Standard preoxygenation technique versus two rapid techniques in pregnant patients

The aim of this study was to compare three different preoxygenation techniques in pregnant women by measuring end-tidal fractional oxygen concentration (FETO2): the traditional technique of 3min tidal volume breathing (VT x 3 min), 8 deep breaths (8 DB) and 4 deep breaths (4 DB). Twenty pregnant volunteers without pulmonary diseases were studied during the third trimester (36-38 weeks' gestation). Women were preoxygentated using a non-rebreathing respiratory circuit with a 3-L reservoir bag and a Capnomac Ultima calibrated before each patient to monitor FETO2 continuously. The three preoxygenation techniques were investigated in random order: VT x 3 min using an oxygen flow of 9 L min-1, 4 DB within 30s using an oxygen flow of 9 L min-1, and 8 DB within one minute using an oxygen flow of 15 L min-1. Between each technique, 5-min room air breathing was allowed to return to baseline FETO2 assessed by the Capnomac Ultima. An FETO2 >/= 90% was achieved more frequently with the VT x 3 min and the 8 DB techniques (76%) than with the 4 DB technique (18%) (P < 0.05). The average time required for obtaining an FETO2 >/= 90% was 107+/-37s. Both the VT x 3 min and the 8 DB techniques are therefore more effective for preoxygenation in pregnant patients than the 4 DB technique. In an acute obstetric emergency before rapid-sequence induction of general anaesthesia, 8 DB preoxygenation technique could be recommended.