Ketamine and oxycodone in the management of postoperative pain

Military Medicine, Jun 2000 by Levanen, Jaakko

Relief of pain, whether post-traumatic or postoperative, is a prerequisite for the prevention of its deleterious effects on the whole organism. Unalleviated pain also increases the victim's or patient's anxiety and apprehension, which in turn increase the intensity of the pain. In the management of pain, opiates have maintained their position as the most common form of analgesic therapy despite the many side effects associated with their use. This double-blind study compared the analgesic effects of low doses of racemic ketamine and the morphine derivative oxycodone on postoperative pain after elective tonsillectomy. Also, the suitability of oxycodone for field use was evaluated with respect to ketamine. Plethysmographic pulse-- wave amplitude changes were compared with the pain visual analogue scale scores as measures of postoperative pain. The results of this study did not reveal any significant differences between the analgesic potencies of the studied drugs and clearly demonstrate that even suboptimal doses of both ketamine and oxycodone can provide appreciable relief of pain.

Introduction

Post-traumatic and postoperative pain are, depending on the type, localization, and extent of the injury or surgery, for the most part inevitable. If allowed to persist, pain in these instances is deleterious to the whole organism, even more so in the critical patient. Unalleviated pain is associated with increased anxiety and apprehension, which in turn increase the intensity of pain.

Parenteral administration of analgesic drugs, nonsteroidal anti-inflammatory agents, opioids, and especially ketamine in field medicine is an integral part in the post-traumatic or postoperative patients treatment. Parenteral administration is preferred to provide not only potent but also rapid pain relief.

In common practice, opioids are still the major agents of pain relief, but they are also accompanied by many side effects that limit their usefulness. Hence, methods to avoid their narcotic-- associated side effects are still being sought.1

The aims of this investigation were to compare the analgesic effects of low doses of racemic ketamine (Ketalar, Parke-Davis) and the morphine derivative oxycodone (Oxanest, Leiras, Turku, Finland], administered as intravenous bolus injections, and especially to evaluate the applicability of oxycodone for field use with respect to ketamine. A primary study of the plethysmographic pulse-wave amplitude as an objective measure of postoperative pain was also performed.

Postoperative pain after elective tonsillectomy was used as the model of pain.

Patients and Methods

Patients

Forty tonsillectomized male conscripts aged 21 to 28 years were randomized to receive either ketamine or oxycodone as the postoperative analgesic. Informed consent was obtained from all patients before their inclusion in the study.

Methods

Anesthesia

All patients received the same standard anesthesia. Induction was with thiopentone 4 to 5 mg IV in combination with alfentanil 1 mg IV and glycopyrronium bromide 0.2 mg IV. Rocuronium bromide 0.6 to 0.8 mg/kg was used for muscle relaxation and supplemented with 10- to 15-mg bolus doses, as indicated by the muscle Relaxograph (Datex Instrumentarium, Helsinki, Finland). After intubation, anesthesia was maintained with 5% desflurane in O^sub 2^/NO^sub 2^ (1:2).

One milliliter of a mixture containing glycopyrronium bromide 0.5 mg and neostigmine methylsulfate 2.5 mg was administered at the end of anesthesia for reversal of muscle relaxation.

The ventilatory volume (7-8 L/min) was adjusted to maintain 5% end-tidal CO^sub 2^. No premedication was used for any of the patients in either group. Glycopyrronium bromide and alfentanil were administered immediately before induction with thiopentone.

Patient Monitoring

The patients' electrocardiograms, blood pressure, pulse rate, oxygen saturation, respiratory rate, and muscle relaxation were monitored during anesthesia. Blood pressure, pulse rate, respiratory rate, and oxygen saturation were monitored in the recovery room.

Additionally, a pulse-wave oximeter (Satlitetrans, Datex Instrumentarium) with a finger probe was used to monitor changes occurring in the relative pulse-wave amplitude during the recovery room period. Pulse-wave amplitude, a relative measure, reflects the changes occurring in the vascular bed, i.e., its increase indicates vasodilation and its decrease indicates vasoconstriction, controlled by local autoregulation and systemic neural and humoral effects. The Satlitetrans oximeter is also provided with an additional feature that displays the pulse wave graphically simultaneously with numerical display of arterial oxygen saturation and pulse rate. Changes in pulse-wave trend were stored in memory as 10-second averages for later computer analyses with the Excel 5.0 program and as printouts for each individual patient.

Sedation, Anxiety, and Awareness

Visual analogue scales with a range from 0 to 10 were used to assess both sedation and anxiety: 0 denoted fully awake or relaxed and 10 denoted asleep or extremely anxious. Sedation and anxiety were assessed both before induction and in the recovery room at 0, 90, and 180 minutes.