Physics Flashcards

Question

Frequency and how it relates to penetration and resolution

Answer 1

Higher frequency (aka wavelength) means better resolution, but worse penetration. Lower frequency gives better penetration but sacrifices resolution.

Answer 2

VFW. Velocity = Frequency * Wavelength

Answer 3

Induction of electrical current within the probe.

Answer 4

There is a potential for generating heat in the monitoring wires as a result of electromagnetic induction, circuit resonance, or an "antenna" effect. Range of Tesla units: .05-3.0 Tesla units Basically, the magnetic field can orient the protons in a hydrogen ion, which is the basic principle of MRI.

Answer 5

To avoid thermal injuries, it is important to make sure that the monitoring wires are kept straight (avoid loops), that they do not touch the patient in more than one location, and that the wires are not worn out or frayed.

Answer 6

Ferrous. The MRI suite is typically divided into four zones. Zone I is the public area with free access. Zone II is the intermediate area between the public and the MRI suite. Zone III is where the introduction of ferromagnetic materials may pose a risk. All movement into Zone III is strictly controlled. Zone IV is the scanner room itself. MRI personnel must screen all individuals entering into Zone III and beyond for any objects or materials that can create a hazard.

Answer 7

nickel, iron, cobalt, tungsten

Answer 8

Pressure wave reflection | yes, pulse pressure is wider farther away

Answer 9

Proximally, the resistance to flow is low due to greater vessel diameter and compliance, therefore degradation of pressure is limited. As blood travels distally in the vascular tree to the arterioles, the resistance to flow increases dramatically with greater decrement in pressure. Thus, pressure waves diminish at the level of the arterioles secondary to increased resistance but the upstream pressure waves are augmented by the retrograde reflection of the previous pressure wave resulting in SBP amplification. Despite amplification mechanisms, mean arterial pressure remains relatively unchanged. Mean arterial pressure in the aorta is only slightly higher than that in the periphery.

Answer 10

Resonance (C) refers to amplification of the arterial pressure signal due to changes in the transducer system itself. The signal is amplified with long, compliant transducer tubing because it generates higher harmonic frequencies that may approximate the resonant frequency of the system and increase the amplitude. An example of this is when you go over speed bumps with a car you may notice that the faster you go over the bumps the more the car will bounce Longer tubing=amplified signal.

Answer 11

myocardial oxygen supply/demand ratio Because the balloon inflates during diastole, it increases coronary perfusion pressure (increases supply) and because it deflates suddenly right at the time the ventricle is about to eject blood, it decreases afterload (decreased wall tension -> decreased oxygen demand).

Answer 12

Because of abrupt balloon deflation, the minimum diastolic pressure falls to lower levels that it would have on a non-assisted beat, this end-diastolic aortic pressure is the impedance the ventricle must overcome to eject blood (i.e. afterload). 3) Consequently, the ventricle can eject all of the stroke volume without developing high pressures, resulting in a lower systolic pressure in the beat following the IABP-assisted beat.

Answer 13

Because of abrupt balloon deflation, the minimum diastolic pressure falls to lower levels that it would have on a non-assisted beat, this end-diastolic aortic pressure is the impedance the ventricle must overcome to eject blood (i.e. afterload). 3) Consequently, the ventricle can eject all of the stroke volume without developing high pressures, resulting in a lower systolic pressure in the beat following the IABP-assisted beat. Look at photo

Answer 14

Among TEE, ECG, and PCWP, TEE is the most sensitive modality for detecting myocardial ischemia followed by ECG then PCWP.

Answer 15

Benzodiazepines should be avoided since an increase in the seizure threshold occurs.

Answer 16

In pH-stat management, CO2 is infused into the blood to maintain normocarbia and normal pH at the hypothermic temperature the patient is at during the operation. So if the patient is being cooled to 27 degrees Celsius, then the blood gas will be corrected for a body temperature of 27 degrees Celsius. As blood gets colder the partial pressures of CO2 and O2 decrease. So in pH-stat management, the CPB circuit infuses CO2 into the blood to maintain a normal pH at whatever the body temperature is at that point in the case

Answer 17

pH-stat management adds CO2 to blood which causes a decrease in pH causing a Bohr shift with the rightward shift of the oxyhemoglobin dissociation curve (increased P50).

Answer 18

Alpha-stat vs. pH-stat management has no bearing on myocardial preservation.

Answer 19

pH-stat management infuses extra CO2 into the blood, causing increased CBF and improved homogenous cerebral cooling during hypothermic cardiopulmonary bypass.

Answer 20

A decrease in barometric pressure caused by an increase in altitude will increase the delivered concentration (percentage) of a volatile anesthetic from a variable-bypass vaporizer but the delivered partial pressure (mm Hg) of the anesthetic remains essentially unchanged. aka percentage

Answer 21

Even after bringing the same vaporizer with the same dialed 1% to 5500 meters (barometric pressure of 0.5 atm or 380 mm Hg), the vaporizer is designed to compensate for the change in barometric pressure and continue to deliver isoflurane at nearly the same partial pressure of 7.6 mm Hg. It does this by increasing the vaporizer output such that the delivered concentration increases to approximately 2% (7.6 mm Hg / 380 mm Hg) despite still being dialed at 1%.

Answer 22

As barometric pressure decreases, the same end-tidal percentage corresponds to a lower partial pressure of volatile anesthetic. This is due to Dalton’s law of partial pressures which says the total pressure exerted by a mixture of gases is the sum of the individual gases’ partial pressures. Therefore, at an altitude of 5500 m, if end-tidal isoflurane reads 1%, the patient will really only receive the partial pressure equivalent of 0.5 MAC. Similarly, if the vaporizer dial is set to deliver 1%, the end-tidal gas monitor should read approximately 2% isoflurane, but the patient is still receiving the partial pressure equivalent of 1 MAC.

Answer 23

effects of the volatile anesthetic are directly dependent on alveolar partial pressure, not alveolar concentration

Answer 24

The percent volatile anesthetic can be converted to partial pressure (mm Hg) by multiplying the percent by 760 mm Hg. For example, 1% isoflurane at sea level produces a partial pressure of 0.01 * 760 mm Hg = 7.6 mm Hg.

Answer 25

Desflurane vaporizers generally operate differently: they are typically heated to 39 °C which creates a constant desflurane vapor pressure of 2 atm within the vaporizer, independent of barometric pressure.t then delivers the anesthetic at a fixed percent concentration, not partial pressure. This means that at higher altitudes, the partial pressure of desflurane delivered to the alveoli is reduced due to the fall in atmospheric pressure (again, due to the Dalton law). In order to compensate, the inspired concentration should be manually increased with the dial setting.

Answer 26

The quality of the ECG tracing can be optimized by placing the leads close together and toward the center of the magnetic field where the radiofrequency of the magnetic field causes minimal changes.

Answer 27

In the setting of a power failure or if using a powered down anesthesia workstation, the oxygen delivery and manual positive pressure ventilation capabilities of the workstations are almost always still functional. If vaporizers are mechanical (e.g. variable-bypass, flow-over) they are also likely to be functional-basically just NOT desflurane. Monitoring (CO2 etc) is always fully dependent on electricity.

Answer 28

FRC is the amount of air left in the lung at the end of a passive tidal volume breath. Adding PEEP can increase FRC.

Answer 29

They need longer in expiration to get the air out of their lungs

Answer 30

Restrictive lung disease

Answer 31

Carbon dioxide can be measured with infrared light, oxygen can not.

Answer 32

End-tidal CO2 (ETCO2) is measured by infrared spectrophotometry where a wavelength of infrared light is passed through a gas sample and the amount of energy detected is inversely proportional to the gas partial pressure. It operates on the principle that the amount of infrared light absorbed at a specific wavelength is proportional to the partial pressure of the gas analyzed because absorption will be greater with a greater amount of gas molecules. Intensity of IR light detected will therefore be inversely proportional to the amount of gas in the sample.

Answer 33

Infrared spectrophotometry only works with gases that are polar, have dissimilar atoms, and are asymmetric. CO2, N2O, and volatile agents are measured in this manner. Because O2, N2, and xenon are nonpolar, symmetric, and do not have dissimilar atoms, they do not absorb infrared light and cannot be measured in this manner.

Answer 34

- Decreased abdominal wall compliance: abdominal surgery, prone positioning, major trauma or burns - Increased intraluminal contents: gastroparesis, ileus, volvulus - Increased intra-abdominal contents: acute pancreatitis, distended abdomen, intra-abdominal infection/abscess/tumors, laparoscopy with excessive inflation pressures, peritoneal dialysis - Capillary leakage: acidosis, hypothermia, increased APACHE-II score, massive fluid resuscitation, massive transfusion - Miscellaneous risk factors: age, bacteremia, coagulopathy, elevated head of bed, obesity, PEEP>10, peritonitis, pneumonia, sepsis, shock

Answer 35

Clinical manifestations are seen earlier in patients with chronic renal insufficiency, cardiomyopathy, and pulmonary disease. BUT chronic renal insufficiency is NOT an independent risk factor for renal insufficiency

Answer 36

Skin temperature is normally within 2 degrees Celsius of core temperature, despite significant changes in ambient temperature and skin blood flow.

Answer 37

Sites Correlating With Core Temperature: 1) Esophageal 2) Tympanic 3) Pulmonary artery 4) Nasopharyngeal

Answer 38

distal 1/3 of esophagus.

Answer 39

Okay (Waka Flocka face)

Answer 40

Radiation exposure is inversely proportional to the square of the distance (1/radius^2). By doubling the radius from the source of radiation, the resultant incident radiation is 1/4th. Eight mrem per second divided by four is two mrem per second at the new distance. Answers A & B & D: 8 mrem/s / (2 feet ^ 2) = 2 mrem/s

Answer 41

Carbon dioxide is the most common type of laser used for airway surgeries and accordingly, is responsible for most airway fires.

Answer 42

glass/plastic

Answer 43

Amber/orange

Answer 44

Amber/orange

Answer 45

The Nd-YAG laser is a general-purpose laser that thermally coagulates several millimeters of tissue upon exposure. The light passes through the cornea but can permanently damage the retina within milliseconds of exposure. Protective eyewear with green filters should be worn to prevent eye damage.

Answer 46

Wide complex QRS is defined as greater than 0.09 seconds duration in children. Wide complex tachycardia with evidence of cardiopulmonary compromise should be treated with synchronized cardioversion (0.5-1 J/kg).If the patient with a wide complex tachycardia is hemodynamically stable without evidence of cardiopulmonary compromise then adenosine may be administered.

Answer 47

Narrow complex tachycardia can be divided into probable sinus tachycardia versus probable supraventricular tachycardia (SVT). P-waves are present in sinus tachycardia and HR is typically less than 220/min for an infant and 180/min for children (150/min for adults). Supraventricular tachycardia has either absent P-waves or morphologically abnormal P-waves with fixed HR typically > 220 for infants and > 180 for children. Vagal maneuvers and/or adenosine are recommended as first line therapy for SVT. If adenosine is ineffective or IV/IO access is not available, then proceed with synchronized cardioversion. Sinus tachycardia therapy includes treating the cause.

Answer 48

Unsynchronized defibrillation is recommended for ventricular fibrillation.

Answer 49

Relative to a more central arterial waveform, a more peripheral arterial waveform will have a higher systolic pressure, a wider pulse pressure, a more delayed and slurred dicrotic notch, and a more pronounced diastolic wave.

Answer 50

1) 0.5 MAC of volatile agent to avoid the profound evoked potential depression seen with 1 MAC 2) Short-acting succinylcholine is used instead of longer acting rocuronium (which would make MEP monitoring inaccurate and unobtainable) 3) Intravenous agents (propofol and remifentanil infusions) to supplement the anesthetic which offer less depression of evoked potentials than inhaled agents

Answer 51

he ratio of dead space ventilation to alveolar ventilation increases significantly due to the small tidal volumes delivered with jet ventilation and accordingly, hypercarbia is a frequent complication of its use.

Answer 52

Of note, placement of a magnet does not typically stop biventricular pacing function, so a conduction delay may not be seen.

Answer 53

Tricuspid annular plane systolic excursion (TAPSE) is a measure of right ventricular function. A TAPSE of 1.1 cm is moderately depressed. Isolated right heart failure is not an indication for CRT.

Answer 54

1) LVEF less than or equal to 35% PLUS 2) Intraventricular conduction delay greater than 120 msec PLUS 3) Heart failure symptoms (NYHA class II, III, or IV) PLUS 4) Sinus rhythm

Answer 55

For each degree Celsius temperature decrease, the pH of blood increases by approximately 0.017. Since the arterial blood gas (ABG) sample is run at 37 °C, the temperature-corrected value is that which corresponds to the patient’s temperature: 10 °C lower. Therefore, the pH at 27 °C would be: 7.25 + (10 x 0.017) = 7.42, corresponding with the closest answer choice of 7.40.

Answer 56

As temperature increases, gases become less soluble and more exists in the gaseous (rather than dissolved) form. Conversely, as temperature decreases, gases become more soluble in solution with less in the gaseous form. Since the partial pressure exerted by a gas is dependent on the amount of gas in the gaseous (rather than dissolved) form, partial pressures of gas decrease as temperature is decreased. Clinically, this is most apparent during hypothermia. When corrected for colder temperatures, an ABG will show decreased partial pressures of oxygen and carbon dioxide. Accordingly, in this example, since the PaCO2 value of 55 mm Hg is obtained from a sample run at 37 °C, the temperature-corrected (to 27 °C) PaCO2 value must be lower. It is important to realize that only the partial pressures of gases in blood (e.g. CO2, O2) change as temperature changes. The total amount (content) of the gases does NOT change.

Answer 57

Aluminum and brass are the two metals considered MRI safe.

Answer 58

Alveolar Gas Equation: PAO2 = FiO2 * (Patm - PH2O) - PaCO2/RER Answer is 34 Where PAO2 is the calculated alveolar partial pressure of oxygen, FiO2 is the inspired percentage of Oxygen (21% on room air), Patm is the atmospheric pressure (760 mm Hg at sea level), pH2O is the partial pressure of water vapor (47 mm Hg), PaCO2 is the arterial partial pressure of carbon dioxide, and RER is the respiratory quotient (considered to be 0.8 normally). Using the values provided in the stem a PAO2 of 34mm Hg is obtained. But use 447 as used in stem

Answer 59

It suggests airway obstruction such as from a kinked endotracheal tube.

Answer 60

Aka alveolar pressure

Answer 61

If the peak and plateau pressure are not significantly different (normal is 4-10 cm H2O), it suggests an issue with respiratory compliance such as poor positioning, pulmonary fibrosis, pneumothorax, obesity, or chest wall deformity or compression. Efforts to fix these problems (if modifiable) should be sought.

Answer 62

Yes it is.

Answer 63

Nasal CPAP decreases atelectasis and maintains recruitment

Answer 64

Functional residual capacity is lower in neonates, but this increases over the first few days of life and reaches adult levels at about day 4.