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Biomedical subjects

A Lloyd-Thomas

Publications and source records attributed to A Lloyd-Thomas.

14 recordsLinked to original sources
PubMed1997

The relation between arterial oxygen tension and cerebral blood flow during cardiopulmonary bypass.

OBJECTIVES: Neurological impairment occurs in up to 25% of infants undergoing cardiopulmonary bypass with or without circulatory arrest. Potential causes include alterations in cerebral blood flow, hypoxia and embolisation. During cardiopulmonary bypass, arterial oxygen tension is maintained at levels which under normal conditions cause cerebral vasoconstriction; this is a potential mechanism for ischaemia. The aim of this study was to explore the relation between arterial oxygen tension and cerebral blood flow during cardiopulmonary bypass. METHODS: Near infrared spectroscopy was used to explore the relation between arterial oxygen tension and cerebral blood flow in 14 patients (median age 8 months; range 1 month to 10 years 11 months). The relations between arterial oxygen tension, arterial carbon dioxide tension, temperature, haematocrit, pump flow rate, mean arterial pressure and cerebral blood flow, were examined using multivariate analysis. RESULTS: There was no relation between cerebral blood flow and arterial oxygen tension, but a highly significant relation was observed between cerebral blood flow and pump flow rate, with cerebral blood flow decreasing 4.2-fold per L.m-2.min-1 decrease of pump flow rate. CONCLUSION: There was no relation between arterial oxygen tension and cerebral blood flow during cardiopulmonary bypass, but low pump flow rate may lead to reduced cerebral blood flow.

Blood Flow Velocity↗
PubMed1995

Oxygen saturation in children in the postoperative period.

Some adult patients have periods of significant oxygen desaturation after surgery but, other than for immediately after surgery in the recovery room, few data are available in children. We monitored overnight paired preoperative and postoperative oxygen saturations in 19 children, and overnight postoperative saturations in 50 additional children to determine whether children have periods of desaturation in the postoperative period. The children underwent surgery usually associated with moderate to severe postoperative pain, and were treated with epidural, intravenous, or intramuscular opioids. In the group of 19 children mean (SD) preoperative oxygen saturation was 96.6% +/- 1.3%, and the mean postoperative saturation was 95.7% +/- 1.2%. The average change was 0.88% +/- 1.52%. The 95% confidence interval of the paired difference was 0.13% to 1.6%. There was no significant difference in the percent of monitored time that the patients spent with an oxygen saturation less than 95%, 90%, 85%, or 80%. In the 50 children monitored only in the postoperative period, mean (SD) saturation was 97.8% +/- 1.9%. The data show that, in contrast to some reports in adults, this group of children did not have multiple episodes of clinically significant oxygen desaturation in the postoperative period.

Adolescent↗
PubMed1994

Cerebral blood volume response to changes in carbon dioxide tension before and during cardiopulmonary bypass in children, investigated by near infrared spectroscopy.

Neurological impairment may occur following cardiopulmonary bypass (CPB) and the effect of CPB on cerebrovascular control may be important in the mechanism of cerebral injury. We have used near infrared spectroscopy (NIRS) to observe cerebral haemodynamics non-invasively before and during CPB. We measured the change in cerebral blood volume (CBV) associated with changing PaCO2 (CBVR). Patients (n = 19) were aged from 1 to 135 (median 14) months. The cerebral blood volume response was determined pre-operatively at normothermia under the influence of standardised anaesthesia employing isoflurane (up to ET conc 0.5%) and during steady-state hypothermic bypass (22-32 degrees C) at an arterial pump flow rate of 1.9-2.4 lm-2.min-1. Complete data was available for 10 patients. The relation between CBV, arterial carbon dioxide tension (PaCO2), mean arterial pressure (MAP) and central venous pressure (CVP) was examined using analysis of covariance (P < or = 0.05) was accepted as significant). The change in CBV associated with changing PaCO2 was corrected for the effects of MAP and CVP. Preoperatively the median CBVR was 0.130 (25th-75th percentile 0.079-0.243) ml.100 g-1.kPa-1 and during hypothermic bypass the median CBVR was 0.093 (25th-75th percentile 0.026-0.255) ml.100 g-1.kPa-1. These values were compared with our reference range derived for normal conscious children using the Kruskal-Wallis test. There was not statistically significant difference between the three groups (P = 0.35). These results, indicating preservation of CBVR during the conditions of anaesthesia and bypass used, are consistent with the observations of previous authors who measured cerebral blood flow response to carbon dioxide by a variety of other methods. Near infrared spectroscopy is proving to be a reliable, non-invasive technique for the investigation of cerebral haemodynamics during CPB.

Adolescent↗
PubMed1994

Filtration of fentanyl is not the cause of the elevation of arterial blood pressure associated with post-bypass ultrafiltration in children.

Modified ultrafiltration after cardiopulmonary bypass in children has been shown to be associated with an increase in arterial blood pressure. As part of a series of studies to investigate the possible causes of this blood pressure elevation, the hypothesis that if filtration was removing a significant amount of fentanyl, then the increase in blood pressure might be due to pain was proposed. Ten children, aged between 0.5 and 9.3 years (median 3.8 years), weighing 5.9 to 25.5 kg (median 15.7 kg), underwent corrective cardiac surgery (incorporating modified ultrafiltration). A standard anesthetic protocol was followed, with up to 78 micrograms/kg of fentanyl given prebypass for analgesia. After completion of cardiopulmonary bypass, modified ultrafiltration was commenced at 100 mL/min until a hematocrit of 35% was reached. Samples were taken of arterial blood (prefiltration, 3, 10, and 20 minutes postfiltration), the venous reservoir blood (prefiltration) and the filtrate (5 and 10 minutes into filtration). Hemodynamic data were recorded both prefiltration and postfiltration. The hemodynamic data showed the expected rise in both systemic arterial pressure and cardiac index after ultrafiltration. The plasma fentanyl concentrations did not significantly change after ultrafiltration: 1.59 to 12.39 ng/mL (median 6.27 ng/mL) prefiltration and 2.05 to 15.59 ng/mL (6.29 ng/mL) at 3 minutes, 2.22 to 12.64 ng/mL (6.87 ng/mL) at 10 minutes, and 1.83 to 11.52 ng/mL (5.85 ng/mL) at 20 minutes postfiltration.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia↗
PubMed1993

Cerebral hemodynamics during cardiopulmonary bypass in children using near-infrared spectroscopy.

We describe a new noninvasive method using near-infrared spectroscopy for monitoring cerebral hemodynamics during cardiopulmonary bypass in children. All patients were undergoing open heart operations for repair of congenital heart defects. Standardized anesthesia, an alpha-stat method of blood gas management, and nonpulsatile flow were used in all cases. All measurements during bypass were made after steady-state conditions had been reached. Cerebral blood flow was measured on 13 occasions in 4 children, aged between 4 and 10 months (median, 5 months). Values of 15.9 to 53.5 mL x 100 g-1 x min-1 were obtained. Cerebral blood volume was measured in 1 patient, aged 4 months. Volumes of 4.3 to 8.0 mL x 100 g-1 were obtained on bypass at full pump flow (2.4 L.min-1 x m-2). On bypass at half flow, the volume increased to 14.7 mL x 100 g-1. Change in cerebral blood volume with changing carbon dioxide tension (CBVR) was measured in 13 patients aged from 1 to 90 months (median, 13.5 months). Preoperatively, CBVR was 0.12 +/- 0.07 mL x 100 g-1 x kPa-1 and was independent of mean arterial pressure, which remained between 40 and 80 mm Hg in all cases. During hypothermic bypass (25 degrees C), CBVR was significantly reduced to 0.05 +/- 0.02 mL x 100 g-1 x kPa-1. In addition, there were three values at mean arterial pressure of lower than 40 mm Hg in which CBVR was negative (-0.04 +/- 0.01 mL x 100 g-1 x kPa-1). We conclude that near-infrared spectroscopy is useful for the noninvasive investigation of cerebral hemodynamics during cardiopulmonary bypass.

Carbon Dioxide↗
PubMed1993

Anaesthesia for airway obstruction in laryngo-onycho-cutaneous syndrome.

A 4-year-old boy with laryngo-onycho-cutaneous syndrome underwent excision of an obstructive vocal cord lesion. There is only one previous case report of laryngeal involvement in this syndrome but the anaesthetic management has not been reported. The anaesthetic management for microlaryngobronchoscopy and laser surgery in this child with upper airway obstruction is described.

Airway Obstruction↗
PubMed1991

Colorimetric end-tidal carbon dioxide monitoring during transfer of intubated children.

We report the use of a cheap, pocket-sized colorimeter to assess the end-tidal carbon dioxide concentration during transfer of intubated children. The device provided breath by breath confirmation of tracheal tube placement and identified one episode of reduced pulmonary perfusion. We would advocate the use of this detector to provide early warning of tracheal tube displacement during the transfer of children weighing more than 15 kg.

Body Weight↗
PubMed1990

Management of congenital tracheal stenosis in infants.

Until recently congenital tracheal stenosis presenting in infants was considered to be almost invariably lethal. With improved diagnostic, anaesthetic and surgical techniques virtually all cases are potentially curable. Prompt recognition and early surgical intervention, combined with skilled perioperative management, will result in a more favourable outcome.

Anesthesia, General↗
PubMed1982

Role of the brain and accessory olfactory system in the block to pregnancy in mice.

Selective lesions have been made to the receptors in the main and accessory olfactory systems. In the absence of the accessory receptors, female mice are not able to show a neuroendocrine response to male pheromones but are able to detect male odours which induce the response. In the absence of main olfactory receptors, such discrimination of male odours is not possible, but the neuroendocrine response resulting in a block to pregnancy is maintained. These experiments suggest that cognitive aspects of olfaction are not essential for pregnancy block to occur and that in mice the dual olfactory systems are functional as well as anatomically distinct. Moreover, strain recognition can occur at the level of the accessory olfactory system without the female being able to display a behavioural awareness of this 'recognition'.

Animals↗