Hypertension is a known silent killer of both human and their close companion dogs, cats and horses. The disease becomes difficult to diagnose as anesthetics mask the actual reading of blood pressure of anaesthetized animal. The anesthetics Pentobarbital sodium, Ketamine and Xylazine alone and in combination are modifying the reading of mean arterial pressure (MAP). Hence, it becomes mandatory to know the effects of anesthetics on MAP. The rats were randomly divided into four groups viz. group-A (n=6), group-B (n=6), group-C (n=7) and group-D (n=5). The MAP of control rats of group A and B were measured under anesthetics Pentobarbital sodium and Ketamine and Xylazine in combination, respectively. However, the MAP of L-NAME-induced hypertensive rats of group-C and group-D were measured under anesthetics pentobarbital sodium and Ketamine and Xylazine in combination, respectively. The MAP of control rats of group-B significantly decreased under anesthetics Ketamine and Xylazine compared to rats of Pentobarbital group-A. Similarly, MAP of hypertensive rats of group-D significantly decreased under anesthetics Ketamine and Xylazine in combination to the level equivalence to MAP of group-A control rats indicting Ketamine and Xylazine combination significantly influencing the MAP of hypertensive rats. Hence, anesthetic combination of Ketamine and Xylazine should not be endorsed in animals since it masks the actual factual reading of MAP.
Hypertension is a known ‘silent disease’ of human population and their close associate like dog and cat too (Sravanti et al., 2016). The disease hypertension is only diagnosed once the sufferers are showing symptoms in advance stage of the disease. The World Health Organization has reported hypertension as one of the main causes of death in human population (Ezzati et al., 2002). The diagnosis of hypertension requires estimation of Mean Arterial Pressure (MAP) under anesthesia. Anesthetics influencing the blood pressure of both normal and hypertensive animals (Goldman and Caldera, 1979). Anesthetic ketamine alone increases the heart rate and MAP, excite the cardiovascular functions and therefore, to combat these effect ketamine prefer to use in combination with alpha adrenergic agonist xylazine (Haskins et al., 1985; Janssen et al., 2004; Koshy et al., 2003). The pentobarbital sodium is another anesthetic influencing the blood pressure (Prawez et al., 2015A). Keeping the impact of anesthetics on cardiovascular functions, the present study was framed to explore the effect of Pentobarbital sodium alone and ketamine and xylazine in combination over the reading of MAP of normal and hypertensive rats. The analysis will also help to reveal which anesthetic under consideration fluctuate the blood pressure to greater extent.
Materials and Methods
The experiment was conducted on healthy male Wistar rats weighing about (150-200g). Rats used in the present study were procured from Laboratory Animal Resource Section of ICAR-Indian Veterinary Research Institute (Izatnagar, India). Prior to start of experiment, the animals were acclimatized to environmental conditions and the study was conducted strictly in accordance to the Institutional Animal Ethical Committee guidelines. The rats were randomly divided into four group viz. group-A (n=6), group-B (n=6), group-C (n=7) and group-D (n=5). The rats of group-A and group-B were control or non-hypertensive group and their MAP measured by invasive method under anesthetics pentobarbital sodium alone and combination of ketamine and xylazine, respectively. Similarly, the rats of group-C and group-D or hypertensive groups were anaesthetized with pentobarbital sodium alone and ketamine and xylazine in-combination, respectively. The pentobarbital sodium at the dose rate of 60 mg/kg of body weight intra-peritoneally and ketamine and xylazine at the dose rate of 75 mg/kg and 10 mg/kg of body weight intramuscularly were administered. Hypertension condition in rats of group-C and group-D were induced by administering L-NG-Nitro Arginine Methyl Ester (L-NAME) orally after dissolving in drinking water at the dose rate of 50 mg/kg of body weight daily for forty two days (Prawez et al., 2016).
Mean Arterial Pressure Analysis
The MAP of rats of different group was measured after completion of forty two days of L-NAME treatment period to induce the hypertension. After forty two days, MAP of rats of different group was measured. Rats were anesthetized with anesthetics of present study and carotid artery cannulated using ocular surgical instruments. Further cannulated carotid artery was connected to pressure transducer and attached to data acquisition system, Power Lab, ADInstrument, Australia. Finally the data acquisition system connected to desktop to display the MAP (Prawez et al., 2015B).
Data of MAP of rats were represented as Mean±SEM and analyzed by Student-Newman-Keuls method for multiple group analysis. The level of statistical significance was compared at p< 0.05 (Snedecor and Cochran, 1989).
The MAP of group-A control ratsunder anesthetic pentobarbital sodium was found 116.03 ± 2.40 mm Hg (n=6). However, MAP of group-B control rats under anesthetics ketamine and xylazine after administering in combination was significantly decreased to 95.40 ± 2.90 mm Hg (n=6) compared to control rats of group-A (Fig. 1 & 2).
Level of Significance at p<0.05 and values are in Mean ± SEM (standard error of mean)
At *p<0.05 group-B significantly vary with group-A
At #p<0.05 group-D significantly vary with group-C
Fig.1: Effect of anesthetics Pentobarbital sodium alone and Ketamine and Xylazine in combination on MAP of hypertensive male Wistar rats
The MAP of L-NAME induced group-C hypertensive rats under anesthetic Pentobarbital sodium was found 166.03 ± 2.40 mm of Hg (n=7). Parallel to result of control group-B, under anesthetics ketamine and xylazine combination significantly decreases the MAP of group-D hypertensive rats to 106.02 ± 9.32 mm Hg (n=5) compared to hypertensive group-C. The MAP of hypertensive rats of group-D was decreased even below the MAP value of control rats of group-A. Decreases in MAP value of hypertensive rats of group-D indicated a remarkable change produced by anesthetic combination ketamine and xylazine and also mask the factual reading of MAP (Fig. 1 & 2).
Fig. 2: Tracing of MAP of anaesthetized rats, (A) Control (Gr. A/Pento), (B) Control (Gr.B/K+X), (C) Hypertensive (Gr. C/Pento) and (D) Hypertensive (Gr. D/K+X)
The diagnosis of disease can become difficult if its factual reading is not retrieve completely. Hence, before diagnosing a disease, the clinician must know about the interfering factors which hamper the diagnosis of diseases. The present study was conducted to explore the effect of anesthetics which are commonly used to handle furious animal for their examination. The anesthetics used may mask the diagnosis of disease. Present study findings suggested that anesthetics un-doughtily concealed the realistic reading of MAP of hypertensive rats to the extent the MAP of diseased animals match with MAP of control rats. Similar decrease in blood pressure of hypertensive rats under anesthetics ketamine and xylazine combination was reported by Bencze et al. (2013), Saha et al. (2007), and Prawez et al. (2015A), validating that combination is not advisable to conduct cardiovascular functional study. Primary mechanism behind fall in blood pressure is associated with anesthetic xylazine, since ketamine has been reported to increases the blood pressure (Haskins et al., 1985). Xylazine helped to nullify the cardiovascular side effect induced sympathetic innervations and stimulating vagal stimulation when used together (Haskins et al., 1985; Rand et al., 1996). Pentobarbital sodium in the present study did not produce any significant hemodynamic/ cardiovascular changes compared to other anesthetics (Bencze et al., 2013).
Hence, the finding of present study recommend that it is not advisable to use ketamine xylazine in combination while estimating the cardiovascular parameters as combination mask the factual reading of cardiovascular parameters.