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Biomedical subjects

R Fletcher

Publications and source records attributed to R Fletcher.

At least 109 records · Page 6Linked to original sources
PubMed1988

Carbon dioxide production in cyanotic children during anaesthesia with controlled ventilation.

Carbon dioxide production and ventilatory efficiency were measured during undisturbed anaesthesia with intermittent positive pressure ventilation in 34 children about to undergo closed or open cardiac surgery. Anaesthesia was provided with fentanyl or halothane and nitrous oxide. There were 15 cyanotic and 19 acyanotic children. Children with cyanotic heart disease produced approximately 20% less carbon dioxide per unit body weight than acyanotic children, but ventilation was approximately 20% less efficient. Adequate ventilation should therefore be obtained when "normal" ventilation in relation to body weight is used in cyanotic children.

Anesthesia, Inhalation↗
PubMed1988

Invasive and noninvasive measurement of the respiratory deadspace in anesthetized children with cardiac disease.

To compare the magnitude of the different "invasive" and "noninvasive" dead space variables and the effect on them of ventilator setting, CO2 single breath tests (SBT-CO2) were obtained using an on-line computerized system based on the Servo ventilator and CO2 Analyzer 930, in 50 children anesthetized for cardiac surgery. The variables were the airway deadspace (VDaw), Bohr's deadspace (VDBohr) obtained noninvasively using end-tidal PCO2 (PETCO2) for alveolar PCO2 in the deadspace equation, and the physiologic deadspace, VDphys. In 42 children with normal single breath tests, VDaw was two-thirds of VDBohr; in 9 children in whom phase III of SBT-CO2 (the "alveolar plateau") was steeper than normal, it was only half of VDBohr. Steeper slopes of phase III were seen particularly in the present of left-right (LR) shunting. VDphys was very similar in magnitude to VDBohr in all children, except those with right-left (RL) shunts. VDaw was the major component of VDphys only in children with normal arterial-end-tidal PCO2 differences, i.e., those without RL shunts. When two ventilator frequencies giving the same alveolar ventilation were compared in children with normal gas exchange, VDBohr as a fraction of tidal volume was least at the lower frequency, as it also is in adults. The data confirm that noninvasive CO2 monitoring and measurement of deadspace gives useful indexes of the adequacy of ventilation in all children except those with RL shunts.

Anesthesia↗
PubMed1987

Social Security disability determinations. Knowledge and attitudes of consultative physicians.

Social Security spends $135 million yearly, contracting with physicians to provide consultative examinations for disability applicants. However, little is known about who these physicians are or how they view the determination of impairment. We surveyed a random sample of 153 physicians from North Carolina who performed consultative examinations for the North Carolina Disability Determinations Agency in 1983 (the consultative group), and a randomly selected group of 165 physicians of similar medical specialties (the comparison group). Response rates were 75% for the consultative group and 66% for the comparison group. Most consultative physicians (63%) performed fewer than 6 examinations per month. Characteristics of the consultative physicians were similar to the comparison group. Both groups were skeptical of the claims of disability applicants; 48% of the consultative and 55% of the comparison group thought that a majority of applicants could be employed. Of the consultative physicians, 53% indicated that they had learned little about disability programs from any source. Most consultative physicians (58%) judged it "almost impossible" to determine impairment on the basis of a single office examination. However, consultative physicians were less likely than the comparison group to view Social Security as difficult to work with (25% vs. 54%; P less than 0.01). Agencies that determine disability ask physicians to perform a task for which they feel ill prepared and have little special knowledge.

Attitude of Health Personnel↗
PubMed1987

Gas exchange during thoracotomy in children. A study using the single-breath test for CO2.

Gas exchange during thoracotomy was studied in 13 children aged 6 months to 14 years (median age 5 years), anaesthetized for repair of coarctation of the aorta or closure of a patent ductus arteriosus. All received halothane in equal parts of N2O/O2 supplemented with fentanyl. CO2 single-breath tests were obtained with a computerised on-line system based on the Servo ventilator. From signals for airway flow pressure, CO2 concentration and timing, the computer calculated the airway deadspace (VDaw) and the static compliance and resistance of the respiratory system. Given a value for PaCO2, the computer also calculated the physiological and alveolar deadspaces. Measurements were taken at six stages during the procedure, starting with the supine position before surgery. After turning to the lateral position, airway deadspace increased by 19%, thus increasing the physiological deadspace fraction. When the pleura was opened, both VDaw and PaO2 were reduced. When the upper lung was retracted, compliance was reduced and also PaO2 - the minimum value noted was 17.3 kPa. Hypoxic PaO2 values were possibly avoided because both ventilation and perfusion were reduced in the retracted lung. The alveolar deadspace fraction increased during these intra-operative stages. Although the net effect of the changes in airway and alveolar deadspace during surgery was a significant increase in physiological deadspace fraction (from 0.23 to 0.28), gas exchange could be maintained at the cost of only moderate increases in peak airway pressure: the mean increase was from 2.4 to 2.8 kPa (24 to 29 cmH2O).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Safety of graded symptom-limited exercise testing in patients with congestive heart failure.

The safety and end points of graded symptom-limited bicycle exercise were assessed in 607 patients before they were randomized to vasodilator or placebo in the Veterans Administration Cooperative Study-Vasodilator Heart Failure Trial. Their mean age was 58 years and left ventricular ejection fraction averaged 30%. The peak exercise responses were as follows: oxygen consumption, 14.5 +/- 3.9 ml/kg/min; heart rate, 132 +/- 24 beats/min; systolic blood pressure, 154 +/- 29 mm Hg. No major complications occurred with the baseline tests. The initial baseline test was stopped in only 10 patients (1.6%) for arrhythmias and in one patient for hypotension. Ventricular tachycardia assessed by ambulatory electrocardiographic monitoring during the second exercise test (before exercise, during exercise, and 4 hr after the test) revealed a prevalence of 5.7% during exercise and 28.8% during the rest of the monitoring period. This study has demonstrated that stable male patients with congestive heart failure can safely exercise on a bicycle ergometer to their peak effort in a well-supervised setting. In addition, we have demonstrated that ambulatory electrocardiographic monitoring is a better method than exercise testing to evaluate presence and extent of ventricular arrhythmias in patients with congestive heart failure.

Adolescent↗
PubMed1986

On-line expiratory CO2 monitoring.

The single breath test for carbon dioxide (SBT-CO2) is the plot of expired FCO2 or CO2% against expired volume. It can be monitored during anaesthesia and in the intensive care unit with modest additions to generally available equipment. This paper describes some aspects of a computer program for presenting SBT-CO2 during controlled ventilation, in particular, the corrections to the primary data necessary for scientific accuracy. Examples are given of how the use of SBT-CO2 has increased our understanding of factors which influence the arterial-end-tidal PCO2 difference (PaCO2-PE,CO2). PaCO2-PE, CO2 is, in a given individual, usually dependent on tidal volume and frequency. Changes in lung volume and manoeuvres such as opening the pleura also affect gas exchange. Monitoring CO2 elimination gives a measure of metabolic rate if ventilation and pulmonary perfusion are maintained. This facilitates ventilatory therapy in situations where CO2 production is greatly increased, e.g. sepsis and tetanus. On the other hand, if metabolism and ventilation are unchanged, a reduction in CO2 elimination implies reduced pulmonary perfusion. This can be seen during increased right-left shunting, such as in surgery in patients with congenital heart disease.

Anesthesia↗
PubMed1986

Static v. dynamic tests in the in vitro diagnosis of malignant hyperthermia susceptibility.

In vitro contracture tests, in which muscle specimens are exposed to halothane or caffeine are, at present, the only generally accepted screening methods for the diagnosis of susceptibility to malignant hyperthermia (MHS). Static tests (performed with the muscle held at constant length) are used more commonly although, in addition, some MH investigation units use dynamic tests, in which the length of the specimen is varied. We have performed dynamic and static tests in parallel on muscle from 112 patients. The dynamic halothane test was more sensitive in discriminating between MHS and MH negative (MHN) individuals than the static halothane test. However, the dynamic caffeine test was less sensitive at discriminating between MHS and MHN individuals, and nothing is to be gained by including it in the investigation.

Caffeine↗