Ketamine for dilatation and currettage procedures: patient acceptance

106 patients undergoing abortion were anesthetized at random with 1 of 3 techniques; ketamine only (53 cases), thiopental followed by ketamine with nitrous oxide-oxygen maintenance (37 cases), or thiopental nitrous oxide-oxygen, d-tubocurarine (61 cases). The intravenous ketamine anesthesia was the easiest to administer for the staff, but 41.5% of the patients stated they would not want ketamine anesthesia again. Recovery room time for the no-ketamine group was shorter than in the 2-ketamine groups. Patients receiving Ketamine were most frequently nauseated. 24.5% of the ketamine-only patients reported unpleasant sensations on going to sleep.     

Ketamine: a review of its pharmacologic properties and use in ambulatory anesthesia.

The administration of intravenous agents is the most commonly used method in Canada and the United States to produce sedation or general anesthesia for dental procedures. Ketamine, a dissociative anesthetic, has several advantageous physical, pharmacokinetic, and pharmacodynamic properties. It can be used to induce anesthesia, sedation, analgesia, and amnesia. Ketamine can maintain functional residual capacity, induce bronchodilation, and avoid cardiovascular depression. However, adverse effects have been demonstrated, such as cardiovascular stimulation and unpleasant emergence phenomena, both of which may be modulated by supplementation with benzodiazepines. An increase in the use of ketamine for ambulatory anesthesia has recently been advocated. This review of the literature supports the use of ketamine as an effective agent for selected anesthetic procedures.     

Comparison of the effect of ketamine added to bupivacaine and ropivacaine, on stress hormone levels and the duration of caudal analgesia

BACKGROUND: The aim of this study was to compare bupivacaine 0.25% and ropivacaine 0.2%, singly and in combination with ketamine, for caudal administration in children. Duration of analgesia, the need for other analgesics and the stress response were measured. METHODS: Eighty children were randomized into four groups of twenty. The bupivacaine group received bupivacaine 0.25% and the ketamine/bupivacaine group received bupivacaine 0.25% plus 0.5 mg/kg ketamine. The ropivacaine group received ropivacaine 0.2%, and the ketamine/ropivacaine group received ropivacaine 0.2% plus 0.5 mg/kg ketamine. The duration of analgesia and analgesic requirements were recorded for each group, as were peri-operative and post-operative concentrations of the stress hormones insulin, glucose and cortisol. RESULTS: Ketamine, added to either bupivacaine or ropivacaine for caudal analgesia, gave a longer duration of analgesia (P < 0.05) than bupivacaine or ropivacaine alone. In all groups, blood insulin concentration was increased, and cortisol concentration reduced. Glucose concentration was significantly increased in all groups (P < 0.05). CONCLUSIONS: Ketamine can safely be added to ropivacaine 0.2% or bupivacaine 0.25% for caudal anesthesia in order to prolong duration of analgesia and reduce the need for additional analgesics. Stress hormone levels are partially attenuated.     

Ketamine

Ketamine is an intravenous drug with special properties that make it the only agent that presently serves as anesthetic, sedative, amnesiac and analgesic. Although it is sometimes forgotten, ketamine is still considered a viable drug. Water soluble, stable and non-irritant when administered intravenously, ketamine has rapid onset after intravenous injection and provides acceptable anesthesia when administered in continuous infusion. There properties make ketamine useful for total intravenous anesthesia. Both propofol and midazolam are effective in reducing ketamine's adverse side effects. Administered in children by oral, nasal, rectal and intramuscular routes, ketamine allows for gentle anesthetic induction. It can also serve as an adjuvant in regional anesthesia to supplement analgesia. In adults ketamine is most often used for major surgery, particularly in the elderly or in high risk patients who are in shock, severely dehydrated or hemodynamically unstable, or in obstetric patients with hypovolemia or hemorrhage. It is probably the anesthetic of choice for patients with hyperreactive airways. Ketamine's strong analgesic effect at subanesthetic doses allows it to be used as an analgesic during postoperative intensive care or as an analgesic-plus-sedative for patients receiving mechanical ventilation. Interest in using ketamine at low doses for cancer and non-cancer patients with chronic pain has grown recently.     

Comparison of sevoflurane and ketamine for anesthetic induction in children with congenital heart disease

Background:  Sevoflurane is widely used in pediatric anesthesia for induction. Ketamine has been preferred in pediatric cardiovascular anesthesia. Aim of this study was to compare the hemodynamic effects and the speed of ketamine and sevoflurane for anesthesia induction in children with congenital heart disease.
Materials and methods:  Children with congenital heart disease undergoing corrective surgery were included in the study. After oral premedication with midazolam (0.5 mg·kg⁻¹), anesthesia induction was started with 5 mg·kg⁻¹ intramuscular ketamine (group K). In the second group, induction was achieved with sevoflurane (group S); the first concentration was 3% and increased after every three breaths. Intravenous access time and intubation times were enrolled for each child. Hemodynamic data and oxygen saturation were recorded every 2 min and any event during induction period was also noted.
Results:  Forty-seven children were included in the study; 23 in group K and 24 in group S. Heart rates and oxygen saturation values were similar between groups during the study. No difference was found between intravenous access time and intubation times. However, blood pressure levels were significantly lower in group S after recording baseline values till the intubation time (at 4, 6, and 8 min). Respiratory complications observed during the study were mild and were less frequent in group K than in group S (4 vs 13).
Conclusion:  Ketamine appears a good alternative for induction in patients with congenital heart disease. It permits preservation of hemodynamic stability with minimal side effects.     

Inotropic effect of ketamine on rat cardiac papillary muscle

The direct effect of ketamine on cardiac muscle was studied using rat left ventricular papillary muscle. At an extracellular calcium concentration [( Ca++]0) of 2.5 mM, rat myocardial contractility is nearly maximum, and a positive inotropic effect was demonstrated by an increase in maximum shortening velocity (Vmax) with ketamine at 10(-5) M but not 10(-4) M. At a [Ca++]0 of 0.5 mM, ketamine 10(-5) and 10(-4) M had a positive inotropic effect as shown by an increase in Vmax (135% +/- 22% and 147% +/- 33%, respectively) and in isometric active force (AF/s) (120% +/- 10% and 152% +/- 44%, respectively). The positive inotropic effect of ketamine was not related to catecholamine uptake inhibition and/or alpha/beta receptor stimulation because it persisted after phentolamine and propranolol and because ketamine had no relaxing effect. Ketamine 10(-5) and 10(-4) M impaired isotonic relaxation, contraction-relaxation coupling under low loading conditions, and the load sensitivity of relaxation, which suggests impairment of the calcium sequestering systems, especially the sarcoplasmic reticulum (SR). Ketamine modified postrest recovery: the first beat (B1) after a 1-min rest period was decreased by ketamine 10(-4) M but not ketamine 10(-5) M. Moreover, the beat-to-beat postrest recovery has been demonstrated to be exponential, and tau, the time constant of the decay was increased by ketamine 10(-4) M (5.4 +/- 0.3 vs. 3.9 +/- 0.2 beats) but not by ketamine 10(-5) M (3.4 +/- 0.4 vs. 3.7 +/- 0.2 beats). These effects on postrest recovery suggest that ketamine impairs SR function. The authors suggest that ketamine had a dual action on rat myocardium: a positive inotropic effect without any relaxing effect, probably related to an increase in calcium influx, and an impairment of SR function. Nevertheless, impairment of SR is only significant at high concentration (10(-4) M) and might overcome the positive inotropic effect only at supratherapeutic concentration.     

Intravenous anesthetics differentially modulate ligand-gated ion channels

BACKGROUND: Heteromeric neuronal nicotinic acetylcholine receptors (nAChRs) are potently inhibited by volatile anesthetics, but it is not known whether they are affected by intravenous anesthetics. Ketamine potentiates gamma-aminobutyric acid type A (GABAA) receptors at high concentrations, but it is unknown whether there is potentiation at clinically relevant concentrations. Information about the effects of intravenous anesthetics with different behavioral profiles on specific ligand-gated ion channels may lead to hypotheses as to which ion channel effect produces a specific anesthetic behavior. METHODS: A heteromeric nAChR composed of alpha4 and beta4 subunits was expressed heterologously in Xenopus laevis oocytes. Using the two-electrode voltage clamp technique, peak ACh-gated current was measured before and during application of ketamine, etomidate, or thiopental. The response to GABA of alpha1beta2gamma2s GABAA receptors expressed in human embryonic kidney cells and Xenopus oocytes was compared with and without coapplication of ketamine from 1 microm to 10 mm. RESULTS: Ketamine caused potent, concentration-dependent inhibition of the alpha4beta4 nAChR current with an IC50 of 0.24 microm. The inhibition by ketamine was use-dependent; the antagonist was more effective when the channel had been opened by agonist. Ketamine did not modulate the alpha1beta2gamma2s GABAA receptor response in the clinically relevant concentration range. Thiopental caused 27% inhibition of ACh response at its clinical EC50. Etomidate did not modulate the alpha4beta4 nAChR response in the clinically relevant concentration range, although there was inhibition at very high concentrations. CONCLUSIONS: The alpha4beta4 nAChR, which is predominantly found in the central nervous system (CNS), is differentially affected by clinically relevant concentrations of intravenous anesthetics. Ketamine, commonly known to be an inhibitor at the N-methyl-D-aspartate receptor, is also a potent inhibitor at a central nAChR. It has little effect on a common CNS GABAA receptor in a clinically relevant concentration range. Interaction between ketamine and specific subtypes of nAChRs in the CNS may result in anesthetic behaviors such as inattention to surgical stimulus and in analgesia. Thiopental causes minor inhibition at the alpha4beta4 nAChR. Modulation of the alpha4beta4 nAChR by etomidate is unlikely to be important in anesthesia practice based on the insensitivity of this receptor to clinically used concentrations.     

Supplementing desflurane-remifentanil anesthesia with small-dose ketamine reduces perioperative opioid analgesic requirements

Relative large-dose intraoperative remifentanil could lead to the need for more postoperative analgesics. Intraoperative N-methyl-D-aspartate receptor antagonists, such as ketamine, decrease postoperative opioid use. We therefore tested the hypothesis that intraoperative small-dose ketamine improves postoperative analgesia after major abdominal surgery with remifentanil-based anesthesia. Fifty patients undergoing abdominal surgery under remifentanil-based anesthesia were randomly assigned to intraoperative ketamine or saline (control) supplementation. The initial ketamine dose of 0.15 mg/kg was followed by 2 microg. kg(-1). min(-1). In both groups, desflurane was kept constant at 0.5 minimum alveolar anesthetic concentration without N(2)O, and a remifentanil infusion was titrated to autonomic responses. All patients were given 0.15 mg/kg of morphine 30 min before the end of surgery. Pain scores and morphine consumption were recorded for 24 postoperative h. Less of the remifentanil was required in the Ketamine than in the Control group (P < 0.01). Pain scores were significantly larger in the Control group during the first 15 postoperative min but were subsequently similar in the two groups. The Ketamine patients required postoperative morphine later (P < 0.01) and received less morphine during the first 24 postoperative h: 46 mg (interquartile range, 34-58 mg) versus 69 mg (interquartile range, 41-87 mg, P < 0.01). No psychotomimetic symptoms were noted in either group. In conclusion, supplementing remifentanil-based anesthesia with small-dose ketamine decreases intraoperative remifentanil use and postoperative morphine consumption without increasing the incidence of side effects. Thus, intraoperative small-dose ketamine may be a useful adjuvant to intraoperative remifentanil. IMPLICATIONS: Supplementing remifentanil-based anesthesia with small-dose ketamine decreased intraoperative remifentanil use and postoperative morphine consumption. These data demonstrate that N-methyl-D-aspartate antagonists, such as ketamine, can be a useful adjuvant to intraoperative remifentanil.     

Continuous intravenous regional anesthesia.

This study evaluates the effectiveness of continuous intravenous regional anesthesia for prolonged operations on the upper extremity. The factors evaluated include patient's sex and age, number of procedures performed, tourniquet on and off times, anesthetic doses, adjunctive drugs used, technical complications, and side effects. Seventy-two procedures were done on 34 patients. The first tourniquet time averaged 58 minutes. Off time averaged 10 minutes. Second tourniquet time averaged 33 minutes, and the mean total tourniquet time was 91 minutes. The mean first anesthetic dose was 275 mg. Mean second anesthetic dose was 128 mg. Mean total anesthetic dose was 402 mg. There were two (6%) technical complications and two (6%) patients had side effects. Continuous intravenous regional anesthesia offers the prolonged anesthesia of brachial plexus block or general anesthesia and the safety, reliability, and ease of intravenous regional anesthesia. Continuous intravenous regional anesthesia should be considered an alternative choice of anesthetic method in upper extremity surgery.     

小剂量氯胺酮的临床应用

氯胺酮是一种具有较强镇静及镇痛作用的静脉全麻药,术后可能出现精神症状,因此在临床应用时有一定顾虑。小剂量氯胺酮(0.1 mg/kg~0.5 mg/kg,IV)产生镇痛作用快速,麻醉持续时间短,对呼吸循环系统影响较轻,副作用减少等特点,现综述如下。1小剂量氯胺酮用于全麻诱导常规使用咪唑安     

The effects of ketamine on cardiovascular dynamics during halothane and enflurane anesthesia.

The cardiovascular effects of a single dose of ketamine administered during halothane or enflurane anesthesia were studied in 24 patients. During halothane anesthesia, ketamine caused a rapid and significant increase in arteriolar peripheral resistance (p less than 0.01) and a decrease in cardiac output, stroke volume, and systolic diastolic, and mean arterial blood pressures. Heart rate was not significantly changed. Ketamine resulted in similar, though less dramatic and slower developing, changes in patients anesthetized with enflurane. These results demonstrate that general anesthesia blocks the cardiovascular-stimulating properties of ketamine. They also indicate that ketamine has significant cardiovascular-depressant qualities when used during halothane or enflurane anesthesia.     

Accurate and simplified determination of ketamine in plasma by gas chromatography mass spectrometry

An accurate and simplified method has been developed for determination of ketamine in human plasma using gas chromatography and electron impact mode mass spectrometry with selected ion recording from 0.5ml of plasma. Standards and samples of plasma underwent the same procedure of two step extraction by methanol. Ketamine concentrations in the plasma were determined from the peak in the selected ion profile of ketamine (m/e: 237). Standard curve was linear with the increasing amount of ketamine (0.63-5.0 micrograms.ml-1) in plasma with mean CV = 5.2% mean RR = 63.8% and r = 0.998. The concentration of ketamine in plasma ranged from 1.6 micrograms.ml-1 to 2.5 micrograms.ml-1 during ketamine anesthesia (2mg.kg-1.h-1) in a surgical patient.     

氯胺酮复合布托啡诺静脉麻醉在小儿日间手术中的应用

目的 研究氯胺酮复合布托啡诺静脉麻醉在小儿日间手术中应用的临床效果.方法 选择美国麻醉医师协会（ASA）分级Ⅰ或Ⅱ级行腹股沟疝修补术、包皮环切术的患儿（1岁～6岁）200例,按随机数字表法分为2组（每组100例）：氯胺酮复合生理盐水组（KS组）和氯胺酮复合布托啡诺组（KB组）.KS组患儿静脉给予氯胺酮2 mg/kg复合生理盐水2 ml行麻醉诱导,KB组患儿则给予氯胺酮2 mg/kg复合2 ml含有30 μg/kg的布托啡诺,若患儿术中出现明显的体动反应,则静脉追加氯胺酮1 mg/kg.记录呼吸、血流动力学变化、苏醒时间、术后CHEOPS疼痛评分（术后即刻、术后1、2、4、8、12、24 h）和镇静评分（术后15、30、60 min）及氯胺酮用量.结果 KB组的氯胺酮用量（42.2±12.9） mg较KS组（75.0±25.3） mg明显减少;且术后平均CHEOPS评分显著降低、术后镇静评分显著较高;麻醉后复苏室内苏醒时间显著延长（P ＜0.05）,但并不延长出室时间.两组患儿的呼吸与血流动力指标差异无统计学意义.结论 氯胺酮复合布托啡诺静脉麻醉能够安全应用于小儿日间手术,减少大剂量氯胺酮所致的副作用,又可以提供较为完善的镇痛与镇静作用,减少小儿苏醒期躁动的发生.     

Pain prevention with intraoperative ketamine in outpatient children undergoing tonsillectomy or tonsillectomy and adenotomy

STUDY OBJECTIVES: To evaluate the effectiveness of ketamine in the prevention of postoperative pain after tonsillectomy. DESIGN: Randomized, prospective, double-blind study. SETTING: University hospital. PATIENTS: 90 ASA physical status I and II patients, aged 5 to 15 years, scheduled for tonsillectomy or adenotonsillectomy. INTERVENTIONS: Patients were divided into three groups. The pain preventive group received intravenous (IV) ketamine 0.5 mg/kg in 2 mL saline before the tonsils were surgically removed, followed by a continuous IV infusion of ketamine at 6 micro/(kg/min). In the ketamine group, 2 mL saline was given before the tonsils were surgically removed; saline infusion (10 mL/h) was continued until bleeding control, and 0.8 mg/kg ketamine was given during bleeding control in 2 mL saline. In the control group, only saline was given. MEASUREMENTS AND MAIN RESULTS: Cardiorespiratory system data, recovery from anesthesia and discharge parameters, tramadol requirement, and complications were recorded. Recovery from anesthesia and discharge parameters were similar among the groups. Total dose of tramadol was lower in the pain preventive group than in the other groups. In the pain preventive group, verbal pain scale scores were lower in the early postoperative period in the fourth and sixth hours (P < 0.05). CONCLUSIONS: Ketamine decreases postoperative analgesic requirements and has analgesic effects when used before surgery in tonsillectomy/adenotonsillectomy.     

Uso preventivo de cetamina nebulizada para controle da dor após amigdalectomia em crianças: estudo randômico e controlado

ObjectivesThe administration of ketamine as nebulized inhalation is relatively new and studies on nebulized ketamine are scarce. We aimed to investigate the analgesic efficacy of nebulized ketamine (1 and 2 mg.kg^?1) administered 30 min before general anesthesia in children undergoing elective tonsillectomy in comparison with intravenous ketamine (0.5 mg.kg^?1) and saline placebo.MethodsOne hundred children aged (7‐12) years were randomly allocated in four groups (n = 25) receive; Saline Placebo (Group C), Intravenous Ketamine 0.5 mg.kg^?1 (Group K‐IV), Nebulized Ketamine 1 mg.kg^?1 (Group K‐N1) or 2 mg.kg^?1 (Group K‐N2). The primary endpoint was the total consumption of rescue analgesics in the first 24 h postoperative.ResultsThe mean time to first request for rescue analgesics was prolonged in K‐N1 (400.9 ± 60.5 min, 95% CI 375.9‐425.87) and K‐N2 (455.5 ± 44.6 min, 95% CI 437.1‐473.9) groups compared with Group K‐IV (318.5 ± 86.1 min, 95% CI 282.9‐354.1) and Group C (68.3 ± 21.9 min, 95% CI 59.5‐77.1; p < 0.001), with a significant difference between K‐N1 and K‐N2 Groups (p < 0.001). The total consumption of IV paracetamol in the first 24 h postoperative was reduced in Group K‐IV (672.6 ± 272.8 mg, 95% CI 559.9‐785.2), Group K‐N1 (715.6 ± 103.2 mg, 95% CI 590.4‐840.8) and Group K‐N2 (696.6 ± 133.3 mg, 95% CI 558.8‐834.4) compared with Control Group (1153.8 ± 312.4 mg, 95% CI 1024.8‐1282.8; p < 0.001). With no difference between intravenous and Nebulized Ketamine Groups (p = 0.312). Patients in intravenous and Nebulized Ketamine Groups showed lower postoperative VRS scores compared with Group C (p < 0.001), no differences between K‐IV, K‐N1 or K‐N2 group and without significant adverse effects.ConclusionPreemptive nebulized ketamine was effective for post‐tonsillectomy pain relief. It can be considered as an effective alternative route to IV ketamine.     

Intraoperative small-dose ketamine enhances analgesia after outpatient knee arthroscopy

Ketamine may prevent postoperative hyperalgesia. In patients undergoing arthroscopic meniscectomy using general anesthesia, we tested whether a single intraoperative dose of ketamine enhanced postoperative analgesia and improved functional outcome compared with a typical multimodal analgesic regimen. After the induction of anesthesia, 50 patients were randomly assigned to ketamine (0.15 mg/kg IV just after the induction of anesthesia) or a vehicle placebo. Standardized general anesthesia included propofol, alfentanil, and nitrous oxide. Bupivacaine (0.5%) and morphine (5 mg) were given intraarticularly at the end of surgery. Postoperative analgesia was initially provided with morphine and subsequently with naproxen sodium (550 mg orally twice daily) and Di-Antalvic (400 mg acetaminophen and 30 mg dextropropoxyphene) as needed. Pain scores, analgesic requirements, side effects, and ability to walk were assessed in the ambulatory unit and at home for three postoperative days. Times to awakening and to discharge were similar in the two groups. However, the Ketamine group had significantly less postoperative pain at rest and during mobilization on Days 0, 1, and 2. Furthermore, they consumed significantly fewer Di-Antalvic tablets than the control group (13 [7-17] vs 27 [16-32], median [25%-75% interquartile range]). Patients given ketamine were also able to walk for longer periods of time on the first postoperative day. In conclusion, adding small-dose ketamine to a multimodal analgesic regimen improved postoperative analgesia and functional outcome after outpatient knee arthroscopy.     

Anesthesia and analgesia for the ambulatory management of fractures in children

The goal of anesthesia in the ambulatory management of fractures in children is to provide analgesia and relieve anxiety in order to facilitate successful closed treatment of the skeletal injury. Numerous techniques short of general anesthesia are available. These methods include blocks (local, regional, and intravenous), sedation (conscious and deep), and dissociative anesthesia (ketamine sedation). Important factors in choosing a particular technique include ease of administration, efficacy, safety, cost, and patient and parent acceptance. Local and regional techniques, such as hematoma, axillary, and intravenous regional blocks, are particularly effective for upper-extremity fractures. Sedation with inhalation agents, such as nitrous oxide, and parenterally administered narcotic-benzodiazepine combinations, are not region-specific and are suitable for patients over a wide range of ages. Ketamine sedation is an excellent choice for children less than 10 years old. With any technique, proper monitoring and adherence to safety guidelines are essential.     

Regional ketamine-induced depression of neuromuscular transmission in man.

The intravenous injection of ketamine in the human arm with isolated circulation, using the same technique as for intravenous regional anesthesia, produces a dose-related depression of neuromuscular transmission, as evidenced by the evoked response to supramaximal stimulation of the ulnar nerve with a nerve stimulator. The dose range of ketamine was 200, 25, 10, 5, 1, 0.5 and 0.25 mg, in 20 ml of 5% dextrose in water. The exact mechanism of this effect is discussed. This depression may have clinical significance under certain circumstances.     

Reevaluation of rectal ketamine premedication in children: comparison with rectal midazolam

BACKGROUND: Results of previous studies of rectal ketamine as a pediatric premedication are clouded because of lack of dose-response relation, inappropriate time of assessing sedative effects, and previous administration or coadministration of benzodiazepines. Therefore, the authors reevaluated the efficacy of rectally administered ketamine in comparison with 1 mg/kg rectal midazolam. METHODS: Sixty-six infants and children (age, 7-61 months) who were American Society of Anesthesiologists physical status I and who were undergoing minor surgeries as in-patients were randomized to receive 5 mg/kg ketamine (n = 16), 7 mg/kg ketamine (n = 16), 10 mg/kg ketamine (n = 17), or 1 mg/kg midazolam (n = 17) via rectum. A blinded observer scored sedation 45 min and 15 min after administration of ketamine and midazolam, respectively, when children were separated from parent(s) for inhalational induction. All children underwent standardized general anesthesia with sevoflurane, nitrous oxide, and oxygen with endotracheal intubation. Blood pressure, heart rate, and oxyhemoglobin saturation were determined before, during, and after anesthesia. Postoperative recovery characteristics and incidence of adverse reactions were also assessed. RESULTS: Most children (88%) who received rectally 10 mg/kg ketamine or 1 mg/kg midazolam separated easily from their parents compared with those (31%) who received 7 or 5 mg/kg rectal ketamine (P < 0.05). Similarly, more children who received 10 mg/kg ketamine or 1 mg/kg midazolam underwent mask induction without struggling or crying compared with those who received 7 or 5 mg/kg ketamine (P < 0.05). There were no clinically significant changes in blood pressure, heart rate, and oxyhemoglobin saturation after administration of either drug. Immediately after surgery, more children receiving midazolam or 5 mg/kg ketamine were agitated compared with 7 or 10 mg/kg ketamine. Ketamine, 7 and 10 mg/kg, provided postoperative analgesia, but the largest dose of ketamine was associated with delayed emergence from general anesthesia. CONCLUSIONS: The results indicate that rectally administered ketamine alone produces dose-dependent sedative effects in children, when evaluated at its predicted peak plasma concentration. Ketamine, 10 mg/kg, has a delayed onset but is as effective as 1 mg/kg midazolam for sedating healthy children before general anesthesia. However, 10 mg/kg rectal ketamine is not recommended for brief surgeries because of prolonged postoperative sedation.