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

Low tidal volume (V-T) ventilation has become the preferred approach in patients in the ICU. Sedation reduces V-T by attenuating respiratory drive. Even in deep sedation, some patients exhibit high V-T. We aimed to determine factors associated with low V-T 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, P-aO2/F-IO2 < 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 V-T (>= 8 mL/kg predicted body weight [PBW]) and low V-T (> 8 mL/kg PBW) groups. RESULTS: Among 235 matched data sets from 100 subjects, 101 and 134 data sets were in the low V-T and high V-T groups, respectively. Set pressure was not different between the groups. PEEP was lower in the low V-T group, and opioids were more frequently used in the high V-T group. Strong ion difference (SID) was higher in the low V-T group. Multivariate analysis revealed that higher SID, lower total nonvolatile weak anion (A(TOT)), and absence of opioid administration were associated with attaining low V-T ventilation. Furthermore, V-T/PBW and SID demonstrated a weak inverse correlation, whereas V-T/PBW and A TOT exhibited a weak correlation. V-T/PBW was lower in the group with higher SID and lower A(TOT), indicating a tendency of metabolic alkalosis. CONCLUSIONS: Despite weak effects of high SID and low A(TOT), efficient management of the buffering function might be a feasible strategy to achieve low V-T ventilation.