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Dean R Hess

Publications and source records attributed to Dean R Hess.

36 records · Page 2Linked to original sources
PubMed2004

Pulmonary artery occlusion increases the ratio of diffusing capacity for nitric oxide to carbon monoxide in prone sheep.

OBJECTIVE: To test the hypothesis that the ratio of diffusing capacity of the lung for nitric oxide (DLno) to diffusing capacity of the lung for carbon monoxide (DLco) would be affected by occlusion of a fraction of the pulmonary vascular bed. DESIGN: Interventional physiologic study. SETTING: Animal laboratory of a university hospital. SUBJECTS: Thirteen sheep. INTERVENTIONS: We simultaneously measured single-breath DLno and DLco in anesthetized and mechanically ventilated sheep (fraction of inspired oxygen [Fio(2)] of 1.0) before and after pulmonary artery occlusion by inflation of a balloon (n = 6), and by autologous clot embolism (n = 4). To see if the effect also occurred on Fio(2) of 0.21, four animals were studied during ventilation with room air, one of which was also in the Fio(2) of 1.0 group (14 total experiments with 13 sheep). RESULTS: On Fio(2) of 1.0, the mean DLno/Dlco ratio rose by 35% from 4.76 +/- 0.41 in control to 6.42 +/- 0.82 after balloon occlusion (p = 0.002), and by 54% from 7.55 +/- 2.09 to 11.6 +/- 2.61 (p = 0.005) after autologous clot embolism (+/- SD). An equivalent relative increase of 27% took place during ventilation with room air, but the DLno/DLco ratio was lower (3.14 +/- 0.22 in control and 3.98 +/- 0.38 after balloon occlusion). Independent of the method of obstruction or Fio(2), the increase in DLno/DLco ratio was mostly due to a drop in DLco. The DLno/Dlco ratio reduced much of the intersubject variability of either DLno or DLco alone. CONCLUSION: The DLno/DLco ratio increased after pulmonary artery occlusion regardless of the method of occlusion or Fio(2). This increase may be a result of a greater sensitivity of DLco than DLno to a regional reduction in capillary blood flow.

Animals↗
PubMed2004

Factors affecting oxygen delivery with bi-level positive airway pressure.

INTRODUCTION: Portable pressure ventilators, or bi-level ventilators, do not typically have an oxygen control, and thus supplemental oxygen is usually administered by adding it into the mask or the circuit. We conducted this study to test the hypothesis that delivered oxygen concentration using this configuration is affected by the choice of leak port, oxygen injection site, and ventilator settings. METHODS: A lung model simulating spontaneous breathing was connected to the head of a manikin. An oronasal mask was attached to the manikin. A single-limb circuit was attached to the mask and a bi-level ventilator. Three leak ports were compared: leak in the mask, plateau exhalation valve with mask leak port occluded, and leak port in the circuit with mask leak port occluded. Bi-level positive airway pressure (BiPAP) settings of 10/5, 15/5, 20/5, 15/10, 20/10, and 25/10 cm H(2)O were used at respiratory rates of 15 and 25 breaths/min. Oxygen was added into the mask or into the circuit at the ventilator outlet, using flows of 5 and 10 L/min. Carbon dioxide was added into the lung model to produce an end-tidal P(CO(2)) of either 40 or 75 mm Hg. RESULTS: Delivered oxygen concentration was not affected by respiratory rate (p = 0.22) or end-tidal P(CO(2)) (p = 0.74). The oxygen concentration was greater when oxygen was added into the circuit with the leak port in the mask (p < 0.001), whereas oxygen concentration was greater when oxygen was added into the mask with the leak port in circuit (p = 0.005). Oxygen concentration was significantly lower with the leak port in the mask (p < 0.001), with a higher inspiratory positive airway pressure (p < 0.001), and with a higher expiratory positive airway pressure (p < 0.001). The highest oxygen concentration was achieved with oxygen added to the mask, with the leak port in the circuit, and with the lowest settings of inspiratory (10 cm H(2)O) and expiratory (5 cm H(2)O) positive airway pressure. CONCLUSIONS: Delivered oxygen concentration during BiPAP is a complex interaction between the leak port type, the site of oxygen injection, the ventilator settings, and the oxygen flow. Because of this, it is important to continuously measure arterial oxygen saturation via pulse oximetry with patients in acute respiratory failure who are receiving noninvasive ventilation from a bi-level ventilator.

Equipment Design↗
PubMed2004

Information retrieval in respiratory care: tips to locate what you need to know.

We need current information to support effective practice. This information can be accessed relatively quickly and inexpensively, using nothing more than a computer and an Internet connection. This demands skills in searching and accessing that information. In many hospitals, computers with an Internet connection are readily available in the clinical wards, allowing those with skills in retrieving medical information to find that information near the bedside where it is needed. This report describes techniques to access information on the Internet from various sources. This information exists at high levels, such as PubMed, the National Guideline Clearinghouse, and the Cochrane Library. However, there is also much information available on the Internet that has not been validated or subjected to peer review. Thus, it is important not only to find information but also to separate useful from useless information.

Computers↗
PubMed2004

What is evidence-based medicine and why should I care?

The principles of evidence-based medicine provide the tools to incorporate the best evidence into everyday practice. Evidence-based medicine is the integration of individual clinical expertise with the best available research evidence from systematic research and the patient's values and expectations. A hierarchy of evidence can be used to assess the strength of evidence upon which clinical decisions are made, with randomized studies at the top of the hierarchy. The efficient approach to finding the best evidence is to identify a systematic review or evidence-based clinical practice guidelines. Calculated metrics, such as sensitivity, specificity, receiver-operating-characteristic curves, and likelihood ratios, can be used to examine the evidence for a diagnostic test. High-level studies of a therapy are prospective, randomized, blinded, placebo-controlled, have a concealed allocation, have a parallel design, and assess patient-important outcomes. Metrics used to assess the evidence for a therapy include event rate, relative risk, relative risk reduction, absolute risk reduction, number needed to treat, and odds ratio. Although not all tenets of evidence-based medicine are universally accepted, the principles of evidence-based medicine nonetheless provide a valuable approach to respiratory care practice.

Evidence-Based Medicine↗
PubMed2004

The evidence for noninvasive positive-pressure ventilation in the care of patients in acute respiratory failure: a systematic review of the literature.

Noninvasive positive-pressure ventilation (NPPV) is increasingly being used in the care of patients suffering acute respiratory failure. High-level evidence supports the use of NPPV to treat exacerbation of chronic obstructive pulmonary disease (COPD). NPPV has also been successfully used with selected patients suffering acute hypoxemic respiratory failure and to allow earlier extubation of mechanically ventilated COPD patients. The evidence for NPPV for acute cardiogenic pulmonary edema is inconclusive. With selected patients NPPV decreases the rate of intubation, mortality, and nosocomial pneumonia. Predictors of NPPV failure include greater severity of illness, lower level of consciousness, lower pH, more air leak around the patient-mask interface, greater quantity of secretions, poor initial response to NPPV, and the presence of pneumonia. NPPV obviates intubation in > 50% of appropriately selected patients. Both nasal and oronasal interfaces have been successfully used to apply NPPV, but the oronasal interface is often preferred for acute respiratory failure. Any ventilator and ventilator mode can be used to apply NPPV, but portable pressure ventilators and pressure-support mode are most commonly used. Inhaled bronchodilators can be administered during NPPV, and NPPV can be delivered with helium-oxygen mixture. Institution-specific practice guidelines may be useful to improve NPPV success.

Acute Disease↗
PubMed2004

Retrospective studies and chart reviews.

A retrospective study uses existing data that have been recorded for reasons other than research. A retrospective case series is the description of a group of cases with a new or unusual disease or treatment. With a case-control study, cases with and without the condition of interest are identified, and the degree of exposure to a possible risk factor is then retrospectively compared between the 2 groups. With a matched case-control study, control subjects are selected such that they resemble (match) the cases with regards to certain characteristics (eg, age, comorbidity, severity of disease). Retrospective study designs are generally considered inferior to prospective study designs. Therefore, a retrospective study design should never be used when a prospective design is feasible.

Case-Control Studies↗
PubMed2004

How to write an effective discussion.

Explaining the meaning of the results to the reader is the purpose of the discussion section of a research paper. There are elements of the discussion that should be included and other things that should be avoided. Always write the discussion for the reader; remember that the focus should be to help the reader understand the study and that the highlight should be on the study data.

Biomedical Research↗
PubMed2003

In vitro evaluation of aerosol bronchodilator delivery during mechanical ventilation: pressure-control vs. volume control ventilation.

OBJECTIVE: To determine the effect of inspiratory time and inspiratory flow pattern on albuterol delivery by aerosol during mechanical ventilation. DESIGN: A ventilator was connected to a lung model and set to deliver a tidal volume of 0.6 l, PEEP 5 cmH(2)O, and respiratory rate of 15/min. We evaluated inspiratory times of 1 and 2 s, lung mechanics of 0.05 l/cmH(2)O compliance and 50 cmH(2)O/l/s resistance, or 0.02 l/cmH(2)O compliance and 5 cmH(2)O/l/s resistance, and three inspiratory flow patterns (constant flow volume-controlled ventilation, descending ramp flow volume-controlled ventilation, and pressure-controlled ventilation). Albuterol was delivered into the ventilator circuit by a nebulizer containing 5 mg (4 ml) albuterol or a pMDI and spacer (four actuations; 360 micro g). A filter between the Y-piece and the lung model collected the aerosol, which was analyzed for albuterol by spectrophotometry. RESULTS: For the nebulizer there were significant differences in albuterol delivered for inspiratory time, flow pattern, and lung mechanics. For the pMDI there were no significant differences for the amount of albuterol delivered for inspiratory time, flow pattern, or lung mechanics. CONCLUSIONS: Albuterol delivery by nebulizer is affected by inspiratory time and inspiratory flow pattern. When a pMDI is used, the amount of albuterol delivered is not affected by inspiratory flow pattern or inspiratory time.

Aerosols↗
PubMed2003

Position of exhalation port and mask design affect CO2 rebreathing during noninvasive positive pressure ventilation.

OBJECTIVE: Noninvasive positive pressure ventilation may be considered a first line intervention to treat patients with hypercapnic respiratory failure. However, CO2 rebreathing from the ventilator circuit or mask may impair CO2 elimination and load the ventilatory muscles. This study was conducted to evaluate the effect of exhalation port location and mask design on CO2 rebreathing during noninvasive positive pressure ventilation. DESIGN: Lung model evaluation. SETTING: Experimental laboratory of a large university-affiliated hospital. SUBJECTS: A dual-chamber test lung was used to simulate the ventilatory mechanics of a patient with obstructive lung disease. INTERVENTION: Hypercapnic respiratory failure (end-tidal CO2 of 75 mm Hg) and obstructive lung disease were simulated in a double-chamber lung model. A facial mask (inner volume of 165 mL) with exhalation port within the mask (Facial-MEP) or the same mask with exhalation port in the ventilator circuit (Facial-WS) and a total face mask with exhalation port within the mask (inner volume 875 mL, Total Face) were tested during continuous positive airway pressure and pressure support ventilation provided by a single-limb circuit ventilator at the same frequency and tidal volume. MEASUREMENTS AND MAIN RESULTS: A capnometer and a flow transducer were placed in the lung model upper airway to measure the volume of CO2 rebreathed and tidal volume (Vt). The inspiratory load was estimated from the pressure variation in the lung model driving chamber (PDR). Volume of CO2 rebreathed was smaller during Facial-MEP compared with the other masks in all tested conditions (p <.001). The Vt and PDR necessary to decrease end-tidal CO2 20% (from 75 to 60 mm Hg) was different among the tested masks (Facial-MEP, Vt 701 +/- 9 mL, PDR 8.1 +/- 0.1 cm H2O/sec; Facial-WS, Vt 745 +/- 9 mL, PDR 10.2 +/- 0.1 cm H2O/sec; Total Face, Vt 790 +/- 12 mL, PDR 11.4 +/- 0.2 cm H2O/sec, p <.001). CONCLUSION: Facial-MEP with its exhalation port within the mask and the smallest mask volume demonstrated less rebreathed CO2 and a lower PDR than either the Facial-WS or Total Face masks. Additional studies are necessary to confirm if mask design can clinically affect patient's inspiratory effort during noninvasive positive pressure ventilation.

Carbon Dioxide↗
PubMed2003

Care of the ventilator circuit and its relation to ventilator-associated pneumonia.

Ventilator circuits should not be changed routinely for infection control purposes. The maximum duration of time that circuits can be used safely is unknown. Evidence is lacking related to ventilator-associated pneumonia (VAP) and issues of heated versus unheated circuits, type of heated humidifier, method for filling the humidifier, and technique for clearing condensate from the ventilator circuit. Although the available evidence suggests a lower VAP rate with passive humidification than with active humidification, other issues related to the use of passive humidifiers (resistance, dead space volume, airway occlusion risk) preclude a recommendation for the general use of passive humidifiers. Passive humidifiers do not need to be changed daily for reasons on infection control or technical performance. They can be safely used for at least 48 hours, and with some patient populations some devices may be able to be used for periods of up to 1 week. The use of closed suction catheters should be considered part of VAP prevention strategy, and they do not need to be changed daily for infection control purposes. The maximum duration of time that closed suction catheters can be used safely is unknown. Clinicians caring for mechanically ventilated patients should be aware of risk factors for VAP (eg, nebulizer therapy, manual ventilation, and patient transport).

Humans↗
PubMed2002

In vitro evaluation of aerosol bronchodilator delivery during noninvasive positive pressure ventilation: effect of ventilator settings and nebulizer position.

OBJECTIVE: Respiratory failure due to exacerbation of obstructive lung disease has been successfully treated with noninvasive positive pressure ventilation (NPPV). However, there have been no reports of factors affecting aerosol delivery during NPPV. Our objective was to determine the effect of ventilator settings and nebulizer position on albuterol delivery during NPPV. DESIGN: Bench model study. SETTING: University laboratory. SUBJECTS: None. INTERVENTIONS: A Respironics BiPAP S/T-D30 with a standard circuit was attached to a lung model simulating spontaneous breathing. Inspiratory/expiratory pressures of 10/5, 15/5, 20/5, 15/10, 20/10, and 25/10 cm H2O were tested at respiratory rates of 10 and 20/min. A nebulizer was filled with 5 mg of albuterol in 4 mL of solution, driven with 8 L/min oxygen, and placed at either a proximal (ventilator outlet) or distal (between leak port and lung model connection) position. Albuterol delivery was estimated by measuring the amount of the albuterol collected on a filter placed at the inlet of the lung model. MEASUREMENT AND MAIN RESULTS: Albuterol delivery varied from 5.2 +/- 0.4% to 24.5 +/- 1.3% of the nominal dose and was significantly affected by the position of the nebulizer, respiratory rate, and BiPAP settings (p <.001 in each case). The greatest albuterol delivery was observed with the nebulizer operating at the distal position and a respiratory rate of 20/min. At this respiratory rate and nebulizer placement, albuterol delivery increased with increasing inspiratory pressure levels and decreased as expiratory pressure levels were increased. Nebulizer flow did not affect function of the ventilator. CONCLUSIONS: At optimum nebulizer position (between the leak port and patient connection) and ventilator settings (high inspiratory pressure and low expiratory pressure), as much as 25% of the nominal albuterol dose may be delivered during NPPV.

Aerosols↗
PubMed2002

Lung recruitment: the role of recruitment maneuvers.

There is increasing appreciation that lung-protective strategies are beneficial in patients with acute respiratory distress syndrome. Using low tidal volume in these patients improves survival. However, low tidal volume ventilation may promote alveolar de-recruitment. This has led some to advocate the use of "open lung" strategies that stress the use of high positive end-expiratory pressure levels and recruitment maneuvers. A recruitment maneuver is a sustained increase in airway pressure with the goal to open collapsed lung tissue. A variety of approaches have been used as recruitment maneuvers, including increasing the level of positive end-expiratory pressure, sustained inflation maneuvers, sigh breaths, spontaneous breathing, and others. There have been a number of recent reports describing improvements in arterial oxygenation with the use of recruitment maneuvers. However, the impact of recruitment maneuvers on patient-important outcomes such as survival is unknown.

Anesthesia, General↗
PubMed2002

Mechanical ventilation strategies: what's new and what's worth keeping?

Many technologic and management strategies related to mechanical ventilation have been introduced in recent years. Strategies that avoid intubation and get patients extubated sooner decrease costs related to mechanical ventilation. In general, "people" solutions such as weaning protocols are preferable to "technology" solutions such as new ventilator modes. It must be remembered that mechanical ventilation is supportive-it is not curative-and has the potential to do harm if applied incorrectly. There is an increasing list of examples in which short-term physiologic outcomes such as improvements in blood gas values are not related to patient-important outcomes such as survival. When new mechanical ventilation technology and strategies are introduced, a question we need to ask ourselves is whether these are solutions for problems or whether these are simply solutions in search of problems.

Blood Gas Analysis↗
PubMed2002

Liquid nebulization: emerging technologies conference summary.

Most physicians and respiratory therapists are knowledgeable of the use of aerosolized drugs, but many are less familiar with the performance characteristics of the nebulizer. In fact, the general opinion is that the performance of the nebulizer is relatively unimportant. However, there is accumulating evidence that the nebulizer itself does make a difference. The decision to replace a good performing nebulizer with a poor performing nebulizer may decrease the delivered dose in half or more. Although this is less important for routine bronchodilator therapy, it may make a big difference with newer aerosolized drugs. Increasingly, the Food and Drug Administration is approving drugs to be used with a specific nebulizer brand and new nebulizer designs are becoming available for use with these drugs. There are several reasons why I think this conference was important. First, new aerosol drug formulations are becoming available and these will require better performing nebulizers. Second, we as clinicians need to be knowledgeable of the newer generations of nebulizers so that we can make informed purchase decisions. Third, and perhaps most important, we must gain an increased appreciation for aerosol therapy as a science. The proceedings of this conference do much to synthesize the current state-of-the art related to new nebulizer systems. This provides, in a complete and cogent manner, the scientific basis for which clinicians can improve their knowledge of the new generation of nebulizers.

Administration, Inhalation↗