Physics Flashcards

Question

Voltage and current

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

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

Answer 6

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.

Answer 7

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

Answer 8

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

Answer 9

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

Answer 10

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

Answer 11

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.

Answer 12

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

Answer 13

- Soda lime (sodium hydroxide) - Baralyme (calcium hydroxide, barium hydroxide) - Litholyme Sodium hydroxide -- > Compound A and Carbon Monoxide with halogenated volatiles

Answer 14

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

Answer 15

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)

Answer 16

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

Answer 17

- 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

Answer 18

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

Answer 19

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

Answer 20

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

Answer 21

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

Answer 22

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

Answer 23

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

Answer 24

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

Answer 25

- 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

Answer 26

- 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

Answer 27

excessive positive pressure - barotraua excessive negative pressure - rebreathing

Answer 28

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

Answer 29

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

Answer 30

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

Answer 31

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

Answer 32

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

Answer 33

- adequate humidification - low resistance to flow - microbiological protection - warms - economical

Answer 34

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

Answer 35

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

Answer 36

- 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)

Answer 37

- 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

Answer 38

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

Answer 39

same principle as haemodialysis peritoneum acts as membrane

Answer 40

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

Answer 41

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

Answer 42

- 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

Answer 43

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

Answer 44

without humidification, respiratory tract dries out, keratinise, reduced ciliary clearance, inflammation, mucus plugging - passive : HME - Active : hot water baths, nebuliser, cascade

Answer 45

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

Answer 46

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

Answer 47

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.

Answer 48

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

Answer 49

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

Answer 50

Non-electrical Electrical Infrared

Answer 51

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

Answer 52

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

Answer 53

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

Answer 54

- 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

Answer 55

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

Answer 56

- 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

Answer 57

SVmax - SVmin / SVmean 10% + suggests fluid responsiveness

Answer 58

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

Answer 59

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

Answer 60

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

Answer 61

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

Answer 62

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

Answer 63

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

Answer 64

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

Answer 65

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

Answer 66

- 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

Answer 67

- 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

Answer 68

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

Answer 69

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

Answer 70

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

Answer 71

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

Answer 72

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

Answer 73

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

Answer 74

- 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

Answer 75

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

Answer 76

1. CO2 - 10600nm (far IR) - absorbed by all tissues. cellular water boils and cells burst - precise surgical cutting and coagulation - ENT 2. Nd-YAG - 1060nm (near IR) - photocoaulgatuon. can be passed down endoscopes 3. Argon - 500nm (visible) - dermatological

Answer 77

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

Answer 78

- 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

Answer 79

- 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