Monitors Flashcards
Standard monitors for general anesthesia: There are 4
Under general anesthesia the oxygenation, ventilation, circulation and temperature should be monitored. Oxygenation monitoring includes the inspired gas FiO2, low oxygen concentration alarm, and quantitative blood oxygenation (pulse ox). Ventilation monitors include end tidal CO2 and expired tidal volume (answer A), as inspired measurements do not necessarily reflect the volume the patient received depending on the breathing system. Circulation should be measured by continual electrocardiogram and intermittent blood pressure, computerized ST segment analysis is not considered an ASA standar
Map at aorta vs radial artery. Systolic at aorta vs radial artery
Exaggeration of the pressure waveform increases as the pressure wave travels distally through the arterial tree leading to an increasing systolic pressure. The MAP decreases as the pressure wave travels distally (very, very minor effect), and must be smaller than the aortic MAP for forward flow to occur.
If you vasodilate-how does that change the systolic pressure between Airta and radial?
Increases the difference in systolic between them all while lowering the MAP
What are the The natural frequency and dampening coefficient?
A way to think of natural frequency (which is completely wrong!!!!!!), but might help you get your head around it is this: think of natural frequency as how many points in time that the blood pressure waveform can be measured – the more often it is measured, the more accurate the resulting waveform will look like the theoretical real waveform. Increasing the natural frequency would then increase its fidelity. Decreasing the natural frequency would lead to a less accurate waveform in which the waveform becomes flattened.
The dampening coefficient is a property of the fluid within the tubing which extinguishes motion (and therefore dampens the system), and is different than the natural frequency To further explain this complex subject, the fluid in the tubing dampens the signal from the artery. The higher the natural frequency, the wider the range of dampening coefficients that will still provide an accurate waveform.
So, at a higher and lower frequency with higher and lower dampening coefficients:
The higher the natural frequency, the wider the range of dampening coefficients that will still provide an accurate waveform. As such, think of increasing natural frequency in line with fidelity. The dampening is due to the dampening coefficient. Lets say that the monitoring system has a high dampening coefficient. At a low natural frequency, it will be overdamped. At a high enough natural frequency its dynamic response will be reliable. At the same time lets imagine a very low dampening coefficient. At a low natural frequency it will be underdamped, but at a higher natural frequency it will not. In general it takes a smaller increase in the monitors natural frequency to overcome an underdamped than an overdampened system
What can overdamp an arterial BP waveform?
Increasing the length of the tubing, having multiple connections, loose connections, clots, kinks, and air bubbles decrease the natural frequency of the system (see question 4) and lead to overdamping. Increasing the compliance of the tubing (not decreasing) also leads to overdamping, therefore stiff tubing is recommended. Zeroing the system is unrelated to damping.
So, in a nutshell-what decreases frequency, and what does that do to damping?
Keep this in mind: when natural frequency decreases, damping increases, and vice versa. Therefore, factors that correlate with increased damping are: length, viscosity (of conducting fluid), and density (of conducting fluid). Things that correlate inversely with increased damping (or increases in these things lead to less damping) include increased radius, and tube stiffness.
When placing an a line, what 2 things can help avoid complications?
The length of catheterization and size of the catheter have the most effect. smaller catheter (width)=larger gauge. Other factors that increase the likelihood of ischaemia following arterial line placement are propylene composition, high dose vasopressors, artery size, puncture attempts (possibly), and female gender. Longer catheters may be (counter-intuitively) somewhat protective.
What is a cuff that is too big for the atm? What will that do to the reading?
An oversized blood pressure cuff has multiple definitions including as a WIDTH greater than 40-50% the circumference of the arm, or greater than 20% the diameter of the arm. Also the BLADDER LENGTH should encircle 60% of the arm.* With oversized cuffs, less pressure is needed to occlude the systolic pulse and therefore, blood pressure will be underestimated. A smaller cuff will do the opposite (blood pressure is overestimated). There is no evidence that inappropriately sized cuffs lead to nerve damage or ischaemia.
For every 1 cm that the cuff is above the heart, how do you calculate the real BP?
For every 1 cm the blood pressure cuff is above the heart, 0.7 mm Hg should be added. Hence 80 mm Hg + (0.7 mm Hg/cm X 10 cm) = 87 mm Hg.
Lead 5 is most sensitive for: Lead 2 is most sensitive for:
The V5 (& V4) lead is most sensitive lead to indicate left ventricular myocardial ischaemia, and examines left coronary distribution. Lead II allows the highest likelihood to examine the p-wave (rhythm analysis) and may also pick up right coronary distribution ischaemia.
Which of the following situations is myocardial ischaemia detection most difficult with two ECG lead (II & V5) analysis
Left bundle branch block makes detection of myocardial ischaemia on two lead analysis near impossible.
Burns during MRI
Both pulse oximetry cables and ECG cables have acted as antennas, gathering enough energy to cause burns. The BP cuff thing too, but not as much as the EKG and the pulse ox which touch the patient
Does CVP correlate to LVEDV?
No
