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Biomedical subjects

T E Oh

Publications and source records attributed to T E Oh.

At least 37 records · Page 2Linked to original sources
PubMed1995

Superimposed inspiratory work of the Siemens Servo 300 ventilator during continuous positive airway pressure.

OBJECTIVE: To compare the superimposed inspired work of breathing (SIW) of the Siemens Servo 300 ventilator with the Siemens Servo 900 C ventilator. DESIGN: Comparisons made at continuous positive airway pressure (CPAP) levels of 0, 4, and 8 cmH2O, and at trigger sensitivities of -1 and -2 cmH2O, and flow triggering. SETTING: General intensive care unit in a University teaching hospital. PATIENTS: 7 patients receiving CPAP. At all levels of CPAP, the SIW was significantly less with the Siemens Servo 300 ventilator as compared to the Siemens Servo 900 C ventilator despite similar trigger sensitivities. No significant difference was found in the SIW of the Servo 300 ventilator when comparing trigger sensitivities of -1 cmH2O, -2 cmH2O, and flow triggering. Different levels of CPAP had no effect on SIW. CONCLUSIONS: The Siemens Servo 300 ventilator entails less superimposed inspiratory work of breathing than the Siemens Servo 900 C ventilator.

Adult↗
PubMed1995

Pulmonary consequences of carbon dioxide insufflation for laparoscopic cholecystectomies.

Twenty patients having laparoscopic cholecystectomies were studied for changes in thoracic and lung compliance at 5, 10 and 15 mmHg of intra-abdominal pressure. Fifteen mmHg of intra-abdominal pressure decreased the thoracic and the lung static compliance by 49 and 39% respectively. This was unaffected by the degree of head elevation. During the procedure the end-tidal carbon dioxide increased by a mean of 1.6 kPa at 1 h and 2.0 kPa at 2 h. This did not appear to be related to either the mean intra-abdominal pressure or the total volume of carbon dioxide insufflated. The physiological changes and implications for anaesthetic practice are considered.

Abdomen↗
PubMed1995

An adaptation of the objective structured clinical examination to a final year medical student course in anaesthesia and intensive care.

The Department of Anaesthesia and Intensive Care at the Chinese University of Hong Kong provides a 4 week course in our specialty for final year medical students. Our curriculum covers basic concepts in anaesthesia and intensive care, management of common medical emergencies and the safe performance of basic practical skills. For the last 4 years we have used an adaptation of the Objective Structured Clinical Examination to assess learning. Question stations included the use of manikins to assess practical skills, such as cardiopulmonary resuscitation and airway management, identification and description of the use of equipment and interpretation of clinical scenarios and investigations. We believe that our adaptation of the Objective Structural Clinical Examination is better than traditional methods of examination and it has allowed us to identify deficiencies in our teaching methods. The Objective Structured Clinical Examination has been well received by our students and is perceived by them to be a fair reflection of their level of knowledge and skill attainment during the course.

Anesthesiology↗
PubMed1995

Severe hyperventilation and respiratory alkalosis during pressure-support ventilation: report of a hazard.

A 53-year-old woman with a flaccid quadriparesis developed severe hyperventilation and respiratory alkalosis during pressure-support ventilation. A gas leak in the ventilator system caused a loss of positive end-expiratory pressure and autocycling of the ventilator. Large ventilator breaths were then delivered because a high level of pressure support was set in a patient with low respiratory impedance. The complication is rare and its occurrence requires a combination of patient and equipment factors. Awareness of the responsible factors will promote detection and prevention of the hazard.

Alkalosis, Respiratory↗
PubMed1995

Pressure support ventilation during isoflurane anaesthesia.

We have studied the respiratory effects of 5 and 10 cmH2O pressure support ventilation during anaesthesia with 1.5% end-tidal concentration of isoflurane in nine healthy, spontaneously breathing, adult patients. Some of the patients demonstrated an irregular respiratory pattern with periods of apnoea and we therefore went on to study a further seven patients with a continuous 500 s recording of airflow. Pressure support ventilation augmented mean (SD) tidal volume from 212 (56) ml to 360 (88) ml at 5 cmH2O and to 509 (108) ml at 10 cmH2O (n = 16, p < 0.05). Mean (SD) respiratory rate decreased from 26 (6) min-1 to 22 (6) min-1 at 5 cmH2O and 17 (5) min-1 at 10 cmH2O pressure support (n = 16, p < 0.05). Mean (SD) inspiratory work of breathing decreased from 1.77 (0.70) J. min-1 to 0.31 (0.36) J.min-1 at 5 cmH2O and 0.16 (0.26) J.min-1 at 10 cmH2O pressure support ventilation (n = 9, p < 0.05). Analysis of the respiratory rhythm in the second group of seven patients revealed an oscillating respiratory pattern in four patients at 5 cmH2O and six of the seven patients at 10 cmH2O pressure support ventilation. The metabolic advantage of the decreased work of breathing during pressure support ventilation during anaesthesia is unlikely to balance the disadvantage of an oscillating respiratory rhythm.

Adolescent↗
PubMed1995

Leukotriene B4 as a marker of cerebral dysfunction.

It has been postulated that leukotriene B4 is involved in the pathogenesis of postischaemic cerebral oedema. We set out to determine if a relationship exists between jugular bulb leukotriene B4 and other indicators of cerebral ischaemia. No association could be demonstrated for either intracranial pressure, jugular bulb blood oxygen saturation or lactate oxygen index. Our results provide insufficient evidence to suggest that measurement of leukotriene B4 has any place in the management of head-injured patients.

Adolescent↗
PubMed1995

Accuracy of the tonometric function of recycled gastric tonometer catheters.

We investigated the accuracy of recycled gastric tonometer catheters, using a prospective laboratory model, within the Intensive Care Unit of a University teaching hospital. Ten used tonometer catheters and three new catheters were exposed to known constant PCO2 levels between 23-65 torr (3.06-8.66 kPa) in a gas mixing chamber, at a temperature of 35.5-38 degrees C and a relative humidity > 95%. The tonometer balloons were primed with normal saline, and after a 30-minute equilibration time, the saline was sampled for PCO2 measurements. Steady-state PCO2 (PCO2(SS)) and gastric mucosal pH (pHi) values were derived using a correction factor and the Henderson-Hasselbalch equation. There was no difference in the mean or distribution of PCO2(SS) values between recycled and new catheters. The PCO2(SS) values of recycled catheters were within the 95% confidence limits of those of new catheters. Individual catheter values did not differ significantly from each other (ANOVA P = 0.05). Using an arterial HCO3- value of 21 mmol/l, the calculated pHi values of used catheters varied < 1.5% of the mean pHi of new catheters. The tonometric performance of recycled gastric tonometer catheters was similar to that of new catheters when tested in vitro.

Carbon Dioxide↗
PubMed1994

A prospective evaluation of pharmacokinetic model controlled infusion of propofol in paediatric patients.

We have tested a published algorithm for pharmacokinetic model controlled infusion of propofol to supplement 67% nitrous oxide for general anaesthesia in Chinese children aged 4-10 yr. Initially we studied 10 children undergoing minor procedures with spontaneous ventilation; mean duration of surgery was 38 min and mean propofol infusion rate 497 micrograms kg-1 min-1. The precision of the model was 24.8% and bias -18.5%. The model was revised using an iterative linear least squares regression procedure and the revised model tested prospectively in another 20 children. The precision of the revised model was 21.5% (range in individuals 8.4-43.1%) and bias -0.1% (range -30 to 42%). Mean propofol infusion rate required to maintain anaesthesia was 474 micrograms kg-1 min-1 (range 125-737 micrograms kg-1 min-1). The mean blood concentration required for satisfactory anaesthesia was 6.6 micrograms ml-1 (range 3-11 micrograms ml-1) and the mean blood concentration at the time of waking, which occurred 40 min after switching off the infusion, 0.86 microgram ml-1 (range 0.40-1.45 micrograms ml-1). Our patient population required different pharmacokinetic variables from those in the previous study. Recovery was slow because of the high infusion rates required to maintain satisfactory anaesthesia and large difference between the blood concentration required for anaesthesia and that at which waking occurred.

Algorithms↗
PubMed1994

Recovery after propofol infusion anaesthesia in children: comparison with propofol, thiopentone or halothane induction followed by halothane maintenance.

We have compared the recovery profiles of 163 healthy Chinese children after general anaesthesia for minor surgical procedures. Patients were allocated randomly to receive one of four anaesthetic techniques: propofol infusion for induction and maintenance using a pharmacokinetic model-controlled syringe pump set initially at a target concentration of 8 micrograms ml-1 and then adjusted according to clinical requirements; propofol 2.5-3.5 mg kg-1, thiopentone 4-5 mg kg-1 or 2-3% halothane for induction of anaesthesia followed by 1-2% halothane for maintenance of anaesthesia. All patients breathed a mixture of 70% nitrous oxide in oxygen through a laryngeal mask airway and received an appropriate regional anaesthetic block. Recovery was assessed using the time to achieve full Steward score, open eyes on command, orientation and the time required to complete a simple puzzle. Recovery was slowest with the propofol infusion (mean 39.8 (SD 12.9) min when eyes opened on command). The recovery times were significantly shorter with the three other techniques (propofol bolus 21.9 (9.9) min, thiopentone 23.4 (11.3) min, halothane 20.1 (8.9) min), and the choice among these three methods had no significant influence on the recovery profile.

Anesthesia Recovery Period↗
PubMed1994

Midazolam and flumazenil pharmacokinetics and pharmacodynamics following simultaneous administration to human volunteers.

Resedation after antagonism of midazolam sedation with flumazenil may occur because some individuals have rapid elimination of flumazenil but slow elimination of midazolam. To determine whether there are parallel or divergent rates of elimination of the two drugs between individuals, the pharmacokinetic profiles of midazolam and flumazenil were studied simultaneously in 12 adult male volunteers. Free drug concentration data for the two drugs were incorporated into a receptor occupancy model and psychomotor testing was performed and correlated with receptor occupancy. Variation was found between individuals in the pharmacokinetics of the two drugs. There were significant correlations between Cltot (P < 0.01) but not in t1/2 alpha, t1/2 beta, Vc, or VDss. In individuals, midazolam elimination half-life ranged from less than half that of flumazenil to more than three times that of flumazenil. There was a relatively poor, although statistically significant linear correlation found between calculated receptor occupancy and critical flicker fusion frequency, r = 0.50, P < 0.01, and linear analogue scales of sedation r = 0.56, P < 0.005; and anxiolysis, r = 0.54, P < 0.005. There is divergence in the disposition and elimination of midazolam and flumazenil in some individuals. A benzodiazepine receptor occupancy model is useful for predicting the consequent differences in clinical effect when the drugs are given together.

Adult↗
PubMed1994

Factors affecting outcome following cardiopulmonary resuscitation.

Many patients who receive cardiopulmonary resuscitation (CPR) for cardiac arrest do not survive to leave hospital. Factors associated with adverse outcomes include unwitnessed cardiac arrest in general wards, particularly at night, prolonged resuscitation, asystole, associated disorders (e.g. sepsis, malignancy, renal failure, and left ventricular dysfunction), absent pupillary responses, hypoxaemia, low PetCO2 during resuscitation, and severe acid base imbalance. Outside hospitals, cardiac arrests result in more favourable outcomes if they occur at work, and bystander CPR and early defibrillation are initiated. On admission to ICU, likely predictors of death or severe neurological disability include prolonged coma, impaired brainstem reflexes, and persistent convulsions. Experience with cerebrospinal fluid enzymes and electrophysiological measurements is limited. Multivariate scoring systems are not sufficiently reliable. The importance of hyperglycaemia, the required level of CPR training, and the appropriateness of responding to some cases, remain debatable.

Acid-Base Imbalance↗
PubMed1994

Difficult weaning from mechanical ventilation.

Weaning from mechanical ventilation may be influenced by factors relating to equipment, techniques and procedures. Criteria to initiate weaning and predictors of weaning outcome are generally unreliable, but mechanical work of breathing, the tidal volume: frequency ratio and the inspiratory pressure: maximal inspiratory pressure ratio may anticipate those likely to fail weaning. The optimal weaning ventilatory mode is not known, but intermittent mandatory ventilation, pressure support ventilation, and continuous positive pressure ventilation are the most commonly used. The resistances of individual components of breathing circuits are extremely important. Blow-by heated humidifiers and ventilators which compensate for the impedances of their inspiratory demand valves impose clinically acceptable spontaneous breathing loads. Close monitoring, adequate respiratory muscle rest, attention to mineral deficiencies, nutrition and pulmonary hygiene are also important parts of the weaning process.

Forecasting↗
PubMed1994

The respiratory depressant effect of morphine. A comparative study in three ethnic groups.

The respiratory response to carbon dioxide was measured in 130 ASA 1 adult male patients from three ethnic groups, European, Nepalese, and Chinese, both before and after premedication with intramuscular morphine sulphate (200 micrograms.kg-1 body weight). Satisfactory results were obtained from 125 patients. Overall, there was no ethnic difference in the effect of morphine on the respiratory response to carbon dioxide, but initially the Chinese group appeared to be more sensitive in their response to carbon dioxide than the Europeans and Nepalese. However, there was a significant correlation between respiratory response to carbon dioxide and pulse rate and on restricting analysis to those patients with a pulse rate equal to or less than 72 beat.min-1, the ethnic difference in carbon dioxide response disappeared. It was concluded that there were no ethnic differences in the respiratory response to carbon dioxide before or after morphine in male Europeans, Nepalese and Chinese but that the respiratory response to carbon dioxide may be influenced by long term physical training.

Adolescent↗
PubMed1993

Bedside measurement of work of breathing.

This paper describes the technique of measuring work of breathing, presented at the 13th International Symposium on Computers in Clinical Medicine and Anaesthesiology, Rotterdam, June 1992. Measuring work of breathing has clinical uses in the Intensive Care Unit. Oxygen consumption does not truly reflect work of breathing. Mechanical work of breathing can be measured by recording continuous pressure and flow and integrating the resultant power. This method is facilitated at the bedside with the use of a PC computer and a spreadsheet program. It is further simplified by software to measure the area under the inspiratory pressure: volume loop.

Anesthesiology↗
PubMed1993

Effects of PEEP on dynamic hyperinflation in patients with airflow limitation.

We have studied the effects of extrinsically applied PEEP (PEEPe) and intrinsic PEEP (PEEPi) on lung volume and peak airway pressure (Paw,peak) in 10 patients with airflow limitation during mechanical ventilation. PEEPe was applied in 2-4 cm H2O increments until values greater than PEEPi were reached. Total lung hyperinflation was quantified by measuring the expired volume resulting from deflation (starting at end inspiration) until cessation of expiratory flow. The previous expired tidal volume was subtracted from this volume to obtain the change in functional residual capacity (delta FRC), the hyperinflation resulting from PEEPi and PEEPe. PEEPi (0.49-1.66 kPa) was demonstrated in all patients before the application of PEEPe and correlated with delta FRC (r = 0.71), with delta FRC increasing by 582 ml/kPa PEEPi (P < 0.05). PEEPe at pressures less than PEEPi increased delta FRC by (mean) 186 (SEM) 34 ml/kPa PEEPe (P < 0.05) and increased Paw,peak by 0.6 (0.12) kPa/kPa PEEPe (P < 0.05). In contrast, PEEPe at pressures greater than PEEPi, increased delta FRC by 695 (128) ml/kPa PEEPe (P < 0.05) and Paw,peak by 1.8 (0.26) kPa/kPa PEEPe. We conclude that PEEPe may be applied cautiously at values less than PEEPi when clinically indicated, but the application of PEEPe at values greater than PEEPi may substantially aggravate lung hyperinflation.

Aged↗
PubMed1993

Cardiovascular effects of i.v. induction in children: comparison between propofol and thiopentone.

We have compared the haemodynamic responses to i.v. propofol 2.5 mg kg-1 with those to thiopentone 5.0 mg kg-1 in 41 healthy Chinese children at induction of anaesthesia. They were allocated to four groups according to their age and induction agent received: group 1 < 2 yr, propofol, n = 9; group II < 2 yr, thiopentone, n = 9; group III 2-12 yr, propofol, n = 12; group IV 2-12 yr, thiopentone, n = 11. Anaesthesia was maintained by spontaneous ventilation with 70% nitrous oxide and 0.5% halothane in oxygen. Arterial pressure and heart rate were monitored by automatic oscillotonometer. Stroke volume was measured by two-dimensional echocardiography and pulse Doppler. Measurements were made before induction and at 1-min intervals for 5 min after induction. The reduction in mean arterial pressure was significantly greater after propofol (28-31%) than after thiopentone (14-21%) (P = 0.001). The reduction in cardiac index (10-15%) after induction was not significantly different between the two agents (P = 0.122). Baroreflex mediated increases in heart rate and systemic vascular resistance were less after propofol than after thiopentone. The baroreceptor reflex was more attenuated in children aged less than 2 yr than in older children.

Anesthesia, Inhalation↗