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• This is a compilation of questions frequently asked on EMS and Anaesthesia rotations.
• It stresses questions often answered incorrectly, providing correct answers to aid learning.

Gas Values

• ET (end-tidal) indicates exhaled CO2, with a normal range of 4.6 to 6.
• Increasing RR and tidal volume can lower ETCO2 levels near the end of a procedure to stimulate spontaneous breathing.
• Fi (fractional/fresh inspired CO2) should ideally be 0, but it's usually slightly above due to CO2 in dead space.
• Increased Fi CO2 indicates low O2 flow or exhausted calcium carbonate in the rebreathing circle.
• Tidal volume (breath size) is typically 10-20ml/kg
• Start ventilator at this volume at 10 bpm and adjust according to CO2 readings.
• Minute ventilation is calculated as RR multiplied by tidal volume.

Blood Pressure

• The most accurate blood pressure parameter is the mean arterial pressure (MAP).
• MAP is calculated as cardiac output multiplied by systemic vascular resistance.
• Aim for MAP > 65 when measured with a central arterial line, or > 70 when using an oscillometric method.
• Renal autoregulation is lost at systolic pressures < 90mmHg.
• Myocardial perfusion becomes inadequate if diastolic pressure falls below <40mmHg.
• Brain autoregulation is lost at pressures <60 and >160mmHg.

Invasive Blood Pressure

• Involves placing an arterial catheter in the dorsal pedal artery (dogs) or facial artery (horses) with the opening facing blood flow.
• A pressure bag with heparinized saline (@300mmHg) fills non-compliant tubing with a heparin saline column.
• A transducer placed at the level of the left ventricle measures electrical resistance changes through a thin membrane.
• The membrane moves with the force of contraction, indicating blood pressure.
• Systolic pressures falsely increase if below the left ventricle due to gravity.
• The line must be "zeroed" at atmospheric pressure to give accurate readings.
• Air bubbles, blood clots, or overly compliant tubing can cause "damping", overestimating pressures.

Blood Pressure Equation

• Blood Pressure = Cardiac Output x Systemic Vascular Resistance.
• Cardiac Output = HR x Stroke Volume.
• Stroke Volume = End Diastolic Volume – End Systolic Volume.
• Therefore Blood Pressure = HR x (end diastolic volume - end systolic volume) x SVR.
• Stroke volume: the volume of blood pumped from the ventricles during contraction.
• To increase stroke volume:
  • Increase preload by administering a CSL fluid bolus, typically at 10 ml/kg.
  • Increase contractility using dobutamine.
  • Decrease afterload using ACP, which causes vasodilation and reduces systemic vascular resistance.

Epidural Effects

• Often decreases blood pressure by blocking the sympathetic trunk, leading to vasodilation and hypotension.
• Can cause paradoxical bradycardia.

Alpha 2 Agonists

• Increase SVR by causing peripheral vasoconstriction.
• This is helpful if the animal is likely to be hypotensive during surgery.

Steps to Take When Blood Pressure Decreases Intraoperatively

• If the animal is too deep, decrease the isoflurane, as vasodilation is a primary side effect.
• If due to bradycardia, administer an anticholinergic such as atropine or glycopyrrolate.
• If due to hypovolemia, administer fluids, keep in mind animals are often bit dehydrated so colloid and chystalloid fluids are used
• If the volume is adequate, administer dobutamine.
• In a worst-case scenario, administer adrenaline.

Arrhythmias

• Atropine: Can cross the BBB and cause seizures
  • should not be given to a horse with colic as the anticholinergic effects cause GIT stasis which will worsen the colic.
• Glycopyrrolate does not cross the BBB and is used more often.

Heart blocks

• First Degree Block: AV node transmission is slower, prolonging the interval between P wave and QRS complex.
• Second-degree Block: Some, but not all, impulses pass from the atria to the ventricles; can be caused by Alpha-2-agonists.
• Type 1 Second-degree Block ("Wenkeback Periodicity"): gradual increase in P-R interval until a blocked beat occurs, followed by a sinus beat.
  • Seen in GIT surgeries where the vagus nerve is stimulated and increased parasympathetic tone occurs
  • Also seen in young fit racehorses due to high vagal tone; disappears with trotting or at induction.
• Type 2 Second-degree Block: Consistent P-r interval, but occasional P-waves fail to conduct a QRS complex. This is commonly due to disease of the AV nerve fibres.
• Third Degree Block: No P waves conduct to the ventricle; atria and ventricles beat independently
  • P wave formation originates at the SA node; a ventricular pacemaker triggers a ventricular escape rhythm, essential for survival.

Ventricular Premature Contraction (VPC)

• Due to an ectopic focus in the ventricles firing before the SA node's next impulse.
• Identified on ECG by QRS widening and the lack of a preceding P wave for the QRS.
• A pulse deficit occurs when a VPC happens before the ventricles fully fill.

Oxygen Saturation

• Pulse-ox/SpO2 measures hemoglobin saturation with oxygen (normal: >95%).
• SAO2 (arterial blood oxygen saturation) should correlate and be >95%; saturation under 60% indicates severe hypoxemia.
• Low values result from low partial pressure of oxygen.
  • Too little oxygen being pumped into the fresh gas should be indicated on the Fi02 reading on the machine.
  • Upper airway blockage e.g. kinked ET tube
  • Pulmonary disease- this stops oxygen from crossing the blood-gas barrier. V/
• V/Q mismatch occurs when blood flows to areas where gas exchange isn't happening, decreasing SpO2 as hemoglobin is not picking up O2.
• Low V:Q ratio indicates over-perfused, under-ventilated areas; CO2 quickly builds up.
• High V:Q ratio means over-ventilated, under-perfused areas; CO2 is low.

Pulse Ox - Falsely High readings

• Anemia: Lower RBC count, but remaining Hb is saturated; pulse-ox reads saturated RBCs without accounting for low RBC count.
• High concentration of MetHb leads to brown mucous membranes e.g. onion or fertilizer poisoning.
• Alpha-2-agonists: Peripheral vasoconstriction makes it difficult for pulse ox to get a reading on certain dogs.

Capnography

• Measures end-tidal CO2 (ETCO2), reflecting CO2 partial pressure at the alveoli (normal range: 4.5-6KPa).
• Increased ETCO2 is caused by hypercarbia due to hypoventilation.
• Treat hypoventilation with IPPV or by decreasing the anaesthetic gas agent.
  • Rebreathing: Trace does not return to baseline.
  • Increased metabolic rate- being on too light a plane of anaesthesia, seizure or malignant hyperthermia.
  • Hypoventilation is the most likely cause:
    • Endobronchial intubation- Elevated PaCO2 and decreased PaO2 due to oxygen entering only the intubated bronchus. -Effects of hypercapnia- Cerebral vasodilation, splanchnic vasoconstriction.

Effects of hypercapnia

• Masks hypertension, bounding pulse, tachycardia, and tachypnoea when animal is too light -Later: oozing wounds, tachycardia with arrhythmias and CARDIAC ARREST
• Decreased ETCO2 can result from:
  • Dec'd cardiac output- when sudden cardiac arrest occurs
  • Hyperventilation
  • hypothermia
  • Decreased metabolic rate:
  • Et tube problem- disconnection or leak

ETCO2 - Detects problems with equipment:

• ET tube in oesophagus – CO2 just flat line or tiny bumps from gastric CO2

• ET tube not patent

• Loose connection

• Air-Leak - Loose connection between sampling tube and capnograph / broken connection or filter.

• Soda lime is exhausted- Rebreathing CO2, capnogram doesn't go back to flatline for inspiration. • High ETCO2 in Circle System: one way valves not working, stuck due to buildup of moisture • Sticking inspiratory valve - Inspiratory flip - Red indicates possible rebreathing

Other information related to ETCO2

• Expiratory valve malfunction can result in prolonged abnormal phase 2 and phase 0.(Detail)
• High ETCO2 in Non-rebreathing systems: indicates fresh gas flow is not high enough.
• Cardiogenic oscillations seen in CO2 capnogram; ventricular filling creates small peaks in the CO2 spikes and a curve peaks in expiration and lowers in inspiration.
• Permissive Hypercapnoea: ETCO2 allowed to build up over time to stimulate the sympathetic nervous system, increasing HR and BP, and to stimulate spontaneous breathing (goal ETCO2: >6.0 mmHg, can exceed 7 mmHg).

Anaesthetic Gases

• MAC Definition: concentration of gases at which 50% of patients won't react to noxious stimuli.
• If animals are getting light turn up the gas at the vaporizer.
• In the vapouriser, there is a chamber where the gas is completely saturated with isoflurane

Drugs

• Morphine causes nausea which leads to vomiting.

Morphine:

-If there is risk of morphine causing vomiting, premed the animal with pethidine or methadone

• Pure agonist so can lead to excitement before sedation
  • In a horse that is getting a premed of morphine (or any pure mu agonist) and an alpha 2 agonist, give the alpha 2 agonist first.

Methadone:

• Less cardiovascular effects, use on patients with cardio problems
• Panting can be seen after injection
• Not as good a sedation as morphine or pethidine.

Pethidine

• Analgesia lasts around 90mins,
• Anticholinergic effects so it can increase heart rate.
• Do not give IV, leads to massive histamine release. IM route only. Will be asked this.

Butorphanol

-Used in colics because it is short acting and also treats visceral pain well in the horse

• Short acting and good sedation •The dose required to bring about analgesia is much higher than that for sedation.

Fentanyl

-Can as bolus can stop animal breathing. Hypoventilation.

Anesthetic drugs

• ACP:
  • Not to be used in cardiovascular compromised patients
• Long acting sedation → better recovery: - In a dog with mitral valve regurgitation, a low dose of ACP will cause some vasodilation.

Alpha 2 Agonists:

• Cause laryngeal collapse, do not use in an upper airway exam.
• Cause a horse to urinate loads under GA -Colic: don't use romifidine because it covers up the pain for too long, use xylazine instead.
• Don't use atropine after medetomidine

Ketamine

-A direct negative ionotrope but stimulates the CNS I-n very sick animals these sympathetic effects may not be see.

• Often Used as a CRI in spinal surgeries in UCDVH,

Propofol

-Induction and CRI • NO analgesia but also Post induction apnea and vasodilation/hypotension worse if inject to fast IV

• • Good in a bitch having a caesarian, as the effects are short lasting so pups won't be sedated when they are extracted.

Alfaxalone

• Fever CVS effects than propofol than expensive
• During Induction: while induction agents are being administered, you must go through your “A,B,C”: o Airway- intubate the patient and inflate cuff, make sure there is no leak, ensure ET tubes have been leak tested prior to intubation. o Breathing – o Circulation- while induction agent is being administered, have your finger on the femoral pulse, making sure it is still present.

Anticholinergic/Antimuscarinic Drugs

• Glycopyrrolate- does not cross BBB - acts slower but longer duration
  • Does not reduce saliva
• Atropine -Causes rapid onset
• Rapid onset
• Signs that a horse is light under GA: -Rapid nystagmus (except ketamine Palpebral normal I the horse

More tips to make sure animal is ok

-Should be less than 2 When recovering a horse that has had an op on one of the limbs, recover with the sore leg uppermost.

• If a dog moves turning up the gas take too long

• Positive pressure ventilation decreases venous return and blood pressure so collects in gas files cavities

• 2-4 times maintenance -> 5-10ml/kg/hr

• Awake - 2.5 ml/kg/hr, Asleep - 5ml/kg/hr

Cases that need special attention

Neonate- more fluid so drugs have a higher volume of distribution Toy Breeds- more accurate way of dosing would be by surface area Vicious Dog - Use alpha 2 because of its reliability Cat with HCM- Alpha-2-agonsists are good due to bradycardic effect and don't want I tachardyta Hepatic Case- Need to give colloids

Ventilation

-If hypercarbia occurs increase respiration.

• Peak inspiratory pressure (PIP) 10-12 cmH2O inhorse

• Non rebreathers require fresh has at each breath The Ayre's T-Piece is suitable for small patents (up to 10-12 kg) During spontaeous venteilation lack requires low as flow as they allow some re breathng of anatomicel dead space gas\ works just like T – piece just coaxial set up. Very

• Reservoir bags better overestimate -Humphreys combining mini lack

• Contrast in CT tumour animals that are not in pain will not feel it int he gut.