Equipment Flashcards
What is a pressure transducer in an arterial line?
Device that converts pressure into electrical signal by movement of a diaphragm.
Incorporates a strain gauge -> increase tension = increase resistance = change in current flow
What is a Wheastone bridge?
4 strain gauges to form the 4 resistance of the bridge.
Allows determination of an unknown resistance in terms of other known resistances
increases the sensitivity for detection of small changes in resistance
What does damping do in arterial line?
Damping prevents a system from overshooting after responding to a change, particularly at frequencies close to the natural frequency of the system
1 atm =
? bar
? mmHg
? kPa
? cmH2O
1.01 bar
760mmHg
101 kPa
1033 cmH2O
What are the components of sodalime?
Calcium hydroxide 97%
Potassium hydroxide 1%
Ethyl violet indicator - turns violet when pH drops due to accumulation of carbonic acid
3–5% NaOH
Heat and water are produced during the reaction.
Hazards of sodalime?
Carbon monoxide production with volatile agents (not servo)
Formation of compound A with sevo -> ?nephrotoxicity
leak, fire hazard, increase resistance
How does ultrasound work?
Piezoelectric effect - conversion of electric energy to mechanical energy (vibration) - allows generation of sound waves at ≥20kHz
Different tissue types have different acoustic impedance, determines the degree of US reflection, absorption.
Advantages and disadvantages of a side stream capnography sensor
Reduced bulk at patient end
Introduces a delay of ~1s
Narrow tubing can be blocked by water vapour
How does capnography work?
Utilises how CO2 absorbs infrared radiation
- An infrared light source emits a beam that passes through the patients exhaled breath
- Light passes through a filter producing of wavelength of 4.26um
Beer-lambert Law - amount of infrared light absorbed is proportional to the concentration of CO2 in the sample
Detector to allow measurement
What effects can introduce inaccuracy to capnography
Use of N2O -> collision broadening effect
Pressure effect -> high PEEP -> increase number of CO2 per unit volume
Components of vacuum insulated evaporator
Storage of liquid oxygen at -160 to -180 degrees
Double walled - inner stainless steel, outer carbon steel shell
–> minimises heat transfer from environment
Kept at 7 Bar, which is the SVP of O2 at -160degrees
Tripod for weighing
7pm relief valve
Evaporator, superheater, 4atm pressure regulator, wall outlet
How does VIE maintain its low temperature
Latent heat of evaporation - as o2 vapour is drawn off for use, more liquid oxygen evaporates to replace, which absorbs heat.
How does cerebral oximetry work?
Uses near infrared spectrometry to assess cerebral oxygenation
- Emission of infrared light
- Detection of scattered and unabsorbed light
- Uses a mixed average of arterial and venous components, reflecting extraction of O2 in brain.
What’s a widely accepted criteria for desaturation on cerebral oximetry?
reduction of >20% from baseline, or absolute value of <50%
Limitations of cerebral oximetry?
Extracranial contamination
Only regional measurement, not deep tissue
No universally accepted calibration, baseline variation and threshold for abnormality
Lack of direct CBF measurement
Reading compromised by regional pathologies
Artefacts from indocyanine green, methylene blue
Advantages of cerebral oximetry?
non-invasive
Easy to set up
Real time feedback
Early warning of cerebral hypoerfusion
Risks of pneumatic limb tourniquets?
Tissue ischaemia (muscle, nerve)
Systemic changes (cardiac, Resp, haem)
Hypothermia
Metabolic (hyperK, lactaemia)
Skin fraction burns
Tourniquet pain
Pneumatic limb tourniquet safe inflation time?
Fixed pressure of 250mmHg UL, 300mmHg LL
Or +100 above SBP
Limit to 1.5 to 2 hours
Deflate for short period of time 10-15mins if exceeding limit
How does residual current device work?
Neutral wire and live coils wound in opposite direction around an iron core.
Monitor of magnetic field, which should cancel each other out under normal circumstances.
Circuit leak = imbalance = cut off supply within 30ms.
Limitations of RCD?
Normal leakage current can trigger shut down
Regular maintenance required
Not a complete protection on its own
Limited protection against an overloaded circuit
- Overheating due to overloaded circuit can still occur.
Components of a guideline for ketamine infusion on ward?
(If you are setting up a service)
Drug factor - concentration of solution, starting dose, dose range, max dose.
Patient eligibility - not for children <2, caution in psychiatric disorder, liver dysfunction, CV disease, raised ICP
Delivery equipment - proper labelling of medication and lines, lockable syringe pump
Monitoring requirement - regular obs, GCS, pain score, monitor for neuropsychiatric effect.
Regular APS service - limit placed on duration, assessment of pain score, changing of dose, side effects
Patient and staff education
Documentation
Components of a WHO time out
confirm all team members are present and attentive
Verify patient identify, procedure, and site
Review critical steps of surgery
Confirm abx prophylaxis requirement
Ensure necessary imaging available
Discuss any patient concerns
5Rs of drug administration?
right time, patient, dose, route, drug
Can you transfuse platelet and PRBC in the same line?
Not recommended.
Though PRBC can be given after platelet, but not the other way around due to risk of platelet aggregation.
