Capnographic Analysis of Minimum Mandatory Flow Rate for Hudson Face Mask: A Randomized Double-blind Study.

Background: Oxygen supplementation through Hudson type face mask is frequently used in perioperative settings. Hudson mask is a variable rate performance device with the risk of rebreathing. Studies using capnography to find out an actual fraction of rebreathing in spontaneously breathing patients are not available.
Aims: In this study, we analyzed the effects of different flow rates through Hudson mask with capnography on fractional inspired carbon dioxide (FiCO ₂ ).
Setting and Designs: Forty patients posted for minor surgeries under monitored anesthesia care were divided into four groups. They received oxygen flow rate of 3 L/min, 4 L/min, 5 L/min, and 6 L/min as per group division, through Hudson mask.
Materials and Methods: Parameters such as pulse rate, noninvasive blood pressure, oxygen saturation, respiratory rate (RR), end-tidal carbon dioxide (EtCO ₂ ), and FiCO ₂ were noted at baseline. After starting oxygen supplementation, these parameters were monitored every minute for ten minutes. Statistical analysis was done using analysis of variance and Kruskal-Wallis test. Pearson correlation was used to establish a relation between RR and FiCO ₂ .
Results and Conclusions: EtCO ₂ and FiCO ₂ were comparable in all four groups with no statistical significance. There was strong positive correlation seen between RR and FiCO ₂ at a flow rate of 3 L/min while negative correlation in other groups. We conclude that FiCO ₂ is similar at all flow rates while breathing through Hudson mask. Increase in RR can cause increase in FiCO ₂ at lower flow rate, which is within physiological tolerance limits.
Competing Interests: There are no conflicts of interest.