Effects of autoclaving and disinfection on 3D surgical guides using LCD technology for dental implant

BACKGROUND

Surgical guides can improve the precision of implant placement and minimize procedural errors and their related complications. This study aims to determine how different disinfection and sterilization methods affect the size changes of drill guide templates and the mechanical properties of 3D-printed surgical guides made with LCD technology.

METHODS

We produced a total of 100 samples. Forty surgical guides were fabricated to assess the implant drill guides' surface and geometric properties. We subjected sixty samples to mechanical tests to analyze their tensile, flexural, and compressive properties. We classified the samples into four groups based on each analytical method: GC, which served as the control group; GA, which underwent autoclave sterilization at 121 °C (+ 1 bar, 20 min); GB, which underwent autoclave sterilization at 134 °C (+ 2 bar, 10 min); and GL, which underwent disinfection with 70% isopropyl alcohol for 20 min.

RESULT

The results show that sterilization at 121 °C and 134 °C affects the mechanical and geometric characteristics of the surgical guides, while disinfection with 70% isopropyl alcohol gives better results.

CONCLUSION

Our study of 3D-printed surgical guides using LCD technology found that sterilization at high temperatures affects the guides' mechanical and geometric properties. Instead, disinfection with 70% isopropyl alcohol is recommended.

Bibliometric analysis on palliative care in Morocco

BACKGROUND

No specific evaluation of palliative care (PC) has been carried out to date despite its effective integration into Moroccan healthcare strategy.

AIMS

To analyse the evolution of PC-related research in Morocco over the last two decades.

METHODS

In this study, articles indexed in Web Of Science and PubMED that include the words Morocco and palliative, in their content, in French and English, with at least one author affiliated to a Moroccan institution and published between 2000 and 2020, were evaluated with bibliometrics methods to determine a timeline, a mapping of publications and collaborations, and the main journals, types and topics of publications.

FINDINGS

A total of 87.1% of articles have been published since 2011. Some 82.1% concern oncology. A total of 48.5% were produced within the same institution and international collaboration represents only 9.9% of the articles.

CONCLUSION

The number of PC related articles have increased since 2011, especially in regions with a greater supply of oncology care.

Quantification of Passive Ventilation Produced by Manual Chest Compressions Using a New Cardiopulmonary Resuscitation Feedback Device

Several studies have shown that chest compressions (CC) alone may produce in addition to blood circulation, a short-term passive ventilation. However, it is not clear whether high CC quality may produce in even greater amount of ventilation volumes. The aim of this study was to evaluate whether CC, using a new feedback device, can produce a substantial and sustainable passive volumes compared to standard CC. Thirty inexperienced volunteers performed CC for 2 min on a developed thoracic lung model and using a new feedback device. Participants were randomized into two groups that performed either CC with feedback first, followed by a trial without feedback, or vice versa. Efficient compression rate (correct CC rate and depth simultaneously) was significantly higher in feedback session (43.6% versus 25.5%; P = 0.006). As well, CC rate and depth efficiency were improved with feedback. Moreover, average tidal volumes and minute volumes that occurred during CC alone were significantly improved in feedback session (79.8 ± 5 ml versus 72.9 ± 7 ml) and (8.8 l/min versus 7.9 l/min), respectively (P < 0.001). Yet, no significant difference was found between the first and the 90th second interval (9.04 l/min versus 8.68 l/min, P = 0.163) in the feedback session. Conversely, a significant difference was evident after the first 15th seconds interval without feedback (8.77 l/min initially versus 8.38 l/min; P = 0.041). This study revealed that the new CPR feedback device improved CC quality in inexperienced volunteers. As well, the passive ventilation volumes were significantly increased and sustained when the device was used.

Imposed Work of Breathing During High-Frequency Oscillatory Ventilation in Spontaneously Breathing Neonatal and Pediatric Models

BACKGROUND

High-frequency oscillatory ventilation (HFOV) is used in cases of neonatal and pediatric acute respiratory failure, sometimes even as the primary ventilatory mode. Allowing patients (at least neonates) on HFOV to breathe spontaneously soon after intubation has been shown to be feasible, and this is becoming a more generally used approach for infants and small children. However, such an approach may increase the imposed work of breathing (WOB), raising the question of whether the imposed WOB varies with the use of newer-generation HFOV devices, which operate according to different functional principles.

METHODS

A bench test was designed to compare the pressure-time product (PTP), a surrogate marker of the imposed WOB, produced with the use of 7 HFOV devices. Scenarios corresponding to various age groups (preterm newborn [1 kg], term newborn [3.5 kg], infant [10 kg], and child [25 kg]) and 2 respiratory system conditions (physiologic and pathologic) were tested.

RESULTS

The PTP varied between devices and increased with the oscillation frequency for all devices, independent of the respiratory system condition. Furthermore, the PTP increased with age and was higher for physiologic than for pathologic respiratory system conditions. We considered a change of ≥ 20% as being of clinically relevant; the effect of oscillation frequency was the most important parameter influencing imposed WOB during spontaneous breathing.

CONCLUSIONS

Variations in imposed WOB, as expressed by PTP values, during spontaneous breathing depend mainly on the oscillator frequency, respiratory system condition, and, though to a lesser extent, on the device itself.

How Ventilation Is Delivered During Cardiopulmonary Resuscitation: An International Survey

BACKGROUND

Recommendations regarding ventilation during cardiopulmonary resuscitation (CPR) are based on a low level of scientific evidence. We hypothesized that practices about ventilation during CPR might be heterogeneous and may differ worldwide. To address this question, we surveyed physicians from several countries on their practices during CPR.

METHODS

We used a Web-based opinion survey. Links to the survey were sent by e-mail newsletters and displayed on the Web sites of medical societies involved in CPR practice from December 2013 to March 2014.

RESULTS

1,328 surveys were opened, and 548 were completed (41%). Responses came from 54 countries, but 64% came from 6 countries. Responders were mostly physicians (89%). From this group, 97% declared following specific CPR guidelines. Regarding practices, 28% declared always or frequently adopting only continuous chest compressions without additional ventilation. With regard to mechanical chest compression devices, 38% responded that such devices were available to them; when used, 28% declared always or frequently experiencing problems with ventilation such as frequent alarms. During bag-mask ventilation in intubated patients, 18% declared stopping chest compression during insufflation, and 39% applied > 10 breaths/min, which conflicts with international CPR guidelines. When a ventilator was used, the volume controlled mode was the most common strategy cited, but there was heterogeneity regarding ventilator settings for PEEP, trigger, F_IO2 , and breathing frequency. S_pO2 and end-tidal CO₂ were the 2 most monitored variables cited.

CONCLUSIONS

Physicians indicated heterogeneous practices that often differ significantly from international CPR guidelines. This may reflect the low level of evidence and a lack of detailed recommendations concerning ventilation during CPR.

Design of a new artificial breathing system for simulating the human respiratory activities

The purpose of this work is the conception and implementation of an artificial active respiratory system that allows the simulation of human respiratory activities. The system consists of two modules, mechanical and electronical. The first one represents a cylindrical lung adjustable in resistance and compliance. This lung is located inside a transparent thoracic box, connected to a piston that generates variable respiratory efforts. The parameters of the system, which are pressure, flow and volume, are measured by the second module. A computer application was developed to control the whole system, and enables the display of the parameters. A series of tests were made to evaluate the respiratory efforts, resistances and compliances. The results were compared to the bibliographical studies, allowing the validation of the proposed system.

Can proportional ventilation modes facilitate exercise in critically ill patients? A physiological cross-over study : Pressure support versus proportional ventilation during lower limb exercise in ventilated critically ill patients

Background

Early exercise of critically ill patients may have beneficial effects on muscle strength, mass and systemic inflammation. During pressure support ventilation (PSV), a mismatch between demand and assist could increase work of breathing and limit exercise. A better exercise tolerance is possible with a proportional mode of ventilation (Proportional Assist Ventilation, PAV+ and Neurally Adjusted Ventilatory Assist, NAVA). We examined whether, in critically ill patients, PSV and proportional ventilation have different effects on respiratory muscles unloading and work efficiency during exercise.

Methods

Prospective pilot randomized cross-over study performed in a medico-surgical ICU. Patients requiring mechanical ventilation >48 h were enrolled. At initiation, the patients underwent an incremental workload test on a cycloergometer to determine the maximum level capacity. The next day, 2 15-min exercise, at 60% of the maximum capacity, were performed while patients were randomly ventilated with PSV and PAV+ or NAVA. The change in oxygen consumption (ΔVO₂, indirect calorimetry) and the work efficiency (ratio of ΔVO₂ per mean power) were computed.

Results

Ten patients were examined, 6 ventilated with PSV/PAV+ and 4 with PSV/NAVA. Despite the same mean inspiratory pressure at baseline between the modes, baseline VO₂ (median, IQR) was higher during proportional ventilation (301 ml/min, 270–342) compared to PSV (249 ml/min, 206–353). Exercise with PSV was associated with a significant increase in VO₂ (ΔVO₂, median, IQR) (77.6 ml/min, 59.9–96.5), while VO₂ did not significantly change during exercise with proportional modes (46.3 ml/min, 5.7–63.7, p < 0.05). As a result, exercise with proportional modes was associated with a better work efficiency than with PSV. The ventilator modes did not affect patient’s dyspnea, limb fatigue, distance, hemodynamics and breathing pattern.

Conclusions

Proportional ventilation during exercise results in higher work efficiency and less increase in VO₂ compared to ventilation with PSV. These preliminary findings suggest that proportional ventilation could enhance the training effect and facilitate rehabilitation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0289-y) contains supplementary material, which is available to authorized users.

Accuracy of delivered airway pressure and work of breathing estimation during proportional assist ventilation: a bench study

Background

Proportional assist ventilation+ (PAV+) delivers airway pressure (P_aw) in proportion to patient effort (P_mus) by using the equation of motion of the respiratory system. PAV+ calculates automatically respiratory mechanics (elastance and resistance); the work of breathing (WOB) is estimated by the ventilator. The accuracy of P_mus estimation and hence accuracy of the delivered P_aw and WOB calculation have not been assessed. This study aimed at assessing the accuracy of delivered P_aw and calculated WOB by PAV+ and examining the factors influencing this accuracy.

Methods

Using an active lung model with different respiratory mechanics, we compared (1) the actual delivered P_aw by the ventilator to the theoretical P_aw as defined by the equation of motion and (2) the WOB value displayed by the ventilator to the WOB measured from a Campbell diagram.

Results

Irrespective of respiratory mechanics and gain, the ventilator provided a P_aw approximately 25 % lower than expected. This underassistance was greatest at the beginning of the inspiration. Intrinsic PEEP (PEEPi), associated with an increase in trigger delay, was a major factor affecting PAV+ accuracy. The absolute value of total WOB displayed by the ventilator was underestimated, but the changes in WOB were accurately detected by the ventilator.

Conclusion

The assistance provided by PAV+ well follows P_mus but with a constant underassistance. This is associated with an underestimation by the ventilator of the WOB. PEEPi can be a major factor contributing to PAV+ inaccuracy. Clinical recommendations should include using a high trigger sensitivity and a careful PEEP titration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0131-y) contains supplementary material, which is available to authorized users.

Impact of ventilation strategies during chest compression. An experimental study with clinical observations

The optimal ventilation strategy during cardiopulmonary resuscitation (CPR) is unknown. Chest compression (CC) generates circulation, while during decompression, thoracic recoil generates negative pressure and venous return. Continuous flow insufflation of oxygen (CFI) allows noninterrupted CC and generates positive airway pressure (Paw). The main objective of this study was to assess the effects of positive Paw compared with the current recommended ventilation strategy on intrathoracic pressure (P(IT)) variations, ventilation, and lung volume. In a mechanical model, allowing compression of the thorax below an equilibrium volume mimicking functional residual capacity (FRC), CC alone or with manual bag ventilation were compared with two levels of Paw with CFI. Lung volume change below FRC at the end of decompression and P(IT), as well as estimated alveolar ventilation, were measured during the bench study. Recordings were obtained in five cardiac arrest patients to confirm the bench findings. Lung volume was continuously below FRC, and as a consequence P(IT) remained negative during decompression in all situations, including with positive Paw. Compared with manual bag or CC alone, CFI with positive Paw limited the fall in lung volume and resulted in larger positive and negative P(IT) variations. Positive Paw with CFI significantly augmented ventilation induced by CC. Recordings in patients confirmed a major loss of lung volume below FRC during CPR, even with positive Paw. Compared with manual bag ventilation, positive Paw associated with CFI limits the loss in lung volume, enhances CC-induced positive P(IT), maintains negative P(IT) during decompression, and generates more alveolar ventilation.

Ventilator-integrated jet nebulization systems: tidal volume control and efficiency of synchronization

BACKGROUND

Jet nebulizers constitute the aerosolization devices most frequently used during mechanical ventilation. Continuous nebulization can influence the delivered tidal volume (V(T)) and lead to significant medication loss during expiration. Ventilators thus provide integrated jet nebulization systems that are synchronized during inspiration and ostensibly keep VT constant.

METHODS

This was a bench study of systems integrated in the Evita XL, Avea, Galileo, and G5 ventilators. The VT delivered with and without nebulization, the inspiratory synchronization of nebulization, and the aerosol deposition were measured with 2 locations of the nebulizer.

RESULTS

Changes in V(T) with the nebulizer were below 20 mL and below 10% of set V(T) for all ventilators. Synchronization was good at the beginning of insufflation, but prolonged nebulization was observed with all ventilators at the end of insufflation, until up to 1 s during expiration: 5-80% of nebulization occurred during expiration with significant aerosol loss in the expiratory limb. Synchrony could be improved by (1) reducing gas compression/decompression phenomena proximal to the jet nebulizer and (2) increasing inspiratory time, which reduced the amount of nebulization occurring during expiration. Placing the nebulizer upstream in the inspiratory limb did not affect inspiratory synchrony but allowed reduction of the amount of aerosol lost in the expiratory limb.

CONCLUSIONS

Jet nebulizer systems integrated in the tested ventilators are reliable in terms of V(T) control. Gas compression in tubing driving gas to the nebulizer delays synchronization and reduces nebulization yield if the nebulizer is placed close to the Y-piece. Increasing inspiratory time with no end-inspiratory pause reduces the expiratory loss of medication if placement of the nebulizer upstream in the inspiratory limb is not feasible.

[Cardiopulmonary resuscitation: risks and benefits of ventilation]

Knowledge of the physiological mechanisms that govern cardiopulmonary interactions during cardiopulmonary resuscitation (CPR) allows to better assess risks and benefits of ventilation. Ventilation is required to maintain gas exchange, particularly when CPR is prolonged. Nevertheless, conventional ventilation (bag mask or mechanical ventilation) may be harmful when excessive or when chest compressions are interrupted. In fact large tidal volume and/or rapid respiratory rate may adversely compromise hemodynamic effects of chest compressions. In this regard, international recommendations that give the priority to chest compressions, are meaningful. Continuous flow insufflation with oxygen that generates a moderate positive airway pressure avoids any interruption of chest compressions and prevents the risk of lung injury associated with prolonged resuscitation.

Potentially harmful effects of inspiratory synchronization during pressure preset ventilation

PURPOSE

Pressure preset ventilation (PPV) modes with set inspiratory time can be classified according to their ability to synchronize pressure delivery with patient's inspiratory efforts (i-synchronization). Non-i-synchronized (like airway pressure release ventilation, APRV), partially i-synchronized (like biphasic airway pressure), and fully i-synchronized modes (like assist-pressure control) can be distinguished. Under identical ventilatory settings across PPV modes, the degree of i-synchronization may affect tidal volume (VT), transpulmonary pressure (PTP), and their variability. We performed bench and clinical studies.

METHODS

In the bench study, all the PPV modes of five ventilators were tested with an active lung simulator. Spontaneous efforts of -10 cmH2O at rates of 20 and 30 breaths/min were simulated. Ventilator settings were high pressure 30 cmH2O, positive end-expiratory pressure (PEEP) 15 cmH2O, frequency 15 breaths/min, and inspiratory to expiratory ratios (I:E) 1:3 and 3:1. In the clinical studies, data from eight intubated patients suffering from acute respiratory distress syndrome (ARDS) and ventilated with APRV were compared to the bench tests. In four additional ARDS patients, each of the PPV modes was compared.

RESULTS

As the degree of i-synchronization among the different PPV modes increased, mean VT and PTP swings markedly increased while breathing variability decreased. This was consistent with clinical comparison in four ARDS patients. Observational results in eight ARDS patients show low VT and a high variability with APRV.

CONCLUSION

Despite identical ventilator settings, the different PPV modes lead to substantial differences in VT, PTP, and breathing variability in the presence spontaneous efforts. Clinicians should be aware of the possible harmful effects of i-synchronization especially when high VT is undesirable.

[Non-invasive ventilation: indication for acute respiratory failure]

Mask or Non-invasive ventilation (NIV) is used for critically ill patients with acute respiratory failure (ARF): acute exacerbation of chronic obstructive bronchopulmonary disease and severe cardiogenic pulmonary edema are considered as the best indications for NIV since it improves the outcome of these patients. This technique is also proposed for hypoxemic respiratory failure, with more various results. To be effective here, NIV must be established early enough and should not delay intubation if required. NIV is also proposed after invasive ventilation or in patients in whom endotracheal intubation is not desirable. Its use has increased and its effectiveness seems to have improved, due to a better understanding of the technique but also thanks to technological progress.

Patient-ventilator asynchrony during noninvasive ventilation: a bench and clinical study

BACKGROUND

Different kinds of ventilators are available to perform noninvasive ventilation (NIV) in ICUs. Which type allows the best patient-ventilator synchrony is unknown. The objective was to compare patient-ventilator synchrony during NIV between ICU, transport—both with and without the NIV algorithm engaged—and dedicated NIV ventilators.

METHODS

First, a bench model simulating spontaneous breathing efforts was used to assess the respective impact of inspiratory and expiratory leaks on cycling and triggering functions in 19 ventilators. Second, a clinical study evaluated the incidence of patient-ventilator asynchronies in 15 patients during three randomized, consecutive, 20-min periods of NIV using an ICU ventilator with and without its NIV algorithm engaged and a dedicated NIV ventilator. Patient-ventilator asynchrony was assessed using flow, airway pressure, and respiratory muscles surface electromyogram recordings.

RESULTS

On the bench, frequent auto-triggering and delayed cycling occurred in the presence of leaks using ICU and transport ventilators. NIV algorithms unevenly minimized these asynchronies, whereas no asynchrony was observed with the dedicated NIV ventilators in all except one. These results were reproduced during the clinical study: The asynchrony index was significantly lower with a dedicated NIV ventilator than with ICU ventilators without or with their NIV algorithm engaged (0.5% [0.4%-1.2%] vs 3.7% [1.4%-10.3%] and 2.0% [1.5%-6.6%], P < .01), especially because of less auto-triggering.

CONCLUSIONS

Dedicated NIV ventilators allow better patient-ventilator synchrony than ICU and transport ventilators, even with their NIV algorithm. However, the NIV algorithm improves, at least slightly and with a wide variation among ventilators, triggering and/or cycling off synchronization.

Bench testing of a new hyperbaric chamber ventilator at different atmospheric pressures

PURPOSE

Providing mechanical ventilation is challenging at supra-atmospheric pressure. The higher gas density increases resistance, reducing the flow delivered by the ventilator. A new hyperbaric ventilator (Siaretron IPER 1000) is said to compensate for these effects automatically. The aim of this bench test study was to validate the compensation, define its limits and provide details on the ventilator's output at varied atmospheric pressures.

METHODS

Experiments were conducted inside a multiplace hyperbaric chamber at 1, 2.2, 2.8 and 4 atmospheres absolute (ATA), with the ventilator connected to a test lung. Transducers were recalibrated at each ATA level. Various ventilator settings were tested in volume and pressure control modes. Measured tidal volumes were compared with theoretical predictions based on gas laws.

RESULTS

Results confirmed the ventilator's ability to provide compensation, but also identified its limits. The compensation range could be predicted and depended on the maximal flow attainable, decreasing linearly with increasing atmospheric pressure. With settings inside the range, tidal volumes approximated set values (mean error 10 ± 5 %). With settings outside the range, the volume was limited to the predicted maximal value calculated from maximal flow. A practical guide for clinicians is provided.

CONCLUSION

The IPER 1000 ventilator attempted to deliver stable tidal volume by adjusting the opening of the inspiratory valve in proportion to atmospheric pressure. Adequate compensation was observed, albeit only within a predictable range, which can be reliably predicted for each setting and ATA level combination. Setting a tidal volume outside this range can result in an unwanted decrease in minute ventilation.

Diaphragm ultrasonography to estimate the work of breathing during non-invasive ventilation

PURPOSE

Ultrasonography allows the direct observation of the diaphragm. Its thickness variation measured in the zone of apposition has been previously used to diagnose diaphragm paralysis. We assessed the feasibility and accuracy of this method to assess diaphragmatic function and its contribution to respiratory workload in critically ill patients under non-invasive ventilation.

METHODS

This was a preliminary physiological study in the intensive care unit of a university hospital. Twelve patients requiring planned non-invasive ventilation after extubation were studied while spontaneously breathing and during non-invasive ventilation at three levels of pressure support (5, 10 and 15 cmH(2)O). Diaphragm thickness was measured in the zone of apposition during tidal ventilation and the thickening fraction (TF) was calculated as (thickness at inspiration - thickness at expiration)/thickness at expiration. Diaphragmatic pressure-time product per breath (PTP(di)) was measured from oesophageal and gastric pressure recordings.

RESULTS

PTP(di) and TF both decreased as the level of pressure support increased. A significant correlation was found between PTP(di) and TF (ρ = 0.74, p < 0.001). The overall reproducibility of TF assessment was good but the coefficient of repeatability reached 18% for inter-observer reproducibility.

CONCLUSIONS

Ultrasonographic assessment of the diaphragm TF is a non-invasive method that may prove useful in evaluating diaphragmatic function and its contribution to respiratory workload in intensive care unit patients.

Intrapulmonary percussive ventilation superimposed on conventional ventilation: bench study of humidity and ventilator behaviour

OBJECTIVE

Intrapulmonary percussive ventilation (IPV) is a form of high-frequency ventilation that can be superimposed on spontaneous breathing or conventional ventilation. Drawbacks include difficulties achieving adequate airway humidification and an inability to monitor delivered volumes and pressures, which may vary with patient characteristics. The objectives of this study were to assess various humidification set-ups, to measure intrapulmonary pressures and volumes resulting from IPV superimposed on a conventional driving ventilator (DV) and to test several ventilators regarding their ability to accept added IPV.

DESIGN

Bench study in a test-lung set-up was used to measure humidification and the effects of adding IPV to a DV under various conditions of compliance, resistance, plateau and positive end-expiratory pressures. Then, five ventilators were tested in combination with IPV.

MEASUREMENTS AND RESULTS

Adequate humidification required a heated humidifier on the inspiratory line downstream of the IPV device. IPV increased end-inspiratory intrapulmonary pressures up to 10 cmH(2)O, increased delivered volumes up to 237 ml and generated intrinsic PEEP from 1.7 to 4.3 cmH(2)O when no PEEP was set on the DV. Intrinsic PEEP was lower or absent when PEEP was set on the DV. With most tested ventilators, IPV prevented reliable flow monitoring. Autotriggering and missing cycles were common and the PEEP effect varied across DVs.

CONCLUSION

Achieving adequate humidification with IPV requires a specific set-up. Superimposing IPV on standard ventilation can increase intrapulmonary pressures and tidal volumes importantly and interfere with the triggering sensors of the ventilator. These factors must be taken into account before clinical use.

Under-humidification and over-humidification during moderate induced hypothermia with usual devices

OBJECTIVE

In mechanically ventilated patients with induced hypothermia, the efficacy of heat and moisture exchangers and heated humidifiers to adequately humidify the airway is poorly known. The aim of the study was to assess the efficacy of different humidification devices during moderate hypothermia.

DESIGN

Prospective, cross-over randomized study.

SETTINGS

Medical Intensive Care Unit in a University Hospital.

PATIENTS AND PARTICIPANTS

Nine adult patients hospitalized after cardiac arrest in whom moderate hypothermia was induced (33 degrees C for 24[Symbol: see text]h).

INTERVENTIONS

Patients were ventilated at admission (period designated "normothermia") with a heat and moisture exchanger, and were randomly ventilated during hypothermia with a heat and moisture exchanger, a heated humidifier, and an active heat and moisture exchanger.

MEASUREMENTS AND RESULTS

Core temperature, inspired and expired gas absolute and relative humidity were measured. Each system demonstrated limitations in its ability to humidify gases in the specific situation of hypothermia. Performances of heat and moisture exchangers were closely correlated to core temperature (r (2)[Symbol: see text]=[Symbol: see text]0.84). During hypothermia, heat and moisture exchangers led to major under-humidification, with absolute humidity below 25[Symbol: see text]mgH(2)O/l. The active heat and moisture exchanger slightly improved humidification. Heated humidifiers were mostly adequate but led to over-humidification in some patients, with inspiratory absolute humidity higher than maximal water content at 33 degrees C with a positive balance between inspiratory and expiratory water content.

CONCLUSIONS

These results suggest that in the case of moderate hypothermia, heat and moisture exchangers should be used cautiously and that heated humidifiers may lead to over-humidification with the currently recommended settings.