Trends but not individual values of central venous oxygen saturation agree with mixed venous oxygen saturation during varying hemodynamic conditions.

BACKGROUND: Previous studies found contradictory results regarding the question whether mixed venous oxygen saturation (Svo2) and central venous oxygen saturation (Scvo2) are equivalent. The inconsistency of study results may result from different study designs and different, partly questionable, statistical approaches. METHODS: The authors performed a prospective clinical trial comparing individual oxygen saturation values as well as the trend of values in blood from the superior vena cava (Scvo2), the right atrium (Srao2), and the pulmonary artery (Svo2) during varying hemodynamic situations. The subjects were 70 patients scheduled to undergo elective neurosurgical operations in the sitting position. Oxygen saturation was measured photospectrometrically in blood samples simultaneously taken at four different time points during supine and sitting positions. Statistical analysis was performed following the recommendations of Bland and Altman. RESULTS: Five hundred two comparative sets of measurements were obtained. Ninety-five percent limits of agreement ranging from +/-6.83 to +/-9.30% for single values were interpreted as clinically unacceptable. In contrast, correlations between changes of Svo2 and Scvo2 as well as of Svo2 and Srao2 were interpreted as clinically acceptable (R > or = 0.755, Pearson correlation coefficient; P < or = 0.0001). CONCLUSIONS: In this sample of patients, exact numerical values of Scvo2 and Srao2 are not equivalent to those of Svo2 in varying hemodynamic conditions. However, for clinical purposes, the trend of Scvo2 may be substituted for the trend of Svo2. In addition, previous studies investigating the agreement between Svo2 and Scvo2 were found to be lacking in their chosen statistical approaches.

Different F-wave recovery after neuromuscular blockade with pancuronium and mivacurium.

We performed this study to assess the recovery period after neuromuscular blockade by electromyographic F-wave analysis, a method that supplies more information about more proximal parts of the motor system than conventionally used methods, e.g., mechanomyography (MMG). In 20 neurosurgical ASA physical status I or II patients anesthesia was induced and maintained with IV fentanyl and midazolam. Patients were randomly assigned to receive either 0.25 mg/kg mivacurium (MV group, n = 10) or 0.1 mg/kg pancuronium (PC group, n = 10) intraoperatively. MMG monitoring of the adductor pollicis muscle was performed continuously. F waves were recorded at the abductor pollicis muscle of the contralateral hand at train-of-four (TOF) ratios of 0.1, 0.25, 0.5, 0.7, 0.75, 0.8, 0.85, 0.9, and 0.95. Recovery of F-wave amplitudes after neuromuscular blockade with pancuronium was significantly slower compared with mivacurium (P = 0.004) during the clinically important recovery period defined by MMG TOF ratios from 0.7 to 0.95. This electrophysiologic finding suggests a differential recovery of the motor system after administration of pancuronium and mivacurium not detected by MMG.

A randomized, controlled study of fluid management in infants and toddlers during surgery: hydroxyethyl starch 6% (HES 70/0.5) vs lactated Ringer's solution.

BACKGROUND: Volume replacement with hydroxyethyl starch (HES), a synthetic colloid, is widely accepted in adults, but only few data exist regarding its use in children. The aim of this study was to assess the effect of a low molecular weight HES solution (HES 70/0.5) compared with lactated Ringer's solution (LR) on haemoglobin levels as an indirect measure of plasma expansion in infants and toddlers, and its perioperative safety. METHODS: Sixty-four patients, aged 1-38 months, were allocated randomly to receive 20 ml x kg-1 body weight of either HES 70/0.5 or LR during the first hour of urological surgery lasting >2 h. Thereafter, only LR was infused to maintain haemodynamic stability. Intraoperative blood loss and administered fluid volumes were analysed. Haemoglobin levels were determined perioperatively and intraoperatively at completion of volume loading. Changes in body weight and the incidence of postoperative oedema were assessed 24 and 48 h after surgery. For the safety analysis, patients were monitored for 72 h. RESULTS: Intraoperative haemoglobin levels decreased significantly more with HES 70/0.5 (30 +/- 10 g.l-1) compared with LR (21 +/- 12 g.l-1) (P < 0.01). The overall administered fluid volumes during surgery did not differ between groups. The postoperative changes in body weight and incidence of postoperative oedema did not differ between groups. No anaphylactoid reactions, pruritus or adverse effects were observed during the study period. CONCLUSIONS: A larger decrease in haemoglobin levels in infants and toddlers after HES 70/0.5 (20 ml.kg-1) compared with LR indicates a more effective plasma expansion. HES might be considered as a volume expander in the paediatric population.

Failure to detect an unusual obstruction in a reinforced endotracheal tube with fiberoptic examination.

Obstruction of an endotracheal tube (ETT) is a potentially life-threatening event. We report an unusual obstruction of a reinforced ETT. The valve-like obstruction was caused by a partial detachment of the inner coating from the embedded spiral of the ETT. It led to an increase in inspiratory airway pressure, failure to detect end-expiratory CO(2), and generated a wheezing sound in forced expiration. Fiberoptic inspection, which is a recommended procedure for a suspected ETT-obstruction, failed to identify this detachment. Exchanging the defective ETT immediately resolved the critical clinical situation. The detachment was most likely caused by re-autoclavation of the ETT, which was a specified single-use product.

Propofol impairs the central but not the peripheral part of the motor system.

Propofol provides some degree of muscle relaxation. Previous studies have investigated the effects of propofol on either the central or peripheral parts of the motor system. In this study, we simultaneously assessed both central (spinal) and peripheral effects. In 15 patients, general anesthesia was induced and maintained with fentanyl and midazolam. Neuromuscular blocking drugs were not administered. To investigate the central portion of the motor system, we monitored spinal F waves, an electrophysiologic variable of alpha-motoneuron excitability. Direct electrophysiologic muscle responses (M waves) and mechanomyography were studied to detect the peripheral effects of propofol on neuromuscular transmission or muscle contraction strength. After baseline recordings, 3 IV boluses of propofol (2 times 1 mg/kg followed by 2 mg/kg) were administered at 5-min intervals. Mean F-wave amplitudes were significantly reduced compared with baseline measurements (mean +/- SD, 0.22 +/- 0.13 mV) after the first (0.13 +/- 0.08 mV; P < 0.05), second (0.08 +/- 0.09 mV; P < 0.05), and third (0.03 +/- 0.04 mV; P < 0.01) propofol injections. M-wave amplitudes and mechanomyography signals remained unchanged. Our data suggest that the central part, but not the peripheral part, of the motor system is impaired after bolus administration of propofol.