Interpretations of responses using the isolated forearm technique in general anaesthesia: a debate.

The isolated forearm technique (IFT) enables an otherwise paralysed patient to communicate awareness to the anaesthetist. We present a debate that focuses on how best to interpret IFT responses. On one side, Pandit argues that there is a range of response types from none through to movement initiated by the patient to alert the researcher. He also presents a de novo numerical scale by which IFT responses could be classed. Each response type reflects the underlying mental state (degree of unconsciousness), and he concludes that the effect of general anaesthesia on patients is not binary but heterogeneous. There can be mental states resulting from anaesthesia that produce adequate levels of conscious impairment sufficient for surgery to proceed, but in which a degree of wakefulness, including a capacity for later recall, is retained (a state previously termed 'dysanaesthesia'). A literature review of IFT (31 trials) is presented to support this assertion. In rebuttal, Russell and Wang argue that IFT response types are not so discrete, and that the IFT technique precludes higher levels of response. They argue that overinterpretation of IFT responses might in fact result in a greater risk of accidental awareness; a binary interpretation of the IFT response is the safest option. All authors agree that the IFT has a role in clinical practice and the study of anaesthetic mechanisms.

The ability of bispectral index to detect intra-operative wakefulness during isoflurane/air anaesthesia, compared with the isolated forearm technique.

Clinical signs are unreliable for guiding anaesthetic administration and it is suggested that using the bispectral index can improve anaesthetic delivery. In the current study, isoflurane administration was guided to a bispectral index range of 55-60. Intra-operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in response to commands. Thirty-four women underwent major gynaecological surgery with isoflurane/air and atracurium. Eleven women responded on 32 occasions with appropriate hand movements to commands given during surgery, of which the bispectral index detected 17 (sensitivity 53%). The bispectral index suggested consciousness 660 times in the absence of any movement responses (specificity 69%). The positive predictive value of the bispectral index was 3%. The median (IQR [range]) bispectral index value associated with an intra-operative response was significantly lower than that associated with eye opening after surgery: 60 (50-68 [36-83]) vs 77 (75-84 [59-90]), respectively (p = 2.25 × 10(-8)). Conversely, end-tidal isoflurane concentration was significantly higher at intra-operative response than at eye opening: 0.3 (0.3-0.4 [0.2-0.9]) vs 0.2 (0.1-0.2 [0.1-0.3]), respectively (p = 7.36 × 10(-8)). For patients who responded more than once during surgery, the bispectral index value associated with a response was not constant. No patient had recall for surgery or the taped commands, and only one could remember dreaming (a good dream). Titrating isoflurane to target a bispectral index range of 55-60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).

The ability of bispectral index to detect intra-operative wakefulness during total intravenous anaesthesia compared with the isolated forearm technique.

It has been suggested that monitoring during total intravenous anaesthesia should include aspects of brain function. The current study used a manually adjusted target-controlled infusion of propofol for anaesthesia, guided to a bispectral index range of 55-60. Intra-operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in responses to commands. Twenty-two women underwent major gynaecological surgery with total intravenous anaesthesia, propofol, remifentanil and atracurium. Sixteen women responded, on 80 occasions, with appropriate hand movements to commands during surgery, of which the bispectral index detected 47 (sensitivity 59%). The bispectral index suggested consciousness 220 times in the absence of movement responses (specificity 85%). The positive predictive value of a bispectral index response was 18%. While two women had vague recall about squeezing fingers, none had recall of surgery. For patients who responded more than once during surgery the bispectral index value associated with a response was not constant. Although there was no difference in the median (IQR [range]) effect site propofol concentration between intra-operative responses (2.0 (1.5-2.3 [1.2-4.0]) µg.ml(-1)) and eye opening after surgery (2.1 (1.7-2.8 [1.5-3.9]) µg.ml(-1)), the median (IQR [range]) bispectral index value at eye opening after surgery was significantly higher than that associated with responses during surgery: 75 (70-78 [51-93]) vs 61 (52-67 [37-80]) respectively, (p < 0.001). The manual control of propofol intravenous anaesthesia to target a bispectral index range of 55-60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).

A randomised comparison of 0.5% bupivacaine with a lidocaine/epinephrine/fentanyl mixture for epidural top-up for emergency caesarean section after "low dose" epidural for labour.

BACKGROUND: When extending a fentanyl-containing, low-dose labour epidural for emergency caesarean section it has been shown that there is no difference in time to surgical readiness between plain bupivacaine 0.5% and mixtures of lidocaine/epinephrine or lidocaine/bupivacaine/epinephrine. However, it is not known whether adding fentanyl to the lidocaine/epinephrine mixture would increase speed of onset or improve the efficacy of the mixture when topping up for an emergency caesarean section. METHODS: In a prospective, single blind study we compared plain 0.5% bupivacaine with a lidocaine/epinephrine/fentanyl mixture for extending previous low-dose epidural analgesia for emergency caesarean section in 68 patients. RESULTS: There was a significantly longer median preparation time for the mixture than for the single drug (3.0 v 1.25 min: P < 0.0005). The median onset time for block of T7 to touch from the start of the top-up was 13.8 min for the mixture and 17.5 min for plain bupivacaine. This difference was not statistically significant and was offset by the longer preparation time. No general anaesthetics were required for poor blocks and the need for other intraoperative supplementation was not significantly different between the groups (bupivacaine 5/34, lidocaine mixture 2/26). CONCLUSIONS: The use of a lidocaine/epinephrine/fentanyl mixture conferred no clear statistically significant benefit over the use of plain 0.5% bupivacaine when used to extend fentanyl containing low-dose labour epidural analgesia for emergency caesarean section, but the lidocaine solution is cheaper and less toxic than the alternatives.

Levels of anaesthesia and intraoperative pain at caesarean section under regional block.

This prospective study recorded levels of analgesia (loss of sharp pin prick sensation) and anaesthesia (loss of touch sensation) in 220 women during caesarean section under regional anaesthesia (70 epidurals, 150 spinals). At delivery the difference between analgesia and anaesthesia varied from 0-7 segments for epidurals and 0-9 segments for spinals. During surgery the level of anaesthesia at the time pain was experienced varied between T5 and T10. No patient with a level of anaesthesia which remained above T5 experienced pain. These results indicate that assessing the adequacy of block by sharp pin prick may be misleading and that in the absence of spinal or epidural narcotics a level of anaesthesia up to and including T5 is required to prevent pain during caesarean section.

A comparison of cold, pinprick and touch for assessing the level of spinal block at caesarean section.

The sensory block levels of 102 women undergoing caesarean section under spinal anaesthesia were assessed by four different methods: sharp pinprick (Neurotip tester pin), cold (ethyl chloride spray), touch (Neurotip tester pin), touch (ethyl chloride spray). While the data indicate a median difference of some 2 segments between the levels of block assessed by sharp pinprick or cold, and touch, there was no constant relationship between these levels of block within the group nor within individual patients: variable and at times very large differences in the levels of block assessed among these modalities existed: up to 10 segments (pinprick - touch); 11 segments (cold - touch). For any one individual, it is not possible to predict the level of block to touch from a known level of block to sharp pinprick or cold. To facilitate comparison of results across future studies it is suggested that block levels to touch sensation should always be reported. The results suggest that, for clinical purposes, there is no difference in outcomes whether Neurotip touch or ethyl chloride spray touch sensations are used. When using diamorphine 100 micrograms/mL mixed with bupivacaine 0.5% w/v in 8% dextrose, no patient felt any pain or discomfort provided the block to Neurotip or ethyl chloride touch sensations included T6 or above.

A double-blind assessment of the analgesic sparing effect of intrathecal diamorphine (0.3 mg) with spinal anaesthesia for elective caesarean section.

In a randomized double-blind study, 40 healthy women undergoing elective caesarean section with spinal anaesthesia received either 0.3 mg diamorphine or saline with bupivacaine 0.5% in 8% dextrose. The study recorded time to the first morphine demand delivered by patient-controlled analgesia (PCA), and total morphine requirement over 24 h. In addition pain, sedation, and pruritus were assessed by non-graduated visual analogue scores (VAS). Six patients in the diamorphine group required no postoperative morphine. The median (interquartile range) time to first morphine demand was significantly longer in the diamorphine group at 340 min (127, never used), than in the control group at 80 min (53, 159) (P 0.0006, 95% confidence interval for the difference between the medians is 60 to 1235 min). The use of PCA morphine over 24 h was significantly less in the diamorphine group than in the controls. The medians (interquartile ranges) were 5 (0, 36) mg vs 45 (26, 72) mg (P 0.0045, 95% confidence interval for the difference between the medians is 12 to 46 mg). In the diamorphine group, postoperative VAS for pain was significantly lower at 2 h and 3 h both at rest (P 0.0003, 0.003) and on moving (P 0.009, 0.002), at 8 h on moving (P 0.01), and at 12 and 24 h at rest (P 0.005, 0.029). Significantly more women suffered pruritus in the diamorphine group for the first 12 h after surgery (P 0.01).

Epidural abscess in association with obstetric epidural analgesia.

A 31-year-old woman gravida 4 para 2 who had received epidural analgesia during labour (duration of catheterization 6.5 h) was readmitted 8 days later with a complaint of flu-like symptoms, severe backache and numbness of her thighs. She had a sensory deficit from T4 to L1 and was unable to stand without support. The severe backache prevented adequate assessment of motor function. An MRI scan suggested an epidural mass. Surgical decompression by hemilaminectomy was carried out within 24 h of admission and revealed an epidural abscess. Culture of the drained pus grew Streptococcus pneumoniae. She made a complete recovery and was discharged home on the tenth day. This case illustrates the problem of diagnosing serious postnatal problems that arise following the now fashionable early discharge from hospital.

A survey of anaesthetic techniques used for caesarean section in the UK in 1997.

A prospective survey of anaesthesia for caesarean section was performed for the year 1 January to 31 December, 1997. Two hundred and fifty maternity hospitals were sent questionnaires from which 129 responses were obtained. The data provided information on anaesthesia for 60 455 caesarean sections. Overall 78% of sections were performed with regional anaesthesia: 47% single shot spinal; 22% epidural; 9% combined spinal epidural (CSE); 22% general anaesthesia. For elective caesarean sections (39% of all sections) regional anaesthesia was used for 87% of cases: 68% single shot spinal; 3% epidural; 15% CSE; 13% general anaesthesia. For emergency procedures regional anaesthesia was used for 72% of cases: 34% single shot spinal; 34% epidural; 4% CSE; 28% general anaesthesia. There was a wide range of regional anaesthesia use among the units, varying from an overall rate of 95% at one extreme to 41% at the other. Similarly, there was a wide range of conversion of regional anaesthesia to general anaesthesia, varying from 0% to 88%. Overall, 10.6% of the general anaesthetics were the result of regional to general anaesthesia conversion.

Epidural clonidine-fentanyl combination for labour analgesia: a comparison with bupivacaine-fentanyl.

This open study of 20 women compared epidural clonidine (300 microg)/fentanyl (100 microg) with bupivacaine (25 mg)/fentanyl (100 microg) in the provision of pain relief in labour. Sensory tests in the clonidine group revealed slight alterations in the appreciation of pin prick and temperature but motor power was unchanged. Analgesia after the first dose was similar in the two groups, but thereafter the analgesia provided by clonidine/fentanyl was less than that from bupivacaine/fentanyl. Despite the incomplete pain relief provided by clonidine/fentanyl, mothers appreciated their essentially normal sensations and muscle power. Midwives also commented favourably on the normal mobility of these labouring mothers. There was no difference between the two groups in the duration of labour or the condition of the infants.

A survey of anaesthesia for caesarean section.

In 1993 a postal survey of maternity hospitals within the UK was carried out to obtain data on the types of anaesthesia used for caesarean section. The poor response rate (79/226, 35%) reflects the paucity of data available in many centres. The data returned indicated a wide range of anaesthetic practice: from units with a general anaesthesia rate less than 10% to those with a general anaesthesia rate approaching 90%. Overall, during the 11-year period covered by the survey there was a significant reduction in the percentage use of general anaesthesia (77% in 1982 declining to 44% in 1992), but because of a 51% increase in the caesarean section rate the real reduction in the actual number of general anaesthetics used was modest (13%). If this holds true nationally, then factors other than a simple change from general anaesthesia to regional anaesthesia must contribute to the reduced maternal mortality from anaesthetic causes.