Pulmonary electrical impedance tomography changes in a model of hemorrhagic shock with endotoxemia and resuscitation

Introduction

Electrical impedance tomography (EIT) is a promising bedside device with the potential to assess changes in regional ventilation and lung blood flow [1]. The purpose of our study was to monitor lung images and changes in impedance by EIT in a model of hemorrhagic shock with endotoxemia followed by fluid resuscitation.

Methods

Twelve anesthetized, mechanically ventilated, supine pigs were submitted to hemorrhagic shock (50% blood volume) and endotoxin infusion. Animals were randomly allocated to control (n = 6) or a treatment group with lactated Ringer's (n = 6). The mean arterial pressure (MAP), central venous pressure (CVP), blood gas, extravascular lung water index (EVLWI), intrathoracic blood volume index (ITBVI), lung compliance and pulmonary EIT (Dräger, Germany) were measured before shock (T_basal), 60 minutes after hemorrhagic shock (T_shock) and hourly in the treatment period (T₁, T₂ and T₃). Statistical analysis was based on one-way ANOVA (P < 0.05).

Results

In T_shock there was a significant decrease in MAP, CVP, SvO₂, lung compliance, cardiac index, EVLWI and ITBVI and an increase in lactate (P < 0.05). Fifty percent of control animals died between T₂ and T₃. In treated animals, at T₃ the EVLWI reached values near those of T_basal whereas ITBVI remained below baseline (P < 0.05) and above T_shock (P < 0.05). There was sensible change in functional EIT images (Figure 1) and significant differences in impedance along time. Significant global impedance change occurred in T₂ relative to T_shock (P < 0.05). Most of the EIT changes were attributable to the ventral lobes (local₁), which showed significant differences in T₂ and T₃ relative to T_basal (P < 0.05) and of T₁, T₂ and T₃ relative to T_shock (P < 0.05).

Figure 1

Functional EIT images along timepoints.

Conclusion

Pulmonary impedance changes induced by the proposed model of shock and resuscitation were monitored successfully with the EIT device. Changes were suggestive of alterations in regional ventilation and ventilation–perfusion mismatch.