Mechanical Ventilation Modes and Respiratory Math

This flashcard set covers the fundamental modes of mechanical ventilation (AC, PSV, SIMV), the distinction between ventilation and oxygenation settings, and the mathematical formulas for Total Cycle Time, Inspiratory Time, and I:E ratios.

Assist Control (AC)

A ventilation mode where all breaths, whether machine-set or patient-triggered, are mandatory breaths that look identical on a graphic and have the same set parameters.

PSV (Pressure Support Ventilation)

A mode consisting entirely of spontaneous breaths where Pressure Support and PEEP are set; it is considered the mode patients are extubated off of to build respiratory muscle strength.

SIMV (Synchronized Intermittent Mandatory Ventilation)

A mode that combines mechanical breaths and spontaneous breaths; if the patient triggers extra breaths, they are supported by pressure support rather than being full machine breaths.

Ventilation Settings

The parameters set on the ventilator to manage the removal of $CO_2$, including Respiratory Rate ($RR$), Tidal Volume ($V_T$), Pressure Support, and Flow.

Oxygenation Settings

The parameters set on the ventilator to manage oxygen levels, specifically PEEP and $FiO_2$.

PEEP (Positive End-Expiratory Pressure)

An oxygenation setting that is functionally equivalent to CPAP, EPAP, and spontaneous CPAP depending on the ventilator brand and model.

Total Cycle Time ($TCT$)

The time for one full breath cycle, calculated using the formulas $TCT = \frac{60}{\text{Respiratory Rate}}$ or $TCT = I_{\text{time}} + E_{\text{time}}$.

Inspiratory Time ($I_{\text{time}}$) in Volume Control

The time duration of inspiration, indirectly set using the formula $I_{\text{time}} = \frac{\text{Tidal Volume (L)}}{\text{Flow (L/s)}}$.

Flow Conversion

To convert Flow from liters per minute to liters per second, the value is divided by 60 ($\text{L/min} \times \frac{1}{60}$).

Relationship between Tidal Volume and $I_{\text{time}}$

A direct relationship; as the Tidal Volume increases, the Inspiratory Time ($I_{\text{time}}$) also increases.

Relationship between Flow and $I_{\text{time}}$

An indirect relationship; as the Flow rate increases, the Inspiratory Time ($I_{\text{time}}$) decreases.

Respiratory Rate and $E_{\text{time}}$ Relationship

Changing the Respiratory Rate will only change the Expiratory Time ($E_{\text{time}}$), not the Inspiratory Time ($I_{\text{time}}$).

I:E Ratio Formula

The ratio of inspiration to expiration, expressed as $1 : \frac{E_{\text{time}}}{I_{\text{time}}}$.

Normal I:E Ratio

The typical ratio for a healthy adult is $1:2$.

Obstructive Disease I:E Ratio

A ratio associated with diseases like Cystic Fibrosis (one of the CBABE diseases), typically set at $1:3$ or $1:4$.

Restrictive Disease I:E Ratio

A ratio typically set at $1:1$ for most restrictive lung diseases.