Comparison of SIMV + PS and AC modes in chronically ventilated children and effects on speech

Background: Two modes of ventilation commonly used in children requiring chronic home mechanical ventilation (HMV) via tracheostomy are Assist Control (AC) and Synchronized Intermittent Mandatory Ventilation with Pressure Support (SIMV + PS). There has been no study comparing these two modes of ventilation in children requiring chronic HMV.

Methods: We studied children requiring HMV capable of completing speech testing. Study participants were blinded to changes and studied on both modes, evaluating their oxygen saturation, end-tidal carbon dioxide (P_ETCO₂), heart rate, respiratory rate, and respiratory pattern. Subjects completed speech testing and answered subjective questions about their level of comfort, ease of breathing, and ease of speech.

Results: Fifteen children aged 12.3 ± 4.8 years were tested. There was no difference in mean oxygen saturation, minimum oxygen saturation, mean P_ETCO₂, maximum P_ETCO₂, mean heart rate, and mean respiratory rate. The maximum heart rate on AC was significantly lower than SIMV + PS, p = .047. Subjects breathed significantly above the set rate on SIMV + PS (p = .029), though not on AC. Subjects found it significantly easier to speak on AC, though there was no statistically significant difference in speech testing. Four subjects had multiple prolonged PS breaths on SIMV + PS. Many subjects exhibited an abnormal cadence to speech, with some speaking during both inhalation and exhalation phases of breathing.

Conclusions: There were few differences between AC and SIMV + PS, with a few parameters favoring AC that may not be clinically significant. This includes the subjective perception of ease of speech. We also found unnatural patterns of speech in children requiring HMV.