Asa Monitors Capno Pulse Ox

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SECTION II.

Monitoring

8

Standard ASA Monitors

Trent Bryson, MD

In 1986 the American Society of Anesthesiologists (ASA) approved the first edition of Standards for Basic

Anesthetic Monitoring. Periodically these standards are updated according to advances in technology

and practice, the most recent being in 2005 (1). The standards are to be considered a minimum

during all general, regional, and monitored anesthetic care and may be exceeded at any time as

deemed necessary. These measures are to only be suspended when interfering with emergent life

supportive measures or in the rare instance when they are impractical or failing to detect clinical

developments.

Continuous presence of a qualified anesthesia provider is a standard set by the ASA.

1. Overview of required elements—Published standards address broad elements instead of specific

devices and are broken down into two required standards (2).

a. Standard I

i. The presence of a qualified anesthesia provider is continuously required throughout the duration of allanesthetic care due to the rapidity with which physiologic derangements may occur during surgical

intervention.

b. Standard II

i. Continual monitoring of oxygenation, ventilation, circulation, and temperature.

ii. Frequency of mandatory monitoring varies between each category, but never exceeds five minutes.

1. If not used, a reason should be recorded on the patient record.

iii. The following are all specifically mandated.

1. Oxygen analyzer with a low inspired concentration limit alarm during general anesthesia

2. Quantitative assessment of blood oxygenation

3. Ensuring adequate ventilation during all anesthetic care including verification of expired oxygen (when

possible), quantitativemeasurement of tidal volume, andcapnography in all general anesthetics.4. Qualitative evaluation of ventilation is required during all other care.

5. Ensure correct placement of endotracheal tube or laryngeal mask airway via expired carbon dioxide

(CO2).

6. Alarms for disconnects when a mechanical ventilator is used

7. Continuous display of ECG

8. Determination of arterial BP and heart rateat least every 5 minutes.

9. Adequacy of circulation is to be determined byquality of pulse either electronically, through palpation,

or auscultation

10. The means to determine temperature must be available and should be employed when changes in

temperature are anticipated or intended.

An audible alarm should be set to notify the anesthesia provider of a hypoxic gas mixture.

2. Oxygen analyzer

a. Most modern anesthesia machines monitor both inspired and expired concentrations of O2.

b. This is essential during anesthesia because it is possible to deliver a hypoxic gas mixture when mixing O2,

air, nitrous oxide, and/or volatile anesthetic agents.

3. Pulse oximetry

a. Provides quantitative analysis of the patient’s saturation of hemoglobin with O2.

Read More



Pulse oximetry Chapter 9 page 61

Capnography Chapter 10 page 65

4. Carbon dioxide (CO2)

a. Inspired and expired CO2 should be monitored.

b. Expired CO2 is frequently displayed through capnography with a displayed value correlating to the peak

expired CO2 of each breath.

c. Capnography

i. Provides qualitative and quantitative information regarding expired CO2.

ii. Quantitatively, this is useful to ensure the endotracheal tube is within the respiratory tract as well as

to ensure adequate cardiac output.

d. Inspired CO2

i. Monitored to ensure that the CO2 absorber of the anesthesia machine is adequately removing all

CO2from the circuit.

ii. If inspired CO2 is greater than zero, changing of the absorbent should be considered. The color of

absorbent turns blue when its capacity is exhausted.

EKG leads are color-coded to assist placement. RA and LA leads are easily remembered: imagine the LAbecomes suntanned (black) driving a car with the window open, while the RA remains untanned (white)

inside the car.

5. Multiple expired gas analysis

a. While not an essential monitor according to the ASA, this allows determination of the percent inspired

and expired of the volatile agents and nitrous oxide.

b. This allows the ability to better determine the delivery of an adequate anesthetic without over or under

dose.

6. ECG

a. The minimum of three leads is to be used, although five leads are used for most adults (3).

b. Consideration must be taken for the surgical field and patient positioning.

i.

Lead placement is commonly altered for cases involving the chest, shoulders, back, and neck.c. Five Lead ECG

i. Includes the right arm (RA), left arm (LA), right leg (RL), left leg (LL), and V.

ii. The five lead arrangement can be used to display I, II, III, aVR, aVL, aVF, and/or V (Fig. 8-1).

Figure 8-1 Normal Five Lead ECG Lead…

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d. Three lead ECG

i. Includes the RA, LA, and LL leads and can be used to display leads I, II, and/or III (Fig. 8-2).

1. A three lead ECG can be modified to display V5 by moving the LA lead to the V5 position in the fifth

intercostal space at the anterior axillary line (Fig. 8-3).

Figure 8-2 Normal Configuration of a Three…

Figure 8-3 Modification of Three Lead ECG…

e. The most commonly monitored leads are II and V5.

i. II is best used to monitor rhythm because it provides the best visibility of the P wave.

ii. V5 monitors for anterior and lateral ischemic events.

For most patients, printing the ECG tracing at the beginning of the case allows for later comparison

should an intraoperative event occur.

iii. Most anesthesia machines will allow you to change how many and which leads are displayed.

1. Some will show all leads simultaneously, although this often removes all other monitors from the display

while viewing all leads.

2. If an arrhythmia or ischemic event appears to be present, temporarily viewing all leads simultaneously

may be helpful for diagnostic purposes.

7. Arterial blood pressure (BP)







a. BP can be monitored invasively or non-invasively.

b. Non-invasive methods

i. Include palpation, ausculatation, Doppler probe, oscillometric cuff, or tonometry.

ii. Palpation, auscultation, Doppler, and tonometry are rarely employed and are not discussed here.

c. Automatic oscillometric

i. The cuff is able to sense oscillations in cuff pressure which correlate with arterial pulsation.

ii. The cuff is inflated beyond the point at which oscillation ceases and then is slowly deflated.

iii. The oscillation in cuff pressure begins at systolic pressure, peaks at mean arterial pressure and

disappears once again at diastolic pressure.

Patients in the beach chair position are especially prone to cerebral ischemia even with “normal”

brachial BPs.

iv. Due to the speed at which the cuff deflates, all three values are mathematically derived, with MAP

being the most accurate (Fig. 8-4).

v. vi. Figure 8-4 Illustration of Oscillometric…

vii. Placement

1. Each cuff is labeled with an arrow pointing to where arterial pulsation is felt best.

2. The cuff is then placed on the arm over the brachial artery, forearm over the radial artery, or thigh/calf

over the popliteal artery.

viii. Patient positioning

1. When monitoring non-invasive pressure, consideration must be taken of patient position.

ix. Invasive BP monitoring

Read More

Invasive arterial blood pressure monitoring,Chapter 11, page 70

8. Temperature

a. Temperature changes should be anticipated and expected under any general anesthetic and

therefore any general anesthetic requires temperature measurement. i. Very brief procedures may be an exception, but the availability of temperature monitoring should be

recorded.

b. The temperature may be measured from many locations including skin, nasopharynx, esophageal,

bladder, rectal, or a pulmonary arterial catheter.

c. Core temperatures obtained from a pulmonary catheter, esophageal stethoscope, or rectal probe are

preferable sources.

apter Summary for Standard Monitors


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References

1.

“Standards for Basic Anesthetic Monitoring,” last amended October 25, 2005. http://www.asahq.org2. Greenberg SB, Murphy GS, Vender JS. Standard monitoring techniques. In: Barash PG, Cullen BF,

Stoelting RK, et al., eds. Clinical Anesthesia. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins,

2009:702.

3. Morgan GE, Mikhail MS, Murray MJ, eds. Patient monitors. In: Clinical Anesthesiology . 4th ed. New York,

NY: McGraw Hill, 2006:117 –154.

9

Pulse Oximetry

Rachel Boggus, MD

Pulse oximetry is one of the most commonly employed monitoring modalities in anesthesia. It is a non-

invasive way to monitor the oxygenation of a patient’s hemoglobin. A sensor with both red and infrared

wavelengths is placed on the patient. Absorption of these wavelengths by the blood is measured and

oxygen saturation (SpO2) can be calculated.

1. Basic Concepts

a. Pulse oximetry measures the amount of oxyhemoglobin using the Lambert-Beer law

i. The Lambert-Beer law is a mathematical means of expressing how light is absorbed by matter

b. There are two main types of oximetry. Fractional oximetry and functional oximetry

i. Fractional oximetry.Oxyhemoglobin/(oxyhemoglobin + deoxyhemoglobin + methemoglobin +

carboxyhemoglobin)

ii. Fractional oximetry measures the arterial oxygen saturation (SaO2)

1. Can only be measured by an arterial blood sample

iii. Functional oximetry oxyhemoglobin/(oxyhemoglobin + deoxyhemoglobin) = SpO2

1. Functional oximetry gives you the SpO2

2. Can be measured noninvasively by a standard pulse oximeter

2. How pulse oximetry works

a. A pulse oximeter emits two wavelengths of light: red (660 nm) and infrared (940 nm)

i. Deoxyhemoglobin absorbs more light in the red band

ii. Oxyhemoglobin absorbs more light in the infrared band

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b. Sensors in the oximeter detect the amount of red and infrared light absorbed by the blood

c. Photoplethysmography is then used to identify pulsatile arterial flow (alternating current

[AC]) and non-pulsatile flow (direct current [DC])

d. The ratio of AC/DC at both 660 and 940 nm is measured using the equation: (AC/DC)660/(AC/DC)940

e. The pulse oximeter calculates the SpO2 by taking the above equation and using an algorithm built into

the software to derive the SpO2

i. The calibration to derive SpO2 from the (AC/DC)660/(AC/DC)940 ratio was made from studies of healthy

volunteers

SpO2 measurements are not accurate below 70%.

3. Accuracy of the pulse oximeter

a. If the SpO2 is between70% and 100% the pulse oximeter isaccurate to within 5%

i. It is not accurate below 70% because calibration of the pulse oximeter involved healthy volunteers

whose SpO2 did not routinely reach levels <70%

ii. For the relationship between SaO2 and PaO2 (see Fig. 9-1) (7)

iii. iv. Figure 9-1 The Oxygen-Hemoglobin Dissociation…

SpO2 of 90% correlates to a PaO2 of 60 mm Hg.

v. It is also not as accurate below 70% because there is moredeoxyhemoglobin present

1. The absorption spectrum of deoxygenated hemoglobin is very steep at 600 nm in the red range so small

changes in the amount of deoxyhemoglobin can cause very wide variances in SpO2 (Fig. 9-2)

2.







3. 4. Figure 9-2 Light Absorption with Oxygenated…

b. Ear probes may be more accurate than finger probes because the probe is closer to the heart

c. Table 9-1 Low Amplitude StatesPulse oximetry is not as accurate in low amplitude states (Table 9-1)

i. Low perfusion makes it difficult for the pulse oximeter to distinguish a true signal from backgroundnoise

4. Dyshemoglobinemias

a. Pulse oximetry only accurately measures oxyhemoglobin and deoxyhemoglobin—all other forms of

hemoglobin are not accurately measured

i. Carboxyhemoglobin is measured as 90% oxyhemoglobin and 10% deoxyhemoglobin

1. Thus, when there are high amounts of carboxyhemoglobin it will overestimate the SpO2

2. This is an important consideration in patients exposed to smoke or fires

ii. Methemoglobin absorbs equal amounts of red and infrared light so the SpO2 will read 85%

1. Methemoglobin is formed when iron goes from it’s+2 ferrous form to the +3 ferric state

2. The ferric state of iron displays a left shift on the oxygen dissociation curve and releases oxygen less

easily3. Table 9-2 Causes of MethemoglobinemiaMethemoglobinemia can be caused by many drugs (Table 9-2)

iii. Patients with sickle cell anemia presenting in a vasoocclusive crisis can have an inaccurate SpO2reading

iv. High levels of bilirubin do not alter SpO2 readings

5. Other Limitations

a. IV dyes

i. Methylene blue, indocyanine green, and indigo carmine all cause transient decreases in the

SpO2 lasting anywhere from 30 seconds to 20 minutes

b. Dark skin pigmentation—melanin inhibits passage of light through tissue

c. Motion artifact—pulse oximeter unable to measure peaks and troughs of waveform correctly

d. Fluorescent light—fluorescent light emits wavelengths in the 660 nm region which interferes with the

red band of the pulse oximeter

e. Nail polish—inhibits passage of light through nail.

apter Summary for Pulse Oximetry

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References

1. Huch A, Huch R, Konig V, et al. Limitations of pulse oximetry. Lancet 1988;1:357 –358.

2. Juban, A. Pulse Oximetry. Crit Care. 1999;3(2):R11 –R17.

3. Schnapp LM, Cohen NH. Pulse oximetry-uses and abuses.Chest 1990;98:1244 –1250.

4. Tremper KK, Barker SJ. Pulse oximetry. Anesthesiology .1989;70:98 –108.

5. Welch JP, DeCesare MS, Hess D. Pulse oximetry: instrumentation and clinical applications. Respir Care.

1990;35:584 –601.

6. Wukitisch MW, Peterson MT, Tobler DR, et al. Pulse oximetry: analysis of theory, technology, and

practice. J Clin Monit . 1988;4:290 –301.7. Martin, Lawrence. All you really need to know to interpret arterial blood gases. 2nd ed. Lippincott

Williams & Wilkins, 1999.

8. “Red and infrared light absorption.” Oximetry.org. Web. Mar 8,

2010.http://www.oximeter.org/pulseox/principles.htm.

10

Capnography

Jessica Spellman, MD

Monitoring of CO2 through capnometry and capnography can be a valuable tool in detecting acute

alterations in ventilation, metabolism, and circulation. Continuous monitoring of CO2 is an AmericanSociety of Anesthesiology (ASA) standard for basic monitoring in all patients receiving general anesthesia

(unless invalidated by the nature of the patient, procedure, or equipment) and for confirming proper

endotracheal tube and LMA placement (1).

Capnography is continuous monitoring of a patient’s capnogram during the respiratory cycle.

1. Definitions (2)

a. Capnometry

i. Measurement and numeric representation of CO2concentration or partial pressure in respiratory gases

during inspiration and expiration

b. Capnogram

i. Concentration time display of CO2 concentrationsampled at a patient’s airway

c. Capnography

i. Continuous monitoring of a patient’s capnogram during the respiratory cycle

2. Methods of capnometry (3)

a. Sidestream capnometers

i. Sample tubing connected to the airway that continually aspirates respiratory gases at a rate of 50 to 400

mL/min to a measurement chamber

ii. Advantages

1. Allows for accurate capnography when attached as close as possible to the patient

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2. Lightweight

3. Can be used to measure CO2 and anesthetic gases

iii. Disadvantages

1. Condensation of humidified gases may cause frequent clogging of the tubing (water traps and filters

must be used to prevent condensation from reaching the measuring chamber)

2. Delay in measurement response time depending on the size and length of the tubing

b. Mainstream capnometers

i. Light absorption chamber directly attached to the airway

ii. Advantages

1. Direct measurement allows for fast response time

iii. Disadvantages

1. Bulky equipment placed directly in endotracheal tube

2. Does not allow for measurement of anesthetic gases

3. Techniques of CO2 measurement (4)

a. Infrared spectrography

i. Employed by most operating rooms

ii. In the measuring chamber, gases are exposed to aninfrared light beam

iii. Each molecule (CO2, anesthetic gases) has a specific absorbance spectrum of the infrared beam that canbe quantified

Colorimetric CO2 analysis is often used to confirm CO2and endotracheal intubation outside of the

operating room.

b. Mass spectrography

i. Measurement of CO2and other gas concentrations on the basis of differing molecular weights

c. Raman spectrography

i. Use of spectral analysis of scattered light energy that results from an argon laser light source exposed to

a gas mixture

d. Colorimetric CO2 analysis (5)

i.

pH sensitive test paperii. When in the presence of CO2, color change occurs

iii. Often used to confirm CO2 and endotracheal intubation outside of the operating room

4. Normal capnogram (6)

5. (Fig. 10-1)





a. Phase I

i. Initiation of expiration

ii. CO2-free gas from anatomic dead space

b. Phase II

i. Expiration of mixture of dead space and alveolar gas

c. Phase III

i. Alveolar plateau

ii. CO2-rich gas from alveoli

d. Phase IV or 0 (7)

i. Inspiration

Figure 10-1 Phases of a Normal Capnogram Reproduced…

6. Clinical uses of capnography (4)

a. Confirmation of endotracheal intubation

Capnography can be used to monitor the adequacy of ventilation in controlled or spontaneously

ventilating patients.

b. Monitoring ofadequacy of ventilationin controlled or spontaneously ventilating patients

c. Noninvasive estimate of PaCO2

i. Assumes the normal 2 to 5 mm Hg difference between expired (PETCO2) and arterial (PaCO2) that existsin the awake state is present

ii. The gradient between PETCO2 and PaCO2 may be increased with age, pulmonary disease, pulmonary

embolus, low cardiac output, and hypovolemia

d. Detection of patient disease

i. Causes of increased CO2 production

1. Fever

2. Sepsis

3. Malignant hyperthermia

4. Hyperthyroidism

5. Shivering

ii.

Causes of decreased PETCO2 1. Decreased cardiac output

2. Hypovolemiaism

3. Pulmonary embolism

4. Hypothermia (6)

5. Hyperventilation (6)

iii. Airway obstruction may be detected due to abnormalities in the capnography tracing

Causes of increased CO2production include: fever, sepsis, malignant hyperthermia, shivering.

Causes of decreased CO2production include: decreased cardiac output, hypovolemia, pulmonary

embolism, hypothermia, hyperventilation.

e. Detection of problems with the anesthetic breathing system i. Rebreathing

ii. Incompetent valves

iii. Circuit disconnect

iv. Circuit leak

7. Interpretation of abnormal capnograms(3,4,6) (Fig. 10-2)

a. Rebreathing of CO2

i. Elevation in baseline CO2 and Phase I





ii. Can eliminate by increasing fresh gas flow or changing CO2 absorber

b. Obstruction to expiratory gas flow

i. Prolonged Phase II and steeper Phase III slope

ii. Occurs with bronchospasm, COPD, kinked endotracheal tube

c. “Curare Cleft”

i. Dip in Phase III

ii. Indicates return of spontaneous respiratory efforts

d. Cardiogenic oscillations

i. Oscillations of small gas movements during phase III and IV (or 0)

ii. Produced by aortic and cardiac pulsations

e. Increased CO2

i. Elevated plateau height

ii. Indicates increased CO2 production states (see above), other source of CO2 (as in laparoscopic surgery),

or inadequate minute ventilation

f. Decreased measured CO2

i. Decreased plateau height

ii. May indicated decreased CO2 production state (see above) or increased minute ventilation

g. Incompetent inspiratory valve i. Prolonged Phase III with elevation of baseline CO2and plateau height

ii. Results in rebreathing

iii. May be difficult to detect without simultaneous analysis of flow waveforms (7)

h. Esophageal intubation

i. Initial presence of CO2 followed by no CO2 detection

j. Figure 10-2 Abnormal Capnograms Reproduced from…

apter Summary for Capnography



References

1. American Society of Anesthesiology. Standards for Basic Anesthetic Monitoring. [Internet]. Park Ridge,

IL: American Society of Anesthesiology, 2005 Oct 25, c2008. [cited 2010 Jul 7].

2. Greenberg SB, Murphy GS, Vender JS. Standard monitoring techniques. In: Barash PG, ed. Clinical

Anesthesia. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009:697 –700.

3. Szocik JF, Barker SJ, Tremper KK. Fundamental principles of monitoring instrumentation. In: Miller RD,

ed. Miller’s Anesthesia. 6th ed. Philadelphia, PA: Elsevier, 2005:1213.

4. Bhivani-Shankar K, Moseley H, Kumar AY, et al. Capnometry and anaesthesia. Can J Anaesth.

1992;39:617 –632.

5. Moon RE, Camporesi EM. Respiratory monitoring. In: Miller RD, ed. Miller’s Anesthesia. 6th ed.

Philadelphia, PA: Elsevier; 2005:1454.

6. Eisenkraft JB, Leibowitz AB. Hypoxia and equipment failure. In: Yao, FS, ed. Yao & Artusio’s

Anesthesiology: Problem-Oriented Patient Management . 6th ed. Philadelphia, PA: Lippincott Williams &

Wilkins; 2008:1184 –1187.

7. Bhavani-Shankar K, Philip JH. Defining segments and phases of a time capnogram. Anesth

Analg 2000;91:973 –977.

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Asa Monitors Capno Pulse Ox