Published in:
01-12-2015 | Technical Note - Neurosurgical Techniques
Ventilator waveforms on anesthesia machine: A simple tool for intraoperative mapping of phrenic nerve and mid-cervical roots
Published in: Acta Neurochirurgica | Issue 12/2015
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Background
A crucial aspect of surgery on the supraclavicular region, lateral neck, and mid-cervical vertebral region is the identification and sparing of the phrenic nerve and cervical (C4) root that are responsible for diaphragmatic innervation. Therefore intraoperative mapping of these nerve structures can be useful for difficult cases. Electrical stimulation with simultaneous observation of the ventilator waveforms of the anesthesia machine provides an effective method for the precise intraoperative mapping of these structures. In the literature, there is only one publication reporting the use of one of the waveforms (capnography) for this purpose.
Methods
Capnography and pressure–time waveforms, two mandatory curves in anesthesiological monitoring, were studied under electrical stimulation of the phrenic nerve (one patient) and the C4 root (eight patients). The aim was to detect changes that would verify diaphragmatic contraction. No modifications in anesthesia or surgery and no additional maneuvers were required.
Results
In all patients, stimulation was followed by identifiable changes in the two waveforms, compatible with diaphragmatic contraction: acute reduction in amplitude on capnography and repetitive saw-like elevations on pressure–time curve. Frequency of patterns on pressure–time curve coincided with the frequency of stimulation; therefore the two recordings were complementary.
Conclusions
This simple method proved effective in identifying the neural structures responsible for diaphragmatic function. We therefore suggest that it should be employed in the various types of surgery where these structures are at risk.