General monitoring + ECG Flashcards
What is a monitor?
A device which measures an output , processes the information and displays it in a form that can be interpreted by the user.
may also include alarms which will sound when values deviate from the normal range
what is the minimum AABGI for general anaestheia?
core monitoring = ECG, pulse oximetry, NIBP
capnography
airway pressures and volumes and respiratory rate
Volatile anaesthetic gas monitoring and inspired oxygen concentration.
Airway pressure monitoring (if ventilated).
temperature if op >30mins
NMB monitoring when NMBA used.
depth of anaesthesia - TIVA
invasive BP/ CVP - critically il/ significant operation.
what is minimum AABGI monitoring for sedation and regional anaesthesia?
NIBP
Sats
ECG
for sedation need ETCO2 if loss of response to voice.
what is the minimum AABGI in recovery post op?
core monitoring
NIBP
Sats
ECG
how often should BMs be monitored in diabetics in general anaesthesia?
once hourly
how often does an anaesthetist need to record data on the anaesthetic chart?
every 5 mins for BP, HR and sats
every 15 mins for CO2, ventilatory parameters etc
more frequently if unstable.
what is the purpose of monitoring?
monitors allow us to measure clinical parameters and warn us of deviations from the norm so we can act on them.
they should supplement clinical assessment
what are the problems with monitoring?
over reliance - treating numbers vs clinical picture. distracts anaesthetists from the patient.
fault in equipment - incorrect medications given - give example of arterial line transducer being above patient and treating hypotension incorrectly.
complications from monitoring - interference and current leak, ecg stickers irritating skin etc
constant alarming - can become less significant
what types of biological potentials can be measured?
Tissues that produce action potentials and changes to membrane potential. There tissues produce currents as their membrane potential changes and action potentials transmit.
ECG - compound potentials in myocardium
EEG (electroencephalogram)- compound potential records from brain activity
EMG *electromyogram) - muscle membrane potential changes
what components are needed to measure biological potentials?
Electrodes - detection of potential - since this is already in form of current, no transducer is required
cables - to carry current to processor
amplifier and processor - amplification of signal and filtering out noise - often by common mode rejection and high/low pass filters
display unit - displayed on a screen or printed on paper.
can you describe how an ECG electrode works?
ECG electrodes constist of silver/silver chloride electrode in contact with conductive gel and surrounded by an adhesive mount.
chloride ions in gel in direct contact with skin can allow current to pass to silver/silverchloride electrode, which again transmits current through to wire. this gel improves contact hence reduces impedance and signal loss.
hence currents present at skin surface can be transmitted through the electrode to the wire.
surrounded by adhesive mount which sticks to skin and improves contact between electrode and skin.
what factors can reduce and improve contact with ecg electrodes
anything on the skin surface can reduce contact e.g. skin or water and greese.
hence skin should be shaved and cleaned and allowed to dry before electrodes attached.
positioning on bony prominences reduces artifacts from respiratory muscles
other than ECG monitoring, when else are electrodes used?
EEG and EMG monitoring
nerve stimulators in looking at effects of NMBA and also in diagnosis of neuromuscular diseases.
defibrillators
what are ECG cables ?
cables connect electrodes to processing unit / amplifier.
cables conduct currents
the cables are colour coded / labelled such that they are positioned correctly and the processor can display correct signal for each lead for interpretation of regional abnormalities.
can be 3 lead or 12 lead or 5 lead depending on indication.
Can you describe the set up of a 12 lead ECG
limb leads = 4
chest leads = 6
By different combinations of limb leads the electrical potential in different vectors of the myocardium can be recorded. e.g. chest leads record changes in the horizontal plane, directly beneath electrode. 1 recorded per electrode
limb lead combinations produce 6 vectors in the vertical plane through comparisons between the different leads with one another or a 0 point.
in total this makes 12 different leads
3 bipolar = compare signals between each of the leads e.g. Lead 1 compares signal between LA and RA
3 unipolar/ augmented = comparing limb leads to a neutral point e.g. aVF compares signal in LL to the 0 point of RA and LA (lead 1)
6 chest leads = record and display currents directly benefit hence in the horizontal plane
Describe the location of each of the 12 electrodes in a 12 lead ECG…
V1 = right side of sternum, 4th intercostal space
V2 = left side of sternum, 4th intercostal space
V4 = apex= 5th intercostal, mid clav line
V6 = 5th intercostal, mid axillary line
V3 and V4 inbetween the others
RA = red
LA = yellow
LL = green
RL = black
draw the einthovens triangle
what direction does depolarisation have to travel to create positive/ negative deflection?
positive = towards
negative = away from
right angle = biphasic
what leads can help locate MI location?
aVL, lead 1, V5, V6 = lateral = circumflex artery
aVF, II and III = inferior, RCA
V1 - V2 = septal
V3- V4 = anterior
