Effect of a lung recruitment strategy lung gas function during general anaesthesia

INTERVENTION: Intraoperative stepped lung recruitment manoeuvre (stepped increases in PEEP [Positive End expiratory Pressure] of 5cmH2O from 0 up to 20cmH2O) using the Maquet Flow‐i anaesthesia machine, applied by the anaesthetist after commencement of laparoscopic gas insufflation, with identification of optimal PEEP using monitoring of dynamic lung compliance, with continued ventilation at 6‐8 mL/kg tidal volume and optimal PEEP + 2 cmH2O at a rate to mantain EtCO2 at 35‐40 mmHg. Data will be logged automatically by the Flow‐i and downloaded at the end of the case. CONDITION: Anaesthesiology ‐ Anaesthetics intraoperative lung atelectasis; ; intraoperative lung atelectasis Respiratory ‐ Other respiratory disorders / diseases PRIMARY OUTCOME: Cumulative sevoflurane consumption, measured internally by the Flow‐i anaesthesia machine ; ; [At end of surgery] SECONDARY OUTCOME: Alveolar deadspace fraction calculated using the modified Bohr‐Enghoff equation from end‐tidal and arterial PCO2 measurements ; [60 Minutes post commencement of laparoscopic gas insufflation] FIO2/PaO2 ratio meaured from inspired gas monitoring and arterial blood gas sampling ; [60 Minutes post commencement of laparoscopic gas insufflation] Measured A‐a gradient for PCO2 meaured from end‐tidal gas monitoring and arterial blood gas sampling ; ; [60 Minutes post commencement of laparoscopic gas insufflation] Measured A/a ratio for sevoflurane, measured from monitored end‐tidal waveform concentrations and in aretrial blood from sampling of 10 ML blood and headspace equilibration method.[60 Minutes post commencement of laparoscopic gas insufflation] Time to eye opening to command repeated every 30 seconds after cessation of fresh gas sevoflurane delivery, observed and recorded by the anaaesthetist[At end of surgery] INCLUSION CRITERIA: Patients undergoing elective laparoscopic bowel surgery under relaxant general anaesthesia planned to take at least 1 hour where placement of an arterial blood pressure monitoring line is considered appropriate for cardiovascular monitoring (systemic arterial blood pressure and/or cardiac output monitoring) for clinical purposes.