Hypothermia During General Anesthesia Interferes with Pain Assessment in Laboratory Rats (Rattus norvegicus)

Abstract

Accurate pain assessment methods are necessary to ensure animal welfare and reliable data collection in animal research.The Rat Grimace Scale (RGS), a facial expression pain scale, allows effective identification of pain. However, the potentialconfounds of this method remain mostly unexplored. General anesthesia, which is used in many laboratory procedures,suppresses thermoregulation and results in hypothermia. We investigated the effects of isoflurane-induced hypothermia onRGS scores. Twenty (10 male and 10 female) Sprague–Dawley rats each received 30 min of anesthesia, followed by 30 minof observation after the return of sternal recumbency. Rats were randomized to receive warming with an electric heatingpad or no warming during both periods. Unwarmed rats became hypothermic within 15 min after isoflurane exposure beganand returned to normothermia within 15 min after returning to sternal recumbency. Warmed rats did not deviate from thenormothermic range. The RGS scores of unwarmed rats were significantly higher than baseline levels for 3 h after anesthesiaand were higher than those of warmed rats at 5 and 180 min after anesthesia. Hypothermia resulted in a larger proportion ofrats crossing a predetermined analgesic intervention threshold. Our findings show that hypothermia induced by isofluraneanesthesia presents a confound to accurate RGS scoring. These results emphasize the importance of maintaining normothermiato avoid inflated pain scores and to obtain accurate pain assessment.

Development and validation of a cynomolgus macaque grimace scale for acute pain assessment

“…Similarly, some cats undergoing sedation and general anesthesia may experience mildly increased facial grimace scores for up to 30 min following anesthesia 87 . No specific mechanism was proposed for either of these induced grimace score alterations and the presence of hypothermia (a condition commonly occurring during anesthesia and surgery of animals and associated with increased grimace scores in a rat study 88 ) was also not reported, so it is unknown whether the changes were induced directly by anesthesia or because of other alterations in physiologic state,. Although the current study did not evaluate macaques until at least 2 h following general anesthesia further research is needed to determine whether and if inhalant or injectable anesthetics have an effect on CMGS scores.…”

Mouse Anesthesia: The Art and Science

“… 289 In addition, hypothermia during rodent anesthesia is common 137 and has recently been shown to interfere with post-operative pain assessments. 290 Thus, it is widely accepted that most procedures involving rodent sedation or general anesthesia include normothermia support and the shortest duration possible. However, in cases of prolonged anesthesia duration, the anesthesia duration effects as a research variable must be addressed.…”

Peri‐anesthetic hypothermia in rodents: A factor to consider for accurate and reproducible outcomes in orthopedic device‐related infection studies

“…In human patients, hypothermia is linked to the need for more postoperative analgesia 50,51 . Similarly, hypothermia in rats results in a more significant proportion of rats crossing a predetermined analgesic intervention threshold 52 . Furthermore, hypothermia induced by isoflurane anesthesia confounds accurate Rat Grimace Scale scoring, a facial expression pain scale allowing effective identification of pain 52 .…”

“…Similarly, hypothermia in rats results in a more significant proportion of rats crossing a predetermined analgesic intervention threshold 52 . Furthermore, hypothermia induced by isoflurane anesthesia confounds accurate Rat Grimace Scale scoring, a facial expression pain scale allowing effective identification of pain 52 . Also, hypothermia is linked to shivering during anesthesia recovery to increase core body temperature, which may cause damage to the surgical site and contribute to postoperative pain 53 .…”

“…52 Furthermore, hypothermia induced by isoflurane anesthesia confounds accurate Rat Grimace Scale scoring, a facial expression pain scale allowing effective identification of pain. 52 Also, hypothermia is linked to shivering during anesthesia recovery to increase core body temperature, which may cause damage to the surgical site and contribute to postoperative pain. 53 These observations highlight the need to implement temperature management strategies that prevent peri-anesthetic hypothermia as much as possible to avoid unnecessary suffering in rodents.…”