Anesthesia SG E1 PDF

E1 SG / Learning Objectives Lecture 1 Anesthesia: insensibility (loss of sensation in body part or whole body) ○ Local vs general Analgesia: absence from sensitivity of pain ○ No longer detecting pain (certain drugs) Sedation: depression of CNS, not fully unconscious...

E1 SG / Learning Objectives Lecture 1 Anesthesia: insensibility (loss of sensation in body part or whole body) ○ Local vs general Analgesia: absence from sensitivity of pain ○ No longer detecting pain (certain drugs) Sedation: depression of CNS, not fully unconscious (pet awake and calm) Tranquilization: relaxing patient where P is still aware of surroundings but doesn’t care ○ ex) drinking a beer Neuroleptanalgesia: Sedative/tranquilizer paired with opiod. General pre-meds. ○ ex) ace + hydro Pharmacokinetics: The study of what the body does to drugs (metabolism, half-lives, etc) ○ Pk ○ Studies for dose amount, safeness Pharmacodynamics: The study of what the drug does to the body. This matters more as an anesthesiologist. ○ Pd % to mg/ml? Move one decimal place to right (x10) Fluid drip rates 10 and 15 drops / ml = macro drip sets (larger dogs) 60 drops / ml = micro drip sets (cats, exotics, or smaller dogs) 1mg = 100mcg (ug) Lecture 2 Who performs patient eval prior to anesthesia? ○ The veterinarian in charge What is consisted within patient eval? ○ Signalment (species, breed, age, sex, alteration), history, PE, blood & urine samples, temperament assessment, mentation, pain, and stress (how this changed before compared to after surgery), advanced diagnostics ○ Labwork healthy pets: PCV, TS, Glucose, and BUN (protein catabolism byproduct) ○ Labwork on older/unhealthy pets: CBC, chemistry, U/A  When should you perform this? ○ Day before procedure or up to 1 week before Why? ○ Risk analysis of procedure to provide client with valuable information ○ Document the entire conversation with the client! Preparation? ○ SAs food withheld = 6-12 hrs pre-sx Water withheld up until premed given (can keep water in cage Study that showed feeding ½ amount canned food 3 hrs prior aided in decreasing gastroesophageal reflux ○ Small ruminants food withheld = 12-18 hrs Water withheld = 8-12 hrs ○ Equines food withheld = 4-12 hrs (full stomach more prone to rupture) Water withheld up until premed given ○ Cattles food = 18 -24 hrs Water = 12 -18 hrs ○ No fasting in rodents, rabbits, or birds High metabolic rates, prone to hypoglycemia ○ Bathing dogs ○ Stabilization Correct dehydration and electrolyte balance Anemia with blood transfusions ○ Antibiotics Anesthetic concerns? ○ Hypotension, hypoventilation (obesity where don’t breathe as well), hypothermia (lower body temp), hypoxemia (decreased oxygen in blood) ○ Most animals under anesthesia have these Dehydration clinical signs not detectable when percent dehydration < 5 → animal still could be feeling bad 12-15% dehydration = SHOCK with tachycardia and death of CRT < 1 = hyperdynamic state and vasodilation, possible shock ASA Physical Status scale (post patient work-up) → patient’s surgical risk I = normally healthy Ps with spay or neuter II = skin tumors, fractures, pregnancy, obesity, brachycephalics III = severe systemic disease with fever, anemia, renal ASA > or equal to 3 increases risk of death IV = threat to life with uremia, toxemia, shock, high fever, V = not expected to survive without surgery with extreme shock or trauma ○ ex) GDV, severe colic Lecture 3 Safety mechanisms in place to prevent use of wrong medical gas when oxygen is flowing from source to patient? ○ Oxygen = green ○ N2O = blue ○ PISS where oxygen fits perfectly within holes ○ DISS where “threading” specific for each gas → ADD PICS!! PISS DISS 3 sources of oxygen used in vet med? ○ Oxygen cylinders Commonly used (E cylinder) Steel or aluminum Open valve SLOWLY as explosion hazard ○ Large cryogenic liquid oxygen containers Large containers installed at facilities with fairly constant O2 demand “Big thermo bottle” More expensive = used in specialty or larger hospitals ○ Oxygen concentrator Absorbs nitrogen and all the gases in air → increases O2 concentration More affordable (first used in the military) but not used in larger clinics Maintenance and time required Basic functioning parts of modern vaporizers? ○ Changes liquid anesthetic agent into vapor in a controlled manor ○ Increasing SA with wicks and spiral tracks ○ Different colors depending on anesthetic agent  Isoflurane = purple E Sevoflurane = yellow ○ Common / fresh gas inlet and outlet Delivers mixture of gases and vapors from machine to breathing system **Which components of machine if used wrong could result in death of P?** 1) Closed pop-off valve (ALWAYS KEEP POP-OFF VALVE OPEN, unless checking it) Oxygen flowing into patient is unable to be removed so alveoli can eventually burst if valve closed New safety feature: pop-off occlusion valve that doesn't allow pressure above certain point (prevents closure of valve) 2) Too little oxygen 3) Too high vaporizer setting Steps to perform machine leak test (pressure check) on anesthesia machine? 1) O2 flow is OFF 2) Close APL valve (ONLY time you would do this) 3) Occlude patient end of Y-piece 4) Press O2 flush button to pressurize system to 30 cmH2O 5) Observe pressure gauge for 30s to a 6) If no drop in pressure / leak = open APL valve and remove occlusion If leak = titrate oxygen to MAX of 300 ml/min. If greater than this needs to be used the machine should NOT be used! Given psi left and oxygen flow rate, calc oxygen remaining (L) and the amount of time it will last? P1/V1 = P2/V2 and check step where divide liters by psi to see if it is the same number. Cylinder E size = 660L and 2200psi Cylinder H size = 6900L and 2200psi CHANGE oxygen cylinder when pressure < 500 psi! P reservoir bag calc ~ always round UP b/c using smaller tidal volume initially (10ml/kg) BW (kg) x tidal volume (mL/kg) x 5 (BW x 50) Manual ventilation with reservoir bag by squeezing bag and temporarily occluding APL valve Lecture 4 Safety concerns with use of anesthesia machine and breathing system if not properly checked? ○ Environmental pollution ○ Patient becomes hypoxemic (decreased O2) 2 types of breathing systems? Pros and cons? ○ Rebreathing- “Circle system” used with unidirectional valves where rebreathing of CO2 is prevented by chemical absorption with CO2 absorption canister Pros: lower oxygen flow rates and easy to set-up Cons: more resistance for smaller P (harder to breathe) and more components ○ Non-rebreathing- preferred for smaller pets Pros: less resistance, little to no dead space and fewer components for possible leakage Cons: higher oxygen flow rates (x10 increase compared to typical 200-300 ml/kg/min flow rates) as machine needs to push out more CO2 → higher CO2 in environment + possibility of hypothermia (increased O2 causes cold) Mapleson D (more common with bain circuit) and mapleson F 2 types of scavenging systems? Pros and cons? ○ Systems that actively remove waste products (gases) acquired from anesthetic procedure ○ Should keep anesthetic agents below 2ppm ○ Passive with charcoal absorption to outside wall/window where it ONLY absorbs halogenated anesthetic gases (SEVO or ISO) NOT CO2 e  Pros: mobile, easy to set-up, low initial cost Cons: replaced after 50g in weight (weigh initially and for each sx), only lower O2 flow rates, more resistance, and environmental impact ○ Active with central vacuum collection with interface (protection from excessive positive and negative pressure) Pros: more effective Cons: expensive Types of ET tubes? Equipment involved? ○ Measure from tip of nose to point of shoulder = length Largest size of tube that will fit without causing trauma to trachea Size based on internal diameter **NOT past thoracic inlet or BEYOND incisors** ○ Width of dog’s philtrum = bevel measurement ○ Most common ET tube = Murphy (“murphy’s eye”) Oval hole positioned on the bevel facing the opening of the tube in case of accidental occlusion (safety feature) ○ Others Magill Cole- uncuffed, uncommon Guarded/armored- silicone rubber which is more expensive and procedures when head moved certain way as these resist kinking (optho procedures) ○ Equipment: Laryngoscope (light source for airway visualization when placed UNDER epiglottis), syringe, one size above and one size below ETT, dry gauze, sterile lube, something to tie in tube (normally rubber bands, stretchy gauge, etc), sometimes stylet Confirming ETT placement? Capnograph reading = high CO2 values Auscultation of breaths bilaterally when manual breath given (most common) Dead space: areas when there is air but no gas exchange ex) trachea, mouth, end of ET tube and Y piece Cuff inflation technique When cuff is inflated and manual breath with bag is initiated → should be no escape of gas ~ 22cm H2Oair should be able to escape of  ○ If not → some air should be removed to prevent overinflation Oxygen flow rate calc… BEGINNING anesthesia: 44 ml/kg/min (want to start off with more) During: 22 ml/kg/min Multiply by kg Lecture 5 Signs associated with different planes of anesthesia ATTACH CHART Normally just perform palpebral reflex as don’t want to touch P’s eye to test corneal reflex as risk for corneal ulcer (also a risk if lack lubing eyes) Describe how P in surgical plane of anesthesia looks ○ Stage I: voluntary movement post drug admin, most variable stage Importance of pre-meds to avoid rough induction ○ Stage II: stage of delirium and involuntary movement, exaggerated responses possible (still responsive to stimuli so do not want to intubate too soon) until regular breathing pattern ex) laryngospasms in cats and pigs, dilated pupils, jaw tone present, breath holding, increased HR, may vocalize, nystagmus in horses Don’t want to be in this stage too long ○ *Stage III: surgical anesthesia stage, relaxed jaw tone (easily pull out tongue) 7m Plane I: “light” that persists until eye movement stops, biopsies or wound closures can be performed in this stage  *Plane II*: MOST procedures performed, vitals stabilized, slower palpebral reflex, strong corneal reflex, no laryngeal reflexes Plane III: “deep”, starting to enter danger zone, decreased RR/HR, no jaw tone, no rxn to surgical stimulation, dilated and central pupils Plane IV: danger zone, hypotension to thick, dilated pupils, slow CRT, lack of muscle tone, no anal sphincter tone, ○ Stage IV: EXTREME CNC depression, anesthetic overdose, pale MM, apnea (breathing stopped), cardiac arrest, flaccid muscle tone, absent ocular reflexes, death List factors that may affect monitoring of patient dept ○ *Ketamine- blinking, swallowing ○ *Propofol- no analgesia (absence of pain detection), apnea ○ CO2 and O2 = increased RR ○ Physical status with sicker patients Goal of clinical signs of anesthesia? Relaxed jaw and anal sphincter tone Steady HR and RR Ventral medial eye rotation Mild or no palpebral reflex No swallowing, coughing, vomiting or laryngospasm Bispectral Index (BI): analyzes EEG values from the brain. Mainly used in human medicine or veterinary research. → 60 = adequate under anesthesia (0 = flat-line EEG, 100 = awake) Lecture 6 Importance of monitoring anesthetized patients? Adequate blood flow … Arterial blood circulation Ventilation Body temp Legal record of events Responsible person aware of P’s status during anesthesia Techniques and/or basic monitors for most anesthetized patients? Anesthetic dept signs ○ Eye position (ventral medial), muscle relax, RR, stimulation response, jaw and anal tone HR, rhythm, and pulse quality ○ ECG and SPO2 REQUIRE pulse! one ○ Feel different sites in different species to assess quality RR and effort ○ Esophageal stethoscope passed to the level of heart ○ Visualize and auscultate Noninvasive BP ○ Doppler Measures systolic arterial pressure only Cuff ~ 30-40% circumference of limb or tail Accuracy affected by? Temp, vasoconstriction, cuff size, white tape Do NOT use white tape to attach cuff as affects BP ○ Oscillometric Systolic, diastolic, and MAP measurement Temp ○ Normally inserted into esophagus (sometimes rectum) ○ Hypothermia common MM & CRT Pulse oximetry (SPO2) ○ Indirect measurement of % O2 saturation of Hb + HR Calculates the difference btw absorption of red and infrared light absorption ○ Placed over non-haired areas (tongue, vulva, prepuce, ear) ○ Accuracy affected by? Poor circulation, movement, pigment, thick tissues, anemia, CO + cyanide poisoning with falsely high reading, methemoglobinemia with low reading, too much light End tidal CO2 (ETCO2) = capnography ○ Measures inspired and expired CO2 + RR ○ Sample adapter placed at end of ETT with connection to Y-piece ○ Increased ETCO2 = hypoventilation (malignant hyperthermia) Common with anesthesia- hypotension ○ Decreased ETCO2 = hyperventilation Hypothermia or airway obstruction ○ Often diagnoses machine leaks Dog BP > 90 mmHg systolic BP (90-120 mmHg) ○ Doppler > 60 mmHg MAP (60-100 mmHg) ○ Oscillometric BP (reads both systolic, diastolic, and MAP) Longer readings NOT accurate in hypotensive, small Ps, movement, arrhythmias, and vasoconstriction CHART PICS ** DIRECT BP analysis = golden standard but rarely used in SA practice (mainly LA) ** → sterile catheter injected into peripheral artery Cat BP 760mmHg Doppler predicts MAP better so can still record as systolic but recognize that not values will be slightly decreased. ○ Better reading Oscillometric best predictor for systolic arterial pressure ECG Measures electrical activity of the heart ○ NOT mechanical so animal could be dead but still have electrical activity present P wave- atrial depolarization PR interval- AV QRS- ventricular depolarization ST- ventricular repolarization T wave- resetting SPO2 CHART Normal vital limits under anesthesia PaO2 > 95% (even small decrease causing severe hypoxemia) ETCO2 = 35-45 mmHg MAP = 60-100 mmHg ○ Equine > 70 mmHg SAP = 90-120 mmHg RR = 10-20 bpm Temp = 98-102.5 HR species variation ○ Dogs = 50-160 ○ Cats = 100-200 ○ Horses = 28-50 (80 foals) ○ Ruminants = 48-90 in cows, 60-150 in sheep Lecture 7 4 mechanisms of heat loss 1) Radiation- losing heat through electromagnetic waves → cold weather, cold floor (varies on type of animal), microwave 2) Convection- losing heat through air or water molecules through skin → fan to cool off, swimming in cold water 3) Conduction- losing heat through objects that contact body → ice pack 4) Evaporation- losing heat through conversation of water to gas → sweating ** radiation and convection contribute MOST to heat loss ** ** Hypothermia Common complication during anesthesia Organ damage? ○ Decreased RR, decreased renal tubular function, elevated serum amylase (GI disruption), hyperkalemia, absent neuro reflexes Mild: 89.6-98.6 with SNS activation, vasoconstriction, shivering, tachycardia Moderate: 82.4-89.6 with bradycardia, slowing RR, low BP, decreasing consciousness, no shivering Severe: < 82.4 with continued decreased HR + RR, no PLR, arrhythmias, unconscious, muscle rigidity 4 most common issues with anesthesia (4 H’s) - Hypothermia f - Hypoxemia - Hypotension (drugs cause decreased CO and systemic vascular resistance) - Hypoventilation (increased ETCO2) Hyperthermia → elevation in core temp due to thermoregulation failure (pyrexia due to infection, inflammation or other issues; NOT the same) Caused by heat stroke, respiratory obstruction, exercise, histamines, seizures, malignant hyperthermia, iatrogenic (most common in anesthesia with excess heating or drugs) Organ damage? ○ → > 107.6 degrees F ○ Inflammatory response and edema to organs ○ DIC, hemorrhage ○ Tachycardia, hypotension ○ Hyperventilation ○ Intestinal ischemia and infarction ○ Coma, seizures Common with cats when hydromorphone, ketamine, and some opioids use. Also rebound hyperthermia from hypothermia during sedation ○ First 5 hours of recovery s Ice packs avoided as potential for vasoconstriction and alcohol on footpads generally is not helpful Celsius to Fahrenheit conversion? (C temp x 1.8) + 32 Heat sense through alpha gamma fiber → dorsal root (sensory) ganglion → hypothalamus (organ within CNS of brain that regulates temperature) → efferent pathway → alpha motor neurons for BV tone, shivering, or sweating ex) certain drugs cause body to THINK they are hot but actually are NOT Methods P can be safely warmed or cooled when indicated? Warmth (combat hypothermia) ○ Passive with blankets and towels ○ Active with forced-air blankets, warmers, warm IV fluids, circulating warm water blankets/pads ○ Do NOT use electric heating pad or blanket!!! Cooling (combat hyperthermia) ○ Active cooling (1st choice) with potential sedation Oxygen Room temp IVF Water applied to skin Shave fur off abdomen ○ 2nd choice strategies Peritoneal dialysis Cool IVF ○ Do NOT overcool (stop @ ~ 104 degrees F) and monitor every 5 MIN! of Basic steps for P recovery from anesthesia? 1) Remove drapes, instruments, and non-essential monitors (leave ETCO2 and SPO2 in place) from P 2) ** Inhalant (vaporizer) NOT turned off until completely sure surgery is over and patient is ready to wake up 3) Empty reservoir bag into scavenging system 4) Turn O2 flow to 50-100 ml/kg/min 5) Disconnect P BEFORE turning into sternal or lateral recumbency ~ cats more prone to tracheal tears ! 6) ETT pulled after 1-2 swallows in cats and 2 swallows in dogs (laryngeal reflux noted BEFORE deflating cuff) 7) Monitor rectal temp every 15-30 min until 98 degrees F 8) Monitor ALL vitals until P is fully awake (holds head up and walks) 9) Pain only assessed after P fully awake and then decide on potential pain meds Difference in treatment methods for fever compared to hyperthermia? Pyrexia? Do NOT cool P as fever is the body's way of working to fight infection. Avoid antibiotics, NSAIDs, and steroids. Can use acetaminophen in dogs ONLY. Hyperthermia? Active cooling with IVF @ room temp, increased O2 (body’s requirement increases with increased metabolic rate), fan, shave abdomen hair. → STOP when at 104 degrees to avoid rebound hypothermia!! IVF maintenance rate = 40-60 ml/kg/day (50 ml)