The performance of two intensive care humidifiers at high gas flows

Abstract

SummaryHigh continuousflow breathing systems are now available to provide fresh gasflows well in excess of 100 I.min-I in continuous positive airway pressure systems used for respiratory support. The performance of two commonly used intensive care humidifiers. the Kendal Conchatherm and the Fisher and Paykel FP310 have been assessed a t j o w s of 50, 75, 100, I25 and 150 I.min-'. Their performance when using two humidifiers connected in parallel and in series was also studied. A t a fresh gasflow of 100 I.min-I the single Conchatherm gave an absolute water vapour concentration of 15.6 g.m-' and the single FP310 11.9 g.m-3. At allflows the best results were achieved using two Conchatherm humidijiers in series. It is concluded that with high continuous flow breathing systems the humidification achieved with conventional humidifiers may be inadequate and it may be necessary to combine two humidifiers to obtain clinically useful humidification. Key wordsEquipment; humidifiers, anaesthetic breathing systems. Humidijication. Ventilation; continuous positive airway pressure.The upper airway normally warms, moistens and filters inspired gas. If this mechanism is bypassed for any length of time, such as by tracheal intubation, then it is accepted that some means of artificial humidification is required. Inspired air is warmed and humidified by the nasooropharynx to reach the upper airway with a relative humidity (RH) of about 90% and a temperature of 32-36°C. Normal nasal breathing adds about 75% of total water content before the inspired gas reaches the larynx. A temperature at the mouth of approximately 32°C and a mean absolute humidity of 27.3 g.m-3 is considered optimal in a patient receiving ventilatory support [I]. Humidification of inspired gases to this level should preserve mucociliary and pulmonary function in most patients. In intubated patients or those with a tracheostomy, the naso-oropharynx is bypassed and the RH falls to 50% or less. Presentation of dry, cold gases direct to the trachea has several adverse effects which include an increase in mucus viscosity, reduced ciliary function, microatelectasis due to obstruction of small airways and larger airway obstruction from tenacious sputum [2]. An ideal humidifier should therefore deliver inspired gases to the tracheal mucosa close to saturation at body temperature.The set temperature should remain constant and both temperature and humidity should be unaffected over a large range of gas flows.Continuous Positive Airway Pressure (CPAP) systems are presently available which utilise high flows in excess of 100 1.min-I [3], greatly in excess of flows used in other systems. There are advantages in using these high flow systems over low flow systems with reservoir bags or ondemand systems [4-61. If the high continuous flow CPAP systems are to be used in the intensive care unit then adequate humidification is required. This study assesses the performance of two humidifiers, the Kendal Conchatherm (Concha) and the Fisher and Paykel FP310 (F&P) over a range of fl...

The use of positive pressure devices by physiotherapists

“…Humidi®cation can be provided during CPAP application. HARRISON et al [77] suggested that two vapour humidi®ers in series need to be added to provide effective humidi®cation at high gas¯ows. There are no published clinical trials which compare outcomes of application of CPAP with and without humidi®cation.…”