Lower airway humidification in spontaneously breathing tracheostomized patients: comparative study of trachea spray versus heated humidifier

BACKGROUND: Our aim was to compare inhalation with molecular water (vaporizing humidifier) and particulate water (trachea spray) in spontaneously breathing tracheostomized patients. METHODS: We performed a randomized, 2-way crossover study and a prospective, comparative, nonblinded study. Tracheal humidity and temperature were measured before and after use of a humidifier and spray for 1 week. RESULTS: After both inhalation and spray, the tracheal temperature and total water content increased significantly (study 1). The temperature gradient between ambient and tracheal air was significantly higher after spray, but not after inhalation (study 2). The water gradient increased nonsignificantly after spray and inhalation. The water gradient after inhalation or spray did not differ significantly. CONCLUSIONS: Molecular water is not superior to particulate water because of temperature and humidity increase after both forms of water delivery. Because of its easy use, portability, and moisturizing effect, a trachea spray may offer additional options in postoperative tracheostomy care.     

Preservation of humidity and heat of respiratory gases during anaesthesia - a laboratory investigation

Humidification and heating of anaesthetic gases are desirable to prevent respiratory tract damage and a fall in body temperature during operative procedures. Numerous studies on the humidity and temperature of inspiratory gases in different breathing systems for anaesthesia have been carried out, but comparisons are difficult since different methods have been used. In this laboratory set-up we studied a non-rebreathing system with and without humidifiers and a circle absorber system with low (0.5 l/min) or medium (5 l/min) fresh gas flows regarding their ability to heat and humidify anaesthetic gases. The humidity of inspired gases was acceptable in the non-rebreathing system using either a Bennett Cascade humidifier or disposable humidifiers and in the circle absorber system using a fresh gas flow of 5 l/min or less. The temperature of the inspired gases was highest with the Bennett Cascade humidifier, followed by the low-flow circle system. The circle absorber system used with low fresh gas flow gave higher inspiratory gas temperature and humidity than the non-rebreathing system with a good disposable humidifier.     

A comparison of five heat and moisture exchangers

Five heat and moisture exchangers were investigated to compare their efficiency of humidification, their ability to filter bacterial spores and their various physical properties. The results are presented and the various mechanisms of heat and moisture exchange are reviewed. The Pall Ultipor BB50, because of its hydrophobic properties, has a slightly different action from heat and moisture exchangers already in use, The place of the Pall Ultipor BB50 in clinical practice is discussed.     

The effect of a heat and moisture exchanger on humidity in a low-flow anaesthesia system

The heat and humidity in a low-flow breathing system was measured in order to study the inherent humidifying properties of the system at low fresh gas flows (< 1 and 2 l.min⁻¹) and whether a heat and moisture exchanger could compensate for the loss of heat and humidification occurring at higher fresh gas flows (5 l.min⁻¹) in these systems. Sixty patients were randomly divided into three groups (< 1, 2 and 5 l.min⁻¹ fresh gas flows) with a heat and moisture exchanger and three groups without a heat and moisture exchanger in the breathing system. Thirty minutes after the start of anaesthesia a control measurement was performed, after which a heat and moisture exchanger was inserted into the breathing system of the three groups randomly allocated to have one. Three more measurements were performed at 10, 30 and 60 min after control. At low fresh gas flows the humidifying properties of the low-flow breathing system are adequate (i.e. provide an absolute humidity > 20 mg.l⁻¹) but at a fresh gas flow of 5 l.min⁻¹ there is a need for a heat and moisture exchanger for adequate humidification of the inspired gas.     

Efficacy of a heat and moisture exchanger in inhalation anesthesia at two different flow rates

In general anesthesia with endotracheal intubation, a circle system with a heat and moisture exchanger (HME) and a low total flow is often used to prevent hypothermia and to maintain inspired gas humidity. The purpose of the present study was to compare the inspired gas humidity and body temperature, in general anesthesia with or without an HME at two different total flow rates. Eighty patients (American Society of Anesthesiologists [ASA] I or II) scheduled to undergo either orthopedic or head and neck surgery were studied. They were divided into four groups, of 20 patients each: total flow of 2 l·min⁻¹ with (group HME2L) or without (group 2L) HME, and a total flow of 4 l·min⁻¹ with (group HME4L) or without (group 4L) HME. The relative and absolute humidity and pharyngeal and inspired gas temperatures were measured for 2 h after endotracheal intubation. The relative humidity was not significantly different among groups 2L, HME2L, and HME4L. Group 4L had significantly lower absolute humidity than group 2L. The pharyngeal temperature did not decrease significantly for 2 h in any of the groups. During general anesthesia with a total flow of 2 l·min⁻¹ in 2 h, HME might not be necessary, while with a total flow of 4 l·min⁻¹, HME could be useful to maintain inspired gas humidity.     

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.     

Influence of passive humidification on respiratory heat loss in tracheotomized patients

BACKGROUND: The aim of this study was to evaluate changes in total respiratory heat loss during use of a heat and moisture exchanger (HME) in tracheotomized patients. METHODS: Tracheal humidity and temperature were measured before the application and during use of the HME (plastic foam impregnated with CaCl2), and total respiratory heat loss was calculated. RESULTS: No significant difference was found between the convective heat exchange before and after use of the HME for a 10-minute period. When the HME was placed on the tracheal opening, the evaporative heat exchange and the total respiratory heat loss decreased significantly. CONCLUSIONS: The results indicate that passive airway humidification is effective in tracheotomized patients even after a 10-minute period. However, the positive effect on the energy balance of the tracheal mucosa after prolonged use of the HME remains to be proven.     

Influence of heat and moisture exchanger respiratory load on transcutaneous oxygenation in laryngectomized individuals: a randomized crossover study

BACKGROUND: High-resistance heat and moisture exchangers (HMEs) have been reported to increase transcutaneous oxygenation (tcpO(2)) values in laryngectomized individuals and to negatively influence patient compliance. The goal of the present study was to validate earlier published results on short-term transcutaneous oxygenation changes by high-resistance HMEs. METHODS: We conducted a randomized crossover study, monitoring the influence of an HME on tcpO(2) over a 2-hour time interval in 20 subjects. RESULTS: No evidence of an immediate HME effect (95% CI: -14.9-13.3 mm Hg, p = .91), or a time-dependent HME effect (95% CI: -.121 - .172 mm Hg/minute, p = .74), on tcpO(2) was found. After fitting the statistical model without time dependency, again no evidence of HME presence was seen (95% CI: -.5 mm Hg - 3.6 mm Hg, p = .15). CONCLUSION: In contrast to earlier suggestions, there is no evidence of increased tcpO(2) levels by high-resistance HMEs in laryngectomized individuals. Thus, using such HMEs has no added clinical value in this respect.     

The effect of a heat and moisture exchanger on gas flow in a Mapleson F breathing system during inhalational induction

Heat and moisture exchangers (HMEs) humidify, warm and filter inspired gas, protecting patients and apparatus during anaesthesia. Their incorporation into paediatric anaesthetic breathing systems is recommended. We experienced delays in inhalational induction whilst using a Mapleson F breathing system with an HME. We have demonstrated that the HME significantly alters gas flow within the breathing system. Approximately half of the fresh gas flow is delivered to the patient, the remainder being wasted into the expiratory limb of the breathing system. We suggest that the HME should be removed from the Mapleson F breathing system until inhalational induction is complete, or that the reservoir bag is completely occluded until an effective seal is obtained with the mask.     

Moisturizing and mechanical characteristics of a new counter-flow type heated humidifier

Background: During mechanical ventilation effective conditioning of inspiredair is important. In this respect, conventional humidifiersdo not perform optimally. By design, a counter-flow-type humidifiershould improve humidification and heating, but may increaseresistance. Methods: We investigated mechanical impedance and work of breathing (usingpressure-flow characteristics and additional pressure–timeproduct) of a new counter-flow-type humidifier, a conventionalheated humidifier, and a passive heat and moisture exchanger(HME) in physical models of the respiratory system. We investigatedmoisturizing performance (amount of vaporized water at differentair flows and ventilatory frequencies) of the two heated humidifiers.Ease of breathing through both heated humidifiers was investigatedin 12 healthy volunteers blinded to the type of humidifier. Results: Moisturizing performance of the conventional heated humidifierwas flow-independent (approximately 32.5 mg vaporized waterper breath at inspiratory flow rates of 30–120 litre min^{– 1}; P > 0.05) but decreased (10%; P < 0.0001) withincreasing ventilatory rates (12–20 min ^{– 1}). Incontrast, moisturizing performance of the counter-flow-typehumidifier (approximately 33.5 mg vaporized water per breath)was both flow- and rate-independent (P = 0.75). In addition,the counter-flow humidifier caused less physical work (approximately25%) and resistance (approximately 50%) (both P < 0.05) thanthe other two devices. The passive HME displayed the least favourablemechanical characteristics. Ten of 12 volunteers felt breathingthrough the counter-flow humidifier easier than through theheated humidifier (P < 0.05). Conclusion: Compared with a conventional humidifier, the new counter-flow-typehumidifier displayed improved air conditioning and mechanicalcharacteristics. Its lower resistance, particularly at low airflows,should be of clinical benefit during spontaneous breathing andtriggered assisted ventilation.     

The effect of heat and moisture exchanger on humidity and body temperature in a low-flow anaesthesia system

BACKGROUND: Artificial humidification of dry inspired gases seems to reduce the drop in body temperature during surgery. The aim of this study was to evaluate the humidity and temperature of anaesthetic gases with heat and moisture exchangers (HMEs). The secondary aim was to evaluate if HMEs in combination with low-flow anaesthesia could prevent a decrease in the body temperature during general anaesthesia. METHODS: Ninety patients scheduled for general surgery were randomised to receive a fresh gas flow of 1.0, 3.0 or 6.0 l min-1 with or without HMEs in a circle anaesthesia system. Relative humidity, absolute humidity, temperature of inspired gases and body temperatures were measured during 120 min of anaesthesia. RESULTS: The inspiratory absolute humidity levels with HMEs were 32.7 +/- 3.1, 32.1 +/- 1.1 and 29.2 +/- 1.9 mg H2O l(-1) and 26.6 +/- 2.3, 22.6 +/- 3.0 and 13.0 +/- 2.6 mg H2O l(-1) without HMEs after 120 min of anaesthesia with 1.0, 3.0, or 6.0 l min(-1) fresh gas flows (P < 0.05, between with and without HME). The relative humidity levels with HMEs were 93.8 +/- 3.3, 92.7 +/- 2.2 and 90.7 +/- 3.5%, and without the HMEs 95.2 +/- 4.5, 86.8 +/- 8.0 and 52.8 +/- 9.8% (P < 0.05, between with and without HMEs in the 3.0 and 6.0 l min(-1) groups). The inspiratory gas temperatures with HMEs were 32.5 +/- 2.0, 32.4 +/- 0.5 and 31.0 +/- 1.9 degrees C, and 28.4 +/- 1.5, 27.1 +/- 0.8 and 26.1 +/- 0.6 degrees C without HMEs after 120 min of anaesthesia (P < 0.05, between with and without HME). The tympanic membrane temperatures at 120 min of anaesthesia were 35.8 +/- 0.6, 35.5 +/- 0.6 and 35.4 +/- 0.8 degrees C in the groups with HMEs, and 35.8 +/- 0.6, 35.3 +/- 0.7 and 35.3 +/- 0.9 degrees C in the groups without the HMEs (NS). CONCLUSIONS: The HMEs improved the inspiratory absolute humidity, relative humidity and temperature of the anaesthetic gases during different fresh gas flows. However, the HMEs were not able to prevent a body temperature drop during low-flow anaesthesia.     

The respiratory effects of isoflurane, enflurane and halothane in spontaneously breathing children

The respiratory effects of halothane, isoflurane and enflurane were assessed during nitrous oxide anaesthesia (N2O 50%) in three groups of unstimulated, spontaneously breathing children who weighed 10-20 kg and were aged 1-6 years. Respiratory variables were measured or calculated from capnographic and pneumotachographic recordings at three multiples of minimal alveolar concentration (MAC). The slope of the carbon dioxide response was measured. Similar increases in end tidal carbon dioxide were found for the three agents at each MAC multiple, and similar decreases in tidal volume and in the slope of the ventilatory response to carbon dioxide. A dose-related tachypnoea occurred with halothane and a significant decrease in the duration of inspiration and the duration of each breath at the deepest level of anaesthesia. A significant increase in both these times occurred with enflurane, and a decrease in respiratory rate. No change in respiratory rate occurred with isoflurane at increasing alveolar concentrations whereas at each level of anaesthesia inspiratory time was significantly reduced.     

Effects of low-dose alfentanil administration on central respiratory drive and respiratory pattern in spontaneously breathing ASA 1 patients

The aim of this study was to assess the short-term effects of the administration of low doses of alfentanil on respiratory drive and respiratory pattern. We studied 17 ASA I patients scheduled for minor surgery or endoscopic procedures. During spontaneous ventilation, Respiratory Rate, Tidal Volume, Total Respiratory Cycle, Inspiratory and Expiratory Time, Mean Inspiratory Flow, P0.1, S(a)O(2) and EtCO(2) were all measured. The inspired oxygen concentration was 21% and measurements were made at baseline, 5 min (T1), 10 min (T2) and 15 min (T3) following an intravenous bolus injection 10 microg.kg(-1) alfentanil. The administration of alfentanil produced a significant (p < 0.05) reduction in S(a)O(2), minute volume and P0.1. In ASA I spontaneously breathing patients, the pre-operative administration of low doses of alfentanil can initially reduce the respiratory centre activity leading to a reduction in minute volume and S(a)O(2). We therefore recommend careful monitoring of cardio-respiratory function in ASA I patients, following the administration of alfentanil.     

Pulmonary ventilation, CO2 response and inspiratory drive in spontaneously breathing young infants during halothane anaesthesia

Pulmonary ventilation, CO2 response and inspiratory drive were studied during halothane anaesthesia prior to surgery in 13 spontaneously breathing infants less than 6 months of age. Pneumotachography and capnography were used. Airway and oesophageal pressures were measured and occlusion tests were performed at functional residual capacity. Measurements were made before and during 8 min of 4% CO2 stimulation. Inspiratory drive increased significantly (P less than 0.001) at CO2 stimulation. This resulted in increased minute ventilation (P less than 0.001) and tidal volume (P less than 0.001) while respiratory rate was unchanged. As VBohrD/VT ratios were the same, the net effect was increased alveolar ventilation (P less than 0.001). CO2 elimination was unpredictable in these young infants and decreased during CO2 stimulation (P less than 0.05), while mean end-tidal CO2 concentration only increased from 5.2 to 6.3% (P less than 0.001). The ventilatory response to 4% CO2 could therefore be deemed to be adequate during the short period (8 min) of CO2 breathing. However, this was achieved at the cost of increased work as witnessed by the increased ratio between minute ventilation and CO2 elimination (P less than 0.01). Stabilisation of end-tidal CO2 concentrations during CO2 inhalation took only 10 s while the maximal increase in ventilation volumes was not achieved until after 150 s. It is concluded that young spontaneously breathing infants anaesthetized with halothane (MAC 1.3) have an increased respiratory drive with greater tidal volumes during CO2 stimulations. Respiratory timing, dynamic compliance and total pulmonary resistance were, however, uninfluenced by 4% CO2 stimulation. Increased monitoring of CO2 output in anaesthetized infants is suggested.     

The temperature and humidity of inspired gases in infants using a pediatric circle system: effects of high and low-flow anesthesia

BACKGROUND: The effects of low-flow anesthesia on the temperature and humidity of the inspired gas in infants during mechanical ventilation is unknown. This study was designed to evaluate the temperature and humidity of the inspired gas in infants using a pediatric circle absorber system with high and low fresh gas flow (HFGF and LFGF) anesthesia. METHODS: Twenty infants participated in this observational, sequential, cross-over study. Each infant was mechanically ventilated with a Kion Anesthesia Workstation, using a pediatric anesthesia circle circuit with both HFGF (6 l.min(-1)) and LFGF (0.6 l.min(-1)) technique. Airway temperature was recorded continuously at 16 sites throughout the breathing circuit. The relative humidity of the inspired gas was measured at the elbow connector adjacent to the CO2 sampling line. RESULTS: The mean airway temperatures of the inspired gas and the changes in mean airway temperatures throughout the breathing circuit during HFGF and LFGF did not differ significantly. The mean relative humidity of the inspired gas at steady state using a LFGF technique, 33.7 +/- 3.6%, was approximately threefold greater than it was with a HFGF technique, 11.9 +/- 5.1% (P < 0.05). CONCLUSIONS: Low-flow anesthesia with a pediatric circle system in infants neither increases the temperature of the inspired gas, nor achieves the minimum humidity of 50% reported to prevent ciliary damage, although the humidity during LFGF did increase threefold compared with HFGF. To maintain the temperature and humidity of the inspired gas during mechanical ventilation in infants, passive or active gas humidification should be used.     

Failure of a heat and moisture exchanger as a cause of disconnection during anaesthesia

Two cases of ventilator tubing mishaps, resulting from defective heat and moisture exchangers, are described. The report emphasises the need for preoperative inspection of the anaesthetic machine and associated equipment as well as the importance of a disconnect alarm device.     

湿热交换过滤器的功能及其并发症研究进展

背景 湿热交换过滤器是一类用于代替上呼吸道和鼻功能的人工装置,具有一定程度的保温、保湿和滤过功能.目的 概述湿热交换过滤器及其并发症,为临床医师的合理选择和使用提供参考.内容 通过总结大量的临床和实验室研究文献,客观地讲述呼吸过滤器的三大功能及其影响因素,同时也详细地介绍了可能发生的并发症.趋向 随着临床和实验室研究的深入,湿热交换过滤器会得到进一步的改进和完善.