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Biomedical subjects

Dean R Hess

Publications and source records attributed to Dean R Hess.

At least 19 recordsLinked to original sources
PubMed2007

Capnography for procedural sedation and analgesia in the emergency department.

Although it is standard of care for patient safety monitoring in anesthesia, capnography is not routinely used for emergency department procedural sedation and analgesia. We discuss the use of capnography as a diagnostic monitoring modality for procedural sedation and analgesia, focusing on the physiology and interpretation of the CO2 waveform and recognition of normal, abnormal, and drug-induced ventilatory patterns.

Analgesia↗
PubMed2006

Conventional mechanical ventilation in acute lung injury and acute respiratory distress syndrome.

Acute lung injury and acute respiratory distress syndrome are inflammatory conditions involving a broad spectrum of lung injury from mild respiratory abnormality to severe respiratory derangement. Regardless of cause (direct or indirect lung injury), pulmonary physiology and mechanics are altered, leading to hypoxemic respiratory failure. the use of positive pressure ventilation itself may cause lung injury (ventilator-induced lung injury, or VILI). VILI may amplify preexisting injury, delay lung recovery, and result in adverse outcomes. This article examines the evidence supporting lung-protective ventilation strategies and addresses the methods, outcomes, and potential obstacles to implementation of such approaches.

Humans↗
PubMed2006

The history and physics of heliox.

Since the discovery of helium in 1868, it has found numerous applications in industry and medicine. Its low density makes helium potentially valuable in respiratory care applications, to reduce work of breathing, improve distribution of ventilation, reduce minute volume requirement, and improve aerosol delivery. This review includes a brief history of the use of heliox (a mixture of helium and oxygen) and addresses issues related to the physics of gas flow when heliox is used. Specifically covered are the Hagen-Poiseuille equation, laminar versus turbulent flow, the Reynolds number, orifice flow, Bernoulli's principle, Graham's law, wave speed, and thermal conductivity.

Animals↗
PubMed2006

Heliox and noninvasive positive-pressure ventilation: a role for heliox in exacerbations of chronic obstructive pulmonary disease?

Evidence-based respiratory therapy for exacerbations of chronic obstructive pulmonary disease (COPD) includes oxygen, inhaled bronchodilators, and noninvasive positive-pressure ventilation. Examining the physics of gas flow, a case can be made either for or against the use of helium-oxygen mixture (heliox) in the care of patients with COPD. The evidence for the use of heliox in patients with COPD exacerbation is not strong at present. Most of the peer-reviewed literature consists of case reports, case series, and physiologic studies in small samples of carefully selected patients. Some patients with COPD exacerbation have a favorable physiologic response to heliox therapy, but predicting who will be a responder is difficult. Moreover, the use of heliox is hampered by the lack of widespread availability of an approved heliox delivery system. Appropriately designed randomized controlled trials with patient-important outcomes, such as avoidance of intubation, decreased intensive-care-unit and hospital days, and decreased cost of therapy, are sorely needed to establish the role of heliox in patients with COPD exacerbation, including those receiving noninvasive positive-pressure ventilation. Lacking such evidence, the use of heliox in patients with COPD exacerbation cannot be considered standard therapy.

Biophysical Phenomena↗
PubMed2006

Noninvasive ventilation in neuromuscular disease: equipment and application.

Noninvasive support of ventilation is commonly needed in patients with neuromuscular disease. Body ventilators, which are used rarely, function by applying intermittent negative pressure to the thorax or abdomen. More commonly, noninvasive positive-pressure ventilation (NPPV) is used. This therapy can be applied with a variety of interfaces, ventilators, and ventilator settings. The patient interface has a major impact on comfort during NPPV. The most commonly used interfaces are nasal masks and oronasal masks. Other interfaces include nasal pillows, total face masks, helmets, and mouthpieces. Theoretically, any ventilator can be attached to a mask rather than an artificial airway. Portable pressure ventilators (bi-level positive airway pressure) are available specifically to provide NPPV and are commonly used to provide this therapy. Selection of NPPV settings in patients with neuromuscular disease is often done empirically and is symptom-based. Selection of settings can also be based on the results of physiologic studies or sleep studies. The use of NPPV in this patient population is likely to expand, particularly with increasing evidence that it is life-prolonging in patients with diseases such as amyotrophic lateral sclerosis. Appropriate selection of equipment and settings for NPPV is paramount to the success of this therapy.

Equipment Design↗
PubMed2005

Ventilatory strategies in patients with sepsis and respiratory failure.

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H2O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.

Journal Article↗
PubMed2005

Device selection and outcomes of aerosol therapy: Evidence-based guidelines: American College of Chest Physicians/American College of Asthma, Allergy, and Immunology.

BACKGROUND: The proliferation of inhaler devices has resulted in a confusing number of choices for clinicians who are selecting a delivery device for aerosol therapy. There are advantages and disadvantages associated with each device category. Evidence-based guidelines for the selection of the appropriate aerosol delivery device in specific clinical settings are needed. AIM: (1) To compare the efficacy and adverse effects of treatment using nebulizers vs pressurized metered-dose inhalers (MDIs) with or without a spacer/holding chamber vs dry powder inhalers (DPIs) as delivery systems for beta-agonists, anticholinergic agents, and corticosteroids for several commonly encountered clinical settings and patient populations, and (2) to provide recommendations to clinicians to aid them in selecting a particular aerosol delivery device for their patients. METHODS: A systematic review of pertinent randomized, controlled clinical trials (RCTs) was undertaken using MEDLINE, EmBase, and the Cochrane Library databases. A broad search strategy was chosen, combining terms related to aerosol devices or drugs with the diseases of interest in various patient groups and clinical settings. Only RCTs in which the same drug was administered with different devices were included. RCTs (394 trials) assessing inhaled corticosteroid, beta2-agonist, and anticholinergic agents delivered by an MDI, an MDI with a spacer/holding chamber, a nebulizer, or a DPI were identified for the years 1982 to 2001. A total of 254 outcomes were tabulated. Of the 131 studies that met the eligibility criteria, only 59 (primarily those that tested beta2-agonists) proved to have useable data. RESULTS: None of the pooled metaanalyses showed a significant difference between devices in any efficacy outcome in any patient group for each of the clinical settings that was investigated. The adverse effects that were reported were minimal and were related to the increased drug dose that was delivered. Each of the delivery devices provided similar outcomes in patients using the correct technique for inhalation. CONCLUSIONS: Devices used for the delivery of bronchodilators and steroids can be equally efficacious. When selecting an aerosol delivery device for patients with asthma and COPD, the following should be considered: device/drug availability; clinical setting; patient age and the ability to use the selected device correctly; device use with multiple medications; cost and reimbursement; drug administration time; convenience in both outpatient and inpatient settings; and physician and patient preference.

Adrenergic beta-Agonists↗
PubMed2005

Ventilator waveforms and the physiology of pressure support ventilation.

Pressure support ventilation (PSV) is a commonly used mode. It is patient-triggered, pressure-limited, and (normally) flow-cycled. Triggering difficulty occurring during PSV is usually due to intrinsic positive end-expiratory pressure. The airway pressure generated at the initiation of inhalation is determined by the pressure support setting and the pressure rise time (pressurization rate) settings on the ventilator. The rise-time setting is clinician-adjustable on many current-generation ventilators. Flow delivery during PSV is determined by the pressure support setting, the pressure generated by the respiratory muscles, and respiratory system mechanics. The delivered tidal volume is determined by the area under the flow-time curve. Patient-ventilator dyssynchrony may occur during PSV if the flow at which the ventilator cycles to exhalation does not coincide with the termination of neural inspiration. The newer generation ventilators offer clinician-adjustable flow-termination during PSV. Ventilator waveforms may be useful to appropriately adjust the ventilator during PSV.

Adult↗
PubMed2005

Tracheostomy tubes and related appliances.

Tracheostomy tubes are used to administer positive-pressure ventilation, to provide a patent airway, to provide protection from aspiration, and to provide access to the lower respiratory tract for airway clearance. They are available in a variety of sizes and styles, from several manufacturers. The dimensions of tracheostomy tubes are given by their inner diameter, outer diameter, length, and curvature. Differences in length between tubes of the same inner diameter, but from different manufacturers, are not commonly appreciated but may have important clinical implications. Tracheostomy tubes can be angled or curved, a feature that can be used to improve the fit of the tube in the trachea. Extra proximal length tubes facilitate placement in patients with large necks, and extra distal length tubes facilitate placement in patients with tracheal anomalies. Several tube designs have a spiral wire reinforced flexible design and have an adjustable flange design to allow bedside adjustments to meet extra-length tracheostomy tube needs. Tracheostomy tubes can be cuffed or uncuffed. Cuffs on tracheostomy tubes include high-volume low-pressure cuffs, tight-to-shaft cuffs, and foam cuffs. The fenestrated tracheostomy tube has an opening in the posterior portion of the tube, above the cuff, which allows the patient to breathe through the upper airway when the inner cannula is removed. Tracheostomy tubes with an inner cannula are called dual-cannula tracheostomy tubes. Several tracheostomy tubes are designed specifically for use with the percutaneous tracheostomy procedure. Others are designed with a port above the cuff that allows for subglottic aspiration of secretions. The tracheostomy button is used for stoma maintenance. It is important for clinicians caring for patients with a tracheostomy tube to understand the nuances of various tracheostomy tube designs and to select a tube that appropriately fits the patient.

Catheterization↗
PubMed2005

Facilitating speech in the patient with a tracheostomy.

A tracheostomy tube decreases the ability of the patient to communicate effectively. The ability to speak provides an important improvement in the quality of life for a patient with a tracheostomy. In mechanically ventilated patients, speech can be provided by the use of a talking tracheostomy tube, using a cuff-down technique with a speaking valve, and using a cuff-down technique without a speaking valve. Speech can be facilitated in patients with a tracheostomy tube who are breathing spontaneously by use of a talking tracheostomy tube, by using a cuff-down technique with finger occlusion of the proximal tracheostomy tube, and with the use of a cuff-down technique with a speaking valve. Teamwork between the patient and the patient care team (respiratory therapist, speech-language pathologist, nurse, and physician) can result in effective restoration of speech in many patients with a long-term tracheostomy.

Equipment Design↗
PubMed2005

Patient positioning and ventilator-associated pneumonia.

Rotational beds, prone position, and semi-recumbent position have been proposed as procedures to prevent ventilator-associated pneumonia (VAP). Rotational therapy uses a special bed designed to turn continuously, or nearly continuously, the patient from side to side; specific designs include kinetic therapy and continuous lateral rotation therapy. A meta-analysis of studies evaluating the effect of rotational bed therapy shows a decrease in the risk of pneumonia but no effect on mortality. Two studies reported a lower risk of VAP in patients placed in a prone position, with no effect on mortality. Studies using radiolabeled enteral feeding solutions in mechanically ventilated patients have reported that aspiration of gastric contents occurs to a greater degree when patients are in the supine position, compared with the semirecumbent position. One study reported a lower rate of VAP in patients randomized to semi-recumbent compared to supine position. Although each of the techniques discussed in this paper has been shown to reduce the risk of VAP, none has been shown to affect mortality. The available evidence suggests that semi-recumbent position should be used routinely, rotational therapy should be considered in selected patients, and prone position should not be used as a technique to reduce the risk of VAP.

Beds↗
PubMed2005

Noninvasive positive-pressure ventilation and ventilator-associated pneumonia.

There is much interest in the use of noninvasive positive-pressure ventilation (NPPV) to prevent intubation and afford a survival benefit for patients. The risk of pneumonia in patients receiving NPPV has been reported in 12 studies. Compared to patients receiving invasive mechanical ventilation (4 studies), the pneumonia rate is lower with the use of NPPV (relative risk [RR] 0.15, 95% confidence interval [CI] 0.04 to 0.58, p = 0.006). Compared to patients assigned to invasive mechanical ventilation (3 studies), in which some of the patients assigned to NPPV did not respond and were eventually intubated, there was also a benefit for the use of NPPV (RR 0.24, 95% CI 0.08 to 0.73, p = 0.01). In studies in which patients assigned to NPPV were compared to patients assigned to standard therapy (5 studies), in which some of the patients in each group were eventually intubated, there was benefit shown for the use of NPPV (RR 0.56, 95% CI 0.31 to 1.02, p = 0.06). When this meta-analysis is repeated without the results of the negative study for NPPV (extubation failure), there is a stronger benefit in support of NPPV to decrease the risk of pneumonia in the remaining 4 studies (RR 0.38, 95% CI 0.20 to 0.73, p = 0.003). A meta-analysis combining the results from the 12 studies reviewed shows a strong benefit for NPPV (RR 0.31, 95% CI 0.16 to 0.57, p = 0.0002). One randomized controlled trial of continuous positive airway pressure compared with standard treatment in patients who developed acute hypoxemia after elective major abdominal surgery reported a lower rate of pneumonia with continuous positive airway pressure (2% vs 10%, RR 0.19, 95% CI 0.04 to 0.88, p = 0.02). In patients who are appropriate candidates for NPPV or continuous positive airway pressure, the available evidence suggests a benefit in terms of a lower risk of pneumonia. Perhaps "endotracheal-tube-associated pneumonia" is a better term than "ventilator-associated pneumonia."

Cohort Studies↗
PubMed2005

Metered-dose inhalers and dry powder inhalers in aerosol therapy.

Inhaled drug delivery is an important part of the armamentarium of clinicians caring for patients with pulmonary disease. An increasing variety of metered-dose inhalers and dry powder inhalers are becoming available. This has been driven by the development of new formulations and the impending ban on chlorofluorocarbon propellants. The result is a proliferation of devices, resulting in a confusing number of choices for the clinician, as well as confusion for patients trying to use these devices correctly. The presenters at this conference included many of the world's authorities on metered-dose inhalers and dry powder inhalers, and were an appropriate mix of academic aerosol scientists, clinician researchers with an interest in aerosol therapy, and aerosol scientists working for industry. Improper inhaler technique is common among patients. One of the important take-home messages of this conference is the importance of clinicians knowledgeable in the use of aerosol delivery devices and clinicians' ability to teach patients how to use these devices correctly. Respiratory therapists are uniquely positioned to provide this service, and there is evidence that respiratory therapists may do this better than others. The proceedings of this conference provide the current state of the art of metered-dose inhalers and dry powder inhalers.

Administration, Inhalation↗
PubMed2005

Albuterol delivery via tracheostomy tube.

HYPOTHESIS: Albuterol delivery through a tracheostomy tube is affected by device (nebulizer vs metered-dose inhaler), interface (mask vs T-piece), bias flow, and humidification. METHODS: A lift bar was placed between the chambers of a dual-chambered lung model such that a ventilator triggered simulated spontaneous breathing at a rate of 20 breaths/min, tidal volume of 0.4 L, and inspiratory-expiratory ratio of 1:2. An 8-mm inner diameter cuffed tracheostomy tube was placed through a semi-circular model that simulated a patient's neck. Four conditions of gas flow and humidification were used for the nebulizer experiments: heated aerosol (approximately 30 L/min, approximately 30 degrees C), heated humidity (approximately 30 L/min, approximately 30 degrees C), high flow without added humidity (approximately 30 L/min), or a nebulizer attached to the tracheostomy tube without additional flow. The nebulizer was filled with 4 mL that contained 2.5 mg of albuterol, and operated at 8 L/min. The nebulizer was tested with a T-piece or tracheostomy mask. For the metered-dose inhaler experiments, a spacer was used and actuation of the inhaler (100 microg per actuation) was synchronized with inhalation (4 actuations separated by > or = 15 s). When the spacer was used without additional flow, a valved T-piece was used with a 1-way valve placed either proximal or distal to the spacer. A filter was attached between the lung model and the distal end of the tracheostomy tube. Albuterol washed from the filter was measured by ultraviolet spectrophotometry. RESULTS: For the nebulizer, the most efficient delivery was with no flow other than that to power the nebulizer and with a T-piece (p < 0.001). The most efficient method for aerosol delivery was metered-dose inhaler with a valved T-piece and placement of the 1-way valve in the proximal position (p < 0.001). The effect of humidity was unclear from the results of this study. CONCLUSIONS: Albuterol delivery via tracheostomy was affected by the delivery device (nebulizer vs inhaler), bias gas flow, and the patient interface.

Administration, Inhalation↗
PubMed2005

Albuterol delivery during noninvasive ventilation.

HYPOTHESIS: Albuterol delivered during noninvasive positive-pressure ventilation is affected by use of a nebulizer or metered-dose inhaler (MDI) and whether the leak port is in the hose or the mask. METHODS: A lung model that simulated spontaneous breathing at 20 breaths/min was used. A bi-level positive-airway-pressure ventilator (Respironics S/T30) was set for an inspiratory positive airway pressure of 15 cm H(2)O and an expiratory positive airway pressure of 5 cm H(2)O. The tidal volume delivered was 0.4 L. Two mask types were used: one in which the leak port was incorporated into the circuit, and another in which the leak port was incorporated into the mask. The nebulizer was filled with 4 mL, which contained 5 mg of albuterol, connected via a T-piece directly to the mask, and operated at 8 L/min for 15 min. For the MDI studies, a spacer was placed between the mask and the circuit, and an MDI was actuated into the spacer, either synchronized with the initiation of inhalation or during the exhalation phase (4 actuations separated by \G 15 s in each case). Albuterol was washed from the filter and measured with ultraviolet spectrophotometry. RESULTS: With the nebulizer, significantly more albuterol was delivered to the filter when the leak port was in the circuit (p = 0.001). Significantly more albuterol was delivered with the nebulizer than with the MDI (p < 0.001). The efficiency of albuterol delivery (percent delivered) was similar for nebulizer and MDI with the leak port in the circuit (p = 0.57), but better with the MDI with the leak port in the mask (p = 0.001). Albuterol delivery was significantly less when the MDI was actuated during exhalation (p = 0.001). CONCLUSIONS: Albuterol delivery with noninvasive positive-pressure ventilation was affected by the type of aerosol delivery device, by the location of the leak port, and by actuating the MDI at the proper time in the respiratory cycle.

Administration, Inhalation↗