Week 8 Gas Analyzer + ABG Flashcards
1
Q
What is the sample port location for a gas analyzer?
A
At the Y-piece of the breathing circuit (closest to the patient).
2
Q
What is the primary function of a gas analyzer?
A
Continuously measures inhaled vs. exhaled gas concentrations.
3
Q
Why is gas analysis important?
A
Reveals how much gas is absorbed into the blood and helps assess how much volatile anesthetic reaches the brain indirectly.
4
Q
What does MAC stand for?
A
Minimum Alveolar Concentration.
5
Q
What does MAC reflect?
A
Anesthetic depth; it is more reliable than dial setting because it shows what’s actually in the lungs.
6
Q
What is Raman Scattering Analysis?
A
Infrared-based, but inaccurate in small tidal volumes, especially in pediatric cases.
7
Q
What is Mass Spectrometry?
A
Expensive, large, not portable, and no longer used in modern ORs.
8
Q
What is a Piezoelectric Analyzer?
A
Detects pressure changes but cannot distinguish specific gases.
9
Q
What is a Photoacoustic Analyzer?
A
Infrared-based, portable and accurate, but cannot measure O₂.
10
Q
How do gas analyzers measure gases?
A
Using the Beer–Lambert Law, which states that gases absorb specific wavelengths of infrared light.
11
Q
What is the principle behind Beer–Lambert Law?
A
Gases absorb specific wavelengths of infrared light, allowing the analyzer to determine gas concentration.
12
Q
Why does oxygen need a separate analyzer?
A
O₂ does NOT absorb infrared light, making it unmeasurable like anesthetic gases.
13
Q
What is a Galvanic Oxygen Analyzer?
A
Contains a lead anode and a gold cathode submerged in an electrolyte solution to measure O₂ levels.
14
Q
What is the core mechanism of a Galvanic Oxygen Analyzer?
A
O₂ diffuses through a semipermeable membrane and undergoes a redox reaction.
15
Q
What is a Paramagnetic Oxygen Analyzer?
A
Uses a magnetic field to attract oxygen molecules and measures concentration based on light reflection.
16
Q
What is the significance of MAC values?
A
Indicates the concentration of anesthetic needed to prevent movement in 50% of patients.
17
Q
What factors affect MAC?
A
Age, temperature, other CNS depressants, and pregnancy.
18
Q
What are the MAC values for common inhaled agents?
A
Sevoflurane: 2.0%, Isoflurane: 1.17%, Desflurane: 6.0%, N₂O: 104%.
19
Q
What does a higher MAC indicate?
A
Lower potency of the anesthetic.
20
Q
What is the clinical application of monitoring MAC?
A
To monitor for excessive anesthetic depth and adjust accordingly.
21
Q
What does blood gas analysis provide information about?
A
Oxygenation, ventilation, and acid-base balance.
22
Q
What does ABG stand for and what does it reflect?
A
ABG stands for Arterial Blood Gas and reflects lung function and gas exchange.
23
Q
What parameters are measured in ABG?
A
PaO₂, PaCO₂, pH, HCO₃⁻, Base Excess, lactate.
24
Q
What does VBG stand for and what is its limitation?
A
VBG stands for Venous Blood Gas and cannot assess oxygenation.
25
What is the clinical use of VBG?
Useful for trends in acid-base balance and CO₂ clearance.
26
What is Mixed Venous Blood Gas (SvO₂) and its significance?
Drawn from the pulmonary artery; provides a more accurate reflection of global tissue oxygen consumption and delivery compared to peripheral venous blood gas.
27
What direct measurements does blood gas analysis provide?
Ventilation and metabolic status via PaO₂, PaCO₂, and HCO₃⁻.
28
What are the normal ranges for pH?
7.35–7.45.
29
What does PaO₂ measure?
Oxygen dissolved in plasma.
30
What is the normal range for PaCO₂?
35–45 mmHg.
31
What does HCO₃⁻ indicate?
The body’s buffer system and metabolic compensation.
32
What is the normal range for lactate?
0.5–1.6 mmol/L.
33
What are the two mechanisms of oxygen transport?
Dissolved in plasma and bound to hemoglobin.
34
What is the formula for calculating CaO₂?
CaO₂ = (1.39 x Hb x SaO₂) + (0.003 x PaO₂).
35
What does the Alveolar Gas Equation relate to?
PaO₂ depends on FiO₂, barometric pressure, and ventilation.
36
What is the P/F Ratio and its normal value?
P/F Ratio (PaO₂/FiO₂) normal value is >400 mm Hg.
37
What does the Oxyhemoglobin Dissociation Curve illustrate?
The relationship between PaO₂ and SaO₂.
38
What does a right shift in the Oxyhemoglobin Dissociation Curve indicate?
Decreased affinity for oxygen, facilitating oxygen release.
39
What is hypoxia?
Low oxygen in tissues due to circulatory issues.
40
What is hypoxemia?
PaO₂ < 60 mmHg, low oxygen in blood due to pulmonary issues.
41
What are the three forms in which carbon dioxide is transported?
Dissolved in plasma, carbaminohemoglobin, and bicarbonate.
42
What happens to pH when CO₂ increases?
More H⁺ is produced, leading to lower pH (Acidosis).
43
What is the Haldane Effect?
Deoxygenated hemoglobin increases CO₂ carrying capacity.
44
What are the causes of hypercapnia?
Rebreathing CO₂, increased CO₂ production, and ventilatory depression.
45
What is a key consideration for blood gas sampling?
Use heparinized syringes and expel air bubbles immediately.
46
What is the first step in blood gas interpretation?
Check pH: Is it acidemia (<7.35) or alkalemia (>7.45)?
47
What is the mnemonic for blood gas interpretation?
ROME – Respiratory Opposite, Metabolic Equal.
48
What indicates respiratory acidosis?
pH ↓, PaCO₂ ↑, HCO₃⁻ normal/↑.
49
What indicates metabolic alkalosis?
pH ↑, PaCO₂ normal/↑, HCO₃⁻ ↑.
50
What is the expected compensation for acute respiratory acidosis?
HCO₃⁻ ↑ by 1 for every 10 ↑ PaCO₂.
51
When is ABG preferred over VBG?
When assessing oxygenation and precise respiratory function.
52
What indicates mixed acid-base disorders?
Normal pH with abnormal PaCO₂ and HCO₃⁻.
53
What type of anesthetic gas analyzer can measure oxygen?
A. A paramagnetic oxygen analyzer
B. A photoacoustic analyzer
C. A galvanic cell oxygen analyzer
D. A Ramen Scattering Analysis analyzer
Answer = A, C
Rationale – Oxygen is a paramagnetic substance that reacts to magnetic fields, which can
be measured by a paramagnetic oxygen analyzer (Elisha et al., 2023). A galvanic cell oxygen
analyzer uses oxygen as a reagent to drive a chemical reaction that generates an electrical
charge proportional to the amount of oxygen in the sample. The other two analyzers use
infrared light and cannot measure the oxygen concentration.
54
What does MAC 1.0 mean?
A. The percent concentration of an anesthetic gas at 1.0 atm necessary to induce
anesthesia.
B. The alveolar concentration needed to blunt the adrenal response to noxious
stimuli.
C. The percentage of anesthetic gas needed to saturate blood.
D. The minimum alveolar concentration needed to inhibit the movement in 50% of
patients in response to noxious stimuli.
Answer = D
Rationale – A MAC 1.0 refers to the minimum alveolar concentration needed to inhibit
movement in 50% of patients in response to a noxious stimulus (Elisha et al., 2023).
55
What does MAC-BAR represent?
A. The percentage concentration of an anesthetic gas needed to inhibit pain in 50%
of patients.
B. The potency of individual anesthetic gases.
C. The minimum areolar concentration of anesthetic gas that must saturate blood
in 50% of patients before inducing sedation.
D. The minimum areolar concentration necessary to blunt adrenal response to
noxious stimuli.
Answer = D
Rationale – MAC-BAR refers to the minimum alveolar concentration of anesthetic gas
needed to blunt the adrenal response in 50% of patients (Elisha et al., 2023)
56
Why does a galvanic oxygen analyzer need to be replaced every so often?
A. The high amounts of oxygen the analyzer is exposed to cause the cell to become
too hot.
B. The anode (lead) is eventually consumed by the continued chemical reaction.
C. The cathode (gold) is eventually consumed by the continued chemical reaction.
D. The galvanic cell requires increased amounts of electricity supplied by the
anesthesia machine which eventually melts the conductors.
Answer B
Rationale – Oxygen drives the chemical reaction that generates an electrical current (Elisha
et al., 2023). The strength of the electrical current is proportional to the amount of oxygen
the sensor is exposed to. This reaction consumes the anode (lead) and eventually needs to
be replaced.
57
How does a gas analyzer detect multiple gases simultaneously?
A. It cannot detect multiple gases simultaneously
B. It uses magnetic waves to measure the density of each gas
C. It reacts to the charged portions of each gas molecule and uses a complex
algorithm to calculate what each gas is.
D. It uses multiple wave lengths of inferred light to determine the concentration of
each gas by measuring the absorption of each wavelength.
Answer D
Rationale – Each gas absorbs a unique wavelength of inferred light (Elisha et al., 2023). By
using multiple wavelengths, the analyzer can determine the concentration of each gas by
measuring how much each wavelength of inferred light is absorbed.
58
Why does a galvanic oxygen analyzer need to be periodically replaced?
A. The electrolyte solution dries out.
B. The semipermeable membrane weakens and eventually ruptures.
C. The lead anode is eventually consumed by the reaction.
D. They never need to be replaced.
Answer C
Rational – The reaction releases electrons (voltage) due to the reaction of lead with
hydroxide (Elisha et al., 2023). This can be seen in chemical equation (2 Pb2+ + 4 OH- -> 2
PbO + 2 H2O + 4 e-). Eventually, all of the lead anode (Pb2+) is used to form PbO, which
means the reaction can no longer happen.
59
Select all that apply: Which of the following conditions are associated with increased
SvO₂ values?
A. Sepsis
B. Cyanide toxicity
C. Hemorrhage
D. Hyperthermia
E. Left-to-right shunt
Answer: A, B, E
Rationale: Increased SvO₂ can occur due to conditions that either increase oxygen
delivery or impair oxygen utilization. Sepsis and cyanide toxicity can reduce oxygen extraction,
leading to elevated SvO₂. Left-to-right shunts increase oxygenated blood flow to the venous
system, artificially elevating SvO₂. In contrast, hemorrhage and hyperthermia decrease SvO₂ due
to reduced oxygen delivery and increased metabolic demand, respectively (Elisha et al., 2
60
Which of the following statements about central venous oxygen saturation (ScvO₂) is
true?
A. ScvO₂ is measured at the junction of the superior vena cava and right atrium
B. ScvO₂ is always higher than SvO₂ under normal conditions
C. ScvO₂ includes blood flow from the superior vena cava, inferior vena cava, and
coronary sinus
D. ScvO₂ is a global indicator of venous oxygen saturation
Answer: A
Rationale: ScvO₂ is measured at the junction of the superior vena cava and right atrium
using modified central venous catheters. Unlike SvO₂, which reflects global venous oxygen
saturation, ScvO₂ primarily represents upper body and head venous return. Under normal
conditions, ScvO₂ is typically lower than SvO₂, not higher
61
A patient presents with respiratory acidosis. Which of the following arterial blood gas
(ABG) findings would be most consistent with uncompensated respiratory acidosis?
A. pH 7.28, PaCO₂ 55 mmHg, HCO₃⁻ 24 mEq/L
B. pH 7.35, PaCO₂ 55 mmHg, HCO₃⁻ 28 mEq/L
C. pH 7.42, PaCO₂ 30 mmHg, HCO₃⁻ 22 mEq/L
D. pH 7.28, PaCO₂ 40 mmHg, HCO₃⁻ 18 mEq/L
Answer: A
Rationale: Uncompensated respiratory acidosis is characterized by a low pH (<7.35) and
an elevated PaCO₂ (>45 mmHg) with a normal bicarbonate (HCO₃⁻). Option A meets these
criteria, as the kidneys have not yet had time to retain HCO₃⁻ for compensation (Elis
62
A base deficit can be calculated to determine bicarbonate replacement needs in a patient
with metabolic acidosis. Which of the following formulas correctly calculates bicarbonate
replacement?
A. (Patient’s HCO₃⁻ - Normal HCO₃⁻) × Weight (kg) × 0.3
B. (Normal HCO₃⁻ - Patient’s HCO₃⁻) × Weight (kg) × 0.3
C. (Normal HCO₃⁻ - Patient’s HCO₃⁻) × Weight (kg) × 0.6
D. (Normal HCO₃⁻ - Patient’s HCO₃⁻) × Weight (kg) × 1.0
Answer: B
Rationale: The total body bicarbonate deficit is calculated as:
(Normal HCO₃⁻ - Patient’s HCO₃⁻) × Weight (kg) × 0.3,
0.3 represents the volume of distribution for bicarbonate in extracellular fluid (Elish
63
Select all that apply: Which of the following mechanisms contribute to increased CO₂
production in the perioperative setting?
A. Fever
B. Malignant hyperthermia
C. Tourniquet release
D. Propofol administration
E. Thyroid storm
Correct Answers: A, B, C, E
Rationale: Fever and thyroid storm contribute to increased CO₂ production by elevating
the metabolic rate, leading to greater oxygen consumption and carbon dioxide generation.
Malignant hyperthermia results in a hypermetabolic crisis, causing massive CO₂ production due
to uncontrolled skeletal muscle contraction and increased cellular metabolism. When a
tourniquet is released, accumulated CO₂ from ischemic tissue is suddenly reintroduced into the
circulation, further increasing CO₂ levels. In contrast, propofol administration reduces metabolic
demand and does not contribute to increased CO₂ production (Butterworth et al., 2022).
64
A patient with sepsis has a temperature of 39.5°C and a PCO₂ of 50 mmHg. How will
their oxyhemoglobin dissociation curve shift?
A. Left shift
B. Right shift
C. No change
D. Flattened curve
Answer: B
Rationale: Hyperthermia (fever) and hypercapnia (high CO₂ levels) are associated with a
right shift in the oxyhemoglobin dissociation curve. This means hemoglobin has a reduced
affinity for oxygen, leading to enhanced oxygen unloading at the tissues, which is beneficial in
conditions with increased metabolic demand, such as sepsis (Pardo, 2023).
