Use of near‐infrared spectroscopy to identify trends in regional cerebral oxygen saturation in horses

Abstract

Summary Reasons for performing study Alterations in cerebral haemodynamics may contribute to perianaesthetic complications in horses. Near‐infrared spectroscopy (NIRS) is frequently used intraoperatively in man to provide information regarding cerebral perfusion. Objectives To determine whether NIRS can identify trends in regional cerebral oxygen saturation (rSO2) in horses and whether there is a correlation between rSO2 and venous oxygen tensions. Methods A cerebral oximeter sensor recorded rSO2 from the dorsal sagittal sinus of 6 healthy horses. Values for rSO2, arterial and venous oxygen and carbon dioxide tensions (PaO2, PvO2, PaCO2 and PvCO2 respectively), along with arteriovenous oxygen saturations (SavO2) were recorded in unsedated (recording period [RP] 1), sedated (RP2) and anaesthetised horses (RP3–5) and during recovery (RP6–8). During anaesthesia, horses were ventilated to achieve states of normo‐ (RP3), hyper‐ (RP4) and hypocapnoea (RP5). Data were evaluated descriptively and analysed using linear mixed‐effects models and Pearson's correlation coefficient. Results Overall mean ± s.d. values for rSO2, PaO2, PvO2, PaCO2, SavO2 and mean arterial pressure varied significantly by RP (P<0.001). Significant decreases in rSO2 were identified between RP1 and the post anaesthetic periods (P<0.001). No significant differences in rSO2 values were identified between RP1 and the intra‐anaesthesia periods or between RP3, RP4 and RP5. Significant correlations were identified between rSO2 and PaO2 (r = 0.448, P<0.001), rSO2 and PvO2 (r = 0.512, P<0.001) and rSO2 and SavO2 (r = 0.469, P<0.001). Conclusions This is the first study to identify trends in rSO2 in horses using NIRS. A positive correlation was identified between rSO2 and PvO2, suggesting that alterations in cerebral oxygenation may be reflected in PvO2. Potential relevance Near‐infrared spectroscopy may be used to monitor trends in rSO2 during equine anaesthesia. Decreasing rSO2 values may act as an early warning signal, alerting clinicians to potential cerebral desaturation events and indicating a need for intervention.

Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses

“…Surgical preparation of the skin was performed, as it was hypothesized that hair and dirt would interfere with the passage of NIR light. Previous investigations of NIRS technology in the horse have accounted for the potential interference of hair by clipping the regions for probe placement; however, this is the first study to undertake skin preparation prior to probe placement [15,21].…”

“…The INVOS 5100c tissue oximeter (Medtronic, Minneapolis, MN, USA) is a twowavelength, dual-receiving optode oximeter that can simultaneously monitor StO 2 or cerebral oximetry (rSO 2 ) at up to four different locations on the body [18][19][20]. The monitor is commercially available and has previously been used by McConnell et al [21] to monitor rSO 2 in horses.…”

Study design synopsis: Bias can cast a dark shadow over studies

“…A manuscript by McConnell et al . (2013) can be used to discuss some issues related to information bias 41 . The objective of this study was “to determine whether near infrared spectroscopy (NIRS) can identify trends in regional cerebral oxygen saturation (rSO 2 ) in horses and whether there is a correlation between rSO 2 and venous oxygen tensions.” The study design included six healthy Nooitgedacht mares from a university teaching herd.…”

Non-invasive estimation of in vivo optical properties and hemodynamic parameters of domestic animals: a preliminary study on horses, dogs, and sheep

“…In NIRS studies on domestic animals, continuous wave (CW) NIRS commercial devices were used, employing steady state light sources and photodetectors sensitive to light attenuation (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33). However, in highly diffusive media, like biological tissue in the NIR region, light attenuation is determined by the complex interplay between light absorption (depending on tissue chromophores like hemoglobin, water, lipid, melanin) and light scattering (depending on refractive index changes and tissue structure) (35).…”

“…Moreover, NIRS could offer a simple tool to investigate cortical hemodynamics and functions following motor, cognitive, and somatosensory stimuli or during clinical procedures like general anesthesia, or also during neurorehabilitation ( 17 ). In the veterinary field, preliminary NIRS measurements for estimating S t O 2 were reported on dog muscle ( 18 , 19 ), horse muscle ( 20–23 ) and horse head ( 24 ). Moreover, NIRS measurements were reported on dog brain ( 25–27 ) and on sheep brain ( 28–33 ) for monitoring the cortical hemodynamic changes to various external stimuli (e.g., auditory, cognitive).…”