Mod1: Monitoring for Cardiac Surgery - PULSE OXIMETRY - TEMPERATURE Flashcards
Pulse Oximetry
What are the overall characteristics of pulse oximetry?
Measurement of oxygen saturation
Uses a sensor containing light source
Great monitoring tool that can tell you something about each of the other monitors
Measure oxygenation, tissue perfusion (via pulse amplitude)
Measures heart rate and rhythm to a degree
Can tell you about rhythm that are not necessarily perfused because the pulse ox will loose its volume
Pulse Oximetry - INDICATIONS
What are pre-op indications for pulse oximetry?
Baseline O2 saturation
Detect unsuspected hypoxemia during line placement after sedation
Pulse Oximetry - INDICATIONS
What’s the purpose of using pulse oximetry intra-op?
Assessment of oxygenation intraoperatively
Pulse Oximetry - INDICATIONS
Why is the use of pulse oximetry very important in cardiac pt?
Hypoxemia = decreased O2 supply
=> contributes to ischemia
Pulse Oximetry - INDICATIONS
How can perfusion be assessed using pulse oximetry?
Adequacy of perfusion likely when pulse oximeter shows reading/waveform
Pulse Oximetry - INDICATIONS
During arrhythmias, how can non perfused beat be detected via pulse oximetry?
Pulse oximetry will loose its volume
Pulse Oximetry
What are advantages of Pulse Oximetry?
Ease of use
Continuous monitoring
Noninvasive
Variable pitch correlates with degree of saturation
Accurate
Pulse Oximetry
What are disadvantages of Pulse Oximetry?
Saturation unobtainable in poor perfusion states
Interference with use of electrocautery
Interference with other monitors
Requires pulsatile flow to operate
In these situations, it becomes increasingly important to assess the pt while using the pulse ox as an assisted device
Pulse Oximetry
Which poor perfusion states could make saturation unobtainable?
Poor perfusion to limbs (e.g., CV disease)
Hypothermia common during CV surgery
Administration vasoconstrictors
<em>In these situations, it becomes increasingly important to assess the pt while using the pulse ox as an assisted device</em>
TEMPERATURE - INDICATIONS
Why is adequate temperature monitoring extremely important during CPB?
Intentional Systemic hypothermia essential component during CPB
Temperatures may be reduced to 20-32˚C
TEMPERATURE - INDICATIONS
What’s the purpose of Intentional Systemic hypothermia during CPB
Protect organs with high metabolic rate
Cerebral protection and Myocardial protection via reduction of oxygen demand
TEMPERATURE - INDICATIONS
What could happen if the body temperature was not reduced during CPB?
Cells will begin to make energy via anaerobic metabolism
And because of the reduced oxygen, sufficient energy will not be available
Toxic metabolites like lactate will be released
TEMPERATURE - INDICATIONS
For every 1˚C reduction in body temperature, metabolic rate reduced by
8%
TEMPERATURE - INDICATIONS
At what body temperature would the metabolic rate be Half the body’s normal metabolic rate?
at 28˚C
TEMPERATURE - INDICATIONS
True or False: Normothermia through active rewarming must be achieved prior to separation from CPB
True
TEMPERATURE - INDICATIONS
What are the effects of Temperatures <28˚C on the SA node?
Increase in erratic SA node pacing and
Ventricular irritability
TEMPERATURE - INDICATIONS
At which temperature could cardiac Fibrillation occur?
Between 28-30˚C
TEMPERATURE - INDICATIONS
True or False: Cardiac fibrillation that result from hypothermia (28-30C) can easily be treated with defibrillation
False
Fibrillation that result from hypothermia (28-30C) is often unaffected by defibrillation
TEMPERATURE - INDICATIONS
What is a possible neurologic consequence of Inadequate brain cooling during circulatory arrest
Neurologic injury
TEMPERATURE - INDICATIONS
What is a possible adverse neurologic consequence of cerebral hyperthermia (overshooting > 41˚ C) during rewarming phase following CPB?
Worsens neurologic damage
TEMPERATURE - SITES OF MEASUREMENT
Why is it important to measure “core”, “central” or “brain temperature”?
Brain is most vital organ
Brain easily susceptible to ischemia during low oxygen flow states
TEMPERATURE - SITES OF MEASUREMENT
Where does core temperature comes from? How can it be monitored?
From tissues that are highly perfused
Whose temperature is uniform and can be highly compared to the brain
Can be monitored via nasopharyngeal, pulmorary atery, esophageal or tympanic membrane
TEMPERATURE - SITES OF MEASUREMENT
What characteristize the locations where peripheral or shell temperatures are measured?
Represent majority body but
Receive smaller proportion blood flow
This is a reason why peripheral temperatures are significantly lower than core temperature
Do not accurately reflect brain temperature
Peripheral temperatures could be measured at Muscle, Fat, or Bone
TEMPERATURE - SITES OF MEASUREMENT
During bypass, why is it important to ensure that the temperature is at closed to brain temperature as possible?
Because we are trying to ensure neuro protection
TEMPERATURE - SITES OF MEASUREMENT
Since direct brain temperature measurements are not possible how is brain temperature assessed?
Surrogate sites are used to “estimate” brain temperature
TEMPERATURE - SITES OF MEASUREMENT
What is the the most reasonable site for measurement of brain temperature? Why is that?
Jugular Venous Bulb
The Jugular bulb is part of the internal jugular vein and is located close to the inner ear
Receives deoxygenated blood from neck and brain
More widened/dilated than the rest of IJV
99% of the bulb blood is from intracerebral vasculatur
TEMPERATURE - SITES OF MEASUREMENT
True or False: Catheters may be inserted into the jugular vein bulb for the sole purpose of measuring temperature
False
Catheters are not inserted for the sole purpose of measuring temperature
TEMPERATURE - SITES OF MEASUREMENT
Why is the the Retrograde catheter used for Jugular bulb temperature measurement typically placed in the Right IJ (into the bulb)?
Because the Right IJ has a larger diameter
CORE TEMPERATURE
True or False: All core temperature sites are adequate for measuring temperature during bypass surgery, and all of them have some sort of lag time, but the arterial inflow line has the smallest amount of temperature discrepency of all of the other measurement sites when compared to jugular bulb temperature
True
CORE TEMPERATURE
Which does research indicates is the best indicator of JVB temperature, and therefore “true” cerebral temperature
Arterial inflow line from CPB circuit
CORE TEMPERATURE
What are other estimates of brain temperature?
Nasopharyngeal
Tympanic membrane
PA catheter
Esophageal
CORE TEMPERATURE
Nasopharyngeal site provides Accurate estimate brain temp
But:
Lag time between it and actual brain temp during rewarming
CORE TEMPERATURE
Tympanic membrane site reflects brain temperature, but:
Lag time
CORE TEMPERATURE
PA catheter provides Accurate estimate of brain temp when pulmonary blood flow is present - before and after CPB, possibly not during, why?
… (slide 22)???
CORE TEMPERATURE
Why should the Esophageal site not be routinely used for temperature measurement in cases involving CPB?
Mediastinal structure = greatly effected by blood returning from pump
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
True or False: Monitoring arterial inflow temperature is a ClassI clinical recommendation
True
Shows evidence of being highly useful and effective
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Which is recommended to be utilized as a surrogate for cerebral temperature during CPB?
The oxygenator arterial outlet blood temperature
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Why should you limit arterial outlet blood temperature to 37 °C during rewarming?
To avoid brain hyperthermia, since
The arterial outlet blood temperature underestimates cerebral temperature
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Based on (Class IIa) Recommendations, which type of temperature measurement is reasonable for weaning and for immediate post-bypass?
Pulmonary artery or
Nasopharyngeal temperature recording
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
True or False: Currently there is no recommendation concerning “optimal” temperature for weaning from bypass
True
SHELL TEMPERATURE
True or False: Monitoring bladder or rectal temperature continues to be standard of practice in many facilities
True
SHELL TEMPERATURE
How many degrees lower can bladder and rectal temperatures be compared to brain stem temperature when rewarming during bypass?
2 to 4 degrees lower
SHELL TEMPERATURE
Why is bladder temperature not considered core temperature?
Because it is inaccurate if renal blood flow and urine production is decreased
SHELL TEMPERATURE
Why is rectal temperature not considered core temperature?
Because it reflects muscular temperature
NOT CORE (traditionally thought as)
SHELL TEMPERATURE
According to Miller, which type of temperature monitors are bladder and rectal temperatures classified as?
Intermediate temperature monitors
SHELL TEMPERATURE
Why does skin temperature provide erroneous readings?
Because it is greatly affected by external factors, such as:
Cooling/warming blankets
Cool environment
SHELL TEMPERATURE
Which temperatures are considered “shell temperatures”
Bladder, Rectal, & Skin temperatures
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
What could happen if “overheating”/Hyperthermia occurs during the rewarming phase of bypass?
Neurologic injury
Evidence supports extreme caution
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Increased rate of which conditions is associated with hypothermia during CPB
Mediastinitis & Acute kidney injury
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Why is it recommended to keep bypass machine outlet (or arterial line inflow) temperature below 37*C?
Because hyperthermia could cause neurologic injury, and
Hypothermia could cause Mediasinitis & Acute kidney injury
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
Why is it recomended to use core temp sources over shell temp sources during CPB?
Core temps lag behind actual brain temperature during rewarming
Shell temps lag behind core during cooling & rewarming
Core > shell at separation of bypass (rewarming phase)
WHICH ONES TO MONITOR DURING CARDIAC SURGERY??
What is a possible neurological adverse effect of overshooting during the rewarming phase of CPB?
CEREBRAL HYPERTHERMIA
