• Michael Schwarzl, Sebastian Seiler, Markus Wallner, Dirk von Lewinski, Stefan Huber, Heinrich Maechler, Paul Steendijk, Sieglinde Zelzer, Martie Truschnig-Wilders, Barbara Obermayer-Pietsch, Andreas Lueger, Burkert M Pieske, and Heiner Post.
• 1Department of Cardiology, Medical University of Graz, Graz, Austria. 2Department of Cardiothoracic Surgery, Medical University of Graz, Graz, Austria. 3Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands. 4Clinical Institute of Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria. 5Department of Endocrinology and Nuclear Medicine, Medical University of Graz, Graz, Austria. 6Department of Internal Medicine, Medical University of Graz, Graz, Austria.
• Crit. Care Med. 2013 Dec 1; 41 (12): e401-10.

ObjectiveWe tested whether mild hypothermia impacts on circulatory and respiratory dysfunction during experimental endotoxemia.DesignRandomized controlled prospective experimental study.SettingLarge animal facility, Medical University of Graz, Austria.SubjectsThirteen anesthetized and mechanically ventilated pigs.InterventionsLipopolysaccharide was administered for 4 hours. With the beginning of lipopolysaccharide infusion, animals were assigned to either normothermia (38°C, n = 7) or mild hypothermia (33°C, n = 6, intravascular cooling) and followed for 8 hours in total.Measurements And Main ResultsAt the end of the protocol, cardiac output was lower in mild hypothermia than in normothermia (4.5 ± 0.4 L/min vs 6.6 ± 0.4 L/min, p < 0.05), but systemic vascular resistance (885 ± 77 dyn·s/cm vs 531 ± 29 dyn·s/cm, p < 0.05) and (Equation is included in full-text article.)(77% ± 6% vs 54% ± 3%, p < 0.05) were higher. Indices of left ventricular contractility in vivo were not different between groups. The high-frequency band in spectral analysis of heart rate variability indicated a better preserved vagal autonomic modulation of sinuatrial node activity in mild hypothermia versus normothermia (87 ± 5 vs 47 ± 5, normalized units, p < 0.05). Plasma norepinephrine levels were elevated compared with baseline in normothermia (2.13 ± 0.27 log pg/mL vs 0.27 ± 0.17 log pg/mL, p < 0.05) but not in mild hypothermia (1.02 ± 0.31 vs 0.55 ± 0.26, p = not significant). At 38°C in vitro, left ventricular muscle strips isolated from the mild hypothermia group had a higher force response to isoproterenol. SaO2 (100% ± 0% vs 92% ± 3%, p < 0.05) and the oxygenation index (PO2/FIO2, 386 ± 52 mm Hg vs 132 ± 32 mm Hg, p < 0.05) were substantially higher in mild hypothermia versus normothermia. Plasma cytokine levels were not consistently different between groups (interleukin 10) or higher (tumor necrosis factor-α and interleukin 6 and 8) during mild hypothermia versus normothermia.ConclusionThe induction of mild hypothermia attenuates cardiac and respiratory dysfunction and counteracts sympathetic activation during experimental endotoxemia. This was not associated with lower plasma cytokine levels, indicating a reduction of cytokine responsiveness by mild hypothermia.

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