Dexmedetomidine Infusion on Intraoperative Propofol,Fentanyl Requirements in Spine Surgery for Pediatric Cancer Patients

Spinal surgery with instrumentation is associated with the risk of iatrogenic injuries to the spinal cord. The combination of somatosensory evoked potential (SSEP) and transcranial electric motor evoked potential (tcemep) monitoring has resulted in a high degree of sensitivity in predicting postoperative neurologic outcomes. Anesthetic agents have a dose-dependent adverse effect on the ability to record evoked potential responses. Many commonly used anesthetic agents produce a dose-dependent amplitude reduction and latency prolongation of evoked responses, which may impair diagnosis of intraoperative spinal cord injury. Neuroprotection is the cornerstone of anesthetic management in neurosurgery. Preserving the quality of SSEP and motor evoked potential (MEP) and minimizing the effects of anesthetic agents on neurologic monitoring are thus investigators' priorities.

Motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring are universally used during spine surgeries, which poses risks to the functional integrity of descending motor and ascending sensory pathways.

MEP baseline recording is obtained at the start of surgery determining the amplitude. The alarming criteria for MEP are attenuation of more than 50 % in motor response amplitude for segmental tcMEP, more than 80 % for long tract tcMEP and/or abolishment of tcMEP data. Any significant change is immediately reported to the surgeons.

Prior to skin incision, SSEP baseline amplitude and latency of cortical potential peaks were recorded (N20 for upper SSEP and P37 for lower SSEP). The alarming criteria of SSEP are 50% decreased amplitude and/or more than 10% increased latency compared to baseline.

The anesthetic agents have effects on the latency and amplitude of MEP and SSEP monitoring which is dose-dependent. Total intravenous anesthesia (TIVA) with propofol and opioid is commonly recommended for surgeries that require MEP and SSEP monitoring. However, propofol administered with a large dose affects MEP monitoring.

Using dexmedetomidine has the ability of sparing hypnotics usage, especially propofol, thus facilitating MEP and SSEP monitoring with providing its beneficial effects.

The addition of dexmedetomidine (0.5 μg/kg loading dose infused over 10 min followed by a constant infusion rate of 0.5 μg/kg/h) to propofol-remifentanil regimen does not exert an adverse effect on MEP and SSEP monitoring in adult patients undergoing thoracic spinal cord tumor resection and the addition of dexmedetomidine reduces the propofol requirements for a comparable BIS measurement. Another study that supports this regimen concluded that SEPs and MEPs were maintained in the patients who are administered with the dexmedetomidine etomidate fentanyl combined anesthesia during spinal surgery. Also, it was find that dexmedetomidine changes SSEP amplitude at clinically nonsignificant levels and may be safely used in intraoperative nerve monitoring at up to 1.2mg/ kg/h .

The most attractive form of display for the calculated power spectrum during anaesthesia is the compressed spectral array (CSA), where the component power is plotted as a function of frequency for each analysed epoch. Power spectrum analysis and subsequent display of data in the CSA format provide a simplified identification of small changes in a complex EEG.

Total intravenous anesthesia (TIVA) with propofol and opioid is commonly recommended for surgeries that require MEP and SSEP monitoring. However, even propofol used with a large dose can also affect MEP monitoring. Despite its efficacy, dose-related adverse effects may occur with propofol including prolonged awakening times, lipemia, and alteration of platelet function. Additionally, although more of a concern with its prolonged use in the ICU setting, recent attention has focused on the potential development of the 'propofol infusion syndrome' during intraoperative care.

Dexmedetomidine, an alpha 2-receptor agonist, is routinely used to provide analgesia and sedation without respiratory depression in critically ill patients. Its hemodynamic stability, negligible respiratory depression, and reduction of other anesthetic and analgesic requirements make it an interesting option for intraoperative use as an adjunctive agent for general anesthesia .When dexmedetomidine is added to a propofol infusion, it decreases the dose of propofol required,provides moderate hypotension, decreases blood loss, and allows monitoring of MEPs and SSEPs. The dose of dexmedetomidine often quoted in the literature is a bolus of 1 μg kg-1 hr-1 over 10 min followed by infusion of 0.2-0.7 μg kg-1 hr-1, but this dose frequently results in bradycardia and hypotension. Recently,this study is planned to evaluate the effects of intraoperative IV infusion of a low-dose (0.5 μg kg-1 hr-1) dexmedetomidine in patients undergoing spine surgery.

Researchers have administered an intraoperative continuous infusion of lower doses of dexmedetomidine without a prior bolus.