Anaesthesia for dogs and cats with respiratory compromise

Question 1

The primary inspiratory muscles

Answer 1

diaphragm and inspiratory (external) intercostals which move the ribs forward and outward

Question 2

What does synchronised respiratory muscle contraction generate?

Answer 2

Breath, which ultimately drives alveolar ventilation and blood gas regulation

Question 2

Role of accessory inspiratory muscles

Answer 2

breathing, esp during respiratory stress or disease, i.e. upper airway muscles innervated by the hypoglossal nerve

Question 3

What monitoring do you need during GA for these pts?

Answer 3

• resp rate & effort
• mm colour
• CRT & reflexes
• SPO2% and pulse rate
• ECG, capnography
• ABP
• temperature

Question 4

When do you need particularly close monitoring for these pts? Why?

Answer 4

• on recovery
  – resp cases decompensated very quickly.

Question 5

IV fluids?

Answer 5

• Be careful

Question 6

Ventilatory support and sighs

Answer 6

Want to give an occasional big breath - this is thought to redistribute surfactant along the lung tissue

Question 7

What is the first change seen in an arrest?

Answer 7

• Capnograph

Question 8

Premeds for dogs, e.g. ASA II-III brachy dog and sicker ASA III-V (resp distress pt) (assuming no serious CV compromise)

Answer 8

1. opioid alone or
2. dexmedetomidine (low dose) OR acepromazine OR benzodiazepine, AND methadone (or butorphanol if no painful procedure planned)

Question 8

How to cool down these pts

Answer 8

• alcohol on pads
• water enema

Question 9

Why is a very low dose dexmedetomidine okay for these pts?

Answer 9

• At a low dose it doesn’t have the bad alpha-2 agonist side effects

Question 10

Others drugs that can be administered to dogs during premed time

Answer 10

1. omeprazole, metoclopramide, maropitant for nausea, regurgitation
2. xylometazoline to reduce decongested nares, terbulatine
3. NSAIDs or paracetamol

Question 11

Premeds for cats

Answer 11

1. Opioid alone or
2. dexmedetomidine OR acepromazine OR benzodiazepine, AND methadone (or butorphanol)
3. alfaxalone AND midazolam AND opioid (methadone or butorphanol) IM or
4. Ketamine AND midazolam IM or IV

Question 12

Other drugs that can be administered to cats during premed time

Answer 12

1. NSAIDs or steroid
2. Terbulatine or salbutamol

Question 13

Induction of anaesthesia (cat & dog) - ASA III-V

Answer 13

1. alfaxalone IV or
2. propofol IV or
3. ketamine IV (less common)

Question 14

Important notes for induction of anaesthesia

Answer 14

• intubate as quickly as possible (have several ET tube sizes ready, inflate cuff)
• spray cats larynx with lidocaine
• access the airway too as this point (BOAS, laryngeal paralysis/collapse/masses/polyps)
• suction may be necessary
• use a laryngoscope

Question 15

Criteria for preoxygenation

Answer 15

animals that are marginal or unable to maintain Hb O2 saturation when breathing too air

Question 16

Ways to administer oxygen

Answer 16

• face mask
• oxygen chamber
• nasal oxygen cannula

Question 16

Benefit of preoxygenation

Answer 16

Unless the animal is cyanotic, it provides a longer time before a pt becomes hypoxic during apnoea periods, e.g. following anaesthetic induction

Question 17

Why is ket induction or premed often recommended?

Answer 17

it’s associated with bronchodilation via central release of catecholamines, stimulating beta-2-adrenergic receptors, and inhibits vagal pathways resulting in an anticholinergic effect on airway smooth muscle. these drugs increase lower airway size and decrease the resistance to inflation of the alveoli

Question 18

Maintenance of anaesthesia

Answer 18

Use appropriate FCF for selected breathing system, minimise dead space (ET tubes cut to suitable length), iso or sevo in oxygen, may need t assist ventilation (use capnography to judge, 8-15 breaths usually ok), may need TIVA (e.g. bronchoscopy)

Question 19

Suitable CRI/TIVA meds

Answer 19

• alfaxalone or propofol

Question 20

Why do you need to be careful with oxygen blasting?

Answer 20

Don’t want to slow down the mucociliary escalator

Question 21

Inspiration:expiration

Answer 21

1:2.5-3. allows passive recoil of the lung (allows pressures of the thorax to normalise between breaths - allowing the heart to fill)

Question 22

If ETCO2<20mmHg

Answer 22

= Hyperventilation. check pulse and bp. check for leaks, extubation, oesophageal intubation, disconnection, rapid rr, inadequate anaesthetic plane, iatrogenic (too much manual or mechanical ventilation)

Question 22

How to check for inspired CO2

Answer 22

on the capnograph - if it doesn't go down to baseline

Question 23

If ETCO2>60mmHg

Answer 23

= Hypoventilation. check for excessive anaesthetic depth, obesity, body position impairing breathing, airway obstruction, bronchoconstriction, fluid or mass in chest, pressure on chest, increased abdominal pressure, insufflation with CO2 (laparoscopy), iatrogenic (inadequate manual or mechanical ventilation)

Question 24

If inspired CO2>5mmHg

Answer 24

= Rebreathing CO2. check for inadequate O2 flow rate, excessive equipment dead space, exhausted CO2 absorbent, 1-way valve malfunction

Question 25

Recovery

Answer 25

- recover in prep area and carefully monitor, supplement with oxygen as hypoxaemia is common if they return to FiO2 21%, be prepared to reintubate if the animal decompensated, low dose sedation may be required