The effect of acute normovolemic haemodilution on cerebral oxygenation.

Acute normovolemic haemodilution (ANH) may cause an imbalance in cerebral oxygen metabolism because it decreases the arterial oxygen content. This study was designed to investigate the effect of ANH on cerebral oxygenation. By using cerebral oximetry, the regional cerebral oxygen saturation (rSO2) was monitored during ANH in 26 patients without systemic illness (initial haematocrit = 42 +/- 1%). The rSO2 did not show a significant change until the Hct reached >30%. However, it decreased significantly thereafter to reach 88% of the baseline value when the ANH was completed with a Hct value of 24 +/- 1% (before ANH; 71 +/- 6% vs. after ANH; 62 +/- 4%, p < 0.01). In conclusion, an ANH can lead to a reduction in cerebral oxygenation when a patient's Hct goes below 30%.

The differential flow of epidural local anaesthetic via needle or catheter: a prospective randomized double-blind study.

The extent of epidural anaesthesia and pattern of spread of contrast medium, using different injection techniques, has not been well documented. Therefore, in this prospective, randomized double-blind study, the extent of anaesthesia and pattern of spread of contrast medium following an epidural bolus injection, via either a Tuohy needle or an epidural catheter, were compared. The study had two parts. In the first, 59 of 79 patients scheduled for a lower extremity operation under epidural anaesthesia were randomly allocated to one of the two groups. Anaesthesia was achieved with an epidural injection of 10 to 15 ml (including a 3 ml test dose) of 0.75% ropivacaine and fentanyl 25 microg via either a Tuohy needle (Group N, n=31) or a catheter (Group C, n=28). The level of sensory anaesthesia was recorded. In the second part, the remaining 20 patients were randomized to initially receive 5 ml of contrast medium via either a Tuohy needle (Group NE, n= 10) or a catheter (Group CE, n = 10). The extent of spread was recorded radiologically. Unilateral or missed blocks and additional dose requirement were absent in Groups N and C. No differences were found in the extent of sensory anaesthesia or the spread of contrast medium. Twenty per cent of catheter tips lay outside the lateral margins of the vertebral bodies. We found that an epidural bolus injection, via either a Tuohy needle or a catheter, made no difference in regard to spread of local anaesthetic or contrast medium in the epidural space.

Coronary artery spasm induced by carotid sinus stimulation during neck surgery.

We observed four transient episodes of marked ST-segment elevation in a 58-yr-old man with no history of coronary artery disease undergoing resection of a metastatic neck mass under general anaesthesia. Elevations of the ST segment were abrupt, with no change in arterial pressure or heart rate, and resolved spontaneously. When the carotid sinus was compressed directly, ST-segment elevation was noted 1 min after the onset of stimulation. After surgery, coronary angiography showed diffuse, slight narrowing of the distal bed of the posterolateral branch of the right coronary artery. Ergonovine caused total occlusion of the posterolateral branch of the right coronary artery with chest pain and ST-segment elevation, confirming the diagnosis of variant angina. The coronary artery spasm seems to have been provoked by vagal activation from carotid sinus stimulation during general anaesthesia.

Clinical trial of esmolol-induced controlled hypotension with or without acute normovolemic hemodilution in spinal surgery.

BACKGROUND: Drug-induced controlled hypotension (CH) combined with acute normovolemic hemodilution (ANH) is being widely used for blood conservation in surgical patients. The purpose of this study was to investigate the efficacy and safety of esmolol-induced CH combined with ANH (hematocrit down to 28%). METHODS: Thirty patients who were scheduled to receive spinal surgery were randomly divided into two groups: an esmolol-induced CH alone group (esmolol group, n=15) and a CH-ANH combined group (E-ANH group, n=15). Controlled hypotension was induced with esmolol 500 micro g/kg, followed by a continuous infusion of 0-300 micro g/kg/min to maintain mean arterial pressure at 55-65 mmHg. RESULTS: The mean infusion rate of esmolol in the esmolol-ANH group was 46+/-6 micro g/kg/min (mean+/-SD), which was significantly lower than the 77+/-9 micro g/kg/min used in the esmolol group (P<0.05). The number of units of homologous blood (packed RBC) transfused perioperatively was 2.2+/-0.6 units in the esmolol-ANH group, which was significantly less than 4.3+/-0.4 units used in the esmolol group (P<0.01). While O2 delivery decreased significantly during CH, O2 consumption remained unchanged in both groups. No complications resulted from CH or ANH in any of the groups. CONCLUSION: Our data suggest that ANH of moderate degree can be combined with esmolol-induced CH to improve blood conservation in surgical patients.