Flashcards in Exam 1 Deck (283)
What does hydrogen ion concentration give us?
What do we know if the H+ ion concentration exceeds hydroxyl ions?
Solution is acidic
What do we know if the H+ ion concentration is less than the hydroxyl ions?
Solution is aklalotic
Which substances dissociate or dissolve into their component parts in water?
Those with polar bonds
What determines whether a substance is a strong acid or strong base?
The degree of dissociation in water
What is the Law of Mass Action?
Rate of chemical reaction is proportional to product of masses of the reacting substances
Which three rules must be followed for acid and base balance?
1. Electrical neutrality
2. Dissociation equilibrium which follow the law of mass action
3. Mass conservation
What are pH alterations due to that lead to metabolic acidosis or alkalosis?
Abnormal bicarbonate reabsorption and hydrogen ion elimination by the kidneys
What are pH alterations due to that lead to respiratory acidosis or alkalosis?
Altered respiratory drive and CO2 levels
Do respiratory and metabolic disorders occur independently?
Rarely, you can have mixed or complex acid-base disorders
What is the degree of water dissociation and hydrogen ion concentration affected by in the modern approach to acid-base balance?
Strong ions, weak acids and carbon dioxide
Which approach to acid-base disorders is explained by the effect of PCO2, SID, Atot?
How do you calculate the SID?
(Na+ + K+ + Ca2+ + Mg2+) - (Cl- + lactate-)
(strong cations - strong anions)
Changes in SID will cause changes in what two concentrations?
Hydrogen ion and hydroxyl ion concentrations
Which ions dissociate completely leading to a direct affect on acid-base balance?
Na+ and Cl-
What does increased SID indicate?
alkalosis and presence of unmeasured cations
What does decreased SID indicate?
acidosis and presence of unmeasured anions
Describe SID in ECF
It is positive and 40-44 mEq/L
What is the degree of dissociation determined by for weak acids?
Temperature and pH
Give an example of two weak acids
albumin and phosphate
What does an increase in weak acid concentration indicate?
What does a decrease in weak acid concentration indicate?
Describe SID and total weak acids in relation to the presence of acid base disorders
They are independent variables and are inversely related in the presence of acid base disorders
What does the Boston approach use for ABG analysis?
acid-base maps and the relationship between CO2 and bicarb
5 questions we ask when analyzing ABGs?
1. What is the suspected or actual cause?
2. Does my physical assessment support these findings?
3. How do I treat the disorder?
4. Do I treat the disorder?
5. Did I cause it preoperatively?
What is the first thing we should ask when looking at any acid-base disorder?
Is the patient hypoxic
What lab value change do we see in respiratory alkalosis?
decreased PCO2 and increased pH
What do we see in the Stewart approach with respiratory alkalosis?
Primary cause of respiratory alkalosis?
Increased minute ventilation/mechanical hyperventilation
Symptoms of respiratory alkalosis? (5)
3. Visual disturbances
5. Possible hypocalcemia
Other causes of respiratory alkalosis? (6)
1. Abnormal respiratory drive from stimulants or toxins such as anxiety or pain
2. CNS abnormalities
3. Pulmonary insult/injury such as PE
4. Liver failure
What do we expect to see in the HCO3- with acute compensation of respiratory alkalosis?
HCO3- will decrease 2 mEq/L for every 10 mmHg decrease in PCO2 down to a 20 mmHg decrease
What do we expect to see in the HCO3- with chronic compensation of respiratory alkalosis?
HCO3 will decrease 5 mEq/L for every 10mmHg decrease in PCO2 down to a 20 mmHg decrease
Treatment for respiratory alkalosis?
decrease minute ventilation/ventilator change, treat cause
What lab value change do we see in respiratory acidosis?
Increased PaCO2 and decreased pH
Primary cause of respiratory acidosis?
Failure of the lungs to eliminate CO2/hypoventilation
Symptoms of respiratory acidosis? (3)
Other causes of respiratory acidosis? (5)
1. Drug associated respiratory depression
2. Neurologic injury
3. Lung injury/disease
4. Neuromuscular and musculoskeletal disease
5. Inadequate NMBD reversal
What change in HCO3 would we expect to see in acute compensation of respiratory acidosis?
HCO3 will increase 1 mEq/L for every 10 mmHg increase in PCO2 > 40mmHg
What change in HCO3 would we expect to see in chronic compensation of respiratory acidosis?
HCO3 will increase by 4 mEq/L for every 10 mmHg increase in PCO2 > 40 mmHg
Treatment for respiratory acidosis?
increase minute ventilation/ventilator changes, treat cause
Which acid-base disorder do you anticipate in a patient who has poor mechanical ventilation, narcosis and/or incomplete reversal of neuromuscular blockade?
What lab value changes would we expect to see in metabolic alkalosis?
increase in bicarb and increased pH
What would the Stewart approach show in metabolic alkalosis?
Increased SID, increased concentration of cations vs anions
What does metabolic alkalosis result from?
net loss of hydrogen ions and or addition of bicarb
What is the most common cause of metabolic alkalosis?
GI acid loss from vomiting or NG suctions causing chloride loss
Symptoms of metabolic alkalosis? (4)
1. Widespread vasoconstriction
Other causes of metabolic alkalosis? (4)
2. Third spacing
Expected PCO2 compensation in metabolic alkalosis?
0.7 x HCO3 + 20
Treatment for metabolic alkalosis?
Hypoventilation, fluid replacement, treat cause
What lab value changes would we expect to see in metabolic acidosis?
Decreased bicarb and decreased pH
Symptoms of metabolic acidosis? (5)
3. Diminished muscular performance esp heart
5. Can lead to shock
How does the oxyhemoglobin dissociation curve shift in metabolic acidosis and what does it cause?
To the right causing increase oxygen delivery to tissues
Causes of metabolic acidosis? (9)
1. Renal injury/failure
5. Lactic acidosis
6. GI losses with a normal AG
8. Carbonic anhydrase inhibitor use
9. Renal tubular acidosis
What is the expected PCO2 in acute compensation of metabolic acidosis?
Winter's Formula is (1.5 X HCO3) + 8 +/- 2
What does the anion gap represent?
The total serum concentration of unmeasured anions and is the difference between measured cations minute measured anions, this is used to investigate metabolic acidosis
Conventional AG calculation?
(Na+ + K+) - (HCO3- + Cl-) = 14-18 mEq/L
Modern AG calculation?
(Na+ + K+) - (HCO3- + Cl- + lactate) = 14-18 mEq/L
What does an abnormal or increased AG indicate?
Metabolic acidosis is caused by unmeasured anions
What does a normal AG indicate?
Metabolic acidosis is caused by lactate build up or hyperchloremia such as excess normal saline use preoperatively
What issue do critically ill patients usually have in the presence of metabolic acidosis and a normal AG?
Which have a far greater impact on the anion gap and why?
UMA because they are found in higher concentrations
What is the delta anion gap or delta ratio equation?
(Measured AG - Normal AG) / (Normal HCO3 - Measured HCO3)
What does the delta ratio dictate?
If the AG is normal, HCO3 decreases and the ratio will be less than 0.4 or low, supporting hyperchloremic metabolic acidosis; if the ratio is between 1 and 2 the acidosis is likely from UMAS and anticipate an abnormal AG
When might the Boston approach to ABG analysis be deficient?
Which two approaches to ABG analysis are often combined to incorporate the sum of the difference in charge of the common ECF ions?
AG and Boston
What is a normal base excess?
-2 to +2
What does full compensation of acid-base imbalance yield?
Expected HCO3 in acute respiratory acidosis?
24 + [(PaCO2 - 40)/10]
Expected HCO3 in chronic respiratory acidosis?
24 + 4[(PaCO2 - 40)/10]
Expected HCO3 in acute respiratory alkalosis?
24 - 2[(40 - PaCO2)/10]
Expected HCO3 in chronic respiratory alkalosis?
24 - 5[(40 - PaCO2)/10] range +/- 2
What is lactic acidosis a product of?
Production of lactate > the liver's ability to clear it and is a product of glucose metabolism
What levels of lactate are significant? Severe?
> 2mEq/L is significant, > 5 mEq/L with metabolic acidosis is severe
What is Type A lactic acidosis?
Seen in hypovolemic or hemorrhagic shock with inadequate oxygen delivery
What is Type B lactic acidosis?
Occurs despite normal oxygen delivery
Causes of metabolic acidosis from wide AG (unmeasured anions) (4)
2. Lactic acidosis
4. Renal failure
Causes of metabolic acidosis from measured anions (4)
2. Normal saline and saline containing fluids
3. Renal tubular acidosis
4. Bladder reconstructions
Causes of metabolic acidosis from free water excess such as hyponatremia and dilation acidosis? (6)
1. Hypotonic fluid administration
2. Sodium loss
5. Hyperosmolar fluids such as mannitol and alcohol
Causes of metabolic alkalosis?
1. Hyperventilation of patient with hx of CO2 retention such as COPD
2. Sodium gain from things such as sodium bicarb and massive transfusions
3. Chloride loss such as in NGT suctioning
Does sodium bicarb improve long term outcomes?
It has not been shown to
What would be an example of a metabolic disorder that we may intentionally cause?
Acidosis caused by permissive hypercapnia to prevent ventilator related lung injury because treatment may cause reverse effects
What is the A-aDO2 equation?
FIO2 (760-47) - PaCO2/0.8
What does A-aDO2 approximate?
Partial pressure of oxygen in the alveoli
What does A-aDO2 allow for the calculation of?
Alveolar-arterial gradient of oxygen and the amount of respiratory/cardiac shunt
What is a normal A-aDO2?
5-10mmHg, although age or chronic lung disease may cause an increase
What is the required cardiovascular monitoring and frequency?
BP and HR monitoring every 5 minutes
When is thermoregulation monitoring required?
When clinically significant changes in body temp are anticipated or suspected or for SCIP protocol
What must be done if we omit a standard of care?
Reason for omission must be charted
What does the beer-lambert equation describe?
The law of absorption
What is the law of absorption in relation to pulse oximetry?
If a known intensity of light illuminates a chamber of known dimensions then the concentration of a dissolved substance can be determined
What must light absorption be measured at?
Wavelengths equal to the number of solutes
(More solutes such as oxygen = more absorption)
4 variations of hemoglobin?
1. Oxyhemoglobin (HbO2)
3. Methemoglobin (metHb)
4. Carboxyhemoglobin (COHb)
What is the gold standard number of wavelength for pulse-oximetry?
What does more wavelengths give us in pulse-oximetry?
Greater assurance of looking at HbO2 and Deoxyhemoglobin
What are the 5 layers that light is transmitted through for pulse-oximetry?
2. Soft tissue
3. Venous blood
4. Arterial blood
5. Capillary blood
What type of movement increases length of the light path and increases absorbency?
Pulsatile expansion of the artery
How was the problem of ambient light solved for pulse-oximetry?
alternating red/infared light
How do we solve low perfusion issues with pulse-oximetry readings?
signal amplified, but the artifact is also amplified
Describe venous blood pulsations
longer signal averaging time, slower to report changes
What is an intervention we utilize that can also absorb light from a pulse-ox?
What is the definition of SaO2?
Ratio of oxyhemoglobin to all hemoglobin
What are fingers relatively sensitive to?
Where is the detection of desaturation and resaturation slower on a pulse-ox?
Which finger do we avoid placing the pulse-ox?
What is a more reliable place for a pulse-ox with epidural blocks?
Toes due to vasodilation
What are three other areas for pulse-ox placement that are less affected by vasoconstriction and reflect desaturation quicker?
tongue, cheek, forehead
How accurate is a pulse-ox?
+/- 2% when measured against ABGs if sat is >70%
Do anesthetic vapors affect pulse-ox?
What type of pressures do pulse-oximeters have difficulty detecting?
high partial pressures
At what wavelength range does carboxyhemoglobin absorb as much light as oxyhemoglobin?
What is the effect of carboxyhemoglobin on SpO2?
Falsely elevates SpO2; for every 1% increase COHb will increase SpO2 by 1%
What is the COHb of many smokers?
Who invented the sphygmomanometer?
Samuel von Basch
What are korotkoff sounds produced by?
turbulent flow beyond the partially occluding cuff
Phase 1 korotkoff sound?
The most turbulent/audible (SBP)
Phase 2-3 korotkoff sound?
Sound character changes, turbulent flow decreases
Phase 4-5 korotkoff sound?
muffled/absent sounds (DBP)
4 limitations to auscultation of blood pressure?
1. Decreased peripheral flow
2. Changes in vessel compliance
4. Incorrect cuff size
What is the maximum cuff pressure for adults? neonates?
300 mmHg for adults; 150 mmHg for neonates
Cuff bladder standards for BP monitoring?
40% of arm circumference
80% of length of upper arm
4 Descriptors of automatic non-invasive techniques for BP?
1. Maximal amplitude is MAP
2. SBP and DBP calculated from algorithm
3. SBP usually 25-50% of MAP amplitude
4. DBP is least accurate
When is automatic non-invasive techniques for BP measurement rough equal to arterial pressure?
when MAP is 75 mmHg or lower
Standards of non-invasive BP monitoring?
+/- 5 mmHg, can be larger depending on the circumstances
Non-invasive BP measuring of MAP during hypertension?
Non-invasive BP measuring of MAP during hypotension
What is the more reliable way to determine blood pressures from non-invasive monitoring?
Clinical limitations of non-invasive BP monitoring?
extremes of heart rate and pressure
4 trauma factors related to frequent cycling of non-invasive blood pressure?
2. Peripheral neuropathies
3. Arterial/venous insufficiency
4. Compartment syndrome
What is the most common monitoring site for arterial blood pressure?
Radial, it is easy to access and complications are uncommon
4 steps to the Allens' test?
1. Examiner compresses radial and ulnar artereis
2. Patient makes a tight fist which exsanguinates the palm
3. Patient opens hand
4. Examiner releases ulnar artery and color to the palm should return in less than 10 seconds
What is the diagnostic accuracy of the Allens' Test?
What is unique about the transfixion technique of arterial line placement?
Front and back walls are punctured intentionally and the catheter is withdrawn until pulsatile blood flow appears
Is the transfixion technique of arterial line placement associated with more frequent complications?
5 other common sites of arterial blood pressure monitoring?
1. Brachial: not the best collateral flow
2. Posterial tibial
4. Dorsalis pedis: smaller and more difficult
5. Femoral: higher complication rate
Describe the automatic flush function of A-lines
1. 1-3 mL/hr to prevent thrombus formation
2. lack of dextrose
3. lack of heparin
Where do we typically level an A-line?
Midchest/midaxillary line to look at the aortic root
How is the waveform maximized with A-lines?
limit stopcocks, limit tubing length, and non-distensible tubing
What is distal pulse amplification due to?
Due to impedance changes along vascular tree
What are the changes in A-line as pressure wave moves to periphery?
1. Arterial upstroke steeper
2. Systolic peak higher
3. Dicrotic notch later because longer for wave to transmit
4. End-diastolic pressure lower
What is the summation of sine waves?
fundamental wave + harmonic wave = typical pressure wave (fourier analysis)
What does the square wave test occur from?
From compressing fast flush, rapid rise in pressure and waiting for it to respond
What should we see post square wave form test?
1-2 rebound oscillations at bottom of square
What does the damping capability of A-line systems do?
1. Decreases system resonance
2. Prevents exaggerated waveforms
What do we see with an underdamped A-line?
Systolic pressure elevated, more exaggerated movement and steeper systolic upstroke
What issues could we have with an underdamped A-line?
tubing too long, wrong tubing
What issues could we have with an overdamped A-line?
air bubble, tubing too long, pressure bag empty
What do we see with overdamped A-lines?
1. Systolic pressure decreased
2. Decreased pulse pressure
3. Loss of detail
7 pathology that can cause A-line waveform changes?
1. Age: loss of distensibility
4. Arterial dissection
7. Vasopressor infusions
When compared with central aortic pressure, peripheral arterial waveforms have a _____ pulse pressure?
Wider pulse pressure because higher SBP and lower DBP in periphery
What initially occurs as a result of increased lung volume from the ventilator delivering a breath? (5)
1. Compression of lung tissue
2. Increased LV preload
3. Increases intrathoracic pressure
4. Decreases afterload
5. Increased LV stroke volume
What occurs as intrathoracic pressure continues to increase as the ventilator delivers a breath?
1. Reduction in venous return and right heart preload
2. Increased PVR causes increased R heart afterload
3. R heart stroke volume drops
4. Left heart preload falls
5. Arterial BP declines
What is systolic pressure variation (SPV)?
Increase or decrease in systolic pressure in relation to end-expiratory presssure
What is normal SPV in ventilated patients?
With SPV what is the normal increase?
With SPV what is the normal decrease?
What does increased SPV indicate?
What is the pulse pressure variation (PPV)?
Utilizes maximum and minimum pulse pressures over entire respiratory cycle
What is a normal PPV?
How do you calculate PPV?
What does an increase in PPV indicate?
Patient could benefit from fluids
What is stroke volume variation (SVV)?
Computer analysis of arterial pulse pressure waveform to correlate resistance and compliance based on age and gender to calculate SV
What is the equation for SVV?
SV max - SV min / SV mean
What is a normal SVV?
What is required to calculate SVV?
ventilated patient with stable RR and Vt 8cc/kg
When is SVV not accurate?
Severe tachycardia and dysrhythmias
2 descriptors of non-diverting sampling?
1. Gas is not removed from the circuit
2. Also called main-stream
2 descriptors of diverting sampling?
1. Gas IS removed from the circuit for analysis elsewhere
2. Also called side-stream
4 challenges of mainstream sampling?
1. Water vapor
4. More interfaces for disconnections
4 challenges of sidestream sampling?
1. Kinking of sampling tube
2. Water vapor
3. Failure of sampling pump
4. Leaks in the line
What is Dalton's Law?
The total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of each gas
What is mass spectrometry?
Concentration determined according to mass
How many gases can mass spectrometry calculate?
Up to eight different gases
What can mass spectrometry calculate?
Partial pressure from measured proportion (%)
What is the total partial pressure from ventilated patients?
What is normal ETCO2?
What does infared analysis calculate?
The number of molecules based on absorption of IR radiation (partial pressures)
What does more molecules mean with infrared analysis?
more IR radiation is absorbed and the more motion from IR (or partial pressure)
How must gas monitoring be calibrated?
For high and low concentrations
What does gas monitoring sampling inside the inspiratory limb give us? (2)
1. Ensures oxygen delivery
2. Analyzes hypoxic mixtures
What does gas monitoring sampling on the expiratory side give us? (2)
1. Ensures complete pre-oxygenation "denitrogenation"
2. ET O2 above 90% is adequate
Is there oxygen monitoring at auxiliary sites?
3 reasons for the low alarm with gas monitors
1. Pipeline crossover
2. Incorrectly filled tanks
3. Failure of a proportioning system
2 reasons for high alarms with gas monitors
1. Premature infants
2. Chemotherapeutics drugs such as bleomycin
What does airway pressure monitoring assess?
Patients mechanical and or spontaneous ventilation
What does airway pressure monitoring determine?
Presence of PEEP
3 descriptors of mechanical airway pressure gauges?
1. No recording data so no trends
2. No alarm system
3. Must be continually scanned
2 descriptors of electronic pressure gauges?
1. Built within ventilator or anesthesia machines
2. Alarm system is integrated
When are low peak inspiratory pressure alarms on?
When the ventilator is on
When does a low peak inspiratory pressure alarm go off?
When pressure does not exceed a preset minimum
Causes of low peak inspiratory pressure alarms? (5)
3. Vent failure
4. Leaks in system
5. OGT in lung on suction
What do you want to do if you see a low peak inspiratory pressure alarm?
Start at one end of circuit and trace it to another, the most common causes is for something to get disconnected
When is a high pressure alarm non-functional?
Pressure controlled ventilation
What is a high pressure alarm usually fixed at?
3 causes of high pressure alarms?
2. Reduced compliance
Describe sustained elevated pressure alarms
Pressure that remains elevated during respiratory cycle
3 causes of sustained elevated pressure alarms?
1. Improperly adjusted APL valve
2. Activation of oxygen flush system
3. Malfunctioning PEEP
What type of pattern does the reaction of a single muscle fiber to a stimulus follow?
What does the repose of the whole muscle depend on?
How many muscle fibers are activated
4 most common patterns of nerve stimulation?
3. Tetanic Stimulation
4. Post-tetanic stimulation
How many Hz is usually used for single twitch nerve stimulation?
What type of muscle relaxants do we see fade with?
Non-depolarizers such as Rocuronium
What is the TOF ratio?
4th twitch/1st twitch
What would be the issue with having no twitches?
Will be unable to reverse and giving something such as neostigmine could actually cause the block to be deeper
What do we expect to see with surgical blocks?
A couple of twitches
Describe the diaphragm and resistance to both types of NMBD? (3)
1. Needs up to 2x as much drug for identical block
2. Recovers faster than periphery
3. Onset of blocks is faster than adductor pollicis
What do we consider if we see the diaphragm moving before the thorax after NMBD reversal?
This does not indicate adequate ventilation!
What are the most sensitive muscles to paralysis?
Orbicularis occuli, masseter, upper airway
What most closely reflects laryngeal adductor muscle?
Corrugator supercilli of facial nerve
What does the EEG show us?
Summation of excitatory and inhibitory PSP's
How are electrodes placed for EEGs?
So that surface anatomy relates to cortical regions
Where are the odd numbers found with EEGs?
all are on the left side of the cranium
What does the "z" indicate with EEG electrodes?
midline along the central sulcus
EEG beta signal Hz for Awake?
> 13 Hz
EEG alpha signals Hz for Eyes closed?
EEG theta and delta signals showing depressed EEG?
Theta: 4-7 Hz
Delta: <4 Hz
What is a processed EEG a combination of?
16 channel EEG to 2-4 channels
What does an ideal EEG show?
What does the BIS monitor do?
Processes EEG signal to monitor LOC
What is the lag time of BIS monitors?
What was BIS monitor use proposed for?
To prevent intraoperative awareness
3 facts of the B-Unaware trial
2. Compared age-adjusted end-tidal MAC
3. to BIS 40-60, no significant difference
What is temperature mainly regulated by?
What is temperature control mediated by? (4)
Dopamin, norepinephrine, acetylcholine, prostaglandins
What nerve fibers generally detect cold?
What nerve fibers generally detect warmth?
What does temperature vary by?
3. Food intake
4. Thyroid function
5. Drugs such as alcohol, nicotine, anesthetics
Describe heat transfer significance in surgery as radiation
Major type of loss in surgical patients
Describe heat transfer significance in surgery as conduction
negligible, patients are on thick foam pads
Describe heat transfer significance in surgery as convection
negligible, rate of air speed in OR small
Describe heat transfer significance in surgery as evaporation
less than 10% in the absence of sweating
Initial temperature in GA?
What is the initial rapid decrease of temperature in GA due to? (3)
1. Volatiles causing direct vasodilation
2. Increases heat loss
3. Preferentially distributes more heat to periphery than core
Continual temperature drop due to GA occurs when and because of what
1. Heat loss exceeds production
2. Occurs hour 2-4
Describe the plateau phase of hypothermia with GA?
1. thermal steady state
2. Heat loss equals heat production leading to being unable to warm-up
3. Occurs 3-4 hours after anesthesia
4. Vasoconstriction prevents loss of heat from core but peripheral heat continues to be lost
5 factors associated with hypothermia in regional anesthesia such as epidural and spinals?
1. Decreases the threshold that triggers vasoconstriction
2. Induces vasodilation in the periphery below area of the block
3. Redistributes heat to periphery similar to GA
4. Decreases shivering threshold
5. Sedatives also inhibit thermoregulatory control
What is normal core temp?
37 degrees celsius or 98.6 F
5 complications associated with hypothermia
1. 3x the incidence of morbid cardiac outcome
2. 3x the incidence of wound infection
3. Impairs platelets, PT, and PTT function
4. Increase need for transfusion by 20%
5. Increases duration of NMB
4 benefits of hypothermia
1. Improved outcome during recovery from cardiac arrest
2. Protective against cerebral ischemia
3. More difficult to trigger MH
4. Reduces metabolism 6% per degree C
4 common sites for core temperature monitoring
3. Pulmonary artery
4. Tympanic membrane
5 factors associated with nasopharynx monitoring of temperature?
1. Close to hypothalamus
2. Not affected by inspired gas if intubated
3. Easy to find
4. Sensor must contact posterior wall
Where do we place esophageal monitoring for temperature?
lower 1/4 to 1/3 of esophagus between the heart and descending aorta
What temperature monitoring site could we have maximal heart sounds?
5 not so good sites of core temperature monitoring?
What is considered room temp?
70 degrees F = 21 degrees C
65 degrees F = 18 degrees C
What does a single blanket reduce heat loss by? 3 blankets?
1 = 30% reduction in heat loss
3 = 50% reduction in heat loss
What do we do with our ETCO2 to approximate PaCO2?
Add about 4 mmHg
What would be the issue with with approximating PaCO2 from ETCO2 in COPD patients?
COPD patients would have a higher PaCO2 than approximated due to increased alveolar dead space
5 physiological effects from hypercarbia?
1. Respiratory acidosis
2. Increase cerebral blood flow due to cerebral vasodilation
3. Increases ICP in susceptible patients
4. Increased pulmonary vascular resistance
5. Potassium shifts from intracellular to intravascular
4 physiological effects from hypocarbia?
1. Respiratory alkalosis
2. Decreased CBF
3. Potassium shifts to the intracellular space
4. Blunts normal urge to breathe
6 other things that ETCO2 informs us of other than ventilation
1. Pulmonary blood flow
2. Aerobic metabolism
3. ETT/LMA placement
4. Integrity of breathing circuit
5. Adequacy of cardiac output
6. VD to Vt
What is Bohr's equation?
VD/Vt = (PaCO2 - PeCO2)/(PaCO2)
What is capnometry?
The measurement and quantification if inhaled/exhaled CO2
What is capnography?
The method of measurement but also the graphic display or time of inhaled/exhaled CO2
What is the best method to confirm endotracheal intubation?
Detection of carbon dioxide breath-by-breath
Describe what you would see on a monitor to confirm ETT placement?
3 successive CO2 waveforms of the same height
3 descriptors of chemical indicators of ETT placement
2. Color change of pH sensitive paper
3. A type of capnometer, doesn't give waveform but does give quantitative information
Relate CO2 concentration to IR reaching the detector
The greater the CO2 in the sample, the less IR that reaches the detector
What is the issue with sidestream analyzers of CO2?
They have a delay time and rise time
4 CO2 monitor requirements?
1. CO2 reading within +/- 12% of actual value
2. Manufacturers must disclose interference caused by ethanol, acetone,, halogenated volatiles
3. Must have a high CO2 alarm for inhaled and exhaled CO2
4. Must have an alarm for low exhaled CO2
Two reasons for low exhaled CO2 alarm
2. No pulse
CO2 production/Delivery to Lungs causes of Increased PetCO2 (7)
1. Increased metabolic rate
6. Increased cardiac output
7. Bicarb admin
Equipment malfunction causes of increased PetCO2 (3)
2. Exhausted CO2 absorber
3. Faulty inspiratory/expiratory valves
Alveolar ventilation causes of increased PetCO2 (5)
2. Respiratory center depression
3. Neuromuscular disease
4. High spinal anesthesia
Equipment causes of decreased PetCO2 (4)
1. Ventilator disconnect
2. Esophageal intubation
3. Complete airway obstruction
4. Leak around ETT
CO2 Production/Delivery to lungs causes of decreased PetCO2 (5)
2. Cardiac arrest
3. Pulmonary embolism
Alveolar ventilation cause of decreased PetCO2?
What is the simple and most widely used technique for monitoring exhaled CO2?
What does the time capnogram display?
inspiratory and expiratory phases over time
Phase 1 of capnogram? (3)
2. Exhalation of dead space from central conducting airways
3. Essentially no CO2
Phase 2 of capnogram? (3)
2. Sampling of gases at transition of airway and alveoli
3. Normally steep
Phase 3 of capnogram? (3)
1. Plateau phase
2. Normally representative of CO2 in alveolus
3. Can be representative of ventilation heterogeneity
Phase 0 or 4 of capnogram? (2)
1. Inspiration of Fresh gas flow (FGF)
2. Remaining CO2 washed out
Where is ETCO2 measured?
End-point of phase 3 at the beta angle
Characteristics of capnogram of inadequate seal around ETT or faulty inspiratory valve (3)
1. Reduced plateau phase 3
2. No beta angle
3. Sloped phase 4 inspiratory phase
Characteristics of capnogram of hyperventilation (2)
1. Reduced inspiratory phase and expiratory phase over time
2. Seen during induction
Characteristics of capnogram of hypoventilation (3)
1. Increased expiratory upstroke
2. ETCO2 increases, alveoli will eventually collapse causing an increased risk of hypoxemia
3. Seen as the case goes on
Characteristics of capnogram of increased airway resistance (4)
1. P3 slope increased
2. P2 upstroke decreased
3. Beta angle and inspiratory phase normal at beginning but reduced over time
4. Shark fin appearance of wave
3 causes of increased airway resistance and which is the most common?
2. Increased Secretions
3. COPD (most common)
What type of patients is it normal to see cardiac oscillations on capnogram?
Characteristics of capnogram of patients re-breathing or soda lime exhaustion (2)
1. Doesn't return to baseline CO2
2. Should not be rebreathing CO2
Characteristic of capnogram for NMBD's wearing off?
Curare cleft, the patient doesn't finish inspiring like normal