Primary FRCA Regional Teaching Day - SBAs

Vivek SinhaST4 AnaestheticsHRI11/05/2013

Physiology 1) A patient on the intensive care unit is being

ventilated in a volume-controlled mode with an FiO2 of 0.6. Arterial blood gas analysis reveals a PaO2 of 7.5kPa and a PaCO2 of 4.7kPa. Which ONE of the following is the best intervention aimed at increasing the PaO2?

a)      Increase the FiO2 b)      Increase the tidal volume c)      Increase the frequency d)      Increase the inspiratory time e)      Increase the expiratory time

Physiology 2) A hormone is produced in the cytoplasm of

an endocrine cell and is then stored in granules within the cytoplasm. On release from the cell it is carried in the blood-stream to a target cell, where it crosses the cell membrane and binds directly to the nucleus, increasing cell gene transcription. Which hormone is best described in these terms?

a)      Adrenaline b)      Thyroxine c)      Aldosterone d)      Thyroid-stimulating hormone e)      Growth hormone

Explanation3 main Classes of Hormone

Peptides (eg. Growth Hormone) Synthesised in cell nucleus and then stored in granules and

released by exocytosis Surface receptor Act via second messengers

Amines Synthesised in the cytoplasm and then stored in granules Two sub-types:

Catecholamines (eg. adrenaline) – act at cell membranes and use second messengers

Thyroid hormones (eg. Thyroxine) – binds directly to nucleus receptors, stimulating transcription

Steroid (eg. Aldosterone) Synthesised from cholesterol Immediately released (not stored) Lipid-soluble Enter cytoplasm and typically bind with receptors there and then

enter nucleus to stimulate transcription

Explanation Adrenaline & TSH – Gs protein-coupled

receptors T3 & T4 stored in follicle stems between

thyroid cells as the protein thyroglobulin 33% Thyroxine (T4) converted to T3 in

target tissues and 45% to Reverse T3

T3 acts on nuclear receptors to alter cellular function via messenger RNA

T4 has much less affinity to nuclear receptor

ExplanationThyroid Follicular Cells

Physiology 3) A patient with chronic obstructive pulmonary disease

presents for assessment for long-term oxygen therapy (LTOT) and is found to have a compensated respiratory acidosis. Which of the following sets of arterial blood gases best demonstrates compensated respiratory acidosis?

a)      pH=7.30, PCO2=7.2kPa, PO2=9.5kPa, HCO3-=25mmol/L

b)      pH=7.36, PCO2=8.5kPa, PO2=7.5kPa, HCO3-=43mmol/L

c)      pH=7.24, PCO2=10.1kPa, PO2=7.0kPa, HCO3-=27mmol/L

d)      pH=7.24, PCO2=3.5kPa, PO2=8.5kPa, HCO3-=18mmol/L

e)      pH=7.20, PCO2=6.2kPa, PO2=9.0kPa, HCO3-=15mmol/L

Physiology 4) Which of the following statements regarding

humoral mechanisms involved in controlling haemorrhage is INCORRECT?

a) Circulating catecholamines increase b) Atrial natriuretic peptide (ANP) levels

increase c) Vasopressin release is mediated via the

Gauer-Henry reflex d) Stimulation of the adrenal cortex promotes

release of aldosterone e) Circulating levels of enkephalins increase

Explanation Aldosterone

Secreted by zona glomerulosa of adrenal cortex

Major regulators Renin-angiotensin system Plasma concentration of potassium ACTH

Miscellaneous regulators Sympathetic nerves Baroreceptors Plasma concentration of sodium Aldosterone feedback

Explanation Enkephalins and endorphins

Endogenous opioids that bind to and activate opioid receptors throughout the CNS

Levels of enkephalins increased when adrenal medulla is stimulated

Gauer-Henry reflex Atrial stretch sensors sense decrease in volume

and transmit signals to increase ADH secretion Gravitational change from 1g to microgravity

may cause cephalad fluid shift, resulting in suppression of ADH secretion and diuresis

Explanation ANP

Plays important role in blood volume and electrolyte homeostasis in normovolemia and in hypervolemic states

Secreted primarily from atria Hypervolemia and elevation of left atrial pressure or

volume are the major known factors stimulating its release (local wall stretch)

Plays important role in blood volume homeostasis by inducing rapid natriuresis and water excretion

Lowers BP and antagonises renin-angiotensin-aldosterone axis

Mild bleeding induces a rapid decrease in ANP secretion

Some studies show increased plasma ANP after prolonged severe haemorrhage (possible biphasic effect of haemorrhage)

Physiology 5) A farmer slips and falls in a remote field

during a hot summer. He has nothing to eat and his only drink is whisky from a hip flask. He is not found for 3 days. On admission to hospital he is peripherally cold, with a heart rate of 110 beats/min and a blood pressure of 85/40mmHg. Which of the following is the most potent stimulus for antidiuretic hormone release?

a)      Stimulation of central osmoreceptors b)      Stimulation of aortic arch baroreceptors c)      Ingestion of alcohol d)      Pain e)      Stress

Explanation Alcohol inhibits ADH Pain and stress stimulate ADH Osmoreceptors are very sensitive

They respond to a change as small as a 1 to 2% increase in tonicity

Baroreceptors are less sensitive (but more potent) than the osmoreceptors

Hypovolaemia is a more potent stimulus for ADH release than is hyperosmolality.

A hypovolaemic stimulus to ADH secretion will override a hypotonic inhibition and volume will be conserved at the expense of tonicity

Physiology 6) Prior to induction of anaesthesia you

preoxygenate the patient with a Bain circuit and a close fitting mask for 5 min. The reason for this is:

a) To increase dissolved oxygen in the blood

b) To flush out nitrogen c) To increase FRC d) To increase oxygen Hg capacity e) To increase the amount of oxygen in

the alveoli with 3l

Explanation Dissolved oxygen plays a tiny part in oxygen

content and transport compared to haemoglobin. 100ml of arterial blood contains approximately 20ml of

oxygen, 19.7ml of which is combined with haemoglobin, whereas only 0.3ml is dissolved in plasma.

In venous blood these figures are 14.9 and 0.1 respectively.

The oxygen content equation is as follows:

Oxygen content = (1.34 x Hb x sats)/100 + 0.023pO2, where the Hb is measured in g/dl and the pO2 is measured in kPa and the solubility coefficient of O2 is 0.023 ml/dl/kPa.

Explanation In normal person breathing room air with

Hb 15g/dl, pO2 13.3kPa and sats 97% Total arterial oxygen content would come to

19.80ml (bound to Hb = 19.497ml and dissolved in plasma = 0.3059ml).

Even if the pO2 is increased to 80kPa Total oxygen content would rise to only

21.337ml (bound to Hb = 19.497ml and dissolved in plasma = 1.84ml).

This is just a 1.08% rise in total oxygen content

Hyperbaric oxygen chamber

Explanation

3L lung volume doesn't correlate with any physiological lung measure and alveoli is a very general term when you discuss preoxygenation

Physiology 7) A 78 year old patient has been admitted to the intensive

care unit for intubation and ventilation due to a low GCS. The family give a history of progressive weakness over several weeks with abdominal pain, decreased appetite, confusion and weight loss. The patient is known to have ischaemic heart disease, peripheral vascular disease, glaucoma, prostatic carcinoma and COPD. Blood results have come back showing Hb 9, Platelets 90, WCC 13, Na 149, K 5.6, Ur 14, Cr 220, Ca 3.6. ECG shows a prolonged PR and prolonged QT.

What is the most likely cause of the ECG findings? a) Congenital b) Hypercalcaemia c) Hyperkalaemia d) Hypernatraemia e) Myocardial Ischaemia

Explanation Very rare for a electrolyte abnormality to produce

prolonged PR and QT as well - as it needs both conduction and repolarisation to be affected

Hypercalcaemia Range

Normal serum corrected calcium = 2.1 – 2.6 mmol/L Mild hypercalcaemia =  2.7 – 2.9 mmol/L Moderate hypercalcaemia = 3.0 – 3.4 mmol/L Severe hypercalcaemia =  > 3.4 mmol/L

ECG Main ECG abnormality seen with hypercalcaemia is

shortening of the QT interval ST segment duration shortened In severe hypercalcaemia, Osborn waves (J waves) may be

seen Ventricular irritability and VF arrest has been reported with

extreme hypercalcaemia

Explanation Typical progressive changes of hyperkalaemia:

Tall, pointed, narrow T waves.  Decreased P wave amplitude, decreased  R wave

height, widening of QRS complexes, ST segment changes (elevation/depression), hemiblock (esp. left anterior) and 1st degree heart block. 

Advanced intraventricular block (very wide QRS with RBBB, LBBB, bi- or tri-fascicular blocks) and ventricular ectopics.

Absent P waves, very broad, bizarre QRS complexes, AV block, VT, VF or ventricular asystole

No significant changes on the ECG occur with hypo-/hypernatraemia

Pharmacology 8) You are asked to provide anaesthesia

for a pregnant woman undergoing emergency appendicectomy. Of the following drugs administered to the woman, which is the least likely to accumulate in the fetus?

a)      Bupivacaine b)      Pethidine c)      Thiopental d)      Diamorphine e)      Diazepam

ExplanationPhysiochemical properties

Increased placental transfer High lipid solubility (eg. Diazepam, most sedatives,

pethidine) MW (<600 dalton for lipid-soluble, <100 dalton for polar) Bases (LAs & most opioids are weak bases) Non-ionised (eg phenobarbital) Low protein-binding

Decreased placental transfer Acids Charged (eg. heparin) Size (heparin, IgM) Altered or bound by enzymes within placenta (eg. amines,

insulin) Firmly and highly bound to

maternal RBC (eg. CO) Plasma proteins (eg dicloxacillin, propranolol)

Explanation Basic drugs

Fetal pH lower (0.1-0.15) than maternal pH Relatively more ionized than in

maternal blood and "ion trapping" may occur, leading to fetal drug accumulation

LAs, Pethidine However, significant ion-trapping of

bupivacaine only occurs in significant acidosis

Pethidine Pethidine and Norpethidine (active

metabolite of pethidine) accumulates in both the mother and fetus with a half-life of 4 and 20 hours respectively in mother and 13 and 62 hours in neonate

Explanation All used inhalational agents cross the placenta

Very little fetal depression if <1MAC & delivery occurs within 10min of induction

Thiopental, propofol, benzodiazepines and ketamine all cross placenta but only benzodiazepines known to produce significant fetal effects

Diamorphine Rapidly eliminated by the placenta

Diamorphine, diazepam & pethidine broken down to lipid-soluble products

Pharmacology 9) A new drug is being tested. Its onset of action

depends on the rate of diffusion across the cell membrane. The following factors increase the rate of diffusion of a substance across a biological membrane, EXCEPT which one?

a) Decreased molecular weight b) Increased concentration gradient c) Decreased solubility of a gas d) Increased lipid solubility e) For a weakly acidic substance, a low

environmental pH

ExplanationFactors Influencing Rate of Diffusion

Graham’s Law Rate of passive diffusion is inversely proportional to

square root of molecular size Fick’s Law

Rate of transfer proportional to concentration gradient across membrane

Ionization For acidic substance more unionized in lower pH

Lipid-solubility Protein-binding Rate of simple diffusion = permeability

constant x membrane area x concentration gradient

Pharmacology 10) An adult patient distressed by

shivering in the postoperative period would be most effectively treated with which ONE of the following?

a)      Pethidine 25mg b)      Doxapram 100mg c)      Clonidine 150 µg d)      Ketanserin 10mg e)      Alfentanil 250 µg

Pharmacology 11) After intravenous administration of

anaesthesia you notice the area around the injection site has become very swollen, erythematous and inflamed. Which of the following is most likely to cause most damage?

a) Rocuronium b) Morphine c) Ondansetron d) Dexamethasone e) Thiopental

Contin Educ Anaesth Crit Care Pain (2010) 10 (4): 109-113.

ExplanationDrugs used in anaesthesia/intensive care unit with potential to cause tissue damage

Hyperosmolar agents Calcium chloride Calcium gluconate Glucose >10% Magnesium sulphate 20% Mannitol 10% and 20% Parenteral nutrition Potassium chloride Sodium bicarbonate Sodium chloride >0.9% X-ray contrast media

Acids/alkalis Aminophylline Amiodarone Amphotericin Co-trimoxazole Diazepam Erythromycin Phenytoin Thiopental Vancomycin

Vascular regulators Epinephrine Dobutamine Dopamine Metaraminol Norepinephrine Prostaglandin Vasopressin

Pharmacology 12) You are to carry out an experiment to assess

the speed of gastric emptying.  A standard dose of a marker drug is to be given to healthy volunteers. You will then measure plasma drug concentration at standard time intervals. Which of the following drugs will be suitable for this:

a) Aspirin b) Gentamicin c) Paracetamol d) Propranolol e) Vancomycin

Explanation pH = pKa + log [BASE]/[ACID] PKa of the drug (Dissociation or ionization constant):

pH at which half of the substance is ionized & half is unionized. pH of the medium:

Affects ionization of drugs. Weak acids best absorbed in stomach. Weak bases best absorbed in intestine. Aspirin (weak acid), pka=3.0

Too much absorbed in stomach to be useful as marker Still absorbed in small intestine despite low unionised fraction, due to large

intestinal surface area Propranolol (weak base), pka= 9.4

Absorbed mainly in small intestine Extensive first-pass metabolism

Paracetamol (weak base), pKa=9.5 Absorbed mainly in small intestine Paracetamol absorption depends on gastric emptying Low first-pass metabolism (approx 25%)

Pharmacology 13) NIDDM patient had a 30 minute knee

arthroscopy. Pre-op BM 7. Given Ondansetron and Dexamethasone for PONV. Post-op BM 13. What is the most likely cause for raised BM post-op?

a) Dexamethasone b) Ondansetron c) Surgical stress d) Missed morning dose of anti-diabetic

medication e) Metabolism of Hartmann's fluid

Pharmacology 14) An asthmatic patient developed

bronchospasm from diclofenac. Which one of the following could this be due to?

a) Thromboxane A2 b) Arachidonic acid c) Leukotriene d) Prostacyclin e) Prostaglandin

Explanation

Pharmacology 15) A 25 year old male has just been transferred to the

operating table for a repair of an umbilical hernia. After pre-oxygenation and induction of general anaesthesia with thiopentone, fentanyl, mivacurium, an i-gel was inserted and the patient was ventilated with IPPV. A bag of gelofusine was being transfused and remifentanil and sevoflurane used for maintenance of anaesthesia. A dose of teicoplanin was given for surgical prophylaxis. 5 minutes into the surgery the patient develops hypotension, bronchospasm, flushing.

Anaphylaxis was diagnosed and appropriate treatment was started. What is the most likely cause of the anaphylaxis.

a) thiopentone b) fentanyl c) mivacurium d) gelofusine e) teicoplanin

World Allergy Organization (WAO)

Explanation Since 1980 more than 4,500 cases of

perianaesthetic anaphylaxis have been reported by French and English authors.

The drugs most frequently responsible for anaphylactic reactions in the French epidemiological survey were

NMBAs (54%) Latex (22.3%) Antibiotics (14.7%) Opioid agents (2.4%) Hypnotic agents (0.8%) Colloids (2.8%) Others (3%)

World Allergy Organization (WAO)

Explanation Among the cases of anaphylaxis attributed to

NMBAs in the literature, the following substances have been incriminated, in decreasing order of importance:

suxamethonium, vecuronium, atracurium, pancuronium, rocuronium, mivacurium and cisatracurium.

If one expresses the number of reactions observed in terms of the number of subjects exposed to NMBAs, the drugs can be divided into 3 groups:

those associated with a high frequency of allergic reactions, including suxamethonium and rocuronium;

those associated with an intermediate frequency of allergy, including vecuronium and pancuronium;

those associated with a low frequency of allergy, including atracurium, mivacurium and cisatracurium.

Contin Educ Anaesth Crit Care Pain (2004) 4 (4): 111-113.

ExpanationCauses of life-threatening allergic reactions during anaesthesia

Neuromuscular blocking agents (70%) Steroid-based compounds (vecuronium and

pancuronium) cause anaphylactic reactions, whereas benzylisoquinoliniums (mivacurium and atracurium) tend to cause anaphylactoid reactions.

Of drug reactions caused by neuromuscular blocking agents,

43% are caused by succinylcholine, 37% vecuronium and 7% atracurium.

Latex (12.6%) Colloids (4.7%)

The risk is greatest with gelatin solutions. All hyperosmolar solutions can release histamine

directly.

Contin Educ Anaesth Crit Care Pain (2004) 4 (4): 111-113.

ExpanationCauses of life-threatening allergic reactions during anaesthesia

Induction agents (3.6%) Incidence of severe reactions to thiopental been reported approx 1

in 14000 Reactions to propofol less common Least common to etomidate

Antibiotics (2.6%) Penicillins most frequently implicated

Benzodiazepines (2%) Opioids (1.7%)

Opioids usually cause anaphylactic reactions; morphine implicated most commonly.

Reactions to synthetic opioids rare Morphine, codeine and meperidine can cause a dose-dependent,

non-immunological cutaneous histamine release Other agents (2.5%)

ExplanationIncidence of anaphylaxis according to the NMBA in France over 6 years ( 1997-2002 )

Rocuronium 1 : 5,100 patients exposed Succinylcholine 1 : 5,500 patients

exposed Vecuronium 1 : 13,000 patients exposed Pancuronium 1 : 14,700 patients exposed Mivacurium 1 : 38,200 patients exposed Atracurium 1: 52,800 patients exposed Cisatracurium 1 : 148,7000 patients

exposed

Explanation Fentanyl

“To date, there have been seven reported cases of fentanyl-induced anaphylaxis” (Br. J. Anaesth. (2011) 106 (2): 283-284)

Teicoplanin “Anaphylactic Reactions: Uncommon - More than 1 in 1000

people who have Teicoplanin” (NHS Choices website) “Anaphylactic Shock: The frequency of these side-effects is

unknown” (NHS Choices website) Gelofusine

“Anaphylactoid reaction to Gelofusine, that contains succinylated gelatin and other plasma expanders carries an estimated incidence of 0.07–0.15%.” (Ioannis Polyzois et al. Anaphylaxis due to gelofusine in a patient undergoing intramedullary nailing of the femur: a case report. Cases Journal 2009, 2:12)

Physics & Measurement 16) A 25-year-old woman who is 16 weeks

pregnant is admitted to hospital with sudden onset of breathlessness and collapse. A transthoracic echocardiogram suggests a massive pulmonary embolus. An ECG is studied and shows sinus tachycardia with right axis deviation. The cardiac axis is likely to lie at which of these angles?

a)      -60 degrees b)      +60 degrees c)      +90 degrees d)      +120 degrees e)      -90 degrees

Explanation

both I and aVF +ve = normal axis both I and aVF -ve = axis in the Northwest Territory lead I -ve and aVF +ve = right axis deviation lead I +ve and aVF -ve

lead II +ve = normal axis lead II -ve = left axis deviation

Physics & Measurement 17) Whilst checking the anaesthetic machine in

theatre you notice that a piece of monitoring equipment has the symbol of a man enclosed in a box. Which ONE of the following is not true regarding the electrical safety of this equipment?

a) It is a floating circuit b) It cannot be used in direct connection with

the heart c) It has a maximal leakage current of 10 μA d) It contains an isolating transformer e) It has a maximal leakage current of 500 μA

Davis PD, Kenny GNC. Basic Physics and Measurement in

Anaesthesia, 5th edn. Oxford: Butterworth Heinemann,

2003; pp. 181-5.

Explanation This is the symbol for type BF equipment.

Therefore has a maximal leakage current of 500 μA and Cannot be used in direct connection with the heart

Equipment classified into 3 groups Class I equipment - any accessible conductible part must be

connected to earth For this system to work correctly, fuses must be present in the

live and neutral wires. Class II equipment has double or reinforced insulation of

any conductible parts Does not have an earth wire.

Class III equipment uses batteries at a voltage unlikely to cause electrocution

But may result in microshock.

Davis PD, Kenny GNC. Basic Physics and Measurement in

Anaesthesia, 5th edn. Oxford: Butterworth Heinemann,

2003; pp. 181-5.

Explanation Further classified by the maximum leakage

current it allows (type B, BF and CF). Type B or BF equipment is used in medical

monitoring equipment. Type B has a maximum leakage current of 100–500

μA under single fault conditions and should not be directly connected to the heart.

It can be class I, II or III. Type BF is type B but also uses a floating circuit. Type CF has a floating circuit and a maximal leakage

current of 10–50 μA. It is used in equipment which may contact the heart directly.

Davis PD, Kenny GNC. Basic Physics and Measurement in

Anaesthesia, 5th edn. Oxford: Butterworth Heinemann,

2003; pp. 181-5.

Explanation Circuit breakers exist that are current-operated

Consist of coils of the live wire around a transformer An equal number of coils of the neutral wire are also

wound around the transformer A third wire connects to a relay that operates the

circuit breaker With equal currents in the live and neutral wire, the

magnetic fluxes are equal and opposite and therefore there is no magnetic field.

With a small leakage current, the magnetic fluxes are different, and a magnetic field that induces a current in the third winding results in the relay breaking the circuit.

Physics & Measurement 18) Consider a hypothetical situation in which

the following gases or vapours are stored separately in cylinders in a hot operating theatre (the thermometer reads 35 degrees Celsius). Which one of the following would NOT contain gas alone, irrespective of the pressure within the cylinder?

a)   Oxygen b)   Nitrogen c)   Nitrous oxide d)   Carbon dioxide e)   Air

ExplanationNitrous Oxide Storage French blue cylinders In a liquid phase with its vapour on top At a gauge pressure of 4400 kPa at room temperature.  As the liquid is less compressible than a gas, the

cylinder should be only partially filled. 

The filling ratio is weight of the fluid in the cylinder divided by weight of water required to fill cylinder 

In the UK, the filling ratio for N2O is 0.75 But in hotter climates the filling ratio needs to be 0.67, to

avoid cylinder explosion.

Hospitals store N2O in large cylinders (e.g. size J) in two groups of cylinder manifolds.

Physics & Measurement 19) Capnography is part of the AAGBI minimal

monitoring requirements for general anaesthesia. Regarding capnography, which of following is the LEAST correct?

a) Capnography is based on the principle that gases with two or more different atoms in the molecule will absorb infrared radiation

b) The particular frequency of infrared radiation is selected by first passing it through a crystal window

c) A reference cell increases accuracy of the system d) The use of infrared radiation with a wavelength of

4.28 µm for the analysis of carbon dioxide should reduce interference from the presence of nitrous oxide

e) In the sidestream capnograph, a sample is drawn at about 150mL/min

Explanation Basic analyser system consists of an infrared

source, sample chamber and detector Basic principle of capnograph is based on Beer

Lambert Law Beer Law

Amount of infrared rays absorbed is proportional to the concentration of the infrared absorbing substance

ie. The more CO2 present, the more infrared rays absorbed

The chamber is made of special material that freely allows infrared waves to pass through (e.g. sapphire).

Explanation

Explanation CO2 maximally absorbs  infrared waves

with wavelengths of about 4.28 micrometers

Nitrous oxide maximally absorbs infrared waves with wavelengths of about 4.5 micrometers

Collision Broadening Absorption pattern of CO2 broadens when

N2O or O2 added Can lead to a potential source of error in

measurement Modern analysers measure the amount of

N2O and O2 present to correct for errors due to collision broadening.

Physics & Measurement 20) A group of doctors from your hospital have recently

returned from a charity trip climbing Mount Everest. They are relieved to be home as they said they couldn’t have a good cup of tea on the mountain. Which of these responses would best explain why?

a) The boiling point of water is 373.15 kelvin b) The boiling point is the temperature of a substance at

which its saturated vapour pressure equals external atmospheric pressure

c) A gas is a substance at a temperature above its critical temperature

d) Boiling point increases with increasing pressure e) The saturated vapour pressure of a substance

increases with increasing temperature

Physics & Measurement

21) Arterial line pressure curve can measure ventricular contraction by

a)      Dicrotic notch b)      Area under the curve c)      Wave upstroke  d)      Height of curve e)     Length of curve

ExplanationInformation in Arterial Waveform Arterial blood pressure The slope of the upstroke of the wave reflects

myocardial contractility (dP/dt). The stroke volume

Calculated by measuring the area from the beginning of the upstroke to the dicrotic notch.

If this is multiplied by the HR, then CO can be estimated.

The position of the dicrotic notch on the down stroke.

A low dicrotic notch is seen in hypovolaemic patients. The slope of the diastolic decay indicates

resistance to outflow (SVR). A slow fall is seen in vasoconstriction.

Physics & Measurement 22) The potential difference across the capacitor

decreases, if the frequency of AC current increases. What is the reason for this?

a) Capacitance inversely proportional to AC frequency

b) Impedence inversely proportional to AC frequency

c) Inductor inversely proportional to AC frequency d) Resistance inversely proportional to AC

frequency e) Conductance inversely proportional to AC

frequency

Explanation Conductance = A measure of a material's

ability to conduct electric charge; the reciprocal of the resistance

Resistance (R) = Opposition to current. (The part which is constant regardless of frequency).

Reactance (X) = measure of the opposition of capacitance and inductance to current.

Reactance varies with the frequency of the electrical signal

Impedance (Z) = measure of overall opposition of a circuit to current.

Takes into account both resistance and reactance.

Explanation

Explanation C=Q/V Energy (E) needed to move an electric charge (Q)

through a p.d. (V): E= QV

As p.d. between plates increases more energy needed to add extra charge

In DC circuit, current will flow initially and then die away as capacitor becomes fully charged

In AC circuit, current will flow as capacitor being constantly charged and discharged

AC frequency directly proportional to current size R=V/I AC frequency therefore inversely proportional to

impedence

Physics & Measurement 23) Long plastics operation approx 4

hours long. Temp measured 34.5. No body warmer or fluid warmer.  What is the main reason for the drop in temp:

a) iv fluids b) convection c) conduction d) radiation e) evaporation

Explanation “Royal” “College” “Exam” “Room”

Conduction

Radiation (~40%) Convection (~30%) Evaporation (8-

15%) Respiration (8-

10%)

Conduction (~5%)

Clinical Scenario 24) You are working as a ship’s doctor in the tropics. The ship

rescues a 40-year-old, 72 kg man from an island who was shipwrecked 2 days previously. He has had nothing to eat or drink for 2 days and the average daytime temperature has been 34 degrees Celsius. He looks severely dehydrated but is conscious and cooperative. Which ONE of the following would be your fluid resuscitation of choice over the next 24 hours?

a) Let him drink water freely b) Cautiously allow to drink water and administer 2000mL of

5% dextrose solution intravenously over the next 24 hours c) Cautiously allow to drink water and administer 3000mL of

Hartmann’s solution intravenously over the next 24 hours d) Prohibit oral fluids and administer 4000mL of 0.9% saline

solution intravenously over the next 24 hours e) Prohibit oral fluids and administer 5000mL of dextrose

saline solution intravenously over the next 24 hours

Explanation

Patient conscious and cooperative so can be given mixture of oral + IV rehydration

Just oral water will not replace lost elecrolytes (neither will just 5% dextrose)

Clinical Scenario 25) You are required to take over an emergency laparotomy in

a 54-year-old, 80 kg male patient with a history of well-controlled hypertension who is otherwise previously fit and well. You insert an oesophageal Doppler probe and note the following haemodynamic observations: heart rate103 beats/min, blood pressure 74/49 mmHG, cardiac output 4.1 L/min, flow time corrected (FTc) 290 milliseconds. Your initial management should be ONE of the following:

a)      Give a 200mL intravenous colloid bolus over 5 minutes b)      Give a 200mL intravenous colloid bolus over 5 minutes

and start an intravenous infusion of dobutamine c)      Give a 200mL intravenous colloid bolus over 5 minutes

and start an intravenous infusion of metaraminol d)      Give a 200mL intravenous colloid bolus over 5 minutes

and start an intravenous infusion of noradrenaline e)      Start an intravenous infusion of gliceryl trinitrate

Explanation

Explanation

Reference ranges in adult with no co-morbidities CO 5-8L/min SV 60-100ml PV

20yrs: 90-120cm/s 50yrs: 70-100cm/s 70yrs: 50-80cm/s

FTc 330-360ms

Explanation Flow time

Systolic ejection time Will clearly vary according to heart rate, so to allow

comparison, corrected to HR of 60bpm (FTc) FTc inversely related to SVR, therefore narrow waveform

base (<330ms) is indicator of vasoconstriction, of which hypovolaemia is commonest cause

PV directly related to left ventricular contractility (age-dependent)

An increase of SV or stroke distance of >10% would be seen as positive response and challenge should be repeated

Concurrent shifts in FTc and PV indicates changes in afterload

Increase in afterload gives simultaneous reduction in FTc and PV (narrow waveform with decreased amplitude)

ExplanationExamples

Narrow waveform base, decreased FTc characteristic of hypovolaemia

ExplanationExamples

Same patient after fluid resuscitation

ExplanationExamples

ExplanationExamples

Clinical Scenario 26) Regarding the management of acute

myocardial infarction presenting with ischaemic symptoms and persistent ST elevation, which ONE of the following would be an absolute contraindication to fibrinolytic therapy?

a) Previous fibrinolysis 5 months ago b) Resuscitated cardiac arrest within the last

hour c) Diabetic retinopathy d) Ischaemic stroke 2 months ago e) Pregnant at 36 weeks gestation

2004 ACC/AHA Practice Guidelines

ExplanationAbsolute Contraindications

Any prior ICH Known structural cerebral vascular lesion (eg.

AVM) Known malignant intracranial neoplasm

(primary or metastatic) Ischaemic stroke within 3 months EXCEPT

acute ischaemic stroke within 3 hours Suspected aortic dissection Active bleeding or bleeding diathesis

(excluding menses) Significant closed-head or facial trauma within

3 months

2004 ACC/AHA Practice Guidelines

ExplanationRelative Contraindications

History of chronic, severe, poorly-controlled HTN Severe uncontrolled HTN on presentation (SBP >180mmHG or

DBP >100mmHg) History of prior ischaemic stroke greater than 3 months,

dementia, or other known intracranial pathology Traumatic or prolonged (>10min) CPR or major surgery (<3

weeks) Recent internal bleeding (<2-4 weeks) Noncompressible vascular punctures Pregnancy Active peptic ulcer Current use of anticoagulants: the higher the INR, the higher

the risk of bleeding For streptokinase: prior exposure (>5 days) Prior allergic reaction to these agents

Clinical Scenario 27) You are fast bleeped to an elderly medicine ward to find a

84 year old morbidly obese patient with weak respiratory effort on 15L non-rebreathe and a weak pulse with an unrecordable blood pressure. Just as you try and assess the patient the patient stops breathing and you call the cardiac arrest team and initiate CPR at 30 compressions to two breaths. After one cycle the AED demonstrates VF and one shock is administered. An i-Gel is inserted and the second cycle of CPR commences. Peripheral IV access has proven difficult with multiple attempts. What is your next action during this cycle of CPR?

a) Remove the i-Gel and perform tracheal intubation with an ETT tube and give 1 mg Adrenaline down the Ett Tube

b) Give 1mg adrenaline IM c) Attempt to gain central venous access and give 1 mg

adrenaline d) Give an intracardiac injection of adrenaline e) Gain intraosseous access and give 1mg Adrenaline

ExplanationResuscitation Council (UK) Guidelines

2010 Delivery of drugs via a tracheal tube is no longer

recommended – if intravenous (IV) access cannot be achieved give drugs by the intraosseous (IO) route.

When treating VF/VT cardiac arrest, adrenaline 1 mg is given once chest compressions have restarted after the third shock and then every 3-5 min (during alternate cycles of CPR).

In the 2005 Guidelines, adrenaline was given just before the third shock. This subtle change in the timing of adrenaline administration is to separate the timing of drug delivery from attempted defibrillation. It is hoped that this will result in more efficient shock delivery and less interruption in chest compressions.

Amiodarone 300 mg is also given after the third shock. Atropine is no longer recommended for routine use in

asystole or pulseless electrical activity (PEA).

Clinical Scenario 28) You have anaesthetised a patient for a routine cystoscopy

and dilatation of urethral stricture. The patient is normally fit and well, is a smoker and previous similar operations have been uneventful. You have inserted a laryngeal mask airway and allowed the patient to spontaneously breathe on a mixture of oxygen/air/desflurane. Induction and transfer to theatre have been uneventful but10 minutes into the procedure you notice the oxygen saturations reading 84%. Attempted bag ventilation is impossible and you notice seesawing of the abdomen. You diagnose laryngospasm tell the surgeon to stop. what would be your next course of action.

a) Give 100% oxygen and increase your concentration of desflurane and apply CPAP

b) Give a dose of alfentanil 1mg c) Give 100% oxygen and give a bolus of propofol and apply

CPAP d) Give 100% oxygen and give a bolus of suxamethonium e) Give 100% oxygen and apply CPAP

Clinical Scenario 29) You have just induced your last patient on an

elective orthopaedic list. He is a 60 year old man for a bunionectomy of left forefoot. You have used 200mg Propofol, 100 micrograms of fentanyl and inserted an LMA and he is breathing spontaneously on a mixture of oxygen/air/sevoflurane. His next blood pressure is 76/30 with a heart rate of 56 bpm.

hat would you do next? a) Give 600 micrograms atropine b) Give 200 micrograms glycopyrrolate c) Give metaraminol 0.5 mg d) Give ephedrine 6 mg e) Give a fluid challenge of 250 mls Hartmanns

Clinical Scenario 30) A 42 year old female is undergoing a laparoscopic

incisional hernia repair for a large abdominal hernia developed after a laparotomy for small bowel obstruction 12 months earlier. During the surgery the patient develops high ventilation pressures, desaturation, distended neck veins , hypotension, reduced air entry and movement on the left side of the chest.

What should be the next step for this patient? a) Endotracheal suction b) Increasing PEEP c) Increasing minute ventilation d) Give muscle relaxant e) Needle decompression and insertion of an intercostal

chest drain