Effects of clonidine premedication on the pressor response to alpha-adrenergic agonists

Hemodynamic Tolerance to IV Clonidine Infusion in the PICU

OBJECTIVES

Clonidine is an antihypertensive drug used for analgosedation in the PICU. Lack of reliable data on its hemodynamic tolerance limits its use. This study explores the hemodynamic tolerance of IV clonidine infusion in a broad population of children with high severity of disease.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

A tertiary and quaternary referral PICU.

PATIENTS

Critically ill children age 0-18 years old who received an IV clonidine infusion for analgosedation of at least 1 hour.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The primary endpoints were the prevalences of bradycardia and hypotension. Secondary endpoints were changes in heart rate, blood pressure, Vasoactive-Inotropic Score, COMFORT Behavior score (a sedation scoring scale), and body temperature during the infusion. The association of bradycardia with other hemodynamic variables was explored, as well as potential risk factors for severe bradycardia. One-hundred eighty-six children (median age, 12.9 mo [interquartile range, 3.5-60.6 mo]) receiving a maximum median clonidine infusion of 0.7 µg/kg/hr (interquartile range, 0.3-1.5) were included. Severe bradycardia and systolic hypotension occurred in 72 patients (40.2%) and 105 patients (58%), respectively. Clonidine-associated bradycardia was hemodynamically well tolerated, as it was not related with hypotension and the need for vasoactive drugs decreased in parallel with a sedation score guided clonidine infusion rate increase. Younger age was the only identified risk factor for clonidine-associated bradycardia.

CONCLUSIONS

Although administration of clonidine is often associated with bradycardia and hypotension, these complications do not seem clinically significant in a mixed PICU population with a high degree of disease severity. Clonidine may have a vasoactive-inotropic sparing effect.

Comparison of surgical conditions following premedication with oral clonidine versus oral diazepam for endoscopic sinus surgery: A randomized, double-blinded study

Background and Aims:

Endoscopic sinus surgery (ESS) provides a challenge and an opportunity to the anesthesiologists to prove their mettle and give the surgeons a surgical field which can make their delicate surgery safer,more precise and faster. The aim of the study was to evaluate the surgical field and the rate of blood loss in patients premedicated with oral clonidine versus oral diazepam for endoscopic sinus surgery.

Material and Methods:

ASA I or II patients who were scheduled to undergo ESS were randomly allocated to group D (n = 30) or group C (n = 30). The patients' vital parameters, propofol infusion rate, and rate of blood loss were observed and calculated. The surgeon, who was blinded, rated the visibility of the surgical field from grade 0-5.

Results:

In the clonidine group, the rate of blood loss, the surgical time, propofol infusion rate was found to be statistically lower as compared to the diazepam group. Also a higher number of patients in the clonidine group had a better surgical score (better surgical field) than the diazepam group and vice versa.

Conclusions:

Premedication with clonidine as compared to diazepam, provides a better surgical field with less blood loss in patients undergoing ESS.

Cocaine Causes Apoptotic Death in Rat Mesencephalon and Striatum Primary Cultures

To study cocaine's toxic effects in vitro, we have used primary mesencephalic and striatal cultures from rat embryonic brain. Treatment with cocaine causes a dramatic increase in DNA fragmentation in both primary cultures. The toxicity induced by cocaine was paralleled with a concomitant decrease in the microtubule associated protein 2 (MAP2) and/or neuronal nucleus protein (NeuN) staining. We also observed in both cultures that the cell death caused by cocaine was induced by an apoptotic mechanism, confirmed by TUNEL assay. Therefore, the present paper shows that cocaine causes apoptotic cell death and inhibition of the neurite prolongation in striatal and mesencephalic cell culture. These data suggest that if similar neuronal damage could be produced in the developing human brain, it could account for the qualitative or quantitative defects in neuronal pathways that cause a major handicap in brain function following prenatal exposure to cocaine.

The role of systematic reviews in pharmacovigilance planning and Clinical Trials Authorisation application: example from the SLEEPS trial

BACKGROUND

Adequate sedation is crucial to the management of children requiring assisted ventilation on Paediatric Intensive Care Units (PICU). The evidence-base of randomised controlled trials (RCTs) in this area is small and a trial was planned to compare midazolam and clonidine, two sedatives widely used within PICUs neither of which being licensed for that use. The application to obtain a Clinical Trials Authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA) required a dossier summarising the safety profiles of each drug and the pharmacovigilance plan for the trial needed to be determined by this information. A systematic review was undertaken to identify reports relating to the safety of each drug.

METHODOLOGY/PRINCIPAL FINDINGS

The Summary of Product Characteristics (SmPC) were obtained for each sedative. The MHRA were requested to provide reports relating to the use of each drug as a sedative in children under the age of 16. Medline was searched to identify RCTs, controlled clinical trials, observational studies, case reports and series. 288 abstracts were identified for midazolam and 16 for clonidine with full texts obtained for 80 and 6 articles respectively. Thirty-three studies provided data for midazolam and two for clonidine. The majority of data has come from observational studies and case reports. The MHRA provided details of 10 and 3 reports of suspected adverse drug reactions.

CONCLUSIONS/SIGNIFICANCE

No adverse reactions were identified in addition to those specified within the SmPC for the licensed use of the drugs. Based on this information and the wide spread use of both sedatives in routine practice the pharmacovigilance plan was restricted to adverse reactions. The Clinical Trials Authorisation was granted based on the data presented in the SmPC and the pharmacovigilance plan within the clinical trial protocol restricting collection and reporting to adverse reactions.

Effect of clonidine premedication on blood loss in spine surgery

Background:

Blood loss in spine surgery is an important issue, even though it has been understudied compared with hip and knee arthroplasty.

Objectives:

In this study, we evaluated the effect of oral clonidine as premedication on blood loss in lumbar spine fusion surgery under anesthesia with propofol and remifentanil.

Patients and Methods:

In this double-blind, randomized clinical trial, 30 patients who were undergoing lumbar spine posterior fusion surgery due to traumatic fracture were allocated randomly into 2 groups. The study group (clonidine group) received a 200-μg oral clonidine tablet 60–90 minutes before anesthesia, and the control group received placebo at the same time. Induction and maintenance of anesthesia and the mean target arterial pressure for controlled hypotension with remifentanil were the same in the 2 groups. We compared the amount of intraoperative blood loss, dose of remifentanil/hour administered, need for nitroglycerine to reach the mean target arterial pressure when remifentanil was insufficient, duration of operation, and surgeon’s satisfaction of a bloodless field between groups.

Results:

There was no statistically significant difference between groups in age (P = 0.115), sex (P = 0.439), weight (P = 0.899), operation time (P = 0.2), or American Society of Anesthesiologists physical status score (P = 0.390).

Intraoperative blood loss and remifentanil dose administered per hour in the clonidine group were significantly less than in the control group (P = 0.002 and P = 0.001, respectively), but there was no significant difference in surgeon’s satisfaction between groups (P = 0.169).

Conclusions:

As an oral premedication, clonidine can reduce surgical blood loss in lumbar spine posterior fusion surgery, even at the same levels of mean arterial pressure (MAP) with the control group. Its use can be studied in more complicated spine surgeries, such as scoliosis and spinal deformity surgeries.

Oral clonidine attenuates the fall in mean arterial pressure due to scalp infiltration with epinephrine-lidocaine solution in patients undergoing craniotomy: a prospective, randomized, double-blind, and placebo controlled trial

BACKGROUND

Scalp infiltration with epinephrine-lidocaine solution in patients undergoing neurosurgery may result in transient but significant hypotension. We investigated whether premedication with alpha2-adrenoreceptor agonist clonidine, which also exhibits alpha1-adrenoreceptor mediated vasoconstriction, would prevent or attenuate this fall in mean arterial pressure (MAP).

METHODS

Sixty-six American Society of Anesthesiologists I and II adult patients, 18 to 50 years, undergoing elective tumor decompression were recruited into this prospective, randomized, double-blind, placebo controlled study, and scheduled to receive either oral pantoprazole 40 mg (placebo group) or oral clonidine 3 microg/kg (clonidine group), 90 minutes before induction of anesthesia. Primary end points studied were heart rate (HR) and MAP in both groups measured just before scalp infiltration (preinfiltration baseline) and then every 30 seconds for 5 minutes after initiation of scalp infiltration with 2.5 microg/mL epinephrine contained in 15 mL of 1% lidocaine solution.

RESULTS

There was no significant change in HR in the 2 groups during the study period compared with baseline values; however, patients in clonidine group had significantly lower HR compared with placebo (*P<0.05). In both groups, MAP fell significantly below baseline 1 minute after start of infiltration. It recovered in the clonidine group after 2.5 minutes but not in the placebo group where it continued to remain low even at 5 minutes. MAP in the placebo group was also significantly lower compared with the clonidine group from 2.5 minutes to 5 minutes.

CONCLUSION

In conclusion, oral clonidine 3 microg/kg administered 90 minutes before induction of anesthesia attenuates the fall in MAP due to scalp infiltration with a dilute concentration of epinephrine-lidocaine solution in patients undergoing craniotomy under isoflurane anesthesia.

Normal Aging Impairs Upregulation of the Beta-adrenergic but not the Alpha-Adrenergic Response: Aging and Adrenergic Upregulation

OBJECTIVES

To determine if centrally reducing sympathetic tone with clonidine will reverse the downregulation in the alpha-adrenergic (alphaAR) and beta-adrenergic (betaAR) responses seen with normal aging.

METHODS

Twelve rigorously screened young adult (mean age, 26 years) and 15 older adult (mean age, 69 years) subjects were studied before and after using the clonidine patch (TTS-2) for 2 weeks. betaAR (isoproterenol at 35 ng/kg/min) and alphaAR (phenylephrine at 1.0 microg/kg/min) were assessed using radionuclide measures of end diastolic, end systolic, and stroke volume indices, cardiac index, and ejection fraction.

RESULTS

Clonidine reduced resting plasma norepinephrine and this reduction was greater in older subjects (-47 +/- 3 versus -26 +/- 6%, P = 0.001). After 2 weeks of clonidine patch, upregulation of the betaAR was significantly higher in young subjects for heart rate (+10.7 +/- 1.5 versus +4.6 +/- 1.5 bpm; P = 0.01). There was no significant age-associated difference in the upregulation of the alphaAR with clonidine for systolic, diastolic, and mean blood pressure or systemic vascular resistance.

CONCLUSIONS

With aging, there is an impaired resensitization of the chronotropic betaAR response with central sympathetic downregulation that is not seen with the alphaAR.

Effects of dexmedetomidine on cerebral circulation and systemic hemodynamics after cardiopulmonary resuscitation in dogs

PURPOSE

Our purpose was to examine the effect of dexmedetomidine, when used with phenylephrine during cardiopulmonary resuscitation (CPR), on the cerebral and systemic circulations.

METHODS

In pentobarbital-anesthetized, mechanically ventilated dogs, we evaluated pial vessel diameters, cerebral oxygen extraction, and systemic hemodynamics before and after cardiac arrest (5 min) and resuscitation, in the presence or absence of dexmedetomidine (n = 7 each; dexmedetomidine or control group).

RESULTS

In both groups: (a) pial arterioles were dilated at 5 and 15 min after CPR, and had returned to baseline diameters at 30 min; (b) sagittal sinus pressure was significantly raised at 5 and 15 min after CPR; and (c) cerebral oxygen extraction was decreased at 5, 15, and 30 min after CPR, and had returned to baseline level at 60 min after CPR. We could find no differences between the two groups in the cerebral circulation after CPR. However, the number of defibrillation electric shocks required to restore spontaneous circulation (5.5 vs 3.6; P < 0.05), the dose of phenylephrine used for CPR (1193 microg vs 409 microg; P < 0.01), and the number of postresuscitation ventricular ectopic beats observed during the first 120 min after successful resuscitation (1606 vs 348; P < 0.05) were all significantly lower in the dexmedetomidine group.

CONCLUSION

Although intravenous dexmedetomidine, as used for CPR, does not have a beneficial effect on either cerebral vessels or cerebral oxygen extraction, it may reduce the number of defibrillation shocks needed and the number of postresuscitation ventricular ectopic beats, and help to bring about stable systemic circulation after CPR.

Oral Clonidine Premedication Exacerbates Hypotension Following Tourniquet Deflation by Inhibiting Noradrenaline Release

Clonidine premedication prevents tourniquet pain and reduces sympathetic nerve activity. We evaluated hemodynamic changes and catecholamine release following tourniquet deflation during spinal anesthesia in patients who received oral clonidine premedication. The final analysis included 24 otherwise healthy patients undergoing lower-limb surgery randomly assigned to two groups: those receiving approximately 5 micrograms/kg of oral clonidine 1 hr before anesthesia (clonidine group, n = 12), and those receiving no premedication (control group, n = 12). After lumbar anesthesia, a tourniquet was applied for approximately 60 minutes to each patient. Electrocardiogram, arterial blood pressure, and consumption of butorphanol for tourniquet pain were monitored. Blood samples were obtained at different times to measure serum concentration of catecholamine. In the clonidine group, mean blood pressure decreased from 87 +/- 7 mmHg at baseline to 65 +/- 10 mmHg after tourniquet deflation (P < 0.05). This peak reduction of mean blood pressure in the clonidine group was significantly lower than in the control group. After receiving clonidine premedication, the plasma noradrenaline concentrations in the clonidine group were significantly lower than those in the control group. Noradrenaline concentration increased in the control group from 162.3 +/- 89.2 pg/mL before tourniquet deflation to 199.3 +/- 95.7 pg/mL afterward (P < 0.01), but there was no significant change in noradrenaline concentration after tourniquet deflation in the clonidine group. We conclude that oral clonidine premedication exacerbated the reduction in mean blood pressure following tourniquet deflation by inhibiting noradrenaline release.

Epidural clonidine suppresses the baroreceptor-sympathetic response depending on isoflurane concentrations in cats

Epidural administration of clonidine induces hypotension and bradycardia secondary to decreased sympathetic nerve activity. In this study, we sought to elucidate the change in baroreflex response caused by epidural clonidine. Thirty-six cats were allocated to six groups (n = 6 each) and were given either thoracic epidural clonidine 4 micro g/kg or lidocaine 2 mg/kg during 0.5, 1.0, or 1.5 minimum alveolar anesthetic concentration (MAC) isoflurane anesthesia. Heart rate (HR), mean arterial blood pressure (MAP), and cardiac sympathetic nerve activity (CSNA) were measured. Depressor and pressor responses were induced by IV nitroprusside 10 micro g/kg and phenylephrine 10 micro g/kg, respectively. Baroreflex was evaluated by the change in both CSNA and HR relative to the peak change in MAP (deltaCSNA/deltaMAP and deltaHR/deltaMAP, respectively). These measurements were performed before and 30 min after epidural drug administration. Epidural clonidine and lidocaine decreased HR, MAP, and CSNA by similar extents. deltaCSNA/deltaMAP and deltaHR/deltaMAP for depressor response were suppressed with epidural lidocaine and clonidine in all groups but the clonidine 0.5 MAC isoflurane group (0.197 +/- 0.053 to 0.063 +/- 0.014 and 0.717 +/- 0.156 to 0.177 +/- 0.038, respectively, by epidural lidocaine [P < 0.05] but 0.221 +/- 0.028 to 0.164 +/- 0.041 and 0.721 +/- 0.177 to 0.945 +/- 0.239, respectively, by epidural clonidine during 0.5 MAC isoflurane). Those for pressor response were suppressed in all groups. We conclude that thoracic epidural clonidine suppresses baroreflex gain during isoflurane anesthesia >1.0 MAC but may offer certain advantages compared with epidural lidocaine during 0.5 MAC isoflurane by virtue of preserving baroreflex sensitivity when inadvertent hypotension occurs.

The effects of clonidine premedication on the blood pressure and tachycardiac responses to ephedrine in elderly and young patients during propofol anesthesia

We studied the pressor and tachycardiac responses to ephedrine in elderly and young patients given either clonidine or midazolam during propofol anesthesia. In the first experiment, elderly (>60 yr) and young (20-45 yr) patients were randomly allocated to one of four groups according to age and premedicated regimens (n = 16 each; elderly-clonidine [EC], elderly-midazolam [EM], young-clonidine [YC], and young-midazolam [YM]). Under propofol anesthesia, ephedrine was injected, and hemodynamic measurements were made. In the second experiment, with clonidine premedication, elderly patients (n = 16) were given a reduced dose of propofol (EC-LP) and young patients (n = 16) were given an increased dose of propofol (YC-HP). Ephedrine was injected, and he- modynamic measurements were performed. The in-creases in mean blood pressure and heart rate were larger in the EC group than in the EM, YM, and EC-LP groups (P < 0.05). In the YC-HP group, the pressor response to ephedrine tended to be augmented as compared with the YC group but was not statistically significant. These results suggest that clonidine premedication augmented the pressor and tachycardiac responses to ephedrine, especially in elderly patients during a standard dose of propofol anesthesia, and that clonidine, age, and propofol could be involved in the augmentation of the blood pressure and tachycardiac responses to ephedrine.

IMPLICATIONS

Clonidine premedication augments the pressor and tachycardiac responses to ephedrine in elderly patients during standard or large doses of propofol anesthesia but does not augment during small doses of propofol anesthesia. Clonidine, age, and propofol could be involved in the augmentation of the pressor and tachycardiac responses to ephedrine.

Oral premedication for operations on the face under local anesthesia: a placebo-controlled double-blind trial

Modern strategies for preventing or controlling pain and anxiety demand a premedication for operations using local anesthesia and for those using sedation or general anesthesia. For optimal patient care, the premedication should be given orally and, with respect to the outpatient basis of the operations, should have a short recovery period. Midazolam, one of the most favored premedications for general anesthesia, has been recommended as a premedication for operations using local anesthesia as well. However, midazolam has only sedative-anxiolytic effects and does not reduce pain sensation, which should be mandatory for operations using local anesthesia. A further requirement is the maintenance of stable hemodynamics for the prevention of postoperative hematomas, especially in the face. For these reasons, another premedication meeting all requirements (anxiolysis, analgesia, and stable hemodynamics) was researched. A randomized, double-blind prospective study was performed from March of 1997 to June of 1998. Five groups totalling 150 patients were included in the study; each group contained 30 patients who had operations performed solely on the face. In the first four groups, the effect of midazolam (0.15 mg/kg(-1)), morphine (0.3 mg/kg(-1)), and clonidine (1.5 microg/kg(-1)) administered orally was compared with a placebo. The fifth group was the control group and received no premedication. To evaluate the effects of the premedications, a corresponding questionnaire was completed independently by the patient and surgeon. With regard to the anxiolytic or analgesic properties of the premedication, 61 percent of the patients preferred pain reduction to anxiety control, and 24 percent of patients preferred reduction of anxiety. The remainder insisted on a reduction of both properties (8 percent) or had no preference (7 percent). Reduction of anxiety was largest in the midazolam and the clonidine groups, but the difference was not significant. The least pain during the application of local anesthesia was experienced by the morphine group (37 percent) and the clonidine group (33 percent), in contrast to the midazolam group (60 percent) (p = 0.04). Morphine and clonidine met the requirements of pain reduction equally well. Nevertheless, considering the rate and intensity of adverse effects with respect to hemodynamic compromises, nausea, and emesis, clonidine is even better suited as an oral premedication for operations on the face using local anesthesia.

Effects of oral clonidine premedication on side effects of intravenous ketamine anesthesia: a randomized, double-blind, placebo-controlled study

STUDY OBJECTIVE

To determine the effects of oral clonidine premedication on hemodynamic changes during the entire course of ketamine anesthesia and incidence of postoperative adverse reactions.

DESIGN

Randomized, prospective, double-blind, placebo-controlled study.

SETTING

Department of Anesthesiology, University of Tsukuba Hospital, Ibaraki, Japan.

PATIENTS

39 ASA physical status I and II patients undergoing superficial surgeries.

INTERVENTIONS

Placebo, clonidine 2.5 micrograms/kg, and clonidine 5 micrograms/kg groups received respective doses of oral clonidine 90 minutes prior to surgery. Anesthesia was induced with ketamine 2 mg/kg intravenously (i.v.), trachea was intubated, and anesthesia was maintained with 67% nitrous oxide, oxygen, and supplemental ketamine (1 mg/kg) when systolic blood pressure and heart rate (HR) exceeded 180 mmHg and 100 bpm, respectively.

MEASUREMENTS AND MAIN RESULTS

In the clonidine 2.5 micrograms/kg group, HR response to tracheal intubation was significantly less, while in the clonidine 5 micrograms/kg group both mean arterial pressure and HR responses were significantly suppressed, compared with the placebo group. Intraoperative coefficients of variations of HR were significantly less in both clonidine groups than the placebo group. Incidence of nightmare and degree of salivation were significantly less in the clonidine 5 micrograms/kg group than in the placebo group.

CONCLUSION

Oral clonidine 2.5 micrograms/kg and clonidine 5 micrograms/kg attenuates cardiostimulatory effects, while clonidine 5 micrograms/kg was associated with reduced incidence and severity of nightmare and salivation attributable to i.v. ketamine.

Hemodynamic responses induced by dopamine and dobutamine in anesthetized patients premedicated with clonidine

To test the hypothesis that the pharmacological effects of dopamine (DOA) and dobutamine (DOB) are altered when there is inhibition of the release of norepinephrine from nerve endings, we examined the hemodynamic responses to DOA and DOB in anesthetized patients premedicated with oral clonidine. Seventy adult patients were assigned to one of two groups (oral premedication with clonidine 5 microg/kg or no premedication). After the induction of general anesthesia, heart rate and systemic blood pressure (BP) were measured for 10 min after each of five IV infusions (3 and 5 microg x kg(-1) x min(-1) of DOA; 0.5, 1, and 3 microg x kg(-1) x min(-1) of DOB) in a randomized, double-blind manner. In patients given clonidine, the mean BP increases induced by DOA 5 microg x kg(-1) x min(-1) were significantly attenuated (P < 0.01), whereas the mean BP increases induced by DOB-0.5, 1, or 3 microg x kg(-l) x min(-1) were significantly enhanced (P < 0.01 or 0.05). The heart rate responses to DOA and DOB did not differ between patients with or without clonidine. Premedication with clonidine alters the effects on BP to both DOA and DOB. When small doses of DOA or DOB are used in clonidine-premedicated patients, differences of pharmacological profiles need to be considered for perioperative management.

IMPLICATIONS

Our randomized, double-blind study suggests that premedication with clonidine may enhance the effect on blood pressure response to a small dose of dobutamine (direct-acting) and attenuate that to a small dose of dopamine (mixed direct-and indirect-acting) in patients anesthetized with fentanyl and nitrous oxide.

Clonidine premedication modifies responses to adrenoceptor agonists and baroreflex sensitivity

PURPOSE

To evaluate the effects of clonidine on responses to adrenoceptor agonists and baroreflex sensitivity, we examined arterial blood pressure (AP) responses to phenylephrine and heart rate (HR) responses to isoproterenol and baroreflex sensitivity (HR response to AP changes due to phenylephrine or nitroglycerin).

METHODS

We studied 60 anaesthetized patients who either did or did not receive 5 micrograms.kg-1 clonidine po before they were anaesthetized. After induction of general anaesthesia, the patients received 3 micrograms.kg-1 phenylephrine, 0.02 microgram.kg-1 isoproterenol, or 2-3 micrograms.kg-1 nitroglycerin, and haemodynamic measurements were taken. Baroreflex sensitivity was expressed as the slope of the linear regression line (msec.mmHg-1; in msec of R-R interval change vs mmHg change in systolic arterial pressure) following the administration of phenylephrine and nitroglycerin.

RESULTS

Patients who received clonidine had greater augmented responses in AP to phenylephrine and in HR to isoproterenol (47.2 +/- 15.6% vs 23.7 +/- 11.9% for increase in systolic AP and 59.8 +/- 22.6% vs 26.2 +/- 11.0% for increase in HR, P < 0.05 respectively). There were no differences between the baroreflex sensitivities in the pressor (phenylephrine) test groups (3.77 +/- 1.08 vs 4.41 +/- 1.66 msec.mmHg-1). In contrast, the slopes of depressor (nitroglycerin) test groups were decreased in patients receiving clonidine (1.98 +/- 0.73 vs 3.68 +/- 1.72 msec.mmHg-1, P < 0.05).

CONCLUSION

The results suggest that premedication with clonidine might enhance critical hypotension during anaesthesia and surgery, but restoration both of AP and HR decrease can be achieved effectively by phenylephrine and isoproterenol i.v., respectively.

The optimal test dose of epinephrine for epidural injection with lidocaine solution in awake patients premedicated with oral clonidine

We attempted to determine the optimal test dose of epinephrine for use with epidural anesthesia in awake patients premedicated with clonidine. Eighty-eight adult patients were randomized into two groups [oral premedication with clonidine 5 microg/kg (CLON) or no premedication (CONT)]. Before induction of general anesthesia, heart rate (HR) and blood pressure (BP) were measured for 3 min after the i.v. injection of 3 mL of 1.5% lidocaine containing epinephrine (0, 1.25, 2.5, 5, 7.5, or 15 microg) in a randomized, double-blind manner. We calculated 95% confidence intervals for the peak HR and BP increases induced by each dose of epinephrine. At 7.5 microg, epinephrine induced a significantly greater increase in HR and BP in CLON than in CONT. The 95% confidence interval for the HR change induced by 7.5 microg of epinephrine in CLON was nearly the same as the accepted standard dose of epinephrine (15 microg) in CONT. We conclude that premedication with clonidine enhances HR and BP responses to the i.v. administration of epinephrine-containing epidural test solutions. Consequently, 7.5 microg of epinephrine may be sufficient to enable detection of accidental injection into a blood vessel in awake patients premedicated with clonidine 5 microg/kg.

IMPLICATIONS

Clonidine, a commonly used preanesthetic medication, alters patients' cardiovascular responses to drugs such as epinephrine. Our randomized, double-blind study suggests that, in awake patients receiving oral clonidine premedication, 7.5 microg of epinephrine (half the usual dose) is adequate as an indicator of accidental injection into the epidural vessels during epidural anesthesia.

Oral clonidine premedication does not alter the efficacy of epidural test doses in adult patients anesthetized with isoflurane

Clonidine premedication has been increasingly used in clinical anesthesia. Though clonidine was found to alter pressor responses to various sympathomimetics, its effect on epidural test dose efficacy to detect intravascular injection has never been evaluated. Eighty healthy patients were randomly assigned to one of four groups, each of which was anesthetized with 1% end-tidal isoflurane and 67% nitrous oxide in oxygen after endotracheal intubation. The control-epinephrine group (n=20) given no clonidine premedication received 3 ml of 1.5% lidocain with 15 μg epinephrine (1:200000) intravenously to simulate an intravenously administered epidural test dose. The control-saline group (n=20) given no clonidine premedication received 3 ml of normal saline intravenously. The clonidine-epinephrine and clonidine-saline groups (n=20 each) were identical to the control groups, but were premedicated with oral clonidine, approximately 5 μg·kg(-1), 90 min before induction of general anesthesia. Heart rate (HR) and systolic blood pressure (SBP) were measured by a blinded observer at 20-s intervals for 4 min after intravenous injections of the test dose or saline. Following intravenous test dose injection, there were no significant diferences between the control-epinephrine and the clonidine-epinephrine groups in mean maximum increments of both HR (28±3vs 30±3 bpm, [mean±standard error], respectively) and SBP (46±6vs 45±4 mmHg, respectively). Six patients in the control-epinephrine and 4 in the clonidine-epinephrine group developed negative HR responses (HR increment <20 bpm). Since HR and SBP were essentially unchanged in the two groups receiving saline, sensitivities (negative predictive values) based on the HR criterion (positive if ≥20 bpm increase in HR) were 80% and 70% (83% and 77%) with and without clonidine premedication, respectively (P>0.05 between groups). However, when a modified HR criterion (positive if ≥10 bpm increase in HR) was used, sensitivities, specificities, and positive and negative predictive values were all 100% with or without clonidine. On the other hand, all of 20 patients in the control-epinephrine and the clonidine-epinephrine groups exhibited positive SBP responses (SBP increment ≥15 mmHg). Therefore, based on the SBP criterion, sensitivities, specificities, and positive and negative predictive values were all found to be 100% regardless of the presence of clonidine. We conclude that oral clonidine 5μg·kg(-1) premedication alters neither (a) hemodynamic responses to the intravenously administered epidural test dose containing 15 μg epinephrine, nor (b) the efficacy for detecting intravascular injection based on either criterion in adult patients under stable isoflurane anesthesia.