Flashcards in CAL: maintenance and monitoring of anaesthesia Deck (24):
How does intercurrent disease affect MAC?
It reduces MAC
What do potent opioids as analgesics do to MAC?
What do you do if you anaesthetised patient is too light prior to commencing surgery?
- Administer more IV agent
- Ventilate patient by squeezing bag to deliver inhalational agent
- You could add NO2 to the above to speed induction (second gas effect)
- Switch inhalational agent to desflurane (lower blood:gas parturition coefficient) if patient is breathing
Do ACP, propofol or isoflurane have any analgesic properties?
No but buprenorphine is an analgesic.
How do you prevent diffusion hypoxia?
Switch NO2 off at least 5 minutes before end of procedure and then deliver 100% oxygen. Without doing this, as NO2 is so insoluble in blood, when administration is discontinued, it all rushes out of blood into the alveoli, displacing other gases in the lungs. Making sure that you are giving 100% oxygen at this point will help to ensure that there is enough oxygen in the lungs that the animal doesn't get hypoxic.
What consideration needs to be made for anaesthesia for a bronchoscopy?
Respiratory tract will be open to the atmosphere so any inhalational agent being administered to the dog will leak into the room --> personnel exposure
What are NMBs? How do they work?
Neuromuscular blocking drugs
ACTION: Most NMBs competitively inhibit acetylcholine (ACh) binding to its nicotinic Ach-R on the NMJ. By inhibiting binding of ACh, they prevent propagation of an action potential from the nerve to the muscle and thus prevent muscle contraction. NMBs cause relaxation of all skeletal muscles. Once animals have been given a NMB, animals cannot move or breathe.
Before giving NMBs under anaesthesia, what should you ensure first? 3
- depth of anaesthesia is adequate and the animal has good analgesia
- monitoring anaesthesia in these animals is difficult as you cannot easily assess reflexes
- you must be able to ventilate the patient since it will not be able to breathe spontaneously once NMB is administered.
How do you monitor anaesthesia when NMB has been given?
Physiological signs - HR, RR, BP, nerve stimulator (to assess the effect of the neuromuscular blockade)
What is a nerve stimulator?
You should also monitor the effect of the neuromuscular blockade (of NMBs) using a nerve stimulator. This machine uses a current to stimulate a nerve resulting in muscle contraction e.g. a twitch of the limb. During NMB, stimulating the nerve does not cause muscle contractions. As the block gradually wears off, weak muscle contractions gradually return.
How do you antagonise NMB at the end of the procedure?
Anti-cholinesterase drug - such as neostigmine and edrophonium (however may mimic vagal stimulation --> bradycardia) so always administer with an anti-cholinergic drug (e.g. atropine and glycopyrollate)
List sites where you can take a peripheral pulse.
dorsal pedal arterial pulse (dorsal tarsus), auricular arterial pulse (dorsal pinna), digital arterial pulse (on the palmar/plantar digit). Strength and characteristics are useful as they are more sensitive to changes / depression of CV function than central pulses.
What is an example of a central pulse?
femoral arterial pulse. These are likely to remain strong even during moderate CVS depression.
How can arterial BP be measured? 3
- Doppler non-invasive method
- oscillometric non-invasive method
- Arterial catheter and pressure transducer (invasive)
Can you take a direct measurement of arterial BP from a plethysmograph wave from pulse oximetry?
How can respiratory function be assessed?
RR and depth, MM colour, pulse oximetry
Why wouldn' a pulse oximeter not detect a decrease in PaO2 from 200mmHg to 100mmHg
since at these PaO2 levels the SaO2 is likely to remain 99-100% saturated (oxygen dissociation curve)
What do we use ETCO2 to estimate? 2
we use ETCO2 to estimate PaCO2 and adequacy of ventilation.
What happens in malignant hyperthermia (MH)?
excessive and uncontrolled cellular metabolism occurs and releases large quantities of CO2 into the blood and very elevated ETCO2 levels so can be detected with capnography.
On a capnograph, what does a lack of return to baseline indicate?
That the trace is abnormal
What are cardiogenic oscillations (bumps on the descending trace) a sign of?
often a normal variation
T/F; there is no CO2 absorbent in a Lack system
What does a decreasing size of each breath on a capnogram suggest?
major CV depression such as cardiopulmonary arrest.