Physics Flashcards by Neil Botting

osmolarity vs osmolality

Osmolarity = number of osmotically active particles in 1 litre of solution
Osmolality = number of osmotically active particles in 1 kg solvent

Osmolality used as temperature alters volume not mass

tonicity is the osmotic properties of a fluid in relation to a membrane

How well did you know this?

Not at all

Perfectly

Measuring osmolarity and osmolality

Osmolarity is calculated (difficult to measure)
glucose + urea + 2 x Na
Osmolality is measured by osmometer - depression of freezing point of water (higher osmolality, lower freezing point)
Osmolar gap = difference between two i.e. unmeasured osmoles (methanol, ethanol, ethylene glycol)

How well did you know this?

Not at all

Perfectly

Osmole

unit of measurement describing number of moles of a compound that contribute to osmotic pressure and that would depress freezing point by 1.86 K

How well did you know this?

Not at all

Perfectly

Colligative properties

properties of a solution which are affected by osmolarity
- depression of freezing point (1.86K per osmole)
- reduction of vapour pressure (less space for solvent on surface)
- increase boiling point
- increase osmotic pressure

How well did you know this?

Not at all

Perfectly

Clinical applications of osmolality

SIADH - reduced osmolality
DI - increased osmolality
TURP syndrome - reduced osmolality
Hyperosmolar states e.g. HSS

How well did you know this?

Not at all

Perfectly

Transducer

Converts one form of energy into another form
Active - generate electric current directly in response to stimulation e.g. piezoelectric
Passive - external power source - change in resistance etc converted to equivalent electric current

How well did you know this?

Not at all

Perfectly

Ultrasound

Sound waves at frequency above human hearing > 20KHz
Medical USS 2.5 - 15 MHz

How well did you know this?

Not at all

Perfectly

Principles

Array of piezoelectric crystals
USS waves generated by piezoelectric effect - electric voltage across piezoelectric crystal makes it vibrate
Frequency of vibration corresponds to frequency of current
USS travels through tissue and reflected at tissue interfaces - when there is a change in density e.g. boundaries between tissues
reflection transduced into display
strong reflections from solid structures are white
weaker reflections grey
absence of reflections e.g. blood black
velocity of sound waves in tissue is 1540m/s

How well did you know this?

Not at all

Perfectly

Ultrasound modes

A-mode - transducer scans a line through the body, echoes plotted on screen as function of depth
B- mode - brightness - linear array of transducers produces beam of USS in a plane, reflections viewed as two dimensional image
M-mode - motion - rapid sequence of B mode follow each other in sequence - examination of moving structure
Doppler mode - Doppler effect - increase in frequency of signal when the source of signal is approaching the observer and decrease in frequencyy as sound source moves away.
change in frequency i.e. increase in frequency of RBC moving towards and decrease in frequency of RBC moving away = doppler shift, can be used to calculate velocity
v = Fd x 1540 / 2 x emitted frequency x angle

How well did you know this?

Not at all

Perfectly

USS image quality

Not all of the USS beam is reflected
- absorption - tissue absorbs acoustic energy
- reflection - only some of acoustic energy is reflected directly back to the probe
- refraction - deflected acoustic energy at difference angle
- divergence - spread out of energy
Improved by
- amplitude - increasing strength of the use wave increases reflected acoustic energy
- frequency - higher frequency better resolution but worse penetration (linear = 10MHz, curvilinear = 5MHz)
- Gain - screen brightness

How well did you know this?

Not at all

Perfectly

How is blood pressure measured

Non-invasively
- Mercury sphigmanometer
- Oscillometery
Invasively
- Arterial line

How well did you know this?

Not at all

Perfectly

Non-invasive non automated BP measurement

Sphygmomanometer
- Centre of cuff over brachial artery
- Width 20% greater than diameter of arm
- Aneroid gauge or column of mercury
- Cuff inflated above systolic, released 2-3mmhg/sec
- Auscultation over brachial artery for Korotkoff sounds
1 = blood flow in artery first appears
2 = muffling
3 = rising in volume
4 = fall
5 = absence
Oscillometric
- cuff / aneroid gauge
- cuff deflated below systolic, needle on aneroid gauge oscillates
- pressure at onset of oscillation = systolic
- max oscillations = mean
- decreasing oscillation = diastolic
Von-Recklinghausen oscillotonometer
- two overlapping cuffs on upper arm
- proximal = sphygmomanometer
- distal = measure oscillation

How well did you know this?

Not at all

Perfectly

Non-invasive automated BP measurement

DINAMAP - device for indirect non-invasive automated MAP
- similar to von-recklingausen
- single cuff, pressure transducer, microprocessor, display
- pressure transducers measured pressure and oscillations
- onset of oscillations = systolic, max = MAP, diastolic derived
- reliable but need 2 min intervals, arrhythmias unreliable, fail to record if < 50
Penaz
- LED through small finger cuff
- light detected other side
- amount of light absorbed by tissues proportional to volume and therefore BP

How well did you know this?

Not at all

Perfectly

Invasive arterial blood pressure measurement

gold standard, beat to beat
intra-arterial cannula - short, stiff
column of fluid pressurised to 300mmHg with 4ml.hr flush
transducer - mechanical energy (movement of diaphragm) to electric
electric signal amplified and processed
- saline column in contact with diaphragm and 4 strain gauges
- tension of strain gauges alter as diaphragm moves
- change in tension changes electrical resistance, measured by wheatsonte bridge

How well did you know this?

Not at all

Perfectly

Complications of arterial cannulation

Early
- haematoma
ischaema (vasospasm)
Late
- ischaemia (thrombosis
- infection
Any time
- exsanguiantion
- intra-arterial injection

How well did you know this?

Not at all

Perfectly

Damping and resonance

resonance - every system has resonant frequency - system will ossilate if left alone. if frequency coincides with frequency of arterial waveform - increased amplitude and distortion
Damping - inherent tendency of system to resist oscillations
- optimal 0.67
- critical 1.0
- over damped - waveform stops quickly due to compliant tubing, air bubble > 1
- underdamped - resonance causes the trace to oscillate and overshoot

How well did you know this?

Not at all

Perfectly

Information from arterial waveform

slope of upstroke - myocardial contractility
downslope - SVR. steep downstroke with low dicrotic notch indicates low SVR. high dicrotic notch implies high SVR
respiratory swing in IPPV - hypovolaemia

How well did you know this?

Not at all

Perfectly

Pulse contour analysis

SV proportional to AUC systolic portion of curve
CO = SV x HR
SVV - min SV divided by max. > 15% suggests fluid responsive

How well did you know this?

Not at all

Perfectly

Cardiac output measurement

Clinical
Non-invasive - TT electrical impendence
Minimally invasive - ODM PICCO
Invasive - PAC

How well did you know this?

Not at all

Perfectly

PAFC

Fick principle - uptake of substance by organ is equal to amount entering and leaving
PAC indirectly measures CO by thermodilution
- cold saline 10ml proximal lumen
- change in temperature measured by thermistor in tip
- rate of change in temperature reflective of CO and calculated by Stewart-hamilton equation (AUC log change in temp over time)

How well did you know this?

Not at all

Perfectly

Pulse contour analysis

Arterial pressure waveform morphology
- slope up - contractility
- AUC up to dicrotic notch - SV
- downstroke / position dicrotic notch - SVR
Computer algorithms to calculate CO
- SVV - change in CO over respiratory cycle
- calibrated - PICCO - CVC / specialised art line measure transpulmonary thermodilution. LIDCO uses lithium. Stewart-Hamilton eq
Uncalibrated use height weight nomograms e.g. lid rapid

How well did you know this?

Not at all

Perfectly

Oesophageal doppler

USS probe at 45 degrees to aorta
USS beam reflected at different frequency when red blood cells are in motion
- measure blood velocity multiplied by CSA aorta
- velocity plotted against time
waveform
- contractility - peak velocity
- preload- flow time
- SV - stroke distance area under the velocity / time curve

How well did you know this?

Not at all

Perfectly

Thoracic electrical bioimpedence

Resistance to alternating current flowing through the body
electrodes neck / chest. resistance to current flowing from outer to inner electrodes measured.
Bioimpedence is related to water content of the thorax
nomograms to estimate volume of electrically participating tissue
impedance changes throughout the cardiac cycle as the volume of blood in the thorax changes - microprocessor analyses and estimates SV
Sensitive to movement, diathermy, arrhythmias

How well did you know this?

Not at all

Perfectly

Electrical current

Rate of flow of electrons past a point in a conductor
Measured in Amperes (SI unit)
- 1 coulomb of charge passing a point in one second.

How well did you know this?

Not at all

Perfectly

Voltage and current

Ohms law V = I x R
V = Voltage I = current R = resistance
Current directly proportional to voltage, inversely proportional to resistance

How well did you know this?

Not at all

Perfectly

Types of current

Direct current
- electrons flow in single direction
- current constant and doesn’t change with time
Alternating
- electrons alternate flow with time
- current alternates between positive and negative values
- UK 50Hz (50 x per second) 240 V

How well did you know this?

Not at all

Perfectly

Electrical injury

Damage to skin or internal organs from electrical circuit. Extent of injury
- current (i.e. amount of electricity)
- pathway - which tissues injured
- duration
- type of current - AC worse than DC

Microshock = usually safe current transmitted directly to the heart via conductor e.g. CVC causes arrhythmias

How well did you know this?

Not at all

Perfectly

Electrical safety - general measures

regular maintenance
patients not in contact with earthed objects
correct humidity
antistatic shoes and flooring

How well did you know this?

Not at all

Perfectly

Electrical safety - equipment classification

Class 1 - any conducting part connected to earth by an earth wire. Faulty live supply - current flows to east and causes safety fuse to melt
Class 2 - conducting part double insulated
Class 3 - voltages no higher than safety extra low voltage < 25V AC - unlikely to cause macro shock

Degree of protection
Type B - can be class 1, 2 or 3, maximum leakage current is < 100mcgA
Type BF 0 uses floating circuit - equipment circuit separated from mains
Type CF - highest protection max leakage < 10mcgA - suitable for cardiac

How well did you know this?

Not at all

Perfectly

Diathermy

Heating effect of high frequency AC electrical current to cut and coagulate.
Monopolar - AC 200KHz - 6MHz. energy between active electrode (instrument) and neutral plate. very high current density at instrument with heating effect. current density low at plate - large area of contact. cutting / coagulation depending waveform
Bipolar - much lower AC frequency. Energy between two points of surgical forceps. current passed through tissue held by forceps. no neutral plate.

How well did you know this?

Not at all

Perfectly

Dangers of diathermy

Burns - accidental discharge, poor application of neutral plate
Fire - flammable material may be ignited
pacemarkers - monocular may inhibit or damage (bipolar safest)

How well did you know this?

Not at all

Perfectly

ICP waveform

Trifid
- respiratory sinusoidal waveform
- arterial pulsatile 3 peaks
- P1 = arterial pulse. P2 = brain compliance. P3 = dicrotic notch (aortic valve closing)
Raised ICP
- Amplitude of all 3 rises
- decreased P1 suggests decreased cerebral perfusion
- increased P2 suggests reduced cerebral compliance

How well did you know this?

Not at all

Perfectly

Electrical charge

physical property that causes it to experience a force in an electromagnetic field
- SI unit is coloumb
- 1 coulomb - quantity of electric charge which passes a point when 1 ampere current flows for 1 second

How well did you know this?

Not at all

Perfectly

Capacitance

measure of ability to hold electric charge
Farad SI unit
A capacitor has 1 Farad of capcitance if potential difference of 1 volt is applied across its plates when they hold 1 coulomb of charge
capacitor - device able to store energy in form of electric charge - two metal plates separated by insulator. storage increased by greater SA and greater distance between two plates. Energy = 1/2 x Q x V

How well did you know this?

Not at all

Perfectly

Defibrillator

Electrical equipment that delivers dose of electrical current to the heart
Two electrical circuits
- charging circuit - DC battery or AC mains with rectifier to convert to DC. Capacitor 5000 V applied across the plate stores electrons
- Discharging circuit - inductor - coil of wire that prolongs the duration over which the electrical discharge takes place. patient, switch (between charging and discharging circuits.

Without inductor - rapid discharge of electrons, doesn’t defibrillate and causes burns

Monophasic - single discharge of current travels in one direction. Biphasic - two consecutive pulses, travels in one direction then back. lower energy required.

How well did you know this?

Not at all

Perfectly

Transthoracic impedence

impedance presented by patient during cardio version. influences by
- paddle size
electrode coupling
paddle position
- obesity

How well did you know this?

Not at all

Perfectly

CO2 absorption options

Soda lime (sodium hydroxide)
Baralyme (calcium hydroxide, barium hydroxide)
Litholyme

Sodium hydroxide – > Compound A and Carbon Monoxide with halogenated volatiles

How well did you know this?

Not at all

Perfectly

Soda Lime

94% calcium hydroxide, 5% sodium hydroxide
Colour dye pH < 10
pH 13.5. 1kg - 120L CO2
Exhaled gases reach canister, CO2 absorbed, heat and water produced which rejoin FGF

Overall reaction
Ca(OH)2 + CO2 –> CaCO3 + H20 + heat

4-8 mesh in size. uniform and smooth flow. high surface area but not too much resistance

Allows low flow, less waste, avoids rebreathing, humidification

How well did you know this?

Not at all

Perfectly

Harmful products sodalime

Compound A (nephrotoxic)
- fluromethylether produced from sevoflurane
- high servo / low FGF
Carbon Monoxide
- produced when system left for time
- higher concentration of volatile
- type of volatile (des)

How well did you know this?

Not at all

Perfectly

Pros and cons of circle system

Pros
- Low flow
- economy of anaesthetic consumption
- reduced pollution
- warming and humidification
Cons
- Slow changes in inspired anaesthetic concentration

How well did you know this?

Not at all

Perfectly

Components of circle system

inspiratory limb with one way valve
expiratory limb with one way valve
vaporiser in circuit / out of circuit
soda lime
bag with APL valve
fresh gas supply

How well did you know this?

Not at all

Perfectly

How do you measure ICP

Clinically - symptoms, papilloedema
Non-invasively - CT imaging
Invasively - EVD, ICP bolt

ICP waveform

Normal - P1 / P2 / P3
P1 = systolic upstroke, P3 = diastolic downstroke P2 = dicrotic notch (brain compliance). P1 > P2 > P3
Lundberg A = plateau waves, steep increase in ICP lasting 5-10 mins. always pathological
Lundberg B = oscillations of ICP 0.5-2waves/min associated with unstable ICP
Lundberg C = oscillations with frequency 4-8 waves / min, relationship with cardiac and respiratory cycles

Neurophysiological monitoring

MEPs - trancranial stimulation of motor cortex, producing muscle contraction. strong correlation to spinal cord ischaemia. monitors descending anterior and lateral corticospinal tracts
SSEPs - electrical impulses delivered to peripheral nerve which are detected in sensory cortex. transmission via dorsal columns.
Stagnara wake up test - wake patient up and get them too ollow commands

Pollution in theatre

gas induction
spillage
leaks
open circuits
failure to turn off vaporiser
Concerns
spontaneous abortion
malignancy
infertility
mortality
global warming

N20 negative effects

bone marrow toxicity (megaloblastic anaemia)
neurotoxicity (subacute degeneration of the spinal cord)
teratogenicity
spontaneous miscarriage
substance absue

Reducing anaesthetic gas pollution

ventilation (15x per hour)
closed circle circuits
soda lime
avoid leaks
avoid gas induction
avoid volatile
low flow
monitoring pollution
scavenging

COSHH recommendations for volatiles

8 hour time weighted average
halothane 10ppm
enflurane 50ppm
isoflurane 50ppm
N20 100ppm

Passive scavenging

patient dependent
no active positive or negative pressure
30mm connector
gases vented to atmosphere by patients spontaneously ventilation or ventilator
Cardiff aldasorber - charchol absorbing volatiles

Active scavenging

collecting system - collect expired gases from breathing system via 30mm connector
transfer system - wide bore tubing
receiving system - reservoir. valved guard against positive or negative pressures
disposal system - vacuum, vented outside

disadvantages of active

excessive positive pressure - barotraua
excessive negative pressure - rebreathing

laminar flow

ultra clean environment
prosthetic implants
400 air changes per hour - air passes through high efficiency filters

Epidural filter

disc shape
hydrophilic supported membrane
Filter size 0.22microns
Filters viruses, bacteria, foreign bodies

Physiological Humidifcation

inspired gas is warmed as it passes over vascular nasal epithelium
- humidified by water evaporation from respiratory surface
- 100% relative humidity just distal to carina
- at 37 degrees 44mg/L

Gases delivered from pipelines are dry to prevent condensation and corrosion

Humidifcation

Passive
- HME
- circle breathing system (soda lime produces heat and water)
- cold water bath - inspired gas bubbled through cold sterile water. full saturation at room temperature, patient further heats
Active
- hot water bath - heating element added to cold water bath to increase absolute humidity. disks are condensation
- gas driven nebuliser - aerosolises water various droplet sizes - venturi effect
- ultrasonic nebuliser - electrical to mechanical energy, fine mist generated from water covered membrane

HME

HMEF
- hygroscopic membrane, pleated to reduce dead space
- 0.2 microns pore size
- 60-70% relative humidity (30g/m3 at 30degrees)
- 15/22mm connectors. sampling tube connection
- warm humidified exhaled gas condenses on filter medium, next inspiratory breath humidified and returns to patient
- 100ml dead space
- Affected by temperature / water vapour content / medium size / flow rates
- cons - resistance to flow, location near patient, obstruction with mucous

Ideal humidifer

adequate humidification
low resistance to flow
microbiological protection
warms
economical

Other filters

Filter needles
- prevent particulate and organism contamination
- 0.2 microns
Fluid filter
- 15 microns to prevent particulate
Blood filters
- 170-250 microns - whole blood
- 20-50 microns 70-80% leucodepletion
- electrostatic - 100% leucodepletion

types of RRT

Intermittent
- IHD ( 300-400ml.min flow rates. tap water / reverse osmosis)
- Peritoneal dialysis
Continious
- CVVHF
- CVVHD
- CVVHDF

Haemofiltration

extracorporeal circuit
blood filtered through semipermeable membrane driven by hydrostatic pressure
ultra filtrate discarded and replaced with suitable solution
Particles < 50kDa filtered by convection (dragged through)

Haemodialysis

extracorporeal circuit
blood passes in countercurrent system next dialysate separated by semipermeable membrane
solutes move across membrane along concentration gradient obeying ficks law

Haemodiafiltration = combination of two

Similarities between CVVHF and CVVHD

Both achieve
- water removal
- solute removal
- correction of electrolytes and acid-base
Set up
- extracorporeal
- central vei
- roller pumps
- filter

Peritoneal dialysis

same principle as haemodialysis
peritoneum acts as membrane

SLED

sustained low efficiency dialysis
intermittent
daily longer sessions
slower solute removal and fluid than IHD but faster than CRRTT

Type of RRT depends on

stability (IHD more CVS derangement)
resources / experience
size of particles to be removed (smaller molecules - dialysis, larger - filtration)

RRT disadvantages

Cost
Nursing workload
Complications of line insertion
Fluid shifts
altered drug metabolism
- low PB removed easily
- Higher Vd have lower RRT clearance
- ABx - teic, linezolid no adjusstment
- mero / tan are filtered - increase dose
- gent and vanc highly filtered - levels and increase dose

Terms in RRT

Dose = volume of plasma ‘purified’ per unit time. typically 25-30ml/kg/hr. Effluent flow rate (dialysate + ultra filtrate)
Filtration fraction = fraction of plasma removed from blood 20-25%
Sieving coefficient = ratio of concentration of solute in ultra filtrate vs plasma. 1 = fully filtered 0 = no filtration. determined by size, polarity, pore size, protein binding

Humidification importance

without humidification, respiratory tract dries out, keratinise, reduced ciliary clearance, inflammation, mucus plugging

passive : HME
Active : hot water baths, nebuliser, cascade

Humidity in theatre

Too low relative humifity
- static electricity
- increased evaporative fluid loss from patient
To high relative humidity
- microbial growth
- unpleasant

Optimium is 40-60% at 20 degrees

Humidification expressed as

Absolute humidity - mass of water vapour per unit volume g/m3
relative - ratio of mass of water to mass of water if fully saturated expressed as percentage

The amount of water vapour a given volume of air can contain increases with increasing temperature. If air is 100% saturated and temperature decreases then condensation occurs. temp at which condensation occurs is the dew point

Measuring humidity

Hair hygrometer
- relative humidity
- hair increases in length proportional to increasing humidity (water is absorbed), moves pointer on scale
wet/dry bulb hygrometer
- two glass thermometers one in air one in water
- thermometer in water reads lower temp due to cooling effect from evaporation. the rate of evaporation is dependent on ambient humidity (lower humidity, more evaporation, lower temperature)
- difference in temperature between two measured and calculate relative humidity
Renaults hygrometer
- silver tubing in ether
- air blown through ether, evaporation and cooling
- condensation on shiny outside
- temperature at condensation is due point (temp when air fully satirated)
relative humidity = svp at dew point / sip ambient temp

Absolute humidity measured by mass spectrometry - molecules ionised then deflected by magnet based on mass:charge ratio - quantify amount of water.

heat definition

state of energy an object has in relation to kinetic energy of atoms or molecules
transfer down temperature gradientt

temperature deifntiion

measure of average kinetic energy of the molecules within a substance
- substances with higher temperature have higher average kinetic energy
- lower temperature lower average kinetic energy
- determines whether heat can be transferred
- SI = Kelvin 1/273.16th triple point of water
(triple point is the temp and pressure when substance can exist in solid, liquid, gas at equilibrium)
- celcius - 0k = -273.15C

Temperature measurement classiication

Non-electrical
Electrical
Infrared

Non-electrical methods of temp measurement

Liquid thermometer
- volume of liquid increases as temp rises
- calibrated against fixed points
- mercury or alcohol
- simple, cheap, reusable
- slow, easily broken
Bourdon gauge
- usually measured pressure
- attach to liquid-containing tube
- inc temp inc vol liquid
- small inc in pressure on hollow spiral tube of bourdon gauge which unwinds and moves pointer
Bimetallic strip
- copper / steel
- different coefficients of expansion
- fixed at ends
- increase in temp –> expansion at different rates –> bending of strip –> move pointer
- cheap, simple, slow
Liquid-crystal
- colour change in response to change in temp (thermochromism)
- cheap, limited range

Electrical methods of temperature measurement

Platinum resistance
- resistance increases with temperature
- circuit, battery, platinum wire, Wheatstone bridge
- accurate, expensive
Thermistor
- semi-conductive material, metal oxide
- resistance decreases with temperature
- Wheatstone bridge
- small, robust, cheap, but drift
Thermocouple
- Seebeck effect - junction of 2 different metals potential difference develops in proportion to temperature
- iron / Constantan
- second cold junction reference
- cheap, rapid, stable, accurate. required amplification

infrared temp measurement

all objects emit electromagnetic radiation, wavelength characteristic and dependent on temp
at 37 degrees, radiation at 9340nm
tympanic thermometer - measures emitted radiation, focused onto detector, converted to electrical signal

NICE temperature guideline

pre-op measure and document. warm if < 36
walk to theatre if able
intra-op - measure and document in anaesthetic room and every 30mins
induction only when above 36
warm fluid
force air warmer if > 30min
measure and document every 15mins in recovery
do not discharge until > 36

consequences of hypothermia

CVS
- bradycardia, vasoconstriction, arrhythmias, J waves
Neuro
- reduced CBF, CMO2, neuroprotection
- reduced level of consciousness at 33, coma 30
Resp
- shivering increased VO2
- increased PVR
Renal
- reduced renal blood flow due to reduced CO
Haem
- decreased platelet, clotting enzyme function
- left HbO2 curve
metabolic
- reduced BMR

Heat loss in theatre

induction - vasodilation and heat loss
radiation 40%
heat loss from exposed body parts to neighbouring objects
treat - increase room temp, cover patient
convection 30%
air layer next to body warms and rises, producing current
treat - forced air warmer
evaporation 20%
sweat and skin
treat - cover patient
respiration 10%
drying gases
treat - humidifying gases

Stroke volume variation

SVmax - SVmin / SVmean
10% + suggests fluid responsiveness

Properties of ideal cardiac output monitor

Cheap
accurate
Easy to insert / non-invasive
Minimal risks to insertion
Provide continuous data
No need to recalibrate / not subject to drift
operator independent

Oesophageal doppler

flow = velocity x area
area = nomogram
velocity = doppler equation
Derives
- PV = contractility
- CO / CI
- Stroke distance - area under systolic waveform (SV from SD and nomogram)
- Flow time corrected - preload 330-360ms

Sterility of equipment

Critical Equipment
- penetrates mucous membranes to enter sterile body area e.g. surgical instruments, needles, endotracheal tubes
Semi-critical
- contacts mucous membranes, doesn’t enter sterile area e.g. laryngoscope blade
Non-critical
- contacts skin only e.g. NIBP, pulse ox

Making equipment sterile..

Decontamination
- removal, inactivation or destruction of pathogens on surface
- can comprise of cleaning, disinfection or sterilisation
Cleaning is first stage of decontamination
- all that is required for non-critical equipment
- removal of foreign material from object
- detergent or enzymatic soak
- must disassemble
- manual - washing with detergent
- mechanical - waster, ultrasonic cleaner
Disinfection
- destroys most bacteria and all viruses
- does not remove bacterial spores or some mycobacteria
- Thermal = boiling 70-100degrees e.g. pasteurisation = heating to 70-80degrees for 30mins
- chemical = heat sensitive equipment e.g. endoscopes. glutaraldehyde, hydrogen peroxide
Sterilisation - complete destruction / killing of all microorganisms including spores
- Steam (autoclave) - reliable and cheap e.g. 121 degrees 1 bar 20 mins
- Dry heat - mewl
- Ethylene Oxide - 50-60 degrees, expensive, toxic
- Radiation - gamma rays

Peripheral nerve monitoring

Clinical
Qualtitative - nerve stimulator
Quantitative - Mechanomyography, acceleromyography, electromyography

Characteristics of peripheral nerve stimulator

Portable
Battery powered
Easy to use
Able to deliver different impulses
- single twitch
- ToF 2Hz
- Supramaximal –> maximal = all muscle fibres supplied by nerve are stimulated. supramaximal is 20% greater
- Tetanic 50Hz

Train of Four

Series of stimulations at 2Hz (4 over 2 seconds) of approx 70mA voltage (supra maximal)
applied to superficial nerve e.g ulnar, facial
Comapre T1 to T0 (controle) and T1:T4
Can calculate extent of block
- Loss of T4 = 75%
- Loss of T3 + T4 = 80%
- Loss of T2 + T3 + T4 = 90%
- Loss of all = 100%
Depolarising - all reduced, no fade (repeated dose lead to phase 2 (similar to non-depolarising)
Non-depolarising - fade

Double burst stimulation

2 tetanic 50Hz separated by 750ms
used when profound block

Infrared spectroscopy and CO2 measurement

Molecules containing 2 or more different atoms absorb IR
Different molecules absorb IR of different wavelengths
Gases in anaesthesia absorb IR at characteristic wavelengths - CO2 at 4.28um
Measuring the fraction of IR radiation of 4.28um absorbed by a gas mixture, allows CO2 partial pressure to be measured

IR analyser

one side hot wire emits IR radiation
IR radiation passes through a filter allowing only specific wavelengths (or multiple)
IR radiation passes through gas chamber (sapphire), opposite side of chamber lens focuses IR onto a photodetector
Reference chamber alongside - CO2 free air - removes fluctuations

Side stream vs main stream

Side stream
- gas sample drawn from exp limb close to patient and carried to analyser via tubing
- moisture trap to prevent water interference
- little addition weight, no additional dead space, can measure gases other than CO2
- Disadvantage is delay of 2-3seconds
Main stream
- gas chamber with sapphire windows incorporated into breathing system
- IR radiation passed through gases directly in the breathing system
- advantage is instant anaylsis
- Disadvantage - must be heated, dead space, only measures CO2

Capnogram waveform

Phase 1 - flat bottom line - inspiration and early expiration of dead space gas. CO2 = zero
Phase 2 - expired mixed anatomical dead space and alveolar gas - rapid CO2 rise
Phase 3 - alveolar plateau - end point is ETCO2
Phase 4 - inspiration, CO2 drops to zero

Severinghaus electrode

Modified pH electrode - measures PCO2 in blood
Two electrodes
Glass - silver / silver chloride electrode, gas permeable membrane. detects change in pH via H+ sensitive glass membrane coated in NaHCO3 (buffer)
Silver / silver chloride reference electrode

2-3 min response, temperature maintaiend at 37 and recalibration

Fibreoptic endoscpes

Total internal reflection
refraction - change in direction of beam of light occurring at boundary of two materials with different refractive indices
Bundles of 15,000 glass fibres, each one coating in glass of different refractive index, allowing light to be transmitted along the bundle
Components. Body:
- eyepiece / focussing +/- screen
- light source
- control lever to move tip
- suction port
Tube:
- fibreoptic light bundle, transmits light to distal tip
- image bundle - image –> eye piece
- suction channel
- wires to move tip
Cleaning immediately - enzymatic detergent
disinfection - liquid per acetic acid

Laser uses

Light amplification by stimulated emission of radiation
- ENT - vocal cord resection
- Ophthalmology - retinal surgery
- Urology - lithotripsy
- Dermatology - skin lesions

Properties of laser light

monochromatic
high energy, low cross sectional area
collimated, parallel beam

Principles of laser

energy applied to an atom causes atom to move from ground state to excited state
electrons move to higher energy orbits
electrons spontaneously fall back to resting orbit - releasing energy in form of photon ‘spontaneous emission’
photons produced similar
when photons released from atoms in excited state trigger photons to be released from neighbouring atoms in excited state - the released photons are identical. stimualted emission
population inversion occurs when > 50% atoms are in excited state

components of laser

energy source
lasing medium - atoms to be energised
mirror to reflect and amplify light
small hole to allow light to leave

types of laser

CO2 - 10600nm (far IR) - absorbed by all tissues. cellular water boils and cells burst - precise surgical cutting and coagulation - ENT
Nd-YAG - 1060nm (near IR) - photocoaulgatuon. can be passed down endoscopes
Argon - 500nm (visible) - dermatological

Laser safety

Minimise risk to patient
- eye wear
- avoid flammable cleaning solutions
- lowest O2 possible
- minimal possible time
- laser safe tubes - non-flammable, reflective, double cuff filled with saline
- damp swabs to protect tissues
Minimis risk to staff
- safety officer
- eye wear
- signs
- locks

Airway fire management

stop surgery, critical incident
flood field with saline
remove breathing circuit and ETT, maintain ventilation with BVM in air
once extinguished, re-intubate and inspect airway with fibrescope
ICU
Acute lung injury
dexamethasone

Circle circuit

CO2 absorber - soda lime
insp and exp limbs with unidirectional valve
vaporiser
reservoir bag / apl valve with switch to ventilator
tubing and FGF
Ads
low flow anaesthesia
variety of ages
preserves heat and moisture
disads
complex
not portable
low flows - slow change in FGF
toxic build up e.g. compound a, carbon monoxide with iso

Brainscape's Knowledge GenomeTM

Physics Flashcards

Brainscape's Knowledge Genome^TM