Attaining Low Tidal Volume Ventilation During Patient Triggered Ventilation in Sedated Subjects.

BACKGROUND

Low tidal volume (VT) ventilation has become the preferred approach in patients in the ICU. Sedation reduces VT by attenuating respiratory drive. Even in deep sedation, some patients exhibit high VT. We aimed to determine factors associated with low VT ventilation in deeply sedated subjects who exhibited an inspiratory effort by examination of the acid/base balance using the Stewart model.

METHODS

The medical records of 630 consecutive subjects admitted to the ICU over 1 y were reviewed retrospectively, and daily data sets of patients with a persistent inspiratory effort, PaO2 /FIO2 < 300 mm Hg, PEEP > 5 cm H2O, and a Richmond Agitation Sedation Scale score of -4 or -5 who received assisted pressure-regulated ventilation were collected. The data sets were stratified into high VT (≥ 8 mL/kg predicted body weight [PBW]) and low VT (> 8 mL/kg PBW) groups.

RESULTS

Among 235 matched data sets from 100 subjects, 101 and 134 data sets were in the low VT and high VT groups, respectively. Set pressure was not different between the groups. PEEP was lower in the low VT group, and opioids were more frequently used in the high VT group. Strong ion difference (SID) was higher in the low VT group. Multivariate analysis revealed that higher SID, lower total nonvolatile weak anion (ATOT), and absence of opioid administration were associated with attaining low VT ventilation. Furthermore, VT/PBW and SID demonstrated a weak inverse correlation, whereas VT/PBW and ATOT exhibited a weak correlation. VT/PBW was lower in the group with higher SID and lower ATOT, indicating a tendency of metabolic alkalosis.

CONCLUSIONS

Despite weak effects of high SID and low ATOT, efficient management of the buffering function might be a feasible strategy to achieve low VT ventilation.