Design Non-rebreather mask

non rebreather face mask

the non-rebreather mask covers both nose , mouth of patient , attaches use of elastic cord around patient s head. nrb has attached reservoir bag, typically 1 liter, connects external oxygen tank or bulk oxygen supply system. before nrb placed on patient, reservoir bag inflated greater two-thirds full of oxygen, @ rate of 15 liters per minute (lpm). approximately ¹⁄₃ of air reservoir depleted patient inhales, , replaced flow o2 supply. if bag becomes deflated, patient no longer have source of air breathe.

exhaled air directed through one-way valve in mask, prevents inhalation of room air , re-inhalation of exhaled air. valve, along sufficient seal around patient s nose , mouth, allows administration of high concentrations of oxygen, approximately 60% - 80% o2. many textbooks report higher oxygen concentrations, formal studies reporting these levels not referenced research. patient must partially deflate reservoir bag during inspiration or high oxygen concentration not achieved, , mask provide liter flow rate setting on flowmeter.

ideally, non-rebreather mask not permit air surrounding environment inhaled. however, due safety concerns regarding anti-suffocation protection in event of source gas failure (i.e. oxygen cylinder being drained completely), 1 of 2 one-way valves removed, allowing inhalation of outside air significant degree. however, non-rebreathing masks disposable, , manufactured in 1 adult size, (from decades of clinical observation) not provide seal individual patient s face, permitting inflow of large amounts of ambient air (air follows path of least resistance), , diluting oxygen provided. hence, few patients receive close 100% oxygen. high flows (> = 30 lpm) oxygen flowmeter required partially overcome room air dilution. further, larger patient s inspiratory flow rate, greater dilution air. little effort required patients, inspire @ flow rates in excess of 50 lpm (easily seen in pulmonary function lab routine spirometric testing).

partial rebreather masks designed capture first 150ml of exhaled breath reservoir bag inhalation during subsequent breath. portion of breath delivered @ end of inhalation , therefore delivered deadspace anatomy gas exchange did not occur. therefore, there no depletion of oxygen nor gain of carbon dioxide during rebreathing component.