Hypotension during central neural block may occur by three main mechanisms: decrease in venous return (in turn influenced by posture, bleeding and inferior vena cava compression), vasodilatation and decreased cardiac output. It is also important to recognize that, occasionally, other factors play a part. Bladder distension during central nerve block has been shown to produce hypotension inappropriate to the level of block [48, 62] and vagal overactivity may contribute in the unsedated patient. Preventive measures to reduce the likelihood of hypotension include correction of hypovolaemia, restriction of the upper level of block, use of a slight head-down tilt to maintain venous return and judicious use of sedation, especially in anxious patients. In the obstetric patient, the single most important factor in eliminating hypotension is the use of full left-lateral tilt. Mechanical methods to improve venous return by compressing the legs are not particularly helpful. Volume loading does not guarantee maintenance of arterial pressure and excessive fluid may be harmful in patients with bladder neck obstruction or at risk of pulmonary oedema. The administration of up to 1 litre before surgery may be particularly advisable if significant blood loss is expected (no matter what the anaesthetic technique), but colloid solutions do not have clear proven benefit over crystalloid. The prevention or treatment of hypotension induced by central block by administration of large volumes of fluid is a more contentious subject, although the practice is widespread. Review of the literature has shown that many studies have been poorly designed and the results have often been contradictory, even in such basic principles as the incidence of hypotension in control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

We have compared, in a randomized, double-blind study, the pharmacokinetics of ropivacaine and bupivacaine during labour. Total and free plasma concentrations of ropivacaine and bupivacaine were measured after the first of two extradural doses. The main dose was 20 mg (test dose) and 30 mg, with a top-up dose of 25 mg when requested. After the main dose, Cpmax (total) of ropivacaine (0.50 mg litre-1) was similar to that of bupivacaine (0.48 mg litre-1). At 20 min, Cpmax (free) of ropivacaine (0.04 mg litre-1) was higher than that of bupivacaine (0.02 mg litre-1) (P = 0.0025). The clinical effectiveness of the block was similar in both groups.

Forty women having requested extradural analgesia for labour were allocated randomly to receive 0.5% ropivacaine or bupivacaine 10 ml as the main dose. When a top-up was requested, 0.25% ropivacaine or bupivacaine 10 ml was given (the same drug as the main dose). The study ended when a second top-up was requested or delivery of the baby occurred. Pain from two contractions was assessed before extradural block by visual analogue scoring and thereafter with every contraction. Sensory block and motor block were assessed at intervals. The only significant difference between the groups was a shorter onset of pain relief after the main dose of bupivacaine; there were no other significant differences in duration, onset of pain relief after top-up, quality of analgesia, spread of sensory block and motor block between the groups. Cardiovascular changes and neonatal outcome were similar in the two groups.

SummaryOver a period of one year, a weekly telephone survey identified 161 stable patients with weaning delay (defined as patients ventilated for at least 6 h per day for more than 2 weeks) in intensive care units in the Northern Region of England. Their median age was 69 years (range 21-88 years). Sixty patients (37%) were admitted with medical conditions, 89 (55%) were postoperative patients, whereas 12 (8%) were surgical but required non-operative admission. One hundred and thirty (89%) were weaned and discharged from the intensive care unit during the year. Twenty-two (14%) died and two were transferred to the home ventilation service. Seven patients remained ventilated in intensive care at the end of the study period. Twenty patients (12%) required more than 28 days of respiratory support. These patients occupied on average 6.0% of available intensive care unit beds in the region. This study suggests that in the Northern Region of England there are a significant number of stable but ventilator-dependent patients occupying intensive care beds.

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