Safety issues during surgical monitoring

While intra-operative neuro-physiologic assessment and monitoring improve the safety of patients, its use may also introduce new risks of injuries. This chapter looks at the electric safety of equipment and the potential hazards during the set-up of the monitoring. The physical and functional physiologic effects of electric shocks and stimulation currents, standards for safety limits, and conditions for tissue damage are described from basic physical principles. Considered are the electrode-tissue interface in relation to electrode dimensions and stimulation parameters as applied in various modalities of evoked sensory and motor potentials as to-date used in intra-operative monitoring, mapping of neuro-physiologic functions. A background is given on circumstances for electric tissue heating and heat drainage, thermal toxicity, protection against thermal injuries and side effects of unintended activation of neural and cardiac tissues, adverse effects of physiologic amplifiers from transcranial stimulation (TES) and excitotoxicity of direct cortical stimulation. Addressed are safety issues of TES and measures for prevention. Safety issues include bite and movement-induced injuries, seizures, and after discharges, interaction with implanted devices as cardiac pacemaker and deep brain stimulators. Further discussed are safety issues of equipment leakage currents, protection against electric shocks, and maintenance.