What occurs if the respiratory rate (RR) is set too low in SIMV mode?

• A. Increased oxygen saturation levels
• B. Increased PaCO2, fatigue, and tachypnea
• C. Reduced work of breathing
• D. Improved ventilatory efficiency

Answer: (B)

In SIMV (Synchronized Intermittent Mandatory Ventilation) mode, if the respiratory rate is set too low, the patient may not receive an adequate number of mandatory breaths. As a result, this can lead to a reduced elimination of carbon dioxide (CO2) from the body, causing an increase in arterial carbon dioxide levels (PaCO2). Elevated PaCO2 may lead to respiratory acidosis, which can trigger fatigue in the respiratory muscles, as the patient may struggle to spontaneously initiate additional breaths to compensate. This increased work to breathe can result in tachypnea, characterized by rapid breathing as the patient attempts to stabilize their oxygenation and CO2 levels.

In summary, setting the respiratory rate too low in SIMV mode negatively impacts ventilation, leading to higher levels of carbon dioxide in the blood, respiratory muscle fatigue, and a compensatory increase in breathing rate.