Delayed recovery of behavior after anesthesia in rats

The Effects of Sedation with Dexmedetomidine-Butorphanol and Anesthesia with Propofol-Isoflurane on Feline Grimace Scale© Scores

This study aimed to evaluate the effects of sedation and anesthesia on Feline Grimace Scale© (FGS) scores. Twelve healthy cats were included in a prospective, blinded and randomized, cross-over study with a 14 day wash-out. Saline or dexmedetomidine-butorphanol (Dex-But) was administered intramuscularly before an anesthetic induction with propofol and maintenance with isoflurane. Saline or atipamezole (Dex-But) was administered at the end of the general anesthesia. Video-filming/image capturing was performed before and up to 24 h post-anesthesia. A total of 125 images were evaluated by four raters blinded to the treatment groups using the FGS (ear position/orbital tightening/muzzle tension/whiskers change/head position; action units (AU); scores 0−2 for each AU). The effects of the sedation/anesthesia were analyzed (p < 0.05). The total FGS and each AU scores were significantly higher with Dex-But than with saline 20 min post-sedation. In the saline group, the total FGS, orbital tightening, and whiskers and head position scores were significantly higher than baseline at 0.5 h post-anesthesia. In the Dex-But group, the total FGS and each AU scores were significantly higher after sedation, whereas the orbital tightening scores were significantly higher at 0.5 h post-anesthesia when compared with the baseline. None of the other comparisons between or within the groups was significantly different. The sedation with dexmedetomidine-butorphanol and anesthesia with propofol-isoflurane changed the FGS scores on a short-term basis; consequently, they may bias acute pain assessment.

Supplement of Lipid Emulsion to Epinephrine Improves Resuscitation Outcomes of Asphyxia-Induced Cardiac Arrest in Aged Rats

Objective

The goal of the study was to investigate the efficacy of lipid supplement to epinephrine-based therapy in resuscitation of asphyxia-induced cardiac arrest in aged rats.

Methods

The study included two parts: in experiment A, rats underwent asphyxial cardiac arrest and cardiopulmonary resuscitation, randomized to receive epinephrine and normal saline (control group, n=22), epinephrine and intralipid 20% (long-chain triglycerides (LCT) group, n=22) or epinephrine and lipovenoes 20% (LCT/medium-chain triglcerides (MCT) group, n=22). Return of spontaneous circulation, recurrence of asystole after resuscitation, hemodynamic metrics, arterial blood gas values, neurological assessment score and indexes of pulmonary transudation were recorded. In experiment B, rats using the same model and resuscitation protocol were randomly divided into 21 groups: Control ₀, Control ₂₀, Control ₄₀, Control ₆₀, Control ₈₀, Control ₁₀₀, Control ₁₂₀, LCT ₀, LCT ₂₀, LCT ₄₀, LCT ₆₀, LCT ₈₀, LCT ₁₀₀, LCT ₁₂₀, LCT/MCT ₀, LCT/MCT ₂₀, LCT/MCT ₄₀, LCT/MCT ₆₀, LCT/MCT ₈₀, LCT/MCT ₁₀₀ and LCT ₁₂₀ (n=10, the subscripts represent respective endpoint of observation in minutes). Myocardial bioenergetics were determined.

Results

In experiment A, the LCT and LCT/MCT groups had a shorter time to return of spontaneous circulation (ROSC) (P=0.001and P<0.001, respectively) and higher survival rate (P=0.033 and P=0.014, respectively) compared with the Control group. The LCT/MCT group had higher MAP (P<0.001 and P=0.001, respectively), HR (P<0.001 and P=0.004, respectively) and RPP (P<0.001 and P<0.001, respectively) compared with the Control and LCT groups, respectively. In experiment B, the LCT/MCT group had a higher energy charge compared with the control group at 20 (P<0.001) and 40 (P<0.001) minutes. The LCT group had higher energy charge compared with the Control group at 40 (P<0.001) and 60 (P<0.001) minutes.

Conclusion

The supplement of lipid emulsion to epinephrine improves resuscitation outcomes of asphyxia-induced cardiac arrest than epinephrine alone in our in vivo model of aged rat. LCT/MCT emulsion may be superior to LCT emulsion in epinephrine-based resuscitation.

The Influence of Isoflurane Anaesthesia on the Rat Grimace Scale

Over 234,000 rats were used in regulated procedures in the UK in 2014, many of which may have resulted in some degree of pain. When using animals in research, there is an ethical and legal responsibility to alleviate or at least reduce pain to an absolute minimum. To do this, we must be able to effectively assess pain in an accurate and timely manner. The Rat Grimace Scale (RGS) is a pain assessment tool, which is suggested to be both accurate and rapid in pain assessment. Many procedures involve the use of general anaesthesia. To date, the effects of anaesthesia on the RGS have not been assessed, limiting its potential utility for assessing pain following anaesthesia. Forty-eight Lister hooded rats were used in this study (24 in part A and 24 in a separate part B). Rats were randomly assigned to one of two treatment groups in part A; short duration isoflurane exposure, short duration control exposure (air) and one of two treatment groups in part B; surgical duration isoflurane exposure or surgical duration control exposure (oxygen). Rats were placed into an anaesthetic induction chamber and isoflurane, or control gas piped into the chamber for either 4 (short duration exposure) or 12 minutes (surgical duration exposure). Following recovery, photographs of the rats’ faces were taken and then scored blindly using the RGS. Short duration isoflurane anaesthesia had no effect on RGS scores. However, when rats are anaesthetised for a longer duration, akin to a simple routine surgical procedure, the RGS score increases significantly and this increase remains on repeated exposure to this duration of anaesthesia over a 4-day period. This should be accounted for when using the RGS to assess pain in rats in the immediate time period following procedures involving the use of isoflurane anaesthesia.

Effects of levosimendan on hemodynamics, local cerebral blood flow, neuronal injury, and neuroinflammation after asphyctic cardiac arrest in rats

OBJECTIVES

Despite advances in cardiac arrest treatment, high mortality and morbidity rates after successful cardiopulmonary resuscitation are still a major clinical relevant problem. The post cardiac arrest syndrome subsumes myocardial dysfunction, impaired microcirculation, systemic inflammatory response, and neurological impairment. The calcium-sensitizer levosimendan was able to improve myocardial function and initial resuscitation success after experimental cardiac arrest/cardiopulmonary resuscitation. We hypothesized that levosimendan exerts beneficial effects on cerebral blood flow, neuronal injury, neurological outcome, and inflammation 24 hours after experimental cardiac arrest/cardiopulmonary resuscitation.

DESIGN

Laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

Sixty-one male Sprague-Dawley rats.

INTERVENTIONS

Animals underwent asphyxial cardiac arrest/cardiopulmonary resuscitation, randomized to groups with levosimendan treatment (bolus 12 µg/kg and infusion for 3 hr [0.3 µg/min/kg]) or vehicle (saline 0.9% bolus and infusion for 3 hr [equivalent fluid volume]). Cardiac index, local cerebral blood flow, and hemodynamic variables were measured for 180 minutes after cardiac arrest/cardiopulmonary resuscitation. Behavioral and neurological evaluations were conducted 24 hours after cardiac arrest/cardiopulmonary resuscitation. Furthermore, neuronal injury, expressed as Fluoro-Jade B-positive cells in the hippocampal formation, cortical and hippocampal inflammatory cytokine gene expression, and blood plasma interleukin-6 values were assessed.

MEASUREMENTS AND MAIN RESULTS

Treatment with levosimendan reduced neuronal injury and improved neurological outcome after 24 hours of reperfusion and resulted in elevated cardiac index and local cerebral blood flow compared with vehicle after cardiac arrest/cardiopulmonary resuscitation. Mean arterial blood pressure was reduced during the early reperfusion period in the levosimendan group. Cortical and hippocampal inflammatory cytokine gene expression and blood plasma interleukin-6 levels were not influenced.

CONCLUSIONS

Levosimendan increased cerebral blood flow after experimental cardiac arrest/cardiopulmonary resuscitation. This effect coincided with reduced neuronal injury and improved neurologic outcome. Findings seem to be independent of inflammatory effects because no effects by levosimendan on cerebral or systemic inflammation could be detected. In summary, levosimendan is a promising agent to improve neurological outcome after cardiac arrest/cardiopulmonary resuscitation.

Outcome model of asphyxial cardiac arrest in rats

An outcome model with asphyxial cardiac arrest in rats has been developed for quantifying brain damage. Twenty-two rats were randomized into three groups. Control group I was normal, was conscious, and had no asphyxia (n = 6). Sham group II had anesthesia and surgery but no asphyxia (n = 6). All 12 rats in groups I and II survived to 72 h and were functionally and histologically normal. Arrest group III (the model; n = 10) had light anesthesia and apneic asphyxia of 8 min, which led to cessation of circulation at 3-4 min of apnea, resulting in cardiac arrest (no flow) of 4-5 min. All 10 rats had spontaneous circulation restored by standard external cardiopulmonary resuscitation. Nine rats survived controlled ventilation for 1 h and observation to 72 h, while one rat died before extubation. All nine survivors were conscious at 72 h, with neurologic deficit scores (0% = best; 100% = worst) of 7 +/- 6% (2-16%). All brain regions at five coronal levels were examined for ischemic neurons. The prevalence of ischemic neurons in five regions was categorically scored. The average total brain histopathologic damage score in group III (n = 9) was 2.1 (p < 0.05 vs. group I or II). A reproducible outcome model of cardiac arrest in rats was documented. It provides a tool for investigating pathophysiological mechanisms of neuronal death caused by a transient global hypoxic-ischemic brain insult.

Improved survival of hemorrhagic shock with oxygen and hypothermia in rats

A previously established model in awake rats of hemorrhagic shock (HS) with 25% spontaneous survival rate (without resuscitation) was used to evaluate the effects of 4 novel life-supporting first aid (LSFA) measures on survival time and rate. After shed blood volume (SBV) of 3.25 ml/100 g, withdrawn over 20 min, hemodynamic and respiratory responses were recorded to 3 h and survival to 24 h. The 5 groups of 20 rats each (total n = 100) were as follows: group I, controls without treatment; II, oxygen 100% inhalation; III, external cooling to rectal temperature 30 degrees C; IV, Ringer's solution 5 ml/100 g rectally; and V, acoustic and surface stimuli for arousal. Survival rates were: control group I, 35% at 3 h and 15% at 24 h; oxygen group II, 75% (P less than 0.05 compared with group I) at 3 h and 60% (P less than 0.05 compared with group I) at 24 h; hypothermia group III, 65% at 3 h and 45% (P less than 0.05 compared with group I) at 24 h; rectal fluid group IV, 50% at 3 h and 40% at 24 h; stimulated group V, 15% at 3 h and 15% at 24 h. Compared with group I, median survival times during HS 0-3 h were longer in groups II and III; and self-resuscitation attempts were longer in groups II, III and IV. We conclude that in untreated severe hemorrhagic shock, chances of survival to delayed arrival of advanced life support with i.v. fluid resuscitation might be increased with O2 inhalation and/or moderate external cooling.

Dying pattern in volume-controlled hemorrhagic shock in awake rats

We previously determined that in awake, unmonitored Sprague-Dawley rats, bleeding of 2.5 ml/100 g over 20 min resulted in hemorrhagic shock (HS) with about a 75% survival rate over 24 h, and bleeding of 3.0 ml/100 g in about 25% survival to 24 h. In the present study, we monitored systolic and mean arterial pressure (MAP), central venous pressure (CVP), breathing movements, electroencephalogram (EEG), and arterial blood gases to 3 h in order to study dying patterns. After cannulation under light anesthesia and awakening for 2 h, the rats were bled over 20 min. Ten rats in each of four groups were studied. Shed blood volume (SBV) in group I was 2.0 ml/100 g; in group II, 2.5 ml; in group III, 3.0 ml; and in group IV, 3.5 ml. Three hour survival rates were 100% for group I, 80% for group II (survival time 149 +/- 65 [106-180] min), 40% for group III (survival time 116 +/- 72 [93-180] min), and 0% for group IV (survival time 32 +/- 38 [5-69] min). MAP decreased at end of bleeding, increased transiently to moderately hypotensive levels (attempted self-resuscitation), and then either recovered to normotension or declined to cardiac arrest (death), which was defined as simultaneous apnea, systolic arterial pressure less than or equal to 30 mmHg without pulsations, and isoelectric EEG. EEG depression began with hypotension to MAP less than or equal to 50 mmHg. During HS, PaO2 increased, and PaCO2, pHa, and Hct all decreased. The results suggest that this model with SBV of 3.25 ml/100 g would give a low, but not zero 3 h survival, and therefore would be suitable for the study of responses to field resuscitation potentials.