Optical Detection of Vascular Penetration During Nerve Blocks: An In Vivo Human Study Andrea Balthasar, MD,* Adrien E. Desjardins, PhD,Þ Marjolein van der Voort, PhD,Þ Gerald W. Lucassen, PhD,Þ Stefan Roggeveen, MSc,þ Ke Wang, PhD,Þ Walter Bierhoff,Þ Alfons G.H. Kessels, MD, MSc,§ Micha Sommer, MD, PhD,* and Maartenvan Kleef, MD, PhD* Background and Objectives: Complications resulting from vas- cular penetration during nerve blocks are rare but potentially devastating events that can occur despite meticulous technique. In this in vivo human pilot study, we investigated the potential for detecting vascular penetra- tion with optical reflectance spectroscopy during blocks of the sympa- thetic chain and the communicating ramus at lumbar levels. Methods: A custom-designed needle stylet with integrated optical fibers was used in combination with a commercial needle shaft. The needle stylet was connected to a console that delivered broadband light to tissue and spectrally resolved light that was scattered near the stylet tip. A total of 18 insertions were performed on 10 patients; testing for vas- cular penetration at the nerve target region was performed with aspiration and with radio-opaque contrast injections, visualized fluoroscopically. Optical absorption by hemoglobin was quantified with a blood parameter that was calculated from each spectrum. The blood parameter provided a measure of the difference between spectra acquired from the nerve target region and reference spectra acquired from blood extracted from a volunteer. Results: In 2 insertions, vascular penetration was detected. Pronounced optical absorption by hemoglobin was observed to be associated with both of these events and absent in all other cases. The difference between the blood parameters obtained when vascular penetration was detected, and all other blood parameters were statistically significant (P = 0.006), with a diagnostic odds ratio of 35.4 (confidence interval, 2.21 to V). Conclusions: The results from this study suggest that optical spec- troscopy has the potential to detect intravascular needle placement, which may in turn increase the safety of nerve blocks. (Reg Anesth Pain Med 2012;37: 3Y7) M inimizing the risk of vascular complications is of critical importance during percutaneous injections for interven- tional pain management. Unintentional intravascular injections of local anesthetics and corticosteroids can contribute to poor procedure outcomes and can lead to neurologic and cardiovas- cular complications including quadriplegia, cortical blindness, stroke, and death. 1 One mechanism of injury is ischemia caused by end-arteriolar occlusion by injection of particulate steroids. 2 Intravascular injections of anesthetics can also result in cardio- toxicity. 3 Kim et al 4 found that intravascular injections, including purely vascular and simultaneous perineural and vascular up- take, occurred at rates of 9.9% and 63.4% for lumbar and cer- vical transforaminal epidural injections, respectively. Current methods for avoiding intravascular penetration are not always effective. Aspiration provides false negatives 3,5 ; suction performed during this test can collapse a vessel and prevent backflow of blood. 6 In a prospective study of transfor- aminal cervical epidural steroid injections, aspiration of blood into the hub of the needle was found to be 97% specific but only 45.9% sensitive for intravascular injection. 7 The use of radio- graphic contrast injected under continuous fluoroscopy with or without digital subtraction is recommended to detect intravas- cular needle placement. 2,8 A radio-opaque contrast injection may not always be effective, however; the spreading pattern can be fleeting and its interpretation is not always straightforward because an injection can be simultaneously intravascular and epidural. 9 Furthermore, slight movements of the needle after the injection could result in a transition from an extravascular to an intravascular position. Optical reflectance spectroscopy could potentially allow for a reliable detection of intravascular needle tip placement. With this technique, broadband light is delivered to the tissue, and it is subsequently scattered and absorbed. By spectrally resolving scattered light, the presence of specific absorbing molecules can be inferred. Optical absorption from oxyhemoglobin and deox- yhemoglobin is particularly prominent in the wavelength range of 500 to 600 nm. 10 Benaron et al 11,12 demonstrated that tissue oximetry can be performed with needle probes. Recently, our research team introduced needles with optical fibers integrated into the cannula 13 and into the stylet 14 and an associated optical console 15 to perform spectroscopic measurements during inser- tions to the epidural space and peripheral nerves. Pilot studies performed in swine, which involved insertions to the epidural space and the brachial plexus, provided initial indications that vascular penetration events can be detected with optical reflec- tance spectroscopy. 16,17 The purpose of this study was to investigate whether optical reflectance spectroscopy has the potential to detect vascular penetration in humans. During blocks of the sympathetic chain and the communicating ramus in humans, a custom-designed needle stylet with integrated optical fibers was used to acquire reflectance spectra from tissues at the needle tip. The reflectance spectra were compared with the results of 2 current methods for ORIGINAL ARTICLE Regional Anesthesia and Pain Medicine & Volume 37, Number 1, January-February 2012 3 From the *Department of Anesthesiology and Pain Medicine, Maastricht University Medical Center, Maastricht; †Philips Research, Eindhoven; ‡Philips Healthcare, Best; and §Department of Clinical Epidemiology & Medical Technology Assessment, Academic Hospital of Maastricht, Maas- tricht, the Netherlands. Accepted for publication September 12, 2011. Address correspondence to: Andrea Balthasar, MD, Department of Anesthesiology and Pain Medicine, Maastricht University Medical Center, P. Debyelaan 25, NL-6229 HX Maastricht, the Netherlands (e-mail: a.balthasar@gmx.de). This study was financially supported by Philips Research, Eindhoven, the Netherlands. None of the authors who are affiliated with clinical institutions (A.B., A.K., M.S., and M.v.K.) have financial interests in the subject matter, materials, or equipment or with any competing materials. These authors received no payment of any kind for their participation in this research project, nor did their institutions receive payment for anything beyond the direct costs of performing this research project at University Hospital Maastricht. Their interests are purely at a scientific level. All of the authors who are affiliated with Philips Research have financial interests in the subject matter, materials, and equipment, in the sense that they are employees of Philips. The prototype system described in this article is currently only a research prototype and is not for commercial use. Copyright * 2012 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0b013e3182377ff1 Copyright © 2011 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.