Miscellanous MCQ - BMJ On Examination Flashcards
What plasma concentration of Magnesium can you suspect toxicity?
What are the symptoms of toxicity?
Mild, Moderate, Severe
Plasma Concentration
(mmol/L) Effect
0.7-1.2: Normal
4-8: Therapeutic, diminished deep tendon reflexes, nausea, flushing, headache and lethargy
5-10: ECG changes (prolonged PR, QT, widened QRS)
10: Muscle weakness, loss of deep tendon reflexes, hypotension
15: SA/AV nodal block, respiratory paralysis
20: Cardiac arrest
What is the compliance of a normal lung?
200 ml/ cmH2O
What can be used to measure respiratory volume and intrapleural pressure in a ventilated patient?
When is static compliance measured in the respiratory cycle?
Intrapleural pressure can be measured indirectly using an oesophageal manometer.
Respiratory volumes can be measured at the mouth using a pneumotachograph.
Static compliance is measured at a period when there is no gas flow, for example during an inspiratory or expiratory pause.
What is static lung compliance?
Static lung compliance is the change in volume for any given change in pressure.
Equation for compliance?
How do you calculate total static lung compliance?
Compliance = ΔV/ΔP
The normal compliance (Cl) of a normal lung is 200 ml/cmH2O.
Total static compliance (Ct) includes the compliance of the chest wall (Ccw) that is also 200 ml/cmH2O.
Summation of elastance = 1/compliance.
Ct = Cl + Ccw
1/Ct = 1/200 + 1/200 =
Trachea:
What vertebral level does it start, and bifurcate?
Average length in an adult?
Starts at C6, bifurcates T4
15 cm long
What reduced Hb affinity for O2? Shifts curve which direction?
Increased 23 DPG, Acidosis (increased CO2), Pyrexia
Shifts to the right
Hb affinity for O2 increases when?
Shifts curve which direction?
Decreased 23 DPG, Alkalaemia, Hypothermia
Shifts left
How do patients anaesthetised lose heat?
40% Radiation is accounts for the initial heat loss
30% - Convection into the operating room air
15% - Evaporative losses from the wound
respiratory losses and general conduction responsible for the remaining heat loss.
What is the triple point of water?
The triple point describes the point where three phases (usually solid, liquid, and gas phases) of a substance exists in equilibrium with one another.
For water, the value is valid at a pressure of 611.73Pa (4.58mmHg) and temperature of 273.16 K.
How much of each does Hartmans contain? sodium chloride potassium calcium lactate.
131 mmol/L of sodium 111 mmol/L of chloride 5 mmol/L of potassium 2 mmol/L of calcium, and 29 mmol/L of lactate.
Normal saline or 0.9% sodium chloride contains 154 mmol/L of both sodium and chloride in water, and it does not contain potassium.
MAO enzyme:
- where is it found?
- what do they do?
- what types are there?
Monoamine oxidase (MAO) enzymes are present in the mitochondria of most tissues (not cytoplasm) including both central and peripherally located catecholamine secreting nerve endings.
They catalyse the inactivation of amines (not formation) by oxidative deamination to aldehyde derivatives.
Two distinct types have been identified (not three):
type A - mainly inactivates (not synthesizes) norepinephrine (or noradrenaline) and 5-hydroxytryptamine,
type B - mainly inactivates tryptamine and phenylethylamine.
Dopamine and tyramine are inactivated by both enzymes. Both types A and B are found in the liver and brain, and type B predominates in the basal ganglia.
What are some features of acute aspirin poisoning?
The features of acute aspirin poisoning include:
Hyperventilation Nausea and vomiting Hypoglycaemia (particularly in children), hyperglycaemia has also been reported Acute renal failure (rare) Rhabdomyolysis GI perforation Hypotension Tinnitus and Hearing loss.
What equation measures physiological dead space?
What is the approximate physiological dead space?
What % of TV?
Bohr Equation- is the sum of the anatomical dead space and the alveolar dead space.
It is approximately 2-3 ml/kg which equates to about 30% of the tidal volume.
What equation is used to measure anatomical dead space?
Fowlers method
What are the four phases of the Valsalva manouvre?
Phase I - An initial increase in venous return from intrathoracic vessels causes a transient decrease in HR and increase in BP.
Phase II - As the high intrathoracic pressure in maintained there is a decrease in the venous return which is sensed by baroreceptors. This causes an increase in HR and decrease in BP. The BP tends to return to normal by the end of phase II.
Phase III - Sudden release of forced expiration and/or glottal opening results in a return of the intrathoracic pressure to normal. This causes pooling of blood into intrathoracic vessels resulting in a decrease in BP, whilst the HR remains elevated.
Phase IV - During phase IV the intrathoracic pressure remains normal and the continued increase return of systemic venous blood produces a reflex bradycardia associated with an increase in BP to normal.
How can you calculate pulmonary vascular resistance?
Pulmonary vascular resistance (PVR) is a derived value based on the following:
The analogy is Ohm’s law:
Potential difference (V) = Flow of current (I) × Resistance (Ω)
Therefore R = V/I
PVR = (MPAP − PCWP)/CO × 80
What drugs can cause pulmonary fibrosis?
Paraquat Antimitotic drugs Amiodarone Asbestos Aspiration of gastric contents, and Fumes. Methotrexate
What is a thermocouple?
A thermocouple is a device that is used to measure temperature “electronically”. It consists of a pair of dissimilar metal (bimetallic) wires or strips bonded together, typically copper and constantan.
What principle is the thermocouple function based upon?
The magnitude of the thermojunction electromotive force (emf) is proportional to applied temperature (the Seebeck effect).
Most to least potent opioid?
Fentanyl, Alfentanil, Remifentanil, Pethidine, Morphine
Fastest to slowest onset/ offset opioid?
Alfentanil, Remifentanil, Fentanyl, Morphine, Pethidine
Where is 2,3 DPG made?
2,3-diphosphoglycerate, or 2,3-DPG, is created in erythrocytes during glycolysis by the Rapoport-Luebering shunt.
What causes increase in 2,3 DPG?
The production of 2,3-DPG is likely an important adaptive mechanism, because the production increases for several conditions in the presence of diminished peripheral tissue O2 availability, such as:
- hypoxaemia
- chronic lung disease
- anaemia
- congestive heart failure.
