Chien-Chiang Liu

Low dose of intrathecal hyperbaric bupivacaine combined with epidural lidocaine for cesarean section--a balance block technique.

The present study was designed to develop a combined spinal/epidural anesthetic technique for cesarean section. We compared the effects of different doses of intrathecal hyperbaric bupivacaine (0.5%) combined with epidural lidocaine (2%). We attempted to interrupt somatosensory pathways with spinal anesthesia but to avoid acute high thoracic sympathetic block. The visceral afferent pathways were to be blocked relatively slowly with epidural lidocaine. Eighty term parturients were randomly divided into four groups. In Group A, 2.5 mg of bupivacaine intrathecally combined with 22.2 +/- 4.6 mL of lidocaine epidurally provided insufficient muscle relaxation. In Group B, 5 mg of bupivacaine with 10.1 +/- 2.0 mL of lidocaine resulted in satisfactory anesthesia with rapid onset and minimum side effects. Anesthesia in Group C (7.5 mg of bupivacaine) and Group D (10 mg of bupivacaine) was mostly due to spinal block. Complications included hypotension, nausea, and dyspnea. The combined spinal/epidural technique, using 5 mg of bupivacaine and with sufficient epidural lidocaine to reach a T4 level, had the advantages of both spinal and epidural anesthesia with few of the complications of either.

Propofol concentration monitoring in plasma or whole blood by gas chromatography and high-performance liquid chromatography.

We compared the measurement of propofol concentrations in plasma or whole blood by high-performance liquid chromatography (HPLC) to that of gas chromatography (GC). Blood samples were collected from patients who had received bolus injection or continuous infusion of propofol. The results showed that the two methods correlated well both in plasma and whole blood samples. However, significant biphasic differences of propofol concentrations between plasma and whole blood specimens were observed in the bolus injection group. Differences were larger in the infusion group. This discrepancy in concentrations resulted from the infusion or clearance of propofol, and the lag of redistribution across blood cell membranes. In conclusion, monitoring of propofol concentrations by the methods of GC and HPLC gives equivalent results. For propofol concentration monitoring, plasma samples are preferred, but immediate centrifugation is needed. (Anesth Analg 1995;81:175-8)

The Effect of Carrier Intravenous Fluid Speed on the Injection Pain of Propofol

P ain is a common side effect during propofol injection (1). Pain intensity can be reduced by injecting the drug into a larger vein in the antecubital fossa (1,2) or by diluting it with Intralipid or 5% dextrose (3,4). Nevertheless, injection into a fastflowing intravenous infusion did not have the expected effect (5,6). Moreover, it is reported that increasing diluent flow increases the pain associated with injection. There is less pain when the carrier intravenous (IV) fluid is stopped completely and only undiluted propofol is infused (7). Since this finding has not been proved, we designed this randomized, double-blind study to investigate whether the speed of carrier IV fluid would influence the intensity of pain.

Arteriovenous concentration differences of propofol during and after a stepdown infusion

To compare the arterial and venous concentration differences of propofol, six healthy adult patients received a propofol infusion by the Bristol three-stage manual stepdown technique. Both the mean arterial and venous concentrations of propofol remained relatively stable during the 40-min infusion. Simultaneous blood sampling from the artery and vein during the infusion period resulted in arterial concentrations significantly higher than venous concentrations. This relationship was reversed after stopping the infusion. The mean ± SD (range) venous to arterial concentration differences were −28.8% ± 18.3% (−71% to 1.7%) during the infusion and 18.9% ± 13.4%(−1.5% to 40.9%)after the infusion. We conclude that venous concentrations were not useful to estimate the arterial value during and after a stepdown propofol infusion. Arterial sampling is more appropriate in pharmacologic studies of propofol. (Anesth Analg 1994;79:1148–50)

AN ENHANCED PATIENT CONTROLLED ANALGESIA (EPCA) FOR THE EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY (ESWL)

The conventional patient-controlled-analgesia (PCA) can be further improved in terms of less drug consumption and better pain control if advanced feedback control algorithm is applied. The purpose of this research was to develop an enhanced patient-controlled analgesia (EPCA) using a hierarchical fuzzy logic control system with two levels and to apply it to patients in an extracorporeal shock wave lithotripsy (ESWL) operation. The two-level control system utilizes the conventional PCA as a basic level on the top of which is added an adaptive self-learning fuzzy logic control (SLFLC) level. Twenty-three patients involved in these clinical trials were to study the clinical effectiveness of EPCA for the management or pain during the ESWL process. A two-button device was designed, one button for severe pain (SP) and another for mild/moderate pain (MP) to investigate the frequencies of analgesic demands or delivery related to either severe or mild/moderate pain. The results show that the average percentage of demand/delivery to total demand/delivery due to MP is significantly higher than that due to SP, which implies the pain levels that most patients experienced were mostly mild to moderate in the ESWL process with the EPCA. The drug consumption of alfentanil with the EPCA is comparable to that with a fixed FLC; however, it is much lower than that with conventional PCA. In conclusion, the efficiency of the therapy, pain relief, and the patients’ satisfaction of pain management with the EPCA in the ESWL operation are superior to those with the conventional PCA.

Computer Control of Propofol Infusion using Quantitative and Qualitative Approaches

Abstract A two-level hierarchical structure using quantitative and qualitative approaches for controlling propofol infusion rate is proposed in this paper. The first level merges online measurements (i.e. systolic arterial pressure and heart rate) to interpret the primary depth of anaesthesia. The second level uses an average three-comparanent pharmacokinetic model to predict the propofol concentration in the blood of the patient Then, using fuzzy set theory to combine these two levels, a lookup table to administer the propafol infusion rate is obtained. This lookup table has given confidence of anaesthetists to perform automatic. control of propofol in clinical trials at the next stage.