Humidification devices

Humidification is concerned with the addition of water vapour to a gas and can be measured as either absolute or relative. Adequate humidification is a vital consideration in anaesthesia given that the anatomical source of natural gas humidification (the nasopharynx) is generally bypassed, which can lead to complications including hypothermia, thickening of respiratory secretions, mucus plugging and airway keratinization. Humidification may be passive or active. Equipment involved in passive humidification includes HME filters, soda lime and cold water baths, with these devices able to achieve varying efficiencies without extrinsic energy input. Active humidification devices (including hot water baths) are capable of delivering a higher relative humidity but are associated with higher cost and potential hazards. While not strictly classed as true humidification devices, nebulizers are considered in this article as they add water droplets into a gas flow using a Venturi system, spinning discs or ultrasound vibration technology.     

Humidification devices

Humidification is a process of adding water vapour to a volume of one or more gases. Natural humidification is achieved in the nasal cavity, but this process is often bypassed during anaesthesia and critical care. Various devices are used for artificial humidification the commonest being the heat and moisture exchanger, often combined with a microbial filter. Electrically heated water baths and other devices are discussed.     

Humidification of inspired gases during mechanical ventilation

Humidification of inspired gas is mandatory for all mechanically ventilated patients to prevent secretion retention, tracheal tube blockage and adverse changes occurring to the respiratory tract epithelium. However, the debate over "ideal" humidification continues. Several devices are available that include active and passive heat and moisture exchangers and hot water humidifiers Each have their advantages and disadvantages in mechanically ventilated patients. This review explores each device in turn and defines their role in clinical practice.     

The Hygroscopic Condenser Humidifier A new device for general use in anaesthesia and intensive care

The design and performance of the Hygroscopic Condenser Humidifier (HCH) are described. In principle the HCH consists of two parts, a conventional Heat-Moisture-Exchanger (HME) and a hygroscopic unit. The hygroscopic action is shown to improve the water retention efficiency of the device by about a factor of two as compared with optimal HME designs. As a result, humidification levels corresponding to around 80% relative humidity at 37 degrees C are obtained in the trachea and this is also achieved when completely dry gases are delivered to the patient. The unit can therefore be used for all procedures in anaesthesia and in intensive care.     

Heat and moisture exchangers with bacterial filters: a laboratory evaluation

Six commercially available heat-moisture exchanger (HME) humidifiers with built-in bacterial filtration were evaluated by laboratory tests. Physical characteristics, humidification efficiency, resistance to flow and filtration capability were investigated. The resistance was comparable for all units and did not change notably with exposure to humidity. Deadspace values were in the range 55-92 ml and weight values between 34-55 g. The humidification efficiency of two units (Group 1) was clearly less (54%-63% at 11 tidal volume), than for the other four devices (Group 2) (77%-82%). This corresponds to an average humidification output of 22.0 g/m3 for Group 1 as compared to an output of 29.9 g/m3 for Group 2. The average filtration capability of Group 1 was 99.9998%, which is somewhat higher than the 99.9973% obtained for Group 2. There are significant differences between the humidification efficiency and deadspace of different units, with the Pall Conserve device having the least satisfactory performance. All units exhibit good filtering properties, with the Pall Conserve device performing best in this respect.     

Delivery of molecular versus particulate water in spontaneously breathing tracheotomized patients

BACKGROUND: Adequate humidification of inspired gas with active or passive humidifiers is a standard of care for tracheotomized patients. In this study, a comparison is made between the tracheal climate after tracheobronchial humidification either with molecular water (via a vaporizing humidifier) or particulate water (via spray) in spontaneously breathing tracheotomized patients. METHODS: We performed a randomized, 2-way crossover study on 10 tracheotomized patients. Tracheal humidity and temperature were measured prior to and after use of a vaporizing humidifier and aerosol spray, respectively. RESULTS: After use of both the vaporizing humidifier and the aerosol spray, the end-inspiratory total water content and water gradient in the upper trachea increased significantly, compared with baseline values before application. After end of use of the vaporizing humidifier, the total water content and the water gradient decreased significantly faster than after application of the aerosol spray. CONCLUSIONS: Delivery of both molecular and particulate water significantly increases the tracheal climate and conditioning in the tracheal airways. Because the tracheal humidity remained on a higher level after aerosol spray, we speculate that particulate water may be efficient on tracheal humidification for longer. However, the positive effect on tracheal humidity after prolonged application of the aerosol spray remains to be proven.     

Humidification during high-frequency oscillation ventilation is affected by ventilator circuit and ventilatory setting

Background:  High-frequency oscillation ventilation (HFOV) is an accepted ventilatory mode for acute respiratory failure in neonates. As conventional mechanical ventilation, inspiratory gas humidification is essential. However, humidification during HFOV has not been clarified. In this bench study, we evaluated humidification during HFOV in the open circumstance of ICU. Our hypothesis is that humidification during HFOV is affected by circuit design and ventilatory settings.
Methods/Materials:  We connected a ventilator with HFOV mode to a neonatal lung model that was placed in an infant incubator set at 37°C. We set a heated humidifier (Fisher & Paykel) to obtain 37°C at the chamber outlet and 40°C at the distal temperature probe. We measured absolute humidity and temperature at the Y-piece using a rapid-response hygrometer. We evaluated two types of ventilator circuit: a circuit with inner heating wire and another with embedded heating element. In addition, we evaluated three lengths of the inspiratory limb, three stroke volumes, three frequencies, and three mean airway pressures.
Results:  The circuit with embedded heating element provided significantly higher absolute humidity and temperature than one with inner heating wire. As an extended tube lacking a heating wire was shorter, absolute humidity and temperature became higher. In the circuit with inner heating wire, absolute humidity and temperature increased as stroke volume increased.
Conclusion:  Humidification during HFOV is affected by circuit design and ventilatory settings.     

Humidification in intensive care

The normal physiological function of the upper respiratory tract is to filter and humidify inspired air. In intensive care units the upper respiratory tract is frequently bypassed. The importance of humidifying and warming the dry, cold, piped gas is well documented. The results of lack of adequate humidification include endotracheal tube obstruction, impairment of the mucociliary elevator and altered pulmonary function. Optimal levels of humidification are as yet undefined and useful clinical markers of adequate humidification are not available. As a result there is a bewildering array of humidification devices available at present, the most recent of which are heat and moisture exchangers with or without specific filtration properties. This article reviews available data on these humidification devices, and recommends an approach to their appropriate use, based on the probable physiological needs of individual patients.     

Humidification of the respiratory tract in anesthesia

The upper airways humidify, warm and purify the air breathed in. When these are bypassed by an endotracheal intubation catheter, cold dry air goes straight to the bronchi; this leads to local and generalized changes, which are all the more pronounced the longer the intubation lasts. Drying of the tracheobronchial mucosa leads to an early decrease in mucus production, with an increase in its viscosity, a progressive arrest of ciliary function with, finally, a destruction of the vibratory cilia. These lesions create a build-up of thick mucus which hinders humidification of the gas flow and increases bronchial resistances. The disturbed VA/Q relationship leads to a decreased secretion of surfactant. The usual loss of water by way of the lungs is about 30 mg.l-1 of air. Evaporation of this water uses up calories. Most authors suggest that, so as to compensate for the heat and water loss, inhaled gases should be warmed to between 25 and 30 degrees C and be saturated with water to 100%, i.e. 23-30 mg water per litre of air. The water and heat loss can be reduced by using either partial or total rebreathing of expired gases, or a device for heat and moisture exchange, or a humidifier. The most efficient circuits are those which include a soda lime canister. They can be made even more efficient by using different devices. Although this humidification is sufficient for large tidal volumes and a surrounding temperature greater than 22 degrees C, it is not enough for Bain's circuit.(ABSTRACT TRUNCATED AT 250 WORDS)     

A randomized controlled trial to determine the effects of humidified carbon dioxide insufflation during thoracoscopy

Background: The humidification of gas insufflated during laparoscopy can reduce the degree of postoperative hypothermia and may result in less peritoneal reaction and less postoperative pain. The present study was designed to determine whether the beneficial effects of humidified gas insufflation also applied to thoracoscopy. Methods: Six pigs were each studied on three separate occasions with insufflation into the right thoracic cavity of either humidified gas, standard dry gas, or with no insufflation (control procedure). Core body temperature was recorded every 15 min, and biopsies of the parietal pleura were taken at the end of each study for electron microscopy. Results: Humidification of insufflated gas significantly minimized the fall in core temperature during the procedure. Electron microscopy showed that dry gas insufflation resulted in greater structural injury to the pleura than humidified gas insufflation. Conclusions: The potential benefits of humidifying insufflation gas during thoracoscopy warrant its evaluation in the clinical setting. Received: 13 January 1998/Accepted: 8 May 1998     

Lärm auf Intensivstationen Ein Beitrag zur Lärmreduktion durch Modifikation der Atemgasbefeuchtung

Today, noise pollution is an evident and ubiquitous problem even in intensive care units. Noise can disturb the physiological and psychological balance in patients and staff. Especially intubated patients and those breathing spontaneously through a T-piece are exposed to the noise emitted by the nebuliser used to humidity the respiratory gas. This may make patients feel uncomfortable. To reduce noise pollution in the ICU a modified T-piece has been developed and investigated. In order to heat and humidity the respiratory gas a Conchaterm III unit (Kendall company) and a thermo flow cylinder (De Vilbiss company) is necessary. While respiratory gas is flowing, water is sucked out of the heated thermoflow cylinder and nebulised according to the Venturi-Bernoulli principle. To adjust the oxygen concentration of the respiratory gas a plastic ring must be turned to either close (98% oxygen) or open a valve allowing room air to mix (40% oxygen). Noise pollution of the unit varies with admixture of room air. With a new device – a special oxygen – air mixing chamber – the oxygen concentration of the respiratory gas can be adjusted outside the thermoflow cylinder, hardly producing any noise pollution. Therefore the principle of nebulisation could be changed to humidification. A thermoflow cylinder without the nebulisation unit allows the respiratory gas to flow through the thermoflow cylinder over heated and evaporating water, hardly causing any noise pollution. In both types of T-pieces the temperature of the respiratory gas is controlled and corrected by the Conchaterm unit. As the result of these modifications, noise pollution has been reduced from 70?dB(A) to 55?dB(A). In the modified T-piece, the quality of humidification has been evaluated with a fresh gas flow of 22?l/min and at a gas temperature of 37°?C, not only collecting condensed water but also lost water. The modified T-piece allows a physiological humidification of the respiratory gas. The modified T-piece is a simple and efficacious substitute. Patients and staff are protected from adverse noise effects and patient well-being might be improved.     

Passive and active inspired gas humidification in infants and children

The hypothesis that both active and passive airway humidification prevents hypothermia in infants and children, but that neither decreases the duration of postoperative recovery was tested. Twenty-seven ASA physical status 1 or 2 patients were studied who weighed between 5 and 30 kg, underwent superficial operations, were anesthetized with halothane and 70% N2O, and whose lungs were ventilated via a Rees modification of an Ayre's t-piece. The children were randomly assigned to receive active airway humidification and warming using an MR450 Servo airway heater and humidifier set at 37 degrees C (n = 10), passive airway humidification using the Humid-Vent 1 heat and moisture exchanger placed between the Ayre's t-piece and the endotracheal tube (n = 8), or no airway humidification and heating (control, n = 9). Distal tracheal and tympanic membrane temperatures and airway humidity were recorded during the first 90 min of surgery. Rectal temperature was measured during the postanesthetic recovery period. Relative humidity of inspired respiratory gases was approximately 30% in the control group and approximately 90% in the group given active airway humidification. Initial inspired humidity in the passive humidification group (50%) increased to approximately 80%, a level not significantly different from that in the active group after 80 min of anesthesia. Central body temperature increased 0.25 degrees C during active active airway humidification and heating, whereas temperature decreased 0.25 degrees C during passive humidification and 0.75 degrees C without airway humidification. Distal tracheal temperature was significantly higher in the groups given passive and active humidification than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

一体式输氧装置预防高血压脑出血患者肺部感染

目的探讨不同氧气湿化装置对高血压脑出血患者肺部感染的影响。方法将145例高血压脑出血患者随机分为对照组61例和干预组84例。对照组患者在常规护理的基础上,应用传统的氧气湿化瓶持续吸氧;干预组患者运用一体式输氧装置持续吸氧。结果干预组肺部感染发生率显著低于对照组(P<0.05)。对照组和干预组氧气湿化液的致病菌检出率分别为38.33%和5.00%,对照组的氧气湿化液与痰培养病原菌具有一致性。结论一体式输氧装置可降低高血压脑出血患者肺部感染。     

Deep sedation with intravenous infusion of combined propofol and ketamine during dressing changes and whirlpool bath in patients with severe epidermolysis bullosa

Continuous i.v. infusion of propofol, or propofol plus ketamine for deep sedation and analgesia was carried out in two patients with severe epidermolysis bullosa (EB) during extensive dressing changes and deep whirlpool baths. Intermittent small doses of narcotics were given as supplement for pain relief as needed. Both patients had typical features of severe EB, including extremity contractures, severe digit deformity, difficult airways, extensive blisters and broken skin with denuded areas and severe wound infections. SpO(2) was roughly estimated by holding the probe around the earlobe periodically and no other monitors could be applied because of the skin conditions and the settings of the procedures. Retrospective anesthesia record review showed that the combined propofol and ketamine infusions provided satisfactory sedation with significantly reduced narcotic requirements compared with propofol alone. There were no noticeable side effects when ketamine was added. Ketamine appears to be a good addition to propofol and narcotics to provide sedation and analgesia when there are great concerns for respiration depression, apnea, difficult pain management and potential unstable hemodynamics during dressing changes and whirlpool baths in severe EB patients.     

Randomized, controlled study comparing sitz-bath and no-sitz-bath treatments in patients with acute anal fissures

AIM: To determine the efficacy and safety of sitz baths in the management of acute anal fissures. METHOD: Individual patients were randomized to either receive sitz baths or no sitz baths for 4 weeks in addition to oral psyllium husk. Patients were asked to soak their hips and buttocks in a tub containing plain lukewarm water for 10 min, once after defecation in the morning and again at bedtime. Each week, the patients were called to assess pain scores and healing of fissures, whereas the level of satisfaction was recorded at the end of 4 weeks. Main outcome measures were validated pain scores and levels of satisfaction. RESULTS: Fifty-eight subjects were recruited for this study. In all, 52 of them completed the trial (27 in the sitz bath group and 25 in the control group). Although the pain score was lesser in the sitz bath group than in the control group, it failed to reach statistical significance. There were no significant differences in fissure healing between the two groups over the 4-week study period. However, patients in the sitz bath group reported better satisfaction levels than the control group (P < 0.01). Although no serious adverse effects were observed, two patients from sitz bath group developed perianal skin rash. CONCLUSION: This study suggests that sitz baths improve patient satisfaction in acute anal fissures. However, the healing and overall pain relief was not significant enough to attract attention. It was also found to be associated with adverse effects in few patients.     

气管切开后两种雾化吸入方式的效果观察

目的探讨气管切开后一种较为理想的雾化吸入方式,提高湿化效果。方法将40例气管切开患者分为对照组和观察组各20例。对照组采用气道间断滴药加常规氧气雾化吸入法,观察组采用气道间断滴药加改良氧气雾化吸入法,比较两组湿化效果。结果观察组气道出血、痰痂形成、肺部感染发生率低于对照组,但两组比较,差异无统计学意义(均P>0.05);两组每日吸痰次数比较,差异有统计学意义(P<0.01)。两组痰液成分测定值比较,差异有统计学意义(P<0.05)。结论改良气管切开氧气雾化法能将雾化药液充分吸入气道,可降低痰液的粘稠度,提高气道湿化效果。     

Preservation of humidity and heat of respiratory gases in spontaneously breathing, tracheostomized patients

Background : Ventilation with endotracheal intubation bypasses the upper airway and the normal heat and moisture exchanging process of inspired gases. A continuous loss of moisture and heat occurs and predisposes patients to serious airway damage. We therefore prospectively studied one heated humidifier system, one cold humidifier system and one heat and moisture exchanger in spontaneously breathing, tracheostomized intensive care unit patients to determine the ability to preserve patients' heat and water. Methods : Following a randomized order, 10 patients were spontaneously ventilated for 24-h periods with the Nam 35r? humidifier (Europe Medical, France, a cold water humidifier), the heat and moisture exchanger Trach-Ventr? (Gibeck, Sweden), and the Aerodyner? humidifer (Kendall, USA). In each patient, during the inspiration phase, the following measurements were performed: mean values of temperature and relative humidity of inspired gases. The absolute humidity was calculated. Values were obtained in each patients after 40 min and 24 h. Results : The Trach-Ventr? filter and the Aerodyner? humidifier had better humidification and thermic capacities than the Nam 35r? humidifier (P<0.001). With the Nam 35r? humidifier, no patient had temperature of inspired gas >29°C. Concerning absolute humidity of inspired gases, the Nam 35r? humidifier achieved a lower performance than the other two tested systems (P<0.001). Conclusion : In spontaneously breathing, tracheostomized intensive care unit patients, the Trach-Ventr? heat and moisture exchanger and the Aerodyner? heated system achieved satisfactorily preservation of heat and humidity of inspired gases.     

Intraoperative temperature monitoring sites in infants and children and the effect of inspired gas warming on esophageal temperature

This study tested the hypotheses that 1) temperatures of "central" sites are similar in infants and children undergoing noncardiac surgery and 2) airway heating and humidification increases distal esophageal temperature. Twenty children were randomly assigned to receive 1) active airway humidification using an airway heater and humidifier set at 37 degrees C (N = 8), 2) passive airway humidification using a heat and moisture exchanger (N = 6), or 3) no airway humidification and/or heating (control, N = 6). There were no statistically significant differences between tympanic membrane, esophageal, rectal, and axillary temperatures. The temperatures of the peripheral skin surface (forearm and fingertip) were significantly lower than tympanic membrane temperature and significantly different from each other. Although esophageal and tympanic membrane temperatures in the entire group were similar, esophageal temperatures in patients receiving active and passive airway humidification were about 0.35 degrees C above tympanic temperatures after induction of anesthesia. In contrast, esophageal temperatures in patients without airway humidification were 0.25 degrees C below tympanic temperatures after induction of anesthesia. Esophageal-tympanic membrane temperature differences in the patients given active and passive humidification differed significantly from the corresponding sum in the control group at all times, but not from each other.     

Humidification during low-flow anesthesia in children

Purpose The aim of this study was to compare the effect of low-flow anesthesia with or without a heat and moisture exchanger with high-flow anesthesia on airway gas humidification in children. Methods One hundred twenty children were randomly assigned to one of three groups: low-flow anesthesia with 0.5l·min⁻¹ of total gas flow (LFA,n=40), low-flow anesthesia with 0.5l·min⁻¹ using a heat and moisture exchanger (HME,n=40), and high-flow anesthesia with 6l·min⁻¹ (HFA,n=40). The temperature and relative humidity of the inspired gas were measured throughout anesthesia. Results The relative humidity of the inspired gas in the HME group was increased compared with that of the LFA and HFA groups 20 min after induction (p<0.05). The airway humidification in the LFA group was higher than that in the HFA group 10 min after induction (p<0.05). The temperature of the inspired gas in the HME group was increased compared with that in the LFA and HFA groups after 70 min (P<0.05). Conclusion Low-flow anesthesia is less effective in providing adequate humidification of inspired gas than low-flow anesthesia with a heat and moisture exchanger, but significantly better than high-flow anesthesia in children.