The technique commonly used for painless rapid inhalational induction of anaesthesia in children involves delivery of sevoflurane at the maximum vaporizer dial setting (8%) and at high fresh gas flow rate (4-8 L/min) via a rebreathing system. The rationale for using the highest dial setting of sevoflurane is to achieve sufficient alveolar concentration for unconsciousness as early as possible. However, the rate of fresh gas flow (FGF) is chosen arbitrarily. There is no recommendation for what FGF should be used during induction in children. A high FGF reduces the time required to achieve the desired sevoflurane concentration in the circuit-patient system. But it may lead to wastage of anaesthetic gases making it un-economical and leading to environmental pollution. On the other hand, if the FGF is too low, the time taken to achieve desired inhalational agent concentration in the system would be too long, thus reducing OT turnover and increasing the stress of induction on the child. Required FGF also varies with the physical size of the patient. The rate of delivery of an anaesthetic agent to the lungs depends on the minute alveolar ventilation. Thus if we can tailor the FGF during induction to the patient’s minute ventilation (MV), we can achieve a desired balance between rapid induction with minimal wastage. This study has been designed to ascertain the MV based FGF that offers the best balance between rapid induction and minimal wastage in pediatric patients( hypothesis).

After informed parental consent, 30 children, between 1 yr and 10 yrs of age, scheduled to undergo superficial procedures under general anaesthesia with LMA will be randomly divided into 3 groups (Groups 0.5MV, MV and standard FGF).All the children will undergo pre-anaesthetic evaluation. Standard fasting guidelines will be followed before taking the patient to OT. All cases will be performed on a single anaesthesia machine (Drager Primus) for uniformity of measurements. Paediatric closed circuit and 1L reservoir bag will be used for each case.

Prior to induction, the circuit will be flushed of any residual anaesthetic gases and then primed with the patient end occluded, the APL valve set at 10 cm H2O, sevoflurane vaporizer at 8% and FGF (100% O2) at 6L/min for 30 seconds7. Anaesthesia induction will then be started via facemask with sevoflurane at 8% dial setting in 100% O2 at FGF determined by MV. Baseline weight based MV for each patient will be determined from Radford’s nomogram. Patients in Group MV will receive FGF equal to MV. Similarly, Group 0.5MV and MV will receive FGF equal to half MV and one time MV respectively.

Starting time (T0) will be taken as the time of application of the facemask on the child’s face. Once the child is calm, ECG leads, pulse-oximeter and NIBP cuff will be attached. After the loss of eyelash reflex (time = T1), sevoflurane vaporizer dial setting will be reduced to 5% attempting to maintain spontaneous ventilation. Inspired and end tidal sevoflurane concentration, MAC, fraction of inspired oxygen (FiO2) and end tidal carbon dioxide (EtCO2) concentration will be measured with a multi gas analyser. Patients were observed for adequate depth of anaesthesia for IV cannulation and LMA placement (regular    respiration, loss of muscle tone, jaw    relaxation, trapezius squeeze test). Once these conditions are achieved, IV access will be secured, followed by insertion of an appropriately sized Laryngeal Mask Airway (time = T2). Patients will be observed for any reflex movement or tachycardia (HR rise by > 20% from prior to LMA insertion) during LMA insertion. Propofol boluses of 1ml/kg will be administered in case of inadequate depth at the time of LMA insertion.

The total amount of sevoflurane consumed during induction will be recorded from the “logbook” function of the anaesthesia machine. T1, T2, T3, total sevoflurane consumption during induction and incidence of movement or tachycardia at the time of LMA insertion will be compared among the 3 groups.The cost for the period of the different flow rate settings at T1, T2 and T3  was calculated according to the formula (cost (Indian national rupees [INR]) = P*F*T*M*C/2.412*d), where P was vaporizer setting (%), F was fresh gas flow (2 l/min), T was the duration of sevoflurane administration (min), M is the molecular weight of sevoflurane (200), C is the cost (rupees per ml) of sevoflurane, and d is the density of sevoflurane (1.52 g/ml).