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Lumb & Jones, 6th Ed. > Chp. 14: Monitoring Ventilation > Flashcards

Chp. 14: Monitoring Ventilation Flashcards

1
Q

Respiration

A

Cellular utilization of oxygen in the process of generating energy in the form of ATP

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2
Q

Aerobic respiration

A

Glycolysis of carbohydrates in cytoplasm in presence of oxygen > Pyruvate moves into mitochondria > conversion to acetylCoA > enters TCA cycle > oxidative phosphorylation (electron transport chain and chemiosmosis)

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3
Q

Where is the PCO2 highest?

A

Mitochondria

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4
Q

PACO2 equation

A

PACO2 = [VCO2 x 0.863] / VA

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5
Q

What is the impact of increased CO2 on acid-base status?

A

High CO2 results in higher H2CO3 formation and generation of H+ ions, leading to acidemia and a compensatory increase in HCO3-.

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6
Q

What are the potential physiologic consequences of hypercapnic acidemia?

A

Catecholamine release and tachyarrhythmias, increase CO, electrolyte shifts (eg. hyperkalemia), rightward shift of O2-Hgb dissociation curve, cerebral vasodilation

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7
Q

What are the potential physiologic consequences of hypocapnic alkalemia?

A

Cerebral and myocardial vasoconstriction with decreases in blood flow, decreased CO, leftward shift of O2-Hgb dissociation curve, hypokalemia, predisposition to arrhythmias

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8
Q

If a patient has a fixed airway obstruction, what happens to RR and inspiratory phase?

A

RR decreases and the inspiratory phase is longer

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9
Q

If a patient has alveolar or pleural space disease, what happens to RE and lung sounds?

A

Increased RE and increased lung sounds (pneumonia) or decreased lung sounds (pleural fluid).

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10
Q

Capnometry

A

Measurement of the partial pressure of CO2 in respiratory gas

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11
Q

Capnometer

A

Diagnostic tool that measures partial pressure of CO2 in respiratory gas

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12
Q

Capnogram

A

Cyclical waveform of respiratory gas CO2 plotted agains time or expired volume

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13
Q

Capnography

A

Continuous analysis and recording of the measurement of partial pressure of CO2 in respiratory gases over time or expired volume

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14
Q

Capnograph

A

Instrument that analyzes CO2 in respiratory gases and displays a capnogram

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15
Q

What is the major information gained from an apnea monitor?

A

Presence of inhalation/exhalation and a respiratory rate

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16
Q

What is the most reliable primary method for identifying whether an ETT is correctly placed within the airway?

A

Capnometry/capnography

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17
Q

What is the gold standard for PaCO2 analysis?

A

Arterial blood gas

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18
Q

How does a blood gas measure CO2?

A

A glass electrode covered with a CO2 permeable membrane is used (Severinghaus electrode). CO2 diffuses across the permeable membrane into a bicarbonate solution. Carbonic acid is created and devolves into H+ and HCO3-. pH (generation of H+ ions) is logarithmically related to the concentration of CO2 in the sample, creating a voltage difference between the glass electrode and reference electrode.

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19
Q

When is colorimetry useful for CO2 measurement?

A

To determine endotracheal intubation, predict ROSC, for ventilation monitoring over many hours when quantitative methods unavailable

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20
Q

What is the wavelength at which CO2 has the strongest absorption band?

A

4.3 um

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21
Q

What two molecules may cause cross-interference with CO2 measurement via infrared spectroscopy?

A

N2O and water vapor

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22
Q

Beer-Lembert Law

A

Absorption of IR radiation at the specified wavelength is proportional to the concentration of the molecule being measured

A = elc

A is absorbance
e is the molecular absorption coefficient
l is the length of the optical path
c is the molecular concentration

23
Q

What is a blackbody emitter?

A

A broadband source of IR radiation where filters are utilized to eliminate IR outside the desired range. A chopping action creates a time-varying signal, which is important for separating the desired IR signal from any background noise or interference.

24
Q

Describe microstream technology, a narrowband IR source.

A

A glass electrode containing several gases, including nitrogen and CO2, is expose to a radio frequency voltage. Nitrogen molecules experience excitation and their interaction with CO2 causes excitation of those molecules. When CO2 returns to its resting state, it emits radiation, which is used as the narrow spectrum IR source.

25
Q

What is the effect of water vapor on CO2 measurement?

A

If it condenses at the sample cell, it will absorb IR radiation and lead to a falsely increased CO2 readings.

26
Q

What solutions exist to limit water vapor interference with CO2 readings?

A

Heating of sensors, water traps, absorbent filters, and specialized permeable tubing.

27
Q

What is collision broadening?

A

Causes apparent increases in CO2 due to the molecular interaction with cases such as N2O and O2, which result in widened absorption spectra.

28
Q

Mainstream capnometry

A

Utilizes IR technology with the sensor placed between the patient and the breathing system.

29
Q

Advantages of mainstream capnometry

A

Rapid response times, higher accuracy with small tidal volumes and faster respiratory rates, no need to separately scavenge sampled gases, no waste of inhalant agents

30
Q

Disadvantages of mainstream capnometry

A

Added weight and mechanical headspace to airway with limited adaptability, susceptibility to damage, secretions on cuvette window causing interference with readings

31
Q

Sidestream capnometry

A

Airway adapters are attached to a long sampling line to connect to the sample cell housed within a distant monitor. Samples are constantly aspirated at variable rates (50-200mL/min). Water permeable tubing, filters, and water traps are used to limit water vapor contamination.

32
Q

Advantages of sidestream capnometry

A

Lightweight ETT adapter, minimize deadspace, protected sensor within monitor housing, ability to monitor ETCO2 in non-intubated patients with nasal catheters

33
Q

Disadvantages of sidestream capnometry

A

Delay time (based on sampling rate), need for rerouting of sampled gas (scavenged or returned to circuit), potential for issues with sampling line or water trap devices

34
Q

Raman Spectroscopy

A

A high-intensity argon laser is applied to a gas sample. The laser causes excitation of the molecules within the sample, creating an altered energy state. When the molecules return to their stable state, energy is emitted in a signature specific to that molecule, known as “Raman scatter radiation.” Provides a finerprint-like spectrum. Not currently used in clinical settings.

35
Q

Mass Spectroscopy

A

Measures components of a gas mixture based on mass and charged. Sample is exposed to an electron beam and ionized fragments are then accelerated by an electrical field and separated by a magnetic field. Detectors then measure individual sample components. Impractical for clinical use.

36
Q

Transcutaneous CO2 measurement

A

Non-invasive. Heated electrochemical sensors are placed on the skin. CO2 diffuses through the skin and is measured at the surface. A Severinghaus electrode is used to assess CO2 concentration (like blood gas). OVERestimates in cats, sheep, and dogs.

37
Q

What are the four phases of the capnogram?

A

Phase 0: Inspiratory phase or inspiratory downstroke. Represented by rapid downswing in expiratory CO2 partial pressure. Rapidly reaches zero in a normal waveform.

Phase I: Respiratory baseline. Marks start of expiration and represents emptying of anatomic deadspace, which is CO2 free.

Phase II: Expiratory upstroke. Continued exhalation of a mixture of alveolar gas and deadspace gas from the conducting airways.

Phase III: Alveolar plateau. Continued exhalation of alveolar gas creates a gradually elevating line due to uneven alveolar emptying. Peak of plateau represents ETCO2 at end of exhaled tidal volume.

38
Q

What are the two angles found on the capnogram?

A

alpha angle: Transition from phase II to phase III. Should be approximately 100 degrees. Represents transition from airway gas to alveolar gas.

beta angle: Transition from phase III to phase 0. Should be approximately 90 degrees. Here, ETCO2 is measured.

39
Q

ETCO2 underestimates PaCO2 by how much?

A

Approximately 1-7mmHg in small animals. May be greater in large animals.

40
Q

What factors account for the discrepancy between ETCO2 and PaCo2?

A

Presence of a constant anatomic deadspace

Concentration gradient of CO2 between pulmonary capillary and alveolus

41
Q

What can cause rebreathing of CO2?

A

Dysfunctional one-way valve in breathing circuit, exhausted CO2 absorbent canister, significant amount of mechanical headspace, insufficient oxygen flow rate in a non-rebreathing circuit.

42
Q

Name a respiratory-based intervention for hyperkalemia treatment under GA and describe the mechanism of effect.

A

Hyperventilation. Increased CO2 leads to an increase in H+ concentration in the blood. These ions are exchanged for K+ to maintain electroneutrality, leading to an increase in serum K+. Hyperventilation minimizes this phenomenon.

43
Q

What are the limitations of ETCO2 in anesthetized horses? How can this be improved?

A

There can be significant changes in V/Q matching, resulting in wide variation in P(a-ET)CO2. These differences are improved with controlled ventilation. Capnometry should be paired with blood gas analysis.

44
Q

Why is ETCO2 interpretation limited in reptiles?

A

Adaptation of intracardiac shunting.

45
Q

In birds, what causes a negative P(a-ET)CO2 gradient?

A

Unidirectionalal gas flow and gas exchange occurring through a cross-current mechanism

46
Q

Volumetric capnography (VCap)

A

Plots exhaled CO2 against expired volume, allowing for determination of physiologic deadspace (the sum of anatomic and alveolar deadspace), effective alveolar tidal volume, and volume of CO2 eliminated per breath.

47
Q

Draw a volumetric capnogram

A
48
Q

Provide a diagnosis and rationale for the following capnogram.

A

Normally shaped with elevated plateau, indicative of hypoventilation.

49
Q

Provide a diagnosis and rationale for the following capnogram.

A

Obstruction to exhalation resulting in obtuse alpha angle. May be caused by upper or lower airway issues.

50
Q

Provide a diagnosis and rationale for the following capnogram.

A

Rapid reduction in the alveolar plateau to near zero in the absence of a change in ventilation indicates poor pulmonary perfusion or CV collapse.

51
Q

Provide a diagnosis and rationale for the following capnogram.

A

Capnogram with a baseline that does not return to zero. Prevented with properly functioning anesthetic equipment.

52
Q

Provide a diagnosis and rationale for the following capnogram.

A

Obtuse beta angles indicating dilution of ETCO2 with CO2 free gas and may be due to high sampling rate, leak around the ETT cuff, or high fresh gas flows in a non-rebreathing circuit.

53
Q

Provide a diagnosis and rationale for the following capnogram.

A

Spontaneous ventilatory efforts during mechanical ventilation. When decrease in CO2 concentrations is noted during phase III, it is called a “curare cleft.”

54
Q

Provide a diagnosis and rationale for the following capnogram.

A

Cardiogenic oscillations included on an obtuse beta angle accompanied by oscillations in downstroke. Occurs more frequently at slow RR. Thought to be due to mixing of inspired and expired gas in the trachea due to mechanical activity of heart.

Lumb & Jones, 6th Ed. (17 decks)

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