Preoxygenation: Preoxygenation is the administration of oxygen to a patient prior to intubation to offer ‘the safe apnoea time. The primary mechanism is ‘denitrogenation’ of the lungs. Maximal preoxygenation is attained when the alveolar, arterial, tissue, and venous compartments are all filled with oxygen. Continued oxygenation during apnea can prolong the safe apnea time significantly based on the apneic oxygenation technique and patient factors. Brief of case study: A patient is already admitted to the intensive care unit (ICU) for a lung disorder. Presenting complaint: The patient appears tired and the SpO2 had dropped to 88% on the Continuous Positive Airway Pressure (CPAP) mode. Physical examination: The partial pressure of carbon dioxide (PaCO2): Normal The fraction of inspired oxygen (FiO2): 80 % Oxygen saturation (SpO2): 88 % The patient’s condition was deteriorating. Treatment: The patient was intubated immediately. Preoxygenation was done (3 minutes of 100% FiO2 tidal volume breathing). Discussion: Preoxygenation was extremely important at this stage owing to the high metabolic demands of this patient. The main aim of preoxygenation was to keep SpO2 as close to 100% as possible so that the apnea time could be prolonged (apnea time is defined as the time to reach 88 to 90% SpO2). Beyond this level, the patient can reach the steep portion of the oxygen hemoglobin dissociation curve and can desaturate quickly to dangerous levels.1 The functional residual capacity is the reservoir/storage during the period of apnea. Therefore, maximizing this reservoir with 100% oxygen is important during preoxygenation. Denitrogenation of the residual capacity of the lungs will help to prolong the apnea time and hence prevent dangerous desaturation. One would require at least 3 minutes of preoxygenation to be safe resulting in good denitrogenation. Ref: Lumb AB. Nunn’s Applied Respiratory Physiology. 7th ed. Oxford: Churchill Livingstone; 2010:568. 732
