To Compare the Consumption of Sevoflurane and Desflurane in Low Flow Anaesthesia

OBJECTIVES

PRIMARY To compare the mac hour consumption of sevoflurane and desflurane anaesthetic agents under low flow (one litre/min) conditions To calculate the carbon footprint of sevoflurane and desflurane in the low-flow anaesthesia being used in this study

SECONDARY To test whether a significant generation of carbon monoxide occurs due to the interaction of sevoflurane/desflurane with soda lime in the closed circuit.

Methodology Two groups: 1) low-flow sevoflurane (LFS) 2) low- flow desflurane (LFD) Anaesthesia will be administered according to the recommendations of the ASA Environment Sustainability Committee.

Three strategies to reduce the fresh gas flow and environmental contamination are

1. Induction: Set the Vaporizer to Deliver a Concentration Greater than Intended
2. Intubation: Turn Off the Fresh Gas Flow, Not the Vaporizer.
3. Maintenance: Minimize Fresh Gas Flow During Maintenance.

Five hundred sixty-four patients aged 20-65 and ASA status I-II scheduled for procedures longer than three hours duration at Rajiv Gandhi Cancer Institute \& Research Center (RGCI\&RC) from 2017-2018 will be included in this study.

Patients having severe cardiac and hepatic problems, renal dysfunction and chronic alcoholism are excluded from the study Computer-generated randomisation will be done to allocate the patients into two equal groups for low-flow sevoflurane and low-flow desflurane anaesthesia.

After the arrival of the patients, aVenous cannula will be inserted; midazolam 0.05 mg. kg-1 will be administered intravenously for anxiolysis. Noninvasive monitors, including electrocardiograms, non-invasive blood pressure monitoring, pulse oximetry, axillary temperature, and bispectral index (BIS), will be applied.

Anaesthesia will be induced with fentanyl (2µg.kg-1 ), propofol (2.5 mg. kg-1 ) and atracurium (0.5mg. kg -1 ) to facilitate endotracheal intubation.

All patients will be mechanically ventilated with a mixture of air-oxygen (50% oxygen + 50% air) in addition to the anaesthetic agent according to the study group using the anaesthesia workstation (Primus®, Dräger, Luebeck, Germany).

The tidal volume will be set at 8mL/kg, and the respiratory frequency will be to maintain an end-tidal CO 2 (Et CO2 ) between 30-35mmHg.

After intubation, anaesthesia will be maintained with the fresh gas flow (FRF) of 4 lit./min and 4% Vol sevoflurane or 6% Vol desflurane in the 50% oxygen/air mixture for 5 minutes.

The fresh gas flow will be decreased to 1 L min-1, and after that, dial concentration will be reduced by 0.5% every 2 minutes to maintain 1 MAC(minimum alveolar concentration).

The dial concentration after that will be adjusted to achieve a value of 1 MAC. An adequate neuromuscular blockade will be achieved by administering atracurium boluses of 0.1mg. kg-1 every 20min.

During skin closure, the anaesthetic will be discontinued, and the patient will receive 100% O 2.

At 25% recovery of the first response to train-of-four stimulation, the neuromuscular blockade will be reversed by neostigmine (4µg.kg-1 ) and atropine (15µg.kg-1 ). ABG( Arterial blood gas) were done baseline and post-procedure.

PARAMETERS TO BE RECORDED:

1. Carbon footprint calculation.
2. Consumption of the anaesthetic agent will be recorded from the logbook Draeger Primus™ on termination of anaesthesia
3. Consumed inhalational agent (ml) in 1 MAC hour. Consumption of the inhalational agent (ml) will be converted to MAC hour consumption by dividing it by the entire duration of 1.0 MAC anaesthesia.
4. Calculation of carbon dioxide equivalent. The consumed inhalational agent (ml) will be converted to tones by volume weight conversion formula (1.465 for Desflurane and 1.522 for Sevoflurane) and then multiplied by( Global warming potential) GWP100 (2540 for Desflurane and 130 for Sevoflurane) to get carbon dioxide equivalent.
5. Estimation of carboxy haemoglobin (CoHb) levels as read from ABG analysis on termination of anaesthesia.