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CARDIOVASCULAR ANESTHESIA

The Hemodynamic and Metabolic Effects of Shivering During Acute Normovolemic Hemodilution

Valéria Perez-de-Sá, MD PhD, DEAA^*, Doris Cunha-Goncalves, MD DEAA, Henning Schou, MD PhD, Christer Jonmarker, MD PhD, DEAA, and Olof Werner, MD PhD, DEAA^*

*Children’s Hospital, the Heart Lung Division, and the Department of Anesthesia and Intensive Care at the University Hospital, Lund, Sweden, and from Children’s Hospital and Regional Medical Center, The University of Washington, Seattle, Washington

Address correspondence to Valéria Perez de Sá, MD, PhD, Department of Pediatric Anesthesia and Intensive Care, Children’s Hospital, University Hospital of Lund, Lund, SE-221 85, Sweden. Address email to Valeria.Sa{at}anest.lu.se

To assess the hemodynamic and metabolic effects of shivering during extreme normovolemic hemodilution, we anesthetized 16 pigs with fentanyl-midazolam-pancuronium. Mild hypothermia (36.5° ± 0.1°C) was induced by surface cooling, and the animals were randomized to either a control group (hemoglobin 118 ± 3 g/L) or a hemodilution group (hemoglobin 52 ± 2 g/L). In the latter group, blood was replaced with an isotonic Ringer’s acetate/dextran 70 solution. Shivering was allowed to occur by a controlled decrease in the infusion rate of pancuronium. Shivering increased oxygen consumption (O₂) in both groups (P < 0.001). Initially, this was predominantly compensated for by an increased oxygen extraction ratio (ER), but when O₂ was 2.3 ± 0.2 times baseline, critical levels of mixed venous oxygenation (SO₂ = 18% ± 2%; PO₂ = 22.5 ± 1.5 mm Hg) and ER (82% ± 3%) were recorded in anemic animals. Control animals did not reach critical levels until O₂ was maximal (3.7 ± 0.3 times baseline). Maximal attained O₂ was less (2.9 ± 0.1 times baseline) in the anemic animals (P = 0.01), and at this stage two of these pigs had myocardial lactate production, one of which died in ventricular fibrillation. Coronary perfusion pressure was significantly less (P < 0.001) in the anemic animals. We conclude that in this experimental model, maximal shivering as measured by O₂ was limited in hemodiluted animals, and left ventricular oxygen balance was marginal, as evidenced by a decreased lactate uptake and extraction.

IMPLICATIONS: The effect of acute increases in oxygen consumption (shivering) on severely anemic individuals has not been evaluated. In this experimental model, left ventricular oxygen balance was marginal, as evidenced by decreased lactate extraction.