Validating the use of a carbon dioxide laser for assessing nociceptive thresholds in adult domestic cats (Felis catus)

Abstract

a b s t r a c tThermal sensitivity in cats has historically been assessed using complex devices which require direct application to the patient and can therefore, in themselves, affect the measurement. This study aimed to validate the use of a remote low power (165 mW) carbon dioxide laser device for the assessment of thermal nociceptive thresholds in cats. Repeatabilites were established based on individual responses to three thermal tests on the same day and across 4 consecutive days. A total of 12 thermal tests were conducted on each of eight male and eight female de-sexed adult cats. As a control a non-thermal helium aiming laser was used to ensure the animals were responding to the thermal component of the device. All thermal tests elicited a behavioural response with the large majority being a skin twitch known as the panniculus reflex (97%). None of the non-thermal tests resulted in this reflex behaviour. There was no evidence that cats became sensitised or habituated to the low power thermal stimulus on any given day (P = 0.426) or across days (P = 0.115), or that there was any interaction between the two time factors (P = 0.084). There was also no difference in latency to respond between males and females (P = 0.094), although there was a significant interaction between the day of testing and the sex of the subject (P = 0.042). Significant intra-class correlations demonstrated that individual responses were repeatable over days 1-3 (all P < 0.05) but not over day 4 (P = 0.096). A significant intra-class correlation was also evident across all days when data were combined (P < 0.0001). This technique shows some promise in assessing individual nociceptive thresholds and as a tool to establish associated individual differences. It could, with more exploration, also provide an alternative thermal mechanism for testing the efficacy of analgesics in cats. The significant repeatabilities were low ranging from 0.241 to 0.414, this suggests that a number of extraneous factors may have influenced responses to CO 2 laser stimulation at low power levels (165 mW). Further exploration of this technique on a larger sample than used here may allow elucidation of any other factors, including age or sex effects, that impact upon thermal sensitivity in the domestic cat.

Body weight affects behavioural indication of thermal nociceptive threshold in adult domestic cats (Felis catus)

“…Use of thermal stimuli often results in habituation or sensitisation following successive exposures which are considered to be drawbacks of thermal techniques (Bölcskei et al, 2010). However, similar to other devices used for measuring thermal thresholds in cats (Dixon et al, 2002) the behaviours elicited by the low power CO 2 laser technique show no evidence of habituation or sensitisation over a period of 1 h (Farnworth et al, 2013). Panniculus reflex, being the predominant and relatively invariant behavioural response, also minimises the likelihood that errors associated with subjective interpretation will be made.…”

“…The visible (non-thermal) helium laser used to guide the thermal CO 2 laser has previously been demonstrated to have no discernable effect on the behavioural response latency of cats (Farnworth et al, 2013), therefore it was not used as a control in this experiment. As the power setting was greater than the 165 mW used in Farnworth et al (2013) settings were first tested on two cats not used in the study.…”

“…Approximately 24 h prior to the commencement of testing each cat's fur was clipped to skin level on both sides of the animal as per the technique outlined in Farnworth et al (2013). The cats were not removed from their colony cages during this procedure.…”

“…More recently the CO 2 laser technique was validated as a tool for measuring thermal nociceptive thresholds in domestic cats (Felis catus) (Farnworth et al, 2013). The use of a CO 2 laser is considered ideal as it is non-invasive and can be used at a purely nociceptive level of stimulation (Kramer et al, 2012).…”

“…When a CO 2 laser is used on cats at low power settings the primary behavioural response, taken to indicate thermal nociceptive threshold, is a skin twitch known as the panniculus reflex (Farnworth et al, 2013). Use of thermal stimuli often results in habituation or sensitisation following successive exposures which are considered to be drawbacks of thermal techniques (Bölcskei et al, 2010).…”