A Modified Method to Assess Tidal Recruitment by Electrical Impedance Tomography

Area of Science:

• Critical Care Medicine
• Respiratory Physiology
• Medical Imaging

Background:

• Mechanical ventilation can cause lung injury through tidal recruitment and collapse.
• Electrical impedance tomography (EIT) detects tidal recruitment via regional ventilation delay inhomogeneity (RVDI).
• High tidal volumes (V_T) used in EIT measurements can increase end-inspiratory pressures (P_EI), limiting clinical use.

Purpose of the Study:

• To evaluate if RVDI can be accurately measured using reduced slow inflation V_Ts.
• To determine if lower V_Ts can maintain the accuracy of EIT in detecting tidal recruitment.
• To assess the impact of reduced V_Ts on P_EI during positive end-expiratory pressure (PEEP) titration.

Main Methods:

• Seven pigs with experimental lung injury were mechanically ventilated.
• Tidal recruitment was quantified using computed tomography (CT) at varying PEEP levels.
• RVDI was measured using EIT with slow inflation V_Ts of 12, 9, 7.5, and 6 mL/kg BW.

Main Results:

• Excellent linear correlation between tidal recruitment and RVDI was observed for V_Ts of 12 mL/kg BW (R² = 0.83) and 9 mL/kg BW (R² = 0.83).
• Correlation decreased with further V_T reduction (7.5 mL/kg BW: R² = 0.76; 6 mL/kg BW: R² = 0.71).
• Reduced V_Ts consistently lowered P_EI across all PEEP levels.

Conclusions:

• Tidal recruitment can be adequately monitored by EIT-based RVDI calculation using a slow inflation V_T of 9 mL/kg BW.
• This approach allows for accurate detection of lung injury while reducing P_EI.
• RVDI thresholds for predicting tidal recruitment vary with different slow inflation V_Ts.