Twenty-four-hour tracheal pH monitoring--a simple and non-hazardous investigation

Significance of Mini Bronchoalveolar Lavage Fluid Amylase Level in Ventilator-Associated Pneumonia: A Prospective Observational Study

OBJECTIVES

Aspiration of oropharyngeal or gastric contents in intubated patients can lead to ventilator-associated pneumonia. Amylase in respiratory secretion has been reported as a possible marker of aspiration. We studied whether elevated α-amylase in mini bronchoalveolar lavage specimens can be suggestive of ventilator-associated pneumonia in intubated patients with high clinical suspicion.

DESIGN

Prospective single-center observational study.

SETTING

Department of Critical Care Medicine, tertiary care academic institute.

PATIENTS

Adult patients on mechanical ventilation for more than 48 hours with with clinically suspected ventilator-associated pneumonia as per defined criteria, admitted between December 2014 and May 2016.

METHODS

Mini bronchoalveolar lavage samples were collected within 72 hours of endotracheal intubation. Samples were sent for α-amylase level assay and quantitative culture. Ventilator-associated pneumonia was confirmed from mini bronchoalveolar lavage microbial culture of greater than or equal to 10 cfu/mL, and patients were divided into ventilator-associated pneumonia and no ventilator-associated pneumonia groups. Pre- and postintubation risk factors for aspiration were also noted.

RESULTS

The prevalence of ventilator-associated pneumonia was 64.9% among 151 patients in whom it was clinically suspected. Median (interquartile range) mini bronchoalveolar lavage α-amylase levels in ventilator-associated pneumonia and no ventilator-associated pneumonia groups on the day of study inclusion were 287 U/L (164-860 U/L) and 94 U/L (59-236 U/L), respectively (p < 0.001). Median (interquartile range) α-amylase levels in patients with 0, 1, 2, and 3 preintubation risk factors were 65 U/L (35-106 U/L), 200 U/L (113-349 U/L), 867 U/L (353-1,425 U/L), and 3,453 U/L (1,865-4,304 U/L), respectively (p < 0.001) and 472 U/L (164-1,452 U/L) and 731 U/L (203-1,403 U/L) in patients with 1 and 2 postintubation risk factors, respectively (p < 0.001). A mini bronchoalveolar lavage α-amylase of 163 U/L or more yielded sensitivity and specificity of 73% and 68.6%, respectively, with area under the receiver operating characteristic curve of 0.746 (95% CI, 0.66-0.83).

CONCLUSIONS

Patients with ventilator-associated pneumonia within 72 hours from intubation have significantly elevated α-amylase concentrations in mini bronchoalveolar lavage fluid. Mini bronchoalveolar lavage α-amylase concentrations increase with increasing number of aspiration risk factors.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

Transient receptor potential (TRP) channels in the airway: role in airway disease

Over the last few decades, there has been an explosion of scientific publications reporting the many and varied roles of transient receptor potential (TRP) ion channels in physiological and pathological systems throughout the body. The aim of this review is to summarize the existing literature on the role of TRP channels in the lungs and discuss what is known about their function under normal and diseased conditions. The review will focus mainly on the pathogenesis and symptoms of asthma and chronic obstructive pulmonary disease and the role of four members of the TRP family: TRPA1, TRPV1, TRPV4 and TRPM8. We hope that the article will help the reader understand the role of TRP channels in the normal airway and how their function may be changed in the context of respiratory disease.

The application of exhaled breath gas and exhaled breath condensate analysis in the investigation of the lower respiratory tract in veterinary medicine: A review

The analysis of biomarkers in exhaled breath (EB) and exhaled breath condensate (EBC) may allow non-invasive and repeatable assessment of respiratory health and disease in mammals. Compared to human medicine, however, research data from EB and EBC analysis in veterinary medicine are limited and more patient variables influencing concentrations of EB/EBC analytes may be present. In addition, variations in methodologies between studies may influence results. A comparison of the approaches used in veterinary research by different groups may aid in the identification of potentially reliable and repeatable biomarkers suitable for further investigation. To date, changes in acid-base status and increased concentrations of inflammatory mediators have been the main findings in studies of pulmonary disease states in animals. Whilst these biomarkers are unlikely to represent specific and sensitive diagnostic parameters, they do have potential application in monitoring disease progression and treatment response.

Relationship between gastro-oesophageal reflux and airway diseases: the airway reflux paradigm

Our understanding of the relationship between gastro-oesophageal reflux and respiratory disease has recently undergone important changes. The previous paradigm of airway reflux as synonymous with the classic gastro-oesophageal reflux disease (GORD) causing heartburn has been overturned. Numerous epidemiological studies have shown a highly significant association of the acid, liquid, and gaseous reflux of GORD with conditions such as laryngeal diseases, chronic rhinosinusitis, treatment resistant asthma, COPD and even idiopathic pulmonary fibrosis. However, it has become clear from studies on cough hypersensitivity syndrome that much reflux of importance in the airways has been missed, since it is either non- or weakly acid and gaseous in composition. The evidence for such a relationship relies on the clinical history pointing to symptom associations with known precipitants of reflux. The tools for the diagnosis of extra-oesophageal reflux, in contrast to the oesophageal reflux of GORD, lack sensitivity and reproducibility. Unfortunately, methodology for detecting such reflux is only just becoming available and much additional work is required to properly delineate its role.

Chronic cough: epidemiology

Chronic cough is perhaps the commonest symptom of medical importance with some 12% of the general population having the symptom on a daily or weekly basis. Chronic cough causes a large degree of morbidity, with both the physical e.g. incontinence, and the psychological e.g. social isolation, domains. The causes of chronic cough are numerous, but fall into two broad categories; that causing an asthma-like syndrome characterized by eosinophilic infiltration of the airways, and oesophageal disease, particularly weakly acid reflux. Failure to make, particularly this latter, diagnosis leads to enormous consequences in terms of loss of employment, healthcare utilisation and a psychosocial morbidity.

Aspiration pneumonias: under-diagnosed and under-treated

PURPOSE OF REVIEW

To examine recent advancements of the epidemiology, risk factors, bacteriology, diagnostic measures, and treatment for aspiration pneumonia.

RECENT FINDINGS

In a large prospective study, 10.3% of community-acquired pneumonia requiring hospitalization was associated with aspiration pneumonia, as opposed to 30% when patients were admitted from long-term facilities. A murine stroke model showed increased apoptosis of cell-mediated immune cells due to overactivation of the sympathetic nervous system. Subsequent nasal inoculum of low-dose Streptococcus pneumoniae caused severe pneumonia. Another murine study showed intratracheal administration of hydrochloric acid-primed lungs more susceptible to infection with Klebsiella pneumoniae. Tracheal pH monitoring demonstrated acidification of trachea in 28% of patients with acute stroke deemed to be safe for oral feeding. Various antimicrobial agents used to treat aspiration pneumonia have comparable success rates. However, clindamycin was the only agent that did not propagate emergence of methicillin-resistant Staphylococcus aureus.

SUMMARY

Aspiration pneumonia is prevalent in community-acquired pneumonia. Further studies are needed to elucidate the effects of sympathetic nervous system and aspiration pneumonitis as primers for lung infection. Predicting aspiration risk is difficult and newer diagnostic tools are necessary. Antimicrobials used in aspiration pneumonia have similar success rates although the development of resistant organisms must be monitored.

Randomized clinical trial to determine the effect of nasogastric drainage on tracheal acid aspiration following oesophagectomy

BACKGROUND

The aim of this study was to investigate tracheal acid aspiration after oesophagectomy and to determine whether it is influenced by nasogastric (NG) drainage.

METHODS

Thirty-four patients undergoing oesophagectomy were randomized to one of three methods of NG drainage: a single-lumen tube with free drainage and 4-hourly aspiration, a sump-type tube on continuous suction drainage, or no NG tube. A tracheal pH probe was used to collect information on acid aspiration for 48 h after surgery. A pH < 5.5 was considered abnormal (normal pH 6.8-7.2). Total time with tracheal pH < 5.5, number of reflux episodes and longest reflux time were compared between groups.

RESULTS

There was significant and persistent tracheal acid aspiration in all patients. Patients with a sump-type tube had a significantly shorter total time with tracheal pH < 5.5 than those in the other groups (sump-type tube versus single-lumen tube, P = 0.0069; sump-type tube versus no tube, P = 0.0071). Patients randomized to no NG tube experienced more respiratory complications after surgery than those who had either single-lumen or sump-type tubes (seven of 12 versus four of 22 patients; P = 0.023). Insertion of a NG tube was necessary in the first week after surgery in seven of 12 patients in this group.

CONCLUSION

Routine NG drainage after oesophagectomy is necessary. A sump-type NG tube is better at preventing tracheal acid aspiration and may reduce the incidence of respiratory complications.

Normative Data for pH of Exhaled Breath Condensate

INTRODUCTION

Measurement of pH is one of the simplest and most technically validated biomarkers studied in exhaled breath condensate (EBC). The pH of EBC has been found to be lower than controls in many respiratory disorders. Published data from normal control subjects have been reasonably consistent, but the data sets are not large. This study was undertaken to establish normative EBC pH reference values.

PARTICIPANTS

Four hundred four healthy subjects of all ages were enrolled.

INTERVENTIONS

Each participant provided a single EBC sample using a disposable collector at modest temperature so that EBC was collected as a liquid.

MEASUREMENTS AND RESULTS

Samples of EBC were bubbled with argon gas to standardize for carbon dioxide, and pH was recorded with a calibrated and validated glass microelectrode on stabilization. The median EBC pH was 8.0 with interquartile (25 to 75%) range of 7.8 to 8.1. There were no differences based on age, sex, or race. The distribution is skewed, with 6.4% of EBC samples having a pH range < 7.4.

CONCLUSIONS

An extensive normal data set now exists that reveals EBC pH is maintained in a modestly alkaline and tight range in subjects who consider themselves healthy.

Tracheal pH monitoring and aspiration in acute stroke

BACKGROUND

aspiration can lead to chest infections, increased morbidity and mortality in stroke sufferers. It is important clinically and for research purposes to identify all patients who aspirate. At present, videofluoroscopy is the gold standard for detecting aspiration. The aim of this study was to investigate aspiration in acute stroke patients, who are safe for oral intake as assessed by bedside swallow test and videofluoroscopy, using tracheal pH monitoring.

METHODS

thirty-four stroke patients admitted to the Acute Stroke Unit gave informed consent and underwent tracheal pH monitoring 4-19 days post-stroke. A standardised acid meal was served.

RESULTS

two traces were discarded. Nine of the 32 remaining studies showed a drop in tracheal pH <5.5 following ingestion of an acidic meal. Two patterns of lowered tracheal pH were observed: three cases showed a prolonged fall in pH to <5.5, which took over 15 minutes to return to baseline and six had acute falls in pH to <5.5, which rapidly recovered in under 4 minutes. In six the drop occurred immediately after the meal, and in three a delay was observed prior to the drop.

CONCLUSION

tracheal acidification, which could represent aspiration, has been observed in 9 of 32 stroke patients assessed as safe to take diet and fluids orally by bedside assessment and videofluoroscopy. This is a preliminary investigation that provides information about tracheal pH monitoring in acute stroke patients.

The influence of gastroesophageal reflux disease and its treatment on asthmatic cough

Gastroesophageal reflux is known to cause chronic cough and is also implicated in worsening of asthma. We conducted a prospective study to examine the clinical significance of gastroesophageal reflux disease (GERD) in asthmatic patients with chronic cough to analyze the temporal relationship between reflux events and coughing and to assess the effect of esomeprazole treatment on respiratory symptoms and lung function in these patients. Asthmatic patients (126) with chronic dry cough were studied. Diagnosis of GERD was based on typical symptoms and the effectiveness of therapeutic test or on pH monitoring. Patients without GERD (negative pH results) consisted of the control group. The results of pH monitoring showed that 64% of cough episodes were related to acid reflux and in 91% of reflux events preceded coughing. Esomeprazole treatment (40 mg/day for 3 months) not only diminished GERD symptoms but also improved asthma outcome Baseline FEV(1) and PEF values increased significantly together with a decrease in symptom scores and the use of rescue medication. In most patients included in the extended part of the study for another 3 months, the dose of inhaled steroids could be reduced with sustained GERD therapy. Our data showing that reflux events preceded coughing in most cases and that treatment of GERD resulted in an improvement in different outcome measures of asthma suggest that GERD worsens asthma, and its treatment is of clinical importance to effectively manage these patients.

A new pepsin assay to detect pulmonary aspiration of gastric contents among newly intubated patients

Aspiration of gastric contents by endotracheally intubated patients is associated with significant morbidity and mortality. Previous studies suggest that pepsin in tracheal aspirates may be a valuable marker of occult aspiration. We sought to show the sensitivity and specificity of a new, pepsin-specific assay in humans. A prospective, case-controlled study was conducted with subjects serving as their own controls. After planned endotracheal and nasogastric intubation for elective surgery, 20 participants had tracheal and gastric aspirates withdrawn. A blinded investigator tested samples for the presence of pepsin using the assay. Positive samples were then tested with pepstatin, a specific pepsin inhibitor, to ensure that positive results were due to pepsin. All tracheal aspirates tested negative and all gastric aspirates tested positive for pepsin. Pepstatin halted pepsin activity in all positive samples, ensuring that positive results were due to pepsin. A pepsin-specific assay is extremely reliable for detecting gastric contents in humans.

Acid stress in the pathology of asthma

Although alteration of airway pH may serve an innate host defense capacity, it also is implicated in the pathophysiology of obstructive airway diseases. Acid-induced asthma appears in association with gastroesophageal reflux after accidental inhalation of acid (fog, pollution, and workplace exposure) and in the presence of altered airway pH homeostasis. Endogenous and exogenous exposures to acids evoke cough, bronchoconstriction, airway hyperreactivity, microvascular leakage, and heightened production of mucous, fluid, and nitric oxide. Abnormal acidity of the airways is reflected in exhaled breath assays. The intimate mechanisms of acid-induced airway obstruction are dependent on activation of capsaicin-sensitive sensory nerves. Protons activate these nerves with the subsequent release of tachykinins (major mediators of this pathway) that, in conjunction with kinins, nitric oxide, oxygen radicals, and proteases, modulate diverse aspects of airway dysfunction and inflammation. The recognition that acid stress might initiate or exacerbate airway obstructive symptomatology has prompted the consideration of new therapies targeting pH homeostasis.

Cough. 1: Chronic cough in adults

The investigation and treatment of chronic cough in adults is generally rewarding, provided there is an understanding of its aetiology, particularly when it arises from sites outside the respiratory tract.

Tracheal microaspiration in adult cystic fibrosis

Gastro-oesophageal reflux (GOR) has been implicated in the aetiology of lung disease. Cystic fibrosis (CF) patients have a high incidence of GOR symptoms with demonstrable episodes of oesophageal acidification. We studied 24-hour ambulatory tracheal and oesophageal pH in 11 CF patients with GOR symptoms to identify any episodes of tracheal acidification and define their temporal relation to oesophageal reflux and respiratory symptoms. 8 patients had evidence of significant GOR (DeMeester score mean 58; range 17-107) and in 6 it was gross (DeMeester score > 30). 4 patients had tracheal acidification (defined as tracheal pH < 5.5): all had greatly raised DeMeester scores. Two patterns of lowered tracheal pH were seen: a gradual drift downwards of tracheal pH to < 5.5 which recovered slowly, and an acute fall in tracheal pH to < 5.5 with rapid recovery. Only one patient had a fall in peak expiratory flow in conjunction with a decline in tracheal pH, and no association was found between the presence of tracheal microaspiration and pulmonary function. We conclude that tracheal acidification occurs in adult CF patients with GOR.

Gastroesophageal reflux and tracheobronchial contamination after cardiac surgery: should a nasogastric tube be routine?

Nasogastric (NG) tubes are routinely used in patients undergoing cardiac surgery. This randomized study was designed to assess gastroesophageal reflux (GER) without a NG tube (control) compared with a NG tube managed either by gravity drainage (gravity) or continuous low-grade suction (suction). Antimony pH probes were placed in the lower esophagus and trachea after induction of anesthesia in 51 patients, and pH was recorded every 5 s until the time of tracheal extubation. GER was defined as reversible decrease in esophageal pH to less than 4.0. No significant difference was found between groups in age, weight, gender, duration of postoperative ventilation, morphine use, or antiemetic use. All indicators of GER were seen more frequently in the gravity group compared with the two other groups (P < 0.001). One episode of sudden decrease in tracheal pH was observed in a patient in the gravity group, indicating tracheal aspiration, which was associated with delayed extubation and postoperative pneumonia. The absence of a NG tube is not associated with reflux, probably since the gastroesophageal sphincter remains competent. NG tubes are not routinely necessary for cardiac surgery in patients without risk factors for GER, and increase reflux risk if managed without low-grade suction.

Simultaneous tracheal and oesophageal pH monitoring during mechanical ventilation

OBJECTIVE

To simultaneously record tracheal and oesophageal pH in mechanically ventilated children to determine: (1) the feasibility and safety of the method; (2) the incidence of gastro-oesophageal reflux (GOR) and pulmonary contamination; and (3) their associated risk factors.

DESIGN

Prospective study.

SETTING

Paediatric intensive care unit in a university hospital.

PATIENTS

Twenty mechanically ventilated children (mean age 6.7 years) who met the following inclusion criteria: endotracheal tube with an internal diameter of 4 mm or more (cuffed or uncuffed), mechanical ventilation for an acute disease, no treatment with antiacids, prokinetics, or H2-receptor blockers, and no nasogastric or orogastric tube.

METHODS

The tracheal antimony pH probe was positioned 1 cm below the distal end of the endotracheal tube. The oesophageal antimony pH probe was positioned at the lower third of the oesophagus. pH was recorded on a double channel recorder and analysed with EsopHogram 5.01 software and by examination of the trace. The following definitions were used: GOR index, percentage of time pH < 4; pathological GOR, GOR index > 4.8%; tracheal reflux, fall in tracheal pH < 4, 4.5, or 5, or a decrease of one unit from baseline, in both cases preceded by an episode of GOR. The results were analysed statistically by Fisher's exact and the Kruskal-Wallis test.

RESULTS

The procedure was well tolerated and the median duration of analysable recording was 6 hours (range 5-22.6). Pathological GOR was observed in eight (40%) children. GOR was more frequent with an uncuffed endotracheal tube than with a cuffed one (p = 0.01). Tracheal reflux (pH < 4) was observed in four children (20%) without clinical evidence of pulmonary aspiration. Episodes of tracheal reflux were associated with a GOR index > 10% (p < 0.01) and were more frequent with a maximal inspiratory pressure of < 25 cm H2O (p = 0.03), but were not related to the indication for mechanical ventilation, whether the endotracheal tube was cuffed or not, age, or drug treatment.

CONCLUSIONS

Simultaneous tracheal and oesophageal pH monitoring was feasible in the setting of this study. Tracheal reflux can occur without pathological GOR, and GOR may occur without tracheal reflux. Further prospective studies in larger groups of patients are now justified.

Simultaneous tracheal and oesophageal pH measurements in asthmatic patients with gastro-oesophageal reflux

BACKGROUND

An association between asthma and gastro-oesophageal reflux is well recognised but the underlying mechanism is unclear. One suggestion is that gastric juice is aspirated into the tracheal and upper airways but detection of these events is difficult and involves radioisotopic studies. A new method of making direct measurements of tracheal and oesophageal pH over a 24 hour period is described, together with its application to patients with asthma.

METHODS

The technique involves insertion of simultaneous tracheal and oesophageal pH probes under general anaesthesia. Continuous monitoring of pH over a 24 hour period is possible, permitting comparison with peak flow readings during wakefulness and at night should the patient be disturbed. Representative data from four patients with asthma (mean FEV1 62% predicted) and symptomatic gastro-oesophageal reflux, together with data from three non-asthmatics, is presented.

RESULTS

Thirty seven episodes of gastro-oesophageal reflux lasting more than five minutes were recorded. Of these, five were closely followed by a fall in tracheal pH from a mean (SE) of 7.1 (0.2) to 4.1 (0.4) and a fall in peak expiratory flow (PEFR) of 84 (16) l/min. When gastro-oesophageal reflux occurred without tracheal aspiration the fall in PEFR was 8 (4) l/min.

CONCLUSIONS

This new technique was well tolerated and allowed quantitation of the number, duration, and timing of episodes of tracheal micro-aspiration. Unlike acid reflux without aspiration, these events appear to be related to significant acute changes in lung function in asthmatic patients. Further studies with this new method may elucidate the role of gastro-oesophageal reflux in asthma.