Introduction to Anesthesia Jody Nugent-Deal, RVT, VTS (Anesthesia/Analgesia) (CP-Exotics) Check out chapters 1 and 2 in your textbook!! Anesthesia and Analgesia for Veterinary Technicians, 5 th edition 3 1
Why is anesthesia so cool? 4 Brief History of Anesthesia Naturally derived anesthetics have been used since 1500 BC Plant extracts 1500-1700 AD experiments with inhaled chemical agents Diethyl either Chloroform Nitrous oxide Not widely used until mid-1800 s in humans 5 Brief History of Anesthesia Veterinary community did not start using anesthetics until the mid-20th century Started with inhalants, but the invention of injectable barbiturates revolutionized veterinary anesthesia 1930 s 1950 s halothane and methoxyflurane, 1960 s acepromazine, xylazine 1970 s ketamine 1980 s isoflurane, propofol 1990 s - sevoflurane 6 2
Where Are We Now? Great advances in the last several decades Now have specialties in the field of anesthesia and analgesia The Academy of Veterinary Technician Anesthesia and Analgesia www.avtaa-vts.org American College of Veterinary Anesthesia and Analgesia www.acvaa.org 7 Basic Terminology Anesthetic drugs depress the CNS Anesthesia Without feeling or insensibility Loss of sensation General anesthesia Reversible state of unconsciousness, immobility, muscle relaxation, and loss of sensation throughout the entire body produced by the use of one or more drugs Surgical anesthesia Specific stage of general anesthesia in which there is a sufficient degree of analgesia and muscle relaxation to perform surgery without pain or movement 8 Basic Terminology Sedation Drug-induced CNS depression varies from light to deep or heavy Sedated patients are generally aware of surroundings still an can be aroused by noxious stimuli Dexmedetomidine + opioid Tranquilization Drug-induced state of calm in which a patient is reluctant to move and is aware of their surroundings but unconcerned about what is going on around them acepromazine These two terms are often used interchangeably although they are not really the same 9 3
Basic Terminology Hypnosis Drug-induced sleeplike state that impairs the ability of the patient to respond appropriately to stimuli Etomidate Narcosis drug-induced sleep from which the patient is not easily aroused and is associated with the administration of narcotics Fentanyl CRI 10 Basic Terminology Local anesthetic Loss of sensation in a small area of the body produced by administration of a local anesthetic in the proximity of the area Lidocaine or bupivicaine injection Topical anesthetic Loss of sensation of a localized area produced by administration of a local anesthetic directly to a body surface Ophthalmic drops or lidocaine jelly 11 Basic Terminology Regional anesthesia Loss of sensation in a limited area of the body produced by the administration of a local anesthetic and/or other agent Nerve block or epidural Balanced anesthesia Uses multiple drugs to maximize the benefits of each drug and minimize adverse effects. Gives the anesthetist the ability to provide anesthesia, analgesia, muscle relaxation, and potentially immobilization depending on the type of drugs used. CRI, epidural, nerve blocks, pre-medications, etc. 12 4
The Technician s Role What is our role in anesthesia? Intake of the patient Physical examination/assessment Knowledge of anesthetic agents and equipment Protocol selection with veterinarian Set-up and operation of anesthetic supplies Induction and monitoring Knowledge of advanced techniques Catheter placement Ability to calculate drugs Intubation... Recovery 13 Anesthesia is awesome!! 14 Anesthetic Fundamentals Most anesthetic agents have a low therapeutic index Must calculate properly to avoid overdose Significant changes in cardiovascular and respiratory function Cardiac output Heart rate Respiratory rate and tidal volume Blood pressure Core body temperature You MUST monitor your patient!!! 15 5
Anesthetic Fundamentals Must assess the basics MM, CRT, HR, RR, temperature, jaw tone, eye position, blood pressure, etc. Understand the monitors you are using and know their limitations Must know what is normal before you can understand what is abnormal Must keep detailed and accurate anesthetic records 16 Patient Preparation Complete PE performed by the veterinarian and the technician inducing and maintaining anesthesia Auscultation of heart and lungs Diagnostics Minimum PCV, TS, AZO, BG Ideally a full CBC and chemistry panel is performed Radiographs Echocardiogram Special diagnostic tests 17 Patient Preparation PCV- measurement of total blood volume Elevated = dehydration and less circulating blood volume Decreased = anemia decreased production or destruction of RBCs or loss of blood volume Plasma protein measurement of blood protein Elevated = dehydration Decreased = decreased protein production by liver Liver may have a difficult time metabolizing drugs Tissue edema Difficulty maintaining adequate blood volume 18 6
Patient Preparation WBC neutrophils, basophils, eosinophils, monocytes, lymphocytes Increased infection, high parasite count, etc. Decreased cancer Platelets essential to blood coagulation Urinalysis kidney function USG can the kidneys concentrate urine 19 Patient Preparation Chemistry assesses multiple organ system within the body Electrolytes, kidney and liver function Blood Coagulation PT, APTT, BMBT Performed on those that have a known clotting disorder or poor liver function 20 Patient Preparation Radiographs should be taken as needed based on patient condition Echocardiogram should be performed as needed based on patient condition Misc. tests should be performed as needed based on patient condition 21 7
Body Condition Scoring Page 17 in 5 th edition textbook BCS ranges from 1-9 with 1 being emaciated and 9 being grossly obese BCS important to help assess overall wellbeing of patient as well as drug calculation Drug calculation based on lean body weight 22 Patient Preparation What happens when the owner refuses to run diagnostics? What happens when the owner refuses an IV catheter? 23 Working With Clients Patient history Ask the right questions! Do not ask yes and no questions. Does your dog drink a normal amount of water per day? incorrect Your dog doesn t drink much water, does she? incorrect How much water does your dog drink per day? correct 24 8
Working With Clients What should we ask the client during intake? What is the duration of? What is the volume or severity of? What is the frequency of? What does look like? 25 Working With Clients Ask detailed questions about patient history and previous medical issues. Has the patient had any negative reactions to anesthesia before? Is the patient experiencing any exercise intolerance, weakness, seizures, fainting (syncope), any other behavioral changes 26 Working With Clients Always confirm procedure and the surgery site Ensure the owner understands the estimated costs Always confirm the owner s wishes regarding diagnostics Clinical pathology Ensure you have a number to reach the owner quickly in the event of an emergency 27 9
Basic Anesthetic Fundamentals Planning the anesthesia includes critically thinking about the procedure, species, drug availability, and pain expected The signalment- species, breed, age, sex and reproductive status helps in preparing for anesthesia Huge difference between anesthetizing a 50 year old parrot and a 1 year old lab 28 Basic Anesthetic Fundamentals Each species has a unique response to anesthetic drugs Some species and even some individuals are more sensitive to opioids compared to others. Does this mean we don t use opioids in that population? Nope! We are just more cautious. Dosing requirements vary across species Horses may have rougher recoveries from inhalants compared to other species 29 Basic Anesthetic Fundamentals Anticholinergics are avoided in ruminants due to thickened secretions Ruminants more sensitive to xylazine Dogs can show seizure-like activity when given ketamine alone Horses may fracture limbs on recovery and require special attention Ruminants are prone to bloat 30 10
Basic Anesthetic Fundamentals Boxers and giant breeds are more sensitive to acepromazine Brachycephalic animals have hypoplastic tracheas, everted saccules, elongated soft palate, stenotic nares, prone to obstruction Sighthounds are sensitive to barbiturates 31 Basic Anesthetic Fundamentals Pediatric, neonatal and geriatric patients are less capable of metabolizing injectable drugs due to hepatic function Slow recovery May need lesser dose 32 Preparing For Anesthesia Proper patient identification is essential Compare patient ID with patient scheduled for surgery Ensure correct surgery is being performed on the correct area Seems like common sense but mistakes happen in every hospital regardless of human or veterinary, large or small 33 11
Hydration Assessment Dehydrated patients may need to be stabilized prior to anesthetic induction Often fluids overnight or a bolus prior to induction will help correct fluids deficits How is hydration assessed? Look at MM are they moist or tacky Tent the skin between the shoulder blades Look at the eyes 34 Assessing Hydration < 5% dehydrated Not detectable ~ 5% dehydrated Mild dehydration Minimal loss of skin turgor, semi-dry MM, normal eyes ~ 8% dehydrated Moderate dehydration Moderate loss of skin turgor, dry MM, weak pulses, sunken eyes > 10% dehydrated Considerable skin turgor, extremely MM, tachycardia, weak/thready pulse, hypotension, severely sunken eyes, altered state of consciousness 35 Assessing Level Of Consciousness LOC patient s responsiveness to stimuli Decreased LOC indicates abnormal brain function Drugs, brain function, dehydration, neurologic disorders Normal responsiveness is alert and reponsive BAR QAR Lethargic mildly depressed Obtunded very depressed Stuporus sleeplike state not responsive Comatose cannot be aroused by any means 36 12
ASA I American Society of Anesthesiologists (ASA) Physical Status Scale Minimal Risk Normal healthy animal, no underlying disease ASA II Slight risk, minor disease present Animal with slight to mild systemic disturbance, animal able to compensate Neonate or geriatric animals, obese ASA III Moderate risk, obvious disease present Animal with moderate systemic disease or disturbances, mild clinical signs Anemia, moderate dehydration, fever, low-grade heart murmur or cardiac disease American Society of Anesthesiologists (ASA) Physical Status Scale ASA IV High risk, significantly compromised by disease Animals with preexisting systemic disease or disturbances or a severe nature Severe dehydration, shock, uremia, or toxemia, high fever, uncompensated heart disease, uncompensated diabetes, pulmonary disease, emaciation ASA V Extreme risk, moribund Surgery often performed in desperation on animal with life threatening systemic disease Advance cases of heart, kidney, liver or endocrine disease, profound shock, sever trauma, pulmonary embolus, terminal malignancy E denotes emergency Protocol Selection Facilities and equipment Familiarity with anesthetic agent Type of procedure Cost of drugs Degree of urgency 39 13
Pre-induction Care Ensure that the patient has been properly fasted Species specific Age specific Disease specific Dogs and cats prone to vomiting after premedications and regurgitation of food if not fasted properly normal patients 12 hours without food and water 40 Regurgitation If a patient regurgitates during anesthesia, MUST lavage esophagus and oral cavity Check ph of contents If ph less than 4 should add sodium bicarb to flush to neutralize acid Reduces strictures of the esophagus 41 Catheterization ALL patients should have an IV catheter placed prior to anesthesia Very few exceptions to this rule Why is this necessary? Need a patent IV catheter to provide fluid therapy, blood products, CRIs, positive inotropes, vasopressors, emergency drugs It should NEVER be the owners choice on if a catheter is placed!!! Some drugs can cause tissue sloughing if administer outside the vessel 42 14
Catheterization Common vessel sites Species dependent Canine cephalic, lateral saphenous, jugular Feline cephalic, medial saphenous, jugular Many different ways to tape and secure an IV catheter Jugular catheters can consist of a regular insyte catheter or a multi-lumen catheter 43 IV Catheter 44 Catheter Placement Set-up supplies prior to animal being present Choose a few different catheter sizes Have tape and gauze prepared Flush Clip generous area Use aseptic technique Chlorhex scrub Saline Choose largest bore catheter 45 15
Fluid Therapy Body is made up of about 60% water Body water separated by cell membranes Intracellular within cells Extracellular outside cells Interstitial fluid compartment Intravascular fluid compartment Body fluids consist of water and solutes Small molecular weight electrically charged particles called ions Large molecular weight plasma proteins called colloids 46 Fluid Therapy Electrolytes when dissolved separate into positively charged ions cations and negatively charged ions anions Electrolytes are essential for several fundamental physiologic processes Heart function, blood clotting, neuromuscular functions Solutes such as protein participate in regulation of blood pressure, blood clotting, drug transport 47 Fluid Therapy Homeostasis constant state within body crated and maintained by normal physiologic processes Solutes and fluids are constantly moving between cells and compartments to maintain homeostasis Osmolarity all body fluids maintain an osmolarity around 300mOsm/L Dehydration, exercise, heat stroke, vomiting/diarrhea can increase osmolarity while disease like chronic heart failure can decrease it 48 16
Anesthetic Fluids All IV fluids are solutions that consist of one or more solutes dissolved in water Most fluids contain one or more electrolytes Many IV fluids exist Must choose the correct fluid for the patient s specific needs Each fluid has a different solute profile Fluids are broken down into two groups Crystalloids and colloids 49 Anesthetic Fluids Crystalloid fluids Contain water and small molecular weight solutes such as electrolytes that pass freely through vascular endothelium Routinely used in most anesthetized patients that are considered healthy Common Crystalloids include LRS, Normosol, Plasma-Lyte, NaCl, 5% dextrose 50 Anesthetic Fluids Isotonic fluids Balanced fluids that contain several ions sodium, potassium, chloride most common Some cases magnesium and calcium Check out table 2-8 pg 37 in textbook Normal saline is isotonic but not balanced Used in specific cases brain disease, blood transfusions More acidic, causes metabolic acidosis 51 17
Anesthetic Fluids Hypertonic saline used for hypovolemia and shock Given as bolus Pulls fluid from extravascular spaces and temporarily increases intravascular space 5% dextrose not given as a replacement fluid Used as a carrier solution for other drugs Different than 50% dextrose 52 Anesthetic Fluids Colloids contain large molecular weight solutes that do not freely diffuse across the vascular endothelium and therefore stay in the intravascular space for long periods of time Ideal for bolusing hypotension, hypovolemia Hypoproteinemia Common synthetic colloids Hetastarch, hexstend, vetstarch Natural colloids Blood and plasma 53 Anesthetic Fluids Blood and plasma contain albumin and are often used for anemia, hypoproteinemia, coagulation disorders Oxyglobin hemoglobin-based oxygen carriers Not available in USA right now 54 18
Anesthetic Fluids Fluid therapy rates Traditionally 10 ml/kg/hr AAHA suggestions 3-5 ml/kg/hr Other suggestions 10 ml/kg/hr first hour, then decrease to 5 ml/kg/hr Vary based on health status of patient Heart disease Anuria Hypovolemia Anemia 55 Anesthetic Fluids Why do we give fluids? Anesthetic drugs cause vasodilation leads to hypotension Bleeding Open body cavity leads to fluid loss Calculating fluid rates Must know drip rate of set Macrodrip 10 or 15 drops/ml Microdrip 60 drops/ml 56 Anesthetic Fluids Fluids pumps Syringe pumps Burette 57 19
Calculating Fluids Box 2-4 pg 46 in textbook Determine body weight Determine prescribed weight Calculate infusion rate Weight (kg) X rate (ml/kg/hr) = mls/hr 10kg X 5 ml/kg/hr = 50 mls/hr 58 Calculate drip rate Choose micro or macrodrip Calculating Fluids Infusion rate ml/hr X time conversion (hr/min) X delivery rate (gtt/ml) = gtt/min 50 ml/hr X 1hr/60min X 60 gtt/ml = 50 gtt/min Now must figure out drops/sec so just divide by 60 50 gtt/min X 1min/60sec = 0.8 drops/sec Easy peasy!! 59 Calculating a Dextrose Solution To create a new solution from a given solution (where V = volume; C = concentration) V 1 x C 1 = V 2 x C 2 Example: How many ml of a 50 % dextrose solution will you need to make a 5 % dextrose solution in a liter bag of LRS? V 1 x 50 % = 1000 ml x 5 % V 1 = 1000 x 5 % (% cancel out) 50 % V 1 = 100 ml of 50 % dextrose required NOTE: 100 ml of LRS must be removed from the bag prior to adding the 100 ml of 50 % dextrose in order for this equation to be correct. 20
Calculating a Dextrose Solution You have anesthetized a 9 week old kitten for a fracture repair. The BG is 60. Should we treat? Calculating a Dextrose Solution The doctor has asked you to make a 2.5% dextrose solution added to 100mL of LRS How many mls of 50% dextrose will you need to add to 100 ml of LRS? Formula V 1 X C 1 = V 2 X C 2 Calculating a Dextrose Solution V 1 x 50 % = 100 ml x 2.5 % V 1 = 100 x 2.5 % (% cancel out) 50 % V 1 = 5 ml of 50 % dextrose required You should remove 5 ml of LRS prior to adding dextrose 21