Initial strategic options in the Green Zone can be discussed under three broad headings: Optimisation of haemodynamics should also be considered at this time as this may have been overlooked while trying to restore the airway, leading to compromise of oxygen delivery to the tissues. Optimising the oxygen concentration in the functional residual capacity of the lung increases the safe apnoea time which minimises the future threat of harm from tissue hypoxia in the event that alveolar oxygen delivery is subsequently interrupted. Optimising the blood oxygen saturation minimises the immediate threat of harm from tissue hypoxia. Optimisation of patient physiology should consist of optimising both the oxygen saturation of the blood and the oxygen concentration in the alveoli. In the Green Zone, the imminent threat of critical hypoxia has been removed and the patient is in a position of relative safety.
It should be recognised that, with the exception of acute airway obstruction, most episodes of advanced airway management commence from the Green Zone. Even in emergency situations where conscious state, oxygen saturations or airway patency may be compromised to some degree, necessitating some form of urgent airway intervention, the same opportunities exist to optimise, strategise and mobilise resources before this is initiated. Irrespective of the exact value of the SpO2 reading, provided the oxygen saturation is considered 'adequate' in context, confirmed alveolar oxygen delivery always represents entry into the Green Zone and presents the team with the same opportunities to optimise and plan. Conversely following severe desaturation, recover of an ETCO2 trace accompanied by a return of the SpO2 level to only 85% would clearly confirm the occurrence of alveolar oxygen delivery. Normal SpO2 may be maintained outside the Green Zone by preoxygenation stores despite an obstructed airway & absent alveolar oxygen delivery. It is important to recognise that entry into the Green Zone is not synonymous with achieving a normal SpO2. Relationship between the Green Zone & the SpO2
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