British Journal of Anaesthesia 1991; 67: 323-325
THE LOADING DOSE IN CONTINUOUS INFUSION EXTRADURAL ANALGESIA IN OBSTETRICS E. F. JANES AND J. W. McCRORY
The study was approved by the District Ethics Committee. Informed consent was obtained from all patients taking part. Sixty women requesting extradural analgesia during the first stage of labour were allocated randomly to one of three groups. The following exclusion criteria were applied: significant cardiovascular disease or hypertension requiring pharmacological control; antepartum haemorrhage; prior administration of opioids; cervical dilatation < 5 cm at the most recent vaginal examination. An i.v. infusion of Hartmanns solution was commenced, but no fluid preload was given. The extradural space was identified at the level of the L2-3 interspace, using a 16-gauge Tuohy needle and a loss of resistance to air technique. An KEY WORDS extradural catheter was passed cephalad, leaving Anaesthetics, local: bupivacaine. Anaesthetic techniques: 3 cm within the space after withdrawal of the extradural infusion, loading dose. Tuohy needle. The catheter wasfixedin place and the patient placed in the semirecumbent wedged position. Continuous extradural infusion of local anaesA solution of 0.08% bupivacaine solution was thetic solution has become an acceptable method prepared by dilution of 0.5% bupivacaine 8 ml in of pain relief in labour, several advantages being 0.9% saline to a volume of 50 ml. claimed in comparison with bolus administration All patients were given 0.5% bupivacaine 3 ml [1, 2]. Most published accounts of this technique as a test dose, followed by 0.08% bupivacaine recommend that a loading dose of local anaesthetic 1.5 ml in groups B and N, or 0.9 % saline in group (in addition to an initial test dose) be given before S, to flush the catheter and filter deadspace. After the infusion is started [1-3]. 5 min, accidental subarachnoid injection was In a study by Ewan [3], 53 % of hypotensive excluded. This was followed by extradural episodes occurred within 30 min of a loading dose administration of 0.08% bupivacaine solution of 0.5 % bupivacaine 8 ml. Macleod obtained a 8 ml (group B); 0.9 % saline solution 8 ml smaller incidence, without significantly affecting (group S); nothing (group N). onset of satisfactory analgesia, by using an equal An extradural infusion of 0.08% bupivacaine volume of 0.08% bupivacaine [4]. In the latter 20 ml h~x (delivered by electric syringe pump) was study the amount of bupivacaine in the loading dose was small (6.4 mg) compared with that in the test dose (15 mg). The object of this study was to determine if such a loading dose contributes to the E . F . J A N E S , M.B., CH.B.; J. W. MCCRORY, F.C.ANAES.; Department of Anaesthesia, Royal Victoria Infirmary, onset of analgesia by extra fluid volume or extra Newcastle upon Tyne NE1 4LP. Accepted for Publilocal anaesthetic. cation: April 10, 1991.
We have investigated the need for a loading dose of local anaesthetic before continuous extradural analgesia. After a standard test dose, patients received 0.08% bupivacaine 8 ml, isotonic saline 8 ml or nothing. A continuous infusion of 0.08% bupivacaine 20 ml h~1 was then commenced. The mean times to onset of satisfactory pain relief were similar in the first two groups, but prolonged significantly in the third. This group also required more interventions for inadequate analgesia, although not significantly so. Mean time to achieve highest level of block was significantly shorter in the first group.
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METHODS AND RESULTS
SUMMARY
BRITISH JOURNAL OF ANAESTHESIA
324
TABLE I. Mean (range) times to onset of analgesia and to highest level of block, and number of interventions in the three groups
Number of patients Time to onset of satisfactory analgesia (min) Mean time to highest level of block (min) Number with inadequate analgesia at 25 min Number requiring intervention for hypotension
Group S
Group N
19 12.7 (7-20) 33.7 (20-50) 1 4
20 13.3 (9-30) 46.5 (20-50) 2 2
20 24 (16-40) 53 (20-50) 7 2
intervention. A greater number of patients in group B required intervention for hypotension (defined as a greater than 25 % decrease in systolic arterial pressure) than in the two other groups. However, the total numbers of interventions for both pain and hypotension were too few to allow statistical analysis. The maximum height of block produced was similar in all groups (T7), but the time to achieve that level of block was significantly shorter in group B in comparison with the two other groups (P < 0.001), between which there was no difference. No patient in any group developed motor block of severity greater than 1 (subjective feeling of weakness) and there was no difference between the groups. COMMENT
The results suggest that onset of analgesia is delayed when a test dose alone is administered in a continuous extradural infusion technique. This may be anticipated, as it has been shown that fluid infused at a rate of 10 ml h"1 may take 30 min to cover diree lumbar segments [5]. Administration of a loading dose of 0.08% bupivacaine 8 ml significantly reduced the delay, but appeared to have no advantage compared with an equal volume of isotonic saline. It must be presumed that such a loading dose merely acts as a diluent for the local anaesthetic administered in the test dose, thereby "spreading" it within the extradural space. However, the extra local anaesthetic in the loading dose was not without effect, as a significant decrease in the time to achieve maximum block height was demonstrated. Dye injected into an established block has been shown to occupy the whole of the local anaesthetic sleeve present [5]. However, it has been suggested in a previous study [4] that the loading dose is "pushed" cephalad by the continuous infusion,
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 18, 2015
then started. After a further 20 min, an additional bolus of 0.08 % bupivacaine 8 ml was given if the patient found the resultant analgesia inadequate. This was repeated 10 min later if analgesia was still inadequate. After the test dose, heart rate and systolic and diastolic arterial pressures were measured using an automatic non-invasive recorder (Accutorr, Datex) at 1-min intervals for 5 min, at 5-min intervals for 25 min, and again at 1 h. The height of block was assessed by loss of cold discrimination using an ethyl chloride spray, and recorded at the same times as the cardiovascular variables. The severity of motor block was assessed using a four-point scale: 0 = no weakness; 1 = able to lift foot clear of bed; 2 = able to slide the foot up the bed i 3 = unable to slide the foot up the bed. The time to onset of satisfactory analgesia was recorded as the time from loading dose to the first non-painful contraction (in the patient's view). The study was concluded 1 h after administration of the test dose. Parametric data were analysed using one-way analysis of variance. The quantity of non-parametric data was inadequate to permit analysis. There were 19 subject in group B, 20 in group S and 20 in group N. One patient was excluded because of development of a unilateral block. There were no statistical differences between the groups in age, weight, height, parity or degree of cervical dilatation at the time of insertion of the extradural needle. There was no difference between mean times to onset of satisfactory analgesia in groups B (12.7 min) and S (13.3 min), but onset in group N (24 min) was prolonged significantly in comparison with the two other groups (P > 0.0001). In group N, seven patients (35 %) required one intervention for inadequate analgesia, compared with one patient in group B (5 %) and two in group S (10%) (table I). No patient required a second
Group B
EXTRADURAL INFUSION so that a greater concentration reaches the upper thoracic segments. In that study, a reduction in time to achieve maximum block height was obtained when the loading dose of bupivacaine was increased from 8 ml of 0.08% to 8 ml of a 0.5% solution. It would appear that the amount of local anaesthetic in the loading dose is related inversely to the time to achieve maximum height of block.
REFERENCES 1. Evans KRL, Carrie LES. Continuous epidural infusion of bupivacaine in labour; a simple method. Anaesthesia 1979; 34: 310-315. 2. Davies AO, Fettes IW. A simple safe method for continuous infusion epidural analgesia in obstetrics. Canadian Anaesthetists Society Journal 1981; 28: 484-^187. 3. Ewan A, McLeod DD, Madeod DM, Campbell A, Tunstall ME. Continuous epidural infusion analgesia in obstetrics. A comparison of 0.08% and 0.25% bupivacaine. Anaesthesia 1986; 41: 143-147. 4. Macleod DM, Tey HK, Byers GF, Dollery WC, Tunstall ME. The loading dose for continuous infusion epidural analgesia. Anaesthesia 1987; 42: 377-381. 5. Matouskova A, Hanson B, Rosmark U. Continuous miniinfusion of bupivacaine into the epidural space during labor. Part I: Radiographic visualisation of the epidural space. Acta Obstetrida et Gynaecologia Scandinavica 1979; (Suppl.) 83: 15-29.
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 18, 2015
In summary, a loading volume alone was necessary for acceptable onset of analgesia in a continuous extradural analgesia technique. Extra local anaesthetic decreased the time to achieve maximum block height, and increased the incidence of hypotension.
325
THE LOADING DOSE IN CONTINUOUS INFUSION EXTRADURAL ANALGESIA IN OBSTETRICS E. F. JANES AND J. W. McCRORY
The study was approved by the District Ethics Committee. Informed consent was obtained from all patients taking part. Sixty women requesting extradural analgesia during the first stage of labour were allocated randomly to one of three groups. The following exclusion criteria were applied: significant cardiovascular disease or hypertension requiring pharmacological control; antepartum haemorrhage; prior administration of opioids; cervical dilatation < 5 cm at the most recent vaginal examination. An i.v. infusion of Hartmanns solution was commenced, but no fluid preload was given. The extradural space was identified at the level of the L2-3 interspace, using a 16-gauge Tuohy needle and a loss of resistance to air technique. An KEY WORDS extradural catheter was passed cephalad, leaving Anaesthetics, local: bupivacaine. Anaesthetic techniques: 3 cm within the space after withdrawal of the extradural infusion, loading dose. Tuohy needle. The catheter wasfixedin place and the patient placed in the semirecumbent wedged position. Continuous extradural infusion of local anaesA solution of 0.08% bupivacaine solution was thetic solution has become an acceptable method prepared by dilution of 0.5% bupivacaine 8 ml in of pain relief in labour, several advantages being 0.9% saline to a volume of 50 ml. claimed in comparison with bolus administration All patients were given 0.5% bupivacaine 3 ml [1, 2]. Most published accounts of this technique as a test dose, followed by 0.08% bupivacaine recommend that a loading dose of local anaesthetic 1.5 ml in groups B and N, or 0.9 % saline in group (in addition to an initial test dose) be given before S, to flush the catheter and filter deadspace. After the infusion is started [1-3]. 5 min, accidental subarachnoid injection was In a study by Ewan [3], 53 % of hypotensive excluded. This was followed by extradural episodes occurred within 30 min of a loading dose administration of 0.08% bupivacaine solution of 0.5 % bupivacaine 8 ml. Macleod obtained a 8 ml (group B); 0.9 % saline solution 8 ml smaller incidence, without significantly affecting (group S); nothing (group N). onset of satisfactory analgesia, by using an equal An extradural infusion of 0.08% bupivacaine volume of 0.08% bupivacaine [4]. In the latter 20 ml h~x (delivered by electric syringe pump) was study the amount of bupivacaine in the loading dose was small (6.4 mg) compared with that in the test dose (15 mg). The object of this study was to determine if such a loading dose contributes to the E . F . J A N E S , M.B., CH.B.; J. W. MCCRORY, F.C.ANAES.; Department of Anaesthesia, Royal Victoria Infirmary, onset of analgesia by extra fluid volume or extra Newcastle upon Tyne NE1 4LP. Accepted for Publilocal anaesthetic. cation: April 10, 1991.
We have investigated the need for a loading dose of local anaesthetic before continuous extradural analgesia. After a standard test dose, patients received 0.08% bupivacaine 8 ml, isotonic saline 8 ml or nothing. A continuous infusion of 0.08% bupivacaine 20 ml h~1 was then commenced. The mean times to onset of satisfactory pain relief were similar in the first two groups, but prolonged significantly in the third. This group also required more interventions for inadequate analgesia, although not significantly so. Mean time to achieve highest level of block was significantly shorter in the first group.
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 18, 2015
METHODS AND RESULTS
SUMMARY
BRITISH JOURNAL OF ANAESTHESIA
324
TABLE I. Mean (range) times to onset of analgesia and to highest level of block, and number of interventions in the three groups
Number of patients Time to onset of satisfactory analgesia (min) Mean time to highest level of block (min) Number with inadequate analgesia at 25 min Number requiring intervention for hypotension
Group S
Group N
19 12.7 (7-20) 33.7 (20-50) 1 4
20 13.3 (9-30) 46.5 (20-50) 2 2
20 24 (16-40) 53 (20-50) 7 2
intervention. A greater number of patients in group B required intervention for hypotension (defined as a greater than 25 % decrease in systolic arterial pressure) than in the two other groups. However, the total numbers of interventions for both pain and hypotension were too few to allow statistical analysis. The maximum height of block produced was similar in all groups (T7), but the time to achieve that level of block was significantly shorter in group B in comparison with the two other groups (P < 0.001), between which there was no difference. No patient in any group developed motor block of severity greater than 1 (subjective feeling of weakness) and there was no difference between the groups. COMMENT
The results suggest that onset of analgesia is delayed when a test dose alone is administered in a continuous extradural infusion technique. This may be anticipated, as it has been shown that fluid infused at a rate of 10 ml h"1 may take 30 min to cover diree lumbar segments [5]. Administration of a loading dose of 0.08% bupivacaine 8 ml significantly reduced the delay, but appeared to have no advantage compared with an equal volume of isotonic saline. It must be presumed that such a loading dose merely acts as a diluent for the local anaesthetic administered in the test dose, thereby "spreading" it within the extradural space. However, the extra local anaesthetic in the loading dose was not without effect, as a significant decrease in the time to achieve maximum block height was demonstrated. Dye injected into an established block has been shown to occupy the whole of the local anaesthetic sleeve present [5]. However, it has been suggested in a previous study [4] that the loading dose is "pushed" cephalad by the continuous infusion,
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 18, 2015
then started. After a further 20 min, an additional bolus of 0.08 % bupivacaine 8 ml was given if the patient found the resultant analgesia inadequate. This was repeated 10 min later if analgesia was still inadequate. After the test dose, heart rate and systolic and diastolic arterial pressures were measured using an automatic non-invasive recorder (Accutorr, Datex) at 1-min intervals for 5 min, at 5-min intervals for 25 min, and again at 1 h. The height of block was assessed by loss of cold discrimination using an ethyl chloride spray, and recorded at the same times as the cardiovascular variables. The severity of motor block was assessed using a four-point scale: 0 = no weakness; 1 = able to lift foot clear of bed; 2 = able to slide the foot up the bed i 3 = unable to slide the foot up the bed. The time to onset of satisfactory analgesia was recorded as the time from loading dose to the first non-painful contraction (in the patient's view). The study was concluded 1 h after administration of the test dose. Parametric data were analysed using one-way analysis of variance. The quantity of non-parametric data was inadequate to permit analysis. There were 19 subject in group B, 20 in group S and 20 in group N. One patient was excluded because of development of a unilateral block. There were no statistical differences between the groups in age, weight, height, parity or degree of cervical dilatation at the time of insertion of the extradural needle. There was no difference between mean times to onset of satisfactory analgesia in groups B (12.7 min) and S (13.3 min), but onset in group N (24 min) was prolonged significantly in comparison with the two other groups (P > 0.0001). In group N, seven patients (35 %) required one intervention for inadequate analgesia, compared with one patient in group B (5 %) and two in group S (10%) (table I). No patient required a second
Group B
EXTRADURAL INFUSION so that a greater concentration reaches the upper thoracic segments. In that study, a reduction in time to achieve maximum block height was obtained when the loading dose of bupivacaine was increased from 8 ml of 0.08% to 8 ml of a 0.5% solution. It would appear that the amount of local anaesthetic in the loading dose is related inversely to the time to achieve maximum height of block.
REFERENCES 1. Evans KRL, Carrie LES. Continuous epidural infusion of bupivacaine in labour; a simple method. Anaesthesia 1979; 34: 310-315. 2. Davies AO, Fettes IW. A simple safe method for continuous infusion epidural analgesia in obstetrics. Canadian Anaesthetists Society Journal 1981; 28: 484-^187. 3. Ewan A, McLeod DD, Madeod DM, Campbell A, Tunstall ME. Continuous epidural infusion analgesia in obstetrics. A comparison of 0.08% and 0.25% bupivacaine. Anaesthesia 1986; 41: 143-147. 4. Macleod DM, Tey HK, Byers GF, Dollery WC, Tunstall ME. The loading dose for continuous infusion epidural analgesia. Anaesthesia 1987; 42: 377-381. 5. Matouskova A, Hanson B, Rosmark U. Continuous miniinfusion of bupivacaine into the epidural space during labor. Part I: Radiographic visualisation of the epidural space. Acta Obstetrida et Gynaecologia Scandinavica 1979; (Suppl.) 83: 15-29.
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 18, 2015
In summary, a loading volume alone was necessary for acceptable onset of analgesia in a continuous extradural analgesia technique. Extra local anaesthetic decreased the time to achieve maximum block height, and increased the incidence of hypotension.
325
