	Concern if >40 Troubleshooting: ?ETT kink ?patient biting on the tube ?mucus plug ?bronchospasm ?pneumothorax
Upper pressure level	P-high is what provides the driving pressure for the release breath, which is the mechanism whereby APRV provides mechanical support to the work of breathing.	Phigh		Inadequate P-high may cause inadequate ventilator support, causing increased work of breathing
Lower pressure level	P-low is the lowest pressure applied by the ventilator to the respiratory system	Plow	depends on the patient's condition
Inspiratory pressure	Total inspiratory pressure and equals PEEP plus the pressure support	Pinsp	depends on the patient's condition
Pressure Support	Positive pressure mechanical ventilation in which the patient triggers every breath	PS	depends on the patient's condition
Resistance	resistance of the respiratory tract to airflow during inhalation and expiration	R	>15cmH2O/L/s	Troubleshooting ?ETT kink ?Patient biting, ?mucous plug ?bronchospasm
Respiratory rate	the rate at which a person inhales and exhales	RR	16-20 breaths per minute
Expiratory time	Expiratory time is defined as the period from the start of expiratory flow to the start of inspiratory flow	Te	depends on the patient's condition
Inspiratory time	For ventilators, the inspiratory time is the amount of time it takes to deliver the tidal volume of air to the lung	Ti	depends on the patient's condition
Tidal volume	Tidal volume is the volume of air delivered to the lungs with each breath by the ventilator	VT	depends on the patient's condition	The tidal volume is about 6-8 mL/kg of ideal body weight for patients with healthy lungs

NOTE: The author used sample settings from Draeger ventilators. Please follow your hospital policy on ventilator modes and settings and the specific ventilator brand's operation manual.

Nursing management of patients on mechanical ventilators will be discussed in another post.

Reference:

rsp_new_nomenclature_ventilation_modes_icu_booklet_9066477_en.pdf (draeger.com)