Exploration Activity

1. Exploration Activity • Read pages 51-118 of anesthesia text. • 1. Pre-medication • calms or sedates • reduces side effects of general anesthetics • reduces amount of general anesthetic required • decrease pain and discomfort post-operatively

2. Definition • General Anesthesia • is a state of controlled and reversible unconsciousness characterized by a lack of pain and memory with decreased reflex responses to all manner of stimuli. • Boredom punctuated by panic!!!

3. GA Induction • 2 ways to induce general anesthesia • injection • Inhalation • Using a hammer is not an acceptable practice • Sleep is not a form of anesthesia

4. Balanced Anesthesia • A technique where several different drugs are given in order to anesthetize an animal with a greater margin of safety. This decreases the required dose of each and diminishes the possibility of toxic effects from any one drug.

5. Components of GA • Pre-medication/pre-anesthetic • Induction • Maintenance • Recovery

6. Induction • The process by which an animal leaves the normal conscious state and enters a state of anesthesia is know as anesthetic induction. • It is performed 10-20 minutes after pre-medication (Depending if IM or subQ) • The patient normally has a decreasing state of consciousness during induction but there can be an excitement phase in the middle.

7. Induction • Inducing agents are generally very short acting so we generally intubate and put the patient on gas anesthetic as a maintenance anesthetic.

8. Maintenance • Achievement of a stable period of anesthetic where surgery and other painful or involved and precise procedures can be performed. • The patient is stable and unchanging, but is in a state of unconsciousness that is not allowed to become excessive or light. It is unresponsive to stimuli like noise, pain, and light. The level or depth of anesthesia is variable depending on the type of surgery being done. (dental cleaning versus bone surgery)

9. Monitoring respiration • Watch anterior thorax • Watch rebreathe bag • Monitor flutter valves • Check movement of abdomen • Abdominal movement, when excessive, may indicate difficulty breathing.

10. Recovery • Recovery is the return to the conscious state after anesthetic. This achieved by lowering the concentration of the anesthetic to low and eventually zero amounts. It can also be achieved by administering reversal agents for the specific drug administered.

11. Drug exit from the body • Injectable drugs exit through the liver and kidneys. • Thiobarbituates are redistributed in body fat, for initial recovery and then slowly metabolized by the liver and excreted through the kidneys. • Inhalation agents are primarily excreted through the lungs although in some there is metabolism in the liver as well.

12. General Anesthetic Death • Can occur because of suppression of cardiovascular, respiratory or thermoregulatory function. • Must monitor the heart and respiration, color, capillary refill time, temperature and amount of anesthetic and oxygen and other anesthetic gases at all times at regular intervals (at least every 5 minutes with a stable patient)

13. Big things to monitor • Heart (rate and rhythm) • Respiration (rate and depth) • Color and capillary refill time • Temperature of patient • total amount of drugs and other substances given

14. Strategies to increase safety- pre-meds • Anticholinergics-increase heart rate and perfusion • Sedatives- decrease amount of anesthetic given and make induction easier. • Management during induction–by injections • give minimum dose needed to achieve goals. Monitor continuously. • Titration or “give to effect”-means that the patient is monitored and the administration of anesthetic drug is halted when a certain level of anesthesia is reached.

15. Patient individuality • Age, breed, physical condition, pre-anesthetic drugs given and the health of the heart, lungs, liver, and kidneys and the animals ability to excrete the drugs affect response to anesthetic . • We can determine how much the patient needs by knowing as much about them as possible, knowing the drug we are giving very well and titrating to effect.

16. Recovery room dangers • Not through all of the dangers at that time. • Can still vomit, laryngospasm, convulse, develop hypothermia and cardiac and respiratory arrest. Can have post op hemorrhage or post-op shock. • Therefore we must continue to monitor closely in the post op area. • Studies have shown this is the stage of anesthesia where we have the highest death rate

17. Classic Stages and Planes of Anesthesia • Page 55-58 of text • Too light • disoriented • struggling, vocalizing, paddling, chewing, yawning (excitement phase) • reflexes present but diminished • muscle tone strong at beginning and then diminishes.

18. Classical Stages and planes of Anesthesia • Adequately anesthetized • regular respiratory pattern • gagging and swallowing reflexes diminished or absent • Palpebral reflex diminished or absent • unconscious and stable • non-responsive to pain or other stimuli • heart rate and bp normal or only slightly decreased. • Capillary refill <2 sec. • Mucous membranes pink and warm

19. Classic stages and planes of anesthesia • Too deep • spasmodic respiration or cessation of respiration • significantly decreased heart rate, blood pressure • Pale and cold mucous membranes • capillary refill delayed • total skeletal muscle relaxation, no jaw tone

20. Dog spay exploration activity • Page 10 of course pack • 1. Reception history • pre-starve? For how long? • How is her recent health? Any health history? • Family history of anesthetic problems? • Other patient signalment stats • Others?

21. Pre-anesthetic exam • Temperature • heart rate and quality of pulse and rhythm • respiration rate and quality • capillary refill and mucous membrane color • attitude and demeanor of patient • pre-anesthetic blood panel

22. Premedication • Acepromazine • 11.3kg X 0.05mg/kg = 0.565mg • .565 mg/10mg/ml =.0565 ml = .06 ml. • How do you draw up such a small amount • Atropine • 11.3 kg x .02 mg/kg = .226 mg • .226 mg/.5 mg/ml = .452 ml = .45 ml

23. Net effects of ace and atropine • Mild sedation • slight increase in heat rate and bp • makes her more susceptible to other anesthetic drugs • wait 6 - 10 minutes after administration IM of pre-anesthetic agent before giving anesthetic.

24. Anesthetic induction • Goes from fully awake and aware to a drowsier stage. • Becomes disoriented and can become excited. May vocalize and struggle. • Progresses to paddling and whining • muscle tone decreases over time • heart rate will increase then decrease to a lower stable level. • Muscle tone decreases over time. • Pain sensation decreases over time.

25. Responses to surgery • Respiration will increase with stimulation • heart rate increases and bp and pulse also • Major increase in all parameters with first cut or manipulation of the abdominal organs if too light a plane of anesthesia. • Mucous membrane color should remain pink • CRT should remain <2 seconds

26. Practical Application Activity

27. Induction with inhalation agents (pages 62-64) • Reception presentation- an example • This is Fluffy Ness, a Birman cat, here for a spay&declaw. She has been pre-starved for 12 hrs and no water for 3 hours. Last vaccines were in October last year and September before that. She is not in heat and she has never had kittens. She is strictly an indoor cat. She has had a string removed from under her tongue with anesthetic (with no complications using isoflurane) when she was a kitten but has had no other health problems.

28. Fitting mask • Fits tight over face without leakage (should cover entire mouth) • minimize dead space (space between nose and inlet hose) • avoid traumatizing eyes and nose • do not put pressure on trachea

29. Method of induction of cat • Restrain by wrapping in a large towel or in a cat bag • short end close to handler & fold large end over the body and then put weight on it with the neck firmly restrained. • 30 secs of O2 • 10 sec ea of 1,2 ,3,4 % gas (halothane or isoflurane) • monitor until cat becomes lightly anesthetized and then unwrap. • Turn down to 3 % as it gets deeper (pedal reflex still present) and 2% when at a surgical plane (no pain response)

30. Mask induction • Job of assistant is to monitor level of anesthetic depth and communicate it to the other members of the anesthetic team. • Has a very noticeable excitement phase with gas induction, not seen with thiopental or propofol. • Restrainer unwraps cat after excitement phase is finished.

31. Unwrapping the cat • 1st step in deciding to unwrap based on muscle resistance. • Start by laying cat in lateral, if it is still awake it will try and right itself. • Reach under the towel and grab the cats hind legs. Pull on the legs to feel the level of muscle tone. • May unwrap front legs if little resistance is felt. • If still moving, grab front legs and restrain in hand with finger between legs. • It is important to get the cat unwrapped ASAP to be able to visually evaluate the cat and test for muscle tone, pedal reflex, and observe respiration.

32. Communication between partners • Restrainer should continually update the anesthetist about the patients condition and level of anesthesia, so that the anesthetic can be turned down from 4% before the patient gets too deep. • Should be at 3% when no longer struggling. • Monitor pedal reflex and patient should be down to 2% when pedal is absent.

33. Important Habits to develop • Report cats condition out loud to all concerned. • It is better to be slightly light than too deep • You cannot turn the anesthetic down when the animal has died or gone into arrest and expect a favorable outcome. • Once cat is deep enough, move on to the 5 pt. Monitoring process. Check and then prep for surgery. We should keep our patient down for as little time as possible. Don’t dawdle and keep pressing forward. • Time is trauma

34. Hints • Don’t be slow. Some patients go down very quickly. Change levels of anesthetic as soon as reflex is absent. • Turn down too soon rather than too late. Restrain adequately until the muscle tone is diminished. (Halothane with cats that scream) • Can turn down to maintenance level before fully at surgical plane. The patient has time to deepen during surgical prep. • Move on as soon as an animal reaches the surgical plane of anesthesia. • Time is trauma!!

35. Masking down small dogs • Mostly like cat • often don’t need to towel restrain. No sharp claws. • Restrain in a conventional hold. Use several people for larger, stronger dogs. • Use the same reflexes.(muscle tone, palpebral, pedal) • We routinely intubate dogs, thus always assess jaw tone. It will not disappear as rapidly when induced with thiopental.

36. Masking down small dogs • When jaw is slack, place dog in sternal with hind legs in frog position. Hold head with mouth open for anesthetist to intubate. • The anesthetist, who is prepared in advance, removes the mask, intubates, then reattaches the anesthetic vaporizer to the tube. • The vaporizer setting is based on the animals reaction to the tubing process. Turn it up if it is chewing and leave at maintenance if stable. • If chewing with tube in, firmly restrain the jaw

37. INDUCTION WITH THIOPENTAL • Page 59-60 of text book • Advantage- very rapid progress to surgical plane of anesthesia. Mostly circumvents the excitement phase that we see with mask induction with a gas anesthetic. • A standard dose is drawn up in a syringe, then administered IV as needed to allow endotracheal intubation and maintenance on gas anesthetic.

38. Induction with Thiopental • Can be used by itself for minor and quick procedures, but should not be used for extended procedures because the accumulation of the drug in the body may result in very prolonged recovery. • Examples of minor procedures may be x-rays, porcupine quills, endoscopy, or skin biopsy.

39. Induction with thiopental • Normally, patient is pre-medicated with a “cocktail” like BAG. This allows for a lower dose of the inducing agent and a smoother induction with greater safety. Butorphenol, acepromazine, glycopyrollate. • Standard dose is calculated based on weight (10-18 mg/kg) and then 1/2 that dose is injected rapidly IV over a period of about 10 seconds to get to a surgical plane of anesthesia without much excitement. Coursepack calculations • 10mg/kg x 28.4kg = 284 mg / 40mg/ml=7.1ml • 18mg/kg x 28.4kg = 511 mg / 40 mg/ml=12.8ml

40. Induction with thiopental • If patient is deep enough, the procedure is performed without any further anesthetic if it is minor and quick. • If surgery is more involved, the patient is intubated and placed on an anesthetic gas to maintain anesthetic more or less indefinitely.

41. Induction with Thiopental • Thiopental is an irritating chemical with a very alkaline pH. (pH>9) If it goes perivascularly it will cause an inflammatory reaction. • It is useful to give through a preset catheter and administer the lowest concentration that can be handled easily. (2.5% for dogs and cats, 10% for large animals). • If it does go perivascular, infiltrate the area with an equal amount of lidocaine which is acidic and it will neutralize the high pH solution. The follow up with 10x the volume of isotonic saline as a diluent.

42. Thiopental math • We normally discuss doses in gm %. • This means that 2% is 2gm thiopental /100ml sterile water or 20mg/ml. • 5% is 5gm/100ml or 50 mg/ml • How do you make a 4% solution if you have a vial with 1 gm.of thiopental. • Answer: add 25ml sterile water to 1 gm of thiopental.

43. Thiopental Induction Apnea • Apnea means lack of breathing. • Often patient will stop breathing immediately after induction. • Very important to monitor closely at this time. • Watch color, CRT, look at chest, auscult with a stethoscope. • If patient won’t breath- the NAIT way • extend hind legs fully, this stretches the diaphragm. • Feel chest for heart beat, give a gentle squeeze. • Check color/crt and pull on tongue.

44. Thiopental Induction Apnea • If not breathing, do again. • If still not breathing, intubate and inflate the patients lungs at a regular interval. • One theory is that we change the body’s normal reflexes with anesthetic. As we get deeper under anesthetic our body no longer responds to lack of O2 to stimulate the breathing but responds to an increase in CO2 to stimulate breathing.

45. Thiopental Induction Apnea • At induction we go from O2 deprivation driving respiration to CO2 buildup driving respiration. • As an anaesthetic proceeds and thiopental is absorbed, the animal reverts back to O2 drive. • This impacts on how much the animal breathes at the beginning, middle and end of the procedure. • This is a very important reason for the need for constant monitoring. • The animals reflexes and needs will actually change over time.

46. Administration of Thiopental • Calculate the dose for the patient • try and use the minimal dose to achieve your procedural goal. • Range is 10-18 mg/ kg. • Younger animals require a higher dose. • Smaller animals require a higher dose. • Underweight animals require a lower dose or possibly a different drug. • Don’t give to animals with liver disease because after redistribution in body fat, it is ultimately broken down in the liver.

47. Examples • Don’t use on greyhounds. • Chance will remain anesthetized for 6-8 hours with barbiturates while Daisy is under for 20 minutes. • Draw up a dose of 18mg/kg for a 10 kg. hyper terrier and draw up a dose of 10 mg/kg for a 9 year old German Shepherd. • Give 1/2 iv and then wait up to 30 seconds to evaluate the effects. If not enough give another 1/2 of what’s left and wait another 30 seconds. Do this until the animal is deep enough or you run out of drugs.

48. Examples • REMEMBER!! • Every patient is different and you DOSE TO EFFECT. • Age, size, % body fat, and health status all affect the animals reaction to the drugs. • There are more unusual drug reactions to anesthetic drugs than any other drug. • Always be prepared for the worst case scenario.

49. NAITS five things • Heart rate and character • respiration rate and character • MM color/CRT/ temperature • 02 flow and concentration of anesthetic gas • fluid admin rate and total fluids • remember that other facilities may do things differently, but it really is only a variation of this program. • Other useful things are jaw tone, palpebral reflex and eye position.

50. Endotracheal intubation • Pages 65-75 of text book • We will practice this technique at the SPCA in February. • Definition: • placement of a breathing tube into the trachea to facilitate the administration of anesthetic gas and O2 and by passing the nasal passages, oral cavity and pharynx.