measuring and interpreting vital signs

8/18/2019 Measuring and Interpreting Vital Signs

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light waves absorbed by the carbon dioxide.10

PETCO2 correlates to the partial pressure of carbon dioxide in the blood (PaCO2), but only if ventilation and perfusion are stable. If either are unstable, a

V/Q (ventilation/perfusion) mismatch occurs, and the PETCO2 and PaCO2 correlation changes, making the PETCO2 less reliable. This can occur withhypovolemia or a pulmonary embolism.

Note: An oxygen mask may lower the reading by 10% or more.

Capnogram

The capnogram waveform begins before exhalation and ends with inspiration, meaning that breathing out comes before breathing in. It is important to notethat the referenced documentation, as well as common capnography devices, interchanges the terms PETCO2 and ETCO2.

Capnogram Waveform13

The normal capnogram waveform is nearly rectangular, with each section representing the amount of CO2 in the exhalation process. Exhalation begins withalveolar emptying of CO2, which then mixes with dead-space gases. The plateau at the top represents the rich mixture of CO2 released by the alveoli. The

peak before the drop represents ETCO2, with the quick drop representing inhalation.

An increase in height in the waveform indicates an increase in ETCO2, while a drop in the height indicates a drop in ETCO2 levels. If ETCO2 readings areelevated, then CO2 levels are elevated; if ETCO2 levels are low, then the body is not producing adequate amounts of CO2.

Intubation

Capnography is a reliable way to insure endotracheal (ET) tube placement.14,15


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Capnogram Showing an ET Tube in the Esophogus16

If a patient is intubated properly, with the tube through the vocal cords, a normal waveform will appear on the capnogram. Should the tube becomes

dislodged, the waveform changes immediately, allowing for timely correction.

An intubated patient who is not adequately paralyzed or is completely comatose may try to breathe around the ET tube. The movement of the diaphragm isindicated by a notch or a “curare cleft” in the waveform.

Capnogram in Real Time17

Note: A cleft can also indicate a partial disconnection of a mainstream sensor. ALWAYS check the equipment before a determination is made.

Airway Blockages

Capnography can detect an obstructed or partially obstructed airway. Airway blockages release CO2 at a slower rate, causing a slope in the waveform. Thistype of capnogram waveform is loosely identified as a “shark fin.” The sharper the slope, the more severe the airway occlusion.


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Capnogram Shark Fin Waveform18

Hyperventilation

Since the width of the waveform represents the expiratory time, faster ventilations will compress the waveform, while slower ventilations will widen thewaveform.

Capnogram Hyperventilation Waveform19

Hyperventilation lowers ETCO2 values. Since ETCO2 relates closely to the carbon dioxide levels in the blood, low levels may also indicate metabolism

failure. Low carbon dioxide is a state of respiratory alkalosis, which can result in metabolic acidosis.

Hypoventilation

An ETCO2 reading of less than 35 mmHg equals hyperventilation/hypocapnia (alkaline), while an ETCO2 greater than 45 mmHg represents hypoventilation /hypercapnia (acid). Too much CO2 means too little oxygen.


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Capnogram Hypoventilation Waveform20

Other factors that cause an increase in ETCO2 include medications, rising body temperature, CO2 absorption, foreign body airway obstruction, and reactive

airway disease. Responses from ACLS medications may cause changes in the capnogram.21

Errors

Like other machines and electronics, capnography units can fail or have errors. Always check the patency of the circuit before making a decision based uponcapnography. Use this in conjunction with other assessment tools. Remember to treat the patient, not the monitor.

Additional Vital Signs That Should Be Measured

While the next two topics, level of consciousness and blood glucose levels, are not traditionally known as vital signs, they can provide even more keys to apatient’s condition and, when used properly, will greatly assist you in the assessment and treatment of your patients.

Level of Consciousness

Perhaps the most important considerations are level of consciousness and mental status. These are normally evaluated within the first few seconds of contact with your patient. A patient’s level of consciousness is assessed by evaluating responsiveness to you, while mental status is assessed by determining

the patient’s orientation to his or her surroundings and events.9 An unresponsive or disoriented patient may be experiencing a severe life-threatening

condition and needs immediate treatment – time is of utmost importance. Responsiveness is evaluated by utilizing the simple mnemonic of AVPU.

A Alert, the patient is alert and awake (eyes are open) and is able to respond to questions. The patient isalert, but may not be orientated to person, place, time, and event.

V Verbal, the patient is able to respond to verbal stimulus when spoken to (i.e. the patient’s eyes may beclosed but may open when asked questions, or the patient may respond inappropriately).

P Pain, if the patient is not alert and does not respond to verbal stimuli, attempt to obtain a reaction topain from your patient. Common methods for adults are the sternal rub, pinching the earlobes or

fingertips. Does the patient awaken or moan? Or does he or she attempt to stop the painful stimuli, suchas trying to move or push the object away? Was the movement intentional or reactionary? If the patientresponds, then he or she is responsive to pain.

U Unresponsive, the patient is non-responsive to all attempts to elicit a response.


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Image: ET in Esophogus. Illustration by Barbara Power, reviewed by Dr. Robert Pringle, CE Solutions. Accessed 5/2011.16.Image: Cleft. Illustration by Barbara Power, reviewed by Dr. Robert Pringle, CE Solutions. Accessed 5/2011.17.

Image: Shark Fin. Illustration by Barbara Power, reviewed by Dr. Robert Pringle, CE Solutions. Accessed 5/2011.18.Image: Decreasing ETCO2. Illustration by Barbara Power, reviewed by Dr. Robert Pringle, CE Solutions. Accessed 5/2011.19.

Image: Increasing ETCO2. Illustration by Barbara Power, reviewed by Dr. Robert Pringle, CE Solutions. Accessed 5/2011.20.Book Chapter: Holmes, N., Robinson, J., et al. 2007. Respiratory Care. In Best Practices: Evidence Based Nursing Procedures, 2nd Edition. Ambler, PA:

Lippincott Williams & Wilkins, Ch. 6, p. 299.

21.

Journal Article: Van Weerden, G. 1962. Some Clinical Applications of Capnography. The Journal of Medical Electronics, 7:9.22.

measuring and interpreting vital signs

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