Miscellaneous Monitors and Equipment Flashcards
How does the TOF deliver twitches?
4 twitches at 2 Hz at 0.5 second intervals for 2 seconds
When does fade occur?
T4/T1 ration is < 1.0 (usually caused by a NMB or a phase II block by a depolarizing NMB
When is clinical recovery from a NMB achieved?
TOF > 0.9
What is the # of receptors blocked when the T4/T1 ratio is 1.0?
Total receptor blocked: 25-50%
What is the # of receptors blocked when the T4/T1 ratio is 0.9?
of receptors blocked: 75%
What is the # of receptors blocked when the T4/T1 ratio is 0.75?
of receptors blocked: 75
T4 (75) / T1 (100)
What is the # of receptors blocked when the T4/T1 ratio is 0.6-0.75? (This includes when T4 is lost)
80-85%
T4 (0-75) / T1 (25-95)
What is the # of receptors blocked when T2 or T3 are lost?
of receptors blocked: 85-90%
What is the # of receptors blocked when T1 is lost?
Number of receptors blocked: 90-95%
What is the # of receptors blocked when the T is 0 (no twitches)?
Number of receptors blocked: 100%
What is tetanus?
It delivers a high frequency of stimulation.
Rapid sequence of 50 Hz for 5 seconds
Is tetany or TOF a more sensitive method of assessing recovery from NM blockade?
Tetany
What is double burst stimulation?
Delivers two short bursts of 50 Hz tetanus 0.75 seconds apart.
Painful
What is post-tetanus count?
A 50 Hz titanic stimulus is delivered for 5 seconds followed by a series of singe twitches ~ these twitches will fade in strength
***we use this to assess the depth of NMB when no twitches are present (deep block) ~ helps plan for recovery and reversal of NMB
> 6 ~ T1 will return very fast
< 3 ~ return of T1 is far away
How does cerebral oximetry measure cerebral oxygenation?
Near infrared spectroscopy (NIRS)
What are some traits about cerebral oximetry?
Measures venous oxygen saturation
(Decrease O2 delivery, ^ oxygen extraction, decreased venous O2 saturation)
Detects REGIONAL oxygenation
Noninvasive
Two sensors are placed
What % change suggests a reduction in cerebral oxygenation?
> 25%
What is the range of brain waves from high frequency to low frequency (high to low)
Beta > alpha > theta > delta > burst suppression
(Better Always Think Delta Be-Superior)
What are beta brain waves?
High frequency, low voltage
13-30 cycles/sec
Awake mental stimulation and “light anesthesia”
What are alpha brain waves?
8-12 cycles/sec
**associated with awake but restful state with eyes closed
What are Theta waves?
4-7 cycles/sec
General anesthesia and children during normal sleep
What are delta waves?
<4 cycles/sec
Associated with general anesthesia, deep sleep, and/or brain ischemia or injury
What is burst suppression?
Associated with general anesthesia, hypothermia, CPB, and cerebral ischemia
What is Isoelectricity?
Absence of electrical activity
(Associated with very deep anesthesia or death)
How does Ketamine affect the EEG?
Increases high frequency cortical activity and May confused the EEG interpretation ~ patient may be deeper
Which volatile agent affect beta wave activity?
Nitrous oxide
What is the target number for general anesthesia when considering the BIS monitor?
40-60
As the level of anesthesia becomes deeper, what do the EEG waveforms exhibit?
Lower frequency (they become slower)
Higher amplitude (they become taller)
What are some limitations of the BIS?
20-30 second lag
Less accurate in children
BIS < 40 for more than 5 mins correlates with an increased 5-year mortality (supposedly)
What is the Patient Safety Index Monitor?
Similar to BIS, but target range is 25-30
What is a Macroshock?
Larger amount of current is applied to the EXTERNAL surface of the body
What is a Microshock?
Smaller amount of current is applied directly to the myocardium (think PA cath, central line, pacing wires)
What is the maximum allowable current leak in the OR?
(Part of the microshock voltage)
10 micro amps (uA)
100 uA to cause vfib
What is 1mA?
Macroshock
Threshold for touch perception of electric shock
What is 5 mA?
Macroshock
Max current for a harmless electrical shock
What happens at 10-20 mA?
Macroshock
“Let go” current occurs before sustained contraction
What happens at 50 mA?
Macroshock
Loss of consciousness
What happens at 100 mA?
Macroshock
Ventricular fibrillation
Is the OR grounded?
No! Equipment is grounded
The absence of grounding in the OR provides a second layer of protection against shock.
What is a isolation transformer?
This is a device that sits b/t the power coming from the power company and the OR (it is required to supply ungrounded power to the OR)
It only works when equipment connected to it are functioning correctly.
What is a line isolation monitor?
Assesses the integrity of the ungrounded power system in the OR.
It tells you when the OR becomes grounded and how much current could potentially flow through you or a patient.
What are some traits about the line isolation monitor?
Does not (by itself) protect you or the patient from macro/micro shock.
Purpose is to ALERT OR staff of first fault (aka OR has become grounded)
Alarms at 2-5 mA of leak current
What should you do if the line isolation monitor alarms?
The last piece of equipment that was plugged in should be unplugged.
What frequency does a surgical electrocautery unit deliver?
High frequency
(500,000 - 1 million Hz)
**used to cut, coagulate, dissect, and destroy tissue
What does the return electrode in a monopolar electrocautery device do?
return electrode serves as an EXIT POINT by providing a large surface area for the electric current to exit the body and return to the power generator
What does a fault in the return pad mean for the patient?
Risk for burns
If the return pad malfunctions, the electrical current will exit from other means (pt EKG stickers, temp probe, or metal components of the table)
In what case should all metal jewelry be removed?
If a capacitive-couples return electrode is used
(Increased burn risk)
Why should metal jewelry be removed prior to surgery?
Metal jewelry can cause a “re-concentrating” effect
If a patient refuses, ensure jewelry is not in the direct path of electrical current and return pad AND tape jewelry to the skin
At what MAC do volatile agents produce isoelectricity on the EEG?
1.5-2.0
At what # of receptor blockade does the fourth twitch disappear?
80% - 85%
What are X-rays and gamma rays called ionizing radiation?
Because they can ionize atoms (remove electrons from the outer shells)
What are the two effective barriers to X-rays and/or gamma rays?
Lead or concrete
What is a Roentgen?
Unit of radiation exposure
Describe the output of a X-ray machine (some is lost and some is absorbed)
(Think of this as total dose administered)
What is Radiation absorbed Dose? (Rad)?
Quantity of radiation received by an individual.
Think of rads as “total dose administered at the tissue level”
What is radiation equivalent man (REM)?
Unit of occupational radiation exposure
Accounts for differences among types of radiation.
Think of Rems as the “effective dose”
What is the yearly maximum radiation exposure for adults?
5 rem
What is the yearly maximum exposure for the fetus of a pregnant worker?
0.5 rem or 0.05 rem/month
What is the number of electrons used to generate the X-ray beam called?
Milliampere-seconds (mAs)
What describes the quality of X-rays produced?
Kilovolt
What tissues have a very high sensitivity to EMR?
Bone marrow
Intestinal epithelium
Reproductive cells
Fetal tissue
What tissue have a high sensitivity? (Not to be confused with very high)
Optic lens
Thyroid epithelium
Mucus membranes
What tissue has a medium sensitivity to EMR?
Glial cells
Liver
Lung
Pancreas
What tissue has a low sensitivity?
Mature RBCs
Mature bone
Mature cartilage
What are the three ways to limit radiation exposure?
Distance
Duration
Shielding
What is the easy way to protect yourself from radiation?
Distance
What is the MINIMUM safe distance from the radiation source?
6 feet
What equation is used to quantify the amount of exposure at two different locations?
Intensity1=Distance2^2 / Intensity2=Distance1^2
X-rays penetrate easier via low density and less easily via high density. What is the order of increasing density? (Darkest to lightest on an X-ray)
- Gas (air)
- Fat
- Water (soft tissue)
- Bone (metal)
Why is a X-ray taken on inspiration?
Inspiration separates the soft tissue and vessels ~ makes it easier to see on the X-ray
What is the most common X-ray view?
PA (posterior anterior) rays pass from back to front.
In the PA view (on a X-ray), what is the normal width of the heart?
< 50% of the width of the thorax
PA view provides the most accurate assessment of heart size
In the AP view (in a X-ray), what is the normal width of the heart?
< 60% of the width of the thorax
AP provides a less accurate assessment of heart
What is the normal position of the diaphragm on an X-ray?
Domed
Right is usually higher than the left due to liver
What does a unilateral or flattened hemidiaphragm indicate?
Tension pneumo
What does bilateral flattening of the diaphragm on X-ray indicate?
COPD or chronic asthma
What do blunted costophrenic angles indicate?
Pleural effusions
What are air bronchograms?
Dark, air-filled bronchi surrounded by opaque white alveoli
If air bronchograms are present, then the opacity is likely atelectasis
What is interstitial pulmonary edema (I.e. LV failure) characterized by?
Peribronchial cuffing (donuts) and/or linear patterns (Kerley Lines)
What does enlargement of the aortic knob indicate?
Aortic dissection
Valvular insufficiency
PDA
Severe Tetralogy of Fallot
Which lung hilum is normally higher?
Left
What is the mnemonic for evaluating an X-ray?
ABCDEFGHI
A: assess airway
B: bones and soft tissue
C: cardiac
D: diaphragm
E: effusion
F: fields, fissures, foreign bodies
G: great vessels/ gastric bubble
H: hila and mediastinum
I: Impression
Where does a properly placed ETT sit?
Mid trachea about 4-5 cm above the carina (adults)
** if you can’t see the carina, you can use the T4-T5 vertebral interspace as a surrogate for the carina
The level of the medial ends of the clavicles is another option
Where should the distal tip of the central line reside?
In the distal 1/3rd of the SVC b/t the right atrium and most proximal venous valves
what can happen if the tip of the CVL is in the proximal 1/3rd of the SVC?
It is 16-times more likely to thrombose!!
What can happen if the CVL is placed too deep?
Placing the catheter inside the right atrium can cause arrhythmias and/or cardiac perforation
What is the target for a PA cath?
West’s zone 3.
Where is atelectasis most commonly seen on X-ray?
In the posterior segment of the RUL or the superior segment of the RLL
What are the 3 stages of cardiogenic pulmonary edema on X-ray?
Stage 1: cephalization (vascular redistribution)
Stage 2: peribronchial cuffing (donuts), butterfly pattern around Hila, and Kerley lines
Stage 3: alveolar edema, alveolar consolidation, blunted costophrenic angles, rounded left ventricle
What are the three stages ARDs progresses?
- Exudative (12 hours after insult)
- Proliferate (24-48 hours)
- Fibrotic
The deep sulcus sign represents which abnormality?
Pneumothorax
