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This single-blind study examined four levels of monitoring in 402 pediatric cases. Patients were randomly assigned to one of four groups: 1) oximeter and capnograph; 2) only oximeter; 3) only capnograph; or 4) neither oximeter nor capnograph data available to the anesthesia team. An anesthesiologist, not involved in patient care, observed all cases and continuously recorded hemoglobin oxygen saturation (Spo2), ECG, expired CO2, and the oximeter plethysmographic output. Mean age, weight, ASA physical status, airway management (mask or endotracheal tube), and anesthetic technique were similar in each group. Two-hundred sixty problems were documented in 153 patients. Fifty-nine events in 43 patients resulted in "major" desaturation (Spo2 <= 85% for >= 30 s). Fifteen "major" capnograph events (esophageal intubation, disconnection, accidental extubation, or obstructed endotracheal tube) were observed in 11 patients; 8 of these also developed varying degrees of desaturation. One-hundred thirty "minor" desaturation events (Spo2 <= 95% for >= 60 s) and 79 "minor" capnograph events (hypercarbia or hypocarbia) were observed. A number of problems fulfilled criteria in multiple categories. Infants <= 6 months of age had the highest incidence of major desaturation events (18 of 65 [27%]) compared to toddlers 7-24 months of age or children >24 months of age (P < 0.001). Blinding the oximeter data increased the number of patients (12 vs. 31) experiencing major desaturation events (P = 0.003); blinding the capnograph data altered neither the frequency of desaturation events nor the incidence of major capnograph events. Blinding the capnograph data increased the number of patients with minor capnograph events (22 vs. 47; P = 0.0026). More patients experienced multiple problems when neither capnograph nor oximeter data were available compared to when both were available (23 as. 11; P = 0.04). We conclude: 1) The pulse oximeter is far superior to either the capnograph or clinical judgment in providing the earliest warning of desaturation events. 2) Capnography can provide an early warning to potentially life-threatening problems, but such problems often result in desaturation. 3) Capnography reduces the incidence of hypercarbia and hypocarbia. 4) Infants <= 6 months of age are at greatest risk for major desaturation and major capnograph events. 5) The number of problems observed can be significantly reduced when both monitors are used.

(C) 1991 American Society of Anesthesiologists, Inc.