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Accuracy of Capnography in Nonintubated Surgical Patients
Section snippets
PATIENTS AND METHODS
After obtaining Human Subjects Committee approval, 25 patients admitted to the surgical/trauma intensive care unit for perioperative care were studied. There were 15 men and 10 women between the ages of 18 and 71 years. Only those with a pulmonary artery flotation catheter previously inserted for cardiovascular or hemodynamic management, or both, were included. All were extubated and breathing spontaneously with or without supplemental oxygen.
Measurements on an individual patient were completed
RESULTS
Twelve study patients were weaned from mechanical ventilation and extubated within 24 h prior to entry into the protocol; the remaining 13 were admitted to the surgical ICU for either preoperative monitoring or for potential intubation and ventilatory support following trauma. Individual values of PaCO2, PetCO2, P(a-et)CO2, FIo2, Vd/Vt, and Qs/Qt are listed in Table 1.
Simultaneous PaCO2 and PetCO2 values are graphed in Figure 1. A correlation between the two was observed (r = 0.61, p<0.001;
DISCUSSION
In patients with normal lungs, ventilation and perfusion are well matched (V/Q≈0.8). The partial pressure of CO2 at the end of expiration (PetCO2) is almost equal to that of the blood leaving the pulmonary circulation. However, when aberrations occur in the Va/Q distribution, PetCO2 may not accurately reflect PaCO2. This is particularly true in mechanically ventilated patients with underlying respiratory disease in whom ventilation of some lung units may be high relative to the amount of blood
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Manuscript received December 16, 1991; revision accepted April 16.