Lecture 8: Pulmonary Intraop Monitoring/Difficult Airway Algorithm Flashcards
940 nm
Infrared light, oxyhemoglobin absorbs more of this light, corresponds to 100% saturation
660 nm
Red light, deoxyhemoglobin absorbs more of this light, corresponds to 50% saturation
Very rough rule—PaO2 40, 50, 60 for sat ___, ___, ___
70, 80, 90
Sat 100, PaO2 ___
100
Sat 95, PaO2 ___
75
Sat 90, PaO2 ___
60
Sat 75, PaO2 ___
40 (mixed venous blood in pulmonary artery)
Sat 60, PaO2 ___
30
Sat 50, PaO2 ___
27
Can a standard pulse ox. Be used in MRI?
No—may burn patient, dedicated MRI probe needed
Endobronchial intubation will usually go undetected by pulse ox. In…
The absence of lung disease or low FiO2
Limitations of pulse ox—hemoglobin variants
Carboxyhemoglobin (COHb)
Methemoglobin (MetHb)
Carboxyhemoglobin
- From CO poisoning
- CO is viewed as oxyhemoglobin by pulse ox. And shows a SPO2 of 100% (overestimation of oxygenation)
What is used to distinguish between oxyhemoglobin and carboxyhemoglobin?
A co-oximeter
Methemoglobin
Fe 2+ (ferrous) in Hb is oxidized to Fe 3+ (ferric) form and cannot transport O2
Methemoglobin—Cyanosis seen when ___ of Hb is in methemoglobin form
15%
Methemoglobin is caused by…
- Nitrates
- Nitrites
- Sulfonamides
- Benzocaine (hurricane spray)
- Nitroglycerine (NTG)
- Nitroprusside (SNP)
Methemoglobin—does it absorb equally at both wavelengths?
Yes—1:1
Methemoglobin—shows a SPO2 of ___ regardless of true oxygen saturation
85%
Treatment for methemoglobin
Methylene blue or ascorbic acid
What two things do not affect pulse oximetry?
Fetal hemoglobin and bilirubin
Severe hypoxemia—poor accuracy at SPO2 < ___
30%
Pulse ox won’t function well if Hb < ___
3-4 gm/dL
Pulse ox is designed to assume pulsation are ___
Arterial—why right heart failure (for pulmonale) or tricuspid regurgitation disturb SPO2, seen in dependent (down) limb
What dyes interfere with SPO2?
Methylene blue and idocyanine green—will drop SPO2 for 5-10 minutes
Malpositioned sensor effect on SPO2
Penumbra effect, shows SPO2 of 90-95%
Capnography rapidly and reliably indicates ___ but does not reliably detect ___
Esophageal intubation, endobronchial intubation
What is the gold standard for tracheal intubation?
+ ETCO2
Capnometer
Measures CO2
Capnograph
Records and displays CO2
Not all capnometers display a ___
Capnogram
All capnographs are in part ___
A capnometer
CO2 is depicted graphically as a ___
Capnogram
CO2 is recorded by a ___
Capnograph
CO2 is measured by a ___
Capnometer
Normal capnograph components
AB segment BC segment CD segment D point DE segment
AB segment =
Beginning exhalation, dead space gas
BC segment =
Upstroke
Exhalation, mixing of gases (dead space + alveolar gas)
CD segment =
Alveolar plateau, alveolar rich gas
D point =
Highest CO2–end tidal CO2 measurement
DE segment =
Start inspiration
Shark fin ETCO2
Obstructive pattern—COPD, bronchospasm
Curare cleft
Early spontaneous breath
Normal end-tidal CO2 to arterial CO2 gradient (dCO2) is ___
2-5 mm Hg
ETCO2/arterial CO2 (dCO2) gradient reflects…
Alveolar dead space—alveoli ventilated but not perfused
What increases dCO2?
Any significant reduction in lung perfusion/increases in alveolar dead space
PaCO2 will always be ___ than ETCO2 due to ___
Higher, d/t mixing and dilution with the dead space gases
Causes of increased dCO2 (7):
- Decreased pulmonary artery pressure
- Upright posture
- Pulmonary emboli (PE)—air, fat, thrombus, amniotic fluid
- COPD—causes no vascular air spaces at alveolar level
- Mechanical obstruction of pulmonary artery
- Ventilated gas leaving normal pathway—cuff leak, tracheal disruption, bronchopleural fistula
- Decreased CO or hypotension
Causes of increased ETCO2 (9):
- Malignant hyperthermia
- Hypoventilation
- Bicarbonate
- Laparoscopy (CO2 inflation)
- Hyperthermia
- Improved blood flow to lungs after hypotension or resuscitation
- Tourniquet released
- Water in capnograph sensor
- Breathing circuit error—CO2 absorber exhausted, rebreathing, inadequate fresh gas flow, faulty valves in circuit
Causes of decreased ETCO2 (9):
- Hyperventilation
- Airway leak, leak around cuff
- Decreased blood flow to lungs
- Pulmonary embolism
- Decreased CO, arrhythmia
- Incipient pulmonary edema
- Hypothermia
- Inadequate sample volume
- Sample catheter misplaced
What is malignant hyperthermia?
Rare, inherited skeletal muscle syndrome
MH presents as a ___
Hypermetabolic reaction
MH is triggered by…
Exposure to volatile anesthetic gases or depolarizing muscle relaxant (succinylcholine)
Incidence of MH
1/5,000-1/100,000
Early signs of MH (11):
- Abrupt increase in ETCO2
- Cardiac arrhythmias
- Generalized muscle rigidity
- Hypoxia
- Profuse sweating
- Trismus/masseter muscle rigidity (MMR)
- Metabolic-respiratory acidosis
- Mottling of the skin
- Tachycardia
- Tachypnea in spontaneously breathing patients
- Unstable arterial pressure
Late signs of MH (11):
- Acute renal failure
- Circulatory failure
- Dark colored urine due to myoglobinuria
- Disseminated intravascular coagulation
- Elevated blood creative phosphokinase (CPK) levels
- Elevated blood myoglobin levels
- Hyperkalemia
- Hyperthermia (> 38.8 degrees Celsius)***
- Hypotension
- Rhabdomyolysis
- Severe cardiac arrhythmias and cardiac arrest
Treatment of MH
Dantrolene
Initial dose of dantrolene
2.5 mg/kg
Alternative to dantrolene
Ryanodex 2.5 mg/kg—expensive
