Very impressive advances have been made in diagnostic as well as surgical techniques in recent decades (Polis et al., 1999). The majority of companion animals will undergo general anesthesia at least once in their lifetime (Polis et al., 1999). In addition to routine procedures and surgery, general anesthesia is increasingly required in canine patients to facilitate advanced diagnostic and therapeutic interventions (Bille et al., 2012).
Inhalational anesthetics are considered over injectable agents due to their rapid induction, rapid recovery with better control over the depth and duration of anesthesia as well as more desirable physiological responses (Breck et al., 2003). Halogenated anesthetics, such as halothane and isoflurane, can alter heart rate and rhythm (Nakaigawa et al., 1995). In veterinary medicine, halothane (HAL) and isoflurane (ISO) are commonly used in clinical practice (Mutoh et al., 1997).
Hypotension depends on the depth of anesthesia and decreases myocardial contractility at low concentration and also causes vasodilation at high concentration (Muir et al., 2013). Complications have been reported in halothane anesthesia, especially halothane causing hepatitis (Voigt et al., 1997, Otedo, 2004, Kumar et al., 2005). Isoflurane has been reported to have cardiovascular and respiratory side effects from use (Klide, 1976; Steffey and Howland, 1977; Stevens et al., 1971).
In veterinary medicine, halothane (HAL) and isoflurane (ISO) have been used in clinical practice (Mutoh et al., 1997).
Mechanism of Action of Inhalation Anesthetics
Among anesthetics, inhalation anesthetics are unique in that they are administered and largely eliminated from the body via the lungs (Steffey and Mama, 2007). All of these devices help reduce patient morbidity or mortality by improving arterial oxygenation and facilitating lung ventilation (Steffey and Mama, 2007). 7 and is often a model for anesthetic action because the order of potency of anesthetics in animals parallels luciferase inhibition (West et al., 2014).
The anesthetic acts as a stereoselective "receptor" and will implicate a protein as the site of action. 1997) study to reconcile the apparent problem of the nonspecific action of anesthetics on a wide range of protein channels, including glycine, glutamate, GABA, and other neurotransmitter-activated channels.
Inhalant Anesthetic Pharmacokinetics
When the stereoisomers are induced in a lipid substrate, the physical effects on the lipid are similar. 8 The brain/blood coefficient for isoflurane is 2.7; Consequently, the concentration in the brain, when the process reaches equilibrium, will be 2.7 times higher than the concentration in the blood (Steffey and Mama, 2007). High fat/blood partition coefficients mean that the maximum of the gas will accumulate in adipose tissue.
In fatty tissue, the partial pressure of the gas rises very slowly because this tissue has a high capacity. Obese patients may take longer to wake up due to a stockpile of inhaled anesthetics at the end of long periods of anesthesia (West et al., 2014). Fortunately, adipose tissue has relatively low blood flow and does not accumulate effective amounts of anesthetic during the low periods of anesthesia.
The lungs, brain, heart and major organs (liver, kidneys) have relatively high blood flow compared to muscle and fat and are more sensitive to the effects of anesthetics.
Elimination of Inhaled Anesthetics
General Pharmacological Actions of Inhalant Anesthetics ............................... 9-10
Cardiovascular System
Respiratory system
Genital-Renal systems
Halothane…………….......…..……………………........................................10-13
- Pharmacokinetics
- Effects on different organs and systems
- Nervous and musculoskeletal system
- Respiratory system
- Cardiovascular system
- Reproductive system
- Precautions
- Physical - chemical properties of isoflurane
- Pharmacokinetics
- Effects on different organs and systems
- Nervous system
- Respiratory system
- Cardiovascular system
- Gastrointestinal system
- Renal system
- Reproductive system
- Precautions
Guinea pigs are particularly susceptible (Lunam et al., 1985), and there are a few reports of post-anesthetic deaths associated with acute liver injury in goats (Antognini and Eisele, 1993). Halothane is a colorless liquid that is degraded by ultraviolet light, so it can be stored in dark bottles with thymol as a preservative, which does not evaporate to the same extent as halothane. Chemically, halothane is classified as a halogenated hydrocarbon, but it is not chemically related to ethers (West et al., 2014).
Halothane can be used in a closed loop system and does not react with soda lime. About 12% of the absorbed drug is metabolized through the liver to form trifluoroacetic acid (only small amounts), chlorine and bromine radicals, which are excreted in the urine (West et al., 2014). It causes malignant hyperthermia that can be triggered in susceptible humans, pigs, dogs and cats with genetic muscle defects (Muir et al., 2013).
It does not irritate the respiratory mucosa unlike isoflurane, it can be used for induction of anesthesia without causing breathing (Hall and Clarke, 2014). It can cause hypotension related to the depth of anesthesia and, at low concentrations, decrease in myocardial contractile performance and vasodilatation at high concentrations (Muir et al., 2013). 13 increased systemic vascular resistance at the start of surgery, blood pressure tends to rise (Wagner et al., 1995).
It is also contraindicated in patients with cardiac arrhythmias, increased CSF or head injury, myasthenia gravis or pheochromocytoma (cardiac arrhythmias due to catecholamines) (Muir et al., 2013). In small animals, isoflurane can be used satisfactorily in vaporizers in the "in circle" method (Brosnan et al., 1998). Most of the absorbed drug is again excreted by the lungs (Muir et al., 2013).
Initially, increase the tidal volume with the depth of anesthesia. Decreased respiratory rate causes increased hypoventilation (increased PaCO2) over time (Muir et al., 2013). Isoflurane can be used safely in patients with liver or kidney disease, and it has minimal myocardial depressant and catecholamine-sensitizing effects. Isoflurane can be irritating to the respiratory system and is not recommended for mask induction (Clarke, 2008).
Monitoring the anesthetized patient..................................................................16-22
- Respiratory rate, depth and character
- Cardiovascular function
- Arterial blood pressure
- Body Temperature
It is ideal for perioperative monitoring of the percentage of oxygenated hemoglobin in arterial blood (SpO2) (West et al., 2014). Low blood pressure can cause a less accurate pulse oximetry reading because low blood pressure diverts blood flow to vital organs through peripheral vasoconstriction (Barton et al., 1996). Anesthesia with halothane produces the least respiratory depression in the dog than other inhalation agents (Mutoh et al., 1995).
Troubled or labored breathing may indicate the presence of an airway obstruction (Muir et al., 2013). Halothane anesthesia causing a decrease in respiratory rates and depth in bulls was reported in (Greene et al., 1998) and cattle (Takase, 1976) study. The decrease in CO is due to a decrease in stroke volume and anesthetic dose-dependent depression of myocardial contractility (Warltier and Pagel, 1992, Paget et al., 1991).
Volatile anesthetics increased HR compared with conditions in awake and sedated dogs (Paget et al., 1991 and Mutoh et al., 1997). In the study by Paget et al., 1991, little effect of HAL on HR in dogs, a slight increase was observed in dogs. Decreased stroke volume and peripheral vascular resistance effects on lowering blood pressure (Malan et al., 1995; Lowe et al., 1996; Mutoh et al., 1997).
MAP values were recorded lower with SEV and ISO anesthesia compared with HAL (Mutoh et al., 1995 and Frink et al., 1992). A similar hypotensive effect in cattle (Wolf et al., 1968) and buffalo (Bose and Kohli 1983; Gahlawat et al., 1986) has been reported in halothane anesthesia. 21 Halothane anesthesia causes a drop in arterial blood pressure and cardiac output in goats (Hikasa et al., 1998).
While isoflurane causes depression of arterial blood pressure and a minor decrease in cardiac output in cats and dogs (Steffey et al., 1987; Bernard et al., 1990). The peripheral vasodilatory properties of inhaled anesthetics and their effects reduce thermal regulation (Bernard et al., 1990 and Topal, 2005). Decreased metabolic rate, decreased skeletal muscle tone, muscle relaxation along with depression of the thermoregulatory center (Matsukawa et al., 1995) may be associated with decreased rectal temperature.
Study area
Study design ..................................……………..….............................…......24-25
- Fluid therapy
- Anesthetic procedures
- Intubation
- Maintenance of anesthesia
A circle semi-open rebreather anesthesia system was used throughout the study with a calibrated halothane (HAL) and isoflurane (ISO) vaporizer. For group A (n=7) anesthesia was maintained with halothane vaporizer for induction (3.5% to 4%) and group B (n=7) anesthesia was maintained with isoflurane vaporizer for induction (3% . to 4%). HAL and ISO vaporizer setting was adjusted from 1.5% to 2.5% according to the depth of anesthesia.
The vaporizer dial was gradually decreased or increased to the percentage required to maintain the level of anesthesia based on the clinical response to tail pinch, movement, and changes in heart rate (HR), respiratory rate (RR), and blood pressure.
Measurements and monitoring
Statistical analysis
The measurements of the cardiopulmonary parameters of the dogs in each anesthesia group were recorded after induction of anesthesia (0 min) until completion of surgery during each 5-minute interval. Body temperature decreased gradually over 55 minutes in both groups compared to the first readings. But there was no significant difference in body temperature between the HAL and ISO groups (p>0.1) (Figure 10).
Measurements of Heart rate (HR)
Measurements of Respiratory rate (RR)
Measurements of Oxygen saturation (SpO 2 )
Measurements of Arterial blood pressure.........................................................35-37
Diastolic arterial pressures (DAP)
Mean arterial pressures (MAP)
In a similar study, halothane caused a decrease in body temperature in anesthetized humans (Ramachandra et al., 1989). Heart rate increased with isoflurane and halothane anesthesia by anesthetic concentration (Picker et al., 2001). Halothane anesthesia causing a decrease in respiratory rate and depth in bulls was reported in the cattle study (Greene et al., 1998) (Takase, 1976).
Halothane anesthesia causes a fall in arterial blood pressure and cardiac output in goats (Hikasa et al., 1998). The present findings suggest that the respiratory effects of halothane were less depressant than isoflurane anesthesia in dogs. Further detailed investigation into the use of inhalation anesthetics during surgery and effects of anesthesia on other cardiopulmonary parameters (e.g.
The effects of sevoflurane, halothane, enflurane, and isoflurane on hepatic blood flow and oxygenation in chronically instrumented greyhound dogs. The effects of inhalation anesthesia (halothane and isoflurane) on certain clinical and haematological parameters of sheep. The cardiopulmonary effects of sevoflurane, isoflurane and halothane anesthesia during spontaneous or controlled ventilation in dogs.
Comparison of cardiopulmonary effects of isoflurane and halothane after atropine-guaifenesin-thiamylal anesthesia for rumenotomy in steers. Are the functional and metabolic effects of isoflurane on the heart really different from those of halothane and enflurane? Comparison of the effects of isoflurane and desflurane on cardiovascular dynamics and regional blood flow in the chronically instrumented dog.
Effects of 1 MAC desflurane on cerebral metabolism, blood flow, and carbon dioxide reactivity in humans. Comparison of the effects of halothane, isoflurane, and sevoflurane on atrioventricular conduction time in pentobarbital-anesthetized dogs. Effects of halothane on the interactions between myocardial contractility, aortic impedance, and left ventricular performance: theoretical considerations and results.
Cerebral effects of nitric oxide when added to low and high concentrations of isoflurane in the dog. Cardiovascular effects of a new inhalation anesthetic, Forane, in human volunteers at constant arterial carbon dioxide tension.
