New developments in patient-controlled postoperative analgesia

Feasibility of Patient-Controlled Sleep with Dexmedetomidine in Treating Chronic Intractable Insomnia

BACKGROUND

Patient-controlled analgesia (PCA) is an "on-demand" system which allows patients to self-administer intravenous medications in small bolus doses. Based on the principles of PCA, we developed Patient-Controlled Sleep (PCSL) for chronic intractable insomnia where the traditional analgesics in PCA were replaced with dexmedetomidine (Dex), an alpha-2 agonist widely used for premedication, sedation, anxiolysis and analgesia. The purpose of this study was to assess the feasibility of the new method for the treatment of chronic intractable insomnia.

PATIENTS AND METHODS

Patients with chronic intractable insomnia undergoing PCSL (n=20) were evaluated with the Pittsburgh Sleep Quality Index (PSQI), Symptom Checklist 90 (SCL-90), Hamilton Anxiety Scale (HAMA) and Hamilton Depression Scale (HAMD) before and after the treatment. The patient characteristics, overall outcomes and related side effects were also assessed.

RESULTS

Fifteen patients completed the treatment protocol. The duration of PCSL varied from a few days to four months, and the dosage of Dex gradually decreased without eliciting signs or symptoms of tolerance or physical dependence. The sleep quality improvement occurred immediately after the therapy in 12/15 patients, and of which, 7/12 patients achieved continuously improved sleep quality in follow-up.

CONCLUSION

PCSL with Dex might be a potential treatment for patients with chronic intractable insomnia. However, it is an off-label use, and the potential side effects of dexmedetomidine with long-term use needs further evaluation.

Remifentanil compared with morphine for postoperative patient-controlled analgesia after major abdominal surgery: a randomized controlled trial

BACKGROUND AND OBJECTIVE

This randomized, double-blinded clinical study was designed to compare the efficacy and safety of remifentanil and morphine administered using intravenous (i.v.) patient-controlled analgesia (PCA) for postoperative analgesia after major abdominal surgery during the first 24 postoperative hours.

METHODS

Sixty-nine patients were randomly allocated into two groups, each receiving remifentanil or morphine. The first group received i.v. remifentanil PCA with a loading dose of 45 microg, a maintenance dose of 1 microg min(-1), a bolus dose of 15 microg and a lockout interval of 10 min during the first 24 postoperative hours. The second group received i.v. morphine PCA with a loading dose of 5 mg, a maintenance dose of 0.3 mg h(-1), a bolus dose of 1 mg and a lockout interval of 15 min. Age, weight, sex, history of general anaesthesia, duration of surgery and time spent in the post-anaesthesia care unit were recorded. Preoperative pulse rate, systolic and diastolic blood pressures (BP), respiration rate and arterial blood gases were collected. Pulmonary function was tested before induction of anaesthesia, as well as at 4 and 26 h after operation. Pulse rate, systolic and diastolic BP, respiration rate, arterial blood gases, sedation and visual analogue scores, and presence of side-effects in the recovery room and on the ward for 24 h were recorded at 0, 1, 2, 4, 6, 12, 18 and 24 h after operation. Total drug use, number of boluses delivered, number of boluses demanded and delivery/demand ratio were collected.

RESULTS

Sixty patients were evaluated. The groups did not differ in age, weight, sex, history of general anaesthesia, duration of surgery or time spent in the recovery unit. There were also no clinically relevant differences between the groups with regard to haemodynamic and respiratory parameters as well as sedation and visual analogue scores (P > 0.05). More bolus doses were demanded and delivered and the delivery/demand ratio was significantly higher in the remifentanil group (P < 0.05). There was no finding suggesting acute opioid tolerance during remifentanil or morphine PCA.

CONCLUSION

The i.v. remifentanil PCA with the chosen dosage regimen after abdominal surgery produces postoperative analgesia and has cardiovascular side-effects similar to those achieved with i.v. morphine. Special attention must be given to respiratory depression during establishment of PCA with remifentanil.

Recent developments in patient-controlled analgesia

Patient-controlled analgesia (PCA) has become the gold standard for acute pain management since it was first introduced 20 years ago, and its merits have been discussed in quite a large number of publications. This review summarizes the more recent developments, such as new application devices and strategies, including intranasal, spinal, and regional PCA; patient-controlled sedation; experience with children and elderly people; and some data from chronic pain situations. Analyzing PCA literature from 2001 onwards confirms the author's long belief that the PCA principle ("WYNIWYG": what you need is what you get) was the most important aspect of a patient-controlled strategy, more or less independent of the type of drug or machine. Discovering this principle has changed the understanding of pain and suffering.

Clinical pharmacology of tramadol

Tramadol, a centrally acting analgesic structurally related to codeine and morphine, consists of two enantiomers, both of which contribute to analgesic activity via different mechanisms. (+)-Tramadol and the metabolite (+)-O-desmethyl-tramadol (M1) are agonists of the mu opioid receptor. (+)-Tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine reuptake, enhancing inhibitory effects on pain transmission in the spinal cord. The complementary and synergistic actions of the two enantiomers improve the analgesic efficacy and tolerability profile of the racemate. Tramadol is available as drops, capsules and sustained-release formulations for oral use, suppositories for rectal use and solution for intramuscular, intravenous and subcutaneous injection. After oral administration, tramadol is rapidly and almost completely absorbed. Sustained-release tablets release the active ingredient over a period of 12 hours, reach peak concentrations after 4.9 hours and have a bioavailability of 87-95% compared with capsules. Tramadol is rapidly distributed in the body; plasma protein binding is about 20%. Tramadol is mainly metabolised by O- and N-demethylation and by conjugation reactions forming glucuronides and sulfates. Tramadol and its metabolites are mainly excreted via the kidneys. The mean elimination half-life is about 6 hours. The O-demethylation of tramadol to M1, the main analgesic effective metabolite, is catalysed by cytochrome P450 (CYP) 2D6, whereas N-demethylation to M2 is catalysed by CYP2B6 and CYP3A4. The wide variability in the pharmacokinetic properties of tramadol can partly be ascribed to CYP polymorphism. O- and N-demethylation of tramadol as well as renal elimination are stereoselective. Pharmacokinetic-pharmacodynamic characterisation of tramadol is difficult because of differences between tramadol concentrations in plasma and at the site of action, and because of pharmacodynamic interactions between the two enantiomers of tramadol and its active metabolites. The analgesic potency of tramadol is about 10% of that of morphine following parenteral administration. Tramadol provides postoperative pain relief comparable with that of pethidine, and the analgesic efficacy of tramadol can further be improved by combination with a non-opioid analgesic. Tramadol may prove particularly useful in patients with a risk of poor cardiopulmonary function, after surgery of the thorax or upper abdomen and when non-opioid analgesics are contraindicated. Tramadol is an effective and well tolerated agent to reduce pain resulting from trauma, renal or biliary colic and labour, and also for the management of chronic pain of malignant or nonmalignant origin, particularly neuropathic pain. Tramadol appears to produce less constipation and dependence than equianalgesic doses of strong opioids.

Propacetamol and diclofenac alone and in combination for analgesia after elective tonsillectomy

BACKGROUND

Diclofenac and paracetamol have different mechanisms and sites of action. Therefore, we tested if their combination is more effective for analgesia after tonsillectomy than either drug alone with respect to rescue analgesic consumption and visual analog scale values.

METHODS

The analgesic effects of intravenously administered propacetamol (injectable pro-drug of paracetamol) and diclofenac or a combination on postoperative pain were compared in 71 adult elective tonsillectomy patients in a randomized, double-blind study. After induction of anesthesia the patients received monotherapy with 2 g propacetamol (n = 25) or 75 mg diclofenac (n = 25), or a combined treatment with 2 g propacetamol and 75 mg diclofenac (n = 21) in physiologic saline as an infusion. Postoperatively the propacetamol dosage was repeated twice and diclofenac once on the ward. Oxycodone (0.03 mg kg(-1)) was used as a rescue analgesic by patient-controlled analgesia.

RESULTS

On average the patients needed oxycodone 15.3, 13.2 and 10.6 times in the propacetamol, diclofenac and combination groups, respectively (NS). A verbal rating scale and a visual analog scale were employed for assessing post-tonsillectomy pain, nausea and patient satisfaction in all groups. No statistically significant differences were found between the groups. Twelve of the 25 (48%) patients having received propacetamol complained of pain at the cannulation site.

CONCLUSION

Combined treatment with propacetamol and diclofenac with the dosages used provided clinically only a minor advantage over monotherapy with propacetamol or diclofenac with respect to postoperative analgesia or the incidence of side-effects in adult tonsillectomy patients.

Interaction between metamizol and tramadol in a model of acute visceral pain in rats

Tramadol (TRM) and metamizol (MTZ) are drugs with complex mechanisms of action, extensively used in combination in pain management. In the present investigation we have evaluated the interaction between MTZ:TRM in the ethacrinic acid writhing test in rats. Dose-response curves (s.c.) were obtained for each drug individually, combined in fixed potency ratios (1:0.3, 1:1, 1:3), and for MTZ in presence of a fixed-dose of TRM (3.5 mg/kg). Interactions were analysed using isobolograms, interaction indexes (INT-I) and ANOVA. We used naloxone (1 mg/kg s.c.) to determine the opioid-component of the effects (ED80). Isobolograms demonstrated antagonism at the ED20, for 1:0.3 and 1:3 mixtures (p<0.01), whereas 1:1 was additive. At the ED50 and ED80 all combinations showed synergy. Fixed-dose experiments demonstrated that treatment (p<0.0001), dose (p<0.0001), and their interaction (p<0.0001) were statistically significant. Naloxone partially antagonized TRM (67%), but not MTZ; the percentage reversal of the combinations was directly related to the dose of TRM in the combination. The results show that the MTZ:TRM interaction on antinociception is synergistic or antagonistic depending on the level of effect. Synergy is demonstrated at 50% or higher levels, thus supporting the results obtained in humans by our group. Below the ED50 antagonism or additivity is present depending on the ratio of the combination. The mechanisms of the interaction remain unknown.

Pain management in the critically ill child

Children frequently received no treatment, or inadequate treatment, for pain and for painful procedures. The newborn and critically ill children are especially vulnerable to no treatment or under-treatment. Nerve pathways essential for the transmission and perception of pain are present and functioning by 24 weeks of gestation. The failure to provide analgesia for pain results in rewiring the nerve pathways responsible for pain transmission in the dorsal horn of the spinal cord and results in increased pain perception for future painful results. Many children would withdraw or deny their pain in an attempt to avoid yet another terrifying and painful experiences, such as the intramuscular injections. Societal fears of opioid addiction and lack of advocacy are also causal factors in the under-treatment of pediatric pain. False beliefs about addictions and proper use of acetaminophen and other analgesics resulted in the failure to provide analgesia to children. All children even the newborn and critically ill require analgesia for pain and painful procedures. Unbelieved pain interferes with sleep, leads to fatigue and a sense of helplessness, and may result in increased morbidity or mortality.

Safer colonoscopy with patient-controlled analgesia and sedation with propofol and alfentanil

BACKGROUND

The aim of this study was to assess the efficacy of patient-controlled analgesia and sedation with propofol/alfentanil for colonoscopy compared with continuous drug infusion and conventional nurse-administered medication.

METHODS

One hundred fifty patients undergoing colonoscopy on an outpatient basis were randomly assigned to 1 of 3 medication regimens. To maintain blinding, all patients were connected to an infusion pump. Group I patients could self-administer boluses of 4.8 mg propofol and 125 microg alfentanil without restriction. Group II patients received a continuous infusion with 0.048 mg/kg propofol and 0.12 microg/kg alfentanil per minute. Group III patients received intravenous premedication with 0.035 mg/kg midazolam and 0.35 mg/kg meperidine.

RESULTS

There were no differences between the groups with respect to pain (visual analogue scale) and procedure time. Patient-controlled analgesia and sedation with propofol/alfentanil (group I) resulted in less of an increase in the transcutaneous partial pressure of carbon dioxide (p = 0.0004) during colonoscopy and less of a decrease in mean arterial blood pressure (p = 0.0021) during recovery, as well as more complete recovery (p = 0.0019) after 45 minutes compared with conventional administration of midazolam/meperidine. Furthermore, patient-controlled analgesia and sedation yielded a higher degree of patient satisfaction than continuous infusion of propofol/alfentanil (p = 0.0033) or nurse-administered midazolam/meperidine (p = 0.0094).

CONCLUSIONS

Patient-controlled administration of propofol and alfentanil for colonoscopy may provide a better margin of safety than conventional administration of midazolam and meperidine and results in a higher level of patient satisfaction and shorter recovery.

Use of intravenous patient-controlled analgesia for the documentation of synergy between tramadol and metamizol

The quantification of the synergistic interactions (beneficial and adverse) of analgesic drug combinations in humans has been elusive. We propose a new procedure based on analgesic requirements (i.v.-PCA) and pain intensity (VAS-PI). One hundred and one post-hysterectomy patients received at the time of analgesia request (TAR) tramadol (100 mg, group I) or metamizol (1.2 g, group II) alone, or combined in 1:1 (III), 1:0.3 (IV) or 1:3 ratio (V). After 15 min, they received the same treatment by PCA. VAS-PI, analgesic consumption and adverse effects were assessed at TAR, and periodically for 24 h. Data were analysed using interaction indexes and isobolograms. All treatments produced equivalent VAS-PI, per cent efficacy and adverse effects. When drugs were combined in a 1:1 ratio, synergy was present for the analgesic and adverse effects; all other treatments were additive.

Clinical pharmacokinetics of transdermal opioids: focus on transdermal fentanyl

Transdermal delivery allows continuous systemic application of opioids through the intact skin. This review analyses the pharmacokinetic properties of transdermal opioid administration in the context of clinical experience, with a focus on fentanyl. A transdermal therapeutic system (TTS) for fentanyl has been developed. The amount of fentanyl released is proportional to the surface area of the TTS, which is available in different sizes. After the first application of a TTS, a fentanyl depot concentrates in the upper skin layers and it takes several hours until clinical effects are observed. The time from application to minimal effective and maximum serum concentrations is 1.2 to 40 hours and 12 to 48 hours, respectively. Steady state is reached on the third day, and can be maintained as long as patches are renewed. Within each 72-hour period, serum concentrations decrease gradually over the second and third days. When a TTS is removed, fentanyl continues to be absorbed into the systemic circulation from the cutaneous depot. The terminal half-life for TTS fentanyl is approximately 13 to 25 hours. The interindividual variability of serum concentrations, partly caused by different clearance rates, is markedly larger than the intraindividual variability. The effectiveness of TTS fentanyl was first demonstrated in acute postoperative pain. However, the slow pharmacokinetics and large variability of TTS fentanyl, together with the relatively short duration of postoperative pain, precluded adequate dose finding and led to inadequate pain relief or, especially, a high incidence of respiratory depression; such use is now contraindicated. Conversely, in cancer pain, TTS fentanyl offers an interesting alternative to oral morphine, and its effectiveness and tolerability in this indication has been demonstrated by a number of trials. Its usefulness in chronic pain of nonmalignant origin remains to be confirmed in controlled trials. In general, TTS fentanyl produces the same adverse effects as other opioids, mainly sedation, nausea, vomiting and constipation. In comparison with oral morphine, TTS fentanyl causes fewer gastrointestinal adverse events. The risk of hypoventilation is comparatively low in cancer patients. Sufentanil and buprenorphine may also be suitable for transdermal delivery, but clinical results are not yet available. Transdermal morphine is only useful if applied to de-epithelialised skin. However, iontophoresis may allow transdermal administration of opioids, including morphine, with a rapid achievement of steady state concentrations and the ability to adjust delivery rates. This would be beneficial for acute and/or breakthrough pain, and initial clinical trials are in progress.

Reproducible fentanyl doses delivered intermittently at different time intervals from an electrotransport system

The electrotransport transdermal fentanyl system (ET [fentanyl]), uses a small electrical current to enhance delivery of fentanyl to systemic circulation. Intermittent doses can be administered by periodic application of the current. The purpose of this study was to compare the effects of the frequency of intermittent drug delivery by ET (fentanyl) and compare the drug delivery to systemic circulation by ET (fentanyl) with intravenous administration. The topical safety was also determined for the ET (fentanyl) system. Nine adult male volunteers completed this three-treatment, randomized, 24-h, crossover study. ET (fentanyl) treatments with 200 microA direct current applied for 30 min at frequent (hourly) or infrequent (4-hourly) intervals over a 24-h period were compared. Also, the drug delivery to systemic circulation from ET (fentanyl) was compared with intravenous fentanyl 75 microg infused over 30 min every 4 h over a 24-hour period. The mean serum fentanyl concentration achieved with the hourly ET (fentanyl) regimen was higher than that for the 4-hourly ET (fentanyl) regimen as expected from the higher frequency of drug doses. The amount of fentanyl delivered estimated per dose from the ET (fentanyl) system using the iv fentanyl treatment as the reference was similar for the two ET regimens throughout the dosing period. This indicates consistent drug delivery regardless of the frequency of ET dosing. The majority of subjects reported either no, or barely perceptible, erythema 24 h after removal of the system.

Pharmacokinetic considerations

Limited studies of the pharmacokinetics of pain medication suggest altered serum elimination when the liver is hypoperfused or affected by severe cirrhosis. Drugs that are eliminated by Phase I oxidation reactions are sensitive to changes in hepatic blood flow, while drugs eliminated by Phase II glucuronidation are more affected by diseased hepatocytes. Additionally, alterations in renal function decrease elimination of both parent drugs and metabolites, resulting in toxicity for selected opioids such as meperidine and morphine. Caution is suggested in drawing general conclusions from pharmacokinetic patterns of opioid elimination discussed in this review. Practitioners should be aware that drugs with short duration of action may have long half-lives and accumulate in end-stage liver and renal disease. While pharmacokinetic differences have been described in various populations, the clinical effects and adverse outcomes are greatly influenced by numerous independent physiologic alterations seen in critical care patients. Patients with severe alterations in liver and renal function should be administered pain medications judiciously because these patients are predisposed to metabolic disarrays. These patients should not be denied pain care, but they may benefit from smaller, less frequently administered doses, rather than continuous infusion of opioid drugs. Titration of doses to clinical effects with careful patient assessment for adverse effects is crucial for achieving desired therapeutic outcomes with analgesic agents in the ICU.

Patient-controlled epidural versus intravenous pethidine to supplement epidural bupivacaine after abdominal aortic surgery

In a double-blind, randomized, crossover study of 25 patients after abdominal aortic surgery, we compared patient-controlled analgesia (PCA) with epidural versus intravenous pethidine. All patients received continuous epidural infusions of 0.125% bupivacaine adjusted to maintain appropriate sensory levels. The 48 hour study period commenced 36 to 48 hours after surgery and covered postoperative days 2 and 3. There was a crossover in PCA mode (epidural or intravenous) after 24 hours. Plasma pethidine concentration at the end of each 24 hour period and the total 24 hour pethidine dose did not change significantly between postoperative days 2 and 3. Pethidine plasma concentration was lower after 24 hours epidural than after intravenous PCA [125 (SD 108) ng/ml versus 171 (SD 107) ng/ml, P = 0.03], although pethidine dose did not differ significantly [mean 147 (SD 124) mg/24 h]. Visual analog pain scores (VAS) did not differ significantly between postoperative days 2 and 3, or at rest between epidural and i.v. groups. However, VAS with coughing and with abdominal palpation were lower in the epidural PCA group (P = 0.05, 0.008). With a background epidural infusion of 0.125% bupivacaine, PCA with epidural pethidine provided better pain control than PCA intravenous pethidine and this was achieved at lower plasma pethidine concentrations.

Fentanyl delivery from an electrotransport system: delivery is a function of total current, not duration of current

This open-label, parallel study of 28 men was conducted to evaluate the pharmacokinetics and safety of fentanyl delivered by the E-TRANS (fentanyl) electrotransport transdermal system (ALZA Corporation, Palo Alto, CA). The E-TRANS (fentanyl) system provided electrically assisted, transdermal, continuous delivery of fentanyl. Treatments consisted of no current (group A); a constant current of 100 microA for 26 hours plus 4 additional doses at varying currents for varying times during hour 25 (groups B, C, D); a constant current of 100 microA for 26 hours plus 4 additional doses at 1,200 microA over 2.5 minutes during hour 1 (group E); or 500 microA for 0.5 hours and 100 microA for 3.5 hours (group F). No fentanyl was detected in serum when no current had been applied. Mean serum fentanyl concentrations were similar regardless of current duration during hour 25 (treatments B, C, D). Increases in mean serum fentanyl concentrations were significantly lower during additional dosing for treatment E compared with treatments B, C, and D. Serum fentanyl concentrations sufficient for analgesia (1-3 ng/mL) were attained in treatments using the E-TRANS (fentanyl) system with basal current of 100 microA for 26 hours. There were no safety issues after treatment with E-TRANS (fentanyl) system with concurrent opioid antagonist (naltrexone) administration. The only adverse event requiring treatment was a headache (n = 1). The majority of subjects had no or barely perceptible erythema at the application site 24 hours after system removal. Application of E-TRANS (fentanyl) resulted in therapeutically significant serum fentanyl concentrations over a range of applied currents. Overall serum fentanyl concentrations were higher when the skin had been primed by constant-current fentanyl delivery.

[Benefit-risk and monitoring modalities of different techniques and methods of postoperative analgesia]

This review aimed to determine the benefits-risks ratio of postoperative analgesia. The various agents usually used for intravenous postoperative analgesia (paracetamol, NSAID's, opioids), and the techniques for postoperative analgesia (PCA, epidural, perinervous block) are analysed. The rules proposed for the monitoring of postoperative analgesia are considered.

Effect of current density on pharmacokinetics following continuous or intermittent input from a fentanyl electrotransport system

The pharmacokinetics of fentanyl were determined in two open-label crossover studies following 24-h periods of delivery by an electrotransport transdermal system (E-TRANS [fentanyl] system) in young healthy male volunteers. A direct current was applied continuously in study 1 (at 50, 100, and 200 microA; surface area = 5 cm2; n = 8), but in study 2 it was limited to the first 20 min of each hour (at 150, 200, and 250 microA; surface area = 2 cm2; n = 12). The opioid effects of fentanyl were blocked with naltrexone administered every 12 h. With increasing electrical current, the increase in serum fentanyl concentration, amount absorbed, and AUC values were proportional in study 2 but not in study 1. It is hypothesized that the lack of proportionality in study 1 is due to lower current density (microA/cm2) in this study. It appears that for fentanyl, the current density should be about 75 microA/cm2 or greater for a linear relation between current and amount absorbed as seen in study 2. Compared with intravenously infused fentanyl, the serum concentrations resulting from E-TRANS (fentanyl) system application revealed a slightly dampened rate of increase (stratum-corneum barrier effect) and decrease in serum concentrations, and a similar intersubject variability in fentanyl AUC values. Fentanyl pharmacokinetics with either E-TRANS (fentanyl) or intravenous infusion were time-invariant over a 24-h application period, with similar mean half-life values (about 15-18 h). E-TRANS (fentanyl) administration (either continuous or intermittent input) was safe and well tolerated. Adverse effects were mild to moderate; they consisted mainly of local erythema and pruritus (which resolved in most patients within 24 h after system removal) and occasional opioid effects.

Comparison of analgesic efficacy of oxycodone and morphine in postoperative intravenous patient-controlled analgesia

BACKGROUND

Morphine has been the standard opioid in patient-controlled analgesia (PCA). Oxycodone, the analgesic potency of which in i.v. administration has been suggested to be slightly greater than that of morphine, has not yet been studied for its efficacy in PCA.

METHODS

Fifty patients, undergoing a plastic reconstruction of the breast or a major operation of the vertebrae, such as lumbar spinal fusion, used PCA for postoperative pain. Patients were randomized to receive either morphine 45 microg/kg or oxycodone 30 microg/kg as i.v. bolus doses. Patients were assessed for pain with a visual analogue scale (VAS) and side effects at 3, 9 and 24 h. Venous blood samples for the measurement of plasma concentration of oxycodone and that of morphine and its metabolites were taken.

RESULTS

In this study patients needed, on average, the same amount of oxycodone and morphine in the recovery room and on the ward. There was no difference in the quality of analgesia (VAS) or incidence of side effects, such as nausea, vomiting, pruritus and urinary retention. The plasma concentrations of morphine-6-glucuronide showed that this metabolite might contribute to the analgesia resulting from morphine administration.

CONCLUSIONS

The same dose of intravenous oxycodone and morphine administered by PCA pump was needed for immediate postoperative analgesia. The two drugs appear to be equipotent.