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# Frequency The initial ventilator frequency is the number of breaths per minute intended to provide eucapneic ventilation (PaCO2 at patient's normal). The initial frequency is usually set between 10 and 12/min. This frequency, coupled with a tidal volume of 10 to 12 mL/kg, usually produces a minu...

# Frequency The initial ventilator frequency is the number of breaths per minute intended to provide eucapneic ventilation (PaCO2 at patient's normal). The initial frequency is usually set between 10 and 12/min. This frequency, coupled with a tidal volume of 10 to 12 mL/kg, usually produces a minute volume that is sufficient to normalize the patient's PaCO2. Frequencies of 20/min or higher are associated with auto-PEEP and should be avoided. **Alternative Method of Selecting Initial Frequency:** Estimate the patient's minute volume requirement and divide the estimated minute volume by the tidal volume. **Frequency = Estimated minute volume / Tidal volume** **Estimated Minute Volume:** * Males: 4.0 * BSA (body surface area) * Females: 3.5 * BSA (body surface area) BSA (in square meters) can be obtained from a nomogram (e.g., Dubois body surface area chart). **Minute Volume (Male):** (4)(BSA) **Minute Volume (Female):** (3.5)(BSA) **Adjusting Frequency:** The initial frequency setting of 10-12/min assumes normal CO2 production and physiologic dead space. If CO2 production is elevated or physiologic dead space is increased, the minute volume needs to be increased to normalize PaCO2. Since increasing tidal volume increases airway pressures on a volume-limited ventilator, increasing frequency is usually more appropriate. **Blood Gas Monitoring:** Blood gases should be checked 15-30 minutes after stabilizing on the ventilator to assess ventilation and oxygenation. A higher than normal PaCO2 (e.g., >45 mm Hg or >50 mm Hg for patients with chronic CO2 retention) warrants an increase in minute volume, typically by increasing frequency. Conversely, a lower than normal PaCO2 (e.g.,