Heart Rate Response to Atropine Doses Less Than 0.1mg IV to Anesthetized Infants

60 infants, ASA physical status I and II, undergoing elective surgical procedures will be enrolled after signed informed parental consent.

All children will be fasted according to institutional guidelines and unpremedicated. After arriving in the operating room, EKG, pulse oximeter and blood pressure monitors will be applied (Datex-Ohmeda Aisys).

Anesthesia will be induced with 66% N2O in O2 and 8% sevoflurane. Respiration will be supported by a properly sized face mask through which he/she is allowed to breath spontaneously. Respiration will continue spontaneously through a facemask at 2 MAC sevoflurane in 66% N2O.

All children will be positioned supine, warmed with a forced air warmer and given 20 ml/kg IV balanced salt solution over 30 minutes after the IV has been established. The end-tidal pCO2 will maintained 35-45 mmHg and oxygen saturation >96%.

After a 22 or 24G IV cannula is inserted, 0.005 mg/kg atropine will be administered intravenously over 5 seconds through a fast-flowing IV and followed by 5 ml of normal saline to flush it in through the IV deadspace. The study (ECG recording) period will extend from 30 seconds before atropine administration to 5 minutes after injection. During this time the heart rate and rhythm (through lead II) will be monitored and recorded continuously using an analogue interface system. EKG will be recorded on paper continuously for the 330 seconds of the study.

The recording will be analyzed for the heart rate (based on the R-R interval) and arrhythmias by a physician blinded to the study. Blinding means that the individual is unaware of the hypothesis of the study and what medication was administered to account for any changes in heart rate. Bradycardia is defined as a 20% reduction from baseline heart rate while tachycardia is a heart rate > 160 beats/minute(6). Any heart rate < 100/minute will be considered a bradycardia in this age group. Arrhythmia is any disorder of rhythm or rate observed. These will be summarized for each child.

All heart rate responses will be recorded and reviewed. The time to record the heart rate after atropine, which will occur before surgery, will add less than 5 additional minutes to the anesthetic since it will overlap the time taken for other surgical preparatory events.

The blood pressure will be monitored non-invasively immediately before receiving atropine and at one and five minutes after it is given.

The primary outcome is the incidence of bradycardia during the first 5 minutes after atropine will be determined by reviewing the electrocardiogram. All continuous data will be reported as means +/- standard deviation.

Inclusion criteria

• Age : 0-2 years old
• Weight : less than the 95th percentile for age and height ( no more than 15kg )
• ASA classification : I-II
• Meets the hospital and department of anesthesiology guidelines with respect to peri-operative care

Exclusion criteria

• History of heart disease
• Any condition predisposing to arrhythmia
• Any medication known to influence the heart rate
• Child taking anti-cholinergic medication routinely
• The use of succinylcholine anticipated (will cause bradycardia)
• Rapid sequence intubation is required (due to aspiration risk)
• Known difficult airway (may be difficult to bag mask ventilate)