Introduction

The Prone Position in Posterior Spinal Surgery The prone position is frequently utilized for posterior spinal surgeries due to its benefits in enhancing surgical access and facilitating operative maneuvers [1]. However, patients under general anesthesia are incapable of independently adjusting their position, which can precipitate severe complications, including vision loss, peripheral nerve damage, and even permanent disability, if positioning is not executed correctly [2]. Furthermore, the necessity for intraoperative decompression, implantation, and adjunctive orthopedic and radiographic assessments often necessitates position adjustments, thereby heightening the risk of nerve injury. Despite efforts to prevent compression injuries from positioning and protecting the peripheral nerves during surgery, 0.14% of peripheral nerve injuries result from improper operative placements, and brachial plexus nerve injury accounts for 36%[3,4].

The Utility of Multimodal Intraoperative Monitoring (MIOM) provides a real-time assessment of spinal cord and nerve functionality, enabling the detection of nerve damage associated with positional neglect of the upper extremities. This modality not only mitigates the risk of spinal and nerve injuries but has also become an integral component of spinal surgical procedures. Studies have shown that the MIOM technique prevents spinal cord and nerve root injuries during body position placement and cervical spine surgery [5]. However, there needs to be more literature on how nursing staff can manage the risk of position-related nerve injury with the help of MIOM. Given this, this study examines the role of MIOM in early warning of position-related nerve injury and develops nursing countermeasures to provide a reference for operating room care.

Rationale

To improve postural safety and avoid postural-related nerve injury in patients undergoing surrendering prone position surgery of the spine.

Methods

Study Design and Setting

This investigation adopted a cross-sectional and quantitative approach, aimed at enhancing postural safety and circumventing nerve injuries related to positioning in patients undergoing spinal surgery in the prone position.

Participants

Ethical Approval and Recruitment The study received approval from the Institutional Review Board. Eligible participants consisted of patients who underwent posterior spinal surgery with MIOM at the First Affiliated Hospital of Sun Yat-sen University between July 2021 and June 2022. All participants provided informed consent prior to their inclusion in the study.

Inclusion Criteria

Participants were selected based on a preoperative diagnosis encompassing spinal degenerative conditions, trauma, deformities, infections, or tumors. They were classified according to the American Society of Anesthesiologists (ASA) criteria levels I to III. Inclusion also required an intraoperative assessment of spinal cord and nerve root function through a combination of Somatosensory Evoked Potential (SSEP), Motor Evoked Potential (MEP), triggered electromyography, and free electromyography, by the established surgical protocol. Participants were required to provide voluntary consent and sign an informed consent form.

Exclusion Criteria

Patients were excluded if they required frequent intraoperative adjustments in surgical positioning. Additionally, individuals with preoperative neurological dysfunction affecting the upper extremities were not eligible. The use of inotropes and inhalation anesthetics during the monitoring period also warranted exclusion. Other contraindications to MIOM included a history of epilepsy, cranial defects or implanted metal devices, and the presence of a pacemaker[6]. Study Population The study comprised 93 patients, with 54 females and 39 males. The underlying causes for surgery were idiopathic in 46 cases, congenital in 23, tuberculosis in 5, neurofibromatosis in 10, and neuromuscular in 9. The spinal deformities included 8 cases of scoliosis, 14 of kyphosis, and 71 of kyphoscoliosis. Surgical interventions spanned from the T3 to L5 spinal segments and were conducted by a surgical team headed by the principal investigator. Detailed information is listed in Table 1.

Abbreviations: BMI: Body Mass Index; IS: Idiopathic Scoliosis; CS: Congenital Scoliosis; CSR: Congenital Scoliosis Revision; TB: Tuberculosis; NF: Neurofibromatosis; NM: Neuromuscular; NMR: Neuromuscular Revision; SSEP: Spinal Somatosensory Evoked Potential; MEP: Motor Evoked Potential; EMG: Electromyogram

Table 1: Patients’ Preoperative Demographical characteristics and clinical data.

Patient or Public Contribution

This observational study utilized data collected from patients during routine clinical care without the need for additional interventions. The study protocol was approved by the Ethics Committee, and all participants were thoroughly informed and provided consent before the collection of any data.

Description of Experiment, Treatment, or Surgery

Description of Anesthesia Protocol

Endotracheal Intubation was performed for airway management. Notably, no volatile anesthetics were administered during the induction or maintenance of anesthesia, and neuromuscular blocking agents were also excluded from the surgical procedure.

Surgical Positioning

Tailoring to the specific surgical requirements and individual patient morphology, suitable positioning aids were chosen and affixed to the transfer bed. Upon achieving effective anesthesia, the patient was meticulously transferred to the operating bed by a team of four healthcare professionals. Utilizing the axial turning technique, the patient was repositioned into the prone posture with precision and secured to preclude the risk of falls. The patient's eyes, cheekbones, mouth, and nose were checked and confirmed to be suspended; the head was placed on a headrest, and the cervical spine was kept in a neutral position; the thorax and abdomen were kept suspended to avoid pressure on the perineum and breast; the upper limbs were placed on the front and outside of the head with 90° of shoulder and elbow flexion, the legs were naturally bent and kept in a functional position to avoid pressure on both knees, and the toes were naturally lowered and suspended [7]. Intraoperatively, the patient's position was closely observed, and the patient's head and limbs were elevated every 1 to 2 hours to temporarily relieve the local pressure under the conditions permitted by surgery.

Electrophysiological Signal Monitoring Equipment and Methods

Electrophysiological Signal Monitoring Equipment

All participants were monitored using neurophysiological devices manufactured by Natus, which included the application of single-use subcutaneous needle electrodes and disc electrodes of the paste variety. Further details regarding the specific models utilized are delineated in Table 2. Operated by the same neurophysiological professional, the whole process of real-time continuous monitoring and collection of corresponding data.

Table 2: Neurophysiological monitoring equipment and software models.

Electrophysiological Monitoring Method

A 16-channel neurophysiological monitoring system was engaged to concurrently track SSEP, MEP, and EMG, thereby assessing neurophysiological alterations [8]. Post-anesthesia, baseline data were established prior to surgical positioning. Throughout the surgical procedure, real-time monitoring of SSEP, MEP, and EMG waveforms was conducted, with any anomalies meticulously documented. Intraoperative SSEP monitoring is 10 minutes/time, MEP monitoring frequency is 30 minutes/time, and the frequency of monitoring is increased when the surgery is needed or when the key steps are taken, and EMG is monitored in real-time.

MIOM Monitoring Sites

SSEP assessments focused on the functional integrity of the neural pathway extending from peripheral nerves to the cerebral cortex, with stimulation points identified at the median nerve of the upper extremity and the posterior tibial nerve of the lower extremity. MEP evaluations spanned the entire motor conduction pathway, from the motor cortex to the target muscles, encompassing a range of muscles such as the biceps, triceps, brachioradialis, deltoid, thumb adductor, piriformis, lateral femoral, anterior tibial, and muscles responsible for thumb extension and retraction. EMG served to document the electrical activity of muscles, capturing resting potentials under normal conditions.

Assessment of Abnormal Electrophysiological Signals and Nursing Interventions

Criteria for Identifying Intraoperative Neurophysiological Abnormalities: Utilizing the established 50/10 rule as a benchmark against baseline readings, three real-time monitored waveforms were evaluated: SSEP amplitudes that diminished by more than 50% or latencies that extended by more than 10% from baseline were deemed abnormal; similarly, an abrupt 80% reduction or complete loss of MEP amplitude was classified as abnormal [9]. The continuous presence of action potentials in EMG recordings was also indicative of an abnormality.

Intraoperative Care Measures Post-Detection of Abnormalities: In response to abnormal MIOM findings, nursing staff immediately liaised with the surgical team to facilitate patient repositioning and alleviate any undue tension or compression. Effectiveness in position adjustment was gauged by the restoration of SSEP and MEP waveforms to baseline levels or within the normal amplitude range, as well as the normalization of EMG readings. The disposition process for identifying abnormal neurophysiological signals is shown in Figure 1.

Figure 1: The disposition process for identifying abnormal neurophysiological signals.

Data Sources

Ethical approval for this study was granted by the Biomedical Ethics Review Committee of the First Affiliated Hospital of Sun Yat-sen University, enabling the interview of participants and the collection of relevant data.

StatisticalAnalysis

Data were organized in Excel, with mean and standard deviation utilized to delineate variable distributions, and percentages used to represent categorical and ranked variables. All statistical analyses were conducted using SPSS software (version 26, Chicago, Illinois, USA).

Results

Table 3 illustrates that 10 cases (10.75%) exhibited position-related waveform anomalies, comprising 5 instances of combined SSEP/MEP waveform irregularities, a solitary case of MEP waveform abnormality, and 4 EMG waveform anomalies. Upon identification of these anomalies, the operating room nurses swiftly addressed postural discrepancies, and subsequent fine-tuning of patient positioning returned all waveforms to baseline levels. Post-surgical assessments revealed no incidence of new neurological deficits or exacerbation of pre-existing neurological conditions. Figures 2-3 depict the SSEP monitoring variations in the bilateral upper limbs for case 6. Upon application of traction to the left upper extremity, an immediate positive SSEP response was observed, which returned to normal levels within 3 minutes following the prompt cessation of traction by the nursing staff.

DX: Diagnosis; EP: Evoked Potential; IS: Idiopathic Scoliosis; NF: Neurofibromatosis; F: Female; M: Male; BP: Blood Pressure; SSEP: Somatosensory Evoked Potential; MEP: Motor Evoked Potential; EMG: Electromyogram