Anesthesia Rounds 1 Flashcards
You are scheduled to anesthetize a 3 year-old, 48 kg German Shepherd for elective neutering.
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What anesthetic breathing system will you choose for this dog and why?
What is your size of anesthetic bag for this system and required oxygen flows for induction, maintenance, and recovery?
F-circuit
Bag: 60*48 = 2880mL = 3L
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O2 flows:
Induction: 100mls/kg/min = 4.8L
Maintenance: 50mLs/kg/min = 2.5L
Recovery: 100mls/kg/min = 4.8L
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Note in this dog the highest the flowmeter achievable on our SA anesthesia machines is 4L.
You are scheduled to anesthetize a 2 kg DSH for neutering
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What anesthetic breathing system will you choose for this dog and why?
What is your size of anesthetic bag for this system and required oxygen flows for induction, maintenance, and recovery?
Bain
Bag: 60 mls/kg x 2 kg = 120 mls The smallest bag we have is 0.5 L
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O2 flow:
Induction 200-300 mls/kg/min
Maintenance 200 mls/kg/min
Recovery 200 mls/kg/min
=> Flowmeter should be kept at 800 mls/min-1L/min as a minimum.
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For patients less than 5 kg of weight, setting the flowmeter at 1L always prevents rebreathing.
why do we need minimum O2 flow of 800mls/min- 1L/min despite the math for an animal <5kg?
- enables consistent isoflurane delivery and CO2 removal without additional monitoring of end-tidal inhalant or CO2 or patient ventilation
minimum O2 flow on the Bain with spontaneous ventilation to enable non-rebreathing of CO2
150 ml/kg/min
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While some textbooks may indicate 100 mls/kg/min is appropriate for a Bain, this flow with spontaneous ventilation will result in rebreathing of ETC02. Without additional monitoring of end-tidal gases, using a flow <150 mls/kg/min is not recommended.
dexmedetomidine and hydromorphone
- cardio-resp effects of this pre-medication?
The expected cardiorespiratory effects are bradycardia and associated bradyarrhythmias, increase in blood pressure decreasing over time to normal or lower levels once inhalant anesthetic is on, reduction in respiratory rate and reduction in temperature.
With profound sedation from this dexmedetomidine and hydromorphone, what is your planned initial bolus of ketamine:diazepam (1:1)?
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mild sedation?
The initial bolus of Ketamine:Diazepam (1:1 mixture) is 0.05 mls/kg =
2.4 mls WITH PROFOUND SEDATION. with a top-up dose of 0.6 mls.
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Mild sedation the initial dose is more likely 0.1 mls/kg.
With profound sedation from this dexmedetomidine and hydromorphone, what is your planned initial bolus of propofol?
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what about with mild sedation
The initial bolus of propofol is 1 mg/kg WITH PROFOUND SEDATION as might be expected with a dexmedetomidine and hydromorphone given together
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The top up dose needed is CLASSICALLY 1/4 OF WHAT YOU START WITH = 0.25 mg/kg = 1.2 mg =1.2 mls if only a slight increase in depth is required. See anesthetic dosing notes.
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If the dog was mildly sedated, then the initial dose of propofol is typically 2-2.5 mg/kg with a top up dose of 0.5 mg/kg. This is likely in a situation where dexmedetomidine is not in your premed or you do not achieve great sedation.
Lidocaine topical spray during intubation is used in veterinary medicine – why? Considering it is dose metered spray of 10 mg/squirt – what would be the dose of lidocaine administered to a 2.5kg cat? Is this appropriate? When should you avoid topical lidocaine sprays?
Overall clinical doses for peripheral blocks including topical lidocaine spray in small animals should not exceed 5 mg/kg. Note that when doing topical lidocaine and then quickly doing local block for a neuter the doses are additive towards the plasma lidocaine concentration. Literature recommends <5 mg/kg combinations in clinical situations.
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Lidocaine spray= 10 mg / 2.5 kg cat weight = 4 mg/kg administered.
lidocaine peripheral block max dose
Overall clinical doses for peripheral blocks including topical lidocaine spray in small animals should not exceed 5 mg/kg. Note that when doing topical lidocaine and then quickly doing local block for a neuter the doses are additive towards the plasma lidocaine concentration. Literature recommends <5 mg/kg combinations in clinical situations.
is lidocaine spray absorbed systemically?
Topical lidocaine spray on the larynx is absorbed systemically, but the plasma level achieved is less than giving it IV, although still substantial.
signs of lidocaine toxicity
Signs of toxicity are sedation twitching coma and respiratory arrest.
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It would be uncommon to see signs of toxicity with appropriate dosing of topical lidocaine use in combination with other local procedures in the cat. How much you are giving on a mg/kg bases should be considered for both canine and feline patients as the smaller your feline patient, the easier to give > 5-6 mg/kg doses.
lidocaine vs bupivicaine toxicity main signs
Neurologic signs are more common with lidocaine compared to cardiovascular toxicity signs with bupivacaine.
phase 2 rule for dosing lidocaine or bupivicaine
In phase 2- the rule in volume that was given for dosing was 0.2 mls/kg of lidocaine or bupivacaine.
6) Outline the steps in order for anesthetic recovery of a cat
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Note the steps considering you will need to move your cat from the surgical suite to the recovery area in our teaching area as well as clinics. How does anesthetic recovery differ in a dog?
Prior to finishing the surgery, additional analgesics should be administered as required, including additional opioid or NSAID administration.
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The dog or cat will be in dorsal recumbency in the surgery area. When the drapes are removed, the animal will go in lateral recumbency and the Doppler, ECG and all other monitors will be removed. Your manual monitoring that you have been doing will continue into the recovery area. You may have a small handheld pulse-oximeter to assist with your monitoring during transport.
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The intravenous fluids may be disconnected at this time and the PRN will be replaced on the catheter. The catheter will be flushed and maintained until final analgesics are administered IV prior to discharge.
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Your last esophageal temperature will be noted as you remove this temperature probe.
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Depth will be assessed and if possible, the inhalant may be
reduced by 0.25-0.5% for a dog, but you unlikely will want to reduce the inhalant in the cat if the animal is stable. You will prepare your anesthetic machine for moving and move your animal to the recovery room.
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You will not turn your animal off inhalant until organized for recovery and the transfer is complete. If your patient was having anesthetic complications, you would turn them off prior to transfer with the accompanying anesthesiologist.
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Once back in the induction area, the oral cavity will be evaluated to
ensure no reflux is present. Then the animal can be turned off
inhalant and the oxygen level increased to 100 mls/kg/min for a dog.
The system may be flushed with oxygen to speed the removal of inhalant.
This is performed by leaving the popoff valve open and emptying the rebreathing bag with your hand 2-3 times.
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Please do not disconnect and flush the system into the room.
For a small cat, the Bain flow is already high (200 mls/kg/min) and does not need to be increased nor does the system need to be
flushed. If you have reduced your oxygen flow to 130-150 mls/kg/min in a larger cat or dog, then you can return to 200 mls/kg/min oxygen flow in recovery.
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Extubation…
when to extubate? what is the process? when to deflate cuff?
Once a mild medial palpebral has returned or, 5-6 minutes has elapsed, the animal can be disconnected from the circuit and left on room air to assess adequacy of ventilation at 21% oxygen prior to extubation. The ET tube will be untied, and attention should be paid to the tie gauze to ensure it is not stuck within the animals teeth to allow for easy removal. Once a strong medial is present, the ET tube cuff may be deflated and the tube can be moved slightly to induce a swallow reflex. If any reflux has been noted, then the ET tube cuff will not be deflated until the animal swallows. The cuff should not be deflated until signs of recovering and lightening recur.
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Once extubated, the animal’s chest will be visualized to ensure the animal is breathing adequately. The end of the ET tube will be visually inspected at this time to ensure it appears clean. After 2-3 minutes the anesthestic machine circuit can be removed and cleaned.
