Comparative humidity measurements in semiclosed and semiopen systems with the additional use of artificial noses

The administration of dry anesthetic gases for ventilation lasting more than 1 h leads to morphological changes of the tracheobronchial epithelium that may cause postoperative pulmonary complications. Therefore, additional humidification is suggested for ventilation during anesthesia, particularly when using semiopen breathing systems. Recommendations concerning the use of semiclosed systems are controversial: previous studies have shown sufficient humidification on the one hand, and insufficient water content in the inspired air on the other hand. In this study, comparative humidity measurements in a semiopen and a semiclosed system were carried out during anesthesia and mechanical ventilation. We particularly wanted to find out whether placement of the fresh gas inlet into the circle before or behind the soda lime canister influences the humidity of the inspired gas. In addition, we tested three types of "heat and moisture exchanges"--Engstr?m "Edith", Siemens "Servo Humidifier", and Portex "Humid Vent". A total of 58 patients between 23 and 78 years of age were studied. They were divided into three groups. Group I: In 10 patients comparative humidity measurements were carried out using both a semiopen and a semiclosed system. Group II: The time course of water saturation during a 3-h period was determined in 10 patients ventilated with a semiopen and 8 patients ventilated with a semiclosed circle system. Group III: In 20 patients we tested the effect of "heat and moisture exchangers". All patients were intubated and ventilated with the Spiromat 656 and the Circle System 8 (Drger) that made ventilation in both a semiclosed and a semiopen system possible. The humidity measurements were carried out using a psychometric method.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

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.     

The climatisation of anesthetic gases under conditions of high flow to low flow

The aim of climatisation of anesthetic gases in prolonged anesthesia is to maintain tracheobronchial climate comparable to that of spontaneous nasal breathing. The humidity and temperature of inspired gases attained in the circle system at a fresh gas flow of 6.0, 3.0 and 1.5 l/min are inadequate for prolonged anesthesia. According to the results of our study with the scanning electron microscope, the minimal flow technique (0.5 l/min) leads to major improvement of heat (28 to 32 degrees C) and moisture (20 to 27 mg H2O/l) conditions of anesthetic gases in anesthesia systems.     

Maintenance of body temperature in elderly patients who have joint replacement surgery A comparison between the heat and moisture exchanger and heated humidifier

The effect of a heat and moisture exchanger on intra-operative aural canal (core) and mean skin temperatures was investigated in elderly patients who had elective total hip arthroplasty under general anaesthesia with artificial ventilation of the lungs. Group 1 (n = 20) did not receive any form of artificial humidification while in group 2 (n = 20) a heat and moisture exchanger was inserted in the breathing system and in group 3 (n = 20) the inspired gases were humidified and warmed at 40 degrees C by means of a heated humidifier. Time of surgery, intravenous fluid administration and operating theatre temperature were standardised. Mean (SD) aural canal (core) temperature decreased significantly in groups 1 and 2 (p less than 0.001), while there was a fall of 0.3 degrees C (0.6) in group 3, which was not significant. Mean skin temperature decreased during anaesthesia and surgery in both groups 1 and 2 (p less than 0.05), while it increased in group 3. There was a significantly greater loss of body heat in groups 1 and 2 compared with group 3 intra-operatively (p less than 0.001). We conclude tha a heat and moisture exchanger did not prevent the decrease in intra-operative body temperature in elderly patients.     

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.     

Klimatisierung von Narkosegasen bei Einsatz unterschiedlicher Patientenschlauchsysteme

Background. During general anaesthesia gas climate significantly is improved by performance of low flow techniques. Gas climatisation, however, markedly also will be influenced by the temperature loss at, and corresponding water condensation within the hoses, factors which are related to the technical design and material of the patient hose system. The objective of this prospective study was to investigate 1. how anaesthetic gas climatisation during minimal flow anaesthesia is influenced by the technical design of different breathing hose systems in clinical practice. 2. to investigate, whether a sufficient gas climatisation also can be gained with higher fresh gas flows if that hose system is used, proven beforehand to optimally warming and humidifying the anaesthetic gases. Methods. Three different systems, a conventional two-limb hosing consisting of smooth silicone hoses, a coaxial hosing, and a hosing consisting of actively heated breathing hoses, attached to a Dräger Cicero EM anaesthesia machine, were used during minimal flow anaesthesia with a fresh gas flow of 0.5 l/min. Gas temperature and absolute humidity were measured at the tapered connection between the inspiratory limb and the breathing system as well as at its connection to the endotracheal tube. The best gas climatisation was observed if heated breathing hoses were used. Thus, using this hosing, additionally gas temperature and humidity in the inspiratory limb were taken at fresh gas flow rates of 1.0, 2.0 and 4.4 l/min respectively. Measurements were performed in all groups at all general anaesthesias lasting at least 45 minutes during the lists of eight different days each. Results. In minimal flow anaesthesia, with all hose systems likewise, generally an absolute humidity between 17 to 30 mgH₂O/l is reached at the endotracheal tube's connector during the course of the list. Only in the first cases of the day there was a short delay of 15 to 30 minutes before reaching a humidity of at least 17 mgH₂O/l. Only with heated hoses, however, humidity frequently even exceeded 30 mgH₂O/l. If conventional or coaxial hosings were used, during minimal flow anaesthesia gas temperatures in an acceptable range between 23 to 30 °C were measured at the tube connector. With heated hoses, however, warming of the gases was excellent with gas temperatures betwen 28 to 32 °C. In minimal flow anaesthesia climatisation of the anaesthetic gases proved to be best if heated hoses were used. Thus, using heated hose systems another three trials with increasing fresh gas flow rates of 1.0, 2.0 and 4.4 l/min respectively were performed. Whereas climatisation of the anaesthetic gases still was found to be optimal with a fresh gas flow of 1.0 l/min, the humidity dropped drastically to values lower than 17 mgH₂O/l at 2.0 l/min and even down to 10 mgH₂O/l at a flow rate of 4.4 l/min. Gas temperatures, however, turned out to be independent of the flow and remained at 28–32°C, even at a flow as high as 4.4 l/min. Conclusions. Using conventional hose systems and coaxial hosings acceptable, but not optimal climatisation of the anaesthetic gases can be gained if minimal flow anaesthesia is performed. The use of a coaxial hose system seems to lead to improved climatisation in long lasting procedures only. In routine clinical practice, however, conventional and coaxial hose systems are similar in respect to the climatisation of breathing gases. Heated breathing hoses performed markedly better in terms of climatisation of the breathing gas than the coaxial and the conventional hose system. With this hosing not only sufficient but optimal moisture and temperature values are realized. Optimal climatisation, however, only can be gained if low flow anesthetic techniques with fresh gas flows equal or less than 1 l/min are performed. With higher fresh gas flow rates the humidity decreases markedly while high gas temperatures are maintained. It seems justified to assume, that ventilation with warm but dry gases may result in increasingly drying out of the respiratory epithelium of the lower air ways. Heated hoses only should be used if low flow anaesthetic techniques are performed. While moisture content of the breathing gases mainly is influenced by the fresh gas flow rate, temperature mainly is depending on the convectional loss of heat at the inspiratory limb of the hosing.     

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.     

Control of body temperature: use of the respiratory tract as a heat exchanger

The theoretical potential of the respiratory tract as a heat exchanger is enormous because the large alveolor surface area is in intimate contact with pulmonary blood flow. However, this potential is severely limited by some powerful physiologic mechanisms that ensure thermal isolation of alveolar gas, by the detrimental effects of dry gas and extremes of temperature on respiratory epithelium, and by the unfavorable thermal properties of respiratory gases in general. Optimal respiratory cooling using hyperventilation with cold helium-oxygen-CO₂ through a double lumen tube increased the rate of body heat loss by only 1.1°C/hr. Although respiratory cooling alone cannot effect heat transfer of sufficient magnitude to produce rapid cooling far induced hypothermia, it may find use as an adjunct in treating hyperthermic conditions and in induced hypothermia. Respiratory warming does not suffer the limitations of respiratory cooling and should find use in inhalation warming of hypothermic patients and in maintaining the body temperature of patients, especially small babies under anesthesia, who are unable to defend their own central temperature.     

Humidification and heating of anesthetic gases during pediatric anesthesia using the Cicero Anesthesia Workstation]

A series of 52 infants underwent general or urological surgery; all were ventilated with the CICERO. Two different flows of fresh gas were used. In group I (n = 21) the fresh gas flow was set exactly at the level of the minute volume, representing a half-open, non-rebreathing system. In group II (n = 31) the fresh gas flow was adjusted to 10% of the required minute volume. Temperature and relative humidity of the inspired gas were measured continuously close to the tracheal tube. Anaesthesia was accomplished with 2 vol% isoflurane, 21-30 vol% oxygen in nitrous oxide. The results were compared with those achieved with our time-tested paediatric equipment, a SERVO 900D ventilator with a Fisher-Paykel humidifier (Group III, n = 35). Using a high fresh gas flow, no increase in relative humidity in the inspired gas could be detected. The values varied between 12% and 25% (group I). Reducing the flow of fresh gas as indicated above resulted in an increase in the relative humidity (group II). Over the evaluated period of 2 h, humidity increased slowly from an initial mean value of 20% to a maximum of something over 70%. Using the SERVO 900D ventilator combined with the Fisher-Paykel humidifier, humidity reached a value of greater 90% within 10 min after activation of the heated cascade. Humidity in the inspired gas should exceed 70% to avoid damage to infant airways. This will not be attained until after more than 2 h with unaided breathing systems, by when most operations performed on paediatric patients will already be over. Condensed water may aspirated by small infants. This potentially dangerous situation was only encountered in the CICERO circuit, and not in the system protected by the Fisher-Paykel cascade. Dry gases can result in thickened mucous and in obstruction of a small tracheal tube, which requires emergency reintubation. With artificial airways dry gases damage the ciliated epithelia of the trachea and cause loss of water and body heat. The temperature of the "cold" gases varied within a range of 21-33 degrees C and could not be adjusted by the anaesthetist. In the CICERO system, heating the gases at the valve only prevents mechanical failure caused by water condensation. In pediatric anaesthesia, variable heating and non-condensing humidity are essential. The dry and heated gases of the CICERO are not acceptable in the daily practice of paediatric anaesthesia.     

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.     

Reduktion intraoperativer Wärmeverluste und Behandlung hypothermer Patienten durch atemgasklimatisierende Maßnahmen? Wärme- und Feuchtigkeitstauscher vs. aktive Befeuchter im beatmeten Lungenmodell

Heated humidifiers (HH) as well as heat and moisture exchangers (HME) are commonly used in intubated patients as air-conditioning devices to raise the moisture content of the air, thus preventing mucosal damage and heat loss resulting from ventilation with dry inspired gases. In contrary to HME, HH are able to add heat and moisture to the inspired air in surplus, which is often stressed as an advantage in warming hypothermic patients or reducing major heat losses, e.g., during long operations. The impact of air conditioning on the energy balance of man was calculated comparing HME and HH. Methods. The efficiency of a HME (Medisize Hygrovent) and a HH (Fisher &; Paykel MR 730) was evaluated in a mechanically ventilated lung model simulating the physiological heat and humidity conditions of the upper airways. The gas flow from the central supply was dry; the model temperature varied between 32 and 40?°C. By using a HH in the inspiratory limb, a circle system was simulated with water-saturated inspired air at room temperature. The water content of the ventilated air was determined at the tracheal tube connection using a fast, high-resolution humidity meter and was compared with the moisture return of the HME. The energy balance was calculated according to thermodynamic laws. Results. Both HME and HH were able to create physiological heat and humidity conditions in the airways. With the normothermic patient model, the moisture return of the HME was equal to that of the HH set at 34?°C. Increasing the heating temperature resulted only in reduced water loss from the lung; heat and water input in the normothermic model was not possible. This was only effective with almost negligible amounts under hypothermic patient model conditions. Discussion. The water content in the inspired and expired air is the most important parameter for estimating pulmonary heat loss in mechanically ventilated patients. In adults (minute volume ～7?1/min) the main fraction of pulmonary heat loss results from water evaporation from the airways (～6?kcal/h), whereas the heat loss due to convection is negligible (～1.2?kcal/h). In intubated patients ventilated with dry air, the heat loss increases to ～8?kcal/h due to greater water evaporation from the airways. Both HME and HH are able to reduce the pulmonary heat loss to 1–2?kcal/h. In normothermic as well as hypothermic patients, HH do not offer significant advantages in heat balance compared to effective HME. In conclusion, air conditioning in intubated patients is neither a powerful too for maintaining body temperature during long-lasting anaesthesia nor a sufficient method of warming hypothermic patients in intensive care units.     

Forced-air surface warming versus oesophageal heat exchanger in the prevention of peroperative hypothermia

Background: In a prospective, randomized, placebo-controlled study we investigated the efficacy of 2 different heating methods in 24 patients undergoing abdominal surgery of at least 2 h expected duration.
Methods: Group I: control, no active warming. Group II: forced-air surface warming on upper extremities and upper thorax. Group III: warming with oesophageal heat exchanger. All patients had a standardized, combined general and epidural anaesthesia. Core and skin temperatures were measured at induction of general anaesthesia, and subsequently every 30 min, and changes in total body temperature were calculated.
Results: There were no statistically significant differences between the 3 groups regarding demographic data. Patients in groups I and III developed hypothermia, while this was not the case with patients in group II. When using analysis of variance with repeated measurements, there was no significant difference in core temperature, comparing group I and group III ( P =0.299) or the interaction between time and treatment of these groups ( P =0.373). As a consequence, data from groups I and III were pooled and regarded as an internal group on the one hand, and group II as an external group on the other hand. Core temperature, the mean skin temperature and total body temperature were significantly different comparing the internal group and the external group. The interaction between time and treatment was likewise found to be significantly different.
Conclusions: We conclude that in major abdominal procedures lasting 2 h or more, serious hypothermia develops unless effective measures to prevent hypothermia are used. Forced-air warming of the upper part of the body is effective in maintaining normothermia in these patients, while central heating with an oesophageal heat exchanger, at least in its present form, does not suffice to prevent hypothermia.     

A heated humidifier does not reduce laryngopharyngeal complaints after brief laryngeal mask anesthesia

PURPOSE: Warming and humidification of inspired gases is standard care for intubated patients whose lungs are ventilated mechanically for prolonged periods. We examined whether active humidification of inspired gases might reduce laryngo-pharyngeal discomfort in patients undergoing brief laryngeal mask airway (LMA) anesthesia. METHODS: In a prospective trial, 200 adult patients undergoing elective surgery under general anesthesia were randomly assigned to receive ventilation without airway warming and exogenous humidification (Group C-control), or active warming and humidification of inspired gases (Group HUM-humidified), using a humidifier with a heated wire circuit. Inhalational anesthesia was maintained via a circle system. The temperatures and relative humidities of inspired gases were monitored continuously throughout surgery. Postoperative sore throat, dysphonia, and dysphagia were assessed one and 24 hr after anesthesia. Whenever symptoms were present, their severities were graded using a 101-point numerical rating scale. RESULTS: The mean temperature and relative humidity of the inspired gases in Group HUM were greater compared to Group C (36.1+/-0.4 degrees C and 99.5+/-0.5% vs 26.9+/-0.8 degrees C and 76.4+/-10.9%, respectively). Postoperatively, the overall frequencies of laryngeal and pharyngeal discomfort were similar in the two groups (53.8% and 54.9% in Group C vs 51.6% and 41.9% in Group HUM at one and 24 hr respectively, P>0.05). The groups were also similar with respect to the severity scores of laryngo-pharyngeal discomfort. CONCLUSION: Active warming and humidification of inspired gases has no clinically appreciable effect in reducing the incidence and severity of laryngo-pharyngeal complaints after brief (相似文献   

Effects of surgical site and inspired gas warming devices on body temperature during lower abdominal and thoracic surgery

To evaluate the effects of surgical site and inspired gas warming and humidifying devices on body temperature, we studied rectal, tympanic membrane, and esophageal temperature changes in 48 patients. The patients were divided into 4 groups (n = 12), according to surgical site, lower abdominal surgery and thoracic surgery, and according to the warming device used, heat and moisture exchanger (ThermoVent 600) and heated humidifier (Cascade 1). The heated humidifier was controlled to warm inspired gases to about 35°C. All body temperatures fell significantly during surgery. There was no difference in the tympanic membrane and esophageal temperature declines between the two surgical sites, but the decline in rectal temperature was larger in the lower abdominal surgery than in the thoracic surgery. At the end of surgery, all temperatures returned to the value before surgery, and the rectal and tympanic membrane temperatures even exceeded them. There was no difference between the effects of the ThermoVent 600 and Cascade 1. These results suggest that rectal temperature is influenced by the ambient temperature during lower abdominal surgery and that warming and humidifying devices for inspired gases do not prevent, but can restore the decline in body temperature during lower abdominal and thoracic surgery. The heated humidifier showed no advantage over the heat and moisture exchanger in our study.(Harioka T, Sone T, Nomura K, et al.: Effects of surgical site and inspired gas warming devices on body temperature during lower abdominal and thoracic surgery. J Anesth 6: 467–473, 1992)     

Einfluß eines Wärme- und Feuchtigkeitsaustauschers (HME) auf den bronchialen Schleimtransport im Rückatemnarkosesystem

The administration of dry anaesthetic gases for ventilation leads to morphological changes of the tracheobronchial epithelium that may cause postoperative pulmonary complications. Therefore, additional humidification with a heat and moisture exchanger (HME) is suggested for ventilation during anaesthesia, particularly when using semi-open breathing systems. Recommendations concerning the use of a HME in the semi-closed system are controversial. There are no data in the literature as to whether a HME improves mucociliary transport under these conditions. We therefore studied bronchial mucus transport velocity (BTV) with and without the use of a HME in the semi-closed circle system in humans. Patients and methods. The study was approved by the ethics committee of our hospital. In a prospective, randomised trial a total of 22 patients undergoing major abdominal surgery were investigated. In all patients anaesthesia was induced and maintained with midazolam, fentanyl, and vecuronium. After intubation, a HME (BACT/VIRAL HME, Pharma Systems AB, Sweden) was inserted between the endotracheal tube and ventilation tubing in 11 patients; the other 11 were ventilated without a HME and served as controls. Ventilation was assisted with a fresh gas flow of 3?l in a semi-closed system (Dräger Sulla 808 V with an 8 ISO circle system and Ventilog 2 ventilator, Drägerwerk AG, Germany) and a 2:1 mixture of nitrous oxide and oxygen. The fresh gas passed through the soda lime canister. At the end of the operation BTV was measured with a small volume of albumin microspheres labeled with technetium Tc99m, which was deposited on the dorsal surface at the lower ends of the right and left main bronchi via a catheter placed in the inner channel of a fibre-optic bronchoscope [16]. Results. The two groups were comparable with regard to age, sex, preoperative lung function, duration of mechanical ventilation, and dose of anaesthetics (Table 1). There were no statistically significant differences in the BTVs (Fig. 1). Discussion. BTV does not improve with the use of a HME in the semi-closed circle system with a fresh gas flow of 3?l. With modern anaesthesia machines lower fresh gas flows should be administered, whereby the humidity and temperature of the inspired gases are further increased.     

The effect of heat-moisture exchanger and closed-circuit technique on airway climate during desflurane anesthesia

Purpose We assessed whether closed-circuit anesthesia (CCA) could provide a more favorable airway climate than semiclosed anesthesia (SCA), and we also determined the beneficial effect of heat moisture exchangers (HMEs) on the preservation of airway climate during desflurane anesthesia. Methods Forty patients scheduled for colorectal surgery (n = 10 for each group) were randomized to receive a fresh gas flow of 250 or 3000 ml·min⁻¹ with or without HMEs. Anesthesia was maintained by adjusting the inspired concentration of 6% desflurane. Absolute moisture and temperature of inspired gases were measured as the baseline value first at 5 min after tracheal intubation, and then at 10, 20, 45, 60, 90, and 120 min after the induction of anesthesia. Results At 120 min, the inspiratory humidity and temperature were higher in CCA than in SCA. The HME led to major improvements of the humidity (from 22.1 to 35.7 mg H₂O·l⁻¹) and temperature (from 23.6°C to 31.5°C) of anesthetic gases in the CCA group. Conclusion CCA was much more advantageous than SCA for maintaing the patient’s airway climate during the 2-h study. The beneficial effect of HME on the airway climate should be emphasized, especially in patients undergoing general anesthesia.     

Heat and moisture exchangers and the body temperature: a peroperative study

The importance of conditioning the inhaled gas for maintaining the body temperature during artificial respiration was investigated. The mean body temperature (MBT) was deduced from readings from five measuring sites, four of which were situated at the skin and the fifth in the rectum. Temperature recordings were made every 15th min. Twenty patients were admitted to the study. In 10 patients a heat and moisture exchanger was used (the HME group), and the other 10 were ventilated without an HME (the control group). The patients were normoventilated, and a non-rebreathing system was used. All operations were made in the ENT-region of the body. Great care was taken to avoid variation of external factors that may affect the MBT. We found that the MBT decreased 0.2 degrees C/h less in the HME group than in the control group. If corrections were made for differences in amounts of fluids given and age factors, a difference in heat loss of 41.6 kJ/h between the two groups could be derived from this figure. This difference was statistically significant. Our finding correlated fairly well with a predicted reduction of heat loss of 26.0 kJ/h for the type of HME used. A certain margin of error seemed to be inevitable in measuring body temperatures, and the reason for this is discussed. Our results support the fact that the investigation is adequately designed, and that the heat conserved with an HME is rather low.     

Progressive hypoxemia, hypercarbia and hyperthermia associated with prolonged anesthesia--a case report

The authors report a case of 66-year-old female patient, 55 kg, ASA I who, under general anesthesia in supine position, developed gradual hypoxemia (from a baseline PaO2 of 250 to 91 mmHg), carbon dioxide build up (from a baseline PaCO2 31 to 41 mmHg) associated with gradual hyperthermia up to 38.3 degrees C over seven hours, intraoperatively. These observations were noted while using a semi-closed carbon dioxide absorption circuit in conjunction with the Hygroster filter at a fresh gas flow of 4 1/min of 50% nitrous oxide in oxygen. While the ventilation pattern was unchanged throughout the procedure, there was a change in exhaled tidal and minute ventilation volume with a net decrease of 28 ml and 0.4 l/min respectively. Findings are probably the result of pulmonary atelecatasis under general anesthesia due to the use of a relatively high-inspired oxygen concentration (50%). In addition, the use of a high humidity and temperature heat moisture exchanger (HME) filter (Hygroster) in conjunction with the circle absorber system may have resulted in over humidification and aggravated the pulmonary atelecatasis over the long operative time.