PHYSICS PHYSICS MCQsMCQs

Cyprian MendoncaCyprian Mendonca

TopicsTopics

�� Measurement of blood gasesMeasurement of blood gases

�� Measurement of gas flowMeasurement of gas flow

�� Monitoring ECGMonitoring ECG

�� Monitoring & Measurement of oxygenMonitoring & Measurement of oxygen

�� Measurement of blood pressureMeasurement of blood pressure

�� Agent monitoringAgent monitoring

�� SeveringhausSeveringhaus electrodeelectrode

�� Clark electrode Clark electrode (blood: gas factor)(blood: gas factor)

�� Mass spectrometryMass spectrometry

�� Fuel cellFuel cell

�� Infrared analyserInfrared analyser

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Mass spectrometryMass spectrometry

Mass SpectrometryMass Spectrometry

O2CO2 Enflurane

Rapid response time

Multiple gas analysis

Expensive

too bulky

Angle of deflection

depends on

charge mass ratio

Charge/mass

Charge/mass

�� Blood gas analyser directly measures Blood gas analyser directly measures

Pa OPa O22, PaCO, PaCO22 and pHand pH using using

specific electrodes .specific electrodes .

�� Membrane permeable to OMembrane permeable to O22, CO, CO2, 2, HH++

Bicarbonate Bicarbonate

� 2 electrodes

� Reference electrode : Ag /Agcl

� Measuring electrode: pH glass

� Electrolyte: NaHCO3, Kcl

Mesh -HCO3-

H+ glass

electrodes

CO2+H2O H2CO3 H+ +HCO3-

CO2 permeable teflon membrane

H+

H+

H+ sensitive glass

KclBuffer

Ag/Agcl or calomel reference electrode

Reference electrode

Measuring

electrode

Ag/AgCl

leaky membrane

Voltage change in the measuring electrode

V

CO2 pH

Ref Elect Ag/AgCl Ag/Agcl

Hg/Hgcl

Measuring

Electrode

pH glass pH glass

Electrolyte Kcl,

NaHCO3

Kcl

� Excess heparin in the sample lowers the pH value

� Sampled blood can be stored at room temp for up to one hour

� pH is usually calculated using Siggard-Anderson nomogram

� CO2 electrodes are maintained at room temperature

� CO2 electrodes have a response time of 20 secs

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Response time 2Response time 2--3 minutes3 minutes

1 1 kPakPa = 30 minutes= 30 minutes

2ml = 80 units of heparin

� has CO2 sensitive glass

� uses sodium bicarbonate as electrolyte

� is an indirect method of measuring carbon dioxide tension

� is accurate to within 1mmHg

� is temperature-dependent

FTTTTFTTTTIndirect: 0.01 unit of pH change per 0.1 kPa COIndirect: 0.01 unit of pH change per 0.1 kPa CO22

�� Fuel cellFuel cell

�� Clark electrodeClark electrode

�� Paramagnetic oxygen anlaysersParamagnetic oxygen anlaysers

Gold cathode

Finite shelf-life=1year

calibration

self generated voltage

No power supply

slow response

Pb + 2OH- PbO + 2e- + 2H2O

KOHLead anode

�� FiOFiO22 reading is not affectedreading is not affected

�� Life span of cell is affectedLife span of cell is affected

(N(N22O reacts with lead anode)O reacts with lead anode)

polarising voltage 0.7 V

Platinum cathode

KCl

Ag/AgCl anode

�� AnodeAnode

Ag + Cl = AgCl + Ag + Cl = AgCl + ee

�� CathodeCathode

O2 + 2H2O + O2 + 2H2O + 4e4e = 4OH= 4OH

�� ElectolyteElectolyte

NaCl + OH = NaOH + ClNaCl + OH = NaOH + Cl

Electrons donated at anode, consumed at Electrons donated at anode, consumed at

cathodecathode

Polarographic-platinum, Agcl

Fuel cell Clark

Anode Lead Ag/Agcl

Cathode gold platinum

Electrolyte KOH Kcl, Nacl

�� Has a Gold cathodeHas a Gold cathode

�� Has a platinum anode Has a platinum anode (lead)(lead)

�� Uses sodium hydroxide as the Uses sodium hydroxide as the electrolyte solution electrolyte solution (KOH)(KOH)

�� Require a voltage of 6Require a voltage of 6--7 volts applied 7 volts applied across the electrodes across the electrodes (0.7 V for clark)(0.7 V for clark)

�� Is affected by the presence of NIs affected by the presence of N22OO

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�� aa. . InfraredInfrared analyseranalyser

�� b. Raman spectroscopyb. Raman spectroscopy

�� c. Mass spectrometryc. Mass spectrometry

�� d. Refractometerd. Refractometer

�� e. Quartz crystale. Quartz crystal

�� TTTTTTTTFF

�� pHpH

�� Standard bicarbonate : Standard bicarbonate : SiggardSiggard--Anderson Anderson

nomogramnomogram

�� Carboxy haemoglobinCarboxy haemoglobin

�� Oxyhaemoglobin saturation:Oxyhaemoglobin saturation: ODC

�� Base excessBase excess

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a)measures Oxygen concentration a)measures Oxygen concentration

b)is the classical method of calibrating b)is the classical method of calibrating

vaporisers vaporisers

c)is affected by water vapour c)is affected by water vapour

d)does not require prior calibration d)does not require prior calibration

e)is affected by temperaturee)is affected by temperature

FTTTTFTTTTAll affected by water vapour except fuel cellAll affected by water vapour except fuel cell

�� When sine waves of same frequency, amplitude When sine waves of same frequency, amplitude

and phase are added, resulting sine wave will and phase are added, resulting sine wave will

have greater amplitude. If two sine waves are have greater amplitude. If two sine waves are

180180oo out of phase, the resulting sine wave will out of phase, the resulting sine wave will

have zero amplitude and appears as straight have zero amplitude and appears as straight

line. Addition of sine waves in a variable degree line. Addition of sine waves in a variable degree

of out of phase will result in respective change in of out of phase will result in respective change in

the amplitude. the amplitude.

�� In a refractometer increased amplitude gives In a refractometer increased amplitude gives

rise to bright fringe, reduced amplitude gives rise rise to bright fringe, reduced amplitude gives rise

to dark fringe. There are two chambers. One is to dark fringe. There are two chambers. One is

reference chamber and a sample chamber. The reference chamber and a sample chamber. The

change in the phase of sine waves in the sample change in the phase of sine waves in the sample

chamber and resultant displacement of fringe chamber and resultant displacement of fringe

pattern is dependent on the type and pattern is dependent on the type and

concentration of the anaesthetic agent. concentration of the anaesthetic agent.

�� Is based on the principle that O2 is repelled by the Is based on the principle that O2 is repelled by the magnetic fieldmagnetic field

�� Is incorporated into the blood gas analyserIs incorporated into the blood gas analyser

�� can provide breath to breath measurementcan provide breath to breath measurement

�� Can measure CO2Can measure CO2

�� Null deflection paramagnetic analyser has the Null deflection paramagnetic analyser has the advantage of containing no moving partsadvantage of containing no moving parts

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N2 N2

% O2

sample

*Calibration

N2 N2sample

Differential pressure transducer

Pulsed magnetic field

Sample gas with more oxygen attracted to the magnetic field

& produces pressure difference across the transducer

Sample gas

Reference gas

�� 4%4%

�� 21%21%

�� 5%5%

�� 7%7%

�� 0.3%0.3%

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40 mm Hg x 0.13 = 5.3 kPa40 mm Hg x 0.13 = 5.3 kPa

5.3 5.3 –– 0.3 to 0.8 =4.5 to 5 kPa0.3 to 0.8 =4.5 to 5 kPa

� Has a standard paper speed of 50mm/s.

� Has a Normal axis between +30o to -90o

� Has a maximal Q-Tc interval of 0.48s..

� Has a QRS duration of 0.08-0.12s.

� May have an inverted T wave in aVR

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PR =0.12PR =0.12-- 0.2, QT < 0.44, 0.2, QT < 0.44, --3030o o to +90to +90oo

P= 0.1s, 2.5 mm,P= 0.1s, 2.5 mm,

a. applies to both electromagnetic radiation and a. applies to both electromagnetic radiation and

soundsound

b. changes the b. changes the velocityvelocity of reflected soundof reflected sound

c. is based on the piezoc. is based on the piezo--electric properties of electric properties of

crystalscrystals

d. shows the shift to lower frequency if the source d. shows the shift to lower frequency if the source

is moving away from the receiveris moving away from the receiver

e. can indicate the velocity of red ce. can indicate the velocity of red cellsells

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�� A lower signal to noise ratio is better than a A lower signal to noise ratio is better than a

higher ratio higher ratio

�� Diagnostic mode in the ECG monitor has a Diagnostic mode in the ECG monitor has a

frequency response of 0.5 to 40 Hzfrequency response of 0.5 to 40 Hz

�� CM5 configuration is ideal for detecting CM5 configuration is ideal for detecting

arrhythmiaarrhythmia

�� Signal to Noise ratio can be improved by using Signal to Noise ratio can be improved by using

filters.filters.

�� Differential amplifier can reduce the electrical Differential amplifier can reduce the electrical

interferenceinterference

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12. Concerning ECG Monitoring12. Concerning ECG Monitoring

�� A A highhigh signal to noise ratio is better than a signal to noise ratio is better than a

higher ratio higher ratio

�� MonitoringMonitoring mode in the ECG monitor has a mode in the ECG monitor has a

frequency response of 0.5 to 40 Hzfrequency response of 0.5 to 40 Hz

�� Diagnostic mode 0.Diagnostic mode 0.005 to 100 Hz.5 to 100 Hz.

�� CM5 configuration is ideal for detecting CM5 configuration is ideal for detecting

ischaemiaischaemia

�� Signal to Noise ratio can be improved by filtersSignal to Noise ratio can be improved by filters

Monitoring mode : 0.5 - 40 Hz

Diagnostic mode: 0.05 -100Hz : ST segment, QRS not distorted

Right arm = red = C Manubrium

Clavicle =Neutral = green

Left arm = yellow = V5 position

Select lead 1

Amplifier amplifies the signal before it is displayed on the Amplifier amplifies the signal before it is displayed on the

monitor.monitor.

A differential amplifier measures the difference between the A differential amplifier measures the difference between the

potential from two sources. Any interference which is potential from two sources. Any interference which is

common to the input terminal such as 50Hz mains common to the input terminal such as 50Hz mains

frequency is eliminated. This rejection of common input frequency is eliminated. This rejection of common input

frequency is known as common mode rejection. frequency is known as common mode rejection.

�� Nail varnishNail varnish

�� MethyleneMethylene BlueBlue

�� Tricuspid incompetenceTricuspid incompetence

�� MethaemoglobinMethaemoglobin

�� CarboxyhaemoglobinCarboxyhaemoglobin

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�� accuracy : +/accuracy : +/--2%, >70%: +/2%, >70%: +/--3% 503% 50--70%70%

Hypoperfusion

Ambient light

Fluorescent, xenon

Movements

Diathermy

External dyes, Nail varnish (black/green)

Abnormal haemoglobins

HbMet, HbCO, Indocyanine green, Methy. blue

No effectHbF, HbS, Bilurubin, anaemia

Acrylic nails.

�� a. Nitrous oxidea. Nitrous oxide

b. Oxygenb. Oxygen

c. Heliumc. Helium

d. Entonoxd. Entonox

e. Medical aire. Medical air

�� T FFFFT FFFF

�� a. Nitrous oxide: 36.5 a. Nitrous oxide: 36.5 ooCC

b. Oxygen: b. Oxygen: --118.4118.4 ooC C

c. Helium:c. Helium:

d. Entonox: d. Entonox: --77 ooC C

e. Medical air: e. Medical air: --140140 ooCC

15. Regarding measurement of Gas flow

Examples of Constant Orifice/Variable Pressure

devices include

�� PneumotachographPneumotachograph

�� Peak flow meterPeak flow meter

�� RotameterRotameter

�� PitotPitot tubetube

� Wright respirometer

TFFTFTFFTF

Gas flow & Volume measurementGas flow & Volume measurement

�� Pneumotachograph Pneumotachograph

fixed orifice, variable pressure drop, fixed orifice, variable pressure drop, Q = P/RQ = P/R-- Fleisch PneumotachographFleisch Pneumotachograph

-- Screen PneumotachographScreen Pneumotachograph

-- Pitot tube PneumotachographPitot tube Pneumotachograph

-- Hot wire PneumotachographHot wire Pneumotachograph

�� Peak flow meterPeak flow meter

variable orifice, fixed pressure drop flow metervariable orifice, fixed pressure drop flow meter

Gas flow & Volume measurementGas flow & Volume measurement

Q = P/RQ = P/R

�� Direct measurement of Direct measurement of volumevolume

Spirometer & Wright RespirometerSpirometer & Wright Respirometer

�� Variable orificeVariable orifice-- constant pressure constant pressure dropdrop

Rotameter, Peak flowmeterRotameter, Peak flowmeter

�� Fixed orificeFixed orifice-- variable pressure variable pressure dropdrop

Pneumotachograph, Pitot tube.Pneumotachograph, Pitot tube.

16. The concentration of isoflurane in a

breathing system can be measured using

�� a. Mass spectrometera. Mass spectrometer

�� b. Paramagnetic analyserb. Paramagnetic analyser

�� c. Refractometerc. Refractometer

�� d. Infrared analyserd. Infrared analyser

�� e. Ultrasonic analyser : e. Ultrasonic analyser : velocity of soundvelocity of sound

�� T FTTTT FTTT

�� The composition of isothermal binaryThe composition of isothermal binary--gas gas

mixtures can be determined by measuring mixtures can be determined by measuring

the velocity of sound in the gasthe velocity of sound in the gas

17. Flow can be measured by

� The Fick principle

� High frequency sound wave reflection

� Change in temperature of a hot wire

� Pressure drop across a constriction

� Venturi effect

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Fick principle:Fick principle:

blood flow to any organ = Qx / [Axblood flow to any organ = Qx / [Ax--Vx]Vx]Inhaled nitrous oxide is used.Inhaled nitrous oxide is used.

�� Qx: amount of substance removed by the Qx: amount of substance removed by the

organorgan

�� Ax: arterial conc.Ax: arterial conc.

�� Vx: venous concentrationVx: venous concentration

18. Flow meters in anaesthetic machines18. Flow meters in anaesthetic machines

�� N2O can be used in an O2 flow meter without N2O can be used in an O2 flow meter without changes in calibrationchanges in calibration

�� Are variable orifice variable pressure devicesAre variable orifice variable pressure devices

�� Uses a straight tube and a bobbinUses a straight tube and a bobbin

�� Have a linear scaleHave a linear scale

� Both Laminar and turbulent flows are encountered

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N2O, CO2 = MW =44, density similar =1.997 mg/cm3 at N2O, CO2 = MW =44, density similar =1.997 mg/cm3 at 00ooCC

Viscosity =1488 poise at 27Viscosity =1488 poise at 27ooC, CO2 ?C, CO2 ?LV HDLV HD

19. 19. RotaRota meters in anaesthetic machinesmeters in anaesthetic machines

�� Have an accuracy of about 2%Have an accuracy of about 2%

�� Are calibrated at 37Are calibrated at 37ooC and a pressure of 101.3 C and a pressure of 101.3 kPakPa

�� Reading should be taken from the bottom of Reading should be taken from the bottom of the bobbinthe bobbin

�� Are gas specificAre gas specific

�� At low flows, viscosity play important role At low flows, viscosity play important role

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LV, HDLV, HD

Flow meters vs AltitudeFlow meters vs Altitude

�� Q =PrQ =Pr44/nl = /nl = √√P/P/ρρll

HighHigh pressure = false pressure = false highhigh reading, over reading, over --

readsreads

Low pressure = false low reading, underLow pressure = false low reading, under--

readsreads

Back pressure ~ underBack pressure ~ under--readsreads

LV, HDLV, HD

20. Distribution of ventilation is 20. Distribution of ventilation is

measured bymeasured by

a.a. Helium dilution techniqueHelium dilution technique

b.b. Body Body plethysmographyplethysmography

c.c. Nitrogen wash out Nitrogen wash out

d.d. radioactive xenonradioactive xenon

e. 100% oxygen. 100% oxygen

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2020

�� Radioactive albumin : PerfusionRadioactive albumin : Perfusion

�� Radioactive gas (xenon)Radioactive gas (xenon)

21. Wrights respirometer may give a low

reading when

a) high tidal volume is used a) high tidal volume is used (over(over--reads)reads)

b) FiO2 = 0.3b) FiO2 = 0.3

c) Nitrous oxide is usedc) Nitrous oxide is usedd) Humidification is used

e) e) mechanical ventilation is used mechanical ventilation is used (over(over--reads reads

due to high peak flow at the beginning)due to high peak flow at the beginning)

UnderUnder--reads at low flows. Overreads at low flows. Over--reads at high flowreads at high flow

�� WrightWright’’s respirometer is a turbine s respirometer is a turbine

flowmeter flowmeter

�� A series of tangential slits that cause A series of tangential slits that cause

circular motion of the gas flow that circular motion of the gas flow that

produces rotation around the vaneproduces rotation around the vane

�� The vane does not rotate when the flow is The vane does not rotate when the flow is

reversedreversed

�� The composition of gas used does not The composition of gas used does not

influence its performance influence its performance

�� UnderUnder--reads at low flow and over reads at reads at low flow and over reads at

high flowhigh flow

22. Pulse 22. Pulse oximeteroximeter probes probes

[a] [a] Emit near infraEmit near infra--red light.red light.

[b] Once calibrated, do not need re[b] Once calibrated, do not need re--

calibrating.calibrating.

[c] Can cause heating of contact tissues.[c] Can cause heating of contact tissues.

[d] Are damaged by mild detergents[d] Are damaged by mild detergents..

[e] Are rendered inaccurate by 70% isopropyl [e] Are rendered inaccurate by 70% isopropyl

alcoholalcohol

F T T F FF T T F F

23. 23. PneumotachographPneumotachograph

a. measures laminar flowa. measures laminar flowb. measures the pressure differenceb. measures the pressure differencec. is more accurate if heated to a c. is more accurate if heated to a constant temperatureconstant temperatured. can be used to measure the volumed. can be used to measure the volumee. it shows a linear response only e. it shows a linear response only within the calibration rangewithin the calibration range

T T TT TT TT TT

Measures Flow, volume = flow /time

24. Regarding Temperature and 24. Regarding Temperature and

HeatHeat

1.1. Absolute zero is Absolute zero is --273K273K

2. Boiling point of water is +373K

3. Water freezes at +273K

4.4. SI unit of temperature is calorieSI unit of temperature is calorie

5.5. Daltons law states that Volume varies Daltons law states that Volume varies directly with temperaturedirectly with temperature

FTTFFFTTFF

24. Regarding Temperature and 24. Regarding Temperature and

HeatHeat

1.1. Absolute zero Absolute zero is is --273 C or 0 K273 C or 0 K

2. Boiling point of water is + 373K

3. Water freezes at +273K

4.4. SI unit of temperature is SI unit of temperature is KelvinKelvin

5.5. Daltons law states that Volume varies Daltons law states that Volume varies directly with temperaturedirectly with temperature

00ooC = 273 KC = 273 K

Gas lawsGas laws

�� Daltons: In a mixture of gases, pressure Daltons: In a mixture of gases, pressure

exerted by each gas is same as that which exerted by each gas is same as that which

it would exert if it alone occupied the it would exert if it alone occupied the

container.container.

Absolute ZeroAbsolute Zero 0K 0K --273C273C --459F459F

Freezing pointFreezing point 273K 273K 0C0C 32F32F

H2OH2O

Boiling pointBoiling point 373K 100C373K 100C 212F212F

K=C+273K=C+273

C=5/9(FC=5/9(F--32)32)

F=9/5(C+32)F=9/5(C+32)

25, Invasive blood pressure25, Invasive blood pressure

a. is higher in dorsalis pedis artery as compared a. is higher in dorsalis pedis artery as compared

toto brachial artery in supine positionbrachial artery in supine position

�� b. Requires a system pressurised to 300kPa b. Requires a system pressurised to 300kPa

(mm Hg)(mm Hg)

c. records a higher systolic pressure as c. records a higher systolic pressure as

compared to NIBPcompared to NIBP

d. is unreliable in hypertensive patientd. is unreliable in hypertensive patient

e. Records a more accurate mean arterial e. Records a more accurate mean arterial

pressure as compared to NIBPpressure as compared to NIBP

Factors affecting dampingFactors affecting damping

�� fn = fn = √√DD22./pLC./pLC

fn = natural frequency , fn = natural frequency ,

D = diameter of catheter, D = diameter of catheter,

pp = density, = density,

L =length, L =length,

C = compliance.C = compliance.

Resonance and dampingResonance and damping

�� Inertial forces : massInertial forces : mass

�� Elastic forces: springElastic forces: spring

�� Friction forces: mediumFriction forces: medium

�� FluidFluid

�� DiaphragmDiaphragm

�� Viscous effect of fluidViscous effect of fluid

�� Mass Mass ––spring systemspring system

•fn = √D2./pLC

Resonance and damping

Square wave test D2 /D1 = 5 /10 =0.5

Amplitude ratio = D. coeff

1 cycle,; fn = speed / 1 cycle (mm)

D2 D1

300 mmHg

The loss of pressure in the bag, compliant

tubing, stopcocks, length >120 cm, kinking

of the cannula, blood clots and air bubblesStiff tube, diaphragm

�� Critical damping= no oscillations, no Critical damping= no oscillations, no overshoot.overshoot.

�� UnderUnder--damped more than 3 cycles before damped more than 3 cycles before reaching zero.reaching zero.

�� Amplitude ratio of 0.1 = optimum damping Amplitude ratio of 0.1 = optimum damping = damping coefficient 0.6 = damping coefficient 0.6 --0.7, 0.640.7, 0.64

�� fn = fn = √√DD22./pLC./pLC

�� increased compliance reduces natural increased compliance reduces natural frequencyfrequency

�� a) a) 7.5 mm Hg is equivalent to 10 cm H7.5 mm Hg is equivalent to 10 cm H22OO

�� bb) 1 ) 1 kPakPa is equal to a pressure of 7.5 mm is equal to a pressure of 7.5 mm

HgHg

�� cc) 1 bar is equal to 15 psi) 1 bar is equal to 15 psi

�� dd) A mercury barometer used to measure ) A mercury barometer used to measure

atmospheric pressure is sealed with a atmospheric pressure is sealed with a

vacuum above the surface of the liquid vacuum above the surface of the liquid

�� ee) Aneroid gauges do not contain liquid) Aneroid gauges do not contain liquid

Atmospheric pressureAtmospheric pressure

1 bar = 15 psi =1000cm H1 bar = 15 psi =1000cm H220 =750 mm Hg0 =750 mm Hg

=100kPa=100kPa

1 psi =6.89 1 psi =6.89 kPakPa

�� a. is dependent on the viscosity of the fluida. is dependent on the viscosity of the fluid

�� b. doubles if the radius of the cannula is doubledb. doubles if the radius of the cannula is doubled

�� c. doubles if the length of the cannula is halvedc. doubles if the length of the cannula is halved

�� d. is inversely proportional to the length of the d. is inversely proportional to the length of the cannulacannula

�� e. doubles if the pressure is doubled.e. doubles if the pressure is doubled.

�� TFTTTTFTTT

�� Q is proportional to the rQ is proportional to the r44

�� Q =P Q =P rr44/nl/nl

28. With regard to accidental 28. With regard to accidental

electrocutionelectrocution

(a) The risk of ventricular fibrillation increases with (a) The risk of ventricular fibrillation increases with increasing current frequency.increasing current frequency.

(b) (b) The risk of ventricular fibrillation is greater with The risk of ventricular fibrillation is greater with alternating current.alternating current.

(c) The use of battery operated equipment avoids the (c) The use of battery operated equipment avoids the risk of ventricular fibrillation.risk of ventricular fibrillation.

(d) The risks of electrocution is reduced by (d) The risks of electrocution is reduced by earthingearthingthe patient.the patient.

(e) All electrical equipment in the operating theatre (e) All electrical equipment in the operating theatre should be earthed (should be earthed (battery operated).battery operated).

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29.29.

�� a) The blood gas results are normal to this a) The blood gas results are normal to this

patientpatient

�� b) An echocardiogram would be useful.b) An echocardiogram would be useful.

�� c) A ventilation perfusion scan would be helpful c) A ventilation perfusion scan would be helpful

in diagnosisin diagnosis

�� d) An intrapulmonary shunt is accountable for d) An intrapulmonary shunt is accountable for

these findingsthese findings

�� e) An increased dead space is accountable for e) An increased dead space is accountable for

these findings.these findings.

�� FTTFTFTTFT

30.With respect to statistics30.With respect to statistics

� Null hypothesis states that there is no real difference between two sets of data

� Rejection of the null hypothesis leads to acceptance of the alternate hypothesis

�� Beta error occurs if the null hypothesis is Beta error occurs if the null hypothesis is wrongly rejected.wrongly rejected.

�� Alpha error states that the null hypothesis has Alpha error states that the null hypothesis has been wrongly acceptedbeen wrongly accepted

� Power of a study can be increased by raising the number of observations

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BJA, CEACCPBJA, CEACCP

�� The The nullnull hypothesishypothesis would therefore be would therefore be

that intrathat intra--articular morphine is no betterarticular morphine is no better

than placebo.than placebo.

�� A type I A type I error ( alpha)error ( alpha) occurs when the occurs when the

null hypothesis is incorrectly rejected. A null hypothesis is incorrectly rejected. A

type II type II errorerror (beta) occurs when the null (beta) occurs when the null

hypothesis is incorrectly acceptedhypothesis is incorrectly accepted

GOOD LUCKGOOD LUCK