吸入麻醉药的选择：氟烷、异氟烷、七氟烷

Selection Of Anaesthetic Drugs: Halothane, Isoflurane Or Sevoflurane?

吸入麻醉药的选择：氟烷、异氟烷、七氟烷

Speed of Induction and Recovery

诱导与苏醒速度

Sevoflurane is half as soluble in blood as isoflurane, which is approximately half as soluble in blood as halothane. The more insoluble an anaesthetic, the faster the anaesthetic induction, more rapid the changes in depth and faster the recovery. Clinically the difference between these agents is not huge, but animals will recover fastest from sevoflurane and to a lesser degree, isoflurane, and will be more alert - owners notice this difference! Speed of recovery is an important consideration for neonates (C-sections), geriatric patients and for long anaesthetics.

七氟烷的血液溶解度是异氟烷的一半，也是氟烷的将近一半。溶解度越低，诱导、麻醉变深或者苏醒的速度越快。临床上这几种药区别不大，但是与异氟烷相比，使用七氟烷的动物会更加快速地苏醒到更清醒的程度，这将需要宠物主人更加关注这种不同。对于剖腹产或者年老的病号，苏醒的速度非常重要。同样，时间长的手术苏醒速度也很重要。

Circulatory Function

循环功能

All inhalation anaesthetics cause a dose-dependent reduction in mean arterial pressure which is caused by a dose-dependent decrease in cardiac output and stroke volume.  There is a tendency for less cardiac depression with isoflurane and sevoflurane, particularly in cats, and at deeper levels of anaesthesia. The cardiovascular system seems to be more tolerant of changes in anaesthetic depth with isoflurane or sevoflurane compared to halothane.

所有的吸入麻醉剂都会引起剂量依赖性的平均动脉压下降，这是因为有剂量依赖性的心脏输出降低和每搏输出量降低。这种趋势，特别在是猫身上或者是在更深的麻醉的时候，在用异氟烷或者七氟烷的时候更不明显。

The arrhythmogenic potential for halothane is much greater than that for isoflurane­ or sevoflurane.  This is especially important for any patient with cardiac disease manifested by an arrhythmia.  In such patients (e.g., gastric dilata­tion), halothane may be contraindicated.

氟烷相对于异氟烷和七氟烷，更容易引起心率失常。这对于已经有心率失常的心脏病的病号特别重要。

Respiratory Function

呼吸功能

All inhalation anaesthetics cause a dose-dependent respiratory depression, as evidenced by a rise in arterial carbon dioxide tension with increasing anaesthetic dose.  In canine patients, isoflurane tends to produce the most respiratory depression when compared to the other inhalation agents. However, in cats, isoflurane has been shown to cause less respiratory depres­sion when compared to halothane (there is no comparative data for sevoflurane).

所有的呼吸麻醉药都会引起剂量依赖性的呼吸抑制，因为增加麻醉剂量的时候动脉二氧化碳含量会呈增加的趋势就能证明如此。在犬的病例上，异氟烷的呼吸抑制作用比其他麻醉剂要强。尽管如此，在猫身上异氟烷的呼吸抑制作用比氟烷要低。

Metabolism

代谢作用

Traditionally, it was thought that the inhalation anaesthetics were entirely taken up and eliminated by the lungs.  However, of that portion of the anaesthetic taken up by the body's tissue, 25% of halothane is metabolized, compared to 3% of sevoflurane and virtually O% for isoflurane This becomes particularly important for neonatal animals and animals with liver or renal impairment. 

传统认为吸入麻醉剂是由肺部吸收和排出的。但是，有部分麻醉剂由身体组织吸收，其中25%氟烷由身体代谢，3%七氟烷、几乎是0%异氟烷由身体代谢。这对于新生动物或者有肝肾功能损伤的动物非常重要。

In addition, metabolism of inhalation anaesthetics is an important concern from an occupational health aspect. Since metabolism of isoflurane, and to a lesser extent sevoflurane, is minimal, it offers distinct advantages from the perspective of occupational health exposure. In veterinary practices with good waste anaesthetic gas management, occupational exposure still occurs at the time of disconnection, during recovery and when servicing equipment!

另外，麻醉药的代谢对职业健康非常重要。因为异氟烷的身体代谢比七氟烷低，这对于职业健康而言有很长远的意义。如果对废气有很好的管理，兽医临床上职业暴露时间点是在拔管之后和在操作机器的时候。

Pregnant women should minimize their exposure to waste anaesthetic gases, particularly those that are highly metabolized such as halothane and nitrous oxide. AAS advises pregnant woman to wear face masks that scavenge waste anaesthetic gas while working in anaesthesia.