Test 1 part III (CM) Flashcards
What is the oxygen saturation of blood at the proximal pulmonary artery (measured by PAC)? Reflects average O2 saturation of blood returning to heart
SvO2
What is a normal SvO2?
65-80%
What conditions cause an increase in SvO2?
- left to right shunts
- hypothermia
- sepsis
- cyanide toxicity
- wedged PAC
- increase in CO
What conditions cause a decrease in SvO2?
- hyperthermia
- shivering
- seizures
- reduced pulmonary transport of oxygen
- hemorrhage
- decreased CO
Transcutaneous monitoring of the adequacy of oxygenation specific to the brain → O2 supply vs demand within a region of the brain
Cerebral Oximetry
You have to monitor a core temperature with what kinds of anesthesia?
GA > 30 min and RA with anticipated temperature changes
What is normothermia?
37 C
What is hypothermia?
< 36 C
What is hyperthermia?
> 38 C
How does hypothermia occur?
A redistribution of lower-temp blood from vasodilated periphery
How does hyperthermia occur?
- Genetic predisposition to MH
- Infection
- drugs inhibit sweating
- recreational drugs
What are the core temperature monitoring sites?
Tympanic membrane, PA, distal esophagus, nasopharynx
Core temperature is estimated using which sites?
oral, axillary, rectal, bladder
Do rectal and skin temperatures increase with malignant hyperthermia?
No
The transfer of body heat to a cooler environment, all surfaces absorb heat from surroundings
Radiation
Heat transfer via Sweating (rare), surgical wounds/cleansing, respiratory (expire warm, moist air), transcutaneous evaporation (peds!)
evaporation
Heat loss from direct contact with surfaces (OR table), negligible
Conduction
Heat loss to cool air, “wind chill” factor
Convection
What are the top two ways a patient can become hypothermic in the OR?
- Radiation (majority of heat loss)
- Convection (2nd most important contributor)
What adverse outcomes are associated with hypothermia?
- Increased M&M, prolonged PACU stay, increased perioperative costs
- Increased O2 consumption
- Inc Risk CV events
- Sickling w sickle cell dz
- Impaired coagulation
- Decreased drug metabolism
- Reduced MAC volatile anesthetic agents (by 5% per 1C)
- Wound infection
- Delayed healing d/t impaired immune function
What are risk factors for hypothermia?
High physical status, lengthy procedure (>3hr), geriatrics, lean body mass, failure to monitor, combined anesthetic technique (GA + RA)
What are ways to prevent hypothermia in the OR?
Warming before induction can reduce redistribution hypothermia.
1. Preoperative cutaneous warming (warming blanket)
2. airway heating/humidification (HME esp in peds)
3. warm IV fluids
4. warm ambient OR temp (>23C)
5. cutaneous heating
Which is better: Prevention of hypothermia or active rewarming?
Prevention of hypothermia
What is the benchmark for adequate recovery from NMB?
Adductor pollicis TOF ratio >0.9
What is the most common site for monitoring NMB (TOF)?
Ulnar Nerve (gold standard)
Can also use other peripheral, superficial nerves: median, posterior tibial, common peroneal, facial
Occurs when each of the successive twitch responses from T1 through T4 become smaller
Fade
Fade exists with what kinds of blocks?
- Non-depolarizing block
- Phase 2 Depolarizing Block
Comparing the size of T4 twitch to T1 switch provides what?
Train of Four Ratio (TOFR)
Which is the first “organ” to have onset of NMB?
- Eye muscles
- Extremities
- Trunk
- Abdominal Muscles
- Diaphragm
Recovery from NMB is the same order in reverse
Which organ is the most resistant to NMB, but recovers the quickest?
Diaphragm
A method that administers one single supramaximal stimuli (0.1 to 1 hertz (Hz) for 0.1 to 0.2 milliseconds (ms)), most useful at onset of NMB (induction of anesthesia), must have comparison twitch response prior, indicates 100% NMB if no movement detected.
Single Twitch
4 supramaximal stimuli (2 Hz for 2 sec) are given every 0.5 sec, # of twitches correlates with degree of NMB
Train of Four
If you have 3/4 twitches, what % block do you have?
75-80%
If you have 2/4 twitches, what % block do you have?
80-85%
If you have 1/4 twitches, what % block do you have?
90-95%
If you have 0/4 twitches, what % block do you have?
100% block
Intraoperatively, what degree of NMB do you want (how many twitches)?
85% to 95% or 1 to 2 twitches
Assesses the degree of NMB when there is no response to a single supramaximal twitch or TOF (deep NMB is present). This method involves administering 5s of tetanic stimulation, followed by a single supramaximal twitch or TOF. If no response, an intense blockade remains. If response is seen with the single twitch or TOF, then there is some recovery from NMB.
Post tetanic Stimulation
Method that consists of two short bursts of a 50-Hz tetanus separated by 0.75 seconds.
-improves the ability to detect residual paralysis during recovery.
-Normal response is 2 contractions of equal intensity
-Partial NMB is present if 2nd response is weaker than the 1st (fade) - comparable to TOFR <0.6
Double Burst Stimulation
The high frequency delivery of a supramaximal stimulus. Normal response is contraction.
-Non-depolarizing and Phase 2 Depolarizing blocks yield a non-sustained response (Fade). If fade is present, a clinically significant block remains.
-Painful and may cause muscle fatigue
-TOF 4/4 with sustained tetany > 5 sec indicates adequate NMB reversal
Tetanic Stimulation
