An add-on advantage of isoflurane graphical monitoring: Detection of intraoperative bronchospasm.

Abstract

Sir, Post-intubation bronchospasm is one of the life-threatening complications of endotracheal intubation. Intraoperative bronchospasm is detected with the help of chest auscultation, increased peak airway pressure, hypoventilation, and upslope on capnograph (end-tidal CO2 [ETCO2]) along with downslope on sevoflurane graph during expiratory phase of respiratory cycle.[1] Advancement in bronchospasm detection methods, perioperative bronchodilator treatment and preventive measures have played a valuable role in reducing the incidence of perioperative bronchospasm and subsequently hypoxia along with hypercarbia leading to morbidity and mortality. We are reporting an interesting observation seen in newer machines that display isoflurane concentration as a volume time graph. An asthmatic patient with breast cancer was posted for modified radical mastectomy. Standard anaesthesia monitoring was initiated on Datex ohmeda Aestiva 5® (Datex-Ohmeda, Ohmeda Drive, PO Box 7550, Madison, Wisconsin 53707). General anaesthesia was induced with fentanyl 2 μg/kg and propofol 2 mg/kg; orotracheal intubation was facilitated by vecuronium 0.08 mg/kg. Patient was kept on mechanical ventilation. Anaesthesia was maintained with 100-200 μg/kg/min propofol infusion and 50% air-oxygen mixture. After 10 min patient developed an episode of bronchospasm as evidenced by increased airway pressure, rhonchi on auscultation and upsloping ETCO2. We increased oxygen to 100%, started isoflurane at concentration of 3% and added two puff of salbutamol metered dose inhaler in endotracheal tube; we observed downslope in isoflurane graph (end-tidal level of isoflurane [ETIso]) during expiratory phase of respiratory cycle corresponding to upsloping in ETCO2 graph [Figure 1A] (explained by slow and fast alveoli)during bronchospasm. Gradually as the airway pressure decreased along with disappearance of rhonchi, the ETIso graph also became normal (horizontal) along with ETCO2 graph [Figure 1B] within 20 ± 5 min. This left a smaller difference between the inspiratory fraction level of isoflurane (FiIso) and the ETIso. The difference in ETIso and FiIso is due to decrease in the number of slow alveoli on relief of bronchospasm. CO2 concentration being greater in expiration and isoflurane concentration being greater during inspiration results in mirror-image of the two waveforms. Figure 1 Figure ‘1A’ Upslope in capnograph during expiratory phase with corresponding downslope in isoflurane graph just below (isoflurane graph as the mirror image of capnograph) during bronchospasm. Figure ‘1B’ After reversal ... Like sevoflurane graph, isoflurane graph is also the mirror image of capnograph in both normal and bronchospasm conditions. We encountered similar graphical changes in 15 more cases till date in modern anaesthesia work stations with multichannel monitor like Datex ohmeda S/5 Avance®, Drager Pedius® (Drδger Medical GmbH 23542 Lόbeck Germany), Drager Fabius GS premium® and Datex ohmeda Aestiva 5®. Upward phase of isoflurane wave shows level of isoflurane in the breathing circuit at the starting of inspiration. Highest FiIso in the breathing circuit shows maximal mixing of isoflurane vapours coming from the vapouriser with the fresh gas. Intermediate downward phase of isoflurane wave shows the dilution of isoflurane in the circuit by the dead space at the starting of expiration isoflurane graph. Lowest ETIso shows maximum dilution of isoflurane by the exhaled alveolar gases at the end of expiration. Hence, isoflurane graphical monitoring is as useful as sevoflurane graphical monitoring along with capnograph in both detection and timely management of intraoperative bronchospasm to reduce the morbidity and mortality. We suggest the use of isoflurane graphical monitoring routinely in cases undergoing general anaesthesia with modern multi-parameter anaesthesia workstation in order to improve the sensitivity of monitoring thereby reducing the incidence of adverse respiratory events in operation room.