25/6 Weekend SAQ LOs Flashcards
Describe inter ventricular dependence in IPPV
IPPV -> increased intrathoracic pressure on inspiration
Increased pulmonary pressure and right heart after load. Bulging of septum to left compressing LV -> reduce LV preload.
Write out law of LaPlace
Wall tension = transmural pressure x radius / (2x wall thickness)
How does IPPV improve the cardiac function of someone in heart failure?
Heart failure -> venous congestion -> person operates at the top end of the Frank-Stalin curve.
- IPPV preload reduction puts the person back to optimal position on FS curve
- Reduction in after load is good.
Why would ageing cause LV concentric hypertrophy?
Stiff aorta from calcification -> LV after load
What is the consequence of connective tissue replacing LV myocytes?
decrease compliance
concentric hypertrophy
reliance on atrial kick
Tachycardia poorly tolerated
What is the effect of baroreceptor reflex attenuation in aging?
orthostatic hypotension, syncope
What is the relative increase in risk of difficult intubation for pregnant women?
7-10 folds
What is the effect of relaxin in rib cage in pregnancy?
increase AP / transverse diameter of thoracic cage to partially compensate for cephalad diaphragm displacement
Describe the changes in lung volumes in pregnancy
Reduced FRC and RV.
TLC minimal reduction
Vital capacity unchanged.
What is the effect of respiratory alkalosis in pregnancy
Increase foetal CO2 gradient of transfer.
What is the Monroe-Kellie doctrine
Cranium is a closed space with one major outlet
Any increase in one intracranial substance must come at the expense of another or else pressure rises drastically .
Graph of the ICP and ischaemia, what are the axis and units
Y-axis intracranial pressure in mmHg (20-50 focal, >50 global)
X-axis volume of intracranial substance in mL
Describe the hydrostatic change of head down position
~10mmHg for 13cm head down from heart
- Increase arterial pressure slightly, small increase in arterial volume
- Increase venous pressure from to +10, large increase in venous volume
- Compensate by CSF displacement
Describe urea recycling
Urea is freely filtered, 50% reabsorbed, same 50% secreted in LOH and same 50% reabsorbed at medullary collecting duct.
What are the issues of using urea as a marker of renal function?
Not an ideal marker as it is both reabsorbed and secreted
Variation with degree of protein metabolism
[Urea] is inversely proportional to hydration
Describe the graph of GFR vs. Creatinine, units and implications
Y axis - creatinine in micromol/L, range 45-100
X axis - GFR ml/min, range 0-120
Sharp increase in creatinine when GFR < 40
Greater than 50% decrease in GFR before significant increase in creatinine or urea
What is the formula for estimating GFR and what is its problem?
Cockcroft-Gault equation, incorporating lean body weight and serum creatinine
Estimation only, multiple variables
Renal failure -> increased secreted fraction -> overestimation of GFR
In hypovolaemic shock, what other factors can exacerbate lactic acidosis (aside from anaerobic glycolysis)
Increased cardiac work -> increased lactic acid production
decreased liver lactic acid clearance
Increased respiratory work
What is the effect of hypovolaemic shock on the respiratory system
Metabolic acidosis
- Right shift Hb-O2 curve
- Pulmonary vasoconstriction
Increased dead space
Describe the MOA and effect of local anaesthetic and cardiac toxicity
Inhibition of cardiac VDNaC with very high affinity
First phase increased HR and MAP
Second phase myocardial depression
Third phase peripheral vasodilation -> arrhythmia and arrest
What is the effect of tissue-blood partition coefficient on volatile wash in?
N2O < des < sevo
Lower TBPC -> reduce tissue uptake -> increase rate of rise
curve of flow-metabolism uncoupling for sevo.
What are the axis?
Cerebral blood flow vs. CMRO2
What is anaesthetic preconditioning of coronary circulation with sevoflurane
Mimics ischaemic preconditioning.
Activation of vascular K+ ATP channel
Onset in minutes, offset 3-4 days.
Describe the proportion of CO2 buffering in blood
90% HCO3
Carbamino compound 5%
Dissolved 5%
Outline the HCO3 buffering effect
H+ binding to the imidazole groups of histidine residues
CO2 + H2O -> H+ + HCO3-
H+ bound to imidazole groups of Hb and plasma proteins
HCO3 exchanged fro Cl- at membrane via Hamburger effect.
Carbamino compound essentially the same by binding to amino groups.
How much does Haldane effect contribute to CO2 buffering?
70% by carbamino formation
30% by increased imidazole group buffering.
What is the baseline CMRO2?
3.5ml/min/100g
How is the concentration of effect site derived for TCI model?
derived from relationship between plasma concentration and EEG data
How does distribution of pharmacokinetic influence the time to recovery for muscle relaxants?
Bolus dose - recovery from distribution. Higher Vd = faster recovery
After infusion - recovery from metabolism and excretion. Lower VD = faster recovery
How does aminoglycoside influence duration of NMB?
slows the rate of recovery.
Reduce presynaptic ACh release
How is tramadol metabolised and excreted?
Phase 1
2D6 -> O-desmethyltramadol
3A4 -> N-desmethyltramadol
Phase 2
Glucuronidation of tramadol
90% Renal excretion (30% parent, 60% metabolite)
10% into bile
Describe the quantal dose response curve.
% population vs. log [drug dose] graph
Binary endpoint, sigmoid shaped curve
Flat beginning due to high safety margin of Ach as 70% of receptors blockade required for any effect (spare receptor theory)
Final plateau portion represents >95% receptor blockade and adding more NMB does not achieve greater effect.
What is ED95 of NMB.
What is the ED95 of rocuronium
ED95 - dose required to produce 95% depression of the first twitch response in 50% of population.
For Roc, this is 0.3mg/kg
Intubating dose = 2x ED95, the dose to produce 95% first twitch reduction in 95% of population.
What is a supra maximal stimulus and why is it needed?
SMS = initial threshold for stimulation x 2.5
Eliminates variation in muscle response caused by partial depolarisation of nerve.
What are the sites of NMJ monitoring?
Ulnar nerve - adductor pollicis adduction
Facial nerve
Tibial nerve for plantarflexsion of big toe
Common perineal nerve for foot dorsiflexion
For NMB, compare laryngeal muscle and adductor pollicis
Laryngeal muscle has
- Greater blood flow, greater Ach release, greater amount of Ach receptors.
Clinical effect
- Faster onset, less depth, shorter duration.
For NMB monitoring of ulnar nerve, if TOF is >90%, then there is more certainty that laryngeal muscle is also reversed.
what is Lambert-Eaton syndrome?
autoantibody against presynaptic VDCC -> reduced competition with Ach
What is the absorption frequency of CO2 and N2O
CO2 - 4.7 micrometer
N2O - 4.5 micrometer
What are the three axis for intubation?
Oral
Pharyngeal
Laryngeal
What are the changes in neonatal upper airway
Large occiput - neck flexion in supine
Narrow nasal passage, obligate nasal breather, auto PEEP
Large tongue - difficult BMV (Guedel useful)
U-shaped epiglottis, floppy - tip of epiglottis can obstruct intubation view, glottis obstruction with LMA
Higher and more anterior larynx (C3 at birth) - difficult to align intubation axis
Cone shaped outlet, narrowest point at cricoid - increased risk of subglottic stenosis
Short trachea - risk of dislodging of inadvertently advance ETT
Narrow trachea - higher airflow resistance.
What are the proposed mechanism of Ergometrine
Unclear but may work on dopamine, adenosine, or 5HT receptors.
What is the adverse effect of using Nitrous oxide as a tocolytic?
tachyphylaxis
Cerebral VD
Met-Hb (rare)
Amiodarone
- Bioavailability
- Protein binding
- Metabolic and excretion pathway
60-80%
96%
N-des-ethyl-amiodarone, active metabolite
Enterohepatic circulation in bile, minimal renal excretion
Describe the CVS effects of amiodarone
Class I-IV anti-arrhythmic, mainly class III - Increases refractory period, decreases automaticity, prolong QT
Adverse effects
- Mild bradycardia, mild direct negative ionotropy
- Vasodilation via A-blocking -> reduce SVR -> reduce MAP
- Torsades
list the toxic effects of amiodarone
NQR-BITCH
Neurotoxicity - peripheral neuropathy, ataxia
QT prolongation -> torsades
Respiratory effects - high mortality interstitial fibrosis in 5-15% patients on chronic therapy.
Blue-grey skin discolouration / photosensitivity
Inhibition of CYP enzymes
Thyroid - structure similar to thyroxine, 2% incidence, hyper or hypo
Corneal deposits - reversible
Hepatitis / LFT derangement
Describe the sensor -> control -> effector pathway for baroreceptor reflex
S - aortic and carotid bodies Afferent neurons - glossopharyngeal (carotid), vagus (aortic) Control - NTS -> RVLM Efferent - SNS efferent Effector - heart and vessels
Describe the sub-tracts of spinothalamic tract
Anterior - neospinothalamic, sensory discriminative, mainly A-delta input from Lamina 1
Lateral - paleospinothalamic, autonomic/emotional, mainly C fibres.
List some other tracts for pain other than spinothalamic tract
Spinoreticular, spinolimbic, spinoparabrachial
Describe the cardiovascular effects of sleep
REM - increase heart rate
NREM - decrease HR, decrease vascular tone, decrease BP
Describe the respiratory effects of sleep
REM - increase MV by increasing RR, reduce TV
- Reduced ++ pharyngeal muscle tone
- Reduced O2 and CO2 response for ventilation
NREM
- Also reduce pharyngeal tone and ventilatory drive
- Reduce MV, unchanged R, reduce RV
Describe the metabolic effects of sleep
REM
- Increase BMR, increase ACTH / cortisol
NREM
- Reduce BMR, reduce temp, reduce shivering threshold
- Reduce ACTH
- Increase growth hormone, prolactin, melatonin
What is the bimetallic strip?
Safety feature of plnuem vaporiser
Two pieces of metal with different coefficient of thermal expansion.
Increase concentration -> increase uptake -> reduce vaporiser temperature -> divert greater flow to vaporiser chamber
What is a plenum vaporiser and why do we use it?
Plenum vaporiser relies on a pressure gradient provided by fresh gas flow to allow vaporisation of liquid anaesthetic agent.
High resistance and must be outside of the circle.
Delivers controlled vaporisation of liquid anaesthetic agents into a vapour for controlled administration
What are the different types of plenum vaporiser?
Variable bypass - relies on vaporising and bypass stream
Measured flow - separate flow of vapour that’s independently added to patient’s fresh gas flow to produce required concentration of VA (desflurane)
