Melted delivery hose — a complication of a heated humidifier

The polyvinylchloride delivery hose of a Fisher & Paykel dual servo heated anaesthetic humidifier was melted by the intraluminal hose heater, causing a major leakage of anaesthetic gases during a surgical procedure. Under experimental conditions, melting could be reproduced using polyvinylchloride but not polyester elastomer tubings. Only tubings made of materials with high melting point should be used as delivery hose in heated humidifiers with hose heaters.     

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.     

Surface-induced Profound Hypothermia in Infant Cardiac Operations: A New System

A new system of surface-induced profound hypothermia for infant cardiac operations has been developed in order to overcome problems inherent in the current techniques using crushed ice, water baths, and similar methods. The hypothermic chamber consists of two parts: a lower part, containing a refrigeration unit and a blower fan capable of lowering the air temperature in the chamber to ?6°GC, and an upper part made of Plexiglas that has a completely detachable end to allow easy access to cannulas, the anesthesia hose, and the infant. A temperature panel recorder to monitor the infant's esophageal and rectal temperatures and the ambient chamber temperature is incorporated into the unit.Following evaluation in the animal laboratory, the hypothermic chamber has been successfully used in 10 infants without any complications attributable to the technique. This method provides a rapid and uniform drop of the body temperature and even skin cooling, eliminates the possibility of contact skin lesions, saves medical and paramedical personnel time in preparation of the infant and equipment, and allows observation of the child during the cooling phase. This hypothermic chamber has facilitated infant hypothermic operations.     

On the problem of optimal warming and moistening of the inspired gases in controlled and assisted artificial ventilation (author's transl)]

The physiological significance of adequate temperature and humidity of respiratory gases and the problems of technical realization are demonstrated. Humidifying and warming of gases by the principle of bubbling through a heated waterbath are believed to be best. The problems with these techniques e.g. dependence of temperature and relative humidity of the gases delivered to the patient on respiratory minute volume, material of the tubing and room temperature are shown. A simple solution to these problems without the need of electrical heated tubing is offered. A new electronically controlled humidifier (H.R.P.-Humidifier 2000) with special developed tubing is presented. Optimal temperature and relative humidity of the respiratory gases is guaranteed by the high efficiency humidifier, and additional measurement and regulation of temperature close to the patients tracheal tube. The problem of increased amounts of condensed water in the tubing is solved by the H.R.P. special tracheal tube adapter with an automatic water exhaust. In addition the hygienic problems of artificial respiration can be solved optimally in combination with the complete H.R.P.-System 2000.     

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 evaluation of laparoscopic insufflation technique for quality control in the OR.

OBJECTIVE: With increasing technology and computerized systems in the OR, the physician's responsibility is growing. For intraoperative evaluation of insufflation techniques, a data acquisition model for quality control study of potential insufflation problems is necessary. METHODS: A computer-based, online data acquisition model was designed with a Pentium notebook, PCMCIA data acquisition board PCI-460-P1 and a Visual Designer 3.0 measurement program (both Intelligent Instrumentation, Inc., Tucson, AZ), temperature meters Therm 2280-1 and 2283-2 (Ahlborn, Holzkirchen, Germany) and temperature probes 401 AC and 402 AC (YSI, Inc., Yellow Springs, OH) and T-430-2R (Ahlborn, Holzkirchen, Germany). Gas flow was measured with laminar flow element LFE 1 and flow meters Digima premo 720 (both Special Instruments, Noerdlingen, Germany). During 73 standard laparoscopic procedures, gas flow (L/min) in the insufflation hose, pressure (mm Hg) in the hose and abdomen as well as temperature (degrees C) in the hose, abdomen and rectum were measured continuously at 3 Hz rate. RESULTS: Actual values measured show a wide range often not identical with insufflator presetting. Pressure in the abdomen is usually less than hose pressure. Intra-abdominal pressure peaks (< or = 50 mm Hg) occurred during insufficient anesthesia, while leaning on the abdomen, during trocar insertion and other manipulation. Blood-irrigation fluids found in the hose (n=3/73) can lead to bacterial contamination. Negative pressure (-50 mm Hg) was measured due to Endobag removal. Negative flow (< or = 15 L/min) was caused by pressure on the abdomen, insufflator regulation and an empty CO2 gas tank. Gas temperature in the hose equals room temperature but can decrease in the abdomen to 27.7 degrees C due to high gas flow, large amounts of gas used and prolonged insufflation. Further insufflation-related problems were documented. CONCLUSIONS: This computer-based measurement model proved to be useful for quality control study in the OR. Results demonstrate the need for intraoperative evaluation of insufflation techniques for laparoscopy. Although no obvious complication related to insufflation problems occurred, some findings potentially question patient security.     

Peroperative Hypothermia

Heat loss during anesthesia and operation and subsequent hypothermia will increase the postoperative oxygen demand and may endanger patients with restricted cardiopulmonary reserves. Forty patients scheduled for intra-abdominal aortic surgery and 40 patients scheduled for peripheral vascular surgery on the lower limbs were investigated using a warming blanket, humidified heated inspired anesthetic gases at 37-40 degrees C, or both these methods together. A fourth group of patients received no active warming. A warming blanket used alone gave no protection against hypothermia when compared with no active warming. In the abdominal surgical group, there was a steady fall in temperature throughout the operation if no warming method was employed. In this group the use of humidified, heated inspired gases was significantly better than no treatment after 2 h of anesthesia (P less than 0.05). The combination of humidified and heated inspired gases and a warming blanket gave significantly better heat preservation after 40 min (P less than 0.05). Patients undergoing peripheral vascular surgery had similar but smaller drops in temperature with the different types of warming procedures employed. The differences in temperature between the intra-abdominal and extra-abdominal operations were statistically significant after 3 h (P less than 0.05).     

Effect of heated humidified gases on temperature drop after cardiopulmonary bypass

In an attempt to prevent the decrease in nasopharyngeal temperature (NPT) ("afterdrop") after cardiac surgery, 30 patients undergoing hypothermic cardiopulmonary bypass (CPB) were randomly assigned to receive humidified heated inspired gases at 45 degrees C at the proximal end of the endotracheal tube (group I) or dry gases at room temperature (group II), from the time of termination of CPB. All patients received high flow rates on CPB during the rewarming period with the use of vasodilator drugs when necessary. Both groups were comparable with respect to total bypass time, rewarming time, and temperature at termination of CPB. In addition, the NPT was compared with the tympanic membrane temperature (TMT) in group I to assess the validity of the NPT under these conditions. The results indicate that heating and humidifying inspired gases do not prevent afterdrop and do not falsely increase the nasopharyngeal temperature. The reasons for the ineffectiveness of heated humidified gases may include a large heat deficit at termination of CPB despite a normal NPT, and the very small heat content of heated gases. Monitoring the temperature of a site that reflects the heat deficit, and a more complete rewarming during CPB are suggested as a better approach to the prevention of afterdrop.     

Cardiac cryolesions: factors affecting their size and a means of monitoring their formation

Twenty-seven endocardial cryolesions were created in mongrel dogs and analyzed to determine the effects on cryolesion size of both the initial myocardial temperature (37 degrees C versus 12 degrees C) and the pressure within the nitrous oxide delivery line (tank pressure of more than 700 pounds per square inch [psi] versus tank pressure of less than 700 psi). In addition, local myocardial temperatures were monitored to determine their utility in the intraoperative determination of the extent of cryothermic cell death. Cryolesion volume was significantly affected by both the initial myocardial temperature (p less than 0.001) and the line pressure (p = 0.014). In a 37 degrees C myocardium, the mean lesion volume ranged from 0.501 +/- 0.183 cc at line pressures lower than 700 psi to 0.839 +/- 0.258 cc at line pressures greater than 700 psi. In a 12 degrees C myocardium, the mean volume was 1.151 +/- 0.436 cc at line pressures lower than 700 psi and 1.361 +/- 0.288 cc at line pressures higher than 700 psi. A myocardial temperature of 0 degrees C occurs at the edge of the area of cell death. When analyzing the range from -5 degrees to +5 degrees C, the probability of a point at or lower than 0 degrees C falling inside the cryolesion is 84.2%. Monitoring intramyocardial temperature will predict the border of a cryolesion.     

European normative recommendations for medical gas pipeline systems

Several recent decisions have been made in order to increase the security of medical gases delivery in French hospitals. These different changes affect: 1) the hospital itself with the creation of working groups in charge of both monitoring and maintenance of gases networks; 2) the pharmaceutical regulation with promotion of several gases to the status of drugs or need of CE marking for the whole gas network. European rules onset required to give up French former norms (NF) to the profit of "NF EN" rules. Nevertheless, the new norm NF EN 737-3 which concerns medical gases distribution systems does not affect principal clauses of the previous NF S 90-155. It introduces new elements allowing to deploy two types of medical gases networks: the double pressure level used in France and the single pressure level used in the rest of Europe. This new norm, which attempts to harmonize alarm control systems in both types of networks, suffers from important limitations describing the double pressure level systems. Lastly, the final checking proposed by this new norm is very different from the previous one, and is likely to be problematic for the final users within the hospital.     

Efficacy of intraoperative heat administration by ventilation with warm humidified gases and an oesophageal warming system

We measured changes in body temperature in 12 hypothermic (mean aural temperature 34.4 (SD 1.0) degrees C) pigs during general anaesthesia with an open abdominal cavity and the effect of two warming systems: heating of inspired gases to 39 degrees C (intratracheal temperature) and oesophageal warming to 39 degrees C by a water perfused oesophageal heat exchanger. Each animal underwent both treatments and the control period in random sequence. Each condition was studied over 1 h. No additional protection against heat loss (drapes, blankets, i.v. fluids warming, etc.) was used. Anaesthesia, room temperature and relative humidity, amount and temperature of infusions and extension of exposed visceral surfaces were standardized. Mean decrease in body temperature was 1.0 (0.7) degree C (P < 0.005) without warming and 0.6 (0.2) degree C (P < 0.005) with heated inspired gases: this difference was not statistically significant. Oesophageal warming was very efficient as mean body temperature did not change significantly (-0.1 (0.2) degree C; ns).      

The double mask

While the consequences of occupational exposure to anesthetic gases and volatile agents on morbidity in operating room staff are controversial (survey in Swiss investigations show a distinct correlation with subjective complaints, e.g. tiredness and headache on the day of exposure (Table 1). In Sweden, rigorous control of occupational exposure to anesthetic gases has prompted development of various scavenging systems, among which the double mask (Fig. 1) is the latest and most advanced. During mask anesthesia, escaping anesthetic gases are evacuated at the point of leakage via a thin slot between a flexible silicone inner mask and a rigid plastic outer mask. A small plate in the mask produces turbulence in the otherwise laminar flow of anesthetic gases, thus reducing the speed of gas leakage. A silicone chamber is mounted on the mask and connected to a fan, requiring a flow of 35 m3/h for optimal function. This chamber does, however, also associate the system with two practical problems: the system with its evacuation tube is heavier to hold than conventional masks, and it is associated with increased dead-space that is only partly minimized by a modification of the Y-connector. While the handling is largely a matter of routine and the weight of the system is minimized when the evacuation tube is arranged to draw slightly upward, the increased dead space may reduce the practicality of the double mask in infants.     

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.     

A carbon chamber for vital microscopy of bone healing

We describe a carbon chamber implanted in the ulna of fowl. A window permitted daily microscopy of bone formation including observations of tetracyline labelling. The chamber could be heated to 5 degrees above body temperature by 600 kHz radio frequency.     

A carbon chamber for vital microscopy of bone healing

We describe a carbon chamber implanted in the ulna of fowl. A window permitted daily microscopy of bone formation including observations of tetracyline labelling. The chamber could be heated to 5° above body temperature by 600 kHz radio frequency.     

Heated breathing tubes affect humidity output of circle absorber systems

Study Objective: To verify whether the airway climate in circle systems can be improved with heated breathing tubes.

Design: Randomized, controlled, prospective clinical study.

Setting: Operating theater of the Department of Maxillofacial Surgery.

Patients: 26 adult patients undergoing prolonged anesthesia.

Interventions: A total of 26 prolonged anesthetics were conducted in adult patients using a minimal fresh gas flow rate (0.6 L/min) and silicon breathing tubes (16 mm internal diameter) containing a heated coil. Group 1 (n = 10 patients) was the control group; breathing tubes were unheated. In Group 2 (n = 10 patients), breathing tubes were heated to 30°C. In Group 3 (n = 6 patients), breathing tubes were heated to 36°C.

Measurements and Main Results: Humidity and temperature were measured at the Y-piece. Inspiratory temperature in Group 2 was significantly higher than in Group 1. In Group 3, both inspiratory temperature and absolute humidity were significantly higher than in Group 1. After 5 minutes of ventilation, water content and temperature of inspiratory gases were significantly higher in Group 3 than in Group 1.

Conclusion: Low flow systems need at least 120 minutes to achieve a satisfactory airway climate. Heated breathing tubes effectively reduce this delay.     

Heated humidification in major abdominal surgery

The influence of heated humidification on body temperature and postoperative shivering was studied in 30 patients undergoing major intra-abdominal surgery. In the control group (I) the anaesthetic gases, administered in a non-rebreathing system, were humidified by a sponge heat and moisture exchanger. In group II the gases were humidified and heated to 37 degrees C and in group III up to 40 degrees C. Anaesthesia, surface insulation and warming of the infusions were standardized. The temperature was registered at the lower oesophagus and the big toe. Shivering and the feeling of cold were estimated at 15 min intervals postoperatively. A good correlation was found between heat gain during the first hour of recovery, the feeling of cold and intensity of shivering. Intraoperative heat loss was minimal in all groups. Heated humidification had no statistically significant effect on the body temperatures or postoperative shivering and thus provided no additional advantage compared to the control group.     

Active warming of saline or blood is ineffective when standard infusion tubing is used: an experimental study

PURPOSE: To determine the effect of infusion rate, tubing length and fluid composition on the temperature of the infusate reaching the distal end of an infusion tubing with and without active fluid warming. METHODS: Warmed normal saline (W-NS) and packed red blood cells (W-PRBC), were infused with a fluid warmer through a modified infusion set. The fluids were delivered at eight infusion rates from 50 to 999 mL x hr(-1). The infusate temperature was monitored at 20 cm intervals on the iv tubing. The same temperature monitoring protocol was applied to PRBC without warmer (NoW-PRBC). RESULTS: In W-NS and W-PRBC groups, there was a decrease in the infusate temperature, at each flow rate, from the drip chamber to the distal end of tubing ( P <0.001). In NoW-PRBC group, there was a rapid increase in the infusate temperature from the bag to the drip chamber ( P <0.001). Thereafter, there was no change in temperature, except at the 999 mL x hr(-1) infusion rate, where a slight increase in the infusate temperature throughout the tubing was shown. In W-NS and W-PRBC groups increasing the flow rate produced a significant increase in the infusate temperature, at each measurement point ( P <0.001). In the NoW-PRBC group, increasing the flow rate did not alter the infusate temperature. The fluid composition did not influence the infusate temperature. CONCLUSION: There is an important heat exchange within the tubing, which is aggravated at low flow rates. At infusion rates appropriate for pediatric anesthesia the clinical and economic value of fluid warming without the use of heated extension tubing is questionable.     

Supersonic Flows with Nontraditional Transport Described by Kinetic Methods

A new class of supersonic nonequilibrium flows is studied on the basis of solving the Boltzmann and model kinetic equations with the aim to consider new nonlinear structures in open systems and to study anomalous transfer properties in relaxation zones. The Unified Flow Solver is applied for numerical simulations. Simple gases and gases with inner degrees of freedom are considered. The experimental data related to the influence of the so-called optical lattices on the supersonic molecular beams are considered and numerical analysis of the nonequilibrium states obtained on this basis is made. The nonuniform relaxation problem with these distributions is simulated numerically and anomalous transport is confirmed. The conditions for strong changes of the temperature in the anomalous transfer zones are discussed and are realized in computations.     

TEMPERATURE ALARM AND CUT-OUT SYSTEM FOR USE WITH HEATED WATER HUMIDIFIERS

The temperature of the inspired humidified gases of an intubatedpatient may be monitored accurately, close to the airway, bya commercially available thermistor probe and alarm/cut-outdevice for use with heated water humidifiers. The apparatusis designed to alarm when the inspired gas temperature exceedsthe pre-set temperature and when the thermistor probe is inopen or short circuit. When the temperature alarm is activated,the humidifier heater is switched off automatically, thus preventingprolonged transmission of excessively hot gases to the airway.The apparatus has been used successfully in this hospital forseveral months, requiring minimal observer attention and maintenance.