Page 125 - Basic Monitoring in Canine and Feline Emergency Patients

classic capnographs) can result in erroneous ETCO return of spontaneous circulation. A declining or
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measurements and distorted waveforms. Also, low- low ETCO value during CPR may suggest rescuer
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VetBooks.ir flow sample rates minimize dispersion of gases in fatigue or ineffective chest compressions by the res-
the sampling tubes and there is a less likely chance
cuer. It should also alert the clinician to seek other
of aspirating condensed water and secretions mini-
which are rendering chest compressions less suc-
mizing the chances of occlusion. factors contributing to declining cardiac output or
cessful such as ongoing hemorrhage, cardiac tam-
ponade, or pneumothorax.
6.3 Indications for Capnography
in Small Animals
Feeding tube placement
Anesthesia or heavy sedation
Although, radiography remains the ‘gold standard’
The use of a capnograph along with pulse oximetry, method to confirm proper placement of
electrocardiogram, and blood pressure monitoring is nasoesophageal/gastric feeding tubes, capnography
recommended in every patient that undergoes gen- can be used as an adjunct technique. The partial
eral anesthesia or heavy sedation. Becoming familiar pressure of CO in the stomach and esophagus is
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with the normal as well as abnormal waveforms negligible. Therefore, the ETCO value should be
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provided by the capnograph, the clinician/technician zero in correctly placed feeding tubes and higher if
can gain a rapid visual evaluation of ventilation in the tube is mis-placed in the airways.
the anesthetized patient as well as detect problems
encountered along the way. More detail regarding
waveform interpretation is provided in Section 6.4. Upper airway emergencies
Capnography may be beneficial in patients who
require intubation to treat life-threatening upper
Cardiopulmonary resuscitation
airway obstruction or severe upper airway inflam-
As mentioned at the beginning of this chapter, the mation (i.e. brachycephalic syndrome, laryngeal
measurement of ETCO provides the clinician with paralysis, etc.). In most cases, these patients have
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two important pieces of information: an overview received a large volume of sedation and/or anxio-
of the patient’s ventilatory status as well as an idea lytic drugs prior to and in order to facilitate intuba-
of the cardiac output and the blood flow through tion, including but not limited to propofol, opioids,
the heart and pulmonary system. benzodiazepines, alpha-2 agonists, and aceproma-
Since ETCO is proportional to pulmonary zine. It is important to monitor the ETCO in these
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blood flow (the better the blood flow, the more patients to ensure that they are not hypercapnic as a
CO is delivered to the alveoli to breathe out), result of respiratory depression from the sedation/
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ETCO can be used as a measure of chest compres- anesthesia. If hypercapnia is noted, these patients
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sion efficacy during CPR assuming the ventilations may need manual or mechanical ventilation until the
administered are unchanging in rate and size of drugs wear off or can be reversed and their ventila-
breath. During cardiopulmonary arrest there is no tory drive returns.
blood flow nor ventilation. When closed chest com-
pressions are performed, very few alveoli are per-
fused because the blood flow to the lungs is low. By Mechanical ventilation
providing manual ventilation with an AMBU bag, In all patients being mechanically ventilated, it is
many alveoli are ventilated but are not perfused. useful to monitor paired PaCO and ETCO val-
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During this time the ETCO will be low. If the ues. If the ETCO is proved to be representative of
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blood flow to the lungs improves (CPR is success- the PaCO by comparison to the arterial blood gas
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ful and return of spontaneous circulation is analysis in a particular patient, changes in ETCO
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achieved), more alveoli will be perfused and subse- may be assumed to signify similar changes in
quently the ETCO will increase. PaCO . In that way the noninvasive ETCO allows
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During chest compressions in CPR, the goal the patient to avoid numerous arterial punctures (if
value of ETCO should be above 15–20 mmHg. an arterial catheter is not in place already) and the
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Lower values have been associated with a signifi- expense of running multiple blood gas analyses.
cant decrease in the likelihood of the patient having The capnograph also provides a continuous display
Capnography 117