Clinical Monitoring Lecture 2 Flashcards
(86 cards)
1
Q
How can pressure waveform analysis be helpful?
A
- Trying to identify the presence of preload reserve
- Hemodynamic resuscitation begins with adequate preload
- What changes occur in BP from PPV, intrathoracic pressure changes, and lung volume changes
2
Q
What is systolic pressure variation (SPV)?
A
Increase or decrease in systolic pressure in relation to end expiratory pressure→ in mechanically vented pts normal 7-10mmHg total
3
Q
What causes systolic pressure variation?
A
Difference between what is going on in right heart vs left heart
4
Q
How does increase lung volume when vent gives a breath cause systolic pressure variation?
A
- Increase lung vol compresses lung tissue→ displaces pulm venous blood into left heart (increases LV preload)→ decreases afterload→ increase LV stroke volume
- Increase thoracic pressure decreases venous return and right heart preload→ increases pulm resistance and increases right heart afterload → right heart SV drops, left heart preload falls, arterial BP declines
5
Q
What is normal systolic pressure variation?
A
Change up 2-4mmHg
Change down 5-6mmHg
6
Q
What does increased SPV indicate?
A
Volume responsive (possible early hypovolemia) → if more than 2-4mmHg up and more than 5-6mmHg down
7
Q
What if systolic pressure variation is less than 2-4mmHg up and less than 5-6mmHg down?
A
There may be a problem but fluid will not help
8
Q
What is pulse pressure variation (PPV)? What is normal?
A
Utilizes max and min pulse pressures over entire respiratory cycle
Normal: <13%
9
Q
What might pulse pressure variation >13% indicate?
A
Possible volume responsiveness
10
Q
What might pulse pressure variation <13% indicate?
A
Not fluid responsive
11
Q
How is pulse pressure variation calculated?
A
(PPmax - PPmin) / [(PPmax + PPmin)/2]
12
Q
What is the pulse pressure variation if max BP is 150/70 and min BP is 120/60?
A
29% = responsive to fluid
13
Q
What is stroke volume variation?
A
- Computer analysis of arterial pulse pressure waveform
- Correlates resistance and compliance based on gender, age and computes SV
14
Q
What is the formula for SVV? What is normal SVV? What does greater than normal SVV suggest?
A
- SVV= (SV max - SV min)/ SV mean
- Normal 10-13%
- Greater than 13% suggests volume responsiveness
15
Q
What circumstances are needed to get accurate results for SVV?
A
- Ventilated pt with stable RR and Vt 8-10cc/kg
- Closed chest
- Normal intra-abdominal pressure
- Regular cardiac rhythm
16
Q
What are the 2 different methods of expired gas sampling?
A
- Non-diverting (main-stream) : Gas is not removed from circuit–sampled in ventilator
- Diverting (side-stream): Gas is removed from circuit for analysis elsewhere–taken to another piece of equipment and monitored as respiratory gas
17
Q
Where is the best place to obtain respiratory sample?
A
- Closest to the mask→ further away from mask is less exact sample
- Want respiratory sample port coming off flat with tubing to avoid breaking off
18
Q
What are some challenges to respiratory sampling?
A
- Mainstream analyzer: water vapor, secretions, blood, more interfaces for disconnection
- Sidestream analyzer: Kinking of sampling tubing, water vapor, failure of sampling pump, leaks in line
19
Q
What is daltons law?
A
The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each gas
20
Q
How is volumes percent calculated?
A
(Partial pressure/atmospheric pressure) x 100 = volumes percent
21
Q
What is mass spectrometry?
A
Concentration determined according to mass→ how many molecules of each gas are present in the sample (assumes all gases have been detected)
can calculate up to 8 different gases→ calculates partial pressure from % proportion
22
Q
What would be the partial pressure is ETCO2 is 5%?
A
(760-47) x .05 = 35.65mmHg
23
Q
What is arguably one of the most important monitor? (tells us FiO2)
A
- Oxygen analyzers→ must be calibrated for high and low concentrations
- Samples inside inspiratory limb (ensures O2 delivery and analyzes hypoxic mixtures)
- Samples on expiratory limb (ensure complete preoxygenation “denitrogenation” ET O2 above 90% adequate)
24
Q
What are the different types of oxygen analyzers?
A
- Fuel or Galvanic cells: battery powered, short lifespan, looks are current from partial pressure of O2
- Paramagnetic analyzers: Uses magnetic attraction (O2 concentration), real time breath by breath measurement, less calibration
- Now O2 analyzers are built-in internally and last a long time
25
What could be the cause of Low FiO2 alarm?
- Pipeline crossover (think you are turning on O2 but its N2O)
- Incorrectly filled tanks
- Failure of proportioning system (system that allows you to turn up O2 without turning up N2O and turns up O2 when turning up N2O)
26
What could be the cause of High FiO2 alarm?
- Premature infants
- Chemotherapeutic drugs (bleomycin)→ use room air concentration d/t high chance of O2 toxicity
27
What is airway pressure monitoring used for?
- Technique that assesses patients mechanical and/or spontaneous ventilation
- Every machine has this--part of circuit
- Determines presence of PEEP
- Show Inspiratory pressure, NIP, and PEEP
28
What is the function of mechanical pressure gauges?
- Require no power, always on
- No recording of data- manually write down
- No alarm system (unless you set)
- Measuring general pressure (not just O2)
- Must be continually scanned and documented
29
What is the function of the electronic pressure gauges?
- Built within ventilator or anesthesia machine—not printed out but can go back and look at the machine to get value
- Alarm system integrated
30
What could be the cause of a low peak inspiratory pressure alarm? What level should low peak insp pressure be set to?
- Pressure is lower than preset min
- Disconnection, apnea, vent failure, leaks in system, OGT in lung to suction
- Required by AANA/ASA standards (only enable when vent is on)
- Set alarm just below normal peak airway pressure
31
What causes activation of high pressure alarm? What is the typical high pressure limit set at?
- Activated if pressure exceeds certain limit
- Obstruction, reduced compliance, coughing/straining
- 50-80cmH2O
*non function in pressure control ventilation*
32
When would you need to adjust high pressure alarm parameters?
If patient has high inspiratory pressures baseline (ex: ARDS)
33
What is a sustained elevated pressure alarm? What does the pressure exceed?
- Pressure stays elevated during respiratory cycle
- Circuit pressure exceeds 10cmH2O >15 seconds
- improper APL, activation of O2 flush system, malfunctioning PEEP, scavenging system occlusion
34
How does a single muscle fiber react to a nerve stimulator?
Follows all or non pattern
35
What are the types of nerve stimulators?
- Electrical
- Magnetic (not used clinically any more bc no TOF and hard to achieve supramaximal stimulus)
36
What are primary sites for nerve stimulation?
- Ulnar nerve (adductor pollicis muscle)
- Facial nerve (orbicularis oculi and corrugator supercilli)
- Posterior tibial nerve (flexor hallucis longus)
37
Which nerve stimulation site is the gold standard for recovery from NMB?
Ulnar nerve (adductor pollicis)→ easy access
38
What can the facial nerve be used to monitor?
Mirrors onset of laryngeal relaxation
39
When would you choose to monitor NMB at the posterior tibial nerve?
When surgical procedure requires HOB away from anesthesia
40
What are the different patterns of nerve stimulation?
- Single
- TO4
- Tetanic Stimulation
- Post-tetanic Stimulation: telling about recovery process
- Double burst (not used much in anesthesia)
41
What is the simplest nerve stimulator pattern?
Single twitch: delivered in range→ each 10 seconds (.1Hz), each seconds (1.0Hz)
42
What is the stimulus delivered from TOF?
Supramaximal stimuli every 0.5 seconds
43
What is expected from the TOFR for non-depolarizers vs depolarizing NMBs?
- Non depolarizers have fade: TOFR ratio inversely proportional to block
- Depolarizers: no fade or TOFR=1 (equal height)
44
Why is it important to still reverse patient who received NMB even if TOF is 4/4?
May have 4/4 but only have 70% of receptor back (reverse to make sure all of paralytic is gone)
45
What is the stimulation from tetanic stimulation? How does tetanic stimulation look for non-depolarizing vs depolarizing NMB?
- Stimulus at 50Hz for 5 seconds
- Non-depolarizing: fade with stimulation after tetanus (present prior to TOF returning)
- Depolarizing: No fade following tetanus
46
_________ is one of the most resistant muscles to both types of NMBDs
Diaphragm→needs up to 2x as much drug for identical block as adductor pollicis, recovers faster than periphery, onset faster than adductor pollicis
47
What is the most sensitive muscle to paralytics?
Orbicularis oculi, masseter, upper airway
48
Which muscle most closely reflects laryngeal adductor muscle?
Corrugator supercilli or facial nerve
49
Which muscles paralyze fastest?
Central muscles (laryngeal, trachea, eyelids)
50
Which muscles recover the fastest from paralytic?
Central muscles (recover faster than periphery)
51
What are the different depths of blockade for non depolarizing neuromuscular blockers?
- Intense – period of no TOF response, 3 – 6 minutes after intubating dose of non-depolarizing NMBD (Neostigmine reversal impossible; high dose of sugammadex (16 mg/kg) for reversal)
- Deep – absence of TOF but presence of at least one response to post-tetanic count stimulation (deep block but is recovering)
(Neostigmine reversal usually impossible; dose of sugammadex (4 mg/kg) for reversal)
- Moderate – gradual return of the 4 responses to TOF stimulation appears
Neostigmine reversal after 1/4 TOF; dose of sugammadex (2 mg/kg) for reversal
52
What are the phases of blockade for depolarizing NMBs?
- Phase 1- depolarizing NMB→ no fade, no post tetanic facilitation (increase), all 4 responses reduced and equal, TOFR= 1, normal plasma cholinesterase activity
- Phase 2: looks like Non depolarizing NMB→Fade present on TOF, post tetanic facilitation, response similar to NDNMB, abnormal plasma cholinesterase activity
53
What is EEG used to identify?
- Consciousness
- Seizure activity
- Stages of sleep
- Coma
*signal inadequate O2 delivery (ischemia)*
54
How are EEG signals described?
- Amplitude (size/voltage)
- Frequency (number of times per second the signal oscillates)
- Time (duration of sampling of signal)
55
Where are the odd and even electrodes placed for EEG monitoring?
Odd: left hemisphere
Even: right hemisphere
56
What is EEG measuring?
Summation of excitatory and inhibitory post synaptic potentials (electrodes placed so surface anatomy related to cortical regions)
57
What are the different types of brain waves?
Gamma
Beta: >13Hz, alert attentive
Alpha: 8-13Hz, relaxed
Theta: 4-7Hz, light sleep
Delta: <4Hz, deep sleep, unconscious
58
What are peri-op uses for EEG?
- Identifies inadequate blood flow to cerebral cortex
- Guides an anesthetic-induced reduction of cerebral metabolism
- Used to predict neurologic outcome after a brain insult
- Gauges the depth of the hypnotic state of patients under GA
59
How does a processes channel EEG differ from regular EEG?
- Combination of 16 channel EEG into 2-4 channels (BIS)
- Ideally displays bilateral hemispheres
60
What are the ranged of the BIS and what wakefulness do they correlate with?
- 100-80= Responds normally
- 80-60= Pretty awake, responds to commands
- 60-40= general anesthetic with no recall
- 40-20= deep hypnotic state
- <20= burst suppression
*Bis proposed as a method to prevent intraop awarness*
61
What is something that needs to be considered when trending BIS?
Think about synergism (preop versed, NMB, volatiles) and how things add up together
62
What are sensory evoked potentials?
CNS response from electric, auditory, or visual stimuli (responses recorded in cerebral cortex)
63
What are some of the evoked potentials?
- SSEP: simulation from periphery and record in sensory cortex (Common in OR)
- BAEP: brainstem auditory evoked potential
- VEP: flash stimulation of retina
- MEP: motor evoked potential
*need good baseline prior to procedure start*
64
What is latency and amplitude in regards to evoked potentials?
- Latency: time from application of stimulus to response
- Amplitude: size or voltage of recorded signal
65
________ and _________ alter latency and amplitude of SSEPs
Volatiles and narcotics
66
Which volatile alters SSEPs?
Nitrous (increases latency and decreases amplitude)
67
When monitoring SSEPs no greater than ____ MAC of a volatile should be used
0.5MAC (add IV anesthetic like prop, remi, precedex, fent, etc)
*IV drip better for steady anesthesia to prevent swings*
68
What is the purpose of motor evokes potentials?
- Monitor integrity of the motor tracts
- Transcranial motor-evoked potentials (most common MEP with transcranial electrical stimulation over motor cortex)
- Pt musts NOT have NMB on board
69
Temperature is regulated by the ____________ and mediated by ___________, _____________, ____________
- Hypothalamus
- Dopamine, acetylcholine, PGs, etc
70
What fibers transmit cold vs hot temperature signals?
- Cold: A delta fibers
- Heat: C fibers
71
What is the temperature in the OR?
70 degrees F = 21 C
65 degree F = 18 C
72
What are methods of heat transfer that contribute to drop in temp in the OR?
- Radiation (Major type of loss 40% in surgical pts)→ higher BSA greater exposure from radiation heat loss
- Conduction (small amount, pt on thick foam pads) → cold IV fluids increases heat loss
- Convection (small amount, rate of air speed in OR small) →Rooms with laminar airflow have higher loss
- Evaporation (less than 10% in absence of sweating)
73
What causes the initial rapid decrease in temp with general anesthesia?
- Volatiles cause direct vasodilation
- Increases heat loss
- Preferentially distributes more heat to periphery than core
- Over initial 30 minutes (EX: drop from 98 96.5 degrees)
74
What is the average heat loss in the first 30 minutes of surgery?
0.5-1.5 degrees C
75
What are the "phases" of hypothermia with GA?
- Initial drop (first 30 min)
- Continual (slow linear decrease 1-2hr)
- Plateau phase (3-4hr)
76
When does the continual slow linear decrease in temp occur with GA?
- Hour 1-2
- 2 hours marks 3 degree C lower than initial temp
77
When is the thermal steady state achieved after starting GA case?
- When heat loss= heat production
- Hour 3-4
- Vasoconstriction prevents loss of heat from core but peripheral heat continues to be lost
78
How does regional anesthesia impact body temp?
- Decrease the thresholds that trigger vasoconstriction
- Induces vasodilation in the periphery
- Redistributes heat to periphery (similar to GA)
- Decreases shivering (heat production) threshold
- Sedatives also inhibit thermoregulatory control
* Hypothermia in regional anesthesia as well*
79
What is the gold standard site for temperature monitoring?
Pulmonary artery (GOLD STANDARD)→correlates well with tympanic membrane, distal esophagus, and nasopharyngeal temperatures
80
What temperature is reflected with tympanic membrane?
Approximates temp at hypothalamus (risk of perforation)
81
What temp is reflected by nasopharyngeal temperatures?
Brain temp (more prone to error)→ risk epistaxis
82
What is a safe, reliable, easy accessible site to monitor temperature?
Esophageal→place in distal esophagus lower 1/3-1/4, also used as cardiac/pulmonary monitor
83
Which temp sites are not as accurate?
- oral
- axillary
- rectal
- bladder
- skin
84
How do we manage temperature during procedures?
- Maintain airway humidification/heating
- warm IV fluids and blood
- cutaneous warming (increase room temp, insulation with blanket to reduce losses, hot water mattresses)
- Forced air warming (most common to prevent heat loss from radiation- use convection to transfer heat to pt)
85
What are complications of hypothermia?
- 3x increase morbid cardiac outcomes (increase BP, HR, catecholamine levels, increase O2 demand from shivering)
- 3x incidence of wound infection (decrease O2 delivery to tissue)
- Impair plt, Pt and PTT function
- Increase blood loss 16% and transfusion need by 20%
- Increase duration of NMBD (Nimbex and atricurium)
- Pt discomfort
86
What are "benefits" of hypothermia?
- Improved outcome during recovery from cardiac arrest
- Protective against cerebral ischemia
- More difficult to trigger MH
- Reduces metabolism 6-8% per degree C
