Search PubMed⌕ Search

Biomedical subjects

C J Newth

Publications and source records attributed to C J Newth.

At least 37 records · Page 2Linked to original sources
PubMed1996

Anatomic dead space in infants and children.

In adults, anatomic dead space is 2.2 ml/kg. Because of the relatively large head size of infants and children, we hypothesized that extrathoracic and, therefore, total dead space would be relatively larger in pediatric subjects. Extrathoracic dead space was measured by a "water displacement" technique in 40 patients aged 7 days to 14.2 yr who were intubated with cuffed endotracheal tubes. Intrathoracic dead space was measured by continuous analysis of end-tidal and mixed-expired PCO2 and minute ventilation in 10 patients, aged 18 days to 14.7 yr. Extrathoracic dead space per kilogram decreased exponentially with increasing age, ranging from 2.3 ml/kg in early infancy to 0.8 ml/kg in children older than 6 yr. Mean intrathoracic anatomic dead space was 1.03 ml/kg and was not related to age. The following relationship between total anatomic dead space (DStotal; in ml/kg) and age (in yr) is derived: DStotal = 3.28 - 0.56 [ln(1 + Age)], with r = 0.95 and P = 0.0001. Anatomic dead space is age dependent and is > 3 ml/kg in early infancy.

Adolescent↗
PubMed1996

Flow limitation in anesthetized rhesus monkeys: a comparison of rapid thoracoabdominal compression and forced deflation techniques.

Rapid thoracoabdominal compression (RTC) and forced deflation (FD) allow the examination of maximal expiratory flow-volume (MEFV) curves in animals and human infants unable to generate a voluntary maximal expiratory maneuver. We compared flows generated by these two techniques and by constructing isovolume pressure-flow (IVPF) curves examined each method's potential to produce flow limitation. RTC and FD were performed in seven intubated rhesus monkeys from +40 cm H2O inspiratory pressure with deflation pressures ranging from -20 to -100 cm H2O and jacket pressures from +20 to +100 cm H2O (arms outside jacket). We also performed RTC maneuvers in all monkeys with the arms inside the jacket at +100 cm H2O jacket pressure. Maximal expiratory flows achieved by FD and RTC were analyzed at isovolume points. Both techniques produced flow limitation conditions over the last 25% of the MEFV curve. Individual IVPF curves generated by the two techniques demonstrated remarkable differences in shape and flow rates. Maximal transpulmonary pressures achieved with FD were higher than those with RTC in this experiment. Negative effort dependence was observed with higher deflation pressures in the majority of the monkeys. Flows achieved by RTC with the arms in were lower than those achieved with the arms out when compared at identical pressure gradients. We conclude that the difference in expiratory flow rates at isovolume-pressure points is most likely related to different effects on the behavior of intrapulmonary airways and choke point characteristics by the two techniques.

Animals↗
PubMed1995

Effects of maternal and sibling deprivation on basal and stress induced hypothalamic-pituitary-adrenal components in the infant rat.

Prolonged maternal deprivation during early infancy increases basal- and stress-induced corticosterone (CORT) levels, but the underlying mechanism is not clear. In general, stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, with secretion and compensatory synthesis of hypothalamic cortcotropin-releasing hormone (CRH). In the infant rat, we have demonstrated that maximally tolerated acute cold stress induced a robust elevation of plasma CORT throughout the first 2 postnatal weeks. However CRH messenger RNA (CRH-mRNA) abundance 4 h subsequent to cold stress was enhanced only in rats aged 9 days or older. This suggests a developmental regulation of the CRH component of the HPA-response to this stressor. The present study examined whether increased basal and cold stress-induced CORT levels after 24 h of maternal deprivation were due to enhanced CRH-mRNA abundance in the hypothalamic paraventricular nucleus (PVN). CRH-mRNA abundance, and basal- and cold-induced plasma CORT levels were measured in maternally deprived 6 and 9-day-old pups compared to non-deprived controls. Maternal deprivation increased basal and cold-induced CORT levels on both 6 and 9-day-old rats. CRH-mRNA abundance in the PVN of deprived rats did not differ from that in non-deprived rats. Our results indicate that the enhanced basal and stress-induced plasma CORT observed after 24 h maternal deprivation is not due to increased CRH-mRNA abundance in the PVN.

Adrenal Glands↗
PubMed1995

Assessment of lung function in the intensive care unit.

Tests of pulmonary function have become more accurate and less invasive in recent years. Our ability to monitor patients continuously with pulse oximetry, transcutaneous and end-tidal CO2, and intraarterial blood gas monitors has greatly enhanced ICU care. In intubated patients in the PICU detailed lung function studies can be performed, and in general they can be carried out with minimal disruption of routine management. Much work remains to be done to define the changes seen in various disease processes and the effects of therapeutic interventions on functional parameters. Many of the available techniques have already been developed to a point that allows them to be employed in clinical decision making. We expect that assessment of lung volumes, compliance, and resistance will become a routine part of management in children with life-threatening pulmonary diseases in the near future, and that a more intimate knowledge of the pathophysiology of respiratory disorders treated in PICU will lead to improved outcomes.

Bronchoscopy↗
PubMed1995

Validation of the phase angle technique as an objective measure of upper airway obstruction.

Thoraco-abdominal asynchrony (TAA) during upper airway obstruction (UAO) in small children can be documented by phase angle analysis of the Lissajous figure from the output of a noncalibrated respiratory inductance plethysmograph. Phase angle measurements have not been related to levels of inspiratory resistance, nor to the effect of breathing a 79% helium-21% oxygen mixture (heliox) during inspiratory resistance. We examined the effects of graded inspiratory loading (5-1000 cm H2O/L/sec) on TAA as measured by phase angle in 10 male, anesthetized, and intubated Rhesus monkeys, breathing room air and heliox. Phase angles increased with inspiratory loading from a baseline value of 22 +/- 3 degrees to 165 +/- 8 degrees at 1,000 cm H2O/L/sec resistance and correlated significantly with the level of inspiratory loading (r = 0.82). End-tidal carbon dioxide PETCO2 increased from 39 +/- 1 to 49 +/- 3 mm Hg at the highest load, but correlated only weakly with phase angle measurements (r = 0.60) and the level of inspiratory loading (r = 0.56). By changing to heliox breathing at the highest tolerated resistance, PETCO2 dropped significantly from 49 +/- 3 to 40.5 +/- 4 mmHg (P < 0.001) with no significant change in phase angles: 169 +/- 13 degrees and 165 +/- 8 degrees, respectively (P > 0.05). We conclude that heliox therapy for acute alveolar hypoventilation during UAO improves ventilation, but does not decrease TAA at high inspiratory resistance. Continuous monitoring of the relative changes in phase angles is useful to observe the severity of UAO in the early stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Obstruction↗
PubMed1995

Infant lung function testing in the intensive care unit.

As a result of the previous shortage of tools to assess objectively the overall physiological status of the respiratory system in infants and young children, it has been difficult to measure the degree of physiological disorder or the response to therapy in respiratory diseases such as BPD, the pediatric version of ARDS, bronchiolitis, pneumonia, asthma and croup in this patient population. The newborn- four-year old child is particularly difficult to study because of their lack of cooperation and size. The recent progress in computer technology made pulmonary function testing available for this age range and opened up new possibilities for monitoring changes in disease processes affecting the respiratory system. This may improve medical management of infants and children with lung and heart diseases in particular. In 1989, Shannon [49] proposed in this Journal that the minimum physiological information needed for the intelligent use of mechanical ventilation (particularly if lower airway and/or pulmonary parenchymal disease was apparent) required the measurement of at least 4 variables: i) arterial partial pressure of carbon dioxide; ii) arterial oxygen saturation; iii) the mechanical time constant of the lung and iv) FRC. In many circumstances, arterial CO2 is approximated by alveolar (end-tidal) CO2 and the arterial oxygen saturation is obtained from pulse oximetry accurately if perfusion is adequate. The mechanical time constant and FRC are easily measured by the techniques described above and together provide important information concerning appropriate ventilator settings for a given disease. The described techniques bring new insights and awareness, but also new responsibilities in the management of infants and children with respiratory compromise. Not all of these techniques need to be applied to all infants in the ICU. Not all the assumptions upon which some of the techniques we have described are based will prove true. Any such methods which do not withstand solid scientific testing must be quickly discarded and replaced with better and (hopefully) easier methods.

Child, Preschool↗
PubMed1995

Albuterol responsiveness in infants with respiratory failure caused by respiratory syncytial virus infection.

OBJECTIVE: To assess the bronchodilator effect of inhaled albuterol in the acute stage of severe respiratory syncytial virus (RSV) infection. DESIGN: Prospective, nonrandomized study of previously healthy infants who underwent intubation and whose lungs were ventilated because of respiratory failure caused by RSV infection. Ten infants with an endotracheal tube in place and without lung disease were matched for age and weight and served as normal control subjects. METHODS: Lung function tests, including respiratory mechanics by single-breath occlusion, small airway function by forced deflation, and lung volumes by nitrogen washout, were performed before and after inhalation of 900 micrograms albuterol by metered dose inhaler. Bronchodilator response was defined as a change of more than twice the coefficient of variation of repeated baseline measurements. RESULTS: Twenty-three infants (mean +/- SE age = 4.2 +/- 1.1 months) were studied, of whom 20 (87%) had obstructive small airway disease, and 3 (13%) had exclusively restrictive lung function profiles. Ten of the infants with obstructive disease (50%) did not benefit from albuterol, and 9 (45%) had small but significant improvements in lung function. Deterioration of lung function was documented in 1 patient after albuterol inhalation. CONCLUSION: Inhaled albuterol is of limited value as a bronchodilator in infants with RSV-induced respiratory failure and should be discontinued if a beneficial response cannot be observed.

Acute Disease↗
PubMed1995

Effect of lung volume on forced expiratory flows during rapid thoracoabdominal compression in infants.

The rapid thoracoabdominal compression (RTC) technique is commonly used in pulmonary function laboratories to assess flow-volume relationships in infants unable to produce a voluntary forced expiration maneuver. This technique produces forced expiratory flows over only a small lung volume segment (i.e., tidal volume). It has been argued that the RTC technique should be modified to measure flow-volume relationships over a larger portion of the vital capacity range to imitate the voluntary maximal forced expiratory maneuver obtained in older children and adults. We examined the effect of volume history on forced expiratory flows by generating forced expiratory flow-volume curves by RTC from well-defined inspiratory volumes delineated by inspiratory pressures of 10, 20, 30, and 40 cmH2O down to residual volume (i.e., the reference volume) in seven intubated and anesthetized infants with normal lungs [age 8.0 +/- 2.0 (SE) mo, weight 6.7 +/- 0.6 kg]. We compared maximal expiratory flows at isovolume points (25 and 10% of forced vital capacity) and found no significant differences in maximal isovolume flow rates measured from the different lung volumes. We conclude that there is no obvious need to initiate RTC from higher lung volumes if the technique is used for flow comparisons. However, compared with measurements of maximal flows at functional residual capacity by RTC from end-tidal inspiration, the initiation of RTC from a defined and reproducible inspiratory level appears to decrease the intrasubject variability of the maximal expiratory flows at low lung volumes.

Abdomen↗
PubMed1994

Cuffed endotracheal tubes in pediatric intensive care.

We prospectively studied 282 consecutive tracheal intubations (243 patients) in a pediatric intensive care unit during a 7-month period to compare cuffed and uncuffed endotracheal tube (ETT) utilization and outcome. The incidence of postextubation stridor in each ETT group was the major outcome measure after controlling for various patient risk factors. Patients whose ETTs were inserted in the operating room, who were less than 1 year of age, or who had ETTs in place for less than 72 hours were more likely to have had insertion of an uncuffed ETT. Patients whose ETTs were inserted in the emergency department or who were more than 5 years of age were more likely to have had insertion of a cuffed ETT. Those who had a cuffed ETT were older (mean 8.1 vs 2.5 years) and had ETTs in place longer (mean 6.1 vs 3.7 days) than patients with an uncuffed ETT. Of the 188 patients who subsequently had removal of their ETTs, the overall incidence of postextubation stridor was 14.9%, with no significant difference between the two ETT groups even after controlling for patient age, duration of intubation, trauma, leak around ETT before extubation, and pediatric risk of mortality score. Two patients in the cuffed ETT group and four patients in the uncuffed ETT group required reintubation for severe postextubation stridor. Long-term follow-up identified 33 patients (17%) who required hospital readmission. None of these was admitted with an upper airway problem. Two patients who previously had insertion of a cuffed ETT subsequently received tracheostomies for the primary purpose of long-term mechanical ventilation unrelated to any problem with the upper airway. We conclude that cuffed endotracheal intubation is not associated with an increased risk of postextubation stridor or significant long-term sequelae.

Child↗
PubMed1994

Measurement of high lung volumes by nitrogen washout method.

Studies on human infants suggested that thoracic gas volume (TGV) measured at end exhalation may not depict the true TGV and may differ from TGV measured from a series of higher lung volumes and corrected for the volume added. This was explained by gas trapping. If true, we should expect the discrepancy to be more pronounced when functional residual capacity (FRC) and higher lung volumes are measured by gas dilution techniques. We studied lung volumes above FRC by the nitrogen washout technique in 12 spontaneously breathing rhesus monkeys (5.0-11.3 kg wt; 42 compared measurements). Lung volumes directly measured were compared with preset lung volumes achieved by artificial inflation of the lungs above FRC with known volumes of air (100-260 ml). Measured lung volume strongly correlated with and was not significantly different from present lung volume (P = 0.05; r = 0.996). The difference between measured and preset lung volume was 0-5% in 41 of 42 cases [1 +/- 0.4% (SE)]. The direction of the difference was unpredictable; in 22 of 42 cases the measured volume was larger than the preset volume, but in 17 of 42 cases it was smaller. The difference was not affected by the volume of gas artificially inflated into the lungs. We conclude that, overall, lung volumes above FRC can be reliably measured by the nitrogen washout technique and that FRC measurements by this method reasonably reflect true FRC.

Animals↗
PubMed1993

The pharmacokinetics of isoproterenol in critically ill pediatric patients.

The pharmacokinetics of isoproterenol (ISO) in infants and children have never been reported. The authors studied ISO pharmacokinetics in two disparate groups of pediatric intensive care unit patients: postoperative cardiac patients (POC, n = 10), and reactive airway disease patients (RAD, n = 9). In all, 44 blood samples were taken at steady-state from the 19 patients, whereas from 15 patients samples were also taken just before and after discontinuation of ISO infusion. There were 12 male and 7 female patients in the study, and their ages ranged from 2 days to 14 years. The average ISO dosing rate was 0.30 micrograms/kg/minute for the whole study population, ranging from 0.01 to 5.5 micrograms/kg/minute. The POC patients received a significantly lower dosing rate than the RAD patients (0.029 +/- 0.002 vs 0.50 +/- 0.21 micrograms/kg/minute, P < .0001); the average steady-state plasma concentrations of ISO were also lower in the POC patients (1.3 +/- 0.3 versus 13.9 +/- 4.9 ng/mL, P < .0001). The steady-state plasma concentration, normalized to a dosing rate of .05 micrograms/kg/minute, was 1.9 +/- 0.3 ng/mL for all patients, and the clearance was 42.5 +/- 5.0 mg/kg/minute. Postoperative cardiac patients had a significant higher normalized steady-state plasma concentration and moderately significant lower clearance than did RAD patients (2.1 +/- 0.3 versus 1.7 +/- 0.4 ng/mL, P < .05 and 33.2 +/- 4.9 versus 48.4 +/- 7.3, P < .06, respectively). The average plasma half-life of ISO was 4.2 +/- 1.5 minutes, and the volume of distribution was 216 +/- 57 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Estimation of arterial carbon dioxide by end-tidal and transcutaneous PCO2 measurements in ventilated children.

Simultaneous measurements of arterial, end-tidal, and transcutaneous carbon dioxide (PaCO2, PetCO2, PtcCO2, respectively) were obtained in 134 children receiving mechanical ventilation (ages, 2 days to 16 years; mean, 2.5 years). The mean +/- SD PetCO2 bias (PaCO2 - PetCO2) was 3.4 +/- 6.6 mmHg. When the PetCO2 bias was plotted against the PaO2/PAO2 ratio, a change in the scatter was obvious at about 0.3. The PetCO2 bias for patients with PaO2/PAO2 under 0.3 was 7.8 +/- 7.3 mmHg compared to 0 +/- 3.4 in patients with PaO2/PAO2 above 0.3 (P less than 0.001). PetCO2 differed significantly from PaCO2 (P less than 0.001) only for patients with PaO2/PAO2 under 0.3. The slope (PaCO2 versus PetCO2) for these patients was 1.59, while the slope for patients with PaO2/PAO2 above 0.3 coincided with the line of identity (1.00). The mean +/- SD PtcCO2 bias (PaCO2 - PtcCO2) was -1.3 +/- 7.2 mmHg. Skin perfusion was recorded at the area close to the transcutaneous CO2 monitor electrode and was defined as normal when capillary refill was below 3 seconds. The PtcCO2 bias for patients with normal skin perfusion was -0.2 +/- 5.4 mmHg (P = 0.73) compared to -4.1 +/- 9.9 for patients with decreased skin perfusion (P = 0.01). The slope of PtcCO2 against PaCO2 was closer to identity in patients with normal skin perfusion (1.17) than in patients where it was decreased (slope, 1.40). We suggest that PaCO2 estimation by both PetCO2 and PtcCO2 is sufficiently precise and reliable for clinical use in critically ill children. Certain limitations stem from the nature of the techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Intensive care course and outcome of patients infected with respiratory syncytial virus.

PICU admissions of 97 children positive for respiratory syncytial virus on fluorescent antibody screening were reviewed; 68% of 44 patients without history of preceding disease (Group I) and 79% of 53 patients with preceding pulmonary, cardiac, or other disease (Group II) required ventilation. In Group I ventilated children weighted significantly less (P = 0.001) and were of lower chronological (P = 0.02) and post-conceptional ages (P = 0.02) than those not ventilated. Eighteen infants ventilated for apnea weighted significantly less (P = 0.003), were more often born at less than or equal to 37 weeks gestation (P = 0.001) and were at lower post-conceptional age than 11 infants ventilated for progressive respiratory deterioration. There was no significant difference in mean weight, chronological age, post-conceptional age, CO2, or pH between 12 admissions with BPD who required ventilation for RSV infection and 5 who did not require ventilation. Ribavirin administration to five ventilated patients with BPD did not significantly alter the duration of intubation of PICU stay. Six patients with cardiac disease required longer periods of ventilation than others (Group I, P = 0.001; all others in Group II, P = 0.04). No deaths occurred in Group I, while 6 of 53 (11%) patients in Group II died. In this series immuno compromise placed patients at greatest risk of dying. Mechanical ventilation can be safely managed in previously healthy, RSV infected infants and should be initiated before significant cardiorespiratory compromise arises.

Adolescent↗
PubMed1992

Laryngotracheobronchitis as a complication of measles during an urban epidemic.

OBJECTIVE: To evaluate demographic and clinical correlates of laryngotracheobronchitis (LTB) as a complication of measles during a community-wide epidemic. DESIGN: Retrospective review of medical records. SETTING: Childrens Hospital Los Angeles, a large urban pediatric facility, during a regional epidemic of measles studied January through June 1990. PATIENTS: All patients identified at our hospital who met Centers for Disease Control criteria for measles. MEASUREMENTS AND RESULTS: Of 440 patients with measles, 82 also had LTB (18.6%). Patients in whom LTB developed were significantly younger (mean +/- SD: 14.7 +/- 8.2 months) than the cohort (24.8 +/- 30.1 months) (p less than 0.001) and more likely to require hospitalization (91.5%) than the cohort (44.3%) (p less than 0.001). Thirteen patients (17.3%) required intensive care, including 9 (11%) who required endotracheal intubation for a mean of 8.3 +/- 7.1 days. Pulmonary function testing of five patients with an endotracheal tube in place, including three not clinically assessed as having pneumonia, indicated the presence of concomitant lower respiratory tract disease. CONCLUSION: Laryngotracheobronchitis was a frequent and often severe complication of measles. The likelihood that LTB would develop was inversely related to age, generally required inpatient care, and necessitated endotracheal intubation in severely affected patients.

Adolescent↗