Combined microlightguide spectrophotometry and microendoscopy for measurement of oxygen saturation in peripheral nerves

Abstract

Microlightguide measurements of the spectral composition of backscattered light may be used to determine local tissue oxygen saturation and monitor tissue perfusion using intravenous injection of fluorescein dye as a contrast agent. We have used a combination of microlightguide spectrophotometry and microendoscopy to measure intravascular oxygen saturation (HbSaO2%) and monitor blood flow in the sciatic nerve of 12 healthy male Sprague-Dawley rats. The microlightguide and endoscope combination is a relatively new measurement technique. The aims of this study were to determine whether microlightguide spectrophotometry and microendoscopy could be used to measure HbO2 and blood flow in peripheral nerves and to compare the measurements made using the flexible lightguide with the endoscope-lightguide combination. We found no significant difference between the two types of measurement over similar regions of the nerve. mean SaO2% values 77.1% (95% CI = 75.4-78.8) and 78.8% (95% CI = 77.5-80.1) respectively. During a period of hypoxia there was a similar fall in both arterial and nerve oxygen saturation. Following injection of fluorescein, the rate of increase in nerve fluorescence was used as a measure of perfusion. The combination of microlightguide spectrophotometry and microendoscopy allows the exact site of measurement to be directly visualized. The minimally invasive nature of this technique may allow its application to the study of peripheral nerves in human subjects in conditions such as diabetic neuropathy where vascular factors are thought to have an important role in aetiology.

Effect of bupivacaine and adjuvant drugs for regional anesthesia on nerve tissue oximetry and nerve blood flow

“…Systemic data did not differ, in any way that was clinically relevant, between the time points T0, T30, and T60 when compared between each group. This is important due to the response of nerve SO 2 to central hypoxia and cardiovascular changes as described by Ibrahim et al 29 Moreover, this aspect is a potential bias within previous published studies of nerve blood flow measurements in animals where changes in oxygen saturation and circulation were not, or were inadequately, controlled.…”

Increased sural nerve epineurial blood flow in human subjects with painful diabetic neuropathy

“…The equipment and methods used in the measurement of epineurial intravascular oxygen saturation and blood flow have been validated and described in detail elsewhere [15,19].…”

“…Measurements were done using the Erlangen microlightguide spectrophotometer II (EMPHO II, Bodenseewerk Gerätetechnik, Überlingen, Germany) [15,19]. Light was shone onto the surface of the nerve through an endoscope and reflected light was collected, fed through a rotating interference filter disc and monochromatised in a range between 502 to 628 nm.…”

“…Each subject was given a bolus injection of 20% Sodium Fluorescein (Martindale Pharmaceuticals, Romford, UK) into the right cephalic vein at a dose of 1 millilitre per 20 kg body weight [15,19]. Fluorescein excitation was elicited using a 250 W Halogen light source with a 485 nm blue filter.…”

Optical Measurement of Tissue Oxygen Saturation

“…This preliminary study demonstrated that the combined technique could be applied to the least invasive measurement of nerve SO 2 and blood flow in humans and that there appeared to be a correlation between the 2 parameters. The technique was further validated in an animal model, 78 where it was demonstrated that the use of the microendoscope in conjunction with the EMPHO did not cause any significant difference compared with values measured using the lightguide directly. Furthermore, nerve SO 2 values changed proportionally in response to experimentally induced hypoxemia.…”