Nyman G, Hedenstierna G
Department of Medicine and Surgery, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala.
Equine Vet J. 1989 Jul;21(4):274-81. doi: 10.1111/j.2042-3306.1989.tb02167.x.
Ventilation-perfusion relationships were studied by the multiple inert gas elimination technique in seven horses while they were conscious and during inhalation anaesthesia with halothane. A generally good match between ventilation and perfusion was found in the conscious, standing horse. During anaesthesia a huge shunt developed, ie perfusion of completely unventilated lung regions, both in dorsal and left lateral recumbency and whether the horse was breathing spontaneously or mechanically ventilated. The shunt was significantly greater and the arterial oxygen tension (PaO2) significantly lower in dorsal than in left lateral recumbency. Little or no perfusion of low VA/Q regions was observed during anaesthesia, whether ventilation was spontaneous or mechanical. Positive end-expiratory pressure (PEEP) did not significantly improve PaO2 or reduce the shunt. Selective mechanical ventilation of dependent lung regions with PEEP reduced the shunt markedly, an effect that was not achieved by conventional mechanical ventilation with general PEEP. The findings seem compatible with alveolar collapse during anaesthesia, causing shunt, whereas the absence of clearly low VA/Q regions questions the role of airway closure as the major disturbance of gas exchange.
采用多惰性气体消除技术，在7匹马清醒状态及氟烷吸入麻醉期间对通气-灌注关系进行了研究。在清醒站立的马匹中，通气与灌注总体匹配良好。麻醉期间，无论马匹处于背卧位还是左侧卧位，无论自主呼吸还是机械通气，均出现了巨大分流，即完全无通气肺区的灌注。背卧位时的分流明显大于左侧卧位，动脉血氧分压（PaO2）明显低于左侧卧位。麻醉期间，无论自主呼吸还是机械通气，低通气/血流比值（VA/Q）区域的灌注很少或未观察到。呼气末正压（PEEP）并未显著改善PaO2或减少分流。对依赖肺区进行选择性机械通气并加用PEEP可显著减少分流，这一效果是常规机械通气加用一般PEEP所无法实现的。这些发现似乎与麻醉期间肺泡萎陷导致分流相符，而明显低VA/Q区域的缺失对气道闭合作为气体交换主要干扰因素的作用提出了质疑。
