Study on timing of intravenous cannulation before surgery in children

The same anaesthesia machine (Drager Fabius GS, Luback, Germany) will be used in all children with the same circuit volume. The circuit will be emptied and then filled with sevoflurane (8%) and nitrous-oxygen (50:50) for 30 seconds at a high fresh gas flow (6 litre/minute). The timer will be started when the face mask is placed on the child’s face for inhalational induction. The exhaled gas concentrations will be measured continuously. After the loss of eyelash reflex, fresh gas flow will be reduced to 3 litre/minute, the sevoflurane will be reduced to 5% and the timer will be restarted. Spontaneous respiration will be allowed until intravenous cannulation and ventilation will be gently assisted as required. For the first child, the gas flow settings will be maintained for 4 minutes from the loss of eyelash reflex before intravenous cannulation is attempted. All intravenous cannulation will be performed on the dorsum of the hand by an experienced anaesthesiologist, using a 22-gauge stainless steel guide cannula (length 19 mm). At the time of intravenous cannulation attempt, an independent observer, who will be blinded about the predetermined cannulation time, will rate the movement according to a scale (0= no movement, 1= slight extremity tension, 2= extremity withdrawal, 3= generalized movement). The intravenous cannulation will be considered unsuccessful if there is any movement, cough, or laryngospasm (defined as sudden, partial, or complete loss of air exchange with simultaneous loss of capnographic wave, which require positive pressure ventilation), and the procedure will be considered successful in the absence of any reaction. The time for the subsequent child’s intravenous cannulation will be adjusted accordingly using Dixon’s up-down sequential method (starting at 4 minutes with 15 second as the step size). The time for cannulation will be increased by 15 seconds if the time is inadequate in the previous child, and conversely, the time for cannulation will be decreased by 15 seconds if the time is adequate in the previous child. During normal inhalational induction of general anaesthesia the following parameters will be observed- 1. Facemask acceptance grade during induction of general anaesthesia. 2. Time required for the loss of eyelash reflex from the start of general anaesthesia. 3. Exhaled sevoflurane concentration at the time of intravenous cannulation. 4. Patient movement at the time of intravenous cannulation. 5. Presence of cought at the time of intravenous cannulation. 6. Presence of laryngospasm at the time of intravenous cannulation. Duration: From the start of induction of general anaesthesia to the time of intravenous cannulation. Frequency: All these observation will be made only once for each patient.