Matt Harmon

147 Chapter seven The effect of different target temperature levels on mechanical ventila- tion parameters At the end of the TTM period, patients kept at TTM33 had significantly lower etCO 2 when compared to patients kept at TTM36 (3.9 kPa ± 0.98 vs. 4.55 kPa ± 1.31, p<0.0001), whereas PaCO 2 levels and respiratory minute volume were similar between groups (supplemental table 3). In addition, alveolar dead space fraction was significantly higher in TTM33 vs. TTM36 (0.24 ± 0.19 vs. 0.15 ± 0.29, p=0.004). PEEP, V T and Pplat did not differ between groups (supplemental table 3). To study the effect of TTM on etCO 2 and PaCO 2 over time, we performed a mixed effects model (supplemental table 4, figure 4). PaCO 2 levels were significantly lower after 4 hours compared to baseline in both the TTM33 group ( β = 0.41 kPa [95% confidence limit, 0.09 - 0.73 kPa]; p = 0.0014) and the TTM36 group ( β = 0.63 kPa [95% confidence limit, 0.31 - 0.95 kPa]; p = <0.0001). However, there was no difference between groups in PaCO 2 levels. In contrast, etCO 2 levels were lower in the TTM33 group compared to the TTM36group, whereas alveolar dead space fraction was higher. These results were found at a similar respiratory minute volume between both groups. Metabolic acidosis was more pronounced in the TTM33 group, with lower pHa, lower base excess and increased lactate levels. Discussion In this substudy of the TTM-trial, we describe ventilation practice in patients after a cardiac arrest and the effects of different target temperatures on mechanical ventilation settings and parameters of gas-exchange. At the end of TTM (before rewarming), we found that patients are predominantly ventilated with low tidal volumes, equal or below 8 ml/kg. Oxygen was applied liberally, with 48% of patients with supranormal (>13.3 kPa) oxygenation receiving high FiO 2 levels. Non-survivors had lower oxygenation, higher respiratory rates, lower compliance, higher driving pressures and were ventilated with lower tidal volumes compared to survivors at 28-days. In multivariate analysis, respiratory rate, but none of the other ventilation parameters, was independently associated with 28-day mortality. In studying the effect of different target temperatures on mechanical ventilation, we found that TTM33 resulted in lower etCO 2 levels and higher alveolar dead space fraction compared to TTTM36 at similar minute ventilation. This study suggests that a majority of cardiac arrest patients are ventilated according to lung protective standards. These results are similar to the PRoVENT