Proper body positioning during surgery is crucial for effective neuromonitoring, as improper positioning can lead to compromised blood flow and nerve compression, significantly impacting neuromonitoring signals. Mechanisms of impairment include restricted blood flow, which can cause hypoxia and ischemia, and nerve compression, leading to ischemia and dysfunction. These issues can reduce the amplitude and increase the latency of somatosensory evoked potentials (SSEPs), making it difficult to detect changes in sensory pathways. Motor evoked potentials (MEPs) are similarly affected, with decreased amplitude and prolonged latency, complicating motor function assessment. Improper positioning can also cause venous congestion, affecting cerebral perfusion and altering electroencephalogram (EEG) patterns, resulting in diffuse slowing or changes in amplitude and frequency. Anesthesia providers must ensure proper positioning through preoperative planning, use of positioning aids, regular repositioning, and continuous monitoring to maintain accurate neuromonitoring signals and prevent adverse outcomes during surgery.
| Derangement | SSEPs and MEPs | EEG |
|---|---|---|
| Hypotension | Decreased amplitude, increased latency from reduced cerebral and spinal cord perfusion | Diffuse slowing |
| Hypothermia (core < 36°C) | Increased latency, decreased amplitude; reduced nerve conduction velocity | Generalized slowing that can mimic or mask other pathology |
| Hypoxia | Decreased amplitude, increased latency; impaired synaptic transmission and excitability | Diffuse slowing |
| Hypercapnia | Decreased amplitude, increased latency; cerebral vasodilation and increased intracranial pressure | Diffuse slowing |
| Acidosis | Decreased amplitude, increased latency from effects on ion channels and neurotransmitter function | — |
| Alkalosis | — | Hyperexcitability and potentially seizures |
| Hypoglycemia | Decreased amplitude, increased latency from neuronal energy deficits | — |
| Improper positioning | Decreased amplitude, prolonged latency from restricted blood flow and nerve compression | Diffuse slowing or changes in amplitude and frequency from venous congestion |
