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Table 1 Increases in the compressible volume, respiratory impendance components and total work of breathing associated with heated humidifiers and different artificial noses

From: Equipment review: Mechanical effects of heat-moisture exchangers in ventilated patients

  Heated humidifier Low volume High volume HME-filter
Apparatus compressible volume +++ +/0 + ++
Apparatus deadspace 0 + ++ +++
Dead space ventilation 0 + ++ +++
Apparatus inspiratory resistance + + + ++
Apparatus expiratory resistance 0 + + ++
Intrinsic PEEP 0 0 0 +*
Total work of breathing 0 +/0 + ++
  1. All the changes have been scored as follows: 0, negligible; +,mild; ++, moderate; +++, severe. *The increase in intrinsic positiveend-expiratory pressure (PEEP) may be absent in chronic obstructive pulmonarydisease patients with dynamic bronchial collapse. Note that this tabledescribes the typical effects attributed to each humidifier category. Specificdevices of any category may perform much worse or better than indicated. Forexample, in heat-moisture exchanger (HME)-filters, electrostatic rather thanmechanical filtration may reduce all mechanical effects.