Page 119 - Basic Monitoring in Canine and Feline Emergency Patients

VetBooks.ir Tissue cells Systemic capillary

CO 2
H O
CO 2 2
H 2 CO 3
Hb Hb-CO 2

Red
blood cell

Pulmonary capillary

Alveoli

H CO 3
2
H 2 O

CO 2 CO 2
Hb
CO 2
Hb-CO 2
Red
blood cell

Fig. 6.1. Carbon dioxide metabolism. Carbon dioxide is a metabolic byproduct produced by the tissue cells. While
some of the carbon dioxide remains dissolved in the plasma, most carbon dioxide diffuses into the red blood cells.
In the red blood cell, it either binds to water molecules and forms carbonic acid or binds to hemoglobin to form
carboxyhemoglobin. When the blood arrives in the lungs, the carbon dioxide diffuses into the alveoli. At the alveolar
level, the red blood cells are ‘unloading’ CO which is then expelled through the breathing process. CO , carbon
2
2
dioxide; H CO , carbonic acid; H O, water; Hb, hemoglobin; Hb-CO , carboxyhemoglobin.
2 3 2 2
During CPR, measurement of ETCO can relia- ventilatory status as well as information regarding
2
bly provide the clinician with information regard- the cardiac output and blood flow through the
ing the quality of chest compressions as well as an heart and pulmonary system.
indirect assessment of the cardiac output and the
blood flow through the heart and lungs. 6.2 How Capnography Works
In conclusion, measurement of the ETCO pro-
2
vides the clinician with two important pieces of There are two different ways to analyze the CO
2
information: indirect evaluation of the patient’s concentration: plotted against time (time capnogram)

Capnography 111