Concurrent expansion of plasma volume and left ventricular end-diastolic volume in patients after rapid infusion of 5% albumin and lactated Ringer's solution.

STUDY OBJECTIVE: To examine the effects of plasma volume expansion on plasma volume, left ventricular end-diastolic volume (LVEDV), and cardiac index (CI) after rapid fluid infusion, as knowledge of the degree of concordance between plasma and cardiac preload expansion could optimize LVEDV expansion without administering excessive fluid. DESIGN: Randomized, double-blinded study. SETTING: Academic community hospital. PATIENTS: 20 patients undergoing elective coronary artery bypass surgery. INTERVENTIONS: Patients were administered either 5% albumin (5 mL/kg) or lactated Ringer's solution (25 mL/kg) over 30 minutes, just before incision. MEASUREMENTS: Serial measurements of plasma volume, LVEDV by transesophageal echocardiography, and CI were recorded. MAIN RESULTS: Albumin expanded plasma volume and LVEDV to a similar degree (11.3% and 13.2%). In contrast, lactated Ringer's solution increased plasma volume more than LVEDV (21.7% vs 14.4%; P = 0.0005). Increased LVEDV significantly but poorly correlated with increased CI (r(2) = 0.2, P < 0.0001) for both fluids. However, LVEDV expansion was brief and returned to baseline or less within 30 minutes for both fluids despite continued plasma volume expansion and increased CI. Correspondingly, rates of decline from peak expansion were significantly faster for LVEDV than plasma volume expansion for both albumin (-1.9% + 1.9%/min vs -0.1% + 0.1%/min; P = 0.0008) and lactated Ringer's (-1.1% + 0.8%/min vs -0.4% + 0.2%/min; P = 0.006). CONCLUSIONS: Intravenous fluids increased LVEDV to a lesser extent and duration than did plasma volume expansion. Monitoring of LVEDV was a poor guide for fluid administration to maximize CI.

Prospective comparison of continuous femoral nerve block with nonstimulating catheter placement versus stimulating catheter-guided perineural placement in volunteers.

BACKGROUND AND OBJECTIVES: Stimulating catheter-guided perineural placement may potentially increase the success rate and quality of continuous femoral nerve block as compared with a nonstimulating catheter technique. These hypotheses have not been rigorously tested. METHODS: Twenty volunteers underwent placement of bilateral femoral nerve catheters in this prospective, randomized, double-blind study. For each side, a stimulating needle was advanced until quadriceps contractions were obtained at < or =0.5 mA. On one side, a stimulating catheter was advanced 4 to 5 cm beyond the needle tip while eliciting quadriceps contractions via the catheter. If quadriceps contractions decreased or disappeared, the catheter position was adjusted until quadriceps contractions could be elicited at < or =0.5 mA. On the contralateral side, an identical catheter was advanced 4 to 5 cm beyond the needle tip without attempts to elicit quadriceps contractions via the catheter. After bolus injection of 10 mL lidocaine 1%, ropivacaine 0.2% at 10 mL/h was continuously infused through both catheters for 4 hours. Success of femoral block was defined as loss of sensation to cold and pinprick stimuli. Quality of successful block was determined by tolerance to transcutaneous electrical stimulation and force dynamometry of quadriceps strength. RESULTS: Block success was 100% via the stimulating catheters versus 85% via the nonstimulating catheters (P =.07). Overall tolerance to transcutaneous electrical stimulation (P =.009) and overall depth of motor block (P =.03) was significantly higher in the stimulating catheter-guided femoral nerve blocks. CONCLUSIONS: In this volunteer study, there was no statistically significant difference in block success between the two techniques. However, stimulating catheter-guided placement provided an increased overall quality of continuous femoral perineural blockade. Further studies are needed to verify these observations in the clinical setting.

Physiology of spinal anaesthesia and practical suggestions for successful spinal anaesthesia.

There are numerous physiological effects of spinal anaesthesia. This chapter focuses on the physiological effects that are of clinical relevance to the anaesthesiologist, and provides suggestions for successful management of this simple and popular technique. The mechanisms and clinical significance of spinal-anaesthesia-induced hypotension, bradycardia and cardiac arrest are reviewed. The increasing popularity of ambulatory spinal anaesthesia requires knowledge that long-acting local anaesthetics, such as bupivacaine, impair the ability to void far longer than short-acting local anaesthetics, such as lidocaine. The importance of thermoregulation during spinal anaesthesia, and the clinical consequences of spinal-anaesthesia-induced hypothermia are reviewed. Effects of spinal anaesthesia on ventilatory mechanics are also highlighted. Lastly, the sedative and minimum-alveolar-concentration-sparing effects of spinal anaesthesia are discussed to reinforce the need for the judicious use of sedation in the perioperative setting.