British Journal of Anaesthesia 1990; 64: 430-435
POSTOPERATIVE ANALGESIA AFTER PAEDIATRIC ORCHIDOPEXY: EVALUATION OF A BUPIVACAINE-MORPHINE MIXTUREf A. R. WOLF, D. HUGHES, A. WADE, S. J. MATHER AND C. PRYS-ROBERTS
received a caudal block of 0.125% bupivacaine with or without morphine 0.05 mg kg'1. Analgesia, side-effects, ventilatory frequency and oxygen saturation (SaOl) were recorded after operation. None of the 15 patients receiving the bupivacaine-morphine mixture required postoperative opioids, whereas eight of 15 patients receiving bupivacaine alone needed additional opioid analgesia. The incidence of side effects after surgery was similar for the two groups and there was no detectable difference in ventilatory frequency or SaOl.
PATIENTS AND METHODS
After approval from the Hospital Ethics Committee and informed parental consent, we studied 30 children, aged 9 months to 11 yr, undergoing elective orchidopexy. The children were otherwise healthy (ASA status I or II), fasted and unpremedicated. EMLA cream was applied to both hands at least 90 min before surgery; anaesthesia was induced with diiopentone and atropine and maintained with nitrous oxide, oxygen and enflurane given by face mask. After induction of anaesthesia and before surgery, KEY WORDS Anaesthetic techniques: caudal. Anaesthesia: paediatric. patients were placed in the left lateral position and Anaesthetics local: bupivacaine. Analgesics: morphine. Pain- a 20-gauge needle inserted into the caudal space postoperative. through the sacrococcygeal ligament using an aseptic technique. If no blood or CSF was aspirated, a 0.75-ml kg"1 caudal injection of either Caudal injections of bupivacaine are used 0.125 % bupivacaine or10.125 % bupivacaine with routinely to provide analgesia after lower ab- morphine 0.05 mg kg" was given by random dominal and urogenital surgery in children [1,2]. allocation, in each case the composition being However, the analgesic effects of the caudal block often terminate early in the postoperative period A. R. WOLF*, M_A., M.B., B.CHIR., F.F.A.R.C.S.; D . H U G H E S , and supplementary i.m. injections of opioids are M.D., M 3 . , CH.B., F.F.A.R.C.S.; A. WADE, B.SC. J S. J. MATHER, required [3]. Recent studies [4-7] have reported M.B., B.S., F.F.A.R.C.S.; C. PRYS-ROBERTS, D.M., PH.D., the use of caudal morphine in children for F.F.A.R.C.S., F.F.A.R.A.C.S.; Sir Humphry Davy Department of University of Bristol, Bristol Royal Hospital for postoperative analgesia with doses varying from Anaesthesia, Sick Children, Bristol BS2 8HW. Accepted for Publication: 1 0.03 to 0.1 mgkg" . The greater doses provided September 1, 1989. longer-lasting analgesia than bupivacaine, but *Address for correspondence: Sir Humphry Davy Departside-effects (nausea, vomiting, urinary retention ment of Anaesthesia, University of Bristol, Bristol Royal and pruritus) were common and a case of Infirmary, Bristol BS2 8HW. f T h e pilot study to this paper was presented to the ventilatory depression in a 2-yr-old child after Anaesthetic Research Society and subsequently published in 1 a 0.1-mgkg" injection of caudal morphine has British Journal of Anaesthesia 1989; 62: 221P.
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
been reported [8]. Smaller doses have few sideeffects, but are short-acting and unreliable. We The value of combining morphine with bupi- therefore compared the analgesic efficacy and vacaine for caudal analgesia was investigated. side-effects of a combination of bupivacaine and Thirty children, undergoing orchidopexy, morphine with bupivacaine alone.
SUMMARY
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
TABLE I. Patient data and duration of anaesthesia and surgery (median and ranges)
Age (yr) Weight (kg) Duration of procedure (min)
Bupivacaine alone
Bupivacainemorphine
5.2(1.2-10.5) 16.9(11.5-28.0) 45(15-60)
5.0 (0.9-10.6) 17.0 (9.0-12.0) 45(20-60)
metrix pulse oximeter. The data were stored on a BBC microcomputer for subsequent analysis using an established data compression technique [10]. Statistical significance was determined with the Fisher exact test or chi-square analysis with Yates' correction where appropriate for nominal data, the Mann—Whitney U test for non-parametric data and Student's t test for parametric data. The mean and the variance of the computerized ventilatory data were compared using the Z and Ftest [11]. RESULTS
There were 15 patients in each treatment group; mean ages and weights and duration of anaesthesia The nursing staff recorded ventilatory fre- and surgery were similar for both groups (table I). quency every 30 min for the first 6 h after There were significant differences between the operation and then hourly for a further 6 h. groups in the requirement for postoperative i.m. In addition, ventilatory frequency and oxygen analgesia (fig. 1). Three patients in the bupisaturation were recorded using a Hewlett-Packard vacaine alone group required nalbuphine during ECG/impedance pneumography unit and a Novo- the first 1 h after operation, and the cumulative 25
§20 5 15 c £ "S 10
E £ 2
5
0
B M 1
B
B M 4
12
M
B . M. 20
Time (h) FIG. 1. Postoperative analgesic requirements for bupivacaine alone Q3) and bupivacaine-morphine (M). • = Injected nalbuphine; n = oral paracetamol.
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
known only to one person who was then excluded from further contact with the patient. After surgery, the patients were transferred to a recovery area and observed for 1 h before returning to the general ward. The time from induction of anaesthesia to the end of surgery, and the time from the end of surgery to spontaneous opening of the eyes were noted. The quality of analgesia was assessed hourly for the first 6 h and then every 3 h for 20 h, by trained observers who remained unaware of the treatment given. The assessments were based on an observational scoring system modified from Hannallah and colleagues [9], using five criteria: crying, movement, agitation, posture and localization of pain. Each criterion scored 0-2 to give a summed score of 0-10. A total score less than 4 was taken as an indication of adequate analgesia, based on previous experience with this technique [3]. Nalbuphine 0.3 mg kg"1 i.m. or oral paracetamol ISmgkg" 1 was given by the observers as they felt appropriate. Postoperative recordings included the times of administration of nalbuphine and paracetamol, the time to first micturition after surgery and the incidence of side effects such as nausea, vomiting and pruritis. Patients were discharged home the following morning, provided they had passed urine and were fully mobile without pain.
431
BRITISH JOURNAL OF ANAESTHESIA 15
c 10
I -O 5
FIG. 2. Number of patients remaining pain free after surgery without requiring i.m. nalbuphine. *P < 0.05; **P < 0.01. • = Bupivacaine alone; S = bupivacainc-morphine. TABLE II. Postoperative recovery and incidence of side effects
Bupivacaine alone Time to awakening (min) (median (range)) Nausea/vomiting Persistent vomiting Pruritis Time to micturition (h) (mean (SD)
15 (5-30)
Bupivacainemorphine 10 (5-35)
2 0
« 2 2
8.3(3.1)
8.3 (3.4)
"5
number of patients given nalbuphine over 20 h was 8 for the bupivacaine alone group and 0 for the bupivacaine and morphine group. This difference in analgesic requirement was significant (P < 0.05). In addition, three patients required a second injection of nalbuphine during the study period, bringing the total number of administrations of nalbuphine to 11 for the bupivacaine alone group compared with none for the combined bupivacaine and morphine group. Paracetamol requirements were similar for the two groups: after 20 h, 10 patients in the bupivacaine alone group and seven in the bupivacaine and morphine group had received oral paracetamol. Two patients in the bupivacaine alone group were given additional doses of paracetamol. Correspondingly, fewer patients in the bupivacaine alone group maintained adequate postoperative analgesia (a pain score of less than 4) in the absence of nalbuphine (fig. 2). After 20 h, only six of the 15 patients in the bupivacaine alone group had received adequate analgesia, com-
pared with 13 for the bupivacaine and morphine group. The addition of morphine to the caudal block did not delay recovery from anaesthesia and the mean time to the first micturition after surgery was similar for both groups (table II). Five patients in the bupivacaine alone group and six in the bupivacaine and morphine group had episodes of vomiting or retching. Two patients in both groups had three or more episodes of vomiting in the postoperative period. Nasal pruritus occurred in two patients, both in the bupivacaine and morphine group, but this did not distress the patients. Ventilatory frequencies observed by the nursing staff for the first 12 h after operation were similar for both groups (fig. 3). The recorded ventilatory data derived from impedance measurements were analysed separately as data from the first 1 h and data from 1 h to 12 h, because it was felt that ventilatory depression caused by systemic absorption of morphine would be most noticeable during the first hour. The data for an individual patient were extracted as the time spent at each ventilatory frequency and summed for all die patients in the group to derive the total time at each frequency. Absolute values were converted into percentages to allow comparison between groups. We were unable to detect differences in ventilation, and mean ventilatory frequency and variance in the population were similar for the two groups, both in the first 1 h and from 1 h to 12 h (fig. 4). Patients were given oxygen by face mask for a variable period in the recovery ward, and oxygen
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
Time (h)
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
433
40 35 30 25 20 15 6
10
12
Time (h) FIG. 3. Observed ventilatory frequency over the first 12 h after operation (means, SD). = Bupivacaine alone; — = bupivacaine—morphine. 10
0
•JU
-r—r40 20 25 Ventilatory frequency (b.p.m.) FIG. 4. Ventilatory frequency from 1 h to 12 h after operation recorded from impedance monitor. • = Bupivacaine alone; 0 = bupivacaine-morphine. 15.
saturation data were therefore not stored in the first 1 h. The median oxygen saturation for 1-12 h for each patient was extracted and combined for each treatment group to give a mean and standard deviation of the median values. The averaged median value of oxygen saturation for the bupivacaine alone group was slightly higher than the bupivacaine and morphine group, with a value of 98.0% (SD 1.6) compared with 96.7% (SD 2.0), but the difference was not statistically significant and an oxygen saturation of less than 85 % was
not recorded in any patient. Some traces showed isolated decreases in saturation to less than 90%, but these were transient and not associated with a particular treatment group. DISCUSSION
This study demonstrates that the addition of morphine 0.05 mg kg"1 to a 0.125% solution of bupivacaine improved significantly both quality and duration of pain relief after orchidopexy
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
10
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BRITISH JOURNAL OF ANAESTHESIA
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without increasing side effects noticeably. The of patients required further analgesia. This conpresence of morphine in the caudal space did not firms the view that increasing the concentration of result in any detectable differences in oxygen bupivacaine to more than 0.125% [3] or the saturation or ventilatory frequency, although volume to more than 0.75 ml kg"1 [15] offers little more sophisticated tests such as the ventilatory therapeutic advantage for this particular proresponse to carbon dioxide may show depression cedure. of ventilatory drive after extradural opioids [12]. Morphine given by the caudal route is not Minor changes in the carbon dioxide-ventilation merely an exotic alternative to the i.m. route. response curve are of little clinical significance Systemic uptake of caudal morphine is rapid and and probably unrelated to the sudden onset of provides analgesia in the immediate operative and severe ventilatory depression that has been re- postoperative period. However, 1 h after caudal ported occasionally after extradural morphine in injection of morphine 0.05 mg kg"1, plasma conadults. Ventilatory monitoring or close obser- centration is less than 12 ng ml"1 [16], and is vation is needed immediately after caudal admin- unlikely to be associated with significant analgesia. istration of morphine, but it is important to set a Therefore, the prolonged postoperative pain relief time limit to the risk period for ventilatory following caudal morphine is caused probably by depression. The estimate must be conservative, a specific action on the spinal cord. but take into account available clinical experience. Caudal morphine may offer analgesic advantVentilatory depression occurring more than 6 h ages over bupivacaine alone, but the incidence of after extradural administration is extremely rare side effects increases in parallel with both the [13] and associated with factors that include large duration of analgesia and the dose of morphine and repeated doses of extradural morphine, [7]. In this study we were unable to detect an additional opioid or sedative drugs, patients with increase in side-effects caused by addition of significant systemic disease (ASA III/IV) and morphine. The overall incidence of vomiting in rostral delivery of the opioid. The administration this study (11 of 30 (36%)) seems high, but is of a very small dose of morphine at the caudal consistent with previous postoperative studies on limits of the extradural space as a single injection orchidopexy in children. The children were not under light general anaesthesia without additional encouraged actively into attempts at micturition. sedative or opioid drugs minimizes the above risk A more pressurized approach might have resulted factors. We believe, therefore, that when a single in differences between the groups, but we felt that dose technique is used for caudal morphine, passive observation was clinically more realistic. special monitoring can be discontinued safely Caudal morphine has not been established as a after 6 h, provided the patient has shown no signs of excessive sedation within the preceeding 6 h, routine technique in paediatric anaesthesia and and that the patient remains under nursing this may reflect partly the fear of potentially supervision for a total of 12 h after the injection. serious side effects. Minimizing the dose of If additional doses of morphine are given either morphine to provide effective analgesia without caudally or systemically within the first 12 h, side effects is therefore an important goal in the development of the technique. Local anaesthetics monitoring should be continued accordingly. may potentiate the analgesic effects of spinal Caudal blocks with bupivacaine alone can morphine, resulting in improved analgesia at provide excellent analgesia in the early post- lower doses. A recent study in mice [17] has operative period after orchidopexy, but may allow shown that addition of bupivacaine to morphine the false impression that die patient will remain increases the intensity of antinociception with a pain free thereafter. Longer inpatient studies, time course similar to that of morphine alone, but lasting 8 h or more, have shown that, as the caudal of greater potency and reliability. In addition, block wears off, systemic opioid analgesia is doses of morphine or bupivacaine that on their required often [3, 14]. In this present study, own have little or no antinociception may produce eight of 15 patients (53%) receiving 0.125% an enhanced effect when combined. bupivacaine alone required supplementary i.m. analgesia in the postoperative period. These REFERENCES results are similar to a previous study on orchido1. McGown RG. Caudal analgesia in children; five hundred pexy [14] in which, despite the use of higher cases for procedures below the diaphragm. Anaesthesia concentrations and volumes of bupivacaine, 53 % 1982; 37: 808-819.
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
10. 11. 12. 13. 14. 15.
16.
17.
orchopexy pain in pediatric ambulatory surgery. Anesthesiology 1987; 66: 832-834. Dodds C, Wade A. Compression of data from pulse oximetry by delta modulation. British Journal of Anaesthesia 1988; 60: 343P. Glantz SA. Primer of Biostatistics, 1st Edn. New York: McGraw-Hill, 1981. Attia JA, Ecoffey C, Sandouk P, Gross JB, Samii K. Epidural morphine in children: pharmocokinetics and CO, sensitivity. Anesthesiology 1986; 65: 590-594. Rawal N, Arner S, Gustafsson LL, Allvin R. Present state of extradural and intrathecal opioid analgesia in Sweden. British Journal of Anaesthesia 1987; 59: 791-799. Bramwell RGB, Bullcn C, Radford P. Caudal block for post-operative analgesia in children. Anaesthesia 1982; 37: 1024-1028. Malviya S, Fear DW, Roy WL, Lcrman J. Effect of the volume of 0.125% bupivacaine on the effectiveness of caudal analgesia in children. Anesthesia and Analgesia 1989; 68: S179. Wolf AR, Hobbs AJ, Hughes D, Prys-Roberts C. Combined bupivacaine/morphine caudals: duration of analgesia and plasma morphine concentration. Anesthesiology 1989; 70: A1015. Akerman B, Arwestrom E, Post C. Local anesthetics potentiate spinal morphine antinociception. Anesthesia and Analgesia 1988; 67: 943-948.
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2. Broadman LM, Hannallah RS, Norden JM, McGiU A. " Kiddie caudals ": experience with 1154 consecutive cases without complications. Anesthesia and Analgesia 1987; 66: S191. 3. Wolf AR, Valley RD, Fear DW, Roy WL, Lennan J. Bupivacaine for caudal analgesia in infants and children: the optimal effective concentration. Anesthesiology 1988; 69: 102-106. 4. Jensen BH. Caudal block for post-operative pain relief in children after genital operations. A comparison between bupivacaine and morphine. Ada Anaesthesiologica Scandinavica 1981; 25: 373-375. 5. Krane EJ, Jacobson LE, Lynn AM, Parrot C, Tyler DC. Caudal morphine for postoperative analgesia in children: a comparison with caudal bupivacaine and intravenous morphine. Anesthesia and Analgesia 1987; 66: 647-653. 6. Rosen K, Rosen D, Bank E. Caudal epidural morphine for control of pain following open heart surgery in children. Anesthesiology 1989; 70: 418-^120. 7. Krane EJ, Jacobson LE, Tyler DC. Caudal epidural morphine in children: a comparison of three doses. Anesthesiology 1988; 69: A763. 8. Krane EJ. Delayed respiratory depression in a child after caudal epidural morphine. Anesthesia and Analgesia 1988; 67: 79-82. 9. Hannallah RS, Broadman LM, Belman AB, Abramowitz MD, Epstein BS. Comparison of caudal and ilioinguinal/ iliohypogastric nerve blocks for the control of post-
435
POSTOPERATIVE ANALGESIA AFTER PAEDIATRIC ORCHIDOPEXY: EVALUATION OF A BUPIVACAINE-MORPHINE MIXTUREf A. R. WOLF, D. HUGHES, A. WADE, S. J. MATHER AND C. PRYS-ROBERTS
received a caudal block of 0.125% bupivacaine with or without morphine 0.05 mg kg'1. Analgesia, side-effects, ventilatory frequency and oxygen saturation (SaOl) were recorded after operation. None of the 15 patients receiving the bupivacaine-morphine mixture required postoperative opioids, whereas eight of 15 patients receiving bupivacaine alone needed additional opioid analgesia. The incidence of side effects after surgery was similar for the two groups and there was no detectable difference in ventilatory frequency or SaOl.
PATIENTS AND METHODS
After approval from the Hospital Ethics Committee and informed parental consent, we studied 30 children, aged 9 months to 11 yr, undergoing elective orchidopexy. The children were otherwise healthy (ASA status I or II), fasted and unpremedicated. EMLA cream was applied to both hands at least 90 min before surgery; anaesthesia was induced with diiopentone and atropine and maintained with nitrous oxide, oxygen and enflurane given by face mask. After induction of anaesthesia and before surgery, KEY WORDS Anaesthetic techniques: caudal. Anaesthesia: paediatric. patients were placed in the left lateral position and Anaesthetics local: bupivacaine. Analgesics: morphine. Pain- a 20-gauge needle inserted into the caudal space postoperative. through the sacrococcygeal ligament using an aseptic technique. If no blood or CSF was aspirated, a 0.75-ml kg"1 caudal injection of either Caudal injections of bupivacaine are used 0.125 % bupivacaine or10.125 % bupivacaine with routinely to provide analgesia after lower ab- morphine 0.05 mg kg" was given by random dominal and urogenital surgery in children [1,2]. allocation, in each case the composition being However, the analgesic effects of the caudal block often terminate early in the postoperative period A. R. WOLF*, M_A., M.B., B.CHIR., F.F.A.R.C.S.; D . H U G H E S , and supplementary i.m. injections of opioids are M.D., M 3 . , CH.B., F.F.A.R.C.S.; A. WADE, B.SC. J S. J. MATHER, required [3]. Recent studies [4-7] have reported M.B., B.S., F.F.A.R.C.S.; C. PRYS-ROBERTS, D.M., PH.D., the use of caudal morphine in children for F.F.A.R.C.S., F.F.A.R.A.C.S.; Sir Humphry Davy Department of University of Bristol, Bristol Royal Hospital for postoperative analgesia with doses varying from Anaesthesia, Sick Children, Bristol BS2 8HW. Accepted for Publication: 1 0.03 to 0.1 mgkg" . The greater doses provided September 1, 1989. longer-lasting analgesia than bupivacaine, but *Address for correspondence: Sir Humphry Davy Departside-effects (nausea, vomiting, urinary retention ment of Anaesthesia, University of Bristol, Bristol Royal and pruritus) were common and a case of Infirmary, Bristol BS2 8HW. f T h e pilot study to this paper was presented to the ventilatory depression in a 2-yr-old child after Anaesthetic Research Society and subsequently published in 1 a 0.1-mgkg" injection of caudal morphine has British Journal of Anaesthesia 1989; 62: 221P.
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
been reported [8]. Smaller doses have few sideeffects, but are short-acting and unreliable. We The value of combining morphine with bupi- therefore compared the analgesic efficacy and vacaine for caudal analgesia was investigated. side-effects of a combination of bupivacaine and Thirty children, undergoing orchidopexy, morphine with bupivacaine alone.
SUMMARY
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
TABLE I. Patient data and duration of anaesthesia and surgery (median and ranges)
Age (yr) Weight (kg) Duration of procedure (min)
Bupivacaine alone
Bupivacainemorphine
5.2(1.2-10.5) 16.9(11.5-28.0) 45(15-60)
5.0 (0.9-10.6) 17.0 (9.0-12.0) 45(20-60)
metrix pulse oximeter. The data were stored on a BBC microcomputer for subsequent analysis using an established data compression technique [10]. Statistical significance was determined with the Fisher exact test or chi-square analysis with Yates' correction where appropriate for nominal data, the Mann—Whitney U test for non-parametric data and Student's t test for parametric data. The mean and the variance of the computerized ventilatory data were compared using the Z and Ftest [11]. RESULTS
There were 15 patients in each treatment group; mean ages and weights and duration of anaesthesia The nursing staff recorded ventilatory fre- and surgery were similar for both groups (table I). quency every 30 min for the first 6 h after There were significant differences between the operation and then hourly for a further 6 h. groups in the requirement for postoperative i.m. In addition, ventilatory frequency and oxygen analgesia (fig. 1). Three patients in the bupisaturation were recorded using a Hewlett-Packard vacaine alone group required nalbuphine during ECG/impedance pneumography unit and a Novo- the first 1 h after operation, and the cumulative 25
§20 5 15 c £ "S 10
E £ 2
5
0
B M 1
B
B M 4
12
M
B . M. 20
Time (h) FIG. 1. Postoperative analgesic requirements for bupivacaine alone Q3) and bupivacaine-morphine (M). • = Injected nalbuphine; n = oral paracetamol.
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
known only to one person who was then excluded from further contact with the patient. After surgery, the patients were transferred to a recovery area and observed for 1 h before returning to the general ward. The time from induction of anaesthesia to the end of surgery, and the time from the end of surgery to spontaneous opening of the eyes were noted. The quality of analgesia was assessed hourly for the first 6 h and then every 3 h for 20 h, by trained observers who remained unaware of the treatment given. The assessments were based on an observational scoring system modified from Hannallah and colleagues [9], using five criteria: crying, movement, agitation, posture and localization of pain. Each criterion scored 0-2 to give a summed score of 0-10. A total score less than 4 was taken as an indication of adequate analgesia, based on previous experience with this technique [3]. Nalbuphine 0.3 mg kg"1 i.m. or oral paracetamol ISmgkg" 1 was given by the observers as they felt appropriate. Postoperative recordings included the times of administration of nalbuphine and paracetamol, the time to first micturition after surgery and the incidence of side effects such as nausea, vomiting and pruritis. Patients were discharged home the following morning, provided they had passed urine and were fully mobile without pain.
431
BRITISH JOURNAL OF ANAESTHESIA 15
c 10
I -O 5
FIG. 2. Number of patients remaining pain free after surgery without requiring i.m. nalbuphine. *P < 0.05; **P < 0.01. • = Bupivacaine alone; S = bupivacainc-morphine. TABLE II. Postoperative recovery and incidence of side effects
Bupivacaine alone Time to awakening (min) (median (range)) Nausea/vomiting Persistent vomiting Pruritis Time to micturition (h) (mean (SD)
15 (5-30)
Bupivacainemorphine 10 (5-35)
2 0
« 2 2
8.3(3.1)
8.3 (3.4)
"5
number of patients given nalbuphine over 20 h was 8 for the bupivacaine alone group and 0 for the bupivacaine and morphine group. This difference in analgesic requirement was significant (P < 0.05). In addition, three patients required a second injection of nalbuphine during the study period, bringing the total number of administrations of nalbuphine to 11 for the bupivacaine alone group compared with none for the combined bupivacaine and morphine group. Paracetamol requirements were similar for the two groups: after 20 h, 10 patients in the bupivacaine alone group and seven in the bupivacaine and morphine group had received oral paracetamol. Two patients in the bupivacaine alone group were given additional doses of paracetamol. Correspondingly, fewer patients in the bupivacaine alone group maintained adequate postoperative analgesia (a pain score of less than 4) in the absence of nalbuphine (fig. 2). After 20 h, only six of the 15 patients in the bupivacaine alone group had received adequate analgesia, com-
pared with 13 for the bupivacaine and morphine group. The addition of morphine to the caudal block did not delay recovery from anaesthesia and the mean time to the first micturition after surgery was similar for both groups (table II). Five patients in the bupivacaine alone group and six in the bupivacaine and morphine group had episodes of vomiting or retching. Two patients in both groups had three or more episodes of vomiting in the postoperative period. Nasal pruritus occurred in two patients, both in the bupivacaine and morphine group, but this did not distress the patients. Ventilatory frequencies observed by the nursing staff for the first 12 h after operation were similar for both groups (fig. 3). The recorded ventilatory data derived from impedance measurements were analysed separately as data from the first 1 h and data from 1 h to 12 h, because it was felt that ventilatory depression caused by systemic absorption of morphine would be most noticeable during the first hour. The data for an individual patient were extracted as the time spent at each ventilatory frequency and summed for all die patients in the group to derive the total time at each frequency. Absolute values were converted into percentages to allow comparison between groups. We were unable to detect differences in ventilation, and mean ventilatory frequency and variance in the population were similar for the two groups, both in the first 1 h and from 1 h to 12 h (fig. 4). Patients were given oxygen by face mask for a variable period in the recovery ward, and oxygen
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
Time (h)
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
433
40 35 30 25 20 15 6
10
12
Time (h) FIG. 3. Observed ventilatory frequency over the first 12 h after operation (means, SD). = Bupivacaine alone; — = bupivacaine—morphine. 10
0
•JU
-r—r40 20 25 Ventilatory frequency (b.p.m.) FIG. 4. Ventilatory frequency from 1 h to 12 h after operation recorded from impedance monitor. • = Bupivacaine alone; 0 = bupivacaine-morphine. 15.
saturation data were therefore not stored in the first 1 h. The median oxygen saturation for 1-12 h for each patient was extracted and combined for each treatment group to give a mean and standard deviation of the median values. The averaged median value of oxygen saturation for the bupivacaine alone group was slightly higher than the bupivacaine and morphine group, with a value of 98.0% (SD 1.6) compared with 96.7% (SD 2.0), but the difference was not statistically significant and an oxygen saturation of less than 85 % was
not recorded in any patient. Some traces showed isolated decreases in saturation to less than 90%, but these were transient and not associated with a particular treatment group. DISCUSSION
This study demonstrates that the addition of morphine 0.05 mg kg"1 to a 0.125% solution of bupivacaine improved significantly both quality and duration of pain relief after orchidopexy
Downloaded from http://bja.oxfordjournals.org/ at Monash University on April 11, 2015
10
434
BRITISH JOURNAL OF ANAESTHESIA
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without increasing side effects noticeably. The of patients required further analgesia. This conpresence of morphine in the caudal space did not firms the view that increasing the concentration of result in any detectable differences in oxygen bupivacaine to more than 0.125% [3] or the saturation or ventilatory frequency, although volume to more than 0.75 ml kg"1 [15] offers little more sophisticated tests such as the ventilatory therapeutic advantage for this particular proresponse to carbon dioxide may show depression cedure. of ventilatory drive after extradural opioids [12]. Morphine given by the caudal route is not Minor changes in the carbon dioxide-ventilation merely an exotic alternative to the i.m. route. response curve are of little clinical significance Systemic uptake of caudal morphine is rapid and and probably unrelated to the sudden onset of provides analgesia in the immediate operative and severe ventilatory depression that has been re- postoperative period. However, 1 h after caudal ported occasionally after extradural morphine in injection of morphine 0.05 mg kg"1, plasma conadults. Ventilatory monitoring or close obser- centration is less than 12 ng ml"1 [16], and is vation is needed immediately after caudal admin- unlikely to be associated with significant analgesia. istration of morphine, but it is important to set a Therefore, the prolonged postoperative pain relief time limit to the risk period for ventilatory following caudal morphine is caused probably by depression. The estimate must be conservative, a specific action on the spinal cord. but take into account available clinical experience. Caudal morphine may offer analgesic advantVentilatory depression occurring more than 6 h ages over bupivacaine alone, but the incidence of after extradural administration is extremely rare side effects increases in parallel with both the [13] and associated with factors that include large duration of analgesia and the dose of morphine and repeated doses of extradural morphine, [7]. In this study we were unable to detect an additional opioid or sedative drugs, patients with increase in side-effects caused by addition of significant systemic disease (ASA III/IV) and morphine. The overall incidence of vomiting in rostral delivery of the opioid. The administration this study (11 of 30 (36%)) seems high, but is of a very small dose of morphine at the caudal consistent with previous postoperative studies on limits of the extradural space as a single injection orchidopexy in children. The children were not under light general anaesthesia without additional encouraged actively into attempts at micturition. sedative or opioid drugs minimizes the above risk A more pressurized approach might have resulted factors. We believe, therefore, that when a single in differences between the groups, but we felt that dose technique is used for caudal morphine, passive observation was clinically more realistic. special monitoring can be discontinued safely Caudal morphine has not been established as a after 6 h, provided the patient has shown no signs of excessive sedation within the preceeding 6 h, routine technique in paediatric anaesthesia and and that the patient remains under nursing this may reflect partly the fear of potentially supervision for a total of 12 h after the injection. serious side effects. Minimizing the dose of If additional doses of morphine are given either morphine to provide effective analgesia without caudally or systemically within the first 12 h, side effects is therefore an important goal in the development of the technique. Local anaesthetics monitoring should be continued accordingly. may potentiate the analgesic effects of spinal Caudal blocks with bupivacaine alone can morphine, resulting in improved analgesia at provide excellent analgesia in the early post- lower doses. A recent study in mice [17] has operative period after orchidopexy, but may allow shown that addition of bupivacaine to morphine the false impression that die patient will remain increases the intensity of antinociception with a pain free thereafter. Longer inpatient studies, time course similar to that of morphine alone, but lasting 8 h or more, have shown that, as the caudal of greater potency and reliability. In addition, block wears off, systemic opioid analgesia is doses of morphine or bupivacaine that on their required often [3, 14]. In this present study, own have little or no antinociception may produce eight of 15 patients (53%) receiving 0.125% an enhanced effect when combined. bupivacaine alone required supplementary i.m. analgesia in the postoperative period. These REFERENCES results are similar to a previous study on orchido1. McGown RG. Caudal analgesia in children; five hundred pexy [14] in which, despite the use of higher cases for procedures below the diaphragm. Anaesthesia concentrations and volumes of bupivacaine, 53 % 1982; 37: 808-819.
BUPIVACAINE-MORPHINE FOR PAEDIATRIC CAUDAL ANALGESIA
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