Effects of dry air and subsequent humidification on tracheal mucous velocity in dogs

Water Sorption and Structural Properties of Human Airway Mucus in Health and Muco-Obstructive Diseases

Muco-obstructive diseases change airway mucus properties, impairing mucociliary transport and increasing the likelihood of infections. To investigate the sorption properties and nanostructures of mucus in health and disease, we investigated mucus samples from patients and cell cultures (cc) from healthy, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) airways. Atomic force microscopy (AFM) revealed mucin monomers with typical barbell structures, where the globule to spacer volume ratio was the highest for CF mucin. Accordingly, synchrotron small-angle X-ray scattering (SAXS) revealed more pronounced scattering from CF mucin globules and suggested shorter carbohydrate side chains in CF mucin and longer side chains in COPD mucin. Quartz crystal microbalance with dissipation (QCM-D) analysis presented water sorption isotherms of the three types of human airway mucus, where, at high relative humidity, COPD mucus had the highest water content compared to cc-CF and healthy airway mucus (HAM). The higher hydration of the COPD mucus is consistent with the observation of longer side chains of the COPD mucins. At low humidity, no dehydration-induced glass transition was observed in healthy and diseased mucus, suggesting mucus remained in a rubbery state. However, in dialyzed cc-HAM, a sorption-desorption hysteresis (typically observed in the glassy state) appeared, suggesting that small molecules present in mucus suppress the glass transition.

Clinical review of high-flow nasal oxygen therapy in human and veterinary patients

Oxygen therapy is the first-line treatment for hypoxemic acute respiratory failure. In veterinary medicine this has traditionally been provided via mask, low-flow nasal oxygen cannulas, oxygen cages and invasive positive pressure ventilation. Traditional non-invasive modalities are limited by the maximum flow rate and fraction of inspired oxygen (FiO₂) that can be delivered, variability in oxygen delivery and patient compliance. The invasive techniques are able to provide higher FiO₂ in a more predictable manner but are limited by sedation/anesthesia requirements, potential complications and cost. High-flow nasal oxygen therapy (HFNOT) represents an alternative to conventional oxygen therapy. This modality delivers heated and humidified medical gas at adjustable flow rates, up to 60 L/min, and FiO₂, up to 100%, via nasal cannulas. It has been proposed that HFNOT improves pulmonary mechanics and reduces respiratory fatigue via reduction of anatomical dead space, provision of low-level positive end-expiratory pressure (PEEP), provision of constant FiO₂ at rates corresponding to patient requirements and through improved patient tolerance. Investigations into the use of HFNOT in veterinary patients have increased in frequency since its clinical use was first reported in dogs with acute respiratory failure in 2016. Current indications in dogs include acute respiratory failure associated with pulmonary parenchymal disease, upper airway obstruction and carbon monoxide intoxication. The use of HFNOT has also been advocated in certain conditions in cats and foals. HFNOT is also being used with increasing frequency in the treatment of a widening range of conditions in humans. Although there remains conflict regarding its use and efficacy in some patient groups, overall these reports indicate that HFNOT decreases breathing frequency and work of breathing and reduces the need for escalation of respiratory support. In addition, they provide insight into potential future veterinary applications. Complications of HFNOT have been rarely reported in humans and animals. These are usually self-limiting and typically result in lower morbidity and mortality than those associated with invasive ventilation techniques.

In-silico decongested trial effects on the impaired breathing function of a bulldog suffering from severe brachycephalic obstructive airway syndrome

BACKGROUND AND OBJECTIVE

Brachycephalic obstructive airway syndrome (BOAS) susceptible dogs (e.g., French bulldog), suffer health complications related to deficient breathing primarily due to anatomical airway geometry. Surgical interventions are known to provide acceptable functional and cosmetic results; however, the long-term post-surgery outcome is not well known. In silico analysis provides an objective measure to quantify the respiratory function in postoperative dogs which is critical for successful long-term outcomes. A virtual surgery to open the airway can explore the ability for improved breathing in an obstructed airway of a patient dog, thus supporting surgeons in pre-surgery planning using computational fluid dynamics.

METHODS

In this study five surgical interventions were generated with a gradual increment of decongested levels in a bulldog based on computed tomography images. The effects of the decongested airways on the breathing function of a patient bulldog, i.e., airflow characteristics, pressure drop, wall shear stress, and air-conditioning capacity, were quantified by benchmarking against a clinically healthy bulldog using computational fluid dynamics (CFD) method.

RESULTS

Our findings demonstrated a promising decrease in excessive airstream velocity, pressure drop, and wall shear stress in virtual surgical scenarios, while constantly preserving adequate air-conditioning efficiency. A linear fit curve was proposed to correlate the reduction in the pressure drop and decongested level.

CONCLUSIONS

The in silico analysis is a viable tool providing visual and quantitative insight into new unexplored surgical techniques.

A Review of High Flow Nasal Cannula Oxygen Therapy in Human and Veterinary Medicine

Respiratory distress is a common ailment in small animal medicine. Oxygen supplementation is a mainstay of initial therapy. High Flow Nasal Cannula Oxygen Therapy (HFNCOT) has become increasingly popular as a treatment modality in human medicine, and more recently in canine patients. These devices deliver high flow rates of heated and humidified oxygen at an adjustable fraction of inspired oxygen (FiO₂). This article reviews current literature in human patients on HFNCOT as well as studies that have evaluated its use in veterinary patients. A discussion of the respiratory physiology that is associated with respiratory distress, in addition to an overview of currently available oxygen supplementation modalities is provided. The physiologic benefits of HFNCOT are explained, as are technical aspects associated with its use. Recommendations on initial settings, maintenance therapy, and weaning are also described.

Rapid changes in mucociliary transport in the tracheal epithelium caused by unconditioned room air or nebulized hypertonic saline and mannitol are not determined by frequency of beating cilia

Background

Inspired air is heated and humidified in the nose before it reaches lower airways. This mechanism is bypassed during tracheostomy, directly exposing the airways to colder and drier air from the environment, known to negatively affect mucociliary transport; however, little is known about how quickly mucociliary transport deteriorates. This study determines the short-term effect of flowing room air and nebulized hypertonic saline and mannitol on mucociliary transport in the trachea. In an ovine perfused in vitro tracheal model (N = 9) the epithelium was exposed to 25 L/min of flow, heated to lamb body temperature (38 °C) and fully saturated with water vapor as the control, followed by either room air (22 °C and 50% relative humidity) or nebulized solutions of NaCl 7% and mannitol 20% up to 1 min for a short duration, until mucociliary transport had visually changed. Mucus transport velocity (MTV) and cilia beat frequency (CBF) were continuously measured with video-microscopy.

Results

Exposing the tracheal epithelium to air heated to body temperature and fully humidified had stable MTV 9.5 ± 1.1 mm/min and CBF 13.4 ± 0.6 Hz. When exposed to flow of room air, MTV slowed down to 0.1 ± 0.1 mm/min in 2.0 ± 0.4 s followed by a decrease in CBF to 6.7 ± 1.9 Hz, after 2.3 ± 0.8 s. Both MTV and CBF recovered to their initial state when heated and humidified air-flow was re-introduced. Exposing the tracheal epithelium to nebulized hypertonic saline and nebulized mannitol for 1 min increased MTV without a subsequent increase in CBF.

Conclusions

This study demonstrates mucociliary transport can deteriorate within seconds of exposing the tracheal epithelium to flowing room air and increase rapidly when exposed to nebulized hypertonic solutions. The reduction in MTV precedes slowing of CBF with room air and MTV increases without a subsequent increase in CBF during the nebulization. Their relationship is non-linear and a minimum CBF of approximately 6 Hz is required for MTV > 0, while MTV can reach 10.9 mm/min without CBF increasing. Clinically these findings indicate a potential rapid detrimental effect of breathing with non-humidified air via bypassed upper airways and the short-term effects of nebulized osmotic agents that increase MTV.

Effect of a heat and moisture exchanger on temperature and humidity of inhaled gas in isoflurane-anesthetized dogs

OBJECTIVE

To investigate the effects of a heat and moisture exchanger (HME) on the temperature and humidity of inhaled gas in isoflurane-anesthetized dogs.

STUDY DESIGN

Prospective, interventional study.

ANIMALS

A total of four experimental dogs and four client-owned dogs weighing 13.9 ± 7.4 kg (mean ± standard deviation).

METHODS

The four experimental dogs were anesthetized on two occasions with and without an intact HME at least 1 week apart. The four client-owned dogs were anesthetized once only for a surgical procedure and assigned to the HME group or no-HME group in alternate order, resulting in six dogs for each group. All dogs were premedicated, anesthetized with propofol and intubated. The HME was connected to the endotracheal tube. Anesthesia was maintained with isoflurane. A digital thermo-hygrometer was placed between the endotracheal tube and HME. The temperature and relative humidity of the inhaled gas were measured every 5 minutes for 60 minutes and the absolute humidity was calculated at each time point.

RESULTS

The temperature and absolute humidity of the inhaled gas was significantly higher at 5-60 minutes after intubation in the HME group than in the no-HME group. Absolute humidity was maintained above 29 mg H₂O L^-1 in the HME group. No significant time-dependent effects on temperature, relative humidity or absolute humidity of the inhaled gas were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

The temperature and absolute humidity of the inhaled gas were higher when an HME was used during isoflurane anesthesia in dogs. The use of an HME may reduce the risk of dehydration and dysfunction of the airway mucosal epithelium.

Lin E, Poetker DM, Garcia GJM. Clinical Importance of Nasal Air Conditioning: A Review of the Literature

Background

Nasal air conditioning (ie, heating and humidification of inspired air) is an important function of the nasal cavity. This function may be reduced in cases of aggressive nasal surgery. Future virtual surgery planning tools may be used to design surgical approaches that preserve the nasal air conditioning capacity while decreasing airflow resistance. However, it is unclear whether there is a threshold below which impaired nasal air conditioning is associated with negative health consequences.

Objective

This study aims to review the literature on the clinical impact of reduced nasal air conditioning and its implications for nasal surgery outcomes.

Methods

A literature search was performed on PubMed and Scopus databases for articles that investigated the effect of air temperature and humidity on mucociliary clearance, respiratory epithelial structure, and the prevalence and severity of respiratory diseases.

Results

Inspiration of cold, dry air has direct effects on the respiratory epithelium, such as reduced mucociliary clearance and loss of cilia. Nasal surgeries do inflict some changes to the nasal mucosa and geometry that may result in decreased heating and humidification, but it is unclear how long these effects last. Laryngectomy patients serve as a human model for the absence of nasal air conditioning. The heat and moisture exchangers that many laryngectomy patients wear have been shown to improve lung function and reduce pulmonary symptoms associated with breathing unconditioned air, such as increased coughing and thickened mucus.

Conclusion

Nasal air conditioning is an important mechanism to maintain mucociliary clearance and prevent infection by inhaled pathogens. Preservation of nasal air conditioning capacity should be considered in the implementation of future virtual surgery planning tools. However, a threshold for the onset of negative health consequences due to impaired nasal air conditioning is not yet available.

A Randomized Trial of Conditioned or Unconditioned Gases for Stabilizing Preterm Infants at Birth

OBJECTIVE

To determine whether the use of heated-humidified gases for respiratory support during the stabilization of infants <30 weeks of gestational age (GA) in the delivery room reduces rates of hypothermia on admission to the neonatal intensive care unit (NICU).

STUDY DESIGN

A multicenter, unblinded, randomized trial was conducted in Melbourne, Australia, between February 2013 and June 2015. Infants <30 weeks of GA were randomly assigned to receive either heated-humidified gases or unconditioned gases during stabilization in the delivery room and during transport to NICU. Infants born to mothers with pyrexia >38°C were excluded. Primary outcome was rate of hypothermia on NICU admission (rectal temperature <36.5°C).

RESULTS

A total of 273 infants were enrolled. Fewer infants in the heated-humidified group were hypothermic on admission to NICU (36/132 [27%]) compared with controls (61/141 [43%], P < .01). There was no difference in rates of hyperthermia (>37.5°C); 20% (27/132) in the heated-humidified group compared with 16% (22/141) in the controls (P = .30). There were no differences in mortality or respiratory outcomes.

CONCLUSIONS

The use of heated-humidified gases in the delivery room significantly reduces hypothermia on admission to NICU in preterm infants, without increased risk of hyperthermia.

CLINICAL TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Register (www.anzctr.org.au) ACTRN12613000093785.

Nasal high flow treatment in preterm infants

Nasal High Flow (HF) is a mode of ‘non-invasive’ respiratory support for preterm infants, with several potential modes of action, including generation of distending airway pressure, washout of the nasopharyngeal dead space, reduction of work of breathing, and heating and humidification of inspired gas. HF has several potential advantages over continuous positive airway pressure (CPAP), the most commonly applied form of non-invasive support, such as reduced nasal trauma, ease of use, and infant comfort, which has led to its rapid adoption into neonatal care. In recent years, HF has become a well-established and commonly applied treatment in neonatal care.

Recent trials comparing HF and CPAP as primary support have had differing results. Meta-analyses suggest that primary HF results in an increased risk of treatment failure, but that ‘rescue’ CPAP use in those infants with HF failure results in no greater risk of mechanical ventilation. Even in studies with higher rates of HF failure, the majority of infants were successfully treated with HF, and rates of important neonatal morbidities did not differ between treatment groups. Importantly, these studies have included only infants born at ≥28 weeks’ gestational age (GA). The decision whether to apply primary HF will depend on the value placed on its advantages over CPAP by clinicians, the approach to surfactant treatment, and the severity of respiratory disease in the relevant population of preterm infants.

Post-extubation HF use results in similar rates of treatment failure, mechanical ventilation, and adverse events compared to CPAP. Post-extubation HF appears most suited to infants ≥28 weeks; there are few published data for infants below this gestation, and available evidence suggests that these infants are at high risk of HF failure, although rates of intubation and other morbidities are similar to those seen with CPAP. There is no evidence that using HF to ‘wean’ off CPAP allows for respiratory support to be ceased more quickly, but given its advantages it would appear to be a suitable alternative in infants who require ongoing non-invasive support. Safety data from randomised trials are reassuring, although more evidence in extremely preterm infants (<28 weeks’ GA) is required.

Increasing the Quantity of Lungs for Transplantation Using High-Frequency Chest Wall Oscillation: A Proposal

The use of chest physiotherapy in donor patient management occupies an established place in most lung procurement protocols. Although its merits remain controversial and uncorroborated by direct data, some studies support the efficacy of chest physiotherapy in a variety of pulmonary patient populations. Comparative studies have shown that an airway clearance technology utilizing high-frequency chest wall oscillation clears pulmonary secretions as well as or better than chest physiotherapy, but has few of its contraindications and disadvantages. The implementation of high-frequency chest wall oscillation as part of the donor lung procurement protocol may increase rates of successful lung recovery by providing effective clearance of obstructing pulmonary secretions containing destructive by-products of inflammation and entrapped pathogens. High-frequency chest wall oscillation may also improve arterial blood gas values, a critical factor in increasing lung procurement rates. Although speculative, the benefits of high-frequency chest wall oscillation on donor lungs might improve perfusion and oxygenation of other organs for possible transplantation.

Larynx and Cervical Trachea in Humidification and Heating of Inhaled Gases

To evaluate the participation of the larynx and cervical trachea in conditioning inspired gases, we randomly allocated 16 mixed-breed dogs to two groups: group TT (tracheal tube; n = 8) and group LMA (laryngeal mask airway; n = 8). The dogs were anesthetized with pentobarbital sodium and mechanically ventilated for 3 hours. The parameters studied were temperature and absolute humidities of ambient, inhaled, and tracheal air. There was a small increase in tracheal air temperature compared to inhaled air temperature, but no significant difference between groups. The absolute humidity of tracheal air was greater in group LMA than in group TT (23 mg H2O • L–1 and 14 mg H2O • L–1, respectively; p < .0001). The difference in absolute humidity between the tracheal air and the inhaled air was higher in group LMA at all times (p < .0001). We conclude that the larynx and cervical trachea of the dog participate in humidification and heating of inhaled air by means of air contact with mucosa in this airway segment.

The effects of non-invasive respiratory support on oropharyngeal temperature and humidity: a neonatal manikin study

OBJECTIVE

Heating and humidification of inspired gases is routine during neonatal non-invasive respiratory support. However, little is known about the temperature and humidity delivered to the upper airway. The International Standards Organization (ISO) specifies that for all patients with an artificial airway humidifiers should deliver ≥33 g/m(3) absolute humidity (AH). We assessed the oropharyngeal temperature and humidity during different non-invasive support modes in a neonatal manikin study.

METHODS

Six different modes of non-invasive respiratory support were applied at clinically relevant settings to a neonatal manikin, placed in a warmed and humidified neonatal incubator. Oropharyngeal temperature and relative humidity (RH) were assessed using a thermohygrometer. AH was subsequently calculated.

RESULTS

Measured temperature and RH varied between devices. Bubble and ventilator continuous positive airway pressure (CPAP) produced temperatures >34°C and AH >38 g/m(3). Variable flow CPAP resulted in lower levels of AH than bubble or ventilator CPAP, and AH decreased with higher gas flow. High-flow (HF) therapy delivered by Optiflow Junior produced higher AH with higher gas flow, whereas with Vapotherm HF the converse was true.

CONCLUSIONS

Different non-invasive devices deliver inspiratory gases of variable temperature and humidity. Most AH levels were above the ISO recommendation; however, with some HF and variable flow CPAP devices at higher gas flow this was not achieved. Clinicians should be aware of differences in the efficacy of heating and humidification when choosing modes of non-invasive respiratory support.

The Influence of Nebulized Drugs on Nasal Ciliary Activity

INTRODUCTION

Nebulized drugs are used in the treatment of cystic fibrosis (CF) lung disease, asthma, and COPD, and increasingly also in other chronic lung diseases. Their use in CF is reasonably evidence based, but this is not so for use in other orphan diseases. Potential side effects often have not been studied. Therefore, we evaluated the influence of nebulized drugs on ciliary activity in an in vitro model.

METHODS

We constructed an in vitro nebulization model to examine the effect of drugs on ciliary activity. The model was validated by testing solutions with known neutral, positive, or negative effect on ciliary beat frequency (CBF). Next, the influence on CBF of other inhaled drugs was tested.

RESULTS

Nebulization of NaCl 0.9% had no influence on CBF, and was used as paired neutral control in further experiments. Salbutamol (Ventolin(®)) had a ciliostimulatory effect (CBF +18%, CBF at t0-t10-t60 7.1-8.5-8.6 Hz, p = 0.002), while hypertonic saline (CBF - 11%, CBF at t0-t10-t60 6.5-5.1-5.9 Hz, p = 0.018) and dry air (CBF -10%, CBF at t0-t10-t60 6.8-5.8-6.1 Hz, p = 0.008) had a cilioinhibitory effect. Nebulization of tobramycin inhaled solution (TOBI(®)) (p = 0.662), colistimethate (Colistineb(®)) (p = 0.369), rhDNAse (Pulmozyme(®)) (p = 0.069), ceftazidim (Glazidim(®)) (p = 0.875), and aztreonam (Cayston(®)) (p = 0.435) did not affect CBF. Obracin(®), a tobramycin containing solution manufactured for intravenous use, had a negative effect on CBF (CBF - 21%, CBF at t0-t10-t60 6.9-5.2-4.5 Hz, p = 0.004).

CONCLUSION

Inhaled drugs that are used off-label might have an influence on ciliary activity. This must be taken into account when prescribing these drugs for non-CF indications.

Sampling and analyzing alveolar exhaled breath condensate in mechanically ventilated patients: a feasibility study

Recent studies in spontaneously breathing subjects indicate the possibility of obtaining the alveolar fraction of exhaled breath condensate (aEBC). In critically ill mechanically ventilated patients, in whom microbial colonization of the upper airways is constant, collection of aEBC could considerably add to the ability of monitoring alveolar inflammation. We designed this study to test the feasibility of collecting aEBC in mechanically ventilated critically ill patients through a dedicated apparatus, i.e. a CO2 valve combined with a condenser placed in the expiratory limb of the ventilator circuit. We also aimed to assess the adequacy of the samples obtained by measuring different markers of oxidative stress and inflammation. We enrolled 40 mechanically ventilated patients, 20 with and 20 without acute respiratory distress syndrome (ARDS). Measurements of respiratory mechanics, gas exchange and hemodynamics were obtained with a standard ventilator circuit after 30 min of aEBC collection and after inserting the dedicated collecting apparatus. Data showed that intrinsic positive end-expiratory pressure, peak and plateau pressure, static compliance and airway resistance (Raw) were similar before and after adding the collecting apparatus in both ARDS and controls. Similarly, gas exchange and hemodynamic variables did not change and 30 min collection provided a median aEBC volume of 2.100 and 2.300 ml for ARDS and controls, respectively. aEBC pH showed a trend toward a slight reduction in the ARDS group of patients, as opposed to controls (7.83 (7.62-8.03) versus 7.98 (7.87-8.12), respectively, p  =  0.055)). H2O2 was higher in patients with ARDS, compared to controls (0.09 (0.06-0.12) μM versus 0.03 (0.01-0.09) μM, p  =  0.043), while no difference was found in proteins content, 8-isoprostane, 4-hydroxy-2-nonhenal. In conclusion, we demonstrate, in patients receiving controlled mechanical ventilation, that aEBC collection is feasible without detrimental effects on ventilator functioning, respiratory mechanics and gas exchange. In addition, we show that the sample obtained is appropriate for compounds analysis.

Impact of Cardiopulmonary Bypass on Respiratory Mucociliary Function in an Experimental Porcine Model

Background

The impact of cardiac surgery using cardiopulmonary bypass (CPB) on the respiratory mucociliary function is unknown. This study evaluated the effects of CPB and interruption of mechanical ventilation on the respiratory mucociliary system.

Methods

Twenty-two pigs were randomly assigned to the control (n = 10) or CPB group (n = 12). After the induction of anesthesia, a tracheostomy was performed, and tracheal tissue samples were excised (T0) from both groups. All animals underwent thoracotomy. In the CPB group, an aorto-bicaval CPB was installed and maintained for 90 minutes. During the CPB, mechanical ventilation was interrupted, and the tracheal tube was disconnected. A second tracheal tissue sample was obtained 180 minutes after the tracheostomy (T180). Mucus samples were collected from the trachea using a bronchoscope at T0, T90 and T180. Ciliary beat frequency (CBF) and in situ mucociliary transport (MCT) were studied in ex vivo tracheal epithelium. Mucus viscosity (MV) was assessed using a cone-plate viscometer. Qualitative tracheal histological analysis was performed at T180 tissue samples.

Results

CBF decreased in the CPB group (13.1 ± 1.9 Hz vs. 11.1 ± 2.1 Hz, p < 0.05) but not in the control group (13.1 ± 1 Hz vs. 13 ± 2.9 Hz). At T90, viscosity was increased in the CPB group compared to the control (p < 0.05). No significant differences were observed in in situ MCT. Tracheal histology in the CPB group showed areas of ciliated epithelium loss, submucosal edema and infiltration of inflammatory cells.

Conclusion

CPB acutely contributed to alterations in tracheal mucocilliary function.

Quantifying temperature and relative humidity of medical gases used for newborn resuscitation

AIM

The gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as 'cold and dry', in comparison with the heated, humidified gases used for ongoing ventilation in neonatal intensive care units. The aim of this study was to determine exactly how 'cold and dry' these unconditioned gases are.

METHOD

Multiple measurements of temperature and relative humidity (RH) of piped gases were recorded at different sites, and at different times of day, across The Royal Women's Hospital, Melbourne. Ambient temperature and relative humidities were also recorded.

RESULTS

Eighty paired air and oxygen measurements of temperature and RH were recorded. Mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively. Mean RH of piped air was 5.4 (0.7) %; piped oxygen was significantly drier, mean RH 2.1 (1.1) %.

CONCLUSION

Piped gases were delivered at room temperature and were extremely dry. This highlights the importance of research assessing the practicality of heating and humidifying resuscitation gases, and assessing the impact of their use on clinically important neonatal outcomes.

Heated humidification versus heat and moisture exchangers for ventilated adults and children

BACKGROUND

Humidification by artificial means must be provided when the upper airway is bypassed during mechanical ventilation. Heated humidification (HH) and heat and moisture exchangers (HME) are the most commonly used types of artificial humidification in this situation.

OBJECTIVES

To determine whether HHs or HMEs are more effective in preventing mortality and other complications in people who are mechanically ventilated.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2010, Issue 4) and MEDLINE, EMBASE and CINAHL (January, 2010) to identify relevant randomized controlled trials (RCTs).

SELECTION CRITERIA

We included RCTs comparing heat and moisture exchangers (HMEs) to heated humidifiers (HHs) in mechanically ventilated adults and children. We included randomized crossover studies.

DATA COLLECTION AND ANALYSIS

We assessed the quality of each study and extracted the relevant data. Where appropriate, results from relevant studies were meta-analysed for individual outcomes.

MAIN RESULTS

We included 33 trials with 2833 participants, 25 studies were parallel group design (n = 2710) and eight crossover design (n = 123). Only three included studies reported data for infants or children. There was no overall effect on artificial airway occlusion, mortality, pneumonia, or respiratory complications; however, the PaCO(2) and minute ventilation were increased when HMEs were compared to HHs and body temperature was lower. The cost of HMEs was lower in all studies that reported this outcome. There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia and that blockages of artificial airways may be increased with the use of HMEs in certain subgroups of patients.

AUTHORS' CONCLUSIONS

There is little evidence of an overall difference between HMEs and HHs. However, hydrophobic HMEs may reduce the risk of pneumonia and the use of an HME may increase artificial airway occlusion in certain subgroups of patients. Therefore, HMEs may not be suitable for patients with limited respiratory reserve or prone to airway blockage. Further research is needed relating to hydrophobic versus hygroscopic HMEs and the use of HMEs in the paediatric and neonatal populations. As the design of HMEs evolves, evaluation of new generation HMEs will also need to be undertaken.

Vocal fold epithelial response to luminal osmotic perturbation

PURPOSE

Dry-air challenges increase the osmolarity of fluid lining the luminal surface of the proximal airway. The homeostasis of surface fluid is thought to be essential for voice production and laryngeal defense. Therefore, the authors hypothesized that viable vocal fold epithelium would generate a water flux to reduce an osmotic challenge (150 mOsm mannitol) on the lumen. Bidirectional transepithelial water fluxes were measured in vocal folds exposed to physiologically realistic luminal osmotic perturbations in vitro.

METHOD

Thirty-six native ovine vocal folds were exposed to either luminal hyperosmotic or isosmotic perturbations. Vocal fold viability and water fluxes toward the lumen and into the mucosa were measured at prechallenge baseline and for 30 min after challenge.

RESULTS

Vocal fold electrophysiological viability was maintained for the duration of osmotic perturbation. Luminal osmotic exposure increased luminally directed transepithelial water fluxes in 60% of vocal folds. This increase was electrically silent, of short duration, and would not negate the osmotic gradient.

CONCLUSION

Ovine vocal fold epithelia detect osmotic perturbations to the luminal surface in vitro. This ability to detect and respond to changes in surface composition may be important in homeostatic regulation of vocal fold surface fluid during osmotic perturbations in respiration and phonation.

A 72-hour study to test the efficacy and safety of the "Mucus Slurper" in mechanically ventilated sheep

OBJECTIVE

In patients intubated with endotracheal tubes (ETTs), suctioning is routinely performed to remove mucus from within the ETT and trachea. The Mucus Slurper is a novel ETT with built-in suction ports arranged radially at its tip. We evaluated the safety and efficacy of the Mucus Slurper, compared with conventional tracheal suction, to prevent airway obstruction in sheep with the ETT and trachea oriented below horizontal.

DESIGN

Prospective randomized animal study.

SETTING

Animal research facility at the National Institutes of Health.

SUBJECTS

Twelve healthy sheep.

INTERVENTIONS

Sheep were randomized to be intubated with either the Mucus Slurper (study group) or a Hi-Lo Tracheal Tube (Mallinckrodt, St. Louis, MO) (control group) and mechanically ventilated for 72 hrs. In the study group, automatic, timed tracheal aspiration lasted 0.3 secs, was repeated every 2 mins, and was synchronized with the early expiratory phase. In the control group, tracheal suction was performed every 6 hrs or as required.

MEASUREMENTS AND MAIN RESULTS

In the control group, tracheal secretions accumulated progressively within the ETT and the trachea. In the study group, all mucus that reached the tip of the Mucus Slurper was aspirated, keeping the lumen of the ETT, and proximal trachea, free from secretions. In the study group, expiratory water trap protein concentration, a crude index to measure mucus drainage through the ETT, was consistently less than the control group (p < .001). At autopsy, no macroscopic injury to the tracheal mucosa was found in either group. In the study group, the respiratory circuit was less colonized than in the control group. There were no statistically significant differences between the two groups in bacterial colonization of the lungs/bronchi.

CONCLUSIONS

The Mucus Slurper, combined with orientation of the trachea below horizontal, prevents accumulation of secretions within the lumen of the ETT and trachea, without need for conventional tracheal suctioning.

Respiratory gas conditioning and humidification

Respiratory gas conditioning and humidification are important but poorly understood aspects of mechanical ventilation. The physiologic principles and the best methods to achieve appropriate gas conditioning are addressed in this article.

Water-pipe smoking effects on pulmonary permeability using technetium-99m DTPA inhalation scintigraphy

OBJECTIVE

Although extensive work has been done on cigarette smoking and its effects on pulmonary function, there are limited number of studies on water-pipe smoking. The effects of water-pipe smoking on health are not widely investigated. The aim of this study was to determine the effects of water-pipe smoking on pulmonary permeability.

METHODS

Technetium-99m DTPA inhalation scintigraphy was performed on 14 water-pipe smoker volunteers (all men, mean age 53.7 +/- 9.8) and 11 passive smoker volunteers (1 woman, 10 men, mean age 43.8 +/- 12). Clearance half-time (T 1/2) was calculated by placing a monoexponential fit on the time activity curves. Penetration index (PI) of the radioaerosol was also calculated.

RESULTS

PI was 0.58 +/- 0.14 and 0.50 +/- 0.12 for water-pipe smokers (WPS) and passive smokers (PS) respectively. T 1/2 of peripheral lung was 57.3 +/- 12.7 and 64.6 +/- 13.2 min, central airways was 55.8 +/- 23.5 and 80.1 +/- 35.2 min for WPS and PS, respectively (p < or = 0.05). FEV1/FVC% was 82.1 +/- 8.5 (%) and 87.7 +/- 6.5 (%) for WPS and PS, respectively (0.025 < p < or = 0.05).

CONCLUSIONS

We suggest that water-pipe smoking effects pulmonary epithelial permeability more than passive smoking. Increased central mucociliary clearance in water-pipe smoking may be due to preserved humidity of the airway tracts.

Mucociliary function deteriorates in the clinical range of inspired air temperature and humidity

OBJECTIVE

To test whether a reduction in air temperature within the clinical range [37 degrees C to 30, 100% relative humidity (RH)] altered mucus transport velocity (MTV) and ciliary beat frequency (CBF) in an in vitro ovine tracheal model.

DESIGN

Controlled laboratory study.

SETTING

University research laboratory.

SUBJECTS

Farm-reared sheep.

INTERVENTIONS

Tracheae were mounted flat in an organ bath. Krebs Henseleit bathed the serosal surface and air at 100% (RH) was passed over the mucosal surface at 4 l/min. Cilial beat frequency (CBF) was measured photo-electrically and mucus transport velocity (MTV) by timing movement. After 2 h at 37 degrees C (100% RH) the tissue was either maintained with those settings (controls), or the air temperature reduced to 34 degrees C or 30 degrees C. Tissue was taken for histology before and after each experiment.

MEASUREMENTS AND RESULTS

CBF was 19.8+/-2.7 beats/s and MTV 5.7+/-2.6 mm/min in tissue exposed to air at 37 degrees C. Cilial activity continued for up to 6 h in the controls but mucus transport was more fragile. Reduction of the air temperature to either 34 degrees C or 30 degrees C led to a decrease in both CBF and MTV and, frequently, total mucociliary failure. There was a reduction in epithelial mucous cell numbers in all preparations. Tissues exposed to low temperature had additional abnormal histology.

CONCLUSIONS

Delivery of inspired gas at 30 degrees C, or even 34 degrees C, with 100% RH may not be sufficient to prevent epithelial damage occurring during 6 h exposure.

Oral breathing challenge in participants with vocal attrition

Vocal folds undergo osmotic challenge by mouth breathing during singing, exercising, and loud speaking. Just 15 min of obligatory oral breathing, to dry the vocal folds, increases phonation threshold pressure (Pth) and expiratory vocal effort in healthy speakers (M. Sivasankar & K. Fisher, 2002). We questioned whether oral breathing is more detrimental to phonation in healthy participants with a history of temporary vocal attrition. The effects of a 15-min oral or nasal breathing challenge on Pth and perceived expiratory vocal effort were compared for participants reporting symptoms of vocal attrition (N = 18, ages 19-38 years) and normal controls (N = 20, ages 19-33 years). Post-challenge-prechallenge differences in Pth (deltaPth) and effort (deltaEffort) revealed that oral breathing, but not nasal breathing, increased Pth (p < .001 ) and effort (p < .001) at low, comfortable, and high pitch. deltaPth was significantly greater in participants with vocal attrition than in normal controls (p < .001). Nasal breathing reduced Pth for all controls but not for all participants reporting vocal attrition. deltaPth was significantly and linearly correlated with deltaEffort (rvocal attrition = .81, p < .001; rcontrol = .84, p < .001). We speculate that the greater increases in Pth in participants reporting vocal attrition may result from delayed or inadequate compensatory response to superficial laryngeal dehydration. Obligatory oral breathing may place voice users at risk for exacerbating vocal attrition. That sol layer depletion by obligatory oral breathing increased Pth and vocal effort provides support for the role of superficial hydration in maintaining ease of phonation.

[Vocal fold nodules. Risk factors in teachers. A case control study design]

Vocal nodules are structural lesions very common amongst professional voice users such as teachers. We have studied the risk factors that predispose the development of vocal nodules in teachers. Two hundred and forty-two teachers were selected: 120 with vocal nodules and 120 with normal vocal folds. Professional and personal factors as well as classroom environment were studied. A complete evaluation of the voice was performed, aerodynamic measures, tone and extension of the voice, acoustic analysis, perceptual evaluation of the voice as well as a videolaryngostroboscopy which was definitive in the diagnosis. Younger teachers with less years of teaching experience a greater have tendency to develop vocal nodules than the rest. Class-room's dryness, loudness and echo are correlated with the pathological group. The most relevant personal factors in the pathological group were previous vocal pathology, laryngeal surgery, nasal surgery and gastroesophageal reflux. Vocal intensity and vocal frequency ranks were shorter in the pathological group. We could also see that, fonatory flow was less effective in the pathological group.

Respiratory gas conditioning in infants with an artificial airway

There is a strong physiological rationale for delivering the inspiratory gas at or close to core body temperature and saturated with water vapour to infants with an artificial airway undergoing long-term mechanical ventilatory assistance. Cascade humidifiers with heated wire ventilatory circuitry may achieve this goal safely. Whenever saturated air leaves the humidifier chamber at 37 degrees C and condensate accumulates in the circuit, the gas loses humidity and acquires the potential to dry airway secretions near the tip of the endotracheal tube. Heat and moisture exchangers and hygroscopic condenser humidifiers with or without bacterial filters have become available for neonates. They can provide sufficient moisture output for short-term ventilation without excessive additional dead space or flow-resistive load for term infants. Their safety and efficacy for very low birthweight infants and for long-term mechanical ventilation has not been established conclusively. A broader application of these inexpensive and simple devices is likely to occur with further design improvements. When heated humidifiers are appropriately applied, water or normal saline aerosol application offers no additional significant advantage in terms of inspiratory gas conditioning and may impose a water overload on the airway or even systemically. Although airway irrigation by periodic bolus instillation of normal saline solution prior to suctioning procedures is widely practised in neonatology, virtually no data exist on its safety and efficacy when used with appropriately humidified inspired gas. There is no evidence that conditioning of inspired gas to core body temperature and full water vapour saturation may promote nosocomial respiratory infections.

Oral breathing increases Pth and vocal effort by superficial drying of vocal fold mucosa

Oral breathing superficially dehydrates the airway lumen by decreasing the depth of the sol layer in humans and animals. Conversely, nasal breathing can increase the humidity of inspired air. We compared the effects of short-term oral and nasal breathing on Pth and perceived vocal effort in 20 female subjects randomly assigned to two groups: oral breathing (N = 10, age 21-32 years); nasal breathing (N = 10, age 20-36 years). We hypothesized that short-term oral breathing, but not nasal breathing, would increase Pth, and that subjects would perceive this change as an increase in vocal effort. Following 15 minutes of oral breathing, Pth increased at comfortable and low pitch (p < 0.01) with 6 of 10 subjects reporting increased vocal effort. Nasal breathing reduced Pth at all three pitches (p < 0.01), and 7 of 10 subjects reported decreased vocal effort. Over all subjects, 49% of the variance in treatment-induced change in Pth was accounted for by change in vocal effort (R = 0.70). We posit that obligatory oral breathing places healthy subjects at risk for symptoms of increased vocal effort. The facilitatory role of superficial hydration on vocal fold oscillation should be considered in biomechanical models of phonation and in the clinical prevention of laryngeal dryness.

Performance of heated humidifiers with a heated wire according to ventilatory settings

Delivering warm, humidified gas to patients is important during mechanical ventilation. Heated humidifiers are effective and popular. The humidifying efficiency is influenced not only by performance and settings of the devices but the settings of ventilator. We compared the efficiency of humidifying devices with a heated wire and servo-controlled function under a variety of ventilator settings. A bench study was done with a TTL model lung. The study took place in the laboratory of the University Hospital, Osaka, Japan. Four devices (MR290 with MR730, MR310 with MR730; both Fisher & Paykel, ConchaTherm IV; Hudson RCI, and HummaxII; METRAN) were tested. Hummax II has been developed recently, and it consists of a heated wire and polyethylene microporous hollow fiber. Both wire and fiber were put inside of an inspiratory circuit, and water vapor is delivered throughout the circuit. The Servo 300 was connected to the TTL with a standard ventilator circuit. The ventilator settings were as follows; minute ventilation (V(E)) 5, 10, and 15 L/min, a respiratory rate of 10 breaths/min, I:E ratio 1:1, 1:2, and 1:4, and no applied PEEP. Humidifying devices were set to maintain the temperature of airway opening at 32 degrees C and 37 degrees C. The greater V(E) the lower the humidity with all devices except Hummax II. Hummax II delivered 100% relative humidity at all ventilator and humidifier settings. When airway temperature control of the devices was set at 32 degrees C, the ConchaTherm IV did not deliver 30 mg/L of vapor, which is the value recommended by American National Standards at all V(E) settings. At 10 and 15 L/min of V(E) settings MR310 with MR730 did not deliver recommended vapor, either. In conclusion, airway temperature setting of the humidifying devices influenced the humidity of inspiratory gas greatly. Ventilatory settings also influenced the humidity of inspiratory gas. The Hummax II delivered sufficient water vapor under a variety of minute ventilation.

Cellular physiology of the vocal folds

This article discusses cellular architecture and physiology relevant to phonation biology. The mucociliary blanket and its role in external vocal fold lubrication are presented. The epithelium, basement membrane zone, and lamina propria all have specific roles in oscillating tissue. Three cell types, fibroblast, myofibroblast, and macrophage, maintain important and unique roles. Protein turnover in the lamina propria is important, and slowing matrix turnover may be a leading factor in creating some of the characteristics associated with vocal senescence. Lastly, aspects of cellular health and cellular pathology are discussed.

Tracheobronchial trauma associated with airway management in neonates

Airway management procedures are an integral part of caring for the newborn infant with respiratory compromise. Concomitant with these interventions are latrogenic consequences that result in varying degrees of trauma to the tracheobronchial tree. Common interventions such as intubation, mechanical ventilation, use of heated and humidified gases, and endotracheal suctioning are discussed using research-based literature that evaluates the injury to the trachea and the mucociliary transport system.

Tracheobronchial consequences of the use of heat and moisture exchangers in dogs

PURPOSE

To determine the effect of heat and moisture exchange (HME) on the tracheobronchial tree (TBT) using a unidirectional anesthesic circuit with or without CO2 absorber and high or low fresh gas flow (FGF), in dogs.

METHODS

Thirty-two dogs were randomly allocated to four groups: G1 (n=8) valvular circuit without CO2 absorber and high FGF (5 L x min(-1)); G2 (n=8) as G1 with HME; G3 (n=8) circuit with CO2 absorber with a low FGF (1 L x min(-1)); G4 (n=8) as G3 with HME. Anesthesia was induced and maintained with pentobarbital. Tympanic temperature (TT), inhaled gas temperature (IGT), relative (RH) and absolute humidity (AH) of inhaled gas were measured at 15 (control), 60, 120 and 180 min of controlled ventilation. Dogs were euthanized and biopsies in the areas of TBT were performed by scanning electron microscopy.

RESULTS

The G2 and G4 groups showed the highest AH (>20 mgH2O x L(-1)) and G1 the lowest (< 10 mgH2O x L(-1)) and G3 was intermediate (< 20 mgH2O x L(-1)) (P < 0.01). There was no difference of TT and IGT among groups. Alterations of the mucociliary system were greatest in G1, least in G2 and G4, and intermediate in G3.

CONCLUSION

In dogs, introduction of HME to a unidirectional anesthetic circuit with/without CO2 absorber and high or low FGF preserved humidity of inspired gases. HME attenuated but did not prevent alterations of the mucociliary system of the TBT.

A new prototype of an electronic jet-ventilator and its humidification system

BACKGROUND: Adequate humidification in long-term jet ventilation is a critical aspect in terms of clinical safety. AIM: To assess a prototype of an electronic jet-ventilator and its humidification system. METHODS: Forty patients with respiratory insufficiency were randomly allocated to one of four groups. The criterion for inclusion in this study was respiratory insufficiency exhibiting a Murray score above 2. The four groups of patients were ventilated with three different respirators and four different humidification systems. Patients in groups A and B received superimposed high-frequency jet ventilation (SHFJV) by an electronic jet-ventilator either with (group A) or without (group B) an additional humidification system. Patients in group C received high-frequency percussive ventilation (HFPV) by a pneumatic high-frequency respirator, using a hot water humidifier for warming and moistening the inspiration gas. Patients in group D received conventional mechanical ventilation using a standard intensive care unit respirator with a standard humidification system. SHFJV and HFPV were used for a period of 100 h (4days). RESULTS: A significantly low inspiration gas temperature was noted in patients in group B, initially (27.2 +/- 2.5 degrees C) and after 2 days (28.0 +/- 1.6 degrees C) (P < 0.05). The percentage of relative humidity of the inspiration gas in patients in group B was also initially significantly low (69.8 +/- 4.1%; P < 0.05) but rose to an average of 98 +/- 2.8% after 2 h. The average percentage across all four groups amounted to 98 +/- 0.4% after 2 h. Inflammation of the tracheal mucosa was found in patients in group B and the mucosal injury score (MIS) was significantly higher than in all the other groups. Patients in groups A, C and D showed no severe evidence of airway damage, exhibiting adequate values of relative humidity and temperature of the inspired gas. CONCLUSION: The problems of humidification associated with jet ventilation can be fully prevented by using this new jet-ventilator. These data were sustained by nondeteriorating MIS values at the end of the 4-day study period in groups A, C and D.

Mucoid impaction following nasal intubation in a child with an upper respiratory infection

We describe a case of mucoid impaction following nasotracheal intubation in a child with an upper respiratory infection that was successfully treated with a fiberoptic bronchoscope too large to pass through the endotracheal tube lumen. To the best of our knowledge, it is the first report in the anesthesia literature in which the placement of a nasal tracheal tube is implicated as the cause of the mucous obstruction. The physiologic changes that occur with anesthesia and that place patients at increased risk for this phenomenon, as well as the differential diagnosis, treatment, and prevention of this entity, are discussed.

Anaesthesia circuits, humidity output, and mucociliary structure and function

We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15 +/- 1.4 vs 9 +/- 0.8 vs 5 +/- 0.4 mg H2O, P < 0.01) after two hours. Mean cilia length (micron) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8 +/- 0.4 vs 8.6 +/- 1.1 vs 15.4 +/- 2.1, P < 0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3 +/- 0.5 vs 3.2 +/- 1.1 vs 4.2 +/- 0.8, P < 0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H2O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.

A randomized clinical trial comparing an extended-use hygroscopic condenser humidifier with heated-water humidification in mechanically ventilated patients

STUDY OBJECTIVE

To determine the safety and cost-effectiveness of mechanical ventilation with an extended-use hygroscopic condenser humidifier (Duration; Nellcor Puritan-Bennett; Eden Prairie, Minn) compared with mechanical ventilation with heated-water humidification.

DESIGN

Prospective randomized clinical trial.

SETTING

Medical and surgical ICUs of Barnes-Jewish Hospital, St. Louis, a university-affiliated teaching hospital.

PATIENTS

Three hundred ten consecutive qualified patients undergoing mechanical ventilation.

INTERVENTIONS

Patients requiring mechanical ventilation were randomly assigned to receive humidification with either an extended-use hygroscopic condenser humidifier (for up to the first 7 days of mechanical ventilation) or heated-water humidification.

MEASUREMENTS

Occurrence of ventilator-associated pneumonia, endotracheal tube occlusion, duration of mechanical ventilation, lengths of intensive care and hospitalization, acquired multiorgan dysfunction, and hospital mortality.

RESULTS

One hundred sixty-three patients were randomly assigned to receive humidification with an extended-use hygroscopic condenser humidifier, and 147 patients were randomly assigned to receive heated-water humidification. The two groups were similar at the time of randomization with regard to demographic characteristics, ICU admission diagnoses, and severity of illness. Risk factors for the development of ventilator-associated pneumonia were also similar during the study period for both treatment groups. Ventilator-associated pneumonia was seen in 15 (9.2%) patients receiving humidification with an extended-use hygroscopic condenser humidifier and in 15 (10.2%) patients receiving heated-water humidification (relative risk, 0.90; 95% confidence interval=0.46 to 1.78; p=0.766). No statistically significant differences for hospital mortality, duration of mechanical ventilation, lengths of stay in the hospital ICU, or acquired organ system derangements were found between the two treatment groups. No episode of endotracheal tube occlusion occurred during the study period in either treatment group. The total cost of providing humidification was $2,605 for patients receiving a hygroscopic condenser humidifier compared with $5,625 for patients receiving heated-water humidification.

CONCLUSION

Our findings suggest that the initial application of an extended-use hygroscopic condenser humidifier is a safe and more cost-effective method of providing humidification to patients requiring mechanical ventilation compared with heated-water humidification.

A novel method of evaluation of three heat-moisture exchangers in six different ventilator settings

OBJECTIVE

The purpose of this study was to assess and compare the humidification, heating, and resistance properties of three commercially available heat-moisture exchangers (HMEs). To mimic clinical conditions, a previously validated, new, realistic experimental set-up and measurement protocol was used.

DESIGN

Prospective, comparative experimental study.

SETTING

Surgical Intensive Care Unit, University Hospital of Rotterdam.

MATERIALS

An experimental set-up consisting of a patient model, measurement systems, and ventilator and three different HME types.

INTERVENTIONS

The air flow, pressure in the ventilation circuit, pressure difference over the HME, and partial water vapour pressure and temperature at each side of the HMEs were measured. Measurements were repeated every 30 min during the first 2 h and every hour up to 24 h for each HME at six different ventilator settings. The mean inspiratory and maximum expiratory resistance, flow-weighted mean absolute humidity and temperature outputs, and humidification and heating efficiencies of HMEs were calculated.

MEASUREMENTS AND RESULTS

The Dar Hygroster had the highest humidity output, temperature output, humidification efficiency, and heating efficiency values throughout the study (32.8 +/- 21. mg/l, 32.2 +/- 0.8 degrees C, 86.3 +/- 2.3%, and 0.9 +/- 0.01%, respectively) in comparison to the Humid-Vent Filter (25.3 +/- 3.2 mg/l, 31.9 +/- 0.8 degrees C, 72.2 +/- 5.3%, 0.9 +/- 0.02%, respectively) and the Pall Ultipor BB100 breathing circuit filter (23.4 +/- 3 mg/l, 28.3 +/- 0.7 degrees C, 68.8 +/- 5.9%, 0.8 +/- 0.02%, respectively). The inspiratory and expiratory resistance of the HMEs remained below clinically acceptable maximum values (2.60 +/- 0.04 and 2.45 +/- 0.05 cmH2O/l per s, respectively).

CONCLUSION

The Dar Hygroster filter was found to have the highest humidity and temperature output of all three HMEs, the Humid-Vent filter had a satisfactory humidity output only at low tidal volume flow rate and minute volume settings, whereas the Pall Ultipore BB 100 never achieved a sufficient humidity and temperature output.

Interaction between ion transporters and the mucociliary transport system in dog and baboon

To gain insight into the role of epithelial ion channels, pumps, and cotransporters in regulating airway water and mucociliary transport, we administered inhibitors of the Na+ channel (amiloride), 3Na-2K-adenosinetriphosphatase (acetylstrophanthidin), and Na-K-2Cl cotransporter (furosemide) to anesthetized dogs and/or baboons. Tracheal ciliary beat frequency was measured by using heterodyne laser light scattering. Tracheal mucus velocity (TMV) and bronchial mucociliary clearance (BMC) or lung mucociliary clearance were measured by using radioaerosols and nuclear imaging. Respiratory tract fluid output was collected by using a secretion-collecting endotracheal tube. In six dogs, amiloride aerosol -lung deposition, 96 +/- 11 microg (means +/- SE)- had minimal effect, whereas acetylstrophanthidin aerosol (lung deposition, 71 +/- 9 microg) increased BMC, and furosemide (40 mg iv) markedly increased TMV. In five baboons, TMV increased after iv furosemide administration (2 mg/kg) as well as by aerosol (lung deposition, 20 +/- 3 mg), coincident with increases in ciliary-mucus coupling from 11.5 +/- 0. 1 to 29.5 +/- 0.4 and 46.5 +/- 0.7 microm/beat, respectively. Furosemide also increased lung mucociliary clearance in baboons. In dogs, respiratory tract fluid output increased after intravenous furosemide from 2.2 +/- 0.5 to 6.8 +/- 1.7 mg/min. When combined with dry-air inhalation, furosemide failed to stimulate TMV and reversed the inhibition of BMC by dry air. Thus pharmacological manipulation of the Na-K-2Cl cotransporter and the 3Na-2K-adenosinetriphosphatase pump may provide increases of clinical relevance in airway hydration and mucociliary transport.

Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa

OBJECTIVE

To review the available literature on the relationship between the humidity and temperature of inspired gas and airway mucosal function.

DATA SOURCES

International computerized databases and published indices, experts in the field, conference proceedings, bibliographies.

STUDY SELECTION/DATA EXTRACTION

Two hundred articles/texts on respiratory tract physiology and humidification were reviewed. Seventeen articles were selected from 40 articles for inclusion in the published data verification of the model. Selection was by independent reviewers. Extraction was by consensus, and was based on finding sufficient data.

DATA SYNTHESIS

A relationship exists between inspired gas humidity and temperature, exposure time to a given humidity level, and mucosal function. This relationship can be modeled and represented as an inspired humidity magnitude vs. exposure time map. The model is predictive of mucosal function and can be partially verified by the available literature. It predicts that if inspired humidity deviates from an optimal level, a progressive mucosal dysfunction begins. The greater the humidity deviation, the faster the mucosal dysfunction progresses.

CONCLUSIONS

A model for the relationship between airway mucosal dysfunction and the combination of the humidity of inspired gas and the duration over which the airway mucosa is exposed to that humidity is proposed. This model suggests that there is an optimal temperature and humidity above which, and below which, there is impaired mucosal function. This optimal level of temperature and humidity is core temperature and 100% relative humidity. However, existing data are only sufficient to test this model for gas conditions below core temperature and 100% relative humidity. These data concur with the model in that region. No studies have yet looked at this relationship beyond 24 hrs. Longer exposure times to any given level of inspired humidity and inspired gas temperatures and humidities above core temperature and 100% relative humidity need to be studied to fully verify the proposed model.

Importance of airway blood flow on particle clearance from the lung

The role of the airway circulation in supporting mucociliary function has been essentially unstudied. We evaluated the airway clearance of inert, insoluble particles in anesthetized ventilated sheep (n = 8), in which bronchial perfusion was controlled, to determine whether airway mucosal blood flow is essential for maintaining surface transport of particles through airways. The bronchial branch of the bronchoesophageal artery was cannulated and perfused with autologous blood at control flow (0.6 ml.min-1.kg-1) or perfusion was stopped. With the sheep in a supine position and after a steady-state 133Xe ventilation scan for designation of lung zones of interest, an inert 99mTc-labeled sulfur colloid aerosol (2.1-microns diameter) was deposited in the lung. The clearance kinetics of the radiolabeled particles were determined from the activity-time data obtained for right and left lung zones. At 60 min postdeposition of aerosol, average airway particle retention for control bronchial blood flow conditions was 57 +/- 7 (SE)% for the right and 53 +/- 8% for the left lung zones. Clearance of particles was significantly impaired when bronchial blood flow was stopped, e.g., right and left lung zones averaged 77 +/- 6 and 76 +/- 7% at 60 min, respectively (P < 0.05). These data demonstrate a significant influence of the bronchial circulation on mucociliary transport of insoluble particles. Potential mechanisms that may account for these results include the importance of the bronchial circulation for nutrient flow, maintenance of airway wall temperature and humidity, and release of mediators and sequelae associated with tissue ischemia.

Humidity of anaesthetic gases with respect to low flow anaesthesia

It has been demonstrated in an experimental study in swine using the scanning electron microscope that a rebreathing technique utilising minimal fresh gas flowrates significantly improves climatization of anaesthetic gases. Consequently, effects of various anaesthetic techniques on airway climate must be assessed, which covers the need for suitable measuring devices. Basic principles and methods of humidity measurement in flowing anaesthetic gases include gravimetric hygrometry, dew point hygrometry, wet-dry bulb psychrometry, mass spectrometry, spectroscopic hygrometry and electrical hygrometry. A custom-made apparatus for continuous measurement of humidity and temperature in the inspired and expired gas mixtures of a breathing circuit (separated by a valve system, integrated between the endotracheal tube and the Y-piece) is described. Comparative evaluation of this apparatus and the psychrometer was carried out. It could be demonstrated that the apparatus, measuring with capacitive humidity sensors, is more suitable for prolonged use under clinical conditions than the psychrometer. In the second part of the study, climatization of anaesthetic gases under clinical conditions was investigated using fresh gas flowrates of 0.6, 1.5, 3.0 and 6.0 l/min. In the inspiratory limb of the circuit an absolute humidity of 21.3 mg H2O/l and a temperature of 31.5 degrees C were obtained after 120 minutes of minimal flow. Humidity and temperature of inspired air obtained with fresh gas flowrates of 6.0 and 3.0 l/min were found to be inadequate for prolonged anaesthesia. Reducing the fresh gas flow to 1.5 l/min increases heat and moisture content in the respired gases, but conditions are still inadequate for prolonged anaesthesia. Sufficient moisture (> or 20 mg H2O/l) and temperature are obtained under minimal flow conditions after one hour.

Effects of hyperoxia on bronchial wall dimensions and lung mechanics in rats

The effects of exposure to hyperoxic conditions (> 95 kPa at normobaric pressure) on bronchial wall dimensions and lung mechanics were examined in adult rats. Measurements of baseline pulmonary resistance and changes in pulmonary resistance following acetylcholine aerosol inhalation were made in rats exposed to hyperoxia for 48 and 60 h and in control rats exposed to air. Exposures for 48 h were carried out in humid (80% relative humidity) or dry (35-40% relative humidity) conditions. Morphometric measurements of airway wall thickness in lobar bronchi were made in separate groups of similarly exposed rats. Exposure to hyperoxia was associated with an increase in baseline pulmonary resistance (control rats 0.043 (0.016) cmH2O ml-1 s-1, 60 h exposed rats 0.125 (0.042) cmH2O ml-1 s-1) but hyper-responsiveness to acetylcholine inhalation did not occur. Thickness of the airway wall and its subdivisions, epithelium, lamina propria and muscularis, was not altered by hyperoxic exposure in humid conditions. However, epithelial thickening in the lobar bronchi was observed in rats exposed for 48 h to hyperoxia in dry conditions compared to rats exposed in humid conditions (mean (SD) thickness 13.2 (3.3) microns for controls, 14.5 (1.5) microns for humid exposed rats and 16.5 (3.3) microns for dry exposed rats). The increase in pulmonary resistance caused by hyperoxic exposure is unlikely to be due to airway damage as airway hyper-responsiveness did not occur, and is more likely to be associated with the development of alveolar oedema. Environmental humidity may modulate lung damage induced by hyperoxia, as exposure in dry conditions was associated with significant epithelial thickening.

Comparative evaluation of three heat and moisture exchangers during short-term postoperative mechanical ventilation

This study compared performance of three heat and moisture exchangers (HME) during short-term postoperative mechanical ventilation. Temperature and absolute humidity (AH) were measured at various points of the ventilatory circuit. There was no statistical difference between the groups, regarding ambient and body To, body weight, fraction of inspired oxygen, tidal volume, and respiratory rate. Only the hygroscopic HME (groups 2 and 3) provide adequate conditioning with regard to AH and To of the inspiratory gases. The performance of hydrophobic HME (group 1) was inferior and appears to be unsatisfactory. Indirect evaluation (variations of inspiratory gases and tracheal temperatures, AH of the expired gases) confirmed the superiority of the hygroscopic HME. These data suggest that humidification of inspiratory gases with a hygroscopic HME is a defensible practice during short-term postoperative mechanical ventilation. Performance of hydrophobic HME may be weak and can expose the patient to an unacceptable risk of endotracheal tube occlusion.

Reduced effect of inhaled beta 2-adrenergic agonists on lung mucociliary clearance in patients with cystic fibrosis

STUDY OBJECTIVE

It has been suggested that the defective cyclic AMP-dependent Cl- secretion and the increased Na+ absorption from airway epithelia in cystic fibrosis (CF) may lead to dehydrated secretions and impaired mucociliary clearance. Beta 2-adrenergic agonists are unable to stimulate the Cl- transport in the airways in CF while being able to do so in normal airways. Thus, we questioned whether the beta 2-adrenergic agonist, terbutaline, would improve mucociliary clearance in patients with CF as it does in healthy subjects.

DESIGN

A double-blind, randomized cross-over trial.

SETTING

Whole lung and regional mucociliary clearance of a radioaerosol was measured for 3 h by gamma camera. One minute of cough clearance was measured at 3 h. Pulmonary function was measured before and after the gamma camera study.

PATIENTS

Ten young patients with CF were studied; three were heterozygous for deletion of the phenylalanine at position 508 (delta F508), and seven were delta F508 homozygous.

INTERVENTIONS

Inhalation of 1 mg of terbutaline (4 puffs) and placebo via a metered-dose inhaler by spacer.

MEASUREMENTS AND RESULTS

The largest differences in tracheobronchial retention (percent) in the whole lung and regional lung zones were generally observed within 1 h after terbutaline and placebo treatment: whole lung (mean +/- SD), 60 +/- 22 percent and 63 +/- 20 percent; central zone, 41 +/- 19 percent and 50 +/- 25 percent; midzones, 65 +/- 27 percent and 63 +/- 19 percent; and peripheral zones, 77 +/- 28 percent and 72 +/- 28 percent, respectively [p > 0.1]. Whereas none of these differences was statistically significant, subanalyses suggested an improvement in mucociliary clearance by terbutaline in the three delta F508 heterozygous patients but not in the seven delta F508 homozygous patients. One minute of voluntary coughing resulted in clearance of less than 8 percent of the initial radioactivity, with a trend of more peripheral zone clearance after terbutaline compared with placebo. A small significant decrease in airway resistance was detected 3 h after terbutaline.

CONCLUSIONS

We conclude that 1 mg of terbutaline did not improve mucociliary clearance significantly in the patients with CF. Also, the effect of terbutaline was much less than demonstrated earlier in healthy subjects. This is consistent with earlier findings of a lack of beta-adrenergic modulation of Cl- transport in CF. Thus, no rehydration of the dry mucus in CF is expected, and a possible beta 2-agonist-induced increase in ciliary beating would have only a minor effect on overall mucociliary clearance.

Measurement of mucociliary transport velocity in ventilated patients. Short-term effect of general anesthesia on mucociliary transport

OBJECTIVES

The objectives of this study were to evaluate a method for measuring BTV in ventilated patients and to study the short-term effect of general anesthesia with midazolam, Fentanyl, pancuronium and O2:N2O on BTV.

DESIGN

The study included phantom measurements on a bronchoscopy model and the determination of BTV in patients in a convenience sample trial.

SETTING

The study took place in a university hospital.

PATIENTS

Fourteen patients undergoing major abdominal surgery with planned postoperative mechanical ventilation were included in the study. All patients gave their written informed consent to participate in the study.

INTERVENTIONS

Bronchial mucus transport velocity was measured with a small volume (0.05 to 0.08 ml) of technetium 99m-labeled albumin microspheres with an activity of 3 MBq. The radiolabeled bolus was deposited on the dorsal mucosal surface at the distal end of the right and left main bronchus via flexible bronchoscopy. The movement of the microspheres toward the trachea was visualized and recorded using a scintillation camera; quantitative evaluation utilized the condensed image.

MAIN MEASUREMENTS AND RESULTS

The technique was validated in a bronchoscopy model and in an intubated patient by moving a radioactive drop in a catheter through the main bronchi at velocities from 0 to 20 mm/min. The velocities determined by the image processing technique correlated well with the data by the model and patient determination (right bronchus, r = 1.0; left bronchus, r = 1.0). In seven ventilated patients, mechanical irritation by the fiberscope produced no significant effect on BTV. The BTV was measured preoperatively in seven conscious patients one day before surgery while they received local anesthesia with 10 ml of 1 percent lidocaine and postoperatively while they received intubation anesthesia. The preoperative and postoperative BTV values showed no significant differences (10.5; 5.7 to 13.7 mm/min; vs 9.7 (3.7 to 15.3) (median with range).

CONCLUSION

By this method, bronchial transport velocity can be determined in a relatively short time in ventilated patients. General anesthesia with midazolam, Fentanyl, pancuronium and O2:N2O does not influence BTV.

Lung function during anesthesia and respiratory insufficiency in the postoperative period: physiological and clinical implications

This review covers the physiological and clinical implications of lung function during anesthesia and respiratory insufficiency in the postoperative period. We have divided it into 3 main sections: 1) lung function changes induced by anesthesia and surgery, in which the impact on pulmonary mechanics, ventilation/perfusion changes and gas exchange are examined; 2) physiological implications of postoperative respiratory function secondary to decreased alveolar ventilation, development of atelectasis, and interstitial lung edema; and 3) clinical implications of postoperative respiratory failure. In this last section we analyze the current therapeutic modalities available to reduce the incidence of postoperative respiratory failure, as well as related morbidity and mortality.