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* From the Department of Anesthesiology,
and Ophthalmology, Children’s Hospital of Eastern Ontario, University of Ottawa, Ottawa, Ontario, Canada.
Address correspondence to: Dr. Jarmila Kim, Department of Anesthesiology, Children’s Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario K1H 8L1, Canada. Phone: 613-737-2431; Fax: 613-738-4815; E-mail: kim{at}cheo.on.ca
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Abstract |
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Methods: Following Institutional Ethics Committee approval and parental consent, we prospectively studied 51 healthy children between the ages of two and seven years who were undergoing elective bilateral recession surgery in a randomized, double-blind controlled clinical trial. Children were randomized to receive either placebo (normal saline), 0.5% amethocaine or 0.5% ketorolac eye drops at the start and end of strabismus repair surgery. Pain was assessed with a modified Children’s Hospital of Eastern Ontario Pain Score in the recovery room. If the pain score was greater than 6, the patient was administered a single oral dose of acetaminophen (20 mg•kg-1).
Results: The groups had similar demographic data. Duration of surgery and anesthesia, time spent in recovery room and length of hospital stay between the three groups were similar. Pain scores and analgesic requirements while in the hospital were also similar between the groups as was the time to first analgesic administration. There were no side effects observed in any of the three treatment arms.
Conclusion: We conclude that there is no improvement in postoperative pain control after the intraoperative administration of topical 0.5% ketorolac or 0.5% amethocaine when compared to placebo in children undergoing strabismus surgery.
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Introduction |
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The search for superior agents has led to the use of non-steroidal anti-inflammatory drugs (NSAIDs) for pain control after minor eye surgery, including strabismus repair. Topical diclofenac sodium has been shown to reduce prostaglandin E2 (PGE2) levels in corneas of animals undergoing laser photorefractive keratotomy.4 In surgical patients undergoing cataract surgery, diclofenac provides analgesia.5 Ketorolac has similar pharmacological effects as diclofenac.
An alternative to topical NSAIDs is local anesthetic eye drops which have been used for many years in ophthalmology to provide pain control in conscious adults and children.6 Typical procedures in which they are commonly employed are eye examinations, tonometry and minor procedures such as removal of foreign bodies. Amethocaine (tetracaine) produces rapid topical anesthesia of the conjunctiva within a few seconds after administration. One or two drops of a 0.5% solution in the eye has an effect which can last from 30 min to several hours.7
The aim of this study was to compare the effects of topical ketorolac to topical amethocaine and placebo on pain levels in children undergoing bilateral strabismus surgery. We hypothesized that the intraoperative use of topical amethocaine or ketorolac would have superior analgesic properties when compared to placebo. We also hypothesized that topical ketorolac would be as effective as topical amethocaine in reducing pain in children undergoing bilateral strabismus surgery.
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Methods |
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A prospective three-armed double-blind randomized controlled clinical trial design was used to assess the difference between the three treatment groups. Sample size was chosen based upon data from 316 patients enrolled in previous investigations. This previous data predicted the normal time to first analgesic was 90 ± 40 min [mean ± standard deviation (SD)] for a placebo group. To detect a 45-min prolongation of analgesia, i.e., a relative increase of 45%, by topical agents with a power of 80%, and alpha error of 0.05/3 = 0.16, the sample size is 17 patients/group if there is a 5% dropout rate.
Patients were premedicated as deemed necessary by the attending anesthesiologist with oral midazolam at a dose of 0.5 mg•kg-1. Standard patient monitoring was used perioperatively. Induction of general anesthesia was achieved by inhalation with N2O/O2/halothane or by iv propofol at a dose of 2.5–3.5 mg•kg-1. A reinforced laryngeal mask airway (LMA) was inserted and general anesthesia was maintained with halothane and N2O/O2 in a 70/30 mixture. Atropine was not administered routinely to prevent oculocardiac reflex, but was readily available.
Two drops of the study solution were placed in each eye at the start and end of surgery in a double-blind fashion by the attending surgeon. All children were given antiemetic prophylaxis with dexamethasone 150 µg•kg-1 and perphenazine 35 µg•kg-1 intraoperatively. After completion of the operation, the patient was transferred to the recovery room (at varying depths of anesthesia) for continuous monitoring of vital signs and for the assessment of pain and vomiting. Minimum alveolar concentration (MAC) values of inhalational anesthesia were not recorded on departure from the operating room. The LMA was removed either asleep or awake at the discretion of the attending anesthesiologist. Pain was assessed every five minutes by the attending nurse utilizing a modified Children’s Hospital of Eastern Ontario Pain Score (CHEOPS) system (Table I
). If the pain score was greater than 6, the patient was administered acetaminophen orally in a dose of 20 mg•kg-1. If pain was deemed excessive, described as a pain score greater than 6 and unrelieved by oral acetaminophen, codeine was chosen as a second line analgesic at a dose of 1.0 mg•kg-1. Nausea was detected by observing the child retching or verbally admitting to nausea. Excessive vomiting (more than three times) was treated with iv dimenhydrinate at a dose of 1 mg•kg-1. The children were transferred from the postanesthesia recovery room (PARR) to the surgical day care unit (SDCU) upon achieving an Aldrete recovery room score of 10.
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Results |
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). There was no significant difference between the three groups in terms of duration of anesthesia, time spent in the recovery room or duration of stay in the SDCU. Midazolam was given as a premedication in similar proportions to each group. More patients in the placebo group (16/18 patients) had induction with halothane compared to the other two treatment groups (Table III).
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). Analgesic requirements while in hospital were similar in all three groups, both in the recovery room and in the SDCU (Table IV). More children received acetaminophen in the SDCU than in the recovery room. None of the children required more than one dose of acetaminophen and none required codeine as a rescue analgesic. The average time to first administration of analgesics was similar.
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). Dimenhydrinate administration was similar (Table IV). No child required inpatient admission for persistent nausea and vomiting. No other complications were noted. |
Discussion |
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Traditionally, opioids have been used as a first line agent for postoperative pain control in children undergoing strabismus repair. However, PONV is a serious problem associated with this approach. Until recently we did not routinely administer prophylactic analgesics in elective strabismus surgery in children, although recent literature may suggest that prophylactic analgesia is of benefit in this population.
The induction of anesthesia in our study was achieved either by iv propofol or by inhalation with N2O/O2/halothane, at the discretion of the attending anesthesiologist. Although some believe that propofol has a specific antiemetic effect, there exists no physiologic data as to its effect on the chemoreceptor trigger zone or the emetic centre. When used solely as an induction drug, propofol has not been found to be beneficial in reducing the incidence of nausea or vomiting. When used in therapeutic doses throughout surgery, patients are less likely to vomit in the PACU, but are not necessarily discharged earlier or have less vomiting late in recovery.10–13 Similarly, when inhalation anesthesia is administered without narcotics and in the absence of pain the incidence of vomiting is very low (9%).14
Assessment of pain in younger children is difficult because of their limited understanding and verbal abilities. In this study we used a modified CHEOPS scoring system to assess postoperative pain in these patients. We have had considerable experience with the use of this pain scale and find it a valid and reliable method of assessing pain in children. We do, however, agree with Bridge et.al. that there are difficulties with CHEOPS in this specific pain model, as it may not be a specific measure of ocular pain and therefore may not accurately reflect pain scores in this age population.8
As our goal was to avoid opioids and there is no iv preparation of NSAID other than ketorolac available in Canada, an oral preparation of acetaminophen was used as a first choice for rescue analgesia if the CHEOPS score was greater than 6. The absorption half-life for the oral preparation is believed to be 4.5 min without a detectable lag time.15 Overall, 43% of children required acetaminophen postoperatively and this was distributed equally amongst the three groups. Acetaminophen use in PARR and in SDCU demonstrates that the incidence of postoperative pain requiring treatment is low in our population and equally distributed in all three groups. None of the children studied required a second dose of acetaminophen or codeine, the second line rescue analgesic chosen for this study. The lack of codeine use would be expected to minimize the incidence of vomiting.
Postoperative vomiting was a rare event in our study. Emesis was reported in only one child in the placebo group although, overall, seven children received dimenhydrinate postoperatively. Unfortunately, some of these children may have accidentally received dimenhydrinate in the PACU for sedation rather than nausea. The low incidence of vomiting may be attributed to the avoidance of opioids and the use of perphenazine and dexamethasone intraoperatively.16 Unfortunately PONV was only recorded during the short hospital stay. It might have been useful to obtain data for PONV and pain scores after discharge from hospital during the first 24 hr and evaluate the incidence of late nausea and vomiting.
Bridge et al. reported the overall incidence of postoperative vomiting to be 3% in hospital and 23% in the first 24 hr in a similar study.8 They speculated that morphine might have been a contributory emetic stimulus, administered to 43% of children after strabismus repair. In addition, their protocol did not include intraoperative antiemetic prophylaxis.
The current study’s sample size was based upon historical data. This historical data had a relatively large n, but was markedly different then the current study’s population. It was predicted that our placebo group’s time to first analgesia would have a mean and SD of 90 and 40, respectively, but it was actually 57 and 34, respectively. The study still has a power of 80% to detect an absolute difference of 45 min in time to first analgesia, but the power to detect a relative difference in groups of 50%, i.e., time to first analgesia of 57 min vs 85 min is only 29%.
In conclusion, this study did not demonstrate a beneficial effect of topical ketorolac or amethocaine vs placebo for pain control in children undergoing strabismus surgery.
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Footnotes |
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References |
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2 Weinstein MS, Nicolson SC, Schreiner MS. A single dose of morphine sulfate increases the incidence of vomiting after outpatient inguinal surgery in children. Anesthesiology 1994; 81: 572–7.[Medline]
3 Mendel HG, Guarnieri KM, Sundt LM, Torjman MC. The effects of ketorolac and fentanyl on postoperative vomiting and analgesic requirements in children undergoing strabismus surgery. Anesth Analg 1995; 80: 1129–33.[Abstract]
4 Morton NS, Benham SW, Lawson RA, McNicol LR. Diclofenac vs oxybuprocaine eyedrops for analgesia in paediatric strabismus surgery. Paediatr Anaesth 1997; 7: 221–6.[Medline]
5 Fry LL. Efficacy of diclofenac sodium solution in reducing discomfort after cataract surgery. J Cataract Refract Surg 1995; 21: 187–90.[Medline]
6 Carden SM, Colville DJ, Davidson AJ, et al. Adjunctive intra-operative local anaesthesia in paediatric strabismus surgery: a randomized controlled trial. Aust N Z J Ophthalmol 1998; 26: 289–97.[Medline]
7 Watson DM. Topical amethocaine in strabismus surgery. Anaesthesia 1991; 46: 368–70.[Medline]
8 Bridge HS, Montgomery CJ, Kennedy RA, Merrick PM. Analgesic efficacy of ketorolac 0.5% ophthalmic solution (Accular) in paediatric strabismus surgery. Paediatr Anaesth 2000; 10: 521–6.[Medline]
9 Apt L, Voo I, Isenberg SJ. A randomized clinical trial of the nonsteroidal eyedrop diclofenac after strabismus surgery. Ophthalmology 1998; 105: 1448–54.[Medline]
10 Hannallah RS, Britton JT, Schafer PG, Patel RI, Norden JM. Propofol anaesthesia in paediatric ambulatory patients: a comparison with thiopentone and halothane. Can J Anaesth 1994; 41: 12–8.
11 Reimer EJ, Montgomery CJ, Bevan JC, Merrick PM, Blackstock D, Popovic V. Propofol anaesthesia reduces early postoperative emesis after paediatric strabismus surgery. Can J Anaesth 1993; 40: 927–33.
12 Martin TM, Nicolson SC, Bargas MS. Propofol anesthesia reduces emesis and airway obstruction in pediatric outpatients. Anesth Analg 1993; 76: 144–8.
13 Weir PM, Munro HM, Reynolds PI, Lewis IH, Wilton NC. Propofol infusion and the incidence of emesis in pediatric outpatient strabismus surgery. Anesth Analg 1993; 76: 760–4.
14 Murray DJ, Schmid CM, Forbes RB. Anesthesia for magnetic resonace imaging in children: a low incidence of protractive post-procedure vomiting. J Clin Anesth 1995; 7: 232–6.[Medline]
15 Romsing J, Ostergaard D, Senderovitz T, Drozdziewicz D, Sonne J, Ravn G. Pharmacokinetics of oral diclofenac and acetaminophen in children after surgery. Paediatr Anaesth 2001; 11: 205–13.[Medline]
16 Splinter W, Roberts DJ. Prophylaxis for vomiting by children after tonsillectomy: dexamethasone versus perphenazine. Anesth Analg 1997; 85: 534–7.[Abstract]
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