Percutaneous single-fiber reflectance spectroscopy of canine intervertebral disc: is there a potential for in situ probing of mineral degeneration?

BACKGROUND AND OBJECTIVES: Intervertebral disc herniation is a common disease in chondrodystrophic dogs, and a similar neurologic condition also occurs in humans. Percutaneous laser disc ablation (PLDA) is a minimally invasive procedure used increasingly for prevention of disc herniation. Currently, PLDA is performed on thoracolumbar discs with the same laser energy applied regardless of the differing extent of degeneration among mineralized discs. In a previous study performed on 15 normal and 6 degenerated intervertebral discs in chondrodystrophoid canine species, it was demonstrated that percutaneous single-fiber reflectance spectroscopy (SfRS) detected increased light scattering from mineralized intervertebral discs when comparing to normal discs. The objective of this study is to evaluate how SfRS evaluation of mineralized discs in situ fairs with X-ray radiography and computed tomography (CT) diagnoses and if SfRS sensing of the scattering changes correlates with the level of mineral degeneration in nucleus pulposus. MATERIALS AND METHODS: Percutaneous SfRS was performed on a total of 28 intervertebral discs of three dogs post-mortem, through a 20 gauge spinal needle standard to PLDA. The raw SfRS measurement was normalized to extract a dimension-less spectral intensity profile, from which the average over 600-900 nm was used as the SfRS intensity index to compare among the measured discs. The discs were imaged prior to percutaneous SfRS by radiography and CT, and harvested after percutaneous SfRS for histopathologic examinations. RESULTS: Five among 10 discs of dog #1, six among 9 discs of dog #2, and nine out of 9 discs of dog #3 were determined by histopathology to have central focal or multi-focal areas of mineralization occupying 5-75% of the examined area of nucleus pulposus. The overall numbers of discs with detectable and undetectable central mineralization were 20 and 8, respectively. CT resulted in one false positive (FP) and four false negative (FN) diagnoses for dog #1, three FP and zero FN diagnoses for dog #2, and zero FP and one FN diagnosis for dog #3. Of the total 28 discs the CT had an overall positive predictive value (PPV) of 78.8% and an overall negative predictive value (NPV) of 44.4%. X-ray radiography gave five FN diagnoses for dog #1, two FN diagnoses for dog #2, and eight FN diagnoses for dog #3. Of the total 28 discs the radiography had an overall PPV of 100% and an overall NPV of 30.4%. The receiver-operating-characteristic analysis of the SfRS measurement was performed on 24 discs that had a central mineralization not greater than 50%. An area-under-curve of 0.6758 infers that the SfRS intensity weakly indicates the level of mineralization. CONCLUSIONS: Percutaneous SfRS may be useful as an in situ sensing tool for assessing the level of mineral degeneration in intervertebral discs for the prospect of disc-specific dosage adjustment in PLDA.

Comparison of propofol and propofol/ketamine anesthesia for evaluation of laryngeal function in healthy dogs.

Thiopental is an excellent choice for evaluation of laryngeal function. Unfortunately, thiopental is no longer manufactured. In its absence, the ideal anesthetic protocol for laryngoscopy has not been determined. Propofol and propofol/ketamine were compared for the evaluation of laryngeal function in 48 healthy dogs. Laryngeal exposure was moderate to excellent in all dogs and not significantly different between protocols. Saturation of peripheral O2 (SPO2) readings were decreased in the propofol/ketamine group, and deeper respirations were more likely to correlate with normal laryngeal function regardless of treatment group. Doxapram was administered to apneic patients to stimulate respiration and allow for evaluation of laryngeal function. No significant difference in frequency of doxapram administration between groups was noted. Doxapram resulted in higher respiratory scores and significantly increased the ability to determine normal laryngeal function. Ketamine did not allow for a reduction in propofol dose and caused increased respiratory depression, making ketamine a poor addition to propofol for laryngeal function examination. Regardless of the protocol used, laryngeal function should be determined in conjunction with the respiratory phase and depth of respirations. Patients with either absent or shallow respirations should receive doxapram for accurate evaluation of laryngeal function.