Louise's SAQs Flashcards
How does a strain gauge produce electrical signal?
Deflection of the diaphragm introduces strain in the resistance wire.
Change in tension causes a change in resistance which can be measured and recorded.
Increase stretch of resistor = increased resistance
What is a Wheatstone bridge?
pressure transducer with 4 strain gauges which form the 4 resistances in the bridge.
- Increases sensitivity of the pressure gauge
- Allows the determination of an unknown resistance in terms of a known resistance
What does damping prevent?
Damping prevents a system from overshooting after responding to a change, particularly at frequencies close to the natural frequency of the system
What does underdamping cause? what is it caused by?
Co-efficient < 0.64, produces exaggerated peaks and troughs in the waveform.
Due to small tubing, or catheter occluding the vessel.
Pressure units
1 atm = ?mmHg = ?kPa = ?cmH2O = ?Bar
760 mmHg
101.3 kPa
1033cmH2O
1.013 BAR
What is vomiting?
Involuntary, forceful, rapid expulsion of gastric contents through the mouth.
What receptors are found at CTZ?
Ach, 5HT3, D2, H1, opioid
What class of drug is metoclopramide, and what are the mechanisms of action?
Benzamide
Anti-D2
some 5HT4 agonist activity
Cholinergic effect
What is an example of NK-1 antagonist?
Aprepitant
What’s the difference in MOA for promethazine vs. prochloperazine
Prochloperazine (stematil) - mainly anti-D2, some mAchR antagonism
Promethazine - mainly an anti-H1, especially useful for vestibular type N/V
Briefly describe the venous drainage of spinal column
Internal vertebral venous plexus, divided into anterior and posterior vessels within the epidural space
- Drain into vertebral veins
External vertebral venous plexus, anterior and posterior.
- Drain into azygos, lumbar and deep cervical veins
What’s the significance of Batson’s plexus?
Valveless veins from internal vertebral venous plexus. Responsible for cancer metastasis
Which drugs are broken down by plasma pseudocholinesterase?
sux, miva, ester LA
Which drugs are broken down by non-specific plasma esterases
remi
atracurium / cisatracurium
neostigmine
Why would pneumoperitoneum cause increased PVR?
reduced blood flow -> reduced PAP
Increased PCO2 -> increased V/Q mismatch via pulmonary vasoconstriction
How is renal blood flow affected by pneumoperitoneum?
Significantly reduced when pressure >20mmHg.
Due to high renal vascular resistance
Only 5% of GFR at > 20mmHG
Describe the MoA of unfractionated heparin
Heparin binds to ATIII, increases the activity by 1000x by a conformational change in the ATIII, exposing its active site for more rapid interaction with the activated clotting factors.
What are the factors the heparin inhibit?
IIa, IXa, Xa, XIa, XIIa
Mainly internal cascade
Aside from clotting factors, what other effects does heparin have?
inhibit platelet function
Increases the permeability of vessel angiogenesis
Accelerates the clearing of post-prandial lipoprotein lipase from tissues
Define 1 unit of heparin
Volume of heparin containing solution that prevents 1ml of citrated sheep blood from clotting for 1 hours after administration of 0.2ml of 1:100 calcium chloride
What’s HITTS?
heparin inducted thrombocytopenia and thrombosis syndrome
Features of type I HIT?
mild transient thrombocytopenia, PLT > 100
Totally reversed by heparin cessation
occurs in 10% of patients
Not associated with increased risk of thrombosis
Non-immune mediated, caused by drug induced platelet aggregation
Features of type II HIT?
severe thrombocytopenia PLT approaching 0
occurs in 1% of patients
Associated with thrombosis in 30% of cases
Requires anticoagulation
IgG mediated, antibodies form within 5-10 days (can be more rapid with recurrent heparin exposure)
Can continue to worsen after heparin cessation
Heparin side effects aside from HITTS and bleeding?
osteoporosis allergy reduced TPR -> reduced BP alopecia local skin reaction / fat necrosis at injection site
