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Biomedical subjects

R D Branson

Publications and source records attributed to R D Branson.

At least 19 recordsLinked to original sources
PubMed1999

Changes in respiratory mechanics after tracheostomy.

OBJECTIVE: To determine the effects of tracheostomy on respiratory mechanics and work of breathing (WOB). DESIGN: A before-and-after trial of 20 patients undergoing tracheostomy for repeated extubation failure. SETTING: Surgical intensive care unit at a university teaching hospital and a level I trauma center. PATIENTS: A consecutive sample of 20 patients who met extubation criteria (Pa(O2), >55 mm Hg; pH >7.30; and respiratory rate, <30/min on room air continuous positive airway pressure after 20 minutes) but failed extubation on 2 occasions were eligible for the study. INTERVENTIONS: Respiratory mechanics, lung volumes, and WOB were measured before and after tracheostomy. MAIN OUTCOME MEASURES: Patients in whom extubation fails often progress to unassisted ventilation after tracheostomy. The study hypothesis was that tracheostomy would result in improved pulmonary function through changes in respiratory mechanics. RESULTS: Data are given as means +/- SDs. After tracheostomy, WOB per liter of ventilation (0.97+/-0.32 vs. 0.81+/-0.46 J/L; P<.09), WOB per minute (8.9+/-2.9 vs. 6.6+/-1.4 J/min; P<.04), and airway resistance (9.4+/-4.1 vs. 6.3+/-4.5 cm H20/L per second; P<.07) were reduced compared with breathing via an endotracheal tube. These findings, however, do not fully explain the ability of patients to be liberated from mechanical ventilation after tracheostomy. In 4 patients who were extubated before tracheostomy, WOB was significantly greater during extubation than when breathing through an endotracheal or tracheostomy tube (1.2+/-0.19 vs. 0.81+/-0.24 vs. 0.77+/-0.22 J/L). CONCLUSIONS: We believe that the rigid nature of the tracheostomy tube represents reduced imposed WOB compared with the longer, thermoliable endotracheal tube. The clinical significance of this effect is small, although as respiratory rate increases, the effects are magnified. In patients in whom extubation failed, WOB may be elevated because of incomplete control of the upper airway. Future studies should evaluate the cause of increased WOB after extubation.

Adult↗
PubMed1998

Anaesthesia circuits, humidity output, and mucociliary structure and function.

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

Anesthesia, Closed-Circuit↗
PubMed1998

The effects of inadequate humidity.

The use of heated humidification in adults does not appear to be an important factor in maintaining body temperature in adults. Heat and moisture losses certainly can be reduced with heated humidification, but the contribution to temperature regulation appears small. The use of an HME reduces heat loss form the respiratory tract, but this loss is minute compared with losses from the skin, fluid administration, and the operative site. In neonates, the use of heated humidification during surgery may help contribute to thermal balance owing to the unique issues of temperature regulation and control in these patients.

Adult↗
PubMed1998

Humidification in the intensive care unit.

In summary, current data indicate that body temperature cannot be controlled efficiently by changing inspired gas temperature. Inspired gas temperature should therefore be maintained at 32 degrees C to 34 degrees C for intubated patients and other efforts should be made to optimize body temperature.

Body Temperature Regulation↗
PubMed1997

Use of the rapid/shallow breathing index as an indicator of patient work of breathing during pressure support ventilation.

BACKGROUND: Measuring patient work of breathing (WOBpt) has been suggested to provide safe, aggressive weaning from mechanical ventilation. We compared WOBpt and pressure-time-product (PTP) to routine weaning parameters [breath rate (f), tidal volume (VT), frequency/tidal volume ratio (f/VT)] at different levels of pressure support ventilation (PSV). METHODS: Fifteen patients in the surgical intensive care unit requiring prolonged weaning (more than 3 days) were entered in the study. A balloon-tipped esophageal catheter was placed and position confirmed by inspection of pressure and flow waveforms. Each patient was randomly assigned to breathe with 5, 10, 15, and 20 cm H2O of PSV. After 30 minutes, 40 breaths were recorded and analyzed. Measurement of WOBpt PTP, f, VT, and f/VT were made using the Bicore CP-100 monitor. Mean values for each parameter were calculated. PTP and WOBpt were plotted against f/VT to determine correlation coefficient. RESULTS: PTP, WOBpt and f/VT decreased in a stepwise fashion as PSV was increased. The f/VT correlated most closely with WOBpt (r = 0.983) and PTP (r = 0.972). Monitoring f alone also correlated with WOBpt (r = 0.894) and PTP (r = 0.881). All patients were weaned from the ventilator (mean duration, 22 +/- 5.9 days). Nine patients required tracheostomy before final liberation from the ventilator (mean duration, 22 +/- 5.9 days). Nine patients required tracheostomy before final liberation from the ventilator. CONCLUSIONS: Direct measurement of WOBpt is invasive, expensive, and' may be confusing to clinicians. Monitoring f/VT may be useful when changing PSV during weaning.

Acute Disease↗
PubMed1997

Inhaled nitric oxide in acute respiratory distress syndrome.

BACKGROUND: Inhaled nitric oxide has been shown to improve oxygenation in select patients with acute respiratory distress syndrome (ARDS). OBJECTIVE: The purpose of this study was to evaluate the clinical response to four concentrations of inhaled nitric oxide (NO) in 20 patients with ARDS. METHODS: All patients with ARDS were eligible for the study. ARDS was defined as (1) the presence of a predisposing factor; (2) a PaO2/FiO2 ratio < 200; (3) bilateral infiltrates on chest radiograph; and (4) absence of evidence of congestive heart failure and pulmonary artery wedge pressure < 18 mm Hg. Patients received each of four doses (1, 15, 30, and 60 ppm) in random order, each for a 3-hour period. Cardiovascular variables were continuously monitored, and arterial and mixed venous blood gas measurements were obtained at 30 minutes and 3 hours. RESULTS: Thirteen of the 20 patients demonstrated a significant increase in their PaO2/FiO2 (> 20% increase) when treated with inhaled NO. The administration of inhaled NO was associated with an increase in oxygenation at doses of 1, 15, and 30 ppm, but not 60 ppm. Increasing NO dose to more than 1 ppm did not significantly improve response. Mean pulmonary artery pressure decreased with increasing NO concentration, but this did not reach statistical significance. Nine of the 13 responding patients and 2 of the 7 nonresponding patients survived. CONCLUSION: Inhaled NO was successful in increasing PaO2/FiO2 by > 20% in 65% of the surgical patients in this trial. Response to NO could not be predicted by initial PaO2/FiO2 or pulmonary artery pressures. A trial of inhaled NO at a dose of < 10 ppm may be helpful in ARDS patients requiring increasing FiO2 and positive end-expiratory pressure.

Administration, Inhalation↗
PubMed1997

An efficiency comparison of four heat and moisture exchangers used in the laryngectomized patient.

Bypassing the upper airway places the burden of humidification on the lower airway. For this reason passive heat and moisture exchangers (HMEs) are used in the laryngectomized patient in an attempt to minimize the effect of lost upper airway function. We measured efficiency and airflow resistance and calculated the costs of four HMEs used in the laryngectomized patient. The HMEs were measured according a modified International Standards Organization (ISO) 9360 standard. The airflow resistance was measured at flow rates of 15, 30, and 60 L/min. The measurements were repeated three times. Costs were calculated with two realistic scenarios. The study found that there are significant differences in moisture output and airflow resistance between the HMEs tested. There are major daily cost differences between these devices. This study shows that filter material and size influence the HME's moisture output efficiency and airflow resistance considerably. The construction differences and filter and housing type have great influence on the HME's daily costs. We believe that knowledge of the efficiency in combination with the average daily costs of the HMEs allows the clinician to make a balanced choice of which filter to use.

Costs and Cost Analysis↗
PubMed1997

Delivery systems for inhaled nitric oxide.

From a practical standpoint, technical issues related to NO delivery are as important as therapeutic issues. The benefits can be appreciated only if a reliable delivery system is used. Further, hazards and toxicity may be more problematic with an unreliable delivery system. It is incumbent on clinicians using inhaled NO to ensure that the delivery system is safe and reliable.

Administration, Inhalation↗
PubMed1996

Comparison of volume control and pressure control ventilation: is flow waveform the difference?

OBJECTIVE: To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury. DESIGN: Prospective, controlled, crossover study. MEASUREMENTS AND MAIN RESULTS: Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters. CONCLUSIONS: Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

Adult↗
PubMed1996

Ventilatory support in the field.

Ventilatory support during cardiopulmonary resuscitation can be accomplished with an array of methods and devices. These run the gamut from expired air resuscitation, including mouth-to-mouth and mouth-to-mask, to the use of ventilators including ventilator-to-mask and ventilator-to-artificial airway techniques. Appropriate application of these techniques depends on the clinical situation, rescuer training, and availability of equipment. This article discusses the proposed standards of emergency ventilatory support, the advantages and disadvantages of the techniques and devices used, and current controversies surrounding this topic.

Cardiopulmonary Resuscitation↗
PubMed1995

Lung compliance following cardiac arrest.

OBJECTIVE: To determine lung compliance in patients who had out-of-hospital cardiac arrests. METHODS: A prospective, observational study of patients suffering nontraumatic cardiopulmonary arrest and requiring CPR at one university hospital ED. Following termination of resuscitation efforts, lung compliance was measured. Measurements were made while inflating the lung from 250 mL to 2,000 mL (in 250-mL increments) using a calibrated supersyringe. Airway flow and pressure were measured at the endotracheal tube with a pneumotachograph and a pressure transducer. Flow and pressure signals were recorded by a respiratory monitor and used to construct pressure-volume curves for calculation of lung compliance. RESULTS: The 25 cardiac arrest patients (17 men, eight women) had a mean (+/- SD) age of 65 +/- 7 years. Mean lung compliance was 0.051 +/- 0.011 L/cm H2O. Lung compliance was smaller at low lung volumes, suggesting the presence of alveolar collapse. Compliance values from 500 mL to 1,500 mL were similar. Compliance also diminished with increasing duration of CPR. CONCLUSIONS: One previous publication suggested that lung compliance following resuscitation is 0.022 L/cm H2O. The results of this study, using the accepted standard measurements of static lung compliance, suggest that true compliance is twice this value. This finding has important ramifications for future research on ventilation during resuscitation and current ventilation standards.

Adult↗
PubMed1995

Out-of-hospital ventilation: bag--valve device vs transport ventilator.

OBJECTIVE: To examine the patterns of out-of-hospital airway management and to compare the efficacy of bag-valve ventilation with that of the use of a transport ventilator for intubated patients. METHODS: A prospective, nonrandomized, convenience sample of 160 patients requiring airway management in the out-of-hospital urban setting was analyzed. A survey inquiring about airway and ventilatory management was completed by emergency medical services (EMS) personnel, and arterial blood gas (ABG) samples were obtained within 5 minutes of patient arrival in the ED. The ABG parameters were compared for patients grouped by different airway techniques and presence or absence of cardiac arrest (systolic blood pressure < 50 mm Hg) upon ED presentation. RESULTS: Over a one-year period, 160 surveys were returned. The majority (62%) of the patients were men; the population mean age was 61 +/- 19 years. Presenting ABGs were obtained for 76 patients; 17% (13/76) had systemic perfusion and 83% (63/76) were in cardiac arrest. There was no difference in ABG parameters between the intubated cardiac arrest patients ventilated with a transport ventilator (pH 7.17 +/- 0.17, PaCO2 37 +/- 20 torr, and PaO2 257 +/- 142 torr) and those ventilated with a bag-valve device (pH 7.20 +/- 0.16, PaCO2 42 +/- 21 torr, and PaO2 217 +/- 138 torr). The patients ventilated via an esophageal obturator airway (EOA) device had impaired gas exchange, compared with the groups who had endotracheal (ET) intubation (pH 7.09 +/- 0.13, PaCO2 76 +/- 30 torr, and PaO2 75 +/- 35 torr). The intubated patients not in cardiac arrest had similar ABG parameters whether ventilated manually with a bag-valve device or with a transport ventilator. Endotracheal intubation was successfully accomplished in 93% (123/132) of attempted cases. CONCLUSIONS: In this sample, ET intubation was the most frequently used airway by EMS providers. When ET intubation was accomplished, adequate ventilation could be achieved using either bag-valve ventilation or a transport ventilator. Ventilation via the EOA proved inadequate.

Adult↗
PubMed1995

Monitoring ventilator function.

Maintenance of the patient-ventilator system is the primary role of the respiratory care practitioner in the intensive care unit. Patient-ventilator system checks should include monitoring the patient's response to ventilation, evaluating function of the ventilator, maintaining ventilator settings according to physician orders, setting appropriate alarms, maintaining the integrity of the ventilator circuit and humidifier, and documenting all of the above. The concept of ventilator checks should be expanded and thus, the name changed to patient-ventilator system check to emphasize the importance of evaluating the patient. This article reviews the rationale for performing patient-ventilator system checks and measurements.

Equipment Design↗
PubMed1994

Comparison of pressure and flow triggering systems during continuous positive airway pressure.

STUDY OBJECTIVE: Compare the inspiratory work of breathing (WOBI) during pressure triggering (PT), and flow triggering (FT) using two microprocessor ventilators. DESIGN: A randomized, crossover comparison of triggering strategies and ventilators used. SETTING: Surgical intensive care unit. PATIENTS: Ten patients recovering from acute respiratory failure (eight men, two women; mean age, 48 +/- 12 years) breathing on continuous positive airway pressure (CPAP) of 5 cm H2O were studied. INTERVENTIONS: Patients were randomly assigned to either receive 5 cm H2O CPAP via one of two units (Hamilton Veolar or Puritan Bennett 7200ae) using either PT or FT. Each patient had 30-min trials using the following: (1) Veolar FT; (2) Veolar PT; (3) 7200ae FT; and (4) 7200ae FT. MEASUREMENTS AND RESULTS: During each trial period, work of breathing (WOB) and pressure time product (PTP) were measured using a respiratory monitor (Bi-core CP-100). All patients were placed in semi-Fowler position and esophageal balloons were inserted and their position confirmed using the occlusion technique. Continuous measurements of peak negative pressure during inspiration, tidal volume (VT), minute ventilation (VE), respiratory frequency (f) were accomplished with a flow transducer at the proximal airway. FT with the 7200ae was superior to PT as measured by both the WOB (0.58 +/- 0.3 vs 0.84 +/- 0.2 J/L, p < 0.01) and PTP (148 +/- 50 vs 206 +/- 41 cm H2O/s/min, p, 0.05). FT with the Veolar was also superior to PT with respect to the WOB (0.53 +/- 0.2 vs 0.93 +/- 0.2 J/L, p < 0.01) and PTP (140 +/- 39 vs 229 +/- 46 cm H2O/s/min, p < 0.05). CONCLUSION: FT reduces the WOB compared with PT, regardless of the ventilator used. The reduction in WOB during FT is related to improved responsiveness and changes in the posttrigger phase.

Cross-Over Studies↗
PubMed1993

Airway pressure release ventilation.

BACKGROUND: Elevated airway pressures during mechanical ventilation are associated with hemodynamic compromise and pulmonary barotrauma. We studied the cardiopulmonary effects of a pressure-limited mode of ventilation (airway pressure release ventilation) in patients with the adult respiratory distress syndrome. METHODS: Fifteen patients requiring intermittent mandatory ventilation (IMV) and positive end-expiratory pressure (PEEP) were studied. Following measurement of hemodynamic and ventilatory data, all patients were placed on airway pressure release ventilation (APRV). Cardiorespiratory measurements were repeated after a 2-hour stabilization period. RESULTS: During ventilatory support with APRV, peak inspiratory pressure (62 +/- 10 vs 30 +/- 4 cm H2O) and PEEP (11 +/- 4 vs 7 +/- 2 cm H2O) were reduced compared with IMV. Mean airway pressure was higher with APRV (18 +/- 5 vs 24 +/- 4 cm H2O). There were no statistically significant differences in gas exchange or hemodynamic variables. Both cardiac output (8.7 +/- 1.8 vs 8.4 +/- 2.0 L/min) and partial pressure of oxygen in arterial blood (79 +/- 9 vs 86 +/- 11 mm Hg) were essentially unchanged. CONCLUSIONS: Our results suggest that while airway pressure release ventilation can provide similar oxygenation and ventilation at lower peak and end-expiratory pressures, this offers no hemodynamic advantages.

Adult↗