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Anesth Analg 2003;96:1789-1793
© 2003 International Anesthesia Research Society

OBSTETRIC ANESTHESIA

Nalbuphine Versus Ondansetron for Prevention of Intrathecal Morphine-Induced Pruritus After Cesarean Delivery

Somrat Charuluxananan, MD MSc, FRCAT*,{dagger}, Oranuch Kyokong, MD MSc, FRACT*,{dagger}, Wanna Somboonviboon, MD FRCAT*, Arunchai Narasethakamol, MD*, and Pissamai Promlok, MD*

*Department of Anesthesiology and {dagger}Clinical Epidemiology Unit, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand

Address correspondence and reprint requests to Charuluxananan Somrat, MD, Department of Anesthesiology, Faculty of Medicine, Chulalongkorn University, King Chulalongkorn Memorial Hospital, Rama IV Rd., Pathumwan, Bangkok 10330, Thailand. Address e-mail to somratcu{at}hotmail.com


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
In this prospective, randomized, double-blinded study, we compared the prophylactic efficacy of nalbuphine and ondansetron for the prevention of intrathecal morphine-induced pruritus after cesarean delivery. Two-hundred-forty parturients were randomly allocated into four groups. The N-4 group, O-4 group, O-8 group, and placebo group received IV 4 mg of nalbuphine, 4 mg of ondansetron, 8 mg of ondansetron, and 4 mL of normal saline, respectively, immediately after the baby was delivered. In the postanesthesia care unit, we found that the severity of pruritus score in the four groups was significantly different (P < 0.001). The prophylactic success rate for pruritus of the N-4, O-4, O-8, and placebo groups was 20%, 13%, 12%, and 6%, respectively (P < 0.001). The pruritus score between N-4 and placebo and O-4 and placebo was significantly different (P < 0.001 and P = 0.006, respectively). Treatment for pruritus was requested by patients in 25%, 47%, 51%, and 72% of patients in the N-4, O-4, O-8, and placebo groups, respectively (P < 0.001). There were no differences among groups in nausea/vomiting score, pain score, sedation score, or shivering score at 4, 8, and 24 h after surgery. Nalbuphine and ondansetron are more effective than placebo for the prevention of intrathecal morphine-induced pruritus after cesarean delivery.

IMPLICATIONS: Nalbuphine and ondansetron are more effective than placebo for the prevention of intrathecal morphine-induced pruritus after cesarean delivery.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Neuraxial opioids provide excellent postoperative analgesia, but their use is associated with a frequent incidence of troublesome side effects such as pruritus, nausea, and vomiting (1–3). Pruritus is the most common side effect associated with spinal or epidural morphine (3) and may be unpleasant and difficult to treat (4). Naloxone can effectively treat the pruritus even in severe cases, but it may do so at the expense of the analgesic effect (5). Nalbuphine, propofol, and ondansetron have been used effectively for treating pruritus associated with neuraxial opioids in surgical patients (6–9).

We have observed that nalbuphine is more effective than propofol for the treatment of intrathecal morphine-induced pruritus in obstetric patients (10). Yeh et al. (11) reported that prophylactic IV ondansetron greatly reduced the incidence of intrathecal morphine-induced pruritus in patients undergoing cesarean delivery. Therefore, we undertook a prospective, randomized, double-blinded study to compare the effectiveness and side effects of IV ondansetron and nalbuphine in the prevention of intrathecal morphine-induced pruritus in this clinical setting.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After the study protocol was approved by the institutional ethical committee and written, informed consent was obtained from each patient, this prospective, randomized, double-blinded study was performed at the King Chulalongkorn Memorial Hospital, a 1500-bed university hospital. ASA class I or II non-breast-feeding parturients scheduled for cesarean delivery under spinal anesthesia were recruited into this study. Patients who had a known allergy to nalbuphine, ondansetron, propofol, morphine, or bupivacaine and those with preexisting pruritus caused by pregnancy, a coexisting skin disorder, or other pruritogenic systemic diseases were excluded. Patients with a contraindication to spinal anesthesia or those who did not agree to participate in the study were also excluded.

Without premedication, all parturients were hydrated with 500 to 1000 mL of normal saline before the administration of spinal anesthesia. The subarachnoid block was performed with the patient in the left lateral position at either the L2-3 or the L3-4 interspace by use of a 25- or 27-gauge Quincke spinal needle, per our standard practice. Once free flow of clear cerebrospinal fluid had been demonstrated, 2.2 mL of 0.5% hyperbaric bupivacaine and 0.2 mL (0.2 mg) of preservative-free morphine, mixed in the same syringe, were injected. The parturients were then immediately placed in the supine position with left uterine displacement, and supplemental oxygen was delivered through a face mask at 5 L/min. IV fluid and ephedrine were administered as needed to maintain the systolic blood pressure within 30% of its preoperative value or systolic blood pressure >=100 mm Hg. After a satisfactory spinal block was verified by loss of sensation to cold or pinprick, cesarean delivery was performed in the typical fashion.

Two-hundred-forty patients were randomly divided into 4 groups. The patients in the N-4 group (nalbuphine group) received 4 mL of a 4-mg nalbuphine (Nubain; Dupont Pharma, Manati, Puerto Rico) IV injection, the O-4 group (ondansetron-4 group) received 4 mL of a 4-mg ondansetron (Zofran; Glaxo Wellcome, Greenford, UK) IV injection, the O-8 group (ondansetron-8 group) received 4 mL of an 8-mg ondansetron IV injection, and the P group (placebo group) received 4 mL of normal saline immediately after the baby was delivered. All drugs were infused within 5 min, and the time of complete injection was recorded. The block randomization sequence was selected according to a random number table and was written on a paper enclosed in a sealed envelope. Randomly allocated coded syringes were prepared by a nurse anesthetist not involved in the study, and drugs were administered in a double-blinded fashion.

At the postanesthesia care unit (PACU), vital signs were recorded every 15 min for 4 h according to the institutional monitoring protocol. The degree of pruritus and whether treatment was requested (1 = no pruritus; 2 = mild pruritus, treatment not requested; 3 = moderate pruritus, treatment requested; 4 = severe pruritus) (10) was assessed and recorded. At the same time, the patients were evaluated for pruritus, blood pressure, pulse rate, verbal numeric pain score (0 = no pain, 10 = worst imaginable pain), four-point sedation score (1 = fully awake; 2 = somnolent, responds to call; 3 = somnolent, responds to tactile stimulation; 4 = asleep, responds to painful stimulation), four-point rating score for nausea and vomiting (1 = no nausea or vomiting, 2 = queasy, 3 = severe nausea, 4 = vomiting), and four-point shivering score (1 = no shivering, 2 = mild shivering, 3 = moderate shivering, 4 = severe shivering). Patients with a pruritus score >=3 were treated with 20 mg of IV propofol, those with a nausea and vomiting score >=3 were treated with 10 mg of IV metoclopramide, and those with a shivering score >=3 were treated with 25 mg of IV tramadol, according to the institutional protocol. Cardiac arrhythmia was evaluated with cardiac auscultation after any patient reported palpitations and verified by electrocardiogram. Other adverse effects, such as dizziness, hallucinations, respiratory depression, and extrapyramidal signs, were recorded, as was the time to flatus passage and the onset of pruritus time (from the administration of spinal morphine to the occurrence of pruritus). At 4, 8, and 24 h after surgery, the patients were also assessed by a blinded observer.

Power analysis was performed to determine the size of the treatment group. Allowing for the probability of a type II error of 0.1 and a type I error of 0.05 (considering that 75% of patients in the 4-mg nalbuphine group, 55% in the 4-mg ondansetron group, and 55% in the 8-mg ondansetron group did not request treatment for pruritus, from a pilot study), a sample size of 60 in each group was calculated as being required. Statistical analysis of the results was performed by using SPSS Version 10 (SPSS Inc., Chicago, IL). Statistical analysis of the results was performed by using one-way analysis of variance for continuous data and the Kruskal-Wallis test for ordinal data. Post hoc analysis was performed by using the Mann-Whitney U-test with Bonferroni’s correction on pairwise comparisons. The {chi}2 test was used to compare categorical data. The a priori level of significance was set at P <= 0.05.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Two-hundred-forty patients were enrolled in the study. No patient was withdrawn from the study. There was no difference in demographic data or onset of pruritus between groups, as shown in Table 1. None of the patients experienced adverse surgical or anesthesia-related complications during surgery.


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  		Table 1. Demographic and Clinical Characteristics
 
During the 4 h in the PACU, pruritus occurred in 94% of the patients who received the placebo injection. The severity of pruritus scores in the four groups were significantly different, as shown in Table 2 (P < 0.001). Pruritus scores between the N-4 and placebo groups and the O-4 and placebo groups were also significantly different (P < 0.001 and P = 0.006, respec- tively). The severity of pruritus between the O-8 and placebo groups, the N-4 and O-4 groups, and the O-4 and O-8 groups was not significantly different (P = 0.027, P = 0.022, and P = 0.587, respectively). The sites of pruritus were mainly at the trunk, back, neck, and around the nose and eyes. There was no patient with severe pruritus in any group. Most of the patients with moderate pruritus (treatment needed as judged by the patients) were treated successfully with 20 mg of IV propofol (10). Three patients in the O-4, O-8, and placebo groups and two patients in the N-4 group required further treatment and were treated successfully with 0.1 to 0.2 mg of naloxone, except for one each in the N-4 and O-8 groups, who were unresponsive but refused further treatment. The incidence and severity of nausea and vomiting in patients at the PACU were also without significant difference (Table 2).


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  		Table 2. Pruritus and Nausea/Vomiting Score in the Postanesthesia Care Unit
 
Pruritus score, pain score, nausea/vomiting score, sedation score, and shivering score at 4, 8, and 24 h after surgery were similar in all groups. Dizziness, hallucinations, cardiac arrhythmias, and respiratory depression were not observed. In addition, ondansetron was not found to have detrimental effects with regard to postoperative flatus passage.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
Pruritus is the most frequent undesirable symptom associated with neuraxial opioids. In this study, the incidence of pruritus after intrathecal morphine injection in patients undergoing cesarean delivery was frequent (94%). These results are consistent with those reported in the literature (70%–93%) (12–14). This vulnerability to pruritus, thought to be caused by a change of metenkephalin content at opioid receptor sites, may be caused by competition by estrogens in obstetric patients (15). The increased cephalic spread of spinally administered drugs in a pregnant woman at term as compared with the general population may also play a role (16).

The onset of pruritus in this study was similar to that reported in previous studies (8,10,15). Doses of 4 mg of nalbuphine and 4 mg of ondansetron were chosen because these doses had proven successful in the treatment of intrathecal morphine-induced pruritus (6,9,10). The 8-mg dose of ondansetron was also chosen according to the regimen of Yeh et al. (11) to study the dose-response relation in this context. This study revealed that 4 mg of nalbuphine and 4 mg of ondansetron were more successful in preventing intrathecal morphine-induced pruritus than placebo. Although there were no significant differences between the N-4 and O-4 groups, O-4 and O-8 groups, or O-8 and placebo groups with the numbers studied, the tendency suggested that with larger numbers, there could be a significant difference between the O-8 and placebo groups. This may be related to an insufficient statistical power of the study even though the sample size was calculated according to the incidence from a pilot study. More than 400 patients would be required in future trials to detect differences as found in this study. However, this is the first study to investigate the efficacy of nalbuphine for the prevention of intrathecal morphine-induced pruritus in obstetric patients. The incidence and severity of pruritus after prophylactic IV ondansetron in our study were more frequent than those reported by Yeh et al. (11). This may be due to different doses of intrathecal morphine used (0.2 versus 0.15 mg).

The mechanism of pruritus after the neuraxial administration of opioids is not fully understood. It is probably not related to histamine release, because antihistamines are ineffective in the therapy of pruritus caused by spinal morphine (17). Another theory is that the opioid receptors in the central nervous system (CNS) are activated by morphine. Opioid receptors are located both supraspinally and at the spinal cord level. Spinal opioids activate the opioid receptors in the substantia gelatinosa of the spinal cord’s dorsal horn (18). The µ receptor is responsible for pain modulation and some side effects, especially pruritus and nausea or vomiting. This would explain the antipruritic effect of nalbuphine or naloxone, because both of them are specific µ antagonists (19). A third theory is that the pruritus from neuraxial opioids may be related to the excitatory effects of opioids on the nocifensive and nonnocifensive neurons in the anterior and posterior spinal horns (20). Propofol may relieve pruritus related to neuraxial opioids because it has an inhibitory effect on the dorsal horn of the spinal cord (21). There has been evidence that opioids and the serotoninergic system interact closely in the CNS. Ondansetron, a specific 5-hydroxytryptamine-3 receptor antagonist, has an antipruritic effect (8,9,11). The role of ondansetron in nociception has also been reported (22). Fan (23) reported that morphine can activate serotonin type 3 receptors by a mechanism independent of opioid receptors. Therefore, direct irritation of serotonin type 3 receptors in the dorsal horn of the spinal cord and in the medulla by intrathecal injection of morphine is a possible mechanism for pruritus.

Nausea and vomiting are also common after neuraxial opioids. Nausea usually occurs within four hours of injection, and vomiting occurs soon thereafter (24). During their four-hour stay at the PACU, there was no significant difference among groups in the incidence of nausea or vomiting. The sedation score and pain score were not different in any group during the study period.

In this study, the prevalence of pruritus in the placebo group was frequent (94%), and treatment for pruritus was requested in 25%, 47%, 51%, and 72% of patients in the N-4, O-4, O-8, and placebo groups, respectively. Unlike nalbuphine, ondansetron is lipophilic and may be excreted in breast milk, although there are no reports defining the concentration of this drug in breast milk (25). Although use of nalbuphine would be associated with a somewhat larger cost of care, this might be balanced by increased patient satisfaction because of a decreased incidence of pruritus. In summary, nalbuphine and ondansetron were both found to be more effective than placebo for prophylaxis of intrathecal morphine-induced pruritus in patients undergoing cesarean delivery. Neither drug, however, was effective in all patients.


   Acknowledgments
 
Supported by a research grant from the Rachadapisek-sompoj Fund (Silver Jubilee of HM. King Bhumibhol), Faculty of Medicine, Chulalongkorn University.

The authors express their appreciation to Wasan Punyasang, Piyalamporn Havanond, and Somrat Lertmaharit for statistical analysis and to staff members of the Clinical Epidemiology Unit, Faculty of Medicine, Chulalongkorn University, for helpful support.


   References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Accepted for publication February 24, 2003.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press