Ventilatory response to carbon dioxide after epidural clonidine injection

Amphetamines modulate fentanyl-depressed respiration in a bidirectional manner

BACKGROUND

The opioid epidemic remains one of the most pressing public health crises facing the United States. Fentanyl and related synthetic opioid agonists have largely driven the rising rates of associated overdose deaths, in part, because of their surreptitious use as substitutes for other opioids and as adulterants in psychostimulants. Deaths involving opioids typically result from lethal respiratory depression, and it is currently unknown how co-use of psychostimulants with opioids affects respiratory toxicity. Considering psychostimulant overdoses have increased over 3-fold since 2013, and half of those co-involved opioids, this is a cardinal question.

METHODS

Naloxone, d-amphetamine (AMPH), and (±)-methamphetamine (METH) were evaluated for their effects on basal and fentanyl-depressed respiration. Minute volume (MVb) was measured in awake, freely moving mice via whole-body plethysmography to quantify fentanyl-induced respiratory depression and its modulation by dose ranges of each test drug.

RESULTS

Naloxone immediately reversed respiratory depression induced by fentanyl only at the highest dose tested (10 mg/kg). Both AMPH and METH exhibited bidirectional effects on MVb under basal conditions, producing significant (p ≤ 0.05) depressions then elevations of respiration as dose increased. Under depressed conditions the bidirectional effects of AMPH and METH on respiration were exaggerated, exacerbating and then reversing fentanyl-induced depression as dose increased.

CONCLUSIONS

These results indicate that co-use of amphetamines with fentanyl may worsen respiratory depression, but conversely, monoaminergic components of the amphetamines may possibly be exploited to mitigate fentanyl overdose.

Postoperative Analgesia in Neonates and Infants Using Epidural Chloroprocaine and Clonidine

INTRODUCTION

In neonates and infants, epidural analgesia has gained popularity as a means of providing postoperative analgesia, limiting opioid-related adverse effects and improving the postoperative course. In addition to a local anesthetic agent, adjunctive agents may be added to further augment analgesia. Clonidine is an α2-adrenergic agonist that is frequently added to single-shot caudal analgesia, but there are limited data regarding its use in a continuous epidural infusion, especially in patients ≤12 months of age.

METHODS

We retrospectively reviewed the hospital records of neonates and infants who received postoperative epidural infusions with 2-chloroprocaine, and clonidine was identified over a 4-year period.

RESULTS

The study cohort included 52 neonates and infants ranging in age from 0 to 12 months and in weight from 2.1 to 10.1 kilograms. The catheters were dosed with either 1.5% 2-chloroprocaine (n=47) or 3% 2-chloroprocaine (n=5) with clonidine (median concentration 0.2 µg/mL) infused at a median rate of 0.72 mL/kg/hour. Pain scores were uniformly ≤3 at all evaluation points during the first 72 postoperative hours with a limited need for supplemental systemic opioids. No serious adverse effects were noted.

CONCLUSION

With the recognized limitations of a retrospective study, these preliminary data demonstrate the safety of adding clonidine to an epidural infusion of 2-chloroprocaine in neonates and infants less than 12 months of age. Future studies are needed to determine its analgesic efficacy compared to 2-chloroprocaine alone and the optimal clonidine concentration for postoperative epidural infusions.

Comparison of lumbar epidural bupivacaine with fentanyl or clonidine for postoperative analgesia in children with cerebral palsy after single-event multilevel surgery

AIM

To compare diazepam use, muscle spasm, analgesia, and side effects when clonidine or fentanyl are added to epidural bupivacaine in children with cerebral palsy after multilevel orthopaedic surgery.

METHOD

Fifty children were prospectively randomized to receive clonidine (n=24, mean age 10y 10mo [SD 2y 11mo]) or fentanyl (n=26, mean age 10y 11mo [SD 2y 10mo]).

RESULTS

There was no difference in primary outcome measures: median diazepam use (fentanyl 0, interquartile range [IQR] 0-0; clonidine 0, IQR 0-0; p=0.46), any muscle spasm (no muscle spasms in: fentanyl, 36%; clonidine, 62%; p=0.11), painful muscle spasm (fentanyl 40%; clonidine 25%; p=0.46), or pain score ≥6 (none: fentanyl 44%; clonidine 42%; p=0.29). There were differences in secondary outcome measures: no vomiting (clonidine 63%; fentanyl 20%); vomiting occurred more frequently with fentanyl (32% vomited more than three times; clonidine none; p=0.001). Fentanyl resulted in more oxygen desaturation (at least two episodes: fentanyl 20%; clonidine 0; p<0.001). Clonidine resulted in lower mean (SD) area under the curve for systolic blood pressure (fentanyl 106.5 [11.0]; clonidine 95.7mmHg [7.9]) and heart rate (fentanyl 104.9 beats per minute [13.6]; clonidine 85.3 [11.5]; p<0.001).

INTERPRETATION

Clonidine and fentanyl provide adequate analgesia with low rates of muscle spasm, resulting in low diazepam use. The choice of epidural additive should be based upon the most tolerable side-effect profile.

Postoperative analgesia in children when using clonidine or fentanyl with ropivacaine given caudally

Background:

The aim of the study was to compare the efficacy of clonidine and fentanyl as an additive to ropivacaine given via single shot caudal epidural in pediatric patients for postoperative pain relief.

Materials and Methods:

In the present double blind study, 90 children of ASA-I-II aged 3-8 years scheduled for infraumblical surgical procedures were randomly allocated to two groups to receive either ropivacaine 0.25% 1 ml/kg + clonidine 2 μg/kg (group I) or ropivacaine 0.25% 1 μl/kg + fentanyl 1 μg/kg (group II). Caudal block was performed after the induction of general anesthesia. Postoperatively patients were observed for analgesia, sedation, hemodynamics, and side effects/complications.

Results:

Both the groups were similar with respect to patient and various block characteristics. The analgesic properties and hemodynamics were also comparable in both groups (P > 0.05). Side effects such as respiratory depression, vomiting bradycardia were significantly less in group I than group II (P < 0.05) ensuing more patient comfort.

Conclusions:

The analgesic properties of clonidine and fentanyl as additives to ropivacaine in single shot caudal epidural in children are comparable but clonidine offers a more favorable side effect profile. The use of clonidine as additive to ropivacaine in caudal epidural is superior choice to fentanyl because of lack of unwanted side effects and increased patient comfort.

[Dexmedetomidine and clonidine: a review of their pharmacodynamy to define their role for sedation in intensive care patients]

Alpha-2 adrenergic agonists ("alpha-2 agonists") present multiple pharmacodynamic effects: rousable sedation, decreased incidence of delirium in the setting of critical care, preservation of respiratory drive, decreased whole body oxygen consumption, decreased systemic and pulmonary arterial impedance, improved left ventricular systolic and diastolic function, preserved vascular reactivity to exogenous catecholamines, preserved vasomotor baroreflex with lowered set point, preserved kidney function, decreased protein catabolism. These pharmacodynamic effects explain the interest for these drugs in the critical care setting. However, their exact role for sedation in critically ill-patients remains open for further studies. Given the few double-blind randomized multicentric trials available, the present non exhaustive analysis of the literature aims at presenting the utilization of alpha-2 agonists as potential first-line sedative agents, in the critical care setting. Suggestions regarding the use of alpha-2 agonists as sedatives are detailed.

Effects of clonidine on breathing during sleep and susceptibility to central apnoea

We hypothesized that administration of clonidine would decrease the hypocapnic apnoeic threshold (HAT) and widen the CO(2) reserve during non-REM sleep.

METHODS

Ten healthy subjects (4 females) (age 22.3 ± 3.0 years; BMI 25.5 ± 3.4 kg/m(2)) were randomized to receive placebo or 0.1 mg/45 kg of clonidine on 2 separate nights. Ventilation and upper airway resistance were monitored during wakefulness and sleep. Two separate experiments were performed: Protocol 1 (n=8), CO(2) reserve, HAT and HcVR were determined using non-invasive hyperventilation (NIV) to induce hypocapnia for at least 3 min; Protocol 2 (n=6), peripheral hypocapnic ventilatory response (HcVR) was determined by NIV using short (3 breaths) hyperventilation.

RESULTS

Clonidine decreased the systolic blood pressure by 12 ± 10 mmHg but did not affect baseline ventilation or upper airway resistance during wakefulness or sleep. Protocol (1), clonidine was associated with decreased HAT relative to placebo (37.3 ± 3.3 mmHg vs. 39.7 ± 3.4 mmHg, P<0.05), increased CO(2) reserve (-3.8 ± 1.3 mmHg vs. -2.8 ± 1.2 mmHg, P<0.05), and decreased HcVR (1.6 ± 0.6 L/min/mmHg vs. 2.5 ± 1.3 L/min/mmHg, P<0.05). Protocol (2), administration of clonidine did not decrease peripheral HcVR compared to placebo (0.5 ± 0.3 L/min/mmHg vs. 0.7 ± 0.3 L/min/mmHg, P=NS).

CONCLUSION

Clonidine is associated with diminished susceptibility to hypocapnic central apnoea without significant effect on ventilation or upper airway mechanics. Reduced susceptibility to hypocapnic central apnoea is not explained by the peripheral chemoreceptor pathway. This suggests a central rather than a peripheral effect of clonidine on the susceptibility to hypocapnic central apnoea.

Dexmedetomidine and clonidine induce long-lasting activation of the respiratory rhythm generator of neonatal mice: possible implication for critical care

Dexmedetomidine and clonidine are alpha-2 adrenoceptor agonists increasingly used in the critical care unit as sedative agents for their benzodiazepine-sparing effects and their limited depressing effect on breathing. However adverse effects on breathing have been also reported with alpha-2 adrenoceptor agonists and their central effects on the respiratory rhythm generator are poorly known. We therefore examined the effects of dexmedetomidine, clonidine, the alpha-2 adrenoceptor antagonist yohimbine and the benzodiazepine midazolam on the activity of the isolated respiratory rhythm generator of neonatal mice using medullary preparations where the respiratory rhythm generator continued to function in vitro. For the first time, we showed that 5min bath applications of dexmedetomidine or clonidine activated the respiratory rhythm generator for periods over than 30min. Second, we showed that the long-lasting effect of dexmedetomidine implicated receptors other than alpha-2 adrenoceptors as it persisted after their blockade with yohimbine. Third, we reported that 5min bath applications of the benzodiazepine midazolam significantly depressed the respiratory rhythm generator, and that this depression was prevented by pre-treatment with either dexmedetomidine or clonidine. Although further experiments are still required to identify the mechanisms through which dexmedetomidine and clonidine activate the respiratory rhythm generator, our current in vitro results in neonatal mice support the use of dexmedetomidine and clonidine in the critical care unit.

Clinical evaluation of clonidine added to lidocaine solution for subarachnoid analgesia in sheep

Clonidine (CL) is a alpha2-adrenergic agonist that produces analgesia in animals and humans by a non-opiate alpha2-adrenergic action in the spinal cord dorsal horn. The objective of this prospective randomized study was to investigate the clinical effects of CL/lidocaine (LD) combination administered by the subarachnoid route in sheep. Each sheep received each of three treatments, at no shorter than weekly intervals. Treatments consisted of 0.003 mg/kg CL, 1.2 mg/kg LD and a combination of CL (0.003 mg/kg) and LD (1.2 mg/kg) (CLLD). Subarachnoid injections were given in all animals between the last lumbar and first sacral vertebra. Heart rate (HR), arterial pressures, respiratory rate, rectal temperature, analgesia, sedation, and motor blockade were determined before drug administration (basal) and 5, 10, 15 and 30 min after drug administration, and at 30-min intervals until loss of analgesia occurred. The duration of analgesia after subarachnoid CLLD administration was 187 +/- 24 min (mean +/- SD), i.e. more than twice of that obtained with CL (99 +/- 19 min) or LD (55 +/- 4.4 min) alone. In all sheep, CL, administered either alone or with LD, induced moderate sedation. After subarachnoid administration of three treatments, all sheep had ataxia and subsequent sternal recumbency. The CL treatment causes decreases in blood pressure (diastolic arterial pressure and mean arterial pressure) and HR. Data suggest that the CLLD combination could be used subarachnoidally in sheep requiring prolonged surgery.

Oral clonidine does not change ventilatory response to carbon dioxide in sevoflurane-anesthetized children

BACKGROUND

Clonidine is a useful premedicant for pediatric anesthesia. The drug has potential for ventilatory depression. The aim of the current study was to determine the effects of clonidine premedication on the ventilatory response to hypercapnia during sevoflurane anesthesia using the carbon dioxide (CO(2)) steady state method.

METHODS

Sixty children (3-13 yr) were assigned to receive clonidine 4 microg x kg(-1) or placebo. Anesthesia was maintained with spontaneous breathing and 2% sevoflurane. Minute ventilation (VE), respiratory rate (RR), endtidal CO(2) pressure (P(ECO(2)), and arterial hemoglobin oxygen saturation (SpO2) were measured with a facemask tightly fitted before and during 7% CO(2) inhalation.

RESULTS

Compared with placebo, oral clonidine failed to reduce VE volume before CO(2) loading under general anesthesia with 2% sevoflurane. Inhalation of CO(2) increased VE. Oral clonidine did not attenuate the increase in VE induced by hypercapnic challenge under sevoflurane anesthesia. There were no differences in RR, P(ECO(2), or SpO2 between the placebo and clonidine groups before and during CO(2) loading.

CONCLUSION

These data suggest that oral clonidine is a suitable premedication for sevoflurane anesthesia under spontaneous breathing conditions in children.

Ventilatory effects of alpha2-adrenoceptor blockade in awake goats

We sought to determine the extent to which alpha2-adrenoceptor (alpha2-AR) pathways exert a tonic influence on respiratory rhythm under normal physiological conditions. The ventilatory effects of alpha2-AR blockade with SKF-86466 were examined in awake adult goats. The antagonist effect of SKF-86466 at alpha(2)-ARs was evident both as a reversal of the ventilatory disturbances produced by the alpha2-AR agonist clonidine (5 microg/kg IV) and as a rightward shift in the potency of the agonist-evoked response after SKF-86466 pretreatment. Systemic administration of SKF-86466 in cumulative doses (25-250 microg/kg) or as a single bolus injection (500 microg/kg) produced dose-dependent increases in breathing in all animals. The excitatory effect was primarily mediated by increases in respiratory frequency that persisted for at least 120 min after injection (500 microg/kg). The time course and magnitude of the ventilatory response to SKF-86466 was similar in carotid body denervated animals. The ventilatory response to isocapnic hypoxia but not normoxic hypercapnia was significantly elevated after SKF-86466 administration (500 microg/kg). SKF-86466 (25-1000 microg/kg) produced dose-dependent increases in heart rate in all animals but did not significantly change mean arterial blood pressure at any dose. The results demonstrate that alpha2-AR pathways exert a tonic inhibitory influence on respiratory rhythm in the awake goat.

Sedative, analgesic and cognitive effects of clonidine infusions in humans

This placebo-controlled, randomized study evaluated, on separate days, the dose-response relationship for 1 h infusions of clonidine 1, 2 and 4 microg kg(-1) h(-1), in eight healthy volunteers aged 22-30 yr. Response end-points included sedation (bispectral index, visual analogue scale and observer assessment of sedation), analgesia to a cold pressor test, memory (recall of word lists), cognitive function (digit symbol substitution test (DSST)), respiratory function (respiratory rate, end-tidal carbon dioxide, oxygen saturation) and haemodynamic stability (heart rate and mean arterial pressure). Clonidine infusions resulted in significant and progressive sedation, but all subjects were easily awoken to perform tests and evaluations. Statistically significant analgesia, memory impairment and reduced performance on the DSST occurred during 4 microg kg(-1) h(-1) infusions (resulting in a plasma concentration of 2 ng ml(-1). There were no statistically significant changes in cardiorespiratory variables throughout the study.

Sedative, amnestic, and analgesic properties of small-dose dexmedetomidine infusions

This research determined the safety and efficacy of two small-dose infusions of dexmedetomidine by evaluating sedation, analgesia, cognition, and cardiorespiratory function. Seven healthy young volunteers provided informed consent and participated on three occasions with random assignment to drug or placebo. Heart rate, blood pressure, respiratory rate, ETCO(2), O(2) saturation, and processed electroencephalogram (bispectral analysis) were monitored. Baseline hemodynamic measurements were acquired, and psychometric tests were performed (visual analog scale for sedation; observer's assessment of alertness/sedation scale; digit symbol substitution test; and memory). The pain from a 1-min cold pressor test was quantified with a visual analog scale. After a 10-min initial dose of saline or 6 microg. kg(-1). h(-1) dexmedetomidine, volunteers received 50-min IV infusions of saline, or 0.2 or 0.6 microg. kg(-1). h(-1) dexmedetomidine. Measurements were repeated at the end of infusion and during recovery. The two dexmedetomidine infusions resulted in similar and significant sedation (30%-60%), impairment of memory (approximately 50%), and psychomotor performance (28%-41%). Hemodynamics, oxygen saturation, ETCO(2), and respiratory rate were well preserved throughout the infusion and recovery periods. Pain to the cold pressor test was reduced by 30% during dexmedetomidine infusion. Small-dose dexmedetomidine provided sedation, analgesia, and memory and cognitive impairment. These properties might prove useful in a postoperative or intensive care unit setting. IMPLICATIPNS: The alpha(2) agonist, dexmedetomidine, has sedation and analgesic properties. This study quantified these effects, as well as cardiorespiratory, memory and psychomotor effects, in healthy volunteers. Dexmedetomidine infusions resulted in reversible sedation, mild analgesia, and memory impairment without cardiorespiratory compromise.

Transcutaneous CO2 tension effects of clonidine in paediatric caudal analgesia

In adults, clonidine when added to bupivacaine, results in no detectable respiratory depressant effect except when carbon dioxide challenge is performed. However, to date no investigations have quantified this in children. Twenty-four children (nine months to seven years) were randomized in a double-blind study into two groups. After induction, a caudal block was performed with 1 ml.kg-1 0.25% bupivacaine. Clonidine 1 microgram.kg-1 was added in the clonidine group, and 1 ml normal saline in the placebo group. Patients were monitored in the recovery room for three h from arrival to discharge with continuous pulse oximetry, respiratory rate, a transcutaneous CO2 tension (tcPCO2) every 15 min, and a four point sedation score every 30 min. Mean tcPCO2 and respiratory rate values were not different between the two groups. Apnoea and desaturation less than 97% were not observed. The sedation score decreased with time in both groups, and the score time interval was significantly higher in the clonidine group (P < 0.05). All the patients left the recovery room with a sedation score of 1, excepting four in the clonidine group with a sedation score of 2. Clonidine 1 microgram.kg-1 with 0.25% bupivacaine mixture in caudal analgesia in children did not induce an increase in tcPCO2 despite prolonged sedation.

The efficacy and safety of a clonidine/bupivacaine combination in caudal blockade for pediatric hernia repair

We evaluated the analgesic efficacy and hemodynamic and respiratory safety of clonidine when added to bupivacaine for caudal blocks in 58 children aged 38 +/- 2 mo (mean +/- SEM). Patients scheduled for ambulatory hernia repair were randomly given a caudal injection (0.75 mL/kg) of either saline placebo (P group), bupivacaine, 0.25% (B group), bupivacaine plus epinephrine 1:200,000 (BE group), bupivacaine plus clonidine 1 microgram/kg (BC1 group), or bupivacaine plus clonidine 2 micrograms/kg (BC2 group). Postoperative measurements included duration of analgesia, hemodynamics, and respiratory monitoring for 6 h. Thereafter, parents assessed their child's analgesic requirements at home every 3 h for 18 h. The duration of analgesia (median [range]) was significantly longer (P < 0.05) in the BC1 and BC2 groups (360 [270-360] min and 360 [355-360] min, respectively) compared with the P (77[45-190]), B (346[105-360]), or BE group (300[75-360]). Similarly, the BC1 and BC2 groups required less additional analgesic within the first 24 h. All groups showed a significant decrease in mean arterial pressure compared with baseline values, but the differences among the groups were not significant. Bradycardia and respiratory depression were not observed. Clonidine 1 and 2 micrograms/kg can be safely added to bupivacaine caudal blockade in small children for ambulatory hernia repair to achieve an increased duration of analgesia compared with bupivacaine alone or bupivacaine plus epinephrine.

IMPLICATIONS

The addition of clonidine, an antihypertensive drug with analgesic properties, to local anesthetics in caudal blocks prolongs postoperative pain relief and reduces the need for additional pain treatment in children after hernia operation.

The efficacy and safety of a clonidine/bupivacaine combination in caudal blockade for pediatric hernia repair

We evaluated the analgesic efficacy and hemodynamic and respiratory safety of clonidine when added to bupivacaine for caudal blocks in 58 children aged 38 +/- 2 mo (mean +/- SEM). Patients scheduled for ambulatory hernia repair were randomly given a caudal injection (0.75 mL/kg) of either saline placebo (P group), bupivacaine, 0.25% (B group), bupivacaine plus epinephrine 1:200,000 (BE group), bupivacaine plus clonidine 1 microgram/kg (BC1 group), or bupivacaine plus clonidine 2 micrograms/kg (BC2 group). Postoperative measurements included duration of analgesia, hemodynamics, and respiratory monitoring for 6 h. Thereafter, parents assessed their child's analgesic requirements at home every 3 h for 18 h. The duration of analgesia (median [range]) was significantly longer (P < 0.05) in the BC1 and BC2 groups (360 [270-360] min and 360 [355-360] min, respectively) compared with the P (77[45-190]), B (346[105-360]), or BE group (300[75-360]). Similarly, the BC1 and BC2 groups required less additional analgesic within the first 24 h. All groups showed a significant decrease in mean arterial pressure compared with baseline values, but the differences among the groups were not significant. Bradycardia and respiratory depression were not observed. Clonidine 1 and 2 micrograms/kg can be safely added to bupivacaine caudal blockade in small children for ambulatory hernia repair to achieve an increased duration of analgesia compared with bupivacaine alone or bupivacaine plus epinephrine.

IMPLICATIONS

The addition of clonidine, an antihypertensive drug with analgesic properties, to local anesthetics in caudal blocks prolongs postoperative pain relief and reduces the need for additional pain treatment in children after hernia operation.

Clonidine reduces hyperpolarization-activated inward current (Ih) in rat hypoglossal motoneurons

We used intracellular recording techniques to investigate the actions of clonidine on hypoglossal motoneurons (HMs) in rat brainstem slices. Clonidine (10-100 microM) produced a small (2-6 mV), dose-dependent hyperpolarization in HMs, accompanied by an increase in peak input resistance (RN). It also slowed the time course of the depolarizing 'sag' of the voltage response to constant hyperpolarizing current steps. These effects were mimicked by the alpha2-adrenoceptor (alpha2-AR) agonist guanabenz, but not by the Ih-imidazoline receptor agonists moxonidine or rilmenidine. Recorded in single-electrode voltage clamp mode, clonidine decreased input conductance of HMs and reduced the amplitude of a hyperpolarization-activated inward current (Ih). Clonidine's effect on Ih was three-fold: it shifted the half-activation voltage (V1/2) in the hyperpolarizing direction (by 4.4 +/- 0.7 mV at a dose of 10 microM), decreased the maximal current (by approximately 20%), and slowed the time course of Ih activation at all voltage steps. At the most hyperpolarized potential steps, clonidine slowed activation of Ih dramatically, yielding a striking increase in the activation time constant. The alpha2-AR antagonists yohimbine and idazoxan reduced clonidine's effect on V1/2 and on the Ih activation time course, but neither blocked clonidine's reduction of the maximal current, nor its strong slowing of Ih activation at the most hyperpolarized steps. We were unable to mimic or occlude clonidine's actions with the adenylate cyclase inhibitor SQ 22536 nor with the non-specific protein kinase inhibitor H-7. We conclude that clonidine hyperpolarizes HMs via a reduction of the amount of Ih that is active at rest, and that the response is mediated in part by alpha2-ARs. Some effects of clonidine on these neurons do not appear to be receptor-mediated, and may be due to physical block by clonidine of Ih channels.

Caudal clonidine and bupivacaine for combined epidural and general anaesthesia in children

BACKGROUND

Clonidine produces analgesia by actions on alpha 2-adrenoceptors and enhances both sensory and motor blockade from epidural injection of local anaesthetics. Low-dose clonidine has been used so far for caudal injection in children. Our aim was to study the perioperative effects of high-dose caudal clonidine when added to low concentration of bupivacaine for combined epidural and general anaesthesia in children.

METHODS

After induction of general anaesthesia caudal block was performed either with 1 ml.kg-1 bupivacaine 0.175% with the addition of clonidine 5 micrograms.kg-1 (n = 20), or with 1 ml.kg-1 bupivacaine 0.175% (n = 20). The intraoperative anaesthetic requirements, the perioperative haemodynamic effects, respiratory rate, sedation score, postoperative pain scores and side effects were assessed by a blinded observer. A patient-controlled analgesia system was used for postoperative pain relief. The quality of postoperative pain relief was assessed using Smiley's pain analogue scale.

RESULTS

Intraoperative haemodynamic responses did not differ between the groups. However, during emergence from general anaesthesia children in the clonidine group had significantly lower heart rates and blood pressure compared to children in the control group. In addition, heart rates and blood pressures were also lower in the clonidine group in the early postoperative period (P < 0.05). Postoperative analgesia was significantly better in the clonidine group as evidenced by the total number of requests (3 vs 12, P < 0.05) and the total amount of tramadol (20.5 mg vs 72.8 mg, P < 0.05) administered. The duration of the caudal analgesia was significantly longer in the clonidine group (20.9 +/- 7.4 h vs 14.4 +/- 10.9 h, P < 0.05).

CONCLUSION

Our results suggest that caudal clonidine 5 micrograms.kg-1 enhances and prolongs caudal blockade with bupivacaine (1.175% in children. It also blocks sympathoadrenergic responses during emergence from anaesthesia. Sedation and cardiovascular effects are observed up to 3 h into the postoperative period.

Spinal or systemic analgesia after extensive spinal surgery: comparison between intrathecal morphine and intravenous fentanyl plus clonidine

STUDY OBJECTIVE

To compare two different methods of postoperative analgesia after extensive spinal fusion.

DESIGN

Double-blind, randomized study.

SETTING

University-affiliated hospital.

PATIENTS

Twenty four adult patients undergoing scoliosis correction.

INTERVENTIONS

Before the end of surgery, patients received either intravenous clonidine 0.3 micrograms/kg/hr and fentanyl 25 micrograms/kg (after an hourly dose of clonidine 2.5 micrograms/kg) or intrathecal morphine 0.3 mg. A saline infusion was administered to patients receiving morphine intrathecally.

MEASUREMENTS AND MAIN RESULTS

Pain and sedation scores, hemodynamic data, and blood gases were collected in the recovery room at tracheal extubation and then every 2 hours for the next 14 hours. Tracheal extubation was performed at the same time in both groups (i.e., an average of 4 hours after the analgesic regimens were started). Intrathecal morphine provided a mean score of 20 mm on a visual analog scale ranging from 0 mm (no pain) to 100 mm (severe pain), but it resulted in increased PaCO2 at extubation (44 +/- 7 mmHg) and 2 hours later (42 +/- 7 mmHg). PaCO2 was greater than 50 mmHg in four patients receiving intrathecal morphine. Fentanyl-clonidine resulted in equipotent analgesia but was accompanied by sedation (sleeping but arousal by light tactile stimulation) and moderate hypotension (up to 69 +/- 9 mmHg for mean arterial pressure).

CONCLUSIONS

This study shows that there is a major risk of respiratory depression with a single intrathecal dose of morphine 0.3 mg to control postoperative pain after scoliosis surgery. Systemic clonidine-fentanyl may be a possible approach to the postoperative pain treatment of this surgery.

Ventilatory effects of epidural clonidine during the first 3 hours after caesarean section

Many authors have shown the analgesic efficacy of 150-800 micrograms of epidural clonidine in the postoperative period. Its use as an analgesic after caesarean section has recently been studied with higher dosages (400-800 micrograms). Our study aimed at assessing the analgesic and ventilatory effects of two smaller doses of epidural clonidine (150 and 300 micrograms), which were compared to the effects of 10 mg of parenteral morphine (M) during the first 3 h after caesarean section. The duration of the analgesic effect was longest with 150 micrograms of epidural clonidine. Arterial blood pressure decreased from 30 min after the injection to the end of the study in both epidural clonidine groups. A marked sedation was observed in patients receiving 300 micrograms of epidural clonidine and was frequently associated with snoring, obstructive apnoea and episodes of arterial oxygen desaturation. We conclude that 150 micrograms of epidural clonidine provides better and longer analgesia after caesarean section than 10 mg of parenteral morphine, and seems preferable to higher doses (300 micrograms) in this setting, since 300 micrograms of epidural clonidine may produce unacceptable respiratory obstructive disturbances.