Kumar Ajay, Bithal Parmod, Chouhan Rajender Singh, Sinha Prabhat Kumar
Department of Neuroanesthesiology and Intensive Care, New Delhi, India.
J Neurosurg Anesthesiol. 2002 Apr;14(2):153-6. doi: 10.1097/00008506-200204000-00012.
Capnography is one of the basic monitoring techniques in day-to-day anesthesia practice that provides information not only regarding the patient's ventilation, circulation, and metabolism, but also regarding proper functioning of a closed-circle system. The authors report a case in which after endotracheal intubation the end-tidal capnometric reading rose very high, but the capnogram was not seen on the monitor. The unexpectedly high capnometric reading with absent waveform during intermittent positive pressure ventilation without any apparent cause and consequent delayed institution of corrective measures resulted in severe brain bulge. There was severe hypercarbia as a result of a malfunctioning expiratory unidirectional valve that allowed rebreathing. Retrospective retrieval of data showed that a fraction of inspired carbon dioxide was also high and the baseline was raised beyond the usual range of 0 to 40 mm Hg, giving the impression of an absent waveform on the existing scale. In conclusion, one should keep in mind the possibility of expiratory valve malfunction resulting from dislodgment while wheeling the anesthesia machine, the view becoming obscured as a result of condensation of water vapor on the under surface of the plastic case, and one should rely on the capnometric reading unless proved otherwise. Thus, one can prevent potential hazards of rebreathing.
二氧化碳监测是日常麻醉实践中的基本监测技术之一，它不仅能提供有关患者通气、循环和代谢的信息，还能反映闭环系统的正常功能。作者报告了一例病例，气管插管后呼气末二氧化碳监测读数升得非常高，但监护仪上却没有看到二氧化碳波形图。在间歇性正压通气期间，呼气末二氧化碳监测读数意外升高且无波形，又没有明显原因，随后纠正措施实施延迟，导致严重脑膨出。呼气单向阀故障导致重复呼吸，进而出现严重高碳酸血症。回顾性数据检索显示，吸入二氧化碳分数也很高，基线升高超过了通常的0至40毫米汞柱范围，使得在现有刻度上显示出无波形的假象。总之，在搬运麻醉机时应牢记呼气阀因移位而出现故障的可能性，塑料外壳下表面的水蒸气凝结会导致视野受阻，除非另有证明，否则应依赖二氧化碳监测读数。因此，可以预防重复呼吸的潜在危害。
