The development and safety of clinical physiologist-led intraoperative neurophysiological monitoring (IONM) services


Intraoperative neurophysiological monitoring (IONM) provides the surgeon operating on the spine with a highly sensitive and specific early warning of potentially reversible neurological change1. It has become a standard of care during spinal deformity surgery in the US and demand is growing exponentially in Europe. The traditional “wake-up test” has a number of well-documented limitations2,3. that make it inadequate for monitoring during spinal deformity surgery and it has become obsolete in many centres4. Multimodal IONM techniques enable safe and continuous assessment of motor and sensory pathways, as well as individual nerve roots, where necessary. Neurophysiological monitoring technology is evolving at a startling rate and it is increasingly important that the IONM provider is well trained, qualified and highly experienced. Their role is to work alongside surgical and anaesthetic staff to accurately identify true positive neurological changes in spinal cord function and avoid common pitfalls that can lead to false positive and false negative errors.

In the last few years, the Clinical Society of Neurophysiology has acknowledged a UK-wide shortage of Consultant Clinical Neurophysiologists (CCNs). This, combined with shortening Department of Health waiting time targets and increasing numbers of patients requiring neurophysiological monitoring, has led to an unworkable situation which could lead to greater morbidity in terms of irreversible pathophysiology and patient outcomes5. In an effort to improve the quality and throughput of neurophysiological investigations, there has been a marked extension in the working practice of Clinical Physiologists (CPs), formerly known as Medical Technical Officers or Neurophysiology Technicians. Senior, “Highly Specialised” Clinical Physiologists (HSCPs) are now found working in theatres autonomously without any attendance by a CCN or with remote supervision by a CCN.

Suitably qualified and experienced HSCPs must aim to provide comprehensive IONM services that are robust, reliable and readily adaptable to the needs of the individual patient and particular surgical conditions.

Figure 1: IONM monitoring equipment set up in corner of theatre.

High quality IONM not only offers the surgeon protection medically but also medico-legally. If a patient were to sustain a severe iatrogenic neurological complication during spinal surgery, it is possible that damages awarded may run into the millions. The IONM provider may be asked to be a witness in court or produce a statement. For this reason, it is essential that the IONM event log, compiled throughout the surgery by the HSCP and time-locked to the recorded waveforms, is of impeccable quality: continuous, complete and tamperproof.

It is likely that the emergence of HSCP-led services will continue throughout Europe over the next decade and so associated systems must be implemented to monitor quality of practice and ensure that high standards are maintained.

Safety audit

The Scottish National Spine Deformity Service is a well-established centre, based at the Royal Hospital for Sick Children and the Royal Infirmary in Edinburgh, providing care for children and young adults with a range of spinal deformities. Patient conditions may include: idiopathic scoliosis, congenital spine deformities, Scheuermann’s kyphosis, severe spondylolisthesis and neurological conditions such as cerebral palsy and Duchenne muscular dystrophy. The service depends largely upon a highly skilled, experienced and dedicated team of surgeons, clinical physiologists, nurses, anaesthetists, operating department practitioners and many other contributing health professionals.

In 2000, Dr Michael Glasby, a Consultant Clinical Neurophysiologist (CCN), designed and set-up a service with the aim of providing routine intraoperative neurophysiological monitoring of spinal cord function during surgery for treatment of scoliosis or other spinal pathology. Dr Glasby routinely provided this successful service, until his retirement in 2009.

In 2007, prior to his retirement, and in the absence of a CCN successor, the decision was made to “hand-over” the service to a small team of Highly Specialised Clinical Physiologists (HSCPs) working within the Department of Clinical Neurophysiology. Over a period of two years, the HSCPs were intensively trained and in 2009, they began performing IONM in pairs, with no attendance by a CCN.

The HSCP team were mindful of the significant transition from a CCN to a clinical physiologist-led neurophysiology service and the crucial need for quality control. Therefore in 2010, with the full involvement of Mr Christopher Adams (Consultant Spinal Surgeon) and Dr Glasby, the HSCP team embarked on an audit entitled “Can clinical physiologists provide a safe, independent intra-operative monitoring (IOM) service in paediatric spine deformity surgery?”, the full results of which are soon to be published6. This audit was performed in accordance with the current National Institute for Clinical Excellence guidelines (2002) -“Principles of Best Practice in Clinical Audit”7.

Figure 2. Example of loss of left lower limb MEP responses (tibialis anterior and abductor hallucis). Note, left upper limb responses from the abductor minimi digiti remain present.

The audit involved the analysis and comparison of IONM records over two time periods, each lasting two months: April – June 2009 (Group 1) and April – June 2010 (Group 2). All HSCPs were blinded to the study.

The incidence and nature of neurophysiological “events” during these two periods were reviewed retrospectively by the CCN and the data compared with those identified intra-operatively by the HSCP team.

Group 1 (pre-intervention)

The first time period was shortly after the “hand-over” of the IONM service from the experienced CCN to the HSCP team. The waveforms, event logs and reports from

2 spine deformity cases were analysed.

In this period, the HSCPs notified surgeons of an intraoperative “event” in 31% (10 of 32 cases) of cases. The CCN retrospectively agreed with only 20% (2 cases) of these alerts.

In the rest of the cases, where the HSCPs called no IONM event, there were no false negatives with the correct interpretation of IONM.


A multi-disciplinary meeting was held to discuss the issues. It was acknowledged that there had been a significant increase in clinical responsibility for decision-making by the Clinical Physiologists over a relatively short period of time. The HSCPs were now the arbiters as to whether there was or was not an IONM event and this may have led to slightly overzealous alarming. In a bid to improve matters, three areas were targeted for intervention:

  1. Redesign of IONM report – The report created for each case was altered to include drop down summary menus. There was also the introduction of a “bottom line” decision about the presence or absence of an IONM event.
  2. An IONM teaching programme was discussed and implemented. A monthly session with the CCN was organised to discuss topics such as: Methods of Monitoring, Contraindications, Anatomy of the Spine, Report writing and others.
  3. Case review sessions were also implemented. These enabled analysis of how signal changes were interpreted and acted upon. The documented events and communications between the HSCPs and surgical teams were also scrutinised.

Group 2 (post-intervention)

The second time period was a year or so after the “hand-over” of the IONM service from the experienced CCN to the CP team. In this period, the waveforms, event logs and reports from 34 spine deformity cases were analysed.

Again, the incidence and nature of neurophysiological “events” during this period were reviewed retrospectively by the CCN and the data compared with those identified intra-operatively by the HSCP team.

In this period, the HSCPs notified surgeons of an intraoperative “event” in 12% (4 of 34 cases). The CCN retrospectively agreed with 100% of these alerts.

In the rest of the cases, where the HSCPs called no IONM event, there were no false negatives with the correct interpretation of IONM.

Audit Conclusions

  • The role of the HSCP was developed and extended in the absence of a CCN and this placed additional clinical responsibility onto the team.
  • Support was required to facilitate this transition and a number of interventions were put into place. These interventions lead to an improvement in physiologist performance, reducing the rate of false positive alarms.
  • No false negative events occurred in either audited period.
  • No true neurological events transpired.
  • Highly Specialised Clinical physiologists were as safe as a Consultant Clinical Neurophysiologist in the post-intervention series. However, safety in routine practice can only be proven statistically with a larger series. Data collection and analysis is ongoing.

Summary result table


The effectiveness of multimodal intraoperative neurophysiolgical monitoring in improving surgical outcome in spinal deformity surgery is well documented and, as a result, its use has shown a steady increase worldwide. Well-trained and experienced IONM personnel can provide reliable spinal cord monitoring, lowering the risk of devastating post-operative neurological deficits. The high sensitivity and specificity of multimodal techniques8 may encourage surgeons to carry out more challenging and expansive surgical approaches than they would have otherwise, in the hope of improving the quality of life of their patients9.

As intraoperative neurophysiological monitoring becomes the standard of care for spinal deformity surgery across Europe, and this legacy is partly or wholly transferred to Clinical Physiologists, it is vital to ensure that those performing the monitoring and interpreting the data are sufficiently qualified and experienced. Quality of practice must be adequately vetted during this transition, in order to maintain high standards of patient care.


  1. Fehlings, M.G., Brodke, D.S., Norvell, D.C., Dettori, J.R. (2010).The evidence for intra-operative neurophysiological monitoring in spine surgery: does it make a difference? Spine, (35)(9 Suppl), 37-46.
  2. Grottke, O., Dietrich, P.J., Wiegels, S., Wappler, F. (2004) Intraoperative Wake-Up Test and Postoperative Emergence in Patients Undergoing Spinal Surgery: A Comparison of Intravenous and Inhaled Anesthetic Techniques Using Short-Acting Anesthetics. Anesthesia & Analgesia, 99(5), 1521-1527.
  3. Schwartz, D.M., Auerbach, J.D., Dormans, J.P. (2007). Neurophysiological detection of impending spinal cord injury. The Journal of Bone and Joint Surgery AM, (89), 2440-9.
  4. Eggspuehler, A., Sutter, M.A., Grob, D., Jeszenszky, D., Dvorak, J. (2007). Multimodal intraoperative monitoring during surgery of spinal deformities in 217 patients. European Spine Journal ,(16), Supplement 2, 188-196.
  6. Michaelson, C., Adams, C.I., Henderson, L., Glasby, M., Horsburgh, G., Thinn, S. Can clinical physiologists provide a safe, independent intra-operative monitoring (IOM) service in paediatric spine deformity surgery? A completed audit. The Scottish National Paediatric Spine Deformity Service, The Royal Hospital for Sick Children, Edinburgh
  8. Kundnani, V.K., Zhu, L., Tak, H.H., Wong, H.K. (2010). Multimodal intraoperative neuromonitoring in corrective surgery for adolescent idiopathic scoliosis: Evaluation of 354 consecutive cases. Indian Journal of Orthopaedics, (44), 64-72.
  9. Tamaki, T., Kubota, S. (2007). History of the development of intraoperative spinal cord monitoring. European Spine Journal, (16), S140-S146.


The author would like to acknowledge the work and contribution to this audit of the wider spinal team at the Royal Hospital for Sick Children in Edinburgh, particularly: Mr Christopher Adams, Mr Enrique Garrido, Mr Thanos Tsirikos, Dr Michael Glasby, Mrs Ciara Michaelson, Mrs Gillian Horsburgh, Mrs Sharon Thinn, Mr Brian Jordan and Ms Michele Thorpe.


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