MILD HYPOTHERMIA AFTER CARDIAC-ARREST IN DOGS DOES NOT AFFECT POSTARREST CEREBRAL OXYGEN-UPTAKE DELIVERY MISMATCHING

Purpose: To compare measurements of cerebral arteriovenous oxygen cont ent differences (oxygen extraction ratios, oxygen utilization coeffici ents) in dogs after cardiac arrest, resuscitated under normothermia vs . mild hypothermia for 1-2 h or 12 h. Methods: In 20 dogs, we used our model of ventricular fibrillation (no blood flow) of 12.5 min, reperf usion with brief cardiopulmonary bypass, and controlled ventilation, n ormotension, normoxemia, and mild hypocapnia to 24 h. We compared a no rmothermic control Group I (37.5-degrees-C) (n = 8); with brief mild h ypothermia in Group II (core and tympanic membrane temperature about 3 4-degrees-C during the first hour after arrest) (n = 6); and with prol onged mild hypothermia in Group III (34-degrees-C during the first 12 h after arrest) (n = 6). Results: In Group I, the cerebral arterioveno us O2 content difference was 5.6 +/- 1.6 ml/dl before arrest; was low during reperfusion (transient hyperemia) and increased (worsened) sign ificantly to 8.8 +/- 2.8 ml/dl at 1 h, remained increased until 18 h, and returned to baseline levels at 24 h after reperfusion. These value s were not significantly different in hypothermic Groups II and III. T he cerebral venous (saggital sinus) PO2 (P(ss)O2) was about 40 mmHg (r ange 29-53) in all three groups before arrest and decreased significan tly below baseline values, between 1 h and 18 h after arrest; the lowe st mean values were 19 +/- 19 mmHg in Group I, 15 +/- 8 in Group II (N S), and 21 +/- 3 in Group III (NS). Postarrest P(ss)O2 values of less- than-or-equal-to 20 mmHg were found in 6/8 dogs in Group I, 5/6 in Gro up II and 4/6 in Group III. Among the 120 values of P(ss)O2 measured b etween 1 h and 18 h after arrest, 32 were below the critical value of 20 mmHg. Conclusions: After prolonged cardiac arrest, critically low c erebral venous O2 values suggest inadequate cerebral O2 delivery. Brie f or prolonged mild hypothermia after arrest does not mitigate the pos tarrest cerebral O2 uptake/delivery mismatching.