We studied the hemodynamic and bispectral index (BIS) changes in 44 patients undergoing cervical diskectomy with attachment of a Gardner-Wells tong (with two sharp conical pins) to the skull to facilitate intraoperative bone graft insertion. Patients were induced with fentanyl, thiopentone, and rocuronium and maintained with 66% nitrous oxide and 0.5% isoflurane, Before insertion of the pins, patients were randomly allocated to have either saline or lidocaine infiltration of the scalp at the proposed pin sites. Two minutes later, the pins were driven into the scalp. The BIS, mean arterial pressure (MAP), and heart rate (HR) were recorded before (baseline) and at 30, 60, 90, and 120 s after pin insertion. Data were compared with the baseline values and between the groups. A significant increase in MAP and HR occurred throughout the study period in the saline group. Skull pinning increased BIS throughout the study period in the saline group only, with maximal increases observed at 90 and 120 s (66.1 +/- 6.3 at 90 s and 65.7 +/- 6.4 at 120 s versus a baseline value of 62 +/- 8, P < 0.001). The increase in BIS was significant in the saline group compared with the lidocaine group at each time point. In conclusion, increases in MAP, HR, and BIS produced by skull pinning were prevented by prior local anesthetic infiltration.

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.

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