Correlation of the oxygen cost of breathing and length of weaning from mechanical ventilation.

We studied 20 patients (ages 43 to 84 yr), whose forced vital capacity, peak negative inspiratory pressure and alveolar-arterial gradient indicated that they were unlikely to be withdrawn rapidly from mechanical ventilation. Their mean oxygen consumption (VO2) during controlled ventilation (CV) was 292 +/- 21 (SEM) ml/min. During spontaneous ventilation (SV) through endotracheal tube and ventilator circuit, the VO2 rose significantly (p less than .001) to 323 +/- 20 ml/min. The oxygen cost of breathing (OCB) (the difference in VO2 between CV and SV) and the OCB as a fraction of the oxygen consumed during SV (OCB/VO2 SV) both correlated significantly by linear regression analysis with the total time to wean in days (-11.6 + 0.93 for OCB, r = .79; and -12.6 + 293.1 for OCB/VO2 SV, r = .84, p less than .001 for both). As the OCB was correlated with the total wean time, this variable may be a useful index of the effect of many influences on the weaning process.

Left lateral vs. supine, wedged position for development of block after combined spinal-epidural anaesthesia for Caesarean section.

This prospective, randomised controlled trial compared a spinal block developing in the left lateral position (LL), after sitting a combined spinal-epidural for Caesarean section with the woman sitting -- using intrathecal hyperbaric bupivacaine and fentanyl -- with a block developing in the supine, wedged position (SW). The median (IQR) block onset times for loss of cold sensation to T4 bilaterally for LL and SW women were 15 (13-19) and 12 (10.8-14) min, respectively (p = 0.004). Unilateral blocks did not occur in the left lateral group. There were no other significant differences between groups, except the median [range] 1-min Apgar scores, which were 9 [8-10] and 9 [6-9] in the LL and SW groups, respectively (p = 0.04). In summary, the LL position is associated with a relatively slower block onset, but produces a spinal block with similar characteristics to that obtained in the SW position.