Matt Harmon

166 Chapter eight Table 3b . Multivariate model of hypocapnia versus normocapnia in relation to neurological outcome. OR CI P-value Hypocapnia (normocapnia reference) 0.96 0.64 – 1.45 0.85 TTM group (33°C reference) 1.00 0.69 – 1.46 0.99 Age (per year) 1.06 1.04 – 1.08 <0.001 Sex (male reference) 1.58 0.95 – 2.63 0.08 Chronic heart failure (yes/no) 1.95 0.87 – 4.37 0.10 Asthma/COPD (yes/no) 1.41 0.74 – 2.66 0.29 Bystander witnessed arrest (yes/no) 0.55 0.29 – 1.05 0.07 Bystander CPR (yes/no) 0.97 0.62 – 1.53 0.91 Time to ROSC (per min) 1.03 1.02 – 1.05 <0.001 GCS – M (1 vs 2-5) 1.92 1.32 – 2.86 0.001 Shock on admission (yes/no) 2.4 1.33 – 4.34 0.004 First rhythm shockable (yes/no) 0.16 0.09 – 0.29 <0.001 pH (per 1.0 unit increase) 0.22 0.05 – 0.89 0.03 Hypercapnia = PaCO 2 > 6.0 kPa, normocapnia = PaCO 2 4.5 - 6.0 kPa, hypocapnia = PaCO 2 < 4.5 kPa. CI = 95% Confidence interval. OR = Odds Ratio. TTM = Targeted Temperature Management. COPD = Chronic obstructive pulmonary disease. CPR = Cardiopulmonary resuscitation. GCS - M = Glasgow coma scale – Motor. ROSC = return of spontaneous circulation. PaCO 2  = arterial carbon dioxide pressure. OR < 1 indicates better outcome. When analyzed separately in univariable logistic regression models, maximum PaCO 2 as well as lowest pH showed highly significant associations with poor neurological outcome (OR 1.17, 95% CI 1.06 - 1.28; P < 0.001); (OR 0.03, 95% CI 0.01 - 0.09; P < 0.001). When analyzed in a combined logistic regression model only the significant association between lowest pH and poor neurological outcome prevailed, (OR 0.02, 95% CI 0.05 - 0.11; P < 0.001) per unit decrease in pH. PaCO 2 and pH were not highly correlated with a collinearity between the regression coefficients of -0.64. The TTMH-analysis, comparing a normocapnia to a mild hypercapnia group, showed a non-significant term of interaction (P = 0.79) between temperature and PaCO 2 in relation to outcome; thus, we continued with a multivariable model without interaction. This analysis showed neither a significant difference between the mildly elevated (n = 121) and normocapnic (n = 675) PaCO 2 groups, (OR 1.01, 95% CI 0.60 - 1.67; P = 0.98) in relation to neurological outcome nor in the temperature groups (OR 0.96, 95% CI 0.68 - 1.35; P = 0.83). Of the 689 patients in the s-Tau nested cohort analysis, 100 were excluded, either due to our exclusion criteria (n = 64) or missing peak s-tau values (n = 36). The multivariable analysis of the remaining 589 patients, showed no association between PaCO 2 and s-Tau in our models (P = 0.12–1.00). The terms of interaction