Primary Revision Flashcards
Context sensitive half time
Time taken for the plasma concentration of a drug to fall to 50% after stopping that infusion
3 causes of calcified CXR lesions
Asbestosis Mitral valve disease Chicken Pox
Visual symptoms of papilledema
Visual obfuscations Enlargement of blind spot Blurring of vision
Mapleson A minimum flow (SV)
0.8-1x MV
Mapleson B minimum flow (SV)
1.5-2x MV
Mapleson C minimum flow (SV)
1.5-2x MV
Mapleson D minimum flow (SV)
2-3x MV
Mapleson E minimum flow (SV)
2-3x MV
Mapleson A minimum flow (MV)
2x MV
Lack system
co-axial Mapleson A
Bain system
co-axial Mapleson D
Bain system FGF is carried through…
The inner tube
Closing capacity = FRC when?
Age 44 supine Age 66 upright
Identify the structures of the descending tracts
- Medial longitudinal fasciculus
- Lissaur’s tract
- Lateral corticospinal Tract
- Rubrospinal tract
- Pontine reticulospinal tract
- Medullary reticulospional
- Lateral vestibulospinal
- Tectospinal
- Ventral corticospinal
Identify the structures of the ascending tracts
- Fasciculus gracilis
- Fasciculus cuneatus
- Dorsal spinocerebellar tract
- Ventral spinocerebellar tract
- Spinothalamic tract
Anion Gap
[Na] + [K] - [HCO3] - [Cl]
Range 8 - 16 mEq/L
Causes of a high anion gap metabolic acidosis
- High unmeasured anions
- Lactic acidosis
- DKA
- Alcohol, Methanol, Ethelyne Glycol
Clearance
A measure of the body’s ability to remove a drug. It is the volume of plasma, from which a drug is completely removed in a given time (mL/min). This is commonly indexed against body mass (mL/kg/min)
Clearance (formulas)
Cl = Vd / T and since T = 1 / K, Cl = K.Vd
Pharmacokinetics
- Absorbtion
- Distribution
- Metabolsim
- Excretion
Bioavailibility
The fraction of a drug availible to the systemic circulation compared with IV administration. Calculated by area under the curve.
1st Pass metabolism
Metabolism by the gut wall or liver prior to reaching systemic circulation. PR, SL, TD, Inhalational, IV etc. all bipass 1st pass metabolism
First Order Kinetics
Rate of elimination of a drug is directly propertional to drug concentration
Time to reach steady state (first order kinestics)
5 half lives
Elimination profile in a single compartment.
C = C0.e-kt
where:
- C = concentration at time = t
- C0 = concentration at time = 0
- k = rate constant
- t = time
- -kt is a dimentionless term
Describe C0
The concentration of a drug at time = 0.
C0 = dose / Vd
Express C=C0e-kt logarhythmically
ln C = -kt ln C0
or
log C = (-kt/2.303) . log C0
What is the time constant (T)
The time taken for a drug to be completely eliminated, had the original rate of decline continued. The inverse of the rate constant.
What is the value of C at t = T
C = C0 - (e.C0)
i.e. C0 has fallen by a factor of e
Half life
The time taken for conentration to reach half its starting value
Relationship between half life and the time constant (T)
T½ = T.ln2
Which is bigger? the time constant or half life?
time constant > half life
ALWAYS
Since T½ = T.ln2 and ln2 < 1
Why do you wake up quickly following a propofol infusion at steady state?
Conductance between the peripheral and central compartments is low. The terminal elemination take a long time, but plasma concentrations fall rapidly and you wake
Michaelis constant
The concentration of a substrate at which an enzyme system is working at half its maximal capacity
What factors affect hepatic extraction of a drug
- Protein binding
- Blood flow
- Michaelis constant
Volume of Distribution
The apparent volume into which a drug disperses in order to produce the observed plasma concentrations.
Vd = Dose / C0
Seddon-Sunderland Classification
Classifcation of peripheral nerve injury
- Neuropraxia
- Axonotmesis
- Neurotmesis with preservation of perineurium
- Neurotmesis with preservation of epineurium
- Neurotmesis with complete transection of nerve trunk
Isomer
Molecules that have the same molecular formula but whose atoms are arranged differently
Structural Isomer
Molecules with the same molecular formula but different chemical structure
Colloid
A substance that has insoluble microscopic particles suspended within another medium, most commonly a liquid
Blood Gas Solubility Coefficient
The ratio of the amount of a substance in one phase to the amount in another phase, at a stated temperature, when both phases are in equilibrium and of equal volume and pressure
What is the embryological origin of the adrenal medulla?
Chromaffin cells derived from the ectodermal cells of the neural crest
What is the embryological origin of the adrenal cortex?
Mesoderm
What does the adrenal cortex secrete?
- Steroid hormones:
- Glucocorticoids
- Mineralocorticoids
- Androgens
What are glucocorticoids?
Steroid hormones that affect the metabolism of carbohydrates, fats and proteins and are important in mediating the response to fasting and stress
What are the primary effects of glucocorticoids?
- Liver
- Protein catabolism
- Gluconeogenesis
- Cardiovascular
- Maintenance of response to catecholamines
- Kidney
- Weak mineralocorticoid activity
- Immune
- Immunosuppresion
- Slowed healing
What are the primary effects of mineralocorticoids?
- Liver - none
- Cardiovascular - none
- Kidney
- Resorbs Na+ in the Distal Convoluted Tubule at the expense of loss of K+ and H+ lost into the urine
- Expantion of the intravasular compartment
- Immune - none
What factors control the release of Aldosterone?
Aldosterone is released in response to:
- Decreased Na
- Decreased plasma volume
- Increased K
- Activation of the Renin-Angiotensin System
The final common pathway is the binding of angiotensin-II to receptors in the zona glomerulosa. This acts via G-protein to activate phospholipase-C. It facilitates the conversion of corticosterone to aldosterone.
What is Hyperaldosteronism?
Excess circulating aldosterone:
- Primary
- Conn’s Syndrome - adrenal adenoma (60%)
- Bilateral adrenal hyperplasia (30%)
- Carcinoma
- Secondary
- Increased activation of the R-A-A system e.g. CCF or liver cirrosis
What are the core features of hyperaldosteronism?
- Hypertension
- Hypokalaemia
- Metabolic alkalosis
What is SVR?
80 x (MAP - CVP)/CO = 1000 - 1500 dyne/s/cm5
What factors cause a right shift of the oxyhaemaglobin dissociation curve?
Think about which factors require or result in increased oxygen delivery in tissues.
- Increased temperature
- Reduced pH
- Raised PaCO2
- Raised 2,3 DPG
- Pregnancy
- Anaemia
- Post-acclimatisation at altitude
Which components in PRC help prevent depletion of 2,3-DPG?
- Phosphate
- Adenosine
- Glucose
NB, mannitol helps prevent oxidative stress to RBC, but has no impact upon 2,3-DPG
What are the “classical” anti-inflammatory cytokines?
- IL4
- IL-10
- IL-13
- IFN-alpha
- Transforming growth factor-beta
Define Osmolarity
Osmolarity refers to the number of osmoles per litre of specific solvent
Define osmolality
Osmolality refers to the number of osmoles per kg of specific solvent
Maximum concentrating capacity of the kidneys
1200-1400 mOsm.L-1
Minimum mandatory renal solute excretion
800 mOsm/day
