Chapter 22 Anaesthesia Practice for Existing Conditions Flashcards
What is anaesthsia related death rate in small animals?
1 in 500-1000
List criteria for ASA (American Society for Anaesthesiologists) classifications 1-5
What is the goal of anaethesia (3 things)
Analgesia
Anaesthesia
Muscle relaxation
What is meant by MAC reduction
Concept whereby addition fo anaesthetic/analgesic drugs change the required dose of inhalant anaesthetic
List describe the mechanism of action of a calcium channel blocker and list 3 examples
MoA: Block calcium channels in vascualr smooth muscle, cardiac myocytes or pacemeker cells –> relaxation of vessel/myocyte/slowing of AP. Therefore all -ve inotropes and -ve chronotropes
Amlodipine - acts of vascular calcium channels only
Verapamil - acts on cardiac myocytes and pacemaker cells only
Dilatiazem - in between the abve two, some action at all sites
Varying degree of effect depending on site/drug
How many beta receptiors are there? Where are the main sites for each type?
Beta - 1: Heart. Adrenergic simulation –> +ve inotropy and chronotropy. Also juxtaglomerular apparatus of kidney - if stimulated (by drop in BP) –> activation of RAAS
Beta - 2: Brochioles, arteries, detrusor m of bladder. Adrenergic stimulation –> relaxation.
Beta-3: Adipocytes
Eg atenolol, propaolol
List 3 positive inotropes
Dobutamine (a beta-agonist), pimobendan, digoxin e.g. DCM may require dobutamine
List some specific considerations when anaestehtising patient with cardiac disease:
- Echo
- Pre-oxygenate
- Oesophageal stethoscope to allow detection of crackels
- CVP monitoring
- Continue most cardiac drugs as uusal but ACE-inhibitor can be skipped on morning of sx.
- Alpha-2 agonists contraindicated as compromise CO/myocardial oxygen delivery
- Etomidate induction (CV sparing - N.B. Supressed cortisol production…relevant in other conditions), or co-induction (benzo = propofol/alfax)
- Nerveblocks to minimise inhalant
- No lidocaine if 2nd or 3rd degree AV block
- Awareness re Branhams reflex (PDA)
List indications for treatment of ventricular ectopy
- HR >150 bpm
- Multiform ventricular beats
- Hypotension during periods of abnormal beats
- R-on-T phenomenon (QRS follows straight after T, without retrun to baseline)
List some specific considerations when anaestehtising patient with thyroid disease
- Hypertension
- Underlying renal insufficiency
- Thyrotoxic cardiomyopathy
- “Thyroid storm”
- Thyroid neoplasia part of multiple endocrine neoplasia syndrome?
- Post-op laryngeal paralysis
- Post-op hypocalcaemia (wiht removal of parathyroid glands)
- In dogs - full staging before surgery in case of multiple endocrine neoplasia syndrome
- No ketamine - due to cardiomyopathy and risk of thyroid storm
List some specific considerations when anaestehtising patient with DM
- Higher infection risk
- Minimize insulin changes 1/2 dose morning of sx
- Hourly glucose monitoring
List some specific considerations when anaestehtising patient with insulinoma.
Which cells affected in insulinoma
Insulinoma = tumour of pancreatic beta-cells
- Pre-op stabilization with lots of small meals and glucocorticoids (induce insulin resistance)
- BG q30m
Adrenal cortex divided into 3 zones - what are they and what do they produce? What does adrenal medulla produce?
Cortex:
- Zona glomerulosa:* Mineralocorticoids
- Zona fasciculata:* Glucocorticoids
- Zona reticularis:* Androgens
Medulla (Chromaffin cells): Cathecholamines
In cases of phaeo, what is pre-treatment recommendation?
What drugs would be used to treat the following intra-op effects?
- Tachycardia
- Hypertension
- Arrythmia
Phenoxybenzamine 0.5 mg/kg po bid for 2-3 weeks before
- Tachycardia: Beta blocker (esmolol) or calcium channel blocker (diltiazem)
- Hypertension: Nitroprusside
- Arrythmia: Lidocaine
Give corticosteroids post-op if functional tumour
List some specific considerations when anaestehtising patient with respiratory disease
- Pre-op stabilisation eg thoracocentesis
- Consider ketamine premed - brochodilator and maintains respiratory centre sensitivity to PaCO2)
- Pre-oxygenation
- Prepartion for difficult intubation
- Katmine/benzo induction does not produce apnea. Propofol in brachys as fast
- Avoid pre-med if assessing laryngeal function
- Larger volume pepidural infustae to reach thoracic region, do not use local as risk of paralysis to muscles of respiration
- Repidly exhaled inhalant agent i.e. desflourane
- Pressure-limited ventilation of fibrosing pleuritis (<10 cm H2O)
- Care re re-expansion oedema
What if %oxygen delivered to lung if 100% oxygen piped into nasal cannula at rate of 10 ml/kg/min
40%
List some specific considerations when anaestehtising patient with hepatic disease
- Reduced albumin i.e. colloid oncoic pressure and drug carriage
- Coagulopathy
- Hypoglycaemia risk
- Prolonged drug metabolism/clearance
- ?Ascites - hypovolaemia, pressure on diaphragm
- Midaz = benzo of choice (flumazenil reversal)
- Opiods = morphine, hydromorphone or oxymorphone as not require P450 enzyme clearance. Remifentanil cleared by plasma esterases
- Propofol induction as has extra-hepatic sites of metabolism
List some specific considerations when anaestehtising patient with renal disease.
- Uraemic coagulopathy, pneumonitis, encephalopathy
- Ensure Bp maintained (MAP >85 mmHg)
- Avoid sevo (in rats reacted with sodalime to form compund A –> nephrotoxicity
List some specific considerations when anaestehtising patient with sepsis
- May have CIRCI (critical illness related corticosteroid insufficiency) - do not give etomidate. Can consider physiological dose steroids (0.05 - 001 mg/kg dexamethasone)
- Additional iv access
- Measure urine output
- Colloids/blood products as necessary
- Pressors (no-epi initially, if refractory –> vasopressin (is a non-adenergic pressor (ADH) work on renal collecting tubule to re-absorb water and caused vasoconstriction vi V1 receptor in vascular smooth muscle.
What is max pressure for abdo insufflation and why?
Max 14 cm H2O because renal blood flow may be compromised above that
List clinical signs of an air embolus
Clinical signs:
- Sudden ETCO2 drop
- BP drop
- SPO2 drop
- Washing machine murmur
Treatment:
- CPCR
- Place in l lat recumbency (air moves away from r ventricular outflow tract
List some specific considerations when anaesthetising patient needing c-section.
- Clip + prep awake
- Avoid alpha-2 agonist (xylazine shownt otbe detrimental)
- Lidocaine (4 mg/kg) + morphine (0.1 mg/kg) epidural
- Opioids after neonate removal
List some specific considerations when anaestehtising patient for dental procedures
- Pharyngostomy/trans-mylohyoid/tracheostomy intubation
- Nerve blocks
- ET tube cuff maintenance/care
List 4 nerves that can be blocked for dental procedures and the locations:
Rostral maxillary (infraorbital) blocks affect bone, teeth, and intraoral soft tissue from the maxillary third premolar rostral to the midline.
Caudal maxillary blocks affect bone, teeth, and intraoral soft tissue from the last molar rostral to the midline, including the ipsilateral soft and hard palatal mucosa and bone.
Rostral mandibular (mental) blocks affect bone, teeth, and intraoral soft tissue from the mandibular second to third premolar rostral to the midline.
Caudal mandibular (inferior alveolar) blocks affect bone, teeth, and intraoral soft tissue from the mandibular third molar rostral to the midline.
List some specific considerations when anaestehtising patient fro ophtho procedures
- Neuromuscular blockage (atracurium 0.1 mg/kg), last 20-30 mins. Ensure mechnical ventilation. revserse with neostigmine or edrophonium
- Guarded ET tube
- Avoid increased IOP (ketamine, propofol, inhalante –> reduced IOP)
Whre is the bodys thrmoregulatory centre?
Hypothalamus
What are the four mechanisms of heat loss? Lost in order of magnitude and give an example of each
- 50% Radiation = Loss via infrared energy
- 30% Convection = contact with cold air or water
- 10% Conductive = Direct contact with cold surface
- Evaporative = via lungs and feet
List 5 causes of hypoxaemia. Which is most common
- V/Q mismatch
- Shunting
- Hypoventilation
- Low FiO2
- Diffusion barrier
V/Q mismatch most common
What is normal anaesthetised PaCO2
35-55 mm Hg
What causes malignant hyperthermia?
What are clinical signs?
What is treatment?
Cause: Defect in cellular ryanodine receptor, which is involved with calcium induced cellular calcium release in muscles –> muscle spasm and rigidity.
C/s: Hypercarbia (first) > hyperthermia > tachycardia then muscle rigidity, arrythmias, death
Tx: Iv dantrolene, Oxygen only (inhalant can be trigger so ensure new or clean tubing). Muscle biopsy and test relatives
Name two CPCR compression techniques
What is the rate of compressions and breaths?
Cardiac pump
Thoracic pump (big dogs)
100-120 bpm, 12 breaths/min (hyperventilation assoc w worse outcomes)
What ETCO2 values have been associated with better outcomed during CPCR
> 15 mmHg in dogs and >20 in cats
What drugs indicated in CPR
Epinephrine (0.01 mg/kg iv)
Atropine (0.04 mg/kg iv)
Defib if VF
What risk factorst have been associated with post-op pulmonary complications?
- Emergent anesthetic
- Pre-op V/R
- Sx for septic or biliary peritonitis
- ASA ≥3
And in dogs presentiing with IVDD
- Tetraparesis, cervical SC lesions, undergoing>1 GA, post-op V/R
List 8 potentail complications of anaestesia
- Hypothermia
- Malignant hyperthermia
- Hypoxia
- Tracheal tears
- Gastrooesophageal reflux
- Reduced tear production
- Hypotension
- CPA
