Biomedical subjects

D I Sessler

Publications and source records attributed to D I Sessler.

At least 37 records · Page 2Linked to original sources

PubMed2002

Use of cerebral oximetry to detect and manage cerebral desaturation with a rapidly expanding neck hematoma.

BACKGROUND: We report a case in which cerebral oximetry was used to successfully demonstrate when cerebral oxygen saturation is dangerously low. METHODS: In a 60-year-old-man with end-stage multiple myeloma and hyperviscosity syndrome, a rapidly expanding hematoma developed after insertion of an internal jugular central venous catheter. As the hematoma expanded, the patient became lethargic and disoriented (Glasgow Coma Score of E2/M4-5/V2-ETT). His platelet count was 17,000.mm(-3), hemoglobin was 4.5 g/dl, partial thromboplastin time was 51 s, and his international ratio was 1.7. Although carotid pulses became unpalpable, blood pressure and heart rate remained stable. Cerebral oximeter probes positioned on the patient's forehead showed that cerebral oxygen saturation was 22-26% bilaterally. The surgery team was advised to surgically evacuate the hematoma. RESULTS: The hematoma was evacuated and a small needle hole in the right internal jugular vein adjacent to the central-venous catheter was found and repaired. Cerebral oxygen saturation increased to 56-58% within 1 h and stabilized near 60%. The patient awoke with normal cognitive function. CONCLUSION: This case demonstrates how cerebral oximetry can be used to give quantitative evidence of cerebral hypoxia, thus showing that immediate surgical intervention is necessary.

Blood Viscosity↗

PubMed2002

The effect of auricular acupuncture on anaesthesia with desflurane.

In most acupuncture studies it is difficult or even impossible to conduct a truly double-blind trial. However, this is possible when treatments are carried out on anaesthetised patients. Because acupuncture provides analgesia, we tested the hypothesis that needle stimulation of a combination of four ear acupoints would significantly reduce anaesthetic requirement. Ten healthy volunteers were anaesthetised with desflurane and randomly assigned to no treatment or acupuncture; the alternative treatment was given on a subsequent study day. Auricular acupuncture was performed with needles placed at the Shen Men, Thalamus, Tranquiliser and Master Cerebral Points on the right ear. Anaesthetic requirement, determined by the Dixon up-and-down method, was defined by the average desflurane concentration that prevented purposeful movement of the extremities in response to noxious electrical stimulation. Volunteers required a greater desflurane concentration to prevent movement on the control than on the acupuncture day: 4.9 (0.7; SD) vs. 4.4 (0.8) vol. %, p = 0.003. Acupuncture thus reduced anaesthetic requirement by 8.5 (7)%.

Acupuncture Analgesia↗

PubMed2002

Esmolol prevents movement and attenuates the BIS response to orotracheal intubation.

BACKGROUND: Beta-adrenergic agonists enhance behavioural and electroencephalographic arousal reactions. We explored whether adding esmolol, a short-acting beta(1)-adrenoceptor antagonist, to propofol anaesthesia modified the bispectral index (BIS) during induction of anaesthesia and orotracheal intubation. METHODS: Fifty patients were randomly allocated, in a double-blind fashion, to receive esmolol 1 mg kg(-1) followed by 250 micro g kg(-1) min(-1) or saline (control). Esmolol or saline was started 6 min after a target-controlled infusion (TCI) of propofol (effect-site concentration 4 micro g ml(-1)). After loss of consciousness, and before administration of vecuronium 0.1 mg kg(-1), a tourniquet was applied to one arm and inflated to 150 mm Hg greater than systolic pressure. Eleven minutes after the TCI began, the trachea was intubated; gross movement within the first min after orotracheal intubation was recorded. BIS was recorded at 10-s intervals. Mean arterial pressure (MAP) and heart rate were measured non-invasively every min. RESULTS: There were no intergroup differences in BIS, heart rate or MAP before laryngoscopy. BIS increased significantly after orotracheal intubation (compared with the pre-laryngoscopy values) in the control group only, with a maximum increase of 40 (SD 18)% vs 8 (11)% in the esmolol group (P<0.01). Maximum changes in heart rate [45 (19)% vs 23 (14)%] and MAP [62 (24)% vs 45 (23)%] with orotracheal intubation were also significantly greater in the control group than in the esmolol group. More patients in the control than in the esmolol group moved after orotracheal intubation (23 vs 12, P<0.01). CONCLUSION: Esmolol not only attenuated haemodynamic and somatic responses to laryngoscopy and orotracheal intubation, but also prevented BIS arousal reactions in patients anaesthetized with propofol.

Adjuvants, Anesthesia↗

PubMed2002

Acupuncture. A useful complement of anesthesia?

UNLABELLED: Since acupuncture provides analgesia it might be expected to reduce the need for conventional anaesthetic drugs during general anaesthesia. In this review we discuss four double blind, placebo controlled studies evaluating acupunture's ability to reduce analgesic or anesthetic requirement. Three studies (from Greif et al., Morioka et al. and Taguchi et al.) examined whether transcutaneous electrical stimulation of some acupuncture points reduces anaesthetic requirement. Kotani et al. tested the hypothesis that preoperative insertion of intradermal needles in the bladder meridian reduces postoperative pain and oppioid requirement. CONCLUSIONS: none of the first three studies showed that the stimulation of the acupoints produces clinically important reductions in anaesthetic requirement. In contrast, Kotani et al. showed that at least some acupuncture techniques provide substantial postoperative analgesia and significantly reduce opioid requirement.

Acupuncture Analgesia↗

PubMed2002

Use of selective opiate receptor inhibitors to prevent postoperative ileus.

Ileus is a common postoperative complication after major abdominal surgery. Surgical manipulation of the bowel and stimulation of opiod receptor are the main causes of ileus. An investigational drug (ADL 8-2698, Alvinopam) a selective opioid antagonist with a very low oral absorption was recently introduced to clinical medicine. Unlike other opioid antagonist its activity is restricted to GI tract, it is potent, has a long duration of action, is orally effective, does not readily cross the blood-brain barrier even after intravenous administration in animals. Two randomized controlled clinical studies tested its effects in humans. Liu et al.'s study confirmed peripheral restriction of ADL 8-2698 by its lack of central effect on morphine analgesia and pupil miosis. They also showed that ADL 8-2698 prevents increases in gastrointestinal transit time. Taguchi et al. concluded that high dose (6 mg) of ADL 8-2698 archived fast recovery of gastrointestinal function, without antagonising analgesic efficacy of systemic opioid. In summary, selective inhibition of gastrointestinal opioid receptor by a peripherally restricted oral antagonist speeds recovery of bowel function, shortens times of hospitalization and preserves the analgesic effects of opiods.

Adolescent↗

PubMed2002

Supplemental oxygen reduces the incidence of postoperative nausea and vomiting.

Postoperative nausea and vomiting (PONV) are unpleasent for patients and increase the risk of aspiration pneumonia. PONV is the leading cause of unexpected admission following planned day surgery. Despite new anaesthetic drugs and antiemetics, the incidence of PONV remains high. The incidence of PONV depends numerous factors including age, gender, obesity, anxiety, gastroparesis, history of motion sickness, previous PONV, and the duration and type of surgery. Anaesthesia related factors include premedication, ventilation techniques, and postoperative pain management. Recently, the intraoperative inspired oxygen concentration was identified as a factor that influences PONV. Among the three studies that evaluated intraoperative supplemental O2 for prevention of PONV, two found that it halves PONV while the third failed to identify any benefit. Since supplemental O2 is inexpensive and essentially risk-free, it appears preferable to pharmacologic anti-emetics for prevention of PONV in abdominal surgery.

Adolescent↗

PubMed2002

Thermal management and blood loss during hip arthroplasty.

Perioperative hypotermia is a common, but preventable complication of anaesthesia and surgery. Mild perioperative hypothermia increases the incidence of morbid myocardial outcomes, reduces resistance to surgical wound infections, and prolongs both postanaesthetic recovery and hospitalization. Hypotermia causes a coagulopathy due to inhibition of platelet function. In this short review, we will discuss three studies done in the last 6 years, which explored the influence of perioperative hypotermia and blood loss. All evaluated blood loss during hip arthroplasty and had similar methodologies. Two studies demonstrate that blood loss is increased, especially during surgery, in hypotermic patients while a third study failed to identify any thermal influence on blood loss. The benefits of maintaining perioperative normothermia on blood loss thus remain unclear. We thus continue to recommend that surgical patients be kept normothermic.

Adult↗

PubMed2001

Selective postoperative inhibition of gastrointestinal opioid receptors.

BACKGROUND: Postoperative recovery of gastrointestinal function and resumption of oral intake are critical determinants of the length of hospital stay. Although opioids are effective treatments for postoperative pain, they contribute to the delayed recovery of gastrointestinal function. METHODS: We studied the effects of ADL 8-2698, an investigational opioid antagonist with limited oral absorption that does not readily cross the blood-brain barrier, on postoperative gastrointestinal function and the length of hospitalization. We randomly assigned 79 patients--including 1 whose surgery was canceled--to receive one capsule containing 1 mg or 6 mg of ADL 8-2698 or an identical-appearing placebo capsule two hours before major abdominal surgery and then twice daily until the first bowel movement or until discharge from the hospital. Data were analyzed for 26 patients in each of the three groups; all received opioids for postoperative pain relief. Observers who were unaware of the group assignments evaluated the outcomes. RESULTS: Fifteen patients underwent partial colectomy and 63 underwent total abdominal hysterectomy. Patients given 6 mg of ADL 8-2698 had significantly faster recovery of gastrointestinal function than those given placebo. The median time to the first passage of flatus decreased from 70 to 49 hours (P=0.03), the median time to the first bowel movement decreased from 111 to 70 hours (P=0.01), and the median time until patients were ready for discharge decreased from 91 to 68 hours (P=0.03). Effects in the group that received 1 mg of ADL 8-2698 were less pronounced. CONCLUSIONS: Selective inhibition of gastrointestinal opioid receptors by an antagonist with limited oral absorption that does not readily cross the blood-brain barrier speeds recovery of bowel function and shortens the duration of hospitalization.

Adolescent↗

PubMed2001

Ondansetron is no more effective than supplemental intraoperative oxygen for prevention of postoperative nausea and vomiting.

UNLABELLED: Supplemental oxygen maintained during and for 2 h after colon resection halves the incidence of nausea and vomiting. Whether supplemental oxygen restricted to the intraoperative period is sufficient remains unknown. Similarly, the relative efficacy of supplemental oxygen and ondansetron is unknown. We tested the hypothesis that intraoperative supplemental oxygen reduces the incidence of postoperative nausea and vomiting. Patients (n = 240) undergoing gynecological laparoscopy were given a standardized isoflurane anesthetic. After induction, they were randomly assigned to the following three groups: routine oxygen administration with 30% oxygen, balance nitrogen (30% Oxygen group), supplemental oxygen administration with 80% oxygen, balance nitrogen (80% Oxygen group), and Ondansetron 8 mg (immediately after induction), combined with 30% oxygen, balance nitrogen (Ondansetron group). The overall incidence of nausea and/or vomiting during the initial 24 postoperative h was 44% in the patients assigned to 30% oxygen and 30% in the Ondansetron group, but only 22% in those given 80% oxygen. The incidence was thus halved by supplemental oxygen and was significantly less than with 30% oxygen. There were, however, no significant differences between the 30% oxygen and ondansetron groups, or between the ondansetron and 80% oxygen groups. We conclude that supplemental oxygen effectively prevents postoperative nausea and vomiting after gynecological laparoscopic surgery; furthermore, ondansetron is no more effective than supplemental oxygen. IMPLICATIONS: Supplemental oxygen reduces the risk of postoperative nausea and vomiting (PONV) as well or better than 8 mg of ondansetron. Because oxygen is inexpensive and essentially risk-free, supplemental oxygen is a preferable method of reducing PONV.

Adult↗

PubMed2001

Negative pressure rewarming vs. forced air warming in hypothermic postanesthetic volunteers.

We compared changes in core temperature and systemic heat balance with a new negative pressure/warming device (Vital Heat(R) ) that uses negative pressure combined with heat to facilitate warming in vasoconstricted postoperative patients to those resulting from passive insulation or forced air. Seven healthy volunteers were anesthetized and cooled to a tympanic membrane temperature near 34 degrees C. Anesthesia was discontinued and shivering was prevented by using meperidine. The vasoconstricted volunteers were rewarmed for 2 h using three randomly assigned methods: 1) Vital Heat plus cotton blanket; 2) one layer of cotton blanket; 3) forced-air warming. Thermal flux was recorded from 15 skin-surface sites; metabolic heat production was estimated from total body oxygen consumption. Metabolic heat production remained constant throughout the study. Systemic heat loss remained constant during warming with cotton blankets but decreased significantly during the other treatments. Systemic heat balance increased significantly more with forced air (140 +/- 21 kcal) than with Vital Heat (66 +/- 19 kcal) or cotton blankets (47 +/- 18 kcal). Core temperature increased no faster with Vital Heat warming (1.3 +/- 0.4 degrees C) than with a cotton blanket (1.2 +/- 0.4 degrees C). In contrast, core temperature increased more rapidly with forced air warming (2.6 +/- 0.6 degrees C). In this study we show that calories from a negative pressure rewarming device are largely constrained to the forearm and that heat does not flow to the core thermal compartment.

Adult↗

PubMed2001

The analgesic efficacy of tramadol is impaired by concurrent administration of ondansetron.

Tramadol has weak opioid properties, and an analgesic effect that is mediated mainly by inhibition of the reuptake of norepinephrine and serotonin (5-hydroxytryptamine [5-HT]) and facilitation of 5-HT release (1,2) at the spinal cord. Because 5-HT3 receptors play a key role in pain transmission at the spinal level (3), the 5-HT3 antagonist ondansetron may decrease the efficacy of tramadol, as suggested in an abstract by Maroof et al. In that study, a small dose of 1 mg/kg tramadol was administered along with ondansetron 0.1 mg/kg or placebo, 15 min before the induction of anesthesia. Early postoperative pain scored differed significantly between the test groups. We therefore tested the hypothesis that the tramadol requirement by patient-controlled analgesia (PCA) may be increased when ondansetron is administered for antiemetic prophylaxis.

Adult↗

PubMed2001

More epidural than intravenous sufentanil is required to provide comparable postoperative pain relief.

UNLABELLED: The extent to which epidurally administered sufentanil acts directly on spinal opioid receptors remains controversial. We tested the hypothesis that small-dose boluses of sufentanil, given epidurally or IV, provide comparable analgesia at similar plasma sufentanil concentrations. The lipophilicity of sufentanil makes it likely to be absorbed into fat surrounding the epidural space. We therefore also tested the hypothesis that more epidural than IV sufentanil is required to produce comparable analgesia. Analgesia and plasma sufentanil concentrations were evaluated in 20 postoperative patients randomly assigned to patient-controlled epidural or IV sufentanil. Pain was evaluated with visual analog scales by blinded observers. Sufentanil doses and plasma concentrations were measured. Analgesia was similar with epidural and IV sufentanil administration. Plasma sufentanil concentrations were virtually identical in the two groups. However, significantly larger sufentanil doses were required with epidural administration: 238 +/- 50 microg vs 160 +/- 32 microg (P < 0.01). The primary mechanism by which small-dose boluses of epidurally-administered sufentanil produce analgesia seems to be systemic absorption of the drug with subsequent recirculation to the supraspinal opioid receptors. This study demonstrates that the cumulative dose of sufentanil, when administered as a small epidural bolus, is approximately 50% more than that administered IV to provide comparable analgesia. This indicates that the bioavailability of epidurally-administered sufentanil is reduced and suggests that a large proportion of the drug may be absorbed into the epidural fat. IMPLICATIONS: More epidural than IV sufentanil was required to provide comparable postoperative pain relief and similar plasma sufentanil concentrations. These data suggest that when sufentanil is administered in small-dose boluses, much of the drug is absorbed into the epidural fat and that the primary mechanism by which epidurally administered sufentanil produces analgesia is via systemic absorption.

Adolescent↗

PubMed2001

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.

Adolescent↗

PubMed2001

Neither nalbuphine nor atropine possess special antishivering activity.

The special antishivering action of meperidine may be mediated by its kappa or anticholinergic actions. We therefore tested the hypotheses that nalbuphine or atropine decreases the shivering threshold more than the vasoconstriction threshold. Eight volunteers were each evaluated on four separate study days: 1) control (no drug), 2) small-dose nalbuphine (0.2 microg/mL), 3) large-dose nalbuphine (0.4 microg/mL), and 4) atropine (1-mg bolus and 0.5 mg/h). Body temperature was increased until the patient sweated and then decreased until the patient shivered. Nalbuphine produced concentration-dependent decreases (mean +/- SD) in the sweating (-2.5 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.75 +/- 0.25), vasoconstriction (-2.6 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.75 +/- 0.25), and shivering (-2.8 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.79 +/- 0.23) thresholds. Atropine significantly increased the thresholds for sweating (1.0 degrees C +/- 0.4 degrees C), vasoconstriction (0.9 degrees C +/- 0.3 degrees C), and shivering (0.7 degrees C +/- 0.3 degrees C). Nalbuphine reduced the vasoconstriction and shivering thresholds comparably. This differs markedly from meperidine, which impairs shivering twice as much as vasoconstriction. Atropine increased all thresholds and would thus be expected to facilitate shivering. Our results thus fail to support the theory that activation of kappa-opioid or central anticholinergic receptors contribute to meperidine's special antishivering action.

Adult↗

PubMed2001

Induction of anesthesia with ketamine reduces the magnitude of redistribution hypothermia.

UNLABELLED: Hypothermia after induction of general anesthesia results largely from core-to-peripheral redistribution of body heat. Both central inhibition of tonic thermoregulatory vasoconstriction in arteriovenous shunts and anesthetic-induced arteriolar and venous dilation contribute to this redistribution. Ketamine, unique among anesthetics, increases peripheral arteriolar resistance; in contrast, propofol causes profound venodilation that other anesthetics do not. We therefore tested the hypothesis that induction of anesthesia with ketamine causes less core hypothermia than induction with propofol. Twenty patients undergoing elective surgery were randomly assigned to anesthetic induction with either 1.5 mg/kg ketamine (n = 10) or 2.5 mg/kg propofol (n = 10). Anesthesia in both groups was subsequently maintained with sevoflurane and 60% nitrous oxide in oxygen. Forearm minus finger, skin-temperature gradients <0 degrees C were considered indicative of significant arteriovenous shunt vasodilation. Ketamine did not cause vasodilation just after induction, whereas propofol rapidly induced vasodilation. Core temperatures in the patients given ketamine remained significantly greater than those in the patients induced with propofol. These data suggest that maintaining vasoconstriction during induction of anesthesia reduces the magnitude of redistribution hypothermia. IMPLICATIONS: Core hypothermia during the first hour of anesthesia was less after induction of anesthesia with ketamine than propofol. Maintaining arteriovenous shunt vasoconstriction during induction of anesthesia reduces the magnitude of redistribution hypothermia.

Adult↗

PubMed2001

Buspirone and meperidine synergistically reduce the shivering threshold.

UNLABELLED: Mild hypothermia (i.e., 34 degrees C) may prove therapeutic for patients with stroke, but it usually provokes shivering. We tested the hypothesis that the combination of buspirone (a serotonin 1A partial agonist) and meperidine synergistically reduces the shivering threshold (triggering tympanic membrane temperature) to at least 34 degrees C while producing little sedation or respiratory depression. Eight volunteers each participated on four randomly-assigned days: 1) large-dose oral buspirone (60 mg); 2) large-dose IV meperidine (target plasma concentration of 0.8 microg/mL); 3) the combination of buspirone (30 mg) and meperidine (0.4 microg/mL); and 4) a control day without drugs. Core hypothermia was induced by infusion of lactated Ringer's solution at 4 degrees C. The control shivering threshold was 35.7 degrees C +/- 0.2 degrees C. The threshold was 35.0 degrees C +/- 0.8 degrees C during large-dose buspirone and 33.4 degrees C +/- 0.3 degrees C during large-dose meperidine. The threshold during the combination of the two drugs was 33.4 degrees C +/- 0.7 degrees C. There was minimal sedation on the buspirone and combination days and mild sedation on the large-dose meperidine day. End-tidal PCO2 increased approximately 10 mm Hg with meperidine alone. Buspirone alone slightly reduced the shivering threshold. The combination of small-dose buspirone and small-dose meperidine acted synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. IMPLICATIONS: Mild hypothermia may be an effective treatment for acute stroke, but it usually triggers shivering, which could be harmful. Our results indicate that the combination of small-dose buspirone and small-dose meperidine acts synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. This combination may facilitate the induction of therapeutic hypothermia in stroke victims.

Adult↗

PubMed2001

Opioids inhibit febrile responses in humans, whereas epidural analgesia does not: an explanation for hyperthermia during epidural analgesia.

BACKGROUND: Epidural analgesia is frequently associated with hyperthermia during labor and in the postoperative period. The conventional assumption is that hyperthermia is caused by the technique, although no convincing mechanism has been proposed. However, pain in the "control" patients is inevitably treated with opioids, which themselves attenuate fever. Fever associated with infection or tissue injury may then be suppressed by opioids in the "control" patients while being expressed normally in patients given epidural analgesia. The authors therefore tested the hypothesis that fever in humans is manifested normally during epidural analgesia, but is suppressed by low-dose intravenous opioid. METHODS: The authors studied eight volunteers, each on four study days. Fever was induced each day by 150 IU/g intravenous interleukin 2. Volunteers were randomly assigned to: (1) a control day when no opioid or epidural analgesia was given; (2) epidural analgesia using ropivacaine alone; (3) epidural analgesia using ropivacaine in combination with 2 microg/ml fentanyl; or (4) intravenous fentanyl at a target plasma concentration of 2.5 ng/ml. RESULTS: Fentanyl halved the febrile response to pyrogen, decreasing integrated core temperature from 7.0 +/- 3.2 degrees C. h on the control day, to 3.8 +/- 3.0 degrees C. h on the intravenous fentanyl day. In contrast, epidural ropivacaine and epidural ropivacaine-fentanyl did not inhibit fever. The fraction of core-temperature measurements that exceeded 38 degrees C was halved by intravenous fentanyl, and the fraction exceeding 38.5 degrees C was reduced more than fivefold. CONCLUSIONS: These data support the authors' proposed mechanism for hyperthermia during epidural analgesia. Fever during epidural analgesia should thus not be considered a complication of the anesthetic technique per se.

Adult↗

PubMed2001

Automated responsiveness test (ART) predicts loss of consciousness and adverse physiologic responses during propofol conscious sedation.

BACKGROUND: The authors evaluated a device designed to provide conscious sedation with propofol (propofol-air), or propofol combined with 50% nitrous oxide (N2O; propofol-N2O). An element of this device is the automated responsiveness test (ART), a method for confirming that patients remain conscious. The authors tested the hypotheses that the ART predicts loss of consciousness and that failure to respond to the ART precedes sedation-induced respiratory or hemodynamic toxicity. METHODS: The protocol consisted of sequential 15-min cycles in 20 volunteers. After a 15-min control period, propofol was infused to an initial target effect-site concentration of 0.0 microg/ml with N2O or 1.5 microg/ml with air. Subsequently, the propofol target effect-site concentration was increased by a designated increment (0.25 and 0.5 microg/ml) and the process repeated. This sequence was continued until loss of consciousness, as defined by an Observer's Assessment of Alertness/Sedation (OAA/S) score of 10/20 or less, or until an adverse physiologic event was detected. RESULTS: The OAA/S score at which only 50% of the volunteers were able to respond to the ART (P50) during propofol-N2O was 11.1 of 20 (95% confidence interval [CI]: 10.6-11.8); the analogous P50 was 11.8 of 20 (95% CI: 11.4-12.3) with propofol-air. Failure to respond to the ART occurred at a plasma propofol concentration of 0.7 +/- 0.6 microg/ml with propofol-N2O and 1.6 +/- 0.6 microg/ml with propofol-air, whereas loss of consciousness occurred at 1.2 +/- 0.8 microg/ml and 1.9 +/- 0.7 microg/ml, respectively. There were no false-normal ART responses. CONCLUSION: The ART can guide individual titration of propofol because failure to respond to responsiveness testing precedes loss of consciousness and is not susceptible to false-normal responses. The use of N2O with propofol for conscious sedation decreases the predictive accuracy of the ART.

Adult↗