Sedation and Anesthesia

1. Sedation and Anesthesia

2. Learning Outcomes Understand the indications, advantages, disadvantages, effects on the body and the associated adverse side effects of the commonly used pre-anesthetics Explain the rationale, effects on the body and advantages and disadvantages of the commonly used intravenous, intramuscular and inhalation anesthetic agents Understand the important concepts of analgesics and muscle relaxants

3. Pre-anesthetic Medication Advantages Advantages will differ with different drugs but may include Reduced stress to the animal Smoother induction and recovery Decreased amount of induction and, possibly, maintenance agent required Analgesia intraoperatively and post operatively Reduced secretions Reduced autonomic responses Handler safety

4. Pre-anesthetic Medication Disadvantages Are minimal Cost is a common concern The higher cost may be offset by the use of decreased amounts of induction and maintenance agents Time factor Premedication given subcutaneously usually takes 20 minutes to reach peak effect but can last up to two hours If time is an issue, most premedication can be given intramuscularly (IM) or even intravenously (IV) (with caution) Some (e.g. xylazine, acepromazine, opioids and diazepam) have been associated with temporary behavior and personality changes

5. Pre-anesthetic Medication Examples Anticholinergics Phenothiazines Benzodiazepines a2-Agonists Opioids Phencyclidines Neuroleptanalgesics

6. Pre-anesthetic Medication Anticholinergics (Parasympatholytics) Examples: atropine, glycopyrrolate (Robinul-V) Exerts effect by blocking the actions of the parasympathetic neurotransmitter acetylcholine at the muscarinic receptors Reverses the parasympathetic effects

7. Pre-anesthetic Medication Anticholinergics (Parasympatholytics) Indications and effects To prevent or treat bradycardia by suppressing stimulation of the vagal nerve In combination with opioids To reduce salivary and tear secretions Promotes bronchodilation Blocks the stimulation of the vagus nerve preventing bradycardia and reduced cardiac output

8. Pre-anesthetic Medication Anticholinergics (Parasympatholytics) Indications and effects Dilate pupils (mydriatic) Thicker mucus secretions in the airway may occur, especially in the cat and the horse Reduces gastrointestinal activity by inhibiting peristalsis

9. Pre-anesthetic Medication Anticholinergics (Parasympatholytics) Contraindications Tachycardiac patients Possibly with geriatrics or with other conditions such as congestive heart failure that could not handle a potential tachycardia Conditions such as constipation and ileus, which would further reduce peristaltic action of the intestine (i.e. endoscopic procedures)

10. Pre-anesthetic Medication Anticholinergics (Parasympatholytics) Glycopyrrolate and atropine produce basically the same effect Glycopyrrolate has a slower onset of action and generally has less potential for producing a tachycardia or cardiac arrhythmia Atropine is more potent and faster acting Salivation is more effectively suppressed with glycopyrrolate

11. Pre-anesthetic Medication Phenothiazines (Tranquilizers) Indications Good sedation for healthy animals undergoing elective procedures Anti-emetic

12. Pre-anesthetic Medication Phenothiazines Contraindications Convulsing/epileptic patients, seizure history or head trauma Acepromazine may reduce the seizure threshold of the animal Shock (hypovolemia) and hypothermia because of peripheral vasodilation that can lead to hypotension Depressed patients Caution with geriatrics and pediatrics; use a lower dose or consider alternative agents such as benzodiazepines Liver or kidney disease Allergy testing because of antihistamine effect

13. Pre-anesthetic Medication Phenothiazines Other effects Antiarrhythmic effect May cause excitement rather than sedation Personality changes that usually subside within 48 hours

14. Pre-anesthetic Medication Benzodiazepines (Benzodiazepines) Tranquilizers Examples: Diazepam (Valium) Midazolam (Versed) Lorazepam (Ativan)

15. Pre-anesthetic Medication Benzodiazepines (Benzodiazepines) Indications Convulsing/epileptic patients Patients with a history of seizure CSF taps or myelogram procedures Minimal cardiovascular or respiratory depression Useful in geriatric or pediatric animals Ideal for older, depressed or anxious patients Works effectively as an induction agent when used with ketamine

16. Pre-anesthetic Medication Benzodiazepines (Benzodiazepines) Contraindications May cause excitement in some dogs, cats and horses Does not sedate animal but has antianxiety and calming effects May make animal more difficult when inhibitions and anxieties are removed Neonatal animals and animals with poor hepatic function

17. Pre-anesthetic Medication Benzodiazepines (Benzodiazepines) Valium is in a propylene glycol solution, is insoluble in water May precipitate with other drugs Propylene glycol is irritating and may sting at the injection site Does not work well when given via routes other than IV

18. Pre-anesthetic Medication Benzodiazepines (Benzodiazepines) Other points Midazolam is water soluble and readily combines with opioids (oxymorphone, butorphanol) Effects are reversed with flumazenil if adverse effects are seen

19. Pre-anesthetic Medication a2-Agonists Are derivatives of thiazine Examples: Xylazine (Rompun, Anased) Romifidine Detomidine (Dormosedan) Medetomidine (Domitor)

20. Pre-anesthetic Medication a2-Agonists Stimulates the a2-adrenoreceptors causing a decrease in norepinephrine Indication Potential side effects limit use to sedation only, not for preanesthetic medication Can use to sedate a vicious animal before euthanasia

21. Pre-anesthetic Medication a2-Agonists Have some short-lived (16 to 20 minutes) analgesic effects Will cause vomiting in up to 50% of dogs and 90% of cats Xylazine and Detomidine are used most frequently in horses Xylazine also used in ruminants but at much lower dosages

22. Pre-anesthetic Medication a2-Agonists Contraindications Considerable potential for side effects especially if administered IV Profound cardiovascular effects include bradycardia, profound hypotension, decreased contractility and stroke volume and second degree heart block Contraindicated when concerned about respiratory function, hepatic and renal function and if the animal is prone to gastric dilation

23. Pre-anesthetic Medication a2-Agonists Contraindications Associated with temporary behavior and personality changes Reduces pancreatic secretions causing transient hyperglycemia (exacerbates dehydration) Opioids will exacerbate these side effects

24. Pre-anesthetic Medication Opioids Commonly used: Morphine Oxymorphone (Numorphan) Butorphanol (Torbugesic, Torbutrol) Hydromorphone Meperidine (Demerol, Pethidine) Fentanyl

25. Pre-anesthetic Medication Opioids Act by reversible combination with one or more specific receptors in the brain and spinal column Produces a variety of effects Analgesia Sedation Dysphoria Euphoria excitement

26. Pre-anesthetic Medication Opioids Act by reversible combination with one or more specific receptors in the brain and spinal column May act as an agonist or antagonist Pure agonists stimulate all receptors � morphine, fentanyl and oxymorphone Mixed agonists/antagonists block one type of receptor and stimulate another � butorphanol Pure antagonists such as naloxone will reverse the effects of pure and mixed agonists with very little clinical effect on their own

27. Pre-anesthetic Medication Opioids Act by reversible combination with one or more specific receptors in the brain and spinal column Also classified according to their analgesic activity and their addiction potential Pure agonists are more effective for severe pain In order of decreasing potency they are: Fentanyl Oxymorphone Buprenorphine Butorphanol Meperidine pentazocine

28. Pre-anesthetic Medication Opioids Commonly used as an analgesic in premedication, as an induction agent or can be used for balanced anesthesia and post-operative pain control Provides some sedation and may potentiate the action of the sedative that it is given with has a synergistic effect

29. Pre-anesthetic Medication Opioids Commonly used as an analgesic in premedication, as an induction agent or can be used for balanced anesthesia and post-operative pain control Fentanyl, sufentanil and oxymorphone are often part of a balanced anesthetic regimen Fentanyl is available as a transdermal patch in various sizes for long-term analgesia Used as neuroleptanalgesia in combination wit tranquilizer Morphine can be injected epidurally or sub-arachnoidally for regional analgesia

30. Pre-anesthetic Medication Opioids Fentanyl patches Takes 8 to 12 hours to reach effectiveness but will last for several days Very few cardiovascular side effects Does not significantly contribute to vasodilation or hypotension Heating pads can increase transdermal uptake

31. Pre-anesthetic Medication Opioids Reversible by use of pure antagonists such as naloxone or nalmefene Compete with opioids for the specific receptor sites Possible to titrate the naloxone dose so as to remove the side effects yet maintain analgesia

32. Pre-anesthetic Medication Opioids Other effects in addition to analgesia Either stimulate or depress the central nervous system Depends on the dose, species and opioid agent Excitement occurs if given rapidly IV Horse and cat are particularly susceptible to excitatory effects Dogs generally show sedation although hypnosis can be seen in higher doses in sick animals Dogs that are not in pain may show excitement especially if given without any other agents

33. Pre-anesthetic Medication Opioids Other effects in addition to analgesia Cardiopulmonary effects Bradycardia Possible hypotension with release of histamine Especially if given IV Morphine and meperidine Increased muscle contraction in low doses Inotropic effect morphine

34. Pre-anesthetic Medication Opioids Other effects in addition to analgesia Respiratory depression is dose dependent Gastrointestinal effects depend on the agent May initially include diarrhea, vomiting and flatulence Constipation may occur as a result of prolonged GI stasis Addiction

35. Pre-anesthetic Medication Opioids Other effects in addition to analgesia Body temperature decreases and panting in dogs due to a resetting of the thermoregulatory center in the brain Miosis in dogs and pigs and mydriasis the cat and horse Increased responsiveness to noise Cough suppression Excessive salivation Sweating, particularly in the horse

36. Pre-anesthetic Medication Opioids Contraindications Previous history of opioid excitement Morphine has a higher incidence of producing vomiting so should be avoided in cases of GI obstruction and diaphragmatic hernia Classified as a narcotic in Canada and is a Schedule II controlled drug in the US

37. Pre-anesthetic Medication Phencyclidines (cyclohexamine) Ketamine (Ketaset, Ketalean, Vetalar) Tiletamine hydrochloride Telazol, in combination with zolazepam

38. Pre-anesthetic Medication Phencyclidines Produces cardiovascular stimulation Increases muscular rigidity Causes salivation

39. Pre-anesthetic Medication Phencyclidines Indications Immobilization of patient Mucous membrane application via the mouth is effective

40. Pre-anesthetic Medication Phencyclidines Contraindications Never use alone except in the cat Avoid as a preanesthetic medication in the dog Avoid in animals with seizure history Produces poor visceral analgesia Increases cranial pressure Increases ocular pressure Prolonged unreliable recoveries

41. Pre-anesthetic Medication Phencyclidines Convulsion effect can be ameliorated by combining with a tranquilizer Convulsive effect most likely seen in the dog Don�t use in cases with possibility of brain herniation Don�t use where perforation of the eye chamber is suspected

42. Pre-anesthetic Medication Neuroleptanalgesics Any combination of an analgesic and a tranquilizer (i.e. oxymorphone and acepromazine) Indications Heavier sedation (depending on dose) for short procedures (i.e. wound suturing, porcupine quill removal) Cardiac or shock cases

43. Pre-anesthetic Medication Neuroleptanalgesics Contraindications Animal may become hyperactive to auditory stimuli Animal may defecate or vomit May hyperventilate, or pant a lot May cause bradycardia

44. Injectable Anesthetics Brabiturates Propofol Cyclohexamines Etomidate Guaifenesin Fentanyl

45. Injectable Anesthetics Barbiturates Oxybarbiturates Phenobarbital Considered an anticonvulsant, not an anesthetic Pentobarbital (Nembutal, Somnotol Thiobarbiturate Thiopental (pentothal) Methylated oxybarbiturates Mehohexital (Brevital)

46. Injectable Anesthetics Barbiturates Also classified by speed of onset of action Long acting Phenobarbital 8-12 hours Short acting Pentobarbital 45 to 90 minutes Ultra short acting Thiopental 5-15 minutes

47. Injectable Anesthetics Barbiturates Can be used for sedation, anticonvulsants and anesthesia Commonly used as an induction agent Cause unconsciousness at adequate dosages Depress respiration and cardiovascular system to varying extents Give to effect Give as a bolus

48. Injectable Anesthetics Barbiturates Nonreversible Are protein binding Plasma protein levels can alter the rate and amount of absorption of the barbiturates The amount of free drug in the blood will increase if the patient is hypoproteinemic More drug will be available to penetrate into the CNS and cause unconsciousness

49. Injectable Anesthetics Barbiturates Are lipid soluble to varying degrees Lipid solubility increases from the long acting to the ultra short acting The more lipid soluble the easier it is for the drug to cross the blood brain barrier Also recover from the effects of the barbiturate quicker Recovery depends on a combination of redistribution and hepatic metabolism

50. Injectable Anesthetics Barbiturates As blood levels decline because of metabolism, small quantities of the drug will re-enter the bloodstream from muscle and fat Occurs at such a low level and rate that this pathway does not significantly alter levels of consciousness Eliminated from the body by liver metabolism and excretion of the metabolites in the urine

51. Injectable Anesthetics Barbiturates Examples Phenobabital Used mostly as a sedative for excitable dogs or as an anticonvulsant for epileptic type seizures Sedation can last up to 24 hours depending on the dose

52. Injectable Anesthetics Barbiturates Examples Pentobarbital Once commonly used for induction (now the ultra short is most common) Can be used to control seizures but EEG seizure activity will still exist Relatively non-irritating, can be given IM IV significant effect on the animal at one minute with maximum effect at 5 minutes Sheep recover fast and smooth. All other animals have a long rough recovery

53. Injectable Anesthetics Barbiturates Examples Thiopental Comes as a crystalline powder in multidose vials So can be reconstituted in varied concentrations Limited stability once reconstituted Avoid injecting air which may cause premature precipitation

54. Injectable Anesthetics Barbiturates Examples Thiopental Has a high lipid solubility Enters the brain rapidly Redistributes from the brain to other tissues, quicker recovery Redistributed to muscle and fat readily which slows metabolism by the liver Should be avoided in sight hounds because of prolonged recovery

55. Injectable Anesthetics Barbiturates Examples Thiopental Prolonged recovery will occur if subsequent doses have been given for maintenance of anesthesia and if the muscle and fat have been saturated Cumulative effect Recovery slow and rough Best to use only for induction or for a maximum maintenance effect of 30 minutes

56. Injectable Anesthetics Barbiturates Examples Thiopental Significant effect is noted 30 to 60 seconds after injection This barbiturate has a transient arrhythmogenic potential, especially if given by rapid bolus Transient apnea may also be noted Perivascular administration can cause extreme irritation and sloughing of tissue, especially at concentration greater than 2.5% Irrigate the affected tissue with saline Poor relaxation and analgesia when used alone Can be used in combination with propofol for induction

57. Injectable Anesthetics Barbiturates Examples Methohexital Highly lipid soluble, rapidly metabolized Quickest onset, shortest duration and quickest recovery Good choice in sight hounds or animals with extremely lean bodies Extremely sensitive due to poor ability to metabolize and lack of fat storage Liver metabolism is rapid, additional administration is not cumulative

58. Injectable Anesthetics Barbiturates Examples Methohexital Good choice for brachycephalics to obtain smooth, quick induction and intubation Rapid recoveries without hangover effects Induction effect is noted 15 to 60 seconds after injection Can get some convulsive activity in some animals during recovery Lethal dose is only 2 to 3 times the anesthetic dose Can cause profound respiratory depression

59. Injectable Anesthetics Propofol Used for sedation, induction, and/or anesthetic maintenance by repeated bolus injections or continuous infusion Rapid acting with smooth, excitement free induction Rapid smooth recovery because of redistribution to vessel rich areas such as the brain rather than to muscle and fat More easily and rapidly biotransformed by the liver in comparison to barbiturates Much less or no hangover effect First choice for sight hounds or others of similar body types�..if unavailable then methohexital Ideal for injectable maintenance of anesthesia because there is no accumulation

60. Injectable Anesthetics Propofol Minimal cardiovascular effects, but may cause Tachycardia Bradycardia Transient arterial and venous dilation Depressed cardiac contractility Despite these possibilities it is still considered safe in cardiac patients

61. Injectable Anesthetics Propofol Contraindications and cautions Transient apnea has been noted after rapid IV bolus injection Very dependent on how quickly the drug is given Has caused respiratory arrest in some cases Avoid in animals that are hypotensive Blood loss Dehydration Severe illness Recent trauma May see transient excitement and muscle tremors

62. Injectable Anesthetics Propofol Good anticonvulsant Non-irritating with incidental perivascular injection Some muscle relaxation occurs but analgesia is poor Will support bacterial growth because of soy content Opened vials should be discarded within 6 hours to avoid contamination

63. Injectable Anesthetics Cyclohexamines Classified as a dissociative anesthetic Examples include ketamine and tiletamine Produces catalepsy, amnesia and analgesia Inhibits N-methyl-D-aspartate (NMDA) Results in selective superficial analgesia Visceral pain is not abolished

64. Injectable Anesthetics Cyclohexamines Pharyngolaryngeal reflexes are partially intact Excessive skeletal muscle tone Can be minimized by prior administration of tranquilizers, sedatives or benzodiazepine Mild cardiac stimulation Increased blood pressure Decreased cardiac contractility Increased heart rate May induce pulmonary edema or acute heart failure in animals with pre-existing heart conditions

65. Injectable Anesthetics Cyclohexamines Apneustic breathing Rate may increase Arterial pCO2 may be decreased Especially seen after IV administration Hyperresponsive and ataxic during recovery Small percentage of cats will show convulsive activity Minimally sensitizes the heart to catecholamine induced arrhythmias

66. Injectable Anesthetics Cyclohexamines Other side effects Tissue irritation Increased salivation and lacrimation Increase in CSF pressure Open eyes with central dilated pupil Nystagmus Increased intraocular pressure Temporary personality changes Excitement on recovery

67. Injectable Anesthetics Cyclohexamines Effects partially reversed with adrenergic and cholinergic blockade Dogs more likely to seizure Combine with a tranquilizer (acepromazine or diazepam) Metabolized by the liver and excreted somewhat in an unchanged form through kidneys in dog Excreted primarily by kidneys in cat Use with caution in animals with renal or hepatic disease Can be used in cats with urethral obstruction provided no disease is present and obstruction is removed Use with caution in seizure disorders or those undergoing neurological system procedures

68. Injectable Anesthetics Cyclohexamines Ketamine Commonly combined with diazepam or other benzodiazepines as an induction agent Provides muscle relaxation and smoother recoveries than with ketamine alone In species where IV administration is not possible or easily accessible, ketamine can be combined with midazolam and given IM

69. Injectable Anesthetics Cyclohexamines Tiletamine Combined in commercial form with zolazepam (benzodiazepine) in product called Telazol Can be used in all animal species Same action as ketamine/diazepam but can be given IM or subQ Good for exotics and aggressive animals

70. Injectable Anesthetics Etomidate Very safe Rapid and ultrashort acting Rapidly distributing Noncumulative

71. Injectable Anesthetics Etomidate Interacts with GABA receptors Has little or no effect on cardiac output, respiratory rate or blood pressure Very popular for animals with cardiac disease Can be given as repeated bolus or continuous infusion Occasionally may cause vomiting, diarrhea, excitement and apnea on induction and recovery Is a mild respiratory depressant

72. Injectable Anesthetics Etomidate Does not produce a histamine release Produces excessive muscular rigidity and seizures in horses and cattle Rapidly metabolized in the liver Does cross placental barrier but effects on the fetus are minimal as it is rapidly cleared IV injection may be painful and may cause phlebitis especially in the smaller veins

73. Injectable Anesthetics Guaifenesin Glycerol guiacolate Available in white powder; resuspended with sterile water or dextrose Common decongestant and antitussive Used for it�s effect as a central muscle relaxant, mostly in large animals Minimal effects on the diaphragm at relaxant doses Induction and recovery are excitement free Minimal respiratory and cardiac effect Does cross placental barrier but effects on fetus are minimal

74. Injectable Anesthetics Fentanyl Considered primarily an analgesic Can produce unconsciousness Used as an injectable induction agent often in combination with a tranquilizer, sedative or benzodiazepine Referred to as a neuroleptanalgesic Very safe for high risk patients because it does not cause apnea and does not affect cardiac output or contractility

75. Inhalation Anesthetics General considerations Are vapors or gases that are directly absorbed into the bloodstream through the lungs Are rapidly absorbed from the alveoli to the brain Primarily eliminated unchanged by the lungs Biotransformation to metabolites does occur to some degree, by microsomal enzymes

76. Inhalation Anesthetics General considerations Factors that affect the brain concentrations of volatile anesthetic include Delivery of suitable concentrations of agent Factors responsible for delivering the anesthetic from the lungs Factors that affect the lung, brain and tissue uptake

77. Inhalation Anesthetics General considerations Factors that affect the brain concentrations of volatile anesthetic include Delivery of suitable concentrations of agent Vapor pressure Boiling point Anesthetic system

78. Inhalation Anesthetics General considerations Factors that affect the brain concentrations of volatile anesthetic include Factors responsible for delivering the anesthetic from the lungs Alveolar partial pressure of the agent The inspired concentration of the agent The alveolar concentration

79. Inhalation Anesthetics General considerations Factors that affect the brain concentrations of volatile anesthetic include Factors that affect the lung, brain and tissue uptake Solubility Tissue and arterial blood flow Anesthetic concentration Type of tissue and it�s blood supply

80. Inhalation Anesthetics General considerations Factors that affect the lung, brain and tissue uptake Solubility Increased solubility leads to slow induction and recovery Solubility is measured by the blood-gas partition coefficient, the solubility of an agent in the blood Higher the number the greater the solubility Larger amount of agent must be taken in before anesthesia results

81. Inhalation Anesthetics General considerations Potency of inhalation anesthetic agents often expressed as MAC (minimum alveolar concentration) The minimum concentration of an anesthetic that produces no response in 50% of the patients exposed to painful stimuli The lower the MAC the more potent the anesthetic A lower concentration is required to maintain a similar anesthetic depth Values vary among species and are affected by age, temperature, disease, other CNS depressant drugs and pregnancy

82. Inhalation Anesthetics Advantages (over injectable agents) Easier to control and change depth Excreted mainly by respiration Recovery is rapid and there is little metabolism Requires administration of oxygen to the patient Endotracheal tube is present so patent airway is available Minimal respiratory and cardiovascular depression Provides some analgesia and muscle relaxation Less accumulation

83. Inhalation Anesthetics Examples Methoxyflurane (MAC 0.23%) Most potent inhalation anesthetic Advantages Good analgesia and muscle relaxation Minimal arrhythmogenicity low vapor pressure, can be used with a precision or non-precision vaporizer Slow plane changes reduces chance of sudden overdose

84. Inhalation Anesthetics Examples Methoxyflurane Disadvantages Increased solubility so slower induction and recovery Possible renal toxicity Respiratory depression at deep surgical planes Slow response to changes in concentration May be a concern if surgical bleeding occurs Not suitable to mask induction because of excitement that may occur Environmental pollution concern

85. Inhalation Anesthetics Examples Methoxyflurane Due to concerns over safety of personnel administering methoxyflurane, as well as documented increase in birth defects and impairment of kidney and liver function, this is no longer a commonly used inhalation agent If used an ACTIVE scavenger system must be in place Systems should be leak tested and maintained meticulously All reasonable precautions should be taken to avoid inhalation by personnel

86. Inhalation Anesthetics Examples Halothane (MAC 0.8%) Advantages Less respiratory depression Lower solubility that methoxyflurane Faster induction Faster recoveries Faster response to changes in concentration Not nephrotoxic Can mask induce

87. Inhalation Anesthetics Examples Halothane (MAC 0.8%) Disadvantages Higher vapor pressure requires an out of circle precision vaporizer for maximum safety Arrhythmogenic potentials Cardiac depression resulting in hypotension (dose related) Little analgesia Hepatotoxic

88. Inhalation Anesthetics Examples Isoflurane (MAC 1.2% in dogs, 1.6% in cats) Advantages Cardiovascularly safer with reduced arrhythmogenicity and better cardiac output Minimal liver metabolism Lower solubility Faster induction Faster recoveries Faster response to changes in concentration (faster than halothane)

89. Inhalation Anesthetics Examples Isoflurane Disadvantages Respiratory depression Occasional stormy recoveries More expensive Similar higher vapor pressure as halothane, therefore requires an out of circle precision vaporizer Vasodilation results in similar blood pressure as with halothane

90. Inhalation Anesthetics Examples Sevoflurane (MAC 2.4%) Advantages Low solubility Extremely rapid induction and recoveries Nonpungent Produces good muscle relaxation and analgesia Nonarrhythmogenic

91. Inhalation Anesthetics Examples Sevoflurane Disadvantages Respiratory depression similar to isoflurane Rapidly crosses the placental barrier and will cause fetal depression Much more expensive than halothane or isoflurane

92. Inhalation Anesthetics Examples Sevoflurane It is commonly held that this agent is superior to other inhalation anesthetics for most avian species (nondocumented) The smooth rapid induction and recovery minimizes stress on these delicate patients Slight hangover that is present with other inhalants is lessened or absent

93. Inhalation Anesthetics Examples Desflurane (MAC 7.2%) Advantages Extremely low solubility Extremely rapid induction Extremely rapid recovery No hepatotoxicity or nephrotoxicity

94. Inhalation Anesthetics Examples Desflurane Disadvantages Requires a special electrically heated vaporizer Very expensive Pungent and produces airway irritation Provokes coughing and breath holding Mask induction is difficult Can cause malignant hyperthermia in some species Recovery may be too rapid Unpleasant recoveries May require re-sedation

95. Inhalation Anesthetics Examples Nitrous Oxide Advantages Can be used to speed inhalation induction by second gas effect Initially passes from the alveoli into the blood in large volumes The inhalant agent and oxygen are at a lower percentage Effectively increases the concentration of the inhalant agent and oxygen in the alveoli Availability to the blood is affected

96. Inhalation Anesthetics Examples Nitrous Oxide Advantages Provides additional analgesia (varies by species) When used during anesthesia maintenance, it reduces the amount of other anesthetic agent required Minimal cardiovascular and respiratory effects No metabolism

97. Inhalation Anesthetics Examples Nitrous Oxide Disadvantages Cannot be used alone (MAC >100%) Danger of hypoxia if not used properly Reduces inspired oxygen levels to 33% Danger of hypoxia if used in patients with respiratory problems Pneumonia, lung tumors, pulmonary edema, diaphragmatic hernia, or other conditions which compromise the patients ability to oxygenate Cannot be used with animals with gas occupying cavities (i.e. gastric dilation, intestinal obstruction, pneumothorax) Has an increased partial pressure and low solubility in blood Will diffuse into gas occupying cavities faster than the rate at which resident gases leave Causes increased pressure in these cavities

98. Inhalation Anesthetics Examples Nitrous Oxide Method of use For mask induction Initially use 100% O2 with gradual increases in percentage of the inhalant anesthetic agent When high levels of inhalant agent are reached turn on N2O at an N2O:O2 ratio of 2:1 to continue induction This provides 66% N2O / 33% O2

99. Inhalation Anesthetics Examples Nitrous Oxide Method of use If you plan to use N2O as part of your anesthetic maintenance continue with the 2:1 ratio To insure adequate oxygenation of the patient Never have the oxygen levels below 500 mL/min (flow meters may not be accurate below these levels) Never have O2 levels below 30 mL/kg/min (3 times the metabolic requirement)

100. Inhalation Anesthetics Examples Nitrous Oxide Method of use When using N2O with a partial rebreathing or non-rebreathing system make sure total gas flow is at least 130 mL/kg/min of which 33% should be oxygen If the patients oxygen saturation or mucus membrane color deteriorates (gray, cyanotic) at any time throughout the procedure it is best to discontinue nitrous in case hypoxia is impending

101. Inhalation Anesthetics Examples Nitrous Oxide Method of use When the procedure is complete Turn off the N2O at the same time as the inhalant agent If N2O is turned off too soon you may be withdrawing a necessary analgesic source and will have to increase the inhalant anesthetic agent to continue the procedure Increase the O2 flow rate to 100 mL/kg/min with a rebreathing system or 300 mL/kg/min with a non-rebreathing system

102. Inhalation Anesthetics Examples Nitrous Oxide Method of use Keep the patient on this increased flow rate for at least 5 minutes to prevent diffusion hypoxia When N2O is turned off, there is a flow of N2O from the blood back into the alveoli Displaces the oxygen in the lower respiratory tract and limits oxygen availability to the patient

103. Inhalation Anesthetics Examples Nitrous Oxide Method of use Observe the patient for at least 5 minutes after O2 source is removed Insure that the patient is oxygenating well on room air Especially note mucus membrane color and capillary refill time Supplemental O2 by face mask should be used if necessary