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Biomedical subjects

D G Markhorst

Publications and source records attributed to D G Markhorst.

15 recordsLinked to original sources
PubMed2003

Dexamethasone for treatment of patients mechanically ventilated for lower respiratory tract infection caused by respiratory syncytial virus.

BACKGROUND: A study was undertaken to evaluate the efficacy of dexamethasone in patients mechanically ventilated for lower respiratory infection caused by respiratory syncytial virus (RSV-LRTI). METHODS: In a multicentre randomised controlled trial patients were randomised to receive either intravenous dexamethasone (0.15 mg/kg 6 hourly for 48 hours) or placebo. End points were the duration of mechanical ventilation, length of stay (LOS) in the pediatric intensive care unit (PICU) and in hospital, and the duration of supplemental oxygen administration. RESULTS: Thirty seven patients received dexamethasone and 45 received placebo. There was no significant difference in any of the end points between the two groups. In a post hoc analysis patients were stratified into those with mild gas exchange anomalies (PaO(2)/FiO(2) >200 mm Hg and/or mean airway pressure </= 10 cm H(2)O, bronchiolitis group) and those with severe gas exchange anomalies (PaO(2)/FiO(2) </=200 mm Hg and mean airway pressure >10 cm H(2)O, pneumonia group). In the 39 patients with bronchiolitis the duration of mechanical ventilation was 4.3 days shorter in the dexamethasone group than in the placebo group (4.9 v 9.2 days, 95% CI -7.8 to -0.8, p=0.02) and the duration of supplemental oxygen was 3.6 days shorter (7.7 v 11.3 days, 95% CI -8.0 to -0.1, p=0.048). No differences in end points were found in the pneumonia group. CONCLUSIONS: Dexamethasone had no beneficial effect in patients mechanically ventilated for RSV-LRTI but was found to have a beneficial effect in patients with bronchiolitis.

Blood Pressure↗
PubMed2001

Reduction of oscillatory pressure along the endotracheal tube is indicative for maximal respiratory compliance during high-frequency oscillatory ventilation: a mathematical model study.

We hypothesized that during high-frequency oscillatory ventilation (HFOV), a reduction of peak-to-peak oscillatory pressure along the endotracheal tube is maximal when respiratory system compliance is maximal. We made a mathematical model of the endotracheal tube and the respiratory system of a neonate suffering from idiopathic respiratory distress syndrome (IRDS). The model consisted of linear viscous and inertive elements, a non-linear endotracheal tube resistance, and a non-linear compliance allowing for alveolar recruitment and overdistention. Respiratory compliance was maximal at the transition between maximal recruitment and minimal overdistention. A new variable, the oscillatory pressure ratio (OPR), was defined as the ratio between peak-to-peak oscillatory pressures at the distal end and the proximal opening of the endotracheal tube, respectively. The respiratory variables of four patients were fed into the model, and the relationship between respiratory system compliance and OPR was determined. OPR decreased as compliance increased, except for very low compliances below where 0.08 mL. cm H2O(-1), and OPR increased with increasing compliance. The relationship between mean airway pressure P(aw) and OPR revealed that the minimal OPR (range, 0.37-0.78) and maximal respiratory compliance coincided at the same P(aw). However, the relationship did depend on oscillation frequency, applied oscillatory pressure, and endotracheal tube resistance, parameters that may change during clinical application of HFOV. When 81 permutations of nominal and extreme respiratory variables were used in the model, the minimum OPR (0.60 +/- 0.23) and maximum compliance coincided in all cases. These model experiments support our hypothesis. The results indicate that the OPR may be a useful index to optimize lung expansion, where lung recruitment is maximal and overdistention minimal. In vivo tests will be needed to reveal the feasibility and reliability of such an index for biomedical and clinical application.

Airway Resistance↗
PubMed2000

High-frequency oscillatory ventilation in pediatric patients.

BACKGROUND: High-frequency oscillatory ventilation (HFOV) is a ventilatory mode using small tidal volumes with low phasic pressures at supraphysiological frequencies. Beyond the neonatal period there are distinct lung diseases for which HFOV is used. Data of 35 children who deteriorated on conventional ventilation were retrospectively analysed in two tertiary pediatric intensive care units. METHODS: Depending on the underlying pulmonary pathophysiology, three strategies were employed. First, the 'open-lung' strategy designed to rapidly recruit and maintain optimal lung volume in DAD (n=27) and pulmonary hemorrhage (n=5). Second, the 'low-volume' strategy in persistent air leak (n=1) where, after an initial identical approach, mean airway pressure (MAP) is reduced until the air leak ceases. Third, the 'open-airway' strategy in obstructive airway disease (n=5) where MAP is used to recruit and stent the airways. RESULTS: Seven patients died, two due to respiratory failure. Three patients developed an air leak. Nine patients developed chronic lung disease. There was a significant decrease of the oxygenation index (OI) in the survivors. In the two patients who died of respiratory failure, the OI increased. CONCLUSION: If certain conditions are met, HFOV appears a safe and effective mode of ventilation in pediatric respiratory failure.

Adolescent↗
PubMed1999

Diffuse neonatal haemangiomatosis: new views on diagnostic criteria and prognosis.

Diffuse neonatal haemangiomatosis (DNH) is a rare and life-threatening congenital disorder. An extensive retrospective analysis of the literature was performed to evaluate the clinical features, therapies and prognostic factors of DNH. Reports on 68 patients with DNH were obtained. The skin, liver, lungs, brain and intestine were the organs most commonly involved. Congestive heart failure (CHF) was the primary cause of death. The mortality rate was 77.4% in untreated patients and 27% in treated patients. CHF, Kasabach-Merritt syndrome (KMS) and the involvement of five or more organs were important risk factors in DNH. The measurement of cardiac output might give more insight into the potential prognostic value of total blood-volume loss through shunting in the haemangiomas. Reports on 64 patients with neonatal haemangiomatosis limited to only the skin and liver were also obtained. The clinical features and outcome of patients with only cutaneous and hepatic haemangiomas were similar to those of patients with DNH. The inclusion criteria for DNH should be expanded to include similar patients with only cutaneous and hepatic haemangiomas.

Fatal Outcome↗
PubMed1997

Bench test assessment of dosage accuracy and measurement inaccuracy in nitric oxide inhalational therapy during high frequency oscillatory ventilation.

OBJECTIVE: The objective of this study is to determine the accuracy and precision of chemiluminescence and electrochemical nitric oxide (NO) measurements and accuracy of NO dosage with electronic mass flow controllers (MFC) versus rotameters during NO inhalational therapy. METHODS: NO flow was delivered to a high frequency oscillator and mixed with ventilator flow. NO and NO2 concentrations were measured simultaneously with a standard chemiluminescence analyzer and a modified electrochemical analyzer. Dosage accuracy was assessed with gas flows adjusted with either MFC's or rotameters. Accuracy of both analyzers was validated with both NO and ventilator flow regulated with a MFC. RESULTS: In dry air, without pulsatile pressure, MFC controlled NO and ventilator flow resulted in an accuracy expressed as the ratio of calculated concentration to measured concentration (RCM) of 0.995 (CI: 0.983-0.988) when measured with chemiluminescence. When the ventilator rotameter was used instead of a MFC, RCM was 0.856 (CI: 0.835-0.877). With a rotameter for both NO and ventilator flow, RCM increased to 1.175 (CI: 0.793-1.740) with an increase of confidence interval limits. Chemiluminescence was sensitive to humidification of the ventilatory gases (p < 0.05), slightly sensitive to the addition of oxygen and to pulsatile pressure (not significant). RCM obtained with the modified electrochemical analyzer was in close agreement with chemiluminescence RCM, although 95% CI were wider with electrochemical analysis. CONCLUSIONS: During high frequency oscillatory ventilation (HFOV), standard rotameter flow control of both NO and ventilator flow results in unpredictable NO concentrations that would be clinically unacceptable. When one MFC was used for NO flow control, with ventilator flow controlled with a rotameter, this resulted in moderate dosage accuracy. To achieve a still higher accuracy, MFC flow control for both NO and ventilator flow is indicated. During HFOV, standard chemiluminescence analyzers cannot be considered to be the gold standard for determination of the NO concentration delivered. Measurement of NO concentration may not be mandatory for determination of inhaled NO dose during HFOV, but may be used to monitor for unsafe or unwanted events.

Administration, Inhalation↗
PubMed1996

Occupational exposure during nitric oxide inhalational therapy in a pediatric intensive care setting.

OBJECTIVE: To determine the amount of occupational exposure to nitric oxide (NO) and nitrogen dioxide (NO2) during NO inhalational therapy. DESIGN: In a standard pediatric intensive care room, 800 ppm NO was delivered to a high-frequency oscillator and mixed with 100% O2 to obtain 20 ppm NO in the inspiratory gas flow. NO and NO2 concentrations in room air were measured using a chemiluminescence analyzer. Air samples were taken from a height of 150 cm at a horizontal distance of 65 cm from the ventilator in a nonventilated and in a well-ventilated room with and without an expiratory gas exhaust under normal intensive care environmental conditions. SETTING: Pediatric intensive care unit in a university children's hospital. MEASUREMENTS AND RESULTS: Maximal concentrations of NO and NO2 were reached after 4 h NO use. Without exhaust, in a nonventilated room, environmental NO and NO2 concentration rose to a maximum of 0.462 and 0.064 ppm, respectively. With the use of an expiratory gas exhaust, NO and NO2 concentrations were 0.176 and 0.042 ppm, respectively. With normal air-conditioning, these values were 0.075 and 0.034 ppm, respectively, without the use of an expiratory gas exhaust. With expiratory gas exhaust added to normal air-conditioning, values for NO and NO2 were 0.035 and 0.030 ppm, respectively. CONCLUSIONS: The use of 20 ppm NO, even under minimal room ventilation conditions, did not lead to room air levels of NO or NO2 that should be considered toxic to adjacent intensive care patients or staff. Slight increases in NO and NO2 concentrations were measurable but remained within occupational safety limits. The use of an exhaust system and normal room ventilation lowers NO and NO2 concentrations further to almost background levels.

Administration, Inhalation↗
PubMed1995

Transient foramen ovale incompetence in the normal newborn: an echocardiographic study.

UNLABELLED: To assess presence, predominant direction and natural history of interatrial shunt flow in the normal newborn period an uncontrolled pilot study was performed. Twenty term ( > 36 completed weeks gestational age) newborns were studied using cross sectional, M-mode and colour Doppler echocardiography; cardiac, pulmonary or renal disease were excluded before entry to the study. In 11 of 20 normal term newborns a predominant left to right interatrial shunt was detected on the 1st day after birth. This shunting, taking place in ventricular systole, disappeared in 10 cases during the first 6 postnatal days and in 1 case after 6 weeks. No relation was found between the presence of an atrial left to right shunt and gestational age or patency of the ductus arteriosus. CONCLUSION: We conclude that interatrial left to right shunting is common in half of the normal newborns (95% confidence interval 31.5%-76.9%), during the first 6 days of extra-uterine life. Our findings may be explained by a transient period of physiological expansion of extracellular volume in the newborn, resulting in slight atrial stretch, and this in combination with a relatively short foramen ovale flap.

Echocardiography↗
PubMed1990

[A child with neonatal allo-immune neutropenia].

A newborn child with neonatal neutropenia as a result of the presence of maternal IgG isoantibodies against neutrophil granulocyte blood group antigens is reported. Mechanism, diagnostics and therapy of the disease are discussed. The diagnosis not only has consequences for the child, but also for the mother and following pregnancies. A review of the most important causes of neonatal neutropenia is given.

Blood Group Antigens↗
PubMedDate not supplied

Respiratory inductive plethysmography accuracy at varying PEEP levels and degrees of acute lung injury.

BACKGROUND AND OBJECTIVE: This study was performed to assess the accuracy of respiratory inductive plethysmographic (RIP) estimated lung volume changes at varying positive end-expiratory pressures (PEEP) during different degrees of acute respiratory failure. METHODS: Measurements of inspiratory tidal volume were validated in eight piglets during constant volume ventilation at incremental and decremental PEEP levels and with increasing severity of pulmonary injury. RIP accuracy was assessed with calibration from the healthy state, from the disease state as the measurement error was assessed, and at various PEEP levels. RESULTS: Best results (bias 3%, precision 7%) were obtained in healthy animals. RIP accuracy decreased with progressing degrees of acute respiratory failure and was PEEP dependent, unless RIP was calibrated again. When calibration was performed in the disease state as the measurement error was assessed, bias was reduced but precision did not improve (bias -2%, precision 9%). CONCLUSIONS: RIP accuracy is within the accuracy range found in monitoring devices currently in clinical use. Most reliable results with RIP are obtained when measurements are preceded by calibration in pulmonary conditions that are comparable to the measurement period. When RIP calibration is not possible, fixed weighting of the RIP signals with species and subject size adequate factors is an alternative. Measurement errors should be taken into account with interpretation of small volume changes.

Acute Disease↗
PubMedDate not supplied

A system for integrated measurement of ventilator settings, lung volume change and blood gases during high-frequency oscillatory ventilation.

To describe and validate a system for integrated measurement of ventilator settings and dependent physiological variables during high-frequency oscillatory ventilation (HFOV). A custom interface was built for data acquisition. Lung volume change was determined by respirator inductive plethysmography (RIP), modified to sampling rates of 140 Hz. Blood gas analysis was obtained using a continuous intra-arterial blood gas monitoring system. FIO2 was measured by means of an electrochemical sensor. Pressure at the airway opening and trachea (microtip transducer) were sampled. The data acquired were sent to a laptop computer for analysis, display and storage. The system was tested during a lung recruitment procedure in an animal model of respiratory distress. Linearity of the RIP was checked by gas volume injection using a supersyringe. The system operated successfully. Agreement between RIP-measured volume with injected volume was excellent; bias was 5 ml; limits of agreement were 1-9 ml. Graphs were obtained, showing the relationship between imposed mean airway pressure and lung volume change, and oxygenation. The integration of ventilator settings and dependent physiological variables may provide useful information for clinical, instructional and research application.

Animals↗