SAQs Flashcards
What are the pharmaceutical advantages / disadvantages of N2O
Pros
- Liquid form, efficient storage
- Sweet smell, non-irritant, good for gas induction
- Insert, no reaction with rubber, plastic, sodalite
Cons
- Impurities from manufacturing
- Entonox lamination, when stored below pseudo critical temperature of -6 degree
- Supports combustion being an oxidant.
What is the muscle:blood PC and fat: blood PC of N2O?
- 2
2. 3
What are the CNS disadvantages of N2O
Pro-emetic
Inadequate to be used alone for anaesthesia
Increased CBF
minimal effect on EEG. BIS/entropy not helpful
Euphoria with abuse potential
How does N2O affect the DNA?
oxidation of cobalt atom in vitamin B12 which a cofactor for methionine synthase -> impairs DNA synthesis
Causes megaloblastic anaemia, subacute cord degeneration, teratogenesis
What is pain
Pain is an unpleasant sensory or emotional experience associated with, or resembling that associated with, actual or potential tissue damage.
What is type A and type B antigen of the ABO system?
A - N-acetylgalactosamine
B - galactose
What is after load?
the tension in the ventricular wall during systole that overcomes impediments to ventricular ejection.
Intrinsic - La Place’s Law
Extrinsic - Poiseulle’s law
What is the unit of a wood’s unit.
What are the other units of resistance?
mmHg x min / L
Or dyn x s / cm^5
What are the factors that affect extrinsic after load of the left ventricle?
Poiseulle’s Law
radius, most important, determined by
- External compression (pneumoperitoneum)
- Metabolic factors: exercise, increased CO2, adenosine, lactic acid, localised vasodilation.
- Autonomic: a1, b2 affect vessel radius
Length rarely matters.
Blood viscosity has some effect.
What are the factors affecting RV after load?
Pulmonary arterial pressure - greater PAP, greater vessel radius.
Volume - vascular resistance lowest at FRC
Alveolar pressure - high IPPV pressure -> increase west zone 1
Metabolic /autonomic factors
What level is the laryngeal inlet for neonates?
higher, at C3/4
What is the laryngoscope for neonates
Miller’s blade
Graph that describes the range of values of O2 and CO2, for V/Q matching, what are the key characteristics?
PACO2 vs. PAO2, in mmHg
Key points Deadspace (150,0) Apex (132, 28), high V/Q ratio Ideal (100,40) Base (89,42) Mixed venous blood, shunt (40,46)
Why does hypoxia, rather than hypercapnia, occur during V/Q mismatch?
Apex - high V/Q ratio, O2 tension >100mmHg, but finite binding site and limited solubility in blood. Apex thus has a limited role in oxygenation, and cannot compensate for regions with low V/Q ratio
Carbon dioxide is soluble and rate of removal is linear to tension, hence only a mild gradient of change from base to apex.
When body compensates by hyperventilation, CO2 is effectively removed, but only minimal improvement on oxygenation
What affects ventilation and perfusion in an upright lung?
Ventilation is affected by compliance.
Compliance is related to lung volume, affected by gravity
- Base, low volume due to compression, high compliance
- Apex, high volume, low compliance
Perfusion is affected by gravity effect on West zones and hypoxic pulmonary vasoconstriction, which aims to improve V/Q matching
What determines the onset and offset time for different muscles with NMB?
Onset affected by
1) muscle blood flow, faster onset with faster flow
2) muscle size, smaller muscle blocked before large
3) muscle type, slow twitch fibres with lower density of nAChR, so blocked faster due to quicker reach of receptor occupancy. Larynx/diaphragm have greater receptor density.
Onset Larynx > diaphragm > AP
Offset
1) muscle blood flow (diaphragm > larynx > AP)
2) muscle type: fast twitch fibres recover more quickly as they have more nAChR
Offset diaphragm > larynx > AP
What is slow vs. fast twitch fibres?
Slow fibres - adductor pollicis, lower density of nAChR, blocked faster, and slower to recover
Fast twitch fibres, diaphragm, higher density of nAChR, blocked slower, recovers faster
What are the physiological outcome of the anti-inflammatory effects of NSAIDs
Mostly mediated by anti-PGE2
- reduce vasodilation, permeability, white cell chemotaxis, oedema
Which PGs affect platelets?
TXA2, constitutive, vasoconstriction and encourage aggregation
PGI2, inducible, vasodilation and reduce aggregation.
COX2 inhibitor selectively affect PGI2. Unopposed TXA2 causes increased risk of thombosis
How is Lambert’s law applied to pulse oximeter?
Lambert’s law - absorbance is proportional to distance travelled in the medium.
Arterial flow - slight change in distance travelled.
Able to then isolate the pulsatile flow.
How is R ratio calculated?
Ratio = (pulsatile 660 / non-pulsatile 660) / (pulsatile 940 / non-pulsatile 940)
What is SpO2 and SaO2?
SaO2, or the arterial oxygen saturation, is the percentage of hemoglobin molecules in the arterial blood saturated with oxygen.
SpO2, or the peripheral oxygen saturation, is the percentage of hemoglobin molecules in the peripheral blood saturated with oxygen
What is the difference between tachyphylaxis and tolerance?
- Time frame (mins/hrs vs. days to weeks)
- Tachyphylaxis cannot be overcome with increased dose, whereas tolerance can.
What are some mechanisms of tolerance?
PK
- increased metabolism (alcohol)
- Increased elimination
PD
- reduced receptor numbers from repeated exposure
- reduced receptor affinity
- Reduced intracellular signal transduction
- Upregulation of antagonistic mechanisms
- Altered ion channel conductivity
What is an example of sulphonyurea?
gliclazide
What class does acarbose belong to?
Alpha-glucosidase inhibitor
What class does linagliptin and sitagliptin beyond to and what is the mechanism of action?
DPP-4 inhibitor (dipeptidyl peptidase-4 inhibitor)
- competitive antagonist at DPP-4 and prevent GLP-1 / GIP inactivation -> increase insulin secretion and reduce glycagon secretion
Can cause nausea, photosensitivity
What is the MoA of exenatide?
mimics GLP-1
- increase insulin, reduce glucagon
- reduce gastric emptying
- reduce satiety
Side effect hypoglycaemia, N/V
What class does rosiglitazone belong to and what is the MoA?
Thiazolidenedione
Reduce insulin resistance
Can cause weight gain, oedema
Describe an open disposal system
system open to atmosphere
What are the time dependent behaviour?
- Pendulluft - movement of air from high to low pressure, equilibration between slow and fast alveoli
- Surfactant - hysteresis of lung
- Recruitment
- Stress relaxation
Describe the CVS effect of sevoflurane
dose dependent, albeit minimal negative ionotropy
No direct chronotropy
Blunts baroreceptor response -> no change to HR
reduce SVR
BP reduction due to SVR and baroreceptor reflex blunting
List the responses to 30% blood lost
Baroreceptor response
Shift of interstitial fluid to plasma by A1 VC of pre-capillary vessels -> reduce hydrostatic pressure -> net reabsorption
Blood reservoir mobilisation via VC on A1
Restlessness -> SKM pump -> increase venous return
Renal / endocrine
What would be the capnography trace for oesophageal intubation
small, vanishing sinusoidal waveform
What ETCO2 number will indicate good CPR?
> 20 mmHg
What is the cause of terminal upswing in capnography?
Seen in pregnancy, obesity, ARDS, due to continued emptying of lung units with high pCO2
Define “wash-in” of volatile
rate at which FA/Fi approaches 100%.
Correlates with equilibration of inspired and alveolar partial pressures
What is the effect of ageing on lung compliance
Senile emphysema - increase lung compliance but reduce elastic recoil.
Decrease chest wall compliance due to
- Calcification of costal cartilage, joint degeneration, bone related changes (kyphosis)
- Reduce outward recoil, reduce chest wall compliance, increase dynamic work of breathing.
What is the ranking of halogenated volatile agents as green house gases?
Des > iso > sevo
What is the impact of running desflurane (in equivalence of driving a car)?
FI 7% for 6 hours = driving for 1000km.
What is the impact of N2O exposure in theatre?
Oxidation of cobalt ion in B12, inactivation of methionine synthatase
Causes megaloblastic anaemia, neuron degeneration, teratogenic, miscarriage in health care workers.
What are the toxicities of local anaesthethetic ?
LAST - systemic block of VDNAC
Cocaine - dopamine euphoria, profound VC ischaemic necrosis, sympathomimetic
Prilocaine - metHb
Hypersensitivity - PABA in esters, preservatives in lignocaine
What are the glutamate dependent ligand gated, voltage dependent channels/
AMPA
Kainate
NMDA
