title: Intraoperative assessment of human spinal cord perfusion using near infrared spectroscopy with indocyanine green tracer technique.
abstract: BACKGROUND
  Despite the significant interest in the assessment of human cerebral perfusion, investigations into human spinal cord perfusion (SCP) are scarce. Current intraoperative monitoring of spinal cord relies on the assessment of neural conduction as a surrogate for SCP. However, there are various inherent limitations associated with the use of these techniques. Near infrared spectroscopy (NIRS) has been successfully used for monitoring and assessment of human cerebral perfusion and has shown promising results in intraoperative assessment of SCP in animal models.
  
  
  OBJECTIVE
  The aim of this study was to investigate whether it is possible to monitor physiological changes in human SCP intraoperatively using NIRS with indocyanine green (ICG) tracer technique. We used this technique to calculate the human spinal cord carbon dioxide (CO₂) reactivity index. In addition, we investigated whether the lamina causes significant attenuation of NIRS signals.
  
  
  METHODS
  Intraoperative human experimental study.
  
  
  METHODS
  Eighteen patients undergoing elective posterior cervical spine surgery.
  
  
  METHODS
  Carbon dioxide reactivity of human SCP.
  
  
  METHODS
  Nine patients underwent transdural assessment of SCP, with an additional nine patients undergoing translaminar measurements. Patients' SCP was continuously monitored using an NIRO-500 NIRS monitor via a set of purpose built optodes. Their arterial ICG concentration was simultaneously assessed using a pulse dye densitometer. Patients' end-tidal CO₂ was gradually increased by 7.5 mm Hg and then returned back to baseline. Three sets of measurements were taken: baseline, hypercapnic, and return to baseline.
  
  
  RESULTS
  After hypercapnia, SCP increased by a mean of 57.2 ± 23.3% in the transdural group and 46.6 ± 36.3% in the translaminar group. Carbon dioxide reactivity index was 7.6 ± 3.2%ΔSCP/mm Hg in the transdural group and 6.4 ± 5.3 %ΔSCP/mm Hg in the translaminar group. There was no significant difference in the increase in SCP (p=.475) or the CO₂ reactivity index (p=.581) observed between the transdural and the translaminar groups.
  
  
  CONCLUSIONS
  Intraoperative NIRS with ICG tracer technique can identify an increase in the SCP in response to hypercapnia. It is possible to use this technique for monitoring SCP over the dura and the lamina. This technique could potentially be used to provide insight in to the pathophysiology and autoregulation of commonly acquired spinal cord conditions. Further research assessing the use of NIRS for monitoring of SCP is required.
authors: Spinal Injury Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, United Kingdom. Electronic address: amir.r.amiri@googlemail.com.
authors: Amir Reza
authors: AR
authors: Amiri
authors: Cheong Hung
authors: CH
authors: Lee
authors: Terence S
authors: TS
authors: Leung
authors: Michael
authors: M
authors: Hetreed
authors: Michael D
authors: MD
authors: Craggs
authors: Adrian T H
authors: AT
authors: Casey
mesh_terms: D000368:Aged; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism; D005260:Female; D006801:Humans; D007208:Indocyanine Green; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013116:Spinal Cord / Q000098:blood supply*
chemical_list: D002245:Carbon Dioxide; D007208:Indocyanine Green
keywords: Carbon dioxide reactivity; Human; Intraoperative spinal cord monitoring; Near infrared spectroscopy; Spinal cord perfusion