Page 30 - Home Care Catalogue Edition 4A
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Breathing Filters, HMEs and HMEFs • Heat and Moisture Exchangers (HMEs)
Heat and Moisture Exchangers (HMEs)
In normal respiration the upper airway helps to warm and humidify inspired air, and to retain the warmth and moisture contained in expired air. During inspiration, even cold or dry
air is typically heated to 37°C and fully saturated, containing 44mg H2O per litre. In mechanical ventilation or anesthesia the patient’s upper airway may be bypassed by the introduction
of a tracheal tube. As a result the patient’s lungs may be confronted with dry inspired gas.
The drying and cooling effect is exacerbated by the presence of the tracheal tube. During expiration, the normal process of absorption of heat and moisture by the upper airway is lost.
Respiratory epithelium adversely affected by heat and moisture loss
Goblet cell
Intermediate cell
Reduced ciliary function
Columnar cell Basement cell
Prolonged exposure to dry ventilatory gases can lead to:
• Localised in ammation of the trachea
• A reduction in ciliary function
• Retention and thickening of secretions
• Lowering of patient temperature
• Reduction in cardiopulmonary function
• Increased risk of tracheostomy tube occlusion
30mg H2O/L
0.5cm H2O
1.6cm H2O
Box Qty.
Moisture return
Resistance to  ow at 30L/min Resistance to  ow at 60L/min Compressible volume
Minimum tidal volume
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150 31.6mg H2O/L 0.2cm H2O 0.8cm H2O 59ml
31g 22F/15M-22M/15F 200ml
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