PREOXYGENATION: COULD SAFETY MEASURE BE MADE LESS DANGEROUS?.

Abstract

While providing reserve time for dificult airway management, preoxygenation with pure oxygen increases the risk of pulmonary complications due to absorption atelectases. The authors explored when it could be appropriate to prevent atelectases by preoxygenation with decreased FiO₂. ASA I-II elective gynecological surgery patients were randomized among five groups (n = 22 each) with preoxygenation using FiO₂ 100, 70, 60, 60% + PEEP 5 mbar and 50%. Even FiO₂ 70% led to decrease. in safe apnea time (i.e. time interval to Sp²O₂ 95%) by two, while FiO₂ 50% - by more than three times. Furthermore, in five similar additional groups of women with same techniques ofpreoxygenation (n = 10 each) it was shown that for FiO₂ 5 70% very fast pattern of SpO2 fall after the first change ofpulseoxymeter figure (100% by 99%) is typical: interval to SpO2 90% was less than 1 min, while for FiO₂ 100% it lasts for 200 s. Since critical problem is "Cannot intubate, cannot ventilate", the authors tried to focus on the difficultfacemask ventilation prognosis. In the group of 71 elective general surgery patients (31 males, 40 females, ASA I-III) original prognostic model based on seven simple bedside tests (removable dentures, beard, snoring, Mallampati class 2-4, age > 50 y.o., BM > 30 kg/m², sternomental distance < 12 cm) demonstrated the reliability of difficult facemask ventilation negative prognosis of 97,5%. The authors suggest that only in patients with reliable prognosis of easy facemask ventilation prevention ofpulmonary complications by preoxygenation with FiO₂ 50-60% could be safely recommended.