Selldén Eva
Department of Anaesthesia and Intensive Care, Karolinska Hospital, Stockholm, Sweden.
Proc Nutr Soc. 2002 Aug;61(3):337-43. doi: 10.1079/pns2002175.
General anaesthesia causes hypothermia due to decreased metabolic rate and impaired thermoregulation. Many warming devices are in use to prevent heat loss, but little attention has been paid to stimulating the body's own heat generation. All nutrients raise energy expenditure, and the highest thermic effect is ascribed to amino acids and proteins, 30-40 % in the awake state. Amino acids infused during general anaesthesia exert a thermic effect that is enhanced compared with that in the awake state. At awakening from anaesthesia, post-operative hypothermia may be prevented without shivering. The tissues involved and the mechanisms by which nutrients stimulate heat production are still not completely understood. However, these findings support the existence of an inhibitory action normally exerted by central thermosensors, in order to maintain oxidative metabolism within certain limits, to prevent hyperthermia. During anaesthesia central thermosensors are silenced and, hence, amino acid thermogenesis is exaggerated. The amino acid-induced heat generation during anaesthesia predominantly occurs in extra-splanchnic tissues, most probably in skeletal muscle. It may reflect an increased protein turnover, as both protein breakdown and synthesis are energy-consuming processes known to generate heat. Possibly, amino acid infusion provides substrates, otherwise mobilized from the body's own tissues, needed for wound healing and immunological function. However, other cellular mechanisms may also contribute to this non-shivering thermogenesis.
全身麻醉会因代谢率降低和体温调节受损而导致体温过低。目前使用了许多保暖设备来防止热量散失，但人们很少关注刺激身体自身产热。所有营养素都会增加能量消耗，其中氨基酸和蛋白质的热效应最高，在清醒状态下为30% - 40%。全身麻醉期间输注的氨基酸产生的热效应与清醒状态相比有所增强。在麻醉苏醒时，可在不发生寒战的情况下预防术后体温过低。所涉及的组织以及营养素刺激产热的机制仍未完全明确。然而，这些发现支持中枢温度感受器通常存在抑制作用，以将氧化代谢维持在一定限度内，防止体温过高。在麻醉期间，中枢温度感受器被抑制，因此氨基酸产热被夸大。麻醉期间氨基酸诱导的产热主要发生在内脏外组织，很可能是骨骼肌。这可能反映了蛋白质周转增加，因为蛋白质分解和合成都是已知会产热的耗能过程。氨基酸输注可能提供了伤口愈合和免疫功能所需的底物，否则这些底物需从身体自身组织中动员。然而，其他细胞机制也可能促成这种非寒战产热。
