Ethics
The experimental study was approved by the Animal Care and Use Committee of the Astana Medical University, Astana, The Republic of Kazakhstan. The experimental procedures were performed according to the Guide for the Care and Use of Laboratory Animals, Eighth Edition, 2011 formulated by National Academy of Sciences, the United States of America.
Animal housing
A total of 42 adult male Wistar rats, weighing 350–400 g were pushed from Astana Laboratory Animal Center, Astana, the Republic of Kazakhstan. All experiments were performed in the Experimental Animal Center, Astana Medical University, Astana, the Republic of Kazakhstan. The rats were housed in stainless steel cages (5 rats/cage) at conventional controlled conditions (temperature 25 ± 2 °C; relative humidity 50 ± 10%; 12 h light: dark cycle) and had a free access to standard laboratory food and tap water. The rats acclimated to the condition for 1 week prior to experiments and fasted overnight prior to surgery, with free access to water.
Animal instrumentation
Under anaesthesia with Thiopental Sodium (Kiev Medpeparat, Ukraine) 60 mg/kg, i.p., rats were tracheostomized with a stainless-steel tracheal tube, connected to a small animal ventilator (TOPO Dual mode ventilator, Kent Scientific Corp, USA) and mechanically ventilated with a tidal volume of 8 ml/kg using room air. A 24G central venous catheter (Arrow) was inserted into the right femoral vein for drug administration and blood sampling. A 22G catheter (22G venflon, BD, Sweden) was inserted into the right femoral artery connected to pressure transducer for continuous blood pressure monitoring using Dash 5000, GE Healthcare, USA. Average time for the instrumentation was about 10 min. At the end of the instrumentation the rats were given vecuronium bromide (Pfizer, USA) 2 mg/kg, i.v.
Animal randomization
After instrumentation and following a 10 min pause, by means of sealed envelopes the rats were randomly assigned to 3 groups: 1). Morphine group (n = 14), where the rats were given i.v. Morphine (Chimfarm Santo, Kazakhstan), 5 mg/kg, 10 min before inducing asphyxial cardiac arrest (ACA). 2). Ketamine group, (n = 14), where the rats were given i.v. Ketamine (Farmac, Ukraine) 40 mg/kg 10 min before ACA, 3). Control group (n = 14), where the rats were given an equal quantity of NaCl 0.9% 10 min before ACA.
Induction of ACA
ACA was induced by corking of the tracheal tube for 8 min (Fig. 1), and defined as a mean arterial pressure (MAP) < 20 mmHg. Cardio-pulmonary resuscitation (CPR) was initiated by an i.v. injection of epinephrine (0.02 mg/kg), followed by mechanical ventilation (80 breaths/min) using room air, and manual thoracic compressions (180 compressions/min). Restoration of spontaneous circulation (ROSC) was defined as a return of MAP > 60 mmHg. Ventilation was maintained until spontaneous breathing began. Core temperature (rectal) was kept between 36.5 °C and 37.5 °C using a heating pad. Arterial blood samples were taken at baseline, and 10 min after start of CPR. MAP was recorded at baseline, after i.v. injection of the study drugs or saline, at 1, 2, 3, 4, 5 min after induction of ACA and at 1, 5, 10, 15, 20 min in the post-resuscitation period. All surviving rats were euthanized with 180 mg/kg i.v. of Thiopental Sodium (Kiev Medpeparat, Ukraine) at the end of study.
Measurement of biochemical markers
Blood samples were centrifuged, plasma were aliquoted and snap frozen at − 70C. Right after euthanasia brain was retrieved and brain tissue samples were snap frozen at − 70 °C. All samples were stored at -70 °C until analysis. Levels of neuron specific enolase (NSE), and s100 calcium binding protein B (s100B) were measured in plasma samples which were collected at baseline and at 10 min in the post-resuscitation period (n = 7). Level of caspase-3 (CS-3) was measured in brain tissue samples from the surviving rats at the end of the experimental protocol, 20 min in the post-resuscitation period (n = 7). CS-3 level was normalized to the protein concentration in the brain tissue samples and results presented as a concentration per mg protein. All analysis were performed using Enzyme Linked Immunosorbent Assay (ELISA) kits provided by MyBioSource Inc. (San Diego, CA, USA). Protein content in the brain tissue samples was determined using Quick start Bradford protein assay from Bio-Rad (Hercules, CA, USA).
Statistical analysis
As we were not able to find any experimental study of Morphine or Ketamine application for animals with asphyxial cardiac arrest, for our study we calculated the sample size based on data from the research study of Endoh H, et al. [22]. In the experimental study with rats exposed to hypoxic gas (5% oxygen, 95% N2) for 70 min, approximately 90% rats survived in the Morphine (5 mg/kg) pre-treated group, and 40% survived in the control group. At 5% of significance level and 80% power, sample size will be pooled prevalence = 0.4 + 0.9/2 = 0.65.
Sample Size = 2 (1.96 + 0.842)2 × 0.65 (1–0.65)/(− 0.5)2 = 14.26.
based on formula of sample size = 2 (Zα/2 + Zβ)2 × P (1 − P)/(p1 − p2)2.
where Zα/2 = Z0.05/2 = Z 0.025 = 1.96 (From Z table) at type 1 error of 5% and.
Zβ = Z0.20 = 0.842 (From Z table) at 80% power.
p1 − p2 = Difference in proportion of events in two groups P = Pooled prevalence = (prevalence in case group [p1] + prevalence in the control group [p2])/2.
Data were analyzed and presented using SigmaPlot statistical software version 13.0 (Systat Software Inc., San Jose, CA, USA). Data were tested for normal distribution with Shapiro-Wilks test. Differences in values between groups were analyzed using one-way ANOVA on ranks. If significant differences were found, all pairwise multiple comparison procedures using Dunn’s method was applied to compare values between groups. Blood gas data and data of biochemical markers made after 10 min in the post-resuscitation period vs. corresponding baseline levels within each group were compared using a paired t-test. Survival was tested using log-rank Kaplan-Meier test. When significant differences were found, all pairwise multiple comparison procedures were tested using Holm-Sidak method to compare differences between groups. Differences were considered significant at p < 0.05.