Effect of Age on Minimum Alveolar Concentration (MAC) of Sevoflurane in Dogs

Abstract

ABSTRACT. It is well known that the minimum alveolar concentration (MAC) of inhalation anesthetic decreases with increasing age. However, there is limited information regarding the effect of age on MAC in dogs. This study was designed to determine the effect of age on sevoflurane MAC in dogs. MAC was determined in 6 young (2 years old) and 6 old beagle dogs (8 to 10 years old) under artificial ventilation. Anesthesia was induced via mask induction and maintained with sevoflurane in oxygen, and MAC was determined by using a tail clamp method. The sevoflurane MAC for the older dogs was significantly less than that for the younger dogs (1.86  0.29% vs 2.25  0.15%, P=0.007). The MAC of sevoflurane is profoundly affected by age in dogs.KEY WORDS: aging, anesthesia and analgesia, canine, minimum alveolar concentration (MAC), sevoflurane.J. Vet. Med. Sci. 71(11): 1509-1512, 2009 Sevoflurane is a volatile anesthetic agent with a relatively low blood/gas solubility coefficient resulting in rapid induction and recovery from anesthesia [28]. During the last decade, clinical use of sevoflurane has been spreading in veterinary species such as horses [3,14,24,31], cats [15] and dogs [1,2]. Sevoflurane is minimally metabolized and easily cleared in animals; however, it should be remembered that sevoflurane causes dose-dependent hypotension, hypoventilation, impaired cardiac contractility and hypothermia [21]. Because of these side effects, sevoflurane must be carefully titrated, and vigilant monitoring should be employed to avoid excessive anesthetic depth.MAC has been defined as "the minimum alveolar concentration of anesthetic at 1 atmosphere that produces immobility in 50% of those animals exposed to a noxious stimulus" [5]. It has long been known that MAC decreases with age in humans [8,20,22,26,29]. In human medicine, anesthetists can rapidly determine the depth of anesthesia in age-corrected MAC units for volatile anesthetics by using a normogram to estimate age-related MAC [16] and agerelated iso-MAC charts [23]. In the recent practice of veterinary anesthesia, geriatric animals have become a significant proportion of the patient population. Attention to the unique physiology and particular requirements of individuals within this age group will contribute to the provision of safe and effective anesthesia [9,19]. Veterinary practitioners believe that geriatric animals require a lower concentration of inhalation anesthetic to maintain anesthesia based on clinical experience. To the best of our knowledge, however, there are few reports on the relationship of MAC to age in veterinary species [11,17]. Furthermore, the relationship of sevoflurane MAC to age has not been evaluated in dogs. The purpose of the study reported here was to determine the effect of age on sevoflurane MAC in dogs. The authors hypothesized that the sevoflurane MAC value would be inversely related to age in this species.Six young beagles, 2 years of age (all male) and weighing from 9.7 to 11.8 kg (10.8  0.9 kg of mean  SD), and six old beagles, 8 to...

Minimum Alveolar Concentration for Blunting Adrenergic Responses (MAC-BAR) of Sevoflurane in Dogs

“…Differences in study design, individual animal and age may account for variability in MAC results. It is reported that sevoflurane MAC reduced with increasing age of dogs [26], similar to humans [17]. The age of dogs used in the present study were 9 to 11 years, therefore, we surmised that the effect of aging might be a major factor lowering the sevoflurane MAC value.…”

“…After the dogs were allowed to equilibrate for 60 min at ETSEV 2.8 to 3.0%, the electrical stimulus was applied for 10 sec using an electrical stimulator (SEN3301, Nihon Kohden Co., Tokyo, Japan). Positive response to the electrical stimulus for MAC determination was fixed a purposeful movement defined as substantial movement of the head or extremities and did not include coughing, chewing, swallowing or increasing respiratory effort [26,28]. Positive response for MAC-BAR determination was fixed an increase of either heart rate or mean arterial blood pressure (MABP) over 15% above the value recorded at 1 min before applying the electrical stimulus [15].…”

Effects of a Single Bolus Intravenous Dose of Tramadol on Minimum Alveolar Concentration (MAC) of Sevoflurane in Dogs

“…The six dogs used in the present study were aged 8 to 10 years. It was reported that the sevoflurane MAC was reduced with aging up to approximately 17% in the dogs aged 9 years compared to those in the dogs aged 2 years [30]. Therefore, the age of dogs is considered a primary factor in the lowering of sevoflurane MAC of the control dogs.…”

“…Determination of sevoflurane MAC: The sevoflurane MAC was determined by use of the tail clamp method [13,30]. Following the instrumentation, the dogs were treated with or without a single bolus IV of 4 mg/kg tramadol through the 22-gauge catheter.…”

“…The purposeful movement was defined as substantial movement of the head or extremities and did not include coughing, chewing, swallowing, or an increasing respiratory effort. The clamp circumscribed the tail and did not puncture the skin of the dog thereby producing a blunt force on the tail [13,30].…”