How To Set Up Capnography

Capnography is a swell manner to confirm airway device placement and monitor ventilation, just it can do and then much more. Carbon dioxide (CO₂) is a production of metabolism transported via perfusion and expelled through ventilation. End-tidal carbon dioxide (EtCO₂) waveform monitoring allows you lot to measure all three simultaneously, making it the almost important vital sign you use.¹

To evaluate the metabolism, ventilation and perfusion of a patient through EtCO₂ waveform monitoring you need to read the PQRST: proper, quantity, rate, shape and tendency.

Proper ways that you should know the normal readings for quantity, rate, shape and trending of EtCO_ii. In this case, normal means what we find in a healthy person with no metabolism, ventilation or perfusion problems. One of the keen things virtually EtCO_two is that although ventilation rates vary based on age, normal readings for quantity, shape and trends are the same for men and women of all historic period groups, making them piece of cake to remember.

Quantity; target EtCO₂ value should be 35-45 mmHg.

Rate of ventilation should be 12-twenty breaths per infinitesimal (bpm) for adults if the patient is breathing on their ain and 10-12 bpm if yous're ventilating them. Children should be ventilated at a charge per unit of fifteen-30 bpm; 25-50 bpm for infants. Ventilating likewise quickly won't let enough CO₂ build up in the alveoli, resulting in lower EtCO_ii readings. Ventilating besides slowly volition permit extra CO₂ to build up, resulting in higher readings.

Shape of the waveform should usually be a rectangle with rounded corners. Unlike waveform shapes tin can indicate different conditions.

Trending of the quantity, rate and shape of EtCO₂ should be stable or improving.

Although reading EtCO₂ waveforms can be piece of cake, interpreting what you encounter requires agreement how the waveforms and numbers are produced.

An end-tidal capnography waveform measures and
displays the peak amount of CO₂ at the end of exhalation.

Reading the Waves

When it comes to capnography, everyone knows the normal adult respiratory charge per unit of 12-twenty breaths per infinitesimal and most people know, or quickly learn, that the normal quantity of exhaled CO₂ is 35-45 mmHg. What can be intimidating is the idea of reading the shape of the waveform, but in practice information technology'south not difficult at all.

An end-tidal capnography waveform is a simple graphic measurement of how much CO_two a person is exhaling. The normal end-tidal capnography wave form is basically a rounded rectangle.² (See Figure 1, p. 48.) When a person is breathing out CO₂, the graph goes upward. When a person is animate in, it goes back down.

Phase 1 is inhalation. This is the baseline. Since no CO_ii is going out when a patient is breathing in, the baseline is unremarkably cypher.

Phase 2 is the beginning of exhalation. CO₂ begins to travel from the alveoli through the anatomical dead space of the airway causing a rapid ascent in the graph equally the CO_two.

Phase 2 measures the exhaled CO_two from the alveoli mixed with the gas that was in the dead space. This part of the graph goes up as the more concentrated CO₂ gases from lower in the lungs rise up by the sensor.

Phase 3 is when the sensor is receiving the CO₂-rich gas that was in the alveoli. Because this is a fairly stable amount, the graph levels off into a plateau. The measurement at the terminate of the tide of respiration, the superlative measurement at the very stop of phase 3, is the EtCO₂ reading.

Later on the end of stage 3, the patient inhales again, bringing clear air past the sensor, dropping the graph back downward to zero to start over once more at phase one.

Although it can be intimidating to try and memorize what each phase (and the angles betwixt them) represents, you tin can remember of it as follows: The left side shows how rapidly and hands air is moving out of the lungs; the correct side shows how apace and hands air is going in; the top shows how easily the alveoli are emptying.

If all nosotros wanted to read from capnography was ventilation, this would be plenty, but to indirectly measure a patient's perfusion and metabolic condition we must empathize how CO₂ gets to the lungs to be exhaled.

Putting on the Pressure

Many factors touch how oxygen gets into the torso and CO_ii gets out; withal, the biggest influence is the partial pressures of these gasses.

Although hemoglobin, myoglobin and other body chemicals play a office in transporting gasses, it can be helpful to brainstorm by just picturing the partial pressures pushing the gasses from one office of the trunk to the adjacent.³

The normal partial force per unit area of oxygen in ambient air is approximately 104 mmHg. It gets humidified and absorbed by the body equally it'southward inhaled, bringing the partial pressure down to 100 mmHg by the time the oxygen reaches the alveoli. The partial pressure of oxygen in the alveoli is known equally PaO₂.

Oxygen is then pushed from the fractional pressure of 100 mmHg in the alveoli to the lower partial pressure level of 95 mmHg in the capillaries surrounding the alveoli. Oxygen gets carried through the circulatory arrangement, getting absorbed along the way.

Past the time the oxygen gets to the end of its journeying, it has a partial pressure of approximately 40 mmHg, withal high enough to allow it to movement into muscles and organs that accept a lower partial pressure of approximately xx mmHg.four (Run into Figure 2, p. 49.)

If the organs are functioning normally, the oxygen is metabolized, producing the CO_two that we're ultimately going to measure. Although the journey back involves CO₂ moving primarily through the body's buffer arrangement as bicarbonate (HCO3-) its movement is still largely governed past partial pressures.^three

The fractional pressure of carbon dioxide (PCO₂) every bit it leaves the organs is approximately 46 mmHg, just loftier enough to push it into the capillaries which have a partial force per unit area of merely 45 mmHg.⁴ CO₂ travels through venous circulation largely untouched.

In the cease it moves from 45 mmHg at the capillaries surrounding the alveoli into the alveoli themselves. From the alveoli to exhalation the CO_two is approximately 35-45 mmHg.⁴ At this level information technology will go exhaled and measured by the EtCO₂ sensor, letting us know that the patient'due south metabolism, perfusion and ventilation are all working properly taking upward oxygen, converting information technology to CO₂ and releasing it at a normal rate (or not).

If you were to know one more matter about oxygen and CO₂ transport, it'south that high CO₂ reduces the affinity of hemoglobin for oxygen. Referred to as the Bohr effect, during normal body function this is a skillful thing, (the high CO₂ in muscles and organs aid hemoglobin release needed oxygen). However, prolonged periods of high CO₂ and associated acidosis make it hard for hemoglobin to pickup and send oxygen. This can be seen as a shift of the oxyhemoglobin dissociation curve to the correct.^4,5 (See Figure 3, p. l.)

Conversely, if the patient has low CO_two, perhaps because of hyperventilation, it volition crusade an increased affinity for oxygen, allowing hemoglobin to pick oxygen up more than hands. Notwithstanding, if the depression CO₂ is prolonged, the hemoglobin may not release the oxygen into the organs. This is referred to as the Haldane issue and is seen every bit a shift of the oxyhemoglobin dissociation bend to the left. In this example you may take a "normal" pulse oximetry reading even though organs aren't getting the oxygen considering hemoglobin is saturated with oxygen, just this oxygen remains "locked" to the hemoglobin.^four,5 In this manner your EtCO_two reading can help you lot ameliorate translate the validity and meaning of other vital signs like pulse oximetry, blood pressure and more.

Oh! PQRST

At present that we've peeked behind the curtain every bit to how CO_two is produced in metabolism and transported via perfusion, let's use the PQRST (proper, quantity, charge per unit, shape and trending) method to different types of emergency calls.

We read PQRST in social club, asking, "What is proper?" Consider what your desired goal is for this patient. "What is the quantity?" "Is that because of the rate?" If so, attempt to correct the rate. "Is this affecting the shape?" If so, right the status causing the irregular shape. "Is in that location a trend?" Make sure the trend is stable where you want it, or improving. If not, consider changing your current treatment strategy.

Below are several examples.

Advanced Airway/Intubation

P: Ventilation. Confirm placement of the advanced airway device.^6,seven

Q: Goal is 35-45 mmHg.

R: 10-12 bpm, ventilated.

Southward: Most flat-line of apnea to normal rounded rectangle EtCO_two waveform. (See Figure 4a, p. 50.) If the pinnacle of the shape is irregular (e.1000., like two unlike EtCO_ii waves mashed together) it may indicate a problem with tube placement. (See Figure 4b, p. 50.) This shape tin point a leaking cuff, supraglottic placement, or an endotracheal tube in the right mainstem bronchus. This shape is produced when one lung-often the correct lung-ventilates first, followed past CO_two escaping from the left lung. If the waveform takes on a near-normal shape (see Effigy 4c, p. 50) and so the placement of the advanced airway was successful.⁸

T: Consistent Q, R and South with each jiff. Watch for a sudden drop indicating displacement of the airway device and/or cardiac arrest. (See Figure 4d, p. l.)

Cardiac Arrest

P: Ventilation and perfusion. Confirmation of effective CPR. Monitoring for render of spontaneous circulation (ROSC) or loss of spontaneous circulation.^1,six,7,9

Q: Goal is > 10 mmHg during CPR. Expect it to be as loftier as 60 mmHg when ROSC is achieved. (See Figure v, p. 50.)

R: 10-12 bpm, ventilated.

Southward: Rounded low rectangle EtCO₂ waveform during CPR with a loftier fasten on ROSC.

T: Consequent Q, R and Southward with each breath. Lookout for a sudden spike indicating ROSC or a sudden drop indicating displacement of the airway device and/or re-occurrence of cardiac arrest.

Optimized Ventilation

P: Ventilation. May include hyperventilation situations such as anxiety as well every bit hypoventilation states such as opiate overdose, stroke, seizure, or head injury.^1,6,7

Q: Goal is 35-45 mmHg. Control using rate of ventilation. If EtCO₂ is low (i.e., being blown off as well fast), brainstorm by assisting the patient to exhale more slowly or by ventilating at 10-12 bpm. If EtCO₂ is high (i.e., accumulating likewise much betwixt breaths), begin past ventilating at a slightly faster rate.

R: Goal is 12-20 bpm for spontaneous respirations ; 10-12 bpm, for artificial ventilations.

S: Rounded depression rectangle EtCO₂ waveform. Faster ventilation will produce moving ridge shapes that aren't as wide or as alpine since rapid exhalation doesn't take as long and contains less CO₂. (See Figure 6a, p. 51.) Slower ventilation produces wave shapes that are wider and taller as exhalation takes longer and more than CO_ii builds up betwixt breaths. (See Effigy 6b, p. 51.)

T: Consistent Q, R and S with each breath trending towards optimal ventilation.

Shock

P: Metabolism and perfusion. Equally perfusion decreases and organs become into daze-whether hypovolemic, cardiogenic, septic or another type-less CO₂ is produced and delivered to the lungs, so EtCO₂ volition go downwardly, even at normal ventilation rates. In the context of shock, EtCO₂ can assistance differentiate between a patient who's anxious and slightly confused and one who has altered mental condition due to hypoperfusion. It can also bespeak a patient whose metabolism is significantly reduced past hypothermia, whether or not information technology's stupor-related.^1,seven,x,11

Q: Goal is 35-45 mmHg. EtCO₂ < 35 mmHg in the context of shock indicates meaning cardiopulmonary distress and the need for aggressive treatment.

R: Goal is 12-twenty bpm for spontaneous respirations; 10-12 bpm for artificial ventilations. Anxiety and distress can heighten the patient's respiratory charge per unit. Likewise, it may crusade a provider to ventilate too fast. Consider that faster rates will also lower EtCO₂, and may also increment pulmonary venous pressure, decreasing blood render to the middle in a patient who'southward already hypoperfusing.^{half dozen}

S: Rounded low rectangle EtCO_two waveform.

T: Quantity will continuously trend down in shock. The rate of ventilations will increase in early on compensatory daze then decrease in after non-compensated shock. The shape will not change significantly considering of the daze itself. (See Figure 7, p. 51.)

Pulmonary Embolism

P: Ventilation and perfusion. Using EtCO₂ along with other vital signs can aid you identify a mismatch betwixt ventilation and perfusion.

Q: Goal is 35-45 mmHg. EtCO_two < 35 mmHg in the presence of a normal respiratory charge per unit and otherwise normal pulse and blood pressure may signal that ventilation is occurring, but perfusion isn't as the embolism is preventing the ventilation from connecting with the perfusion. This is a
ventilation/perfusion mismatch.¹²

R: Goal is 12-20 bpm for spontaneous respirations; 10-12 bpm for artificial ventilations.

S: Low, rounded rectangle EtCO₂ waveform.

T: Every bit with stupor, the quantity will continuously trend down as the patient'south hypoperfusion worsens.

Asthma

P: Ventilation. Although the classic "shark's fin" shape is indicative of obstructive diseases like asthma, EtCO₂ can provide additional information about your patient.^7,8

Q: Goal is 35-45 mmHg. The tendency of quantity and charge per unit together can assistance indicate if the disease is in an early or late and
severe phase.

R: Goal is 12-20 bpm for spontaneous respirations; ten-12 bpm for bogus ventilations.

S: Tiresome and uneven emptying of alveoli
will cause the shape to slowly curve upwards (phase 3) resembling a shark'due south fin (if the shark is swimming left) instead of the normal rectangle. (See Figure 8, p. 51.)

T: Early on the trend is likely to be a shark'due south fin shape with an increasing rate and lowering quantity. As hypoxia becomes severe and the patient begins to go exhausted, the shark'southward fin shape volition continue, but the charge per unit will slow and the quantity volition rise equally CO_two builds up.

Mechanical Obstruction

P: Ventilation. The "shark's fin" low-expiratory shape is nowadays but is "aptitude" indicating obstructed and slowed inhalation likewise.^viii

Q: Goal is 35-45 mmHg.

R: Goal is 12-20 bpm for spontaneous respirations; 10-12 bpm for artificial ventilations.

Southward: Again, dull and uneven emptying of alveoli mixed with air from the anatomical "dead infinite" will cause the shape to slowly curve up resembling a shark's fin looking left instead of a rectangle. In this case, phase iv inhalation is blocked (e.one thousand., past mucous, a tumor or foreign torso airway obstacle) causing the righthand side of the rectangle to lean left, similar the shark is trying to swim left even faster. (See Effigy 9.)

T: Again, every bit hypoxia becomes astringent and the patient begins to get exhausted, the shark'south fin shape volition keep, but the rate will boring and the quantity will ascent every bit CO_two builds upward.

Emphysema & Pneumothorax

P: Ventilation. Patients with emphysema may accept so much harm to their lung tissue that the shape of their waveform may "lean in the wrong direction." In a similar way, patients with a pneumothorax won't be able to maintain the plateau of phase 3 of the EtCO₂ wave. The shape will commencement high and then trail off as air leaks from the lung, producing a like, high on the left, lower on the right shape.^8,thirteen

Q: Goal is 35-45 mmHg.

R: Goal is 12-twenty bpm for spontaneous respirations; 10-12 bpm for artificial ventilations.

S: An indication of very poor surface expanse for emphysema or leaking alveoli in pneumothorax is that the pinnacle of rectangle slopes down from left to right instead of sloping gradually up. (See Effigy 10.)

T: Consistent Q, R and S with each jiff as always is our goal. You should watch for and correct deviations.

Patient with Diabetes

P: Ventilation and perfusion. EtCO_ii tin can assistance in differentiation between hypoglycemia and diabetic ketoacidosis. Sometimes the difference is obvious, simply in other situations, every diagnostic tool can aid.

Q: Goal is 35-45 mmHg.

R: Goal is 12-20 bpm for spontaneous respirations. A hypoglycemic patient is likely to accept a relatively normal rate of respiration. A patient who's experiencing diabetic ketoacidosis will have increased respirations, lowering the quantity of CO_two. In addition, CO₂ in the course of bicarbonate in the blood will exist used up by the body trying to buffer the diabetic ketoacidosis. In this fashion, low EtCO₂ can aid indicate the presence of significant ketoacidosis.^1,viii,14

S: Rounded rectangle EtCO₂ waveform.

T: Consistent Q, R and S with each jiff for hypoglycemia. A fast charge per unit of respirations and depression quantity for DKA.

Significant Patients & Poor Lung Compliance

P: Ventilation. In addition to using EtCO_ii in the ways described higher up, patients with poor lung compliance, obese patients and pregnant patients may also exhibit a particular moving ridge shape that may indicate that they're highly sensitive on adequate ventilation.⁸

Q: Goal is 35-45 mmHg.

R: Goal is 12-xx bpm for spontaneous respirations; x-12 bpm for artificial ventilations.

S: Rounded low rectangle EtCO₂ waveform, but with a sharp increase in the angle of phase 3 that looks like a modest uptick or "pig tail" on the righthand side of the rectangle, sometimes referred to every bit phase 4 of the waveform. This is CO₂ existence squeezed out of the alveoli by the poorly compliant lung tissue, obese chest wall, or pregnant belly, before the same weight closes off the small bronchi. These patients are progress quickly from respiratory distress to respiratory failure.

T: Consistent Q, R and South with each breath.

Summary

The PQRST method is designed to be a simple and practical way to expand the use of EtCO₂ equally a diagnostic tool, but it's by no means the end of the story.

When used with patients who take been administered paralytics or who are on ventilators, other waveforms can help providers finetune their critical care past identifying medication bug such as inadequate sedation or malignant hyperthermia, mechanical bug such as air leaks and ventilator rebreathing, and physiological bug such as ventilation/perfusion mismatch weather.^3,12

Although no single vital sign is definitive, as a simultaneous mensurate of metabolism, ventilation and perfusion, end-tidal waveform capnography is one of the well-nigh important diagnostic tools available to EMS providers.

Acknowledgment: Special thanks to Patrick Holland, LP, and David Bunting, RRT, AEMT, MS, for their assistance with this article.

References

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2. Bhavani-Shankar K, Philip JH. Defining segments and phases of a time capnogram. Anesth Analg. 2000;91(iv):973-7.

3. American Academy of Orthopaedic Surgeons. Nancy Caroline's emergency intendance in the streets. Jones & Bartlett Learning: Burlington, Mass., 2022.

4. OpenStax. (March half dozen, 2022.) Anatomy and physiology. Retrived May 20, 2022, from www.opentextbc.ca/anatomyandphysiology.

5. Desai R. (2017.) Bohr effect vs. Haldane event. Khan Academy. Retrieved May 20, 2022, from world wide web.khanacademy.org/
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7. DiCorpo JE, Schwester D, Dudley LS, et al. A wave as a window. Using waveform capnography to attain a bigger physiological patient picture show. JEMS. 2022;forty(xi):32-35.

8. Yartsev A. (Sep. 15, 2022.) Abnormal capnography waveforms and their interpretation. Deranged Physiology. Retrieved May xx, 2022, from world wide web.derangedphysiology.com/chief/cadre-topics-
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9. Potato RA, Bobrow BJ, Spaite DW, et al. Association between prehospital cpr quality and end-tidal carbon dioxide levels in out-of-hospital cardiac arrest. Prehosp Emerg Care. 2016;20(three):369-377.

10. Guerra WF, Mayfield TR, Meyers MS, et al. Early detection and handling of patients with severe sepsis by prehospital personnel. J Emerg Med. 2022;44(vi):1116-1125.

eleven. Hunter CL, Silvestri South, Ralls G, et al. A prehospital screening tool utilizing end-tidal carbon dioxide predicts sepsis and severe sepsis. Am J Emerg Med. 2016;34(5):813-819.

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xiv. Bou Chebl R, Madden B, Belsky J, et al. Diagnostic value of cease tidal capnography in patients with hyperglycemia in the emergency department. BMC Emerg Med. 2016;16:seven.

Source: https://www.jems.com/patient-care/how-to-read-and-interpret-end-tidal-capnography-waveforms/

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