Physics = Measurment Flashcards
emergency oxygen flush?
100% oxygen is supplied from the common gas outlet, which has bypassed both flowmeters and vaporisers.
flow of oxygen is usually 45 l/min at a pressure of 400 kPa.
blood gas analysis
Heparin is an acid and will lower the pH of the sample
A warmed ABG from a hypothermic patient will show a higher PaO2, higher PaCO2 and a lower pH than that actually present in the patient’s blood in vivo.
standard bicarbonate is measured in a sample titrated to a PCO2 of 5.3, which eliminates the respiratory component, and is a reflection of the metabolic component.
Cardiac Output monitoring modalities
Oesophageal Doppler Transthoracic impedance PiCCO NICO Thermodilution Lithium dilution. (LIDCO)
Osmolarity solutes?
sodium salts (chloride and bicarbonate), glucose, and urea nitrogen
Caudal anaesthesia dose
Sacral procedure 0.5 ml/kg
Inguinal procedure 0.75 ml/kg
Lower thoracic 1 ml/kg
Mid-thoracic 1.5 ml/kg
Wright respirometer
One way system, exhaled tidal volume and minute volume.
+/- 5 to 10%.
150 revolutions when one litre of gas
minimum flow of 2 litres per minute is required
Humidification
Alveoli 43g/m3, @ 37*C
1 micron - ideal
US nebuloser - 2 MHZ
Damping - sine wave
Critical damping provides the quickest approach to zero amplitude (damping factor = 1).
With an optimally damped system there is a rapid initial decline in the oscillation to zero amplitude but there is then a small overshoot of about 6-7% of the original amplitude. An optimal damping factor of 0.64 is applied to blood pressure monitoring systems.
Axis deviation
If the mean vector is shifted superiorly and leftward (axis of −30° to −90°) left axis deviation (LAD) is present.
I, II, aVF used
Spectrophotometric absorption spectra
The isobestic point occurs at a wavelength around 800 nm. The maximum difference in the absorption of the two forms of haemoglobin occurs at a wavelength of about 650 nm.
Bernoulli’s principle
an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy
Venturi effect
reduction in fluid pressure that results when a fluid flows through a constriction in a tube.
Coanda effect
a flow of gas or liquid attaches itself to a nearby surface and remains attached even when the surface curves away from the initial direction of flow.
Charles’s law:
At constant pressure the volume of a given mass of gas varies directly with absolute temperature
Boyle’s law
At constant temperature the volume of a given mass of gas varies inversely with pressure.
Gay-Lussac’s law
for a given amount of gas held at constant volume, the pressure is proportional to the absolute temperature:
Dalton’s law of partial pressure
The pressure of a mixture of gases is equal to the sum of the pressures of all of the constituent gases alone.
Henry’s law
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
joule (J)
amount of energy expended if a force of one newton (N) is applied through a distance of one metre (N·m)
Kinetic energy (KE) =
½ MV2
potential energy (PE)
mass × height attained × acceleration due to gravity
Work done (WD)
V (potential difference) × I (current) × t (time)
Soda lime granules
94% calcium hydroxide, Ca(OH)2
5% sodium hydroxide, NaOH
1% potassium hydroxide, KOH
Baralyme
20% barium octahydrate and 80% calcium hydroxide
Cardiopulmonary exercise testing (CPX, CPEX, CPET)
An AT below 11 ml/kg/min is associated with increased mortality particularly if there is evidence of myocardial ischaemia during the test.
average barometric pressure at sea level
1 atmosphere 1000 cm of water 760 mmHg 101.325 kPa 1 Bar 14.7 pounds per square inch.
Ohm’s law
V = I × R
Resistors
In series
R1 + R2
In parallel
1/R1 + 1/R2
Capacitance
V = Q/C
In Parallel
C1 + C2
In series
1/C1 + 1/C2
Lambert’s law
each layer of equal thickness of the medium absorbs an equal fraction of the energy traversing it.
Beer’s law
absorbance being directly related to the concentration of a substance
Capnography
Sapphire chamber
Filtered infrared light
- 4.25 micrometres
Collision broadening - other polyatomic moelcules
Oxygen Measurement
Oxygen is paramagnetic (attracted)
Clark electrode - platinum cathode and silver anode
Galvanic fuel cell - gold cathode and a lead anode
Lasers
Carbon dioxide - cut tissues and coagulation
Argon or krypton - light in the blue-green
absorbed by red coloured tissues
ophthalmology, photocoagulation and dermatology
Nd YAG - infra-red Debulk tumours and for photocoagulation.
Sterilisation
Dry heat - Slow 30 mins @ 150*c
Autoclave - Time dependent on temp and pressure
Ethylene Oxide - For those that cant be heated
Long complex, preconditioning, series of cycles
Radiation commonly used
BIS
B - Aware:
Reduced awareness with muscle relaxant
B - unaware:
No difference
BAG - RECALL:
Less awareness with ETAC than BIS
Currently recommended with TIVA and with muscle relaxant
Pulse ox
Wavelengths of 660 nm (red) and 940 nm (infra-red or IR)
Isobestic points 660 and 940nm
Laryngoscopes
Straight: Miller, Soper, Wisconsin Seward
Advanced over epiglottis and lifted (neonates)
Curved: Macintosh, Polio, McCoy
(Right sided)
Placed in Vallecula
Seebeck effecrt
Thermocouple
Thermoelectric effect
The electromotive force at the measuring junction is proportional to temperature.
Gas cylinders
02: C (340) - J
Size E - Machine 680L
Size J - Manifold 6800L
(Volumes double with each letter)
Filling ratio 15 degrees
0.75 in UK
N2O: C - G
Size C 450L
Size E 1800L
Complications
1/10 - Very Common 1/100 - Common 1/1000 - Uncommon 1/10,000 - Rare 1/100,000 -Very Rare
Diamagnetic
N2
CO2
N2O
