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ABSTRACT
Background and Aims: Preoxygenation is supplementation of 100% oxygen prior to induction
of general anaesthesia to increase the body’s oxygen stores. Efficacy of preoxygenation can be
increased by optimising fresh gas flow (FGF) rate and pattern of breathing. Methods: Based on
pattern of breathing—Tidal Volume Breathing (TVB) or Deep Breathing (DB) and FGF‑10 L/min
or 15 L/min—100 subjects of the American Society of Anesthesiologists physical status I/II posted
for elective surgery were recruited and randomised into four groups: T10 ‑ TVB with 10 L/min;
D10 ‑ DB with 10 L/min; T15 ‑ TVB with 15 L/min; and D15 ‑ DB with 15 L/min. A tight‑fitting
anaesthesia mask along with continuous positive airway pressure of 5 cm of H2O with 20° head‑up
was used for preoxygenation. The total time taken and the total number of breaths required to
achieve end tidal oxygen concentration (EtO2) of 90% were noted. Exhaled tidal volume (Vte),
end tidal carbon dioxide, fraction of inspired oxygen, and EtO2 were recorded at each breath.
Analysis of variance (ANOVA) was used for inferential statistics and Tukey’s honestly significant
difference (HSD) test was used to calculate mean difference in total time and number of breaths
amongst the groups. Results: Total time taken was significantly low (P < 0.001) in DB compared to
TVB (D10: 70.2 ± 19.91, D15: 68.4 ± 20.27 vs T10: 112.28 ± 47.96, T15: 113.6 ± 48.57 seconds).
Number of breaths was significantly high (P < 0.001) in TVB with 22.84 ± 8.73, 23.76 ± 11.64,
10.56 ± 3.69, and 8.32 ± 1.8 in T10, T15, D10 and D15, respectively. Vte was significantly low in
TVB (P < 0.001). Conclusion: Rapid preoxygenation can be achieved by DB at high FGF of a
minimum of 10 L/min.
Key words: Apnoea, hypoxia, oxygen, tidal volume, vital capacit