BACKGROUND: We experienced unintentional hyperventilation during mechanical ventilation in pediatric general anesthesia. It is very difficult to decide respiratory rate or tidal volume with a patient's condition for adequate ventilation while respiratory gas monitoring is unavailable in many cases. Therefore, we studied to find a proper respiratory rate (RR) with a fixed tidal volume during mechanical ventilation in general anesthesia. METHODS: We studied 70 children weighing 10-30 kg during general anesthesia. An endotracheal tube was selected according to 3.5+age (yrs)/4. After intubation with midazolam, thiopental sodium and succinylcholine, mechanical ventilation was applied: tidal volume 8-10 ml/kg, peak inspiratory pressure 15-20 mmHg, RR 20 (infant), 18 (under 3 yrs), 16 (under 5 yrs), 14 (above 5 yrs) breaths/min. We adjusted the RR for a PetCO2 30 33 mmHg and arterial blood gas analysis was done 30 minutes each change. We calculated the RR for a PaCO2 of 36 mmHg according to the equation: RR (applied) = estimated RR estimated PaCO2/ideal PaCO2. In addition, the linear regression was analyzed between the age and RR. RESULTS: The estimated regression for RR using Pearson's correlation coefficient was as follows: RR = 19.25-0.07Xage (month). CONCLUSIONS: The equation (RR = 19.25-0.07Xage [month]) could be an index for safe ventilatory management without severe hyper- or hypo-carbia in the pediatric general anesthesia.