Effects of a heat and moisture exchanger and a heated humidifier on respiratory mucus in patients undergoing mechanical ventilation

Indications and practice of home invasive mechanical ventilation in children

BACKGROUND

Developments and technological advances in neonatal and pediatric intensive care units have led to a prolonged life expectancy of pediatric patients with chronic respiratory failure. Therefore, the number of hemodynamically stable pediatric patients with chronic respiratory failure who need mechanical ventilator assistance throughout the day has significantly increased.

AIMS

Numerous conditions, including parenchymal lung diseases, airway disorders, neuromotor disorders, or respiratory defects, can lead to chronic respiratory failure. For individuals who cannot tolerate non-invasive mechanical ventilation (NIMV), invasive mechanical ventilation (IMV) is the only suitable choice. Due to increasing need, mechanical ventilator technology is continuously evolving.

RESULTS

As a result of this process, home-type mechanical ventilators have been produced for patients requiring long-term IMV. Patients with chronic respiratory failure can be safely monitored at home with these ventilators.

DISCUSSION

Home follow-up of these patients has many benefits such as an increase in general quality of life and a positive contribution to their emotional and cognitive development.

CONCLUSION

In this compilation, indications for home-based IMV, features of home invasive mechanical ventilators (HMVs), patient monitoring, and the detailed advantages of using IMV at home will be elucidated.

Ventilation Difficulty Caused by Obstructed Heated Breathing Circuit

For perioperative hypothermia prevention, a heated, humidified breathing circuit equipped with a fluid-warming unit inside the inspiratory limb has been developed. We report a ventilation difficulty caused by an obstructed heated breathing circuit. Cotton surrounding the hot wire, temperature sensor, and fluid tubing in the distal inspiratory limb was irregularly thicker than that of a normal circuit and nearly blocked the lumen. Despite carrying out routine checks on the anesthesia workstation preoperatively, we failed to make a prediagnosis by omitting the flow test after changing the circuit. This case puts emphasis on a routine flow test with a meticulous examination of the heated breathing circuit before every procedure.

Heated Humidified Breathing Circuit Rewarming in Hypothermic Patients Post-Cardiopulmonary Bypass-Pilot Study

OBJECTIVES

Hypothermia on intensive care unit (ICU) admission after cardiac surgery and cardiopulmonary bypass is common. It contributes to postoperative complications including shivering, coagulopathy, increased blood loss and transfusion requirements, morbid cardiac events, metabolic acidosis, increased wound infections, and prolonged hospital length of stay. The current standard of care for rewarming ICU patients is forced air warming blankets. However, high-quality evidence on additional benefit rendered by other warming methods, such as heated humidified breathing circuits (HHBC), is lacking. Therefore, the authors conducted a pilot study to examine whether the addition of HHBC to standard forced air warming blankets in hypothermic patients (≤35°C) admitted to the ICU after cardiac surgery using cardiopulmonary bypass reduced time to normothermia.

DESIGN

Prospective study conducted at a single large academic medical center.

PARTICIPANTS

The study group was composed of 14 patients who were enrolled prospectively between April 1 and June 14, 2019. The study group was compared with a 2:1 matched retrospective control group. The matched group consisted of 28 patients from a 12-month period from July 1, 2018 June 30, 2019.

INTERVENTIONS

Study patients received warming via forced air warming blankets and HHBC and were compared with patients in a control group who received only warming blankets. Time to normothermia, time to extubation, time to normal pH, blood loss, blood transfusions, and coagulation profile laboratory values were compared between the study and control groups.

MEASUREMENTS AND MAIN RESULTS

The present study found no statistical difference in time to normothermia, for which the standard-of-care retrospective group achieved normothermia after a median (Q1-Q3) 4.8 (4.0-6.0) hours compared with 4.4 (3.5-5.5) hours in the prospective group receiving HHBC. All secondary outcomes, including time to extubation, time to normal pH, ICU blood product transfusion, chest tube output, and coagulation profile, were similar.

CONCLUSIONS

The present pilot study detected a similar time to normothermia, extubation, and normal pH when HHBC were added to standard forced air warming blankets in hypothermic patients (≤35°C) admitted to the ICU after cardiac surgery using cardiopulmonary bypass. A future larger prospective study designed to detect smaller, but clinically meaningful, reductions in the time to key clinical events for patients treated with HHBC is feasible and warranted.

The I-READI Quality and Safety Framework: A Health System’s Response to Airway Complications in Mechanically Ventilated Patients with Covid-19

Health care institutions responding to quality and safety challenges during times of crisis, such as emerging infectious diseases or natural disasters, can follow the I-READI conceptual framework: Integration, Root Cause Analysis, Evidence Review, Adaptation, Dissemination, and Implementation. The University of Pennsylvania Health System developed this approach by drawing on lessons learned from rapidly coordinating changes to their ventilator management practices. They modified their practices to improve patient safety after recognizing high rates of airway complications among mechanically ventilated patients with Covid-19. Vertical and horizontal integration of their quality and safety teams helped streamline problem solving, enrich collaboration, and coordinate implementation. Root cause analysis and evidence review framed their practice adaptation, ensuring that they prioritized patient and health care worker safety. Daily safety huddles engaged frontline providers and promoted dissemination of the revised interventions. Telemedicine oversight and real-time ICU dashboards enabled system-wide implementation, goal setting, and continuous performance feedback. Under their revised guidelines, the rate of endotracheal tube obstruction among mechanically ventilated patients with Covid-19 decreased from 9.2% to less than 1%, and reintubation rates decreased from 36% to 9%.

Effectiveness of Humidification with Heat and Moisture Exchanger-booster in Tracheostomized Patients

Background:

The two most commonly used types of humidifiers are heated humidifiers and heat and moisture exchange humidifiers. Heated humidifiers provide adequate temperature and humidity without affecting the respiratory pattern, but overdose can cause high temperatures and humidity resulting in condensation, which increases the risk of bacteria in the circuit. These devices are expensive. Heat and moisture exchanger filter is a new concept of humidification, increasing the moisture content in inspired gases.

Aims:

This study aims to determine the effectiveness of the heat and moisture exchanger (HME)-Booster system to humidify inspired air in patients under mechanical ventilation.

Materials and Methods:

We evaluated the humidification provided by 10 HME-Booster for tracheostomized patients under mechanical ventilation using Servo I respirators, belonging to the Maquet company and Evita 4.

Results:

There was an increase in the inspired air humidity after 1 h with the humidifier.

Conclusion:

The HME-Booster combines the advantages of heat and moisture exchange minimizing the negatives. It increases the amount of moisture in inspired gas in mechanically ventilated tracheostomized patients. It is easy and safe to use. The type of ventilator used has no influence on the result.

Heat and moisture exchangers versus heated humidifiers for mechanically ventilated adults and children

BACKGROUND

Invasive ventilation is used to assist or replace breathing when a person is unable to breathe adequately on their own. Because the upper airway is bypassed during mechanical ventilation, the respiratory system is no longer able to warm and moisten inhaled gases, potentially causing additional breathing problems in people who already require assisted breathing. To prevent these problems, gases are artificially warmed and humidified. There are two main forms of humidification, heat and moisture exchangers (HME) or heated humidifiers (HH). Both are associated with potential benefits and advantages but it is unclear whether HME or HH are more effective in preventing some of the negative outcomes associated with mechanical ventilation. This review was originally published in 2010 and updated in 2017.

OBJECTIVES

To assess whether heat and moisture exchangers or heated humidifiers are more effective in preventing complications in people receiving invasive mechanical ventilation and to identify whether the age group of participants, length of humidification, type of HME, and ventilation delivered through a tracheostomy had an effect on these findings.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase and CINAHL up to May 2017 to identify randomized controlled trials (RCTs) and reference lists of included studies and relevant reviews. There were no language limitations.

SELECTION CRITERIA

We included RCTs comparing HMEs to HHs in adults and children receiving invasive ventilation. We included randomized cross-over studies.

DATA COLLECTION AND ANALYSIS

We assessed the quality of each study and extracted the relevant data. Where possible, we analysed data through meta-analysis. For dichotomous outcomes, we calculated the risk ratio (RR) and 95% confidence interval (95% CI). For continuous outcomes, we calculated the mean difference (MD) and 95% CI or standardized mean difference (SMD) and 95% CI for parallel studies. For cross-over trials, we calculated the MD and 95% CI using correlation estimates to correct for paired analyses. We aimed to conduct subgroup analyses based on the age group of participants, how long they received humidification, type of HME and whether ventilation was delivered through a tracheostomy. We also conducted sensitivity analysis to identify whether the quality of trials had an effect on meta-analytic findings.

MAIN RESULTS

We included 34 trials with 2848 participants; 26 studies were parallel-group design (2725 participants) and eight used a cross-over design (123 participants). Only three included studies reported data for infants or children. Two further studies (76 participants) are awaiting classification.There was no overall statistical difference in artificial airway occlusion (RR 1.59, 95% CI 0.60 to 4.19; participants = 2171; studies = 15; I2 = 54%), mortality (RR 1.03, 95% CI 0.89 to 1.20; participants = 1951; studies = 12; I2 = 0%) or pneumonia (RR 0.93, 95% CI 0.73 to 1.19; participants = 2251; studies = 13; I2 = 27%). There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia compared to HHs (RR 0.48, 95% CI 0.28 to 0.82; participants = 469; studies = 3; I2 = 0%)..The overall GRADE quality of evidence was low. Although the overall methodological risk of bias was generally unclear for selection and detection bias and low risk for follow-up, the selection of study participants who were considered suitable for HME and in some studies removing participants from the HME group made the findings of this review difficult to generalize.

AUTHORS' CONCLUSIONS

The available evidence suggests no difference between HMEs and HHs on the primary outcomes of airway blockages, pneumonia and mortality. However, the overall low quality of this evidence makes it difficult to be confident about these findings. Further research is needed to compare HMEs to HHs, particularly in paediatric and neonatal populations, but research is also needed to more effectively compare different types of HME to each other as well as different types of HH.

Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) in adult critically ill patients: a systematic review, meta-analysis and meta-regression of randomized controlled trials

BACKGROUND

The aims of this systematic review and meta-analysis of randomized controlled trials are to evaluate the effects of active heated humidifiers (HHs) and moisture exchangers (HMEs) in preventing artificial airway occlusion and pneumonia, and on mortality in adult critically ill patients. In addition, we planned to perform a meta-regression analysis to evaluate the relationship between the incidence of artificial airway occlusion, pneumonia and mortality and clinical features of adult critically ill patients.

METHODS

Computerized databases were searched for randomized controlled trials (RCTs) comparing HHs and HMEs and reporting artificial airway occlusion, pneumonia and mortality as predefined outcomes. Relative risk (RR), 95% confidence interval for each outcome and I ² were estimated for each outcome. Furthermore, weighted random-effect meta-regression analysis was performed to test the relationship between the effect size on each considered outcome and covariates.

RESULTS

Eighteen RCTs and 2442 adult critically ill patients were included in the analysis. The incidence of artificial airway occlusion (RR = 1.853; 95% CI 0.792-4.338), pneumonia (RR = 932; 95% CI 0.730-1.190) and mortality (RR = 1.023; 95% CI 0.878-1.192) were not different in patients treated with HMEs and HHs. However, in the subgroup analyses the incidence of airway occlusion was higher in HMEs compared with HHs with non-heated wire (RR = 3.776; 95% CI 1.560-9.143). According to the meta-regression, the effect size in the treatment group on artificial airway occlusion was influenced by the percentage of patients with pneumonia (β = -0.058; p = 0.027; favors HMEs in studies with high prevalence of pneumonia), and a trend was observed for an effect of the duration of mechanical ventilation (MV) (β = -0.108; p = 0.054; favors HMEs in studies with longer MV time).

CONCLUSIONS

In this meta-analysis we found no superiority of HMEs and HHs, in terms of artificial airway occlusion, pneumonia and mortality. A trend favoring HMEs was observed in studies including a high percentage of patients with pneumonia diagnosis at admission and those with prolonged MV. However, the choice of humidifiers should be made according to the clinical context, trying to avoid possible complications and reaching the appropriate performance at lower costs.

The effects of smoking and smoking cessation on nasal mucociliary clearance, mucus properties and inflammation

OBJECTIVE

The aim of the present study was to assess nasal mucociliary clearance, mucus properties and inflammation in smokers and subjects enrolled in a Smoking Cessation Program (referred to as quitters).

METHOD

A total of 33 subjects with a median (IQR) smoking history of 34 (20-58) pack years were examined for nasal mucociliary clearance using a saccharine transit test, mucus properties using contact angle and sneeze clearability tests, and quantification of inflammatory and epithelial cells, IL-6 and IL-8 concentrations in nasal lavage fluid. Twenty quitters (mean age: 51 years, 9 male) were assessed at baseline, 1 month, 3 months and 12 months after smoking cessation, and 13 smokers (mean age: 52 years, 6 male) were assessed at baseline and after 12 months. Clinicaltrials.gov: NCT02136550.

RESULTS

Smokers and quitters showed similar demographic characteristics and morbidities. At baseline, all subjects showed impaired nasal mucociliary clearance (mean 17.6 min), although 63% and 85% of the quitters demonstrated significant nasal mucociliary clearance improvement at 1 month and 12 months, respectively. At 12 months, quitters also showed mucus sneeze clearability improvement (∼26%), an increased number of macrophages (2-fold) and no changes in mucus contact angle or cytokine concentrations.

CONCLUSION

This study showed that smoking cessation induced early improvements in nasal mucociliary clearance independent of mucus properties and inflammation. Changes in mucus properties were observed after only 12 months of smoking cessation.

Effect of heated humidified ventilation on bronchial mucus transport velocity in general anaesthesia: A randomized trial

Objective

To evaluate the effects of heated humidified ventilation on mucociliary function during general anaesthesia.

Methods

Male patients (ASA physical status 1 or 2), scheduled for elective radical retropubic prostatectomy, were allocated to receive sevoflurane general anaesthesia with conventional or heated humidified ventilation. Bronchial mucus transport velocity was assessed via fibreoptic bronchoscope and methylene blue dye at 3h after induction of anaesthesia.

Results

Median (SE) bronchial mucus transport velocity was significantly higher in the heated humidified group ( n = 26) than the conventional ventilation group ( n = 24) (1.7 [0.3] mm/min vs 0.9 [0.1] mm/min).

Conclusion

Heated humidified ventilation effectively maintains mucociliary clearance of patients during sevoflurane general anaesthesia.

Effects of biomass burning on nasal mucociliary clearance and mucus properties after sugarcane harvesting

OBJECTIVE

Biofuel from sugarcane is widely produced in developing countries and is a clean and renewable alternative source of energy. However, sugarcane harvesting is mostly performed after biomass burning. The aim of this study was to evaluate the effects of harvesting after biomass burning on nasal mucociliary clearance and the nasal mucus properties of farm workers.

METHODS

Twenty seven sugarcane workers (21-45 years old) were evaluated at the end of two successive time-periods: first at the end of a 6-month harvesting period (harvesting), and then at the end of a 3-month period without harvesting (non-harvesting). Nasal mucociliary clearance was evaluated by the saccharine transit test, and mucus properties were analyzed using in vitro mucus contact angle and mucus transportability by sneeze. Arterial blood pressure, heart rate, respiratory rate, pulse oximetry, body temperature, associated illness, and exhaled carbon monoxide were registered.

RESULTS

Data are presented as mean values (95% confidence interval). The multivariate model analysis adjusted for age, body-mass index, smoking status and years of working with this agricultural practice showed that harvesting yielded prolonged saccharine transit test in 7.83 min (1.88-13.78), increased mucus contact angle in 8.68 degrees (3.18-14.17) and decreased transportability by sneeze in 32.12 mm (-44.83 to -19.42) compared with the non-harvesting period. No significant differences were detected in any of the clinical parameter at either time-period.

CONCLUSION

Sugarcane harvesting after biomass burning negatively affects the first barrier of the respiratory system in farm workers by impairing nasal mucociliary clearance and inducing abnormal mucus properties.

The temperature and humidity in a low-flow anesthesia workstation with and without a heat and moisture exchanger

BACKGROUND

The Dräger Primus anesthesia workstation has a built-in hotplate to heat the patient's exhaled gas. The fresh gas flow is mixed with the heated exhaled gas as they pass through the soda lime canister. A heat and moisture exchanger (HME) may also be used to further heat and humidify the inhaled gas. In this study we measured the temperature and humidity of the inhaled gas coming from the Dräger Primus with or without a HME.

METHODS

Thirty female patients were randomly divided into 2 groups and their lungs ventilated by the Primus Dräger anesthesia workstation with or without a HME. The humidity and temperature of the inhaled gas were measured 15, 30, 60, 90, and 120 minutes after connecting the patient to the breathing circuit.

RESULTS

After 120 minutes of ventilation with a low-flow breathing circuit, the temperatures of inhaled gas were 25°C ± 1°C and 30°C ± 2°C without and with HME, respectively, with a statistically significant difference between groups (P < 0.001) with 95% confidence interval (CI) of 3.80°C to 6.40°C; and the absolute humidity values of the inhaled gas were 20.5 ± 3.6 mgH(2)O · L(-1) and 30 ± 2 mgH(2)O · L(-1) without and with HME, respectively, with a statistically significant difference between groups (P < 0.001) with 95% CI of 7.37°C to 13.03°C.

CONCLUSIONS

The Primus anesthesia workstation partially humidifies the inspired gas when a low fresh gas flow is used. Insertion of an HME increases the humidity in inhaled gas, bringing it close to physiological values.

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.

Furosemide impairs nasal mucociliary clearance in humans

Furosemide, a potent diuretic, affects ion and water movement across the respiratory epithelium. However, the effects of furosemide, as clinically used, on mucociliary clearance, a critical respiratory defense mechanism, are still lacking in humans. Fourteen young healthy subjects were assigned to three random interventions, spaced one-week apart: no intervention (control), oral furosemide (40mg), and furosemide+oral volume replacement (F+R). Nasal mucociliary clearance was assessed by saccharine test (STT), and mucus properties were in vitro evaluated by means of contact angle and transportability by sneeze. Urine output and osmolality were also evaluated. Urine output increased and reduced urine osmolality in furosemide and F+R compared to the control condition. STT remained stable in the control group. In contrast, STT increased significantly (40%) after furosemide and F+R. There were no changes in vitro mucus properties in all groups. In conclusion, furosemide prolongs STT in healthy young subjects. This effect is not prevented by fluid replacement, suggesting a direct effect of furosemide on the respiratory epithelium.

Methods for studying mucociliary transport

Mucociliary transport dysfunctions can impair the quality of life of patients suffering from chronic rhinossinusitis and lead to severe consequences such as alterations in respiratory physiology or even death as in cases of cystic fibrosis and primary ciliary dyskinesia. Therefore, it is crucial to understand the physiology of the mucociliary apparatus and how its components (cilia, mucus-periciliary layer and its interaction) affect the clearance of respiratory secretions. Aims: This paper aims to review and to discuss different techniques for studying mucociliary transport and their clinical and experimental applicability. Conclusions: The methods listed in this revision provide us with valuable information about different aspects of the mucociliary transport. Some of the methods listed are more suitable for clinical practice and present reproducible results. Others, show only applicability in experimental settings due to technical difficulties or financial limitations. However, it is important to emphasize that up to now there is no method that can evaluate ciliary beating frequency (CBF) in vivo and in situ. Such a method would become a valuable tool in the scientific scenario and in the clinical practice, supporting the diagnosis of ciliary dyskinesias and avoiding the use of invasive procedures to corroborate the clinical suspicion

Nasal mucus transportability in children with cleft palate

OBJECTIVES

Children with cleft palate (CP) have a high prevalence of sinusitis. Considering that nasal mucus properties play a pivotal role in the upper airway defense mechanism, the aim of the study was to evaluate nasal mucus transportability and physical properties from children with CP.

SETTING

Hospital for Rehabilitation of Craniofacial Anomalies, School of Dentistry, University of São Paulo, Bauru, SP, Brazil and Laboratory of Experimental Air Pollution, School of Medicine, University of São Paulo, São Paulo, SP, Brazil.

METHODS

Nasal mucus samples were collected by nasal aspiration from children with CP and without CP (non-CP). Sneeze clearance (SC) was evaluated by the simulated sneeze machine. In vitro mucus transportability (MCT) by cilia was evaluated by the frog palate preparation. Mucus physical surface properties were assessed by measuring the contact angle (CA). Mucus rheology was determined by means of a magnetic rheometer, and the results were expressed as log G* (vectorial sum of viscosity and elasticity) and tan delta (relationship between viscosity and elasticity) measured at 1 and 100 rad/s.

RESULTS

Mucus samples from children with CP had a higher SC than non-CP children (67+/-30 and 41+/-24 mm, respectively, p<0.05). Mucus samples from children with CP had a lower CA (24+/-16 degrees and 35+/-11 degrees , p<0.05) and a higher tan delta 100 (0.79+/-0.24 and 0.51+/-0.12, p<0.05) than non-CP children. There were no significant differences in mucus MCT, log G* 1, tan delta 1 and log G* 100 obtained for CP and non-CP children.

CONCLUSIONS

Nasal mucus physical properties from children with CP are associated with higher sneeze transportability. The high prevalence of sinusitis in children with CP cannot be explained by changes in mucus physical properties and transportability.

Métodos de estudo do transporte mucociliar

Disfunções no transporte mucociliar trazem desde queda na qualidade de vida dos pacientes, como nas rinites e rinossinusites crônicas, até graves conseqüências com risco de seqüelas irreversíveis e mesmo letais, como nos casos de fibrose cística e das discinesias ciliares primárias. Desta forma, torna-se fundamental o conhecimento do funcionamento normal do aparelho mucociliar e de como alterações em seus componentes (cílio, muco-fluido periciliar e interação dinâmica entre ambos) afetam o transporte das secreções respiratórias. OBJETIVOS: Este artigo visa a revisar e discutir as diferentes técnicas de avaliação do transporte mucociliar descrevendo suas peculiaridades e aplicabilidades clínicas e experimentais. CONCLUSÕES: Os métodos citados nesta revisão nos fornecem informações importantes sobre os diferentes aspectos do transporte mucociliar. Alguns apresentam uma maior facilidade de realização e resultados reprodutíveis, já outros apenas mostraram-se com aplicabilidade em protocolos de pesquisa em virtude de dificuldades técnicas e limitações financeiras. Há que se considerar a inexistência de métodos que avaliem ambulatorialmente a freqüência de batimento ciliar (FBC) "in vivo" e "in situ", o que se tornaria uma ferramenta importante, tanto no âmbito científico, quanto na prática clínica, auxiliando no diagnóstico das discinesias ciliares e evitando a realização de procedimentos mais invasivos para a sua confirmação diagnóstica.

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.

Double-heater-wire circuits and heat-and-moisture exchangers and the risk of ventilator-associated pneumonia

OBJECTIVE

To compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW).

DESIGN

A prospective, randomized trial.

SETTING

A metropolitan teaching hospital's general intensive care unit.

PATIENTS

Three hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs.

INTERVENTIONS

Patients were randomized to humidification with use of an HME (n=190), SHW (n=94), or DHW (n=97).

MEASUREMENTS AND MAIN RESULTS

Study end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p=0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p=.03) and ventilation days (AOR, 1.05; 95% CI, 1.0-1.2; p=.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% CI, 0.4-0.2; p=.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p=.2), as were suction frequency, secretion thickness, and blood on suctioning (p=.32, p=.06, and p=.34, respectively). The HME use per patient per day was 1.13.

CONCLUSIONS

Humidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use.

Mucociliary clearance is impaired in acutely ill patients

OBJECTIVE

This study aimed to investigate nasal mucociliary clearance in acutely ill patients who were clinically stable and had no airway manipulation.

DESIGN

Prospective clinical study.

SETTING

Medical ICU.

PATIENTS AND PARTICIPANTS

Sixteen medical patients admitted to the ICU and 16 healthy subjects were studied. Patients who were receiving airway manipulation, including tracheal suctioning, nasogastric or enteral tubes, noninvasive and invasive mechanical ventilation, were excluded.

INTERVENTIONS

Mucociliary clearance was evaluated by saccharine transit time (STT) measurements at ICU admission (admission) and 90 days after hospital discharge (recovery). Healthy subjects were also subjected to two measurements 90 days apart.

MEASUREMENTS AND RESULTS

The STT of patients was 26.4 +/- 11.3 min and 17.9 +/- 8.6 min at admission and recovery (p = 0.002) [mean +/- SD] but did not change along the 90-day interval in healthy subjects (17.2 +/- 10.2 min and 16.7 +/- 10.3 min), respectively. Smokers (patients and healthy subjects) presented prolonged STT when compared to nonsmokers (p = 0.026). STT at admission correlated positively with heart rate (r = 0.560; p = 0.024) and hospital stay (r = 0.634; p = 0.008).

CONCLUSION

Mucociliary clearance is impaired in stable acutely ill patients with no airway manipulation and correlates with simple markers of underlying disease severity. Mucociliary dysfunction may help to explain the increased susceptibility of hospital-acquired respiratory infection in critically ill patients.

Sputum induction as a research tool for the study of human respiratory mucus

The study objectives were to compare in vitro transportability and physical properties of respiratory mucus, obtained invasively by direct collection (DC) right after endotracheal intubation and non-invasively by sputum induction with 3% hypertonic saline solution inhalation (SI) 24 h before the anesthesia. Twenty-two patients with no pulmonary disease scheduled for elective abdominal surgical procedures were studied. The parameters analyzed and the main results are as follows. (1) Transportability by cilia (MCT), SI was higher than DC (0.94+/-0.25 and 0.62+/-0.25; P<0.001). There was a significant correlation between the two methods and DC could be estimated by: DC=0.21+(0.44 SI) (r=0.44; P<0.001). (2) Transportability by cough (CC), SI was higher than DC (68.23+/-32.1 and 33.58+/-19.04 mm; P=0.002). (3) Contact angle (CA), SI was lower than DC (10+/-3 degrees and 22+/-14 degrees ; P=0.025). (4) Rheological properties (no significant difference obtained between SI and DC). These results indicated that SI changes mucus physical properties and transportability in non-expectorators.

Humidification in the long-term ventilated patient; a systematic review

This review aims to identify which method of humidification is most effective in Intensive Care patients intubated and ventilated for longer than 48hours with regard to the prevention of tracheal tube occlusion and the incidence of ventilator associated pneumonia (VAP). The Cochrane Library, Medline, CINAHL and Embase databases were searched for randomised controlled trials (RCTs) that compared any type of heated water humidifier with any type of heat moisture exchange (HME) filter. Two prospective RCTs met the inclusion criteria and were available to include in the main body of the review. These studies showed no difference in the rate of tracheal tube occlusion between devices but a significantly higher level of VAP with the heated humidifier. However, many potential studies were excluded from the review due to insufficient data within the published articles, and both included studies were undertaken in USA and excluded high risk patients. This limits the wide applicability of findings.

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.

Infection in the chronically critically ill: unique risk profile in a newly defined population

Although CCI is defined as prolonged ventilatory failure with tracheotomy stemming from preceding critical illness, the contention that multisystem debilities impact on most CCI patients' care and recovery is a central thesis of this volume. Perhaps reflecting the combined debilities inherent in CCI, infectious complications take their toll in morbidity, mortality, and persistent ventilatory insufficiency. Enhanced susceptibility to infection results from a potent admixture of barrier breakdown, exposure to virulent and resistant nosocomial pathogens, and postulated "immune exhaustion" that stems from the combined impact of comorbidities and the sequellae of critical illness. Strategies to improve outcome in CCI-related infection include standard measures of support especially nutrition, reducing environmental inoculum through pulmonary hygiene measures, skin care, and limiting barrier breaches, and appropriate antimicrobials directed at likely pathogens. Future stratification of patient risk on the basis of immune phenotype or genotype and potential immunomodulatory prophylaxis may be around the corner, as new prospects in the pharmaceutical armamentarium are presently undergoing testing.

Effects of intravenous furosemide on mucociliary transport and rheological properties of patients under mechanical ventilation

The use of intravenous (IV) furosemide is common practice in patients under mechanical ventilation (MV), but its effects on respiratory mucus are largely unknown. Furosemide can affect respiratory mucus either directly through inhibition of the NaK(Cl)2 co-transporter on the basolateral surface of airway epithelium or indirectly through increased diuresis and dehydration. We investigated the physical properties and transportability of respiratory mucus obtained from 26 patients under MV distributed in two groups, furosemide (n = 12) and control (n = 14). Mucus collection was done at 0, 1, 2, 3 and 4 hours. The rheological properties of mucus were studied with a microrheometer, and in vitro mucociliary transport (MCT) (frog palate), contact angle (CA) and cough clearance (CC) (simulated cough machine) were measured. After the administration of furosemide, MCT decreased by 17 +/- 19%, 24 +/- 11%, 18 +/- 16% and 18 +/- 13% at 1, 2, 3 and 4 hours respectively, P < 0.001 compared with control. In contrast, no significant changes were observed in the control group. The remaining parameters did not change significantly in either group. Our results support the hypothesis that IV furosemide might acutely impair MCT in patients under MV.

Effects of Bronchial Transection and Reanastomosis on Mucociliary System

STUDY OBJECTIVES

The mechanisms involved in the impairment of mucociliary function after lung transplantation are not completely understood. The purpose of the present study was to isolate the effects of unilateral bronchial transection and reanastomosis in a rat model.

DESIGN

In situ bronchial mucociliary transport (MCT) was determined proximal and distal to the bronchial anastomosis, as well as in the right bronchus, in 48 rats classified into six groups: intact rats, and rats at 1 day, 2 days, 7 days, 15 days, and 30 days after bronchial transection and reanastomosis of the left main stem bronchus. In vitro mucus transportability and mucus contact angle were studied in another group of eight rats after 1 week of surgery.

RESULTS

Distal to the anastomosis site, left bronchus in situ MCT (mean +/- SD) was 0.26 +/- 0.19 mm/min for the intact group, and 0.11 +/- 0.13 mm/min, 0.07 +/- 0.04 mm/min, 0.03 +/- 0.04 mm/min, 0.07 +/- 0.12 mm/min, and 0.05 +/- 0.06 mm/min for 1 day, 2 days, 7 days, 15 days, and 30 days after surgery, respectively (all significantly reduced, p < 0.05). No intergroup differences were found proximal to the anastomosis (p = 0.30). When comparing the left and right bronchi, differences were detected in both distal (p < 0.0001) and proximal sides (p = 0.0001). No significant differences in mucus transportability in vitro were found (p = 0.15). Mucus contact angle of the left bronchus (52.8 +/- 20.5 degrees ) was significantly greater than that of the mucus from the right bronchus (34.4 +/- 12.9 degrees; p < 0.05).

CONCLUSIONS

We conclude that bronchial transection and reanastomosis lead to a marked impairment of MCT in distal airways, which can in part be explained by alterations in the surface properties of mucus.

Tracheostomy management in the chronically ventilated patient

Tracheotomy is a fundamentally important technique for managing patients who require long-term mechanical ventilation. Appropriate application of tracheotomy requires a skilled approach for timing the procedure, selecting the appropriate tracheostomy tube appliance, caring for the artificial airway once it is in place, and assisting patients with their specialized needs, such as articulated speech, airway humidification, and oral nutrition. Preparing patients for airway decannulation after they have weaned from mechanical ventilation requires a similar level of skill and attention to detail.