Biomedical subjects

H N Chan

Publications and source records attributed to H N Chan.

4 recordsLinked to original sources

PubMed1986

Thiopentone levels during cardiopulmonary bypass. Changes in plasma protein binding during continuous infusion.

Plasma total and unbound concentrations of thiopentone were investigated during exponentially decreasing infusions in seven patients undergoing cardiopulmonary bypass. Total plasma thiopentone concentrations reached a plateau (10.2, SD 2.1 micrograms/ml) soon after the initial bolus dose and commencement of the infusion. Concentrations were maintained until the onset of cardiopulmonary bypass, whereupon total plasma thiopentone concentration fell abruptly to 50.0 (SD 5.8) percent of the prebypass level. The unbound fraction of thiopentone increased from 16.6 (SD 1.9) percent before bypass to a maximum of 29.3 (SD 5.6) percent during bypass (p less than 0.01), decreased to 22.9 (SD 3.3) percent at the end of bypass (p less than 0.01), but was still elevated 5-7 hours later (20.5, SD 2.5 percent). The result of the changes in binding was a smaller decline in unbound thiopentone concentration at the onset of bypass to 76.4 (SD 15.7) percent of the prebypass level. Also, unbound levels returned to the prebypass level by the end of bypass, whereas total levels remained low.

Adult↗

PubMed1985

Evaluation of infusion regimens for thiopentone as a primary anaesthetic agent.

Several multi-stage infusion regimens and a computer controlled exponentially decreasing infusion regimen were evaluated in twelve patients undergoing head and neck surgery or neurosurgery. Thiopentone dosage was based on the mean of pharmacokinetic parameter values from the literature and adjusted for each patient's lean body mass in order to rapidly achieve a predetermined plasma thiopentone concentration of 15 or 20 micrograms/ml in the period following the initial bolus dose to induce anaesthesia. Anaesthesia was satisfactory in all cases. Plasma thiopentone concentrations were maintained between 10-20 micrograms/ml during infusion in the five patients who received either a four or five stage infusion and in the six patients who received the exponential infusion, but not in the single patient who received a two-stage infusion. The mean recovery time was 111 min. The plasma concentrations of total and unbound thiopentone at awakening showed little intersubject variability, despite considerable differences in total dose and duration of infusion, suggesting the absence of acute tolerance to the drug. Plasma clearance of total thiopentone correlated strongly with calculated lean body mass and to a lesser extent with total body weight suggesting that lean body mass, in particular, should be an accurate predictor of thiopentone maintenance dose requirements. This study shows that it is feasible to use thiopentone as a primary anaesthetic agent during surgery by administering the drug either as an exponentially decreasing infusion or as an infusion comprising 4 or 5 stepwise decreasing rates.

Adolescent↗

PubMed1985

Pentobarbitone formation during thiopentone infusion.

The plasma concentrations and elimination half-life of pentobarbitone were determined in 14 surgical patients receiving a continuous, exponentially decreasing, infusion of thiopentone (mean total dose, 1.05 g; SD 0.34; mean duration of infusion 2.4 hours, SD 0.7) as the primary anaesthetic agent. The plasma pentobarbitone concentration increased gradually, to reach a maximum of 1.49 micrograms/ml (SD 0.61) at the end of the thiopentone infusion, which was 15.5 per cent (SD 6.04) of the plasma thiopentone concentration. The elimination half-life of pentobarbitone measured over the following 70 hours in nine of the patients was 34.3 hours (SD 8.2), which is within the range of values reported previously in several studies in which pentobarbitone was administered directly to volunteers. It was concluded that the formation of this active metabolite during 2-3 hour thiopentone infusions was unlikely to be of clinical relevance, but that significant concentrations may occur with longer thiopentone infusions.

Adolescent↗

PubMedDate not supplied

A clinical rationale for assessing rapid automatized naming in children with language disorders.

Three continuous rapid naming tasks (Semel, Wiig, & Secord, 1995) were administered to 2,450 American, English-speaking, academically achieving individuals with typical language development and intellectual ability (ages 6 to 21 years) and 136 individuals with primary language disorders (LD; ages 6, 7, 9, 11, 12, 15-16). Naming time in seconds differed significantly (p < .01) between the groups for color naming (Task 1) at age 12, shape naming (Task 2) at age 6, and color-shape naming (Task 3) at ages 6, 7, 9, and 12. Naming accuracy did not differ significantly (p > .01) between groups at the majority of the age levels compared. In the normative group, naming speed increased with age in a monotonic progression. The developmental trajectory in the LD group was essentially parallel, but elevated. The percentages of individuals who failed the naming-time criteria for Task 3 (color-shape naming) differed significantly in the two groups at all ages compared (p < .05). These findings indicate that the requirements for two-dimensional, continuous naming (Task 3 color-shape naming) resulted in reduced naming speed (longer total times) and interference with fluency in language production in about half of the clinical sample.

Adolescent↗