Physics Flashcards
What is flow?
The amount of a substance passing a point per unit time (F = Q/t)
The two main types of flow are laminar and turbulent
What determines flow?
Hagen Poiseuille equation:
Pi x r4 x dP
—————
8 x n x L
(n = Viscosity)
What is temperature?
Temperature is the thermal state of a substance. Its SI unit is the Kelvin which is based on the thermodynamic triple point of water
What are the components of a scavenging system?
Scavenging systems can be active or passive and will comprise of: —Collecting system —Transfer system —Receiving system —Disposal system (—Exterior)
How can oxygen be measured?
Oxygen can be measured in a gas mixture or in a solution
Gas:
—Fuel cell (lead & gold) (KOH)
—Paramagnetic analyser
Liquid:
—Clark electrode (Silver/silver chloride & Platinum)(KCl)
How can CO2 be measured?
CO2 can be measured either as a gas or dissolved in a liquid. Common ways to measure include: Gas: —Capnograph —Infrared (2 or more different elements)
Liquid:
—Severinghaus electrode (modified pH electrode)
How is cardiac output measured?
Invasively: —PA catheter —PiCCO —LiDCO (rapid) Non-invasively: —Oesophageal Doppler —Bioimpedance
What measurements can be obtained from an Oesophageal Doppler?
Cardiac Output
—Stroke Volume Index
—Flow Time corrected (FTc) = preload
—Peak velocity = contractility
—SVR/afterload (FTc & PV interpretation)
What is LASER?
LASER stands for Light Amplification by Stimulated Emission of Radiation
What information can be obtained from a capnograph?
—Presence of CO2 to confirm endotracheal intubation
—Cardiac output (presence of)
—Bronchospasm
—Breathing pattern/loss of neuromuscular blockade
—Hypo/hyperventilation
What do we mean by MRI?
Magnetic Resonance Imaging:
—using strong magnetic fields to create images
A static magnetic field aligns the H+ ions in the body
Pulses of radiofrequency energy are applied to flip these ions out of alignment
As they fall back into their initial alignment, energy is released
What is risk? What tools do we use to score it?
Risk is the possibility of suffering harm
Scoring systems: —NELA —P-POSSUM —Cardiac: -Lee’s revised cardiac risk -Euroscore —Thoracoscore
What is the number needed to treat?
Describes the number of people who need to receive treatment before 1 person gets benefit.
For anti-emetics = ~5
For some analgesics in chronic pain =~5
NNT = 1/ARR (absolute risk reduction) ARR = Control Event Rate - Experimental Event Rate
When using depth of anaesthesia monitoring, what are the EEG waveforms that indicate surgical anaesthesia?
Beta waves = awake; >12Hz Alpha waves = sedation/light GA; 8-12Hz Theta waves = surgical anaesthesia; 4-8Hz Delta waves = deep anaesthesia; <4Hz Burst suppression = too deep
What is the equation for SVR?
SVR = (MAP - CVP) / CO x 80
In dynes/sec/cm-5
What are the key considerations of a vaporiser?
Plenum vs injected
—SVP
—Splitting ratio
—Wicks/baffles/high internal resistance - fully saturate the gas with vapour
—Latent heat of vapourisation = temp falls as liquid vaporises so requires compensation: heat sink and use of bimetallic strip to adjust flow of splitting ratio
—Calibration to individual volatiles
Problems:
—Overfilling
—‘Pumping’ effect
—‘Pressurising’ effect
How can we measure stroke volume?
Direct measurement of cardiac output (and working back from that)
Indirect by using Echo or Oesophageal Doppler
(Area under the systolic curve)
What are the safety features of an anaesthetic machine?
Power supply:
—Plug in & battery - alarms for failure
Gas supply:
—Pipeline (colour coded, Shrader valves, NIST)
—Cylinders (colour coded, Bodek seal, pin index system)
—Pressure regulators & gauges
Gas flow:
—Pressure regulators
—Flowmeters (mechanical vs electrical; O2 last; hypoxic guard)
—O2 alarm (Ritchie whistle)
—O2 flush
—APL
Vaporisers:
—Colour coding
—Agent specific, filling devices, non-spill
How can you measure BP?
Invasively:
—Arterial line
Non-invasively: —Occlusive cuff method (manual/electronic) - oscillotonometer principle —Von Recklinghausen oscillotonometer —Penaz technique (continuous) - infrared —Doppler US
How do we measure temperature?
Non-electric:
—Liquid expansion thermometers (mercury, alcohol)(Bourdon gauge measures pressure change from gas expansion)
—Bimetallic strip dial thermometer (2 different metals with different expansion coefficients)
—Chemical thermometer - crystals
Electric:
—Thermocouple (2 dissimilar metals, voltage difference = proportional to temp) Seebeck effect
—Resistance thermometer (platinum)
—Thermistor (semiconductor; negative exponential)
Infrared (all objects emit em radiation)
