Acute thyroid hormone administration increases systemic oxygen delivery and consumption immediately following resuscitation from cardiac arrest without changes in thyroid-stimulating hormone

Abstract

This study determined the acute effects of intravenous levothyroxine sodium (LT 4) on systemic oxygen delivery and consumption for 6 h following resuscitation from 9 min of normothermic cardiac arrest in dogs. Male mongrel dogs (15–25 kg) were randomly assigned to two groups of seven. The treated group received a pre-cardiac arrest infusion of 15 μg/kg per h of LT 4 for 1.5 h prior to arrest and for 6 h after, while controls received a comparable volume of 0.9 N saline infusion. Neurologic outcome was recorded at 1, 2 and 6 h following resuscitation. Systemic oxygen consumption (VO 2), carbon dioxide production (VCO 2) and respiratory quotient (RQ) were calculated from directly measured cardiac output, arterial and mixed venous blood gases and contents. Serum levels of circulating canine thyroid-stimulating hormone (cTSH), total thyroxine (T 4), free thyroxine (FT 4), total 3,5,3′-triiodothyronine (T 3), free 3,5,3′-triiodothyronine (FT 3), reverse 3,3′,5′-triiodothyronine (rT 3), and plasma markers of oxidant injury (malonaldehyde (MDA), 4-hydroxynonenal (4-OH) and erythrocyte GSH) were measured before administration and after resuscitation. Following resuscitation, treated dogs maintained significantly higher cardiac output when compared with their control counterparts at 4 h (5.5 ml/g per h vs. 2.9 ml/g per h, respectively, P < 0.05) and at 6 h (5.5 ml/g per h vs. 3.0 ml/g per h, respectively, P < 0.05). The level of VO 2 was significantly higher in treated dogs than control dogs at 1, 4 and 6 h ( P < 0.05). Treated dogs had significantly elevated levels of T 4, FT 4, T 3, FT 3 and rT 3 ( P < 0.01), compared with control dogs. No changes in cTSH were detected between groups or over time. Acute administration of LT 4 enhances systemic oxygen delivery and apparently, therefore, oxygen consumption following resuscitation.