Noninvasive measurement of tissue carbon dioxide tension using a fiberoptic conjunctival sensor: effects of respiratory and metabolic alkalosis and acidosis

Sidestream capnographic monitoring reduces the incidence of arterial oxygen desaturation during propofol ambulatory anesthesia for surgical abortion

BACKGROUND

This study investigated whether early intervention based on additional use of sidestream capnography could reduce the incidence of oxygen desaturation and hypoxic events in patients receiving propofol anesthesia during surgical abortion.

MATERIAL/METHODS

We recruited 704 ASAI-III female patients, 18-52 years old and scheduled for planned painless surgical abortion, and randomized them into a control group (n=359) receiving standard monitoring and an experimental group (n=341) receiving standard monitoring and additional capnography. Exclusion criteria were preexisting cardiovascular disease, preexisting hypotension, bradycardia or arrhythmia, and drug allergy. Anesthesia was induced in all patients with propofol using target-controlled infusion at a target propofol plasma concentration of 4 μg/ml. All patients received flurbiprofen axetil 50 mg and 0.5 μg/kg fentanyl 5 min before anesthesia. Bispectral index was used and maintained between 45 and 60. Main outcome measures were apnea or abnormal ventilation status, rate of oxygen desaturation, occurrence of hypoxia and severe hypoxia, and perioperative side effects.

RESULTS

The experimental group had significantly higher rate of apnea or abnormal ventilation, significantly lower rate of oxygen desaturation, and significant lower occurrence of hypoxia and severe hypoxia compared to the control group. We found no statistically significant differences between the 2 groups in the rates of increased oxygen supplementation, assisted ventilation, bradycardia, hypotension, dosage of atropine, dosage of ephedrine or phenylephrine, and the amount of propofol consumed.

CONCLUSIONS

Sidestream capnographic monitoring improves early detection of alterations in ventilation parameters and reduces the incidence of oxygen desaturation and hypoxemia resulting from propofol anesthesia during surgical abortion.

Capnometry in emergency medicine

Capnometers measure carbon dioxide (CO2) in expired air and provide clinicians with a noninvasive measure of systemic metabolism, circulation, and ventilation. If two of these systems are held relatively constant, changes in CO2 excretion will reflect the third. CO2 measurement has been advocated as a method of ensuring endotracheal intubation. Because the air in the esophagus has very low levels of CO2, the use of capnometers may help prevent unrecognized esophageal intubation in prehospital and emergency department settings. In patients with normal perfusion and ventilation, end-tidal CO2 measurements closely reflect alveolar PCO2. Capnometry may decrease the need for frequent arterial blood gas measurements. A sudden change in end-tidal CO2 measurement may indicate decreased lung perfusion and an early shock state. Thus, capnometry may be useful to monitor critical patients in the ED. In addition, capnometry has potential usefulness as a noninvasive indicator of the efficacy of ongoing CPR efforts. End-tidal CO2 has been shown to correlate with cardiac output, perfusion pressures, and successful resuscitation in experimental models of cardiac arrest. Further clinical studies are needed to define the role of capnometry in emergency medicine.