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Biomedical subjects

C J Newth

Publications and source records attributed to C J Newth.

At least 19 recordsLinked to original sources
PubMed2001

Dynamic respiratory system mechanics in infants during pressure and volume controlled ventilation.

Dynamic respiratory system mechanics can be determined using multiple linear regression (MLR) analysis. There is no need for a particular ventilator setting or for a special ventilatory manoeuvre. The purpose of this study was to investigate whether or not different ventilator modes and the flow-dependent resistance of the endotracheal tube (ETT) influence the determination of resistance and compliance by MLR. Ten paediatric patients who were on controlled mechanical ventilation for various disorders were investigated. The ventilator modes were changed between pressure control (PC) and volume control (VC). Flow and airway pressure were measured and tracheal pressure was continuously calculated. Each mode was applied for 3 min, and 10 consecutive breaths at the end of each period were analysed. Respiratory mechanics were determined by MLR based on either airway pressure, thus including the resistance of the ETT, or tracheal pressure. Resistance was found to be slightly higher in PC than in VC. There was no effect on determination of compliance between the different modes. Elimination of the flow-dependent resistance of the ETT preserved the differences between the modes. The authors conclude that using multiple linear regression compliance is not affected by the actual ventilator mode, whereas resistance is.

Airway Resistance↗
PubMed2000

The pharmacologic mechanism by which inhaled epinephrine reduces airway obstruction in respiratory syncytial virus-associated bronchiolitis.

Inhaled racemic epinephrine relieves airway obstruction in patients with respiratory syncytial virus bronchiolitis. The contribution of alpha- versus beta-adrenoreceptor stimulation toward this clinical effect is unknown. We describe an infant treated with propranolol for supraventricular tachycardia in whom respiratory syncytial virus bronchiolitis developed. Inhaled racemic epinephrine improved his respiratory symptoms, whereas nebulized albuterol did not.

Administration, Inhalation↗
PubMed2000

High-frequency oscillatory ventilation in pediatric respiratory failure: a multicenter experience.

OBJECTIVE: The use of high-frequency oscillatory ventilation (HFOV) has increased dramatically in the management of respiratory failure in pediatric patients. We surveyed ten pediatric centers that frequently use high-frequency oscillation to describe current clinical practice and to examine factors related to improved outcomes. DESIGN: Retrospective, observational questionnaire study. SETTING: Ten tertiary care pediatric intensive care units. PATIENTS: Two hundred ninety patients managed with HFOV between January 1997 and June 1998. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Patients were classified according to presence or absence of preexisting lung disease, symptomatic respiratory syncytial virus infection, or presence of cyanotic heart disease or residual right-to-left intracardiac shunt. In addition, patients for whom HFOV acutely failed were analyzed separately. Those patients with preexisting lung disease were significantly smaller, had a significantly higher incidence of pulmonary infection as the triggering etiology, and had a significantly greater duration of conventional ventilation before institution of HFOV compared with patients without preexisting lung disease. Stepwise logistic regression was used to predict mortality and the occurrence of chronic lung disease in survivors. In patients without preexisting lung disease, the model predicted a 70% probability of death when the oxygenation index (OI) after 24 hrs was 28 in the immunocompromised patients and 64 in the patients without immunocompromise. In the immunocompromised patients, the model predicted a 90% probability of death when the OI after 24 hrs was 58. In survivors without preexisting lung disease, the model predicted a 70% probability of developing chronic lung disease when the OI at 24 hrs was 31 in the patients with sepsis syndrome and 50 in the patients without sepsis syndrome. In the patients with sepsis syndrome, the model predicted a 90% probability of developing chronic lung disease when the OI at 24 hrs was 45. CONCLUSIONS: Given the number of centers involved and the size of the database, we feel that our results broadly reflect current practice in the use of HFOV in pediatric patients. These results may help in deciding which patients are most likely to benefit from aggressive intervention by using extracorporeal techniques and may help identify high-risk populations appropriate for prospective study of innovative modes of supporting gas exchange (e.g., partial liquid breathing or intratracheal pulmonary ventilation).

Blood Gas Analysis↗
PubMed2000

Analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients.

OBJECTIVE: Analysis of dynamic respiratory system mechanics is generally based on a resistance-compliance model in which nonlinearities of the respiratory mechanics indices are not considered. The recently developed SLICE method analyzing consecutive volume slices of the tidal volume was used for determination of non-linear volume-dependent respiratory system mechanics. Volume-dependent compliance C(Slice) and resistance R(Slice) were compared with C(MLR) and R(MLR) obtained by standard multiple linear regression analysis (MLR). DESIGN: Prospective observational study. SETTING: Pediatric intensive care unit in a university hospital. PATIENTS: Fifteen pediatric patients, aged 24 days to 9.6 yrs, weighing 3-67.5 kg. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: With respect to their pulmonary status, the patients were grouped into three clinical groups: patients with no lung diseases, patients with restrictive lung diseases, and patients with obstructive lung diseases. All patients were mechanically ventilated via a cuffed endotracheal tube in the pressure-controlled mode. Flow and airway pressure were measured at the proximal end of the tube and tracheal pressure was continuously calculated. Respiratory mechanics were determined either with the SLICE method or, as reference, by using standard MLR. In most patients, the pressure-volume relationship was nonlinear, particularly in patients with restrictive and obstructive lung diseases. In the presence of considerable nonlinearity, the volume-dependent respiratory mechanics indices obtained by the SLICE method showed better agreement between recalculated and original pressure-volume loops compared with the MLR results. Furthermore, signs of overdistension of the patient's lung became obvious when using the SLICE method, whereas they were undetected by MLR. CONCLUSIONS: The SLICE method is well suited for the analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients. The SLICE method may be used as a first step toward an adaptation of ventilator settings with respect to the actual mechanical status of the patient's respiratory system, and, to prevent pulmonary overdistension.

Journal Article↗
PubMed1999

Effect of inhaled nitric oxide on respiratory mechanics in ventilated infants with RSV bronchiolitis.

OBJECTIVE: To evaluate the bronchodilator effect of inhaled nitric oxide (NO) in infants with respiratory failure caused by respiratory syncytial virus (RSV) bronchiolitis and to compare the effect with the one obtained by salbutamol. DESIGN: Prospective study. SETTING: Pediatric intensive care unit of a university children's hospital. PATIENTS: Twelve acutely ill, intubated infants (mean age 4.5 months, mean weight 4.9 kg) with respiratory failure due to documented RSV bronchiolitis. INTERVENTIONS: Total respiratory system resistance (Rrs) was measured by single breath occlusion at the baseline and after inhaling NO at 20, 40 and 60 ppm for 1 h, and after inhalation of a standard beta2-agonist, salbutamol. Arterial blood gas analysis was performed at each study level on 6 of the 12 patients. RESULTS: The baseline mean Rrs (SE) was 0.29 (0.04) cm H2O/ml per s. At each dose of NO, the mean Rrs (SE) was 0.28 (0.04) cm H2O/ml per s. With salbutamol, the mean Rrs (SE) was 0.21 (0.03) cm H20/ml per s. These values were not significantly different from each other (by ANOVA). Inhaled NO produced a significant decrease in Rrs of greater than 4 times the coefficient of variation of the baseline measurement in 3 of 12 patients. Seven of 12 patients had no significant change while two patients had a significant increase in Rrs. Inhaled salbutamol produced a significant decrease in Rrs in 5 of 11 patients, while 6 showed no change in Rrs. CONCLUSION: Inhaled NO has no apparent bronchodilator effect in the majority of acutely ill infants with RSV bronchiolitis and does not appear to provide any additional benefit over the use of salbutamol. The clinical benefit of inhaled NO as a bronchodilator is questionable under these conditions.

Administration, Inhalation↗
PubMed1999

Impact of respiratory syncytial virus infection on surgery for congenital heart disease: postoperative course and outcome.

OBJECTIVES: a) To describe the postoperative course and outcome of cardiac surgery in children with recent respiratory syncytial virus (RSV) infection; and b) to evaluate whether timing of surgery has any impact on the outcome. DESIGN: Retrospective case series. SETTING: Intensive care unit and medical and surgical wards of a teaching pediatric hospital. PATIENTS: Twenty-five children (aged 25 days to 3.5 yrs; median, 4 months) with congenital heart disease who had cardiac surgery within 6 months after RSV infection. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We reviewed the clinical course and outcome of all patients. The cardiac diagnoses included ventricular septal defect (n = 11), tetralogy of Fallot (n = 3), atrioventricular canal (n = 3), and others (n = 8). Thirteen patients had surgery during the same admission as RSV infection (group I), and 12 patients had surgery electively after being discharged to home after RSV infection (group II). Two patients in group I died; both of these patients had undergone total repair of tetralogy of Fallot within 2 wks after admission for RSV infection. Postoperative complications in group I patients included pulmonary hypertension (n = 5), adult respiratory distress syndrome (n = 1), tracheal stenosis (n = 1), left ventricular dysfunction (n = 1), pericardial effusion (n = 1), secondary bacterial or fungal infection (n = 7), and deep venous thrombosis (n = 1). Of all group I patients, the ones who were operated on early appeared to be at higher risk for complications, especially for postoperative pulmonary hypertension. No patient in group II died, and only two patients had minor complications (one had reactive airway disease, and the other had a transient superior vena cava syndrome after a bidirectional Glenn operation). CONCLUSIONS: Cardiac surgery performed during the symptomatic period of RSV infection is associated with a high risk of postoperative complications, especially postoperative pulmonary hypertension. These complications appeared to be more frequent and of greater severity in patients who had earlier surgery compared with those who had later surgery. More studies are needed regarding the proper timing of cardiac surgery in patients with congenital heart disease and RSV infection.

Cardiac Surgical Procedures↗
PubMed1998

Total lung capacity by N2 washout from high and low lung volumes in ventilated infants and children.

Although there is a strong rationale for the assessment of the subdivisions of lung volume, lung function testing has focused on the measurement of FRC alone in ventilated infants and children. To assess the feasibility, reproducibility, and accuracy of measurements of total lung capacity (TLC), FRC, and their ratio, we determined both lung volumes in 50 critically ill, intubated, and paralyzed infants (mean age [SEM]), 19.9 [4.6] mo) with a variety of lung diseases, by a modified N2 washout technique from end-exhalation and from +40 cm H2O inspiratory pressure, respectively. In the same infants, we also defined TLC by adding inspiratory capacity, measured by pneumotachograph during a passive exhalation from +40 cm H2O to FRC measured by N2 washout. Respiratory mechanics were measured by single-breath occlusion, and the patients were classified according to clinical picture and lung function into groups without lung disease or with restrictive or obstructive disease. The TLC data obtained by both methods showed good agreement for the infants without lung disease or restrictive disease (limits of agreement [LOA]: -3.8/4.6 and -2.9/3.2 ml/kg, respectively). The agreement was less in the infants with airflow obstruction where the N2 washout gave slightly higher values (LOA: -7.1/11.3 ml/kg). Mean FRC/TLC was significantly elevated in the obstructive group, whereas mean FRC alone did not differ from the group without lung disease. Our results suggest that TLC can be measured by both methods in intubated infants, but with limited agreement in obstructive disease. FRC/TLC ratios allow an estimation of the degree of pulmonary hyperinflation.

Child, Preschool↗
PubMed1997

Assessment of pulmonary function in the early phase of ARDS in pediatric patients.

Scant data are available on lung function in acute respiratory distress syndrome (ARDS) in pediatric patients. We measured respiratory mechanics by single-breath occlusion and maximum expiratory flow-volume curves by forced deflation in ten critically ill infants with clinical ARDS. Ten mechanically ventilated infants without lung disease served as the control group. To assess the severity of the lung injury in the infants with ARDS, we modified an adult scoring system that calculates a score (from 0 to 4; > 2.5 indicates severe lung injury) based on the extent of chest radiographic changes, degree of hypoxemia, amount of positive end-expiratory pressure (PEEP), and total respiratory system compliance. The lung injury scores of our patients were in the range of 2.75 to 3.75. The lung injury scores of the control group were zero. The predominant alteration in lung function was restrictive, as characterized by a significant decrease in total respiratory system compliance (0.41 +/- 0.13 ml/cmH2O/kg versus 1.12 +/- 0.16 ml/cmH2O/kg of controls; P < 0.001) and forced vital capacity (21.5 +/- 6.5 ml/kg versus 59.2 +/- 6.3 ml/kg of controls; P < 0.001). Maximum expiratory flow rates at 10% forced vital capacity were significantly increased (23.6 +/- 20.1 ml/kg/sec versus 8.4 +/- 2.5 ml/kg/sec of controls; P < 0.05), confirming the absence of any significant obstructive abnormalities. The passive expiratory flow-volume curves were curvilinear and convex in shape, indicating inhomogeneous lung pathology. The inhomogeneous distribution of lung injury in ARDS restricts the validity of respiratory mechanics measurements that rely on a single-compartment model. However, the forced deflation technique allows accurate spirometric assessments of the severity of restrictive (and obstructive) lung function changes in intubated infants with severe ARDS. Such measurements can be incorporated into lung injury scoring systems to classify the severity of the disease process for the purpose of outcome evaluation and to evaluate the effect of therapeutic interventions.

Case-Control Studies↗
PubMed1997

Acute respiratory distress syndrome caused by respiratory syncytial virus.

Acute respiratory distress syndrome (ARDS) complicating severe respiratory syncytial virus (RSV) infection has been described in only a few infants. In contrast to the low mortality rates usually associated with RSV infections (< 5%), mortality rates in the range of 40-70% have been reported in pediatric patients with ARDS. However, studies on patients with ARDS are usually lumped with respect to causation, and the disease course of RSV-induced ARDS has not been previously studied. We examined the pulmonary function abnormalities of 37 infants with RSV-induced respiratory failure who were admitted to our pediatric intensive care unit for assisted ventilation. Measurements included respiratory mechanics, maximum expiratory flow-volume curves, and lung volumes. These allowed the calculation of a Murray lung injury score (modified for pediatric use) in which radiographic findings, ventilator settings, lung compliance, and blood gas results were considered. We identified ten infants with severe restrictive lung disease who fulfilled the clinical criteria for classification as ARDS. All had lung injury scores above 2.5, compatible with a diagnosis of ARDS. Twenty-seven infants had obstructive patterns of lung function consistent with a clinical diagnosis of RSV bronchiolitis. The patients with RSV-induced ARDS were significantly younger, and had a longer time on assisted ventilation (P < 0.05) and a higher proportion of predisposing illnesses (P < 0.05, odds ratio = 6.67, two-tailed Fisher's exact test) when compared with the patients who had obstructive disease. Only one patient (who had immunodeficiency) died, and all others were successfully managed on conventional mechanical ventilation. We conclude that RSV-induced respiratory failure represents a relatively benign cause of ARDS in pediatric patients. Our observations support the notion of differentiating ARDS with respect to causation, especially when novel and experimental therapy is considered and mortality rates are analyzed.

Causality↗
PubMed1997

Continuous versus intermittent furosemide infusion in critically ill infants after open heart operations.

BACKGROUND: Use of intravenous furosemide is generally avoided in critically ill neonates and infants soon after open heart operations to prevent fluctuations in intravascular volume and resulting circulatory instability. METHODS: To assess and compare the safety and efficacy of continuous versus intermittent intravenous furosemide, we undertook a prospective, randomized trial in 26 consecutive patients less than 6 months of age. Inclusion criteria were presence of low-output syndrome requiring inotropic support (24/26 patients) or pulmonary hypertension requiring vasodilator therapy (10/26 patients) within 6 hours of discontinuation of cardiopulmonary bypass. Eleven patients received 0.1 mg x kg(-1) x h(-1) continuous intravenous furosemide (group 1) and 15 received 1 mg/kg bolus every 4 hours (group 2) for 24 hours. Mean age (3.7 +/- 3.4 versus 1.8 +/- 2.5 months) and weight (4.6 +/- 2.1 versus 4.3 +/- 1.7 kg) were comparable. RESULTS: Group 2 infants showed slightly greater absolute urinary output (2.5 +/- 1.1 mL/kg per hour versus 3.3 +/- 1.1 mL/kg per hour, p = 0.05). However, urinary output per dose of drug was significantly larger in group 1 infants (1.0 +/- 0.4 versus 0.5 +/- 0.2 mL x kg(-1) x h(-1); p = 0.002) with lesser fluctuations (variance, 1.9 +/- 1.6 versus 3.8 +/- 2.1; p = 0.02) and fluid replacement needs (20.6 +/- 3.8 versus 51.8 +/- 14.4; p = 0.001). Electrolyte replacement requirements were similar. A trend toward greater hemodynamic instability in group 2 patients (heart rate variance 88.4 +/- 79.8 versus 128.3 +/- 82.7; p = 0.09; central venous pressure variance 2.8 +/- 1.90 versus 4.1 +/- 3.7; p = 0.07; mixed venous oxygen saturation variance, 32.3 +/- 27.6 versus 45.7 +/- 20.4; p = 0.06) was noted. All patients who completed the study protocol survived operation and were discharged home. CONCLUSIONS: We conclude that (1) commonly used doses of both intermittent and continuous intravenous furosemide infusion can be safely administered to critically ill neonates and infants as early as 6 hours after operation, (2) continuous infusion yields an almost comparable urinary output with a much lower dose of furosemide, and (3) intermittent administration is associated with greater fluctuations in urinary output and greater needs for fluid replacement therapy.

Cardiac Output, Low↗
PubMed1997

Effect of prone and supine positions on functional residual capacity, oxygenation, and respiratory mechanics in ventilated infants and children.

Although numerous reports have described the improvement in PAO2 in patients in the prone position, the underlying mechanism has yet to be determined. Some authors have suggested this phenomenon may be related to an increase in functional residual capacity (FRC); however, no previous studies have described positional changes in FRC in children with severe lung disease or in those under neuromuscular blockade. We measured arterial blood gases, FRC, Rrs, and Crs in supine and prone positions in 30 patients under neuromuscular blockade with lung disorders including moderately severe restrictive (n = 10) and obstructive (n = 10) disease and control subjects without significant lung disease (n = 10). Prone positioning was not associated with a significant increase in FRC in the cohort of 30 patients, nor in any of the subgroups. Although individual patients demonstrated large improvements in oxygenation, a statistically significant (but clinically insignificant) increase in AaPO2 ratio was observed only in the subgroup of patients with obstructive disease (0.35+/-0.03 to 0.38+/-0.04, p = 0.027). There was no correlation between changes in FRC and changes in AaPO2 (r = 0.225, p = 0.23). A significant improvement in Rrs occurred in the prone position compared to supine in patients with obstructive lung disease, decreasing from 0.264+/-0.024 to 0.216+/-0.021 cm H2O/ml/s, p = 0.009. No significant changes in Crs were seen in the prone position. We conclude that prone positioning has no effect on FRC and in this series of 30 patients significantly improved oxygenation only in patients with obstructive airway disease. A significant decrease in Rrs in patients with obstructive lung disease was also observed.

Blood Gas Analysis↗
PubMed1997

Influence of endotracheal tube diameter on forced deflation flow-volume curves in rhesus monkeys.

The forced deflation (FD) technique is the recommended gold standard to generate forced expiratory vital capacity (FVC) curves and to measure maximum expiratory flow-volume (MEFV) relationships in intubated infants and children. However, the influence of the endotracheal tube (ETT) on the site of flow limitation, the shape and the analysis of the resultant MEFV curves have not been defined. Nine anaesthetized (thiopentone, 8 mg x kg(-1) x h(-1)) rhesus monkeys (mean weight (+/-SEM) 10+/-1 kg) were intubated consecutively with ETTs of different internal diameters (ID 3.0-5.5 mm, at intervals of 0.5 mm); the largest representing the appropriate ETT size for the animal. Quadruplicate MEFV curves were generated by FD using the standard +40 cmH2Oinsp/-40 cmH2Oexp pressures and recorded at each ETT diameter. The effect of the different ETT diameters on the FD flow-volume curve was analysed by comparing maximum expiratory flows at isovolume points at 50, 25 and 10% FVC (MEF50, MEF25 and MEF10, respectively). The shape of the resulting MEFV curves could be divided into an initial horizontal part (tube-dependent), and a final descending slope (airway-dependent). No difference in FVC occurred irrespective of the ETT size (p>0.05 by analysis of variance (ANOVA)). MEF50 increased with increasing tube diameter (p<0.05). MEF25 remained unchanged using ETTs which were less than 1.5 mm smaller than the largest ETT. Smaller ETTs resulted in significantly reduced MEF25 (p<0.05). MEF10 was not influenced by the ETT size. We conclude that maximum expiratory flows measured by the forced deflation technique are not influenced by an appropriately sized endotracheal tube at lung volumes below 25% forced vital capacity in our monkey model with normal lungs. We postulate that the effect of endotracheal tubes on maximum expiratory flow volume curves in intubated infants might be of similar or even smaller magnitude, which remains to be established.

Animals↗
PubMed1997

The effects of bronchodilators on spontaneous ventilation and oxygen consumption in rhesus monkeys.

The effects of breathing normal saline, salmeterol, fenoterol, ipratropium bromide, or formoterol, and of i.v. infusion of theophylline on oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart and respiratory rates, and end-tidal carbon dioxide tension (P(ET)CO2) have been defined in 10 anesthetized, intubated rhesus monkeys (mean age 7.0 y, weight 10.2 kg). VO2 increased over control by + 17.1% after salmeterol (p < 0.001), +33.3% after fenoterol (p < 0.001), +23.7% after formoterol (p < 0.001), +3.9% after theophylline (p < 0.01), but did not change after ipratropium bromide and normal saline. VE increased by 63.0% after fenoterol (p < 0.001), 49.8% after formoterol (p < 0.001), 31.7% after salmeterol (p < 0.01), and 29.7% after theophylline (p < 0.001), but not after ipratropium bromide or normal saline. Heart rate response was greatest after fenoterol, formoterol, and salmeterol, respectively. P(ET)CO2 dropped dramatically after theophylline (-15.7%, p < 0.001), but not at all with any of the inhaled beta2-adrenoceptor agonists. In seven animals, salbutamol (albuterol) caused an increase in V(E) and VO2 of 50.1% and 45.9%, respectively, whereas in the presence of a beta2-adrenoceptor antagonist [racemic or (+/-)-propranolol (0.1 mg/kg i.v.)], inhaled salbutamol (2.5 mg/mL for 10 min) could not increase V(E) (+6.2%, p > 0.05) and VO2 (+1.6%, p > 0.05). The increase in VO2 and V(E) after administration of beta2-agonists may be partly the result of direct stimulation of the respiratory center and partly a response to increased metabolic rate. The dramatic increase in VO2 and V(E) after salbutamol was suppressed in the presence of propranolol, which is consistent with a beta-receptor-mediated mechanism.

Adrenergic beta-Agonists↗
PubMed1996

Effort and volume dependence of forced-deflation flow-volume relationships in intubated infants.

The application of negative pressure to the airway opening [called the forced-deflation (FD) technique] allows the examination of maximal expiratory flow-volume curves in intubated infants who are unable to generate a voluntary maximal expiratory maneuver. We explored the questions of effort and volume dependence of flows generated by FD in 18 intubated, sedated, and paralyzed infants [age 10.6 +/- 2.0 (SE) mo; weight 7.2 +/- 0.7 kg] with normal lungs. Effort dependence was assessed by isovolume pressure-flow curves that were constructed in 10 infants from repeated FD maneuvers from total lung capacity (defined as +40 cmH2O) by varying airway opening pressures from 0 (barometric pressure) to -100 cmH2O at intervals of 20 cmH2O. The effect of volume history was assessed by initiating FD maneuvers from different inspiratory volumes delineated by the inspiratory pressures +10, +20, +30, and +40 cmH2O. We compared maximal expiratory flows at isovolume points [50, 25, and 10% forced vital capacity (FVC) of the standard +40/-40 cmH2O FD maneuver] and found that flow limitation consistently occurred in all infants at and below 25% FVC with -40 cmH2O or greater airway opening pressure. We found no significant influence of volume history on maximal flows at and below 25% FVC. Under well-controlled study conditions, we demonstrated excellent reproducibility of maximal expiratory flows at low lung volumes, analogous to those of voluntary forced expiratory maneuvers in adults and older children. This information may be helpful in setting standards for performance and interpretation of FD maneuvers in intubated infants.

Humans↗