Clinical Monitoring During Anaesthesia - Capnography Flashcards
Why monitor anaesthesia?
- to prevent P responses to Sx stimulation
- to detect abnormalities before they turn into major complications
by ensuring tissue perfusion & oxygenation, we can…
- prevent worsening of subclin dz & improve P outcome
- reduce morbidity & mortality assoc’d w/ anaesthesia
When is the highest risk period for patients surrounding anaesthesia?
during the recovery period
When monitoring anaesthesia, what do you specifically monitor?
- CV system
- resp system
- depth of anaesthesia
- body temp
- fluid balance
- anaesthetic equipment
- recovery
What reflexes in the dog/cat are monitored during anaesthesia?
- flexor withdrawal/pedal
- palpebral
- position of the eye
- eye mvmt
- ear flick (cat)
How do you determine in small animals adequate anaesthetic depth?
- HR, RR, BP stable
- Neg flexor withdrawal reflex
- Eyes: no palpebral reflex, ventral rotation, no nystagmus
- minimal jaw tone
- no movement
- neg ear flick
- pink MM
- CRT <2 sec
How do you know an animal is too light
- eye central
- increased HR/BP/RR
- increased jaw tone
+/- palpebral
+/- pale mm
Nystagmus in horses (VERY LIGHT)
how do you know an animal is too deep?
- eye central
- decreased HR, BP, RR
- no palpebral, jaw tone
When monitoring and determining depth of anaesthesia, you notice a central eye. Your patient was given ketamine as part of its premed IM and was maintained on CRI of ketamine. Is this normal?
Ketamine will result in a central eye so this cannot be used to determine depth.
This does NOT occur & of concern if used as an induction agent (duration of action 10-20 mins)
A respiratory monitor
“bleeps” each time the P breathes but DOES NOT tell you anything about efficiency of respirations/ventilation/etc.
If an animal is hypothermic in recovery and shivering, it will
increase Oxygen demand by 400% so need about 85% Oxygen to not become hypoxaemic
Why are IV fluids administered?
inhalants & maintenance w/ propofol/alfaxalone –> vasodilation occurs, circ blood vol is not enough –> relative hypovolaemia
What does capnograph measure?
End-tidal (Et) & inhaled (Fi) CO2
Normal Et value
4.6-6 kPa (35-45 mmHg)
Normal Fi value
0 –> do NOT want any inhalation of CO2 in most conditions
capnographs produce a wave form which is useful to
diagnose respiratory problems
CO2 is an end-product of…
metabolism, then sent to lungs for exhalation
Levels of CO2 depend on…
cell metabolic rate, perfusion of lungs, ventilation
& can be used to diagnose issues w/ breathing system
Capnography monitors…
ventilation, circulation, metabolism
End-tidal or exhaled CO2 equates w/
alveolar & arterial CO2
UNLESS VQ mismatch or other issues
Increased inspired CO2 (Fi) indicates
equipment is faulty
capnography provides range of info including:
- CO2 production (metabolism)
- pulmonary perfusion & CO
- alveolar ventilation
- breathing system & other equipment issues
- efficiency of CPR
- warns of impending cardiac arrest
when looking at a capnograph, how do you determine hypercapnia is occurring? Clinically, what is happening physiologically in the patient?
EtCO2 > 6kPa
ventilation is not keeping up w/ expelling CO2 at the appropriate rate –> build up of CO2
What is the most common cause of hypercapnia?
decreased alveolar ventilation due to: too deep anaesthesia, geriatric, obesity, pregnancy, space-occupying masses, muscle weakness, laparoscopy, endoscopy (expansion of abd contents), pain
What is the 2nd most common cause of hypercapnia
Equipment failure causing rebreathing of CO2 –> exhausted soda lime, dysfxning unidirectional valves, too low FGF, equipment dead space
What are other causes of hypercapnia aside from the most common ones?
increased metabolic rate –> hyperthermia, hyperthyroidism, seizures, etc
What are the 4 main causes of hypocapnia?
- decreased metabolism
- decreased perfusion
- increased alveolar ventilation
- equipment problems
Remember: if you suspect that the hypocapnia seen on a capnograph is due to decreased cardiac output, it is…
an emergency
Explain the 4 phases of a capnograph trace?
I: exhaling anatomical dead space gas, no CO2
II: alveolar air w/ CO2 joins dead space air
III: exhaling only alveolar gas
0: inhalation, normal CO2 drops & majority should be 0 CO2 during this time; if not, then is inhaling CO2
What kind of trace is this?
Normal capnograph trace
What kind of trace is this? Is it normal or abnormal?
Cardiogenic oscillations
Normal trace
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
abnormal
hypoventilation
P hypoventilated so hypercarbic
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Abnormal
Bronchoconstriction or partial airway obstruction/kink
Expiration difficult/restricted leading to accumulation of CO2
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Patient fighting the ventilator
Abnormal
Patient is trying to inhale in the middle of ventilation
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Rapidly decreasing EtCO2
Abnormal
indicates cardiac arrest, rapidly failing cardiac output; OR leak in cuff or breathing system not connected
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Leaky ETT Cuff
Abnormal
when exhaling, the CO2 majority exits into the room around the tube, so lower EtCO2 than what is being exhaled
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Abnormal
Rebreathing of CO2 in a circle system due to leaky valves
leaky valve so circle fails which is unidirectional flow of gas, then can no longer airflow properly so P breathing in CO2
when not reaching baseline during inspiration = massive rebreathing of CO2
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Rebreathing of CO2 in a non-rebreathing system
abnormal
insufficient FGF on non-rebreathing
Gap on baseline = rebreathing CO2
What kind of trace is this? Is it normal or abnormal? What is happening to the patient?
Oesophageal intubation
abnormal
breathing, not no CO2; if you see this and know p is breathing, you intubated in the wrong tube and need to reintubate