Critical patients monitoring Flashcards
What is the most important monitor?
- The most important monitor is a dedicated and experienced anaesthetist able to record, interpret and act on the information given
- Without this essential person the monitors are just random number generators!
Discuss pulse oximetery
Displays percentage oxygen saturation of haemoglobin gives you no idea of amount oh Hg or oxygen content of blood just tells you the saturation of the Hg there.
What affects the accuracy of pulse oximetery?
Accuracy is affected by
–poor circulation (common in critical patients so least useful in these ones)
–ambient light (strip lights cover them they are better)
–movement of the probe
When is a pulse ox useful?
Useful post-op
–Saturating on room air?
–Ian uses a lot on brachycephalics once extubated to make sure still saturated
Discuss the newer generation of pulse oximetry?
Newer generation pulse oximeters are available such as ‘Masimo’™ machines and some incorporate co-oximetry.
- Uses >7 wavelengths of light to acquire data
- Advanced signal processing algorithms and unique adaptive filters
- Potentially more useful in critical anaesthesia
- Give % of amounts of different haemaglobins
Discuss electrocardiogram (ECG)?
- ECG analysis does not give information about the mechanical activity of the heart
- Important for arrhythmia diagnosis and monitoring response to treatment
Electrocardiogram (ECG) what do we see?
- Various arrhythmias may be seen
- Sinus tachycardia most commonly seen
- Tachycardia (sinus) may be the result of
- Nociception (Treatment is analgesia, top up of methadone bit of fentanyl)
- Hypercapnia
- Hypovolaemia (whats MM like, CRT, BP)
- Hypokalaemia (tachycardic patient with no T waves)
- And many more…
–ECG may show characteristic changes depending on the underlying cause
Discuss bradycardia causes?
Bradycardia (less common unless cats shocked cats go bradycardic) causes:
- Drugs (e.g. alpha-2 agonists, opioids)
- Hypothermia (e.g been in theatre for 6 hours)
- Electrolyte disturbances e.g. severe hyperkalaemia (always think K hugeeee T waves)
Knowledge of the patient is vital to determine treatment, discuss?
Alpha-2 agonist-induced bradycardia with second degree AV blocks
- treatment is antagonism of the original dose (atipamezole)
Opioid-induced bradycardia
- Treatment is the administration of an anticholinergic (atropine or glycocholate) (Atropine contraindicated following alpha-2 agonist administration as you will ask that heart to work really hard against a massive after load as alpha 2s cause vasoconstriction)
Look at this second degree AV block and discuss?
Discuss atrial fibrillation in a dog?
- AF does not worry Ian as not much he can do about it
- In this image the ventricles are getting a bit pissed off about it as well
- What he will do is ensure o2, co2 and pressures are good, not getting cold, no pain (nocioceptive). Control what you can control and finish surgery as soon as you can.
Look at this?
Discuss capnography?
- Capnography (carbon dioxide measurement) conveys information relating to both respiratory and cardiac function. CO2 gets back to lungs because the heart pumps it there so therefore most sensitive marker of cardiac arrest in anaesthetised patient.
- B-C: expiration with dead space
- C-d= expiration but alveolar gas
- D= pause
- D-E Not inspiration, this is the pause
Discuss capnography further?
- The end tidal carbon dioxide concentration is measured from the alveolar plateau and should remain constant with unchanged ventilation and cardiac output
- Main-stream and side-stream machines are available
Discuss normals in capnography?
Normal ET CO2 = 35–45 mm Hg (Ian accepts 45-55mmHGg in anaesthetised patients)
- Hyperventilation – Decreased ETCO2
- Hypoventilation - Increased ETCO2
How does capnography appear on cardiac arrest?
Cardiovascular status
–CVS depression / arrest
- Reduced delivery CO2 to lungs
- ETCO2 40-20-10 (can see in pics it dropping rapidly)
What could cause this appearance on capnography?
Called a sharks fin
- Endotracheal tube obstruction
- Caused by a kinked tube. Often caused by blood in tube during dental. Treatment wip tube out and pop a new one in.
- Asthma in cats looks like this
- Anaphylaxis looks like this
What can be seen on this capnography trace?
Rebreathing (where we don’t go down to baseline)
–Many causes
–In non-rebreathing system treat by increase the flow
–In rebreathing system treat by checking/replacing soda-lime
What else can capnography show you?
Other indicators
- Oesophageal intubation
- Leak at cuff/Patient disconnection
- Adequacy of resuscitation
- Can tell you are doing a good job with CPR
What can be seen on this capnography trace?
Normal variation – cardiac oscillations (just heart beating against lungs and pushing out little bits of CO2 so tells you mechanical activity of heart.)
Discuss blood pressure measurement?
- Together with heart rate used as surrogate measure of cardiac output
- Assess haemodynamic status throughout the peri-operative period
Discuss Indirect; oscillometric or Doppler blood pressure measurement?
–Tachycardic/hypovolaemic patients may be unreliable (trends only)
–Doppler measurement using a manually inflated cuff attached to a manometer reads systolic pressure
–In dogs reasonably accurate for systolic (cats the reading is closer to the mean blood pressure than systolic so will accept a little bit lower)
What is gold standard blood pressure measurement?
Direct arterial pressure via an arterial cannula “gold standard”
–Usually placed in the dorsal pedal artery
–Cannula is attached via saline-filled non-distensible tubing to an electrical transducer which gives continuous ‘beat to beat’ diastolic, mean and systolic arterial pressures
Although blood pressure monitoring is important it does not tell us directly about organ perfusion. What may be of equal value?
Assessing urine output may be of equal value in determining renal perfusion
- Aim for 1-2ml/kg/hr intraoperatively
Causes of decreased blood pressure include?
–Intravascular fluid loss (haemorrhage, third space losses)
–Failing myocardial function
–Sepsis
–Relative hypovolaemia common in less critical patients (vasodilation – drugs/sepsis) e.g isoflurane does this treatment is to reduce the Iso
•Important to assess overall clinical picture to treat correctly
Hypothermic patient with bradycardia and low blood pressure. How will you treat?
Anticholinergic treatment and warming to raise heart rate and subsequently blood pressure
Septic patient with tachycardia but poor blood pressure (grossly vasodilated and hypovolaemic). Discuss treatment?
Intravenous fluid therapy to improve status
Patients with advanced sepsis require pressor support. What are these?
–Noradrenaline
–Dopamine
–Phenylephrine
Discuss central venous pressure
- Informs us about cardiac preload
- Used as an approximation of right atrial filling pressure (late guide)
- Acts as a guide to correct fluid therapy (late guide)
–May aid in detection of tricuspid valve problems
•CVP readings can be affected by
–Mechanical ventilation
•A reduction in CVP during the inspiratory phase may also indicate hypovolaemia
Discuss fluid therapy?
- All critical patients should receive fluid support
- Unfortunately rarely ‘monitored’
- Trend towards Goal Directed Therapy
- Covered on clinics!
Discuss cardiac output measurement?
- Not routinely measured in veterinary patients although this may change as more affordable and user friendly monitors are introduced
- Commercially available systems include
–Heat, lithium or dye dilution techniques which collect afterwards and workout volume of blood that it has needed to flow through
–Pulse waveform analysis
•Future technique?
Discuss aims of central nervous system monitoring?
–Adequate ‘depth’ for procedure undertaken
Are monitors helpful?
–Drug requirements
–End-tidal volatile
concentration
–Injectable drug
dose
ET: end tidal
FI: fraction inspired
Discuss Electroencephalogram (EEG)?
Electroencephalogram (EEG)
–Raw signal data
–Spectral edge frequency
–Auditory evoked potentials
•Very limited clinical value
Discuss bispectral index?
Ian’s monitoring preferences order?
In order;
–Dedicated anaesthetist
–Capnograph
–Direct blood pressure/dynamic indices
–ECG
–Central venous pressure
–Pulse oximeter
–Cardiac output
