Propofol. An overview of its pharmacology and a review of its clinical efficacy in intensive care sedation

Inhibition of cytochrome P450 2E1 by propofol in human and porcine liver microsomes

While almost anesthetics are metabolized by the cytochrome P450 (CYP) 3A4, some major volatile ones such as halothane and sevoflurane are metabolized by CYP2E1 in humans. To determine whether 2,6-diisopropylphenol (propofol), a widely used intravenous anesthetic agent, known to inhibit CYP3A4 and CYP1A2, also inhibits CYP2E1, 6-OH hydroxylation of chlorzoxazone, a prototypical CYP2E1 substrate, was estimated using two pools of human microsomes and one pool of porcine microsomes from seven livers. Basal human enzyme activities were characterized by a V(max) of 1426+/-230 and 288+/-29 pmol min(-1)mg(-1) protein and a K(m) of 122+/-47 and 149+/-42 microM, while the corresponding porcine activities were associated with a V(max) of 352+/-42 pmol min(-1)mg(-1) protein and a K(m) of 167+/-38 microM. A competitive inhibition of CYP2E1 by propofol was observed with low inhibition constants in the therapeutic range in both porcine (19 microM) and human (48 microM) liver microsomes. These in vitro results suggest that propofol could have a protective effect on toxic metabolite activation of compounds catalyzed by CYP2E1.

Propofol in a medium- and long-chain triglyceride emulsion: pharmacological characteristics and potential beneficial effects

Hypertriglyceridemia is a possible unwanted effect during long-term propofol sedation while using a formulation containing long-chain triglycerides (LCT) from soybean oil. The use of propofol formulated in a solvent consisting of medium-chain triglycerides (MCT) and LCT might reduce the risk. Because a new solvent may affect the pharmacological profile of propofol, in this prospective, randomized, controlled, and double-blinded study we compared the pharmacodynamic and kinetic characteristics of propofol diluted in MCT/LCT fat solution with those of propofol formulated in LCT fat emulsion. In addition, serum triglyceride levels were measured during and after the administration of both drugs. Thirty patients likely to require mechanical ventilation over at least 48 h were randomized to receive either propofol 2% MCT/LCT (Group 1) or propofol 2% LCT (Group 2). Infusion rates of propofol (2.34 +/- 0.83 mg. kg(-1). h(-1) in Group 1 versus 2.31 +/- 0.6 mg. kg(-1). h(-1) in Group 2), the plasma propofol concentrations during infusion (0.95 +/- 0.53 versus 0.98 +/- 0.32 micro g/mL), and the concentrations and arousal behavior after discontinuation of the drug did not show significant differences. Plasma triglyceride concentrations during sedation did not differ between the groups, whereas there was a tendency toward a more rapid triglyceride elimination in Group 1 after termination of the propofol administration.

IMPLICATIONS

Propofol diluted in an emulsion of medium- and long chain-triglycerides shows equivalent pharmacological properties during long-term sedation compared with its hitherto well known formulation containing long-chain triglycerides only. In addition, potential favorable effects on the plasma triglyceride profile could be found.

The actions of propofol on gamma-aminobutyric acid-A and glycine receptors in acutely dissociated spinal dorsal horn neurons of the rat

The spinal cord plays an important role in modulating anesthetic-induced suppression of nociceptive transmission. To gain some insight into the anesthetic mechanisms of propofol at the spinal level, we investigated the direct action of propofol and its modulation on the gamma-aminobutyric acid-A receptor (GABA(A)R) and the glycine receptor (GlyR) in acutely dissociated rat spinal dorsal horn neurons by using whole-cell patch-clamp electrophysiology. Propofol induced Cl(-) currents (I(Cl)), which were sensitive to bicuculline and, to a lesser extent, to strychnine. The activation, desensitization, and deactivation of propofol-induced I(Cl) were slower than those of GABA- and glycine-induced I(Cl). In addition, this study revealed similar modulatory actions of propofol on GABA(A)R and GlyR. Propofol potentiated both GABA- and glycine-induced I(Cl) at small con-centrations and inhibited both GABA- and glycine-induced I(Cl) at large concentrations. The potentiation of propofol on I(Cl) was caused by slowing current desensitization and deactivation, whereas the inhibition actions might be involved in the cross-desensitization between GABA- and propofol-induced I(Cl) and the cross-inhibition between the GABA(A)R and GlyR. The results suggest that propofol facilitation of GABA(A)R and GlyR at the spinal level could contribute significantly to general anesthetic-induced analgesia and anesthesia.

IMPLICATIONS

The actions of propofol on the gamma-aminobutyric acid-A receptor (GABA(A)R) and the glycine receptor (GlyR) were investigated in acutely dissociated rat spinal dorsal horn neurons by using whole-cell patch-clamp electrophysiology. Propofol was found to potentiate the functions of GABA(A)R and GlyR at the spinal level, which might contribute to propofol-induced analgesia and anesthesia.

Progressive electroencephalogram frequency deceleration despite constant depth of propofol-induced sedation

OBJECTIVE

To investigate a possible time-dependent effect of propofol sedation on electroencephalographic activity, we analyzed the electroencephalogram frequency behavior while keeping patients at a constant level of sedation.

DESIGN

Prospective, controlled trial.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Twenty patients without neurologic or metabolic disorders.

MEASUREMENTS AND MAIN RESULTS

During sedation with propofol (1-4 mg x kg(-1) x hr(-1)), a bifrontally recorded processed electroencephalogram was obtained. For 48 hrs, sedation was kept constant at a level according to Ramsay Scale 3 while we adjusted the dosage of propofol given per hour. At hours 6, 18, 30, and 42, blood samples were taken to assess the plasma concentration of propofol. The electroencephalogram values of 60 mins obtained during 1 hr before blood sampling were taken for further calculation. From the data, relative band power of the beta-, alpha-, theta, and delta-bands, spectral median frequency, and spectral edge frequency 90 and 95 were computed. For statistical analysis, a polynomial three-factorial repeated-measures analysis of variance with covariates was performed. Relative power of beta- and alpha-wavebands showed a constant and significant decrease over time (beta, 15.5%, 10.3%, 10.3%, 7.6%; alpha, 14.8%, 13.4%, 10.0%, 8.3%), whereas relative delta power increased (delta, 56.4%, 63.4%, 70.7%, 72.3%). The theta-waveband remained unchanged. Accordingly, spectral edge frequency 90 and 95 and spectral median frequency decreased significantly. From hours 6 to 18, a significant increase of the plasma propofol concentration was found. Subsequently, the level remained constant.

CONCLUSION

Despite constant sedation, a longer period of propofol application induces a time-dependent electroencephalogram frequency deceleration. The use of electroencephalogram derivatives to monitor depth of sedation in the intensive care unit thus should be regarded cautiously.

The propofol infusion syndrome in infants and children: can we predict the risk?

Propofol has been an immensely successful anaesthetic induction agent but there is an increasing number of reports of serious complications when it has been used as an infusion to provide sedation for prolonged periods. The first reports involved children who died from intractable myocardial failure preceded by a metabolic acidosis, lipaemic plasma, fatty infiltration of the liver and evidence of muscle damage. As more cases have been reported the association between propofol and the syndrome has become more certain. Recently adult cases have appeared and a metabolic explanation has been suggested. The syndrome has a high mortality and the only effective treatment appears to be dialysis.

Working toward better cancer pain management for children

PURPOSE

Management of the pain experienced by children with cancer is critical to minimize the psychological distress and physiologic responses to their illness and its treatment.

OVERVIEW

A team approach to providing care, using guidelines for pharmacologic management intertwined with nonpharmacologic strategies, while individualizing the care of a specific child, is required. Pain management must start with assessment using tools that are age appropriate and well suited to the clinical situation. Dosages of the recommended opioid and nonopioid medications that are suitable for children as well as the role of locally, systemically, and epidurally administered anesthetic agents are described by the authors.

CLINICAL IMPLICATIONS

By following this practical approach, children can be prepared and supported during the various intensive oncology therapies often associated with pain that are now offered in the hope of improving the survival of children with cancer.

Propofol metabolites in man following propofol induction and maintenance

BACKGROUND

The pharmacokinetics of propofol in man is characterized by a rapid metabolic clearance linked to glucuronidation of the parent drug to form the propofol-glucuronide (PG) and sulfo- and glucuro-conjugation of hydroxylated metabolite via cytochrome P450 to produce three other conjugates. The purpose of this study was to assess the urine metabolite profile of propofol following i.v. propofol anaesthesia in a Caucasian population.

METHODS

The extent of phase I and phase II metabolism of propofol was studied in 18 female and 17 male patients after an anaesthesia induced and maintained for at least 4 h with propofol. The infusion rates (mg kg(-1) h(-1)) of propofol were (mean (SD)) 4.1 (1.0) and 4.5 (1.3) for males and females, respectively. Urine was collected from each patient for the periods 0-4, 4-8, 8-12, and 12-24 h after the start of propofol administration. In a preliminary study, the three main glucuro-conjugated metabolites were isolated from urine and characterized by magnetic resonance spectroscopy. The quantification of these metabolites for the different collection periods was then performed by a HPLC-UV assay.

RESULTS

Total recovery of propofol in the metabolites studied amounts to 38%, of which 62% was via the PG metabolite and 38% via cytochrome P-450. This percentage is significantly higher than that previously reported from patients after a bolus dose of propofol. Extreme values for PG (0-24 h period) were included from 73 to 49%. There was no significant difference between female and male patients in the metabolite ratio.

CONCLUSIONS

We conclude that the extent of hydroxylation in propofol metabolism was higher than in previous findings after administration of anaesthetic doses of propofol. Moreover, the ratio between hydroxylation and glucuronidation of propofol is subject to an inter-patient variability but this does not correlate with the dose of propofol. However, the variation of the metabolite profile observed in the present report does not seem to indicate an extended role of metabolism in pharmacokinetic variability.

Treatment of pain in acutely burned children

The child with burns suffers severe pain at the time of the burn and during subsequent treatment and rehabilitation. Pain has adverse physiological and emotional effects, and research suggests that pain management is an important factor in better outcomes. There is increasing understanding of the private experience of pain, and how children benefit from honest preparation for procedures. Developmentally appropriate and culturally sensitive pain assessment, pain relief, and reevaluation have improved, becoming essential in treatment. Pharmacological treatment is primary, strengthened by new concepts from neurobiology, clinical science, and the introduction of more effective drugs with fewer adverse side effects and less toxicity. Empirical evaluation of various hypnotic, cognitive, behavioral, and sensory treatment methods is advancing. Multidisciplinary assessment helps to integrate psychological and pharmacological pain-relieving interventions to reduce emotional and mental stress, and family stress as well. Optimal care encourages burn teams to integrate pain guidelines into protocols and critical pathways for improved care.

Metabolic acidosis, rhabdomyolysis, and cardiovascular collapse after prolonged propofol infusion

The authors present the hospital course of a 13-year-old girl with a closed head injury who received a prolonged infusion of propofol for sedation and, subsequently, died as a result of severe metabolic acidosis, rhabdomyolysis, and cardiovascular collapse. The patient had been treated for 4 days at a referring hospital for a severe closed head injury sustained in a fall from a bicycle. During treatment for elevations of intracranial pressure, she received a continuous propofol infusion (100 microg/kg/min). The patient began to exhibit severe high anion gap/low lactate metabolic acidosis, and was transferred to the pediatric intensive care unit at the authors' institution. On arrival there, the patient's Glasgow Coma Scale score was 3 and this remained unchanged during her brief stay. The severe metabolic acidosis was unresponsive to maximum therapy. Acute renal failure ensued as a result of rhabdomyolysis, and myocardial dysfunction with bizarre, wide QRS complexes developed without hyperkalemia. The patient died of myocardial collapse with severe metabolic acidosis and multisystem organ failure (involving renal, hepatic, and cardiac systems) approximately 15 hours after admission to the authors' institution. This patient represents another case of severe metabolic acidosis, rhabdomyolysis, and cardiovascular collapse observed after a prolonged propofol infusion in a pediatric patient. The authors suggest selection of other pharmacological agents for long-term sedation in pediatric patients.

Use of propofol sedation in a pediatric emergency department: a prospective study

The purpose of this study was to determine the efficacy and safety of propofol sedation for pediatric procedures in the emergency department. For patients needing painful procedures, propofol was administered intravenously. Vital signs, complications, and time to recovery were recorded. Patient amnesia and parent, patient, and operator satisfaction with sedation were assessed. The mean age was 7.4 years; 65% were male. Most underwent fracture reduction. Mean total dose was 3.3 mg/kg. Thirty percent experienced desaturation. One required assisted ventilation. Most had decreases in blood pressure. Mean recovery time was 18 minutes. Satisfaction with sedation was rated "excellent." Propofol was an effective sedation with minimal complications in the emergency department setting.

Microanalysis of propofol in human serum by semi-microcolumn high-performance liquid chromatography with UV detection and solid-phase extraction

OBJECTIVE

To develop a simple analytical method for monitoring the low serum levels of propofol found when administered for the sedation of patients in the intensive care unit (ICU).

METHODS

A high-performance liquid chromatographic method (HPLC) was used with UV detection. Solid-phase extraction (SPE) cartridges and a semi-microcolumn (TSK gel ODS-80Ts, 2.0 mm i.d. x 25 cm, 5 microm) were used to improve sensitivity. Propofol in the eluate obtained from the SPE cartridge was concentrated to about five times the initial concentration.

RESULTS

The sensitivity using the semi-microcolumn was amplified by about three-fold. The assay showed a good linearity with a quantification limit 20 ng/mL. Intra- and inter-assay coefficients of variation were less than 2.2% and 10.0%, respectively. The mean recoveries ranged from 97.6 to 109.5%.

CONCLUSION

The HPLC method described should be useful for measuring the low serum propofol levels found when the drug is used for ICU sedation.

Use of propofol and other nonbenzodiazepine sedatives in the intensive care unit

Sedatives continue to be used on a routine basis in critically ill patients. Although many agents are available and some approach an ideal, none are perfect. Patients require continuous reassessment of their pain and need for sedation. Pathophysiologic abnormalities that cause agitation, confusion, or delirium must be identified and treated before unilateral administration of potent sedative agents that may mask potentially lethal insufficiencies. The routine use of standardized and validated sedation scales and monitors is needed. It is hoped that reliable objective monitors of patients' level of consciousness and comfort will be forthcoming. Each sedative agent discussed in this article seems to have a place in the ICU pharmacologic armamentarium to ensure the safe and comfortable delivery of care. Etomidate is an attractive agent for short-term use to provide the rapid onset and offset of sedation in critically ill patients who are at risk for hemodynamic instability but seem to need sedation or anesthesia to perform a procedure or manipulate the airway. Ketamine administered through intramuscular injection or intravenous infusion provides quick, intense analgesia and anesthesia and allows patients to tolerate limited but painful procedures. The risk/benefit ratio associated with the use of this neuroleptic agent must be weighed carefully. Ketamine is contraindicated in patients who lack normal intracranial compliance or who have significant myocardial ischemia. Barbiturates are reserved mainly to induce coma in patients at risk for severe CNS ischemia, which frequently is associated with refractory intracranial hypertension, or in patients with status epilepticus. When administered in high doses, these drugs have prolonged sedative and depressant effects. Judicious hemodynamic monitoring is required when barbiturate coma is induced. Haloperidol is indicated in the treatment of delirium. Patients should be monitored for extrapyramidal side effects and, when they require higher doses, for potential electrocardiographic prolongation of the QT interval. Dexmedetomidine may evolve into an agent with qualities comparable with midazolam and propofol, and it may even become a drug of choice in select patients. Further study is required, however. Propofol has many of the qualities of an ideal sedative agent. Benzodiazepines and narcotics often are used in concert with propofol to provide reliable amnesia and to relieve pain, respectively. Propofol frequently causes hypotension when administered as a bolus or infusion, particularly in patients with limited cardiac reserve or hypovolemia. More data must be obtained to identify potential deleterious effects of hypertriglyceridemia, and further evaluation of the potential benefits in certain patient populations, such as neurosurgical patients, is needed.

Effects of postoperative sedation with propofol and midazolam on pancreatic function assessed by pancreatitis-associated protein

This prospective randomised controlled study evaluated the effects of postoperative sedation with propofol and midazolam on pancreatic function. We studied 42 intensive care unit patients undergoing elective major surgery who were expected to be sedated postoperatively. Patients were randomly assigned to a propofol group (n = 21) or a midazolam group (n = 21). To assess pancreatic function, the following parameters were measured: pancreatitis-associated protein, amylase, lipase, cholesterol and triglyceride prior to start of sedation on the intensive care unit, 4 h after the sedation was started and at the first postoperative day. Patients in the propofol group received on average (SD) 1292 (430) mg propofol and were sedated for 9.03 (4.26) h. The midazolam group received 92 (36) mg midazolam and were sedated for 8.81 (4.68) h. Plasma cholesterol concentrations did not differ significantly between groups. Triglyceride plasma levels 4 h after the start of infusion were significantly higher in the propofol group (140 (54) mg.dl(-1)) than the midazolam-treated patients (81 (29) mg.dl(-1)), but were within normal limits. There were no significant differences between the two groups regarding amylase, lipase and pancreatitis-associated protein plasma concentrations at any time. No markers of pancreatic dysfunction were outside the normal range. We conclude that postoperative sedation with propofol induced a significant increase of serum triglyceride levels but that pancreatic function is unchanged with standard doses of propofol.

An electrophysiological study of the effects of propofol on native neuronal ligand-gated ion channels

1. Pharmacological evidence suggests that some of the clinical actions of propofol may be mediated, at least in part, by positive modulation of the GABA(A) receptor chloride channel. The effect of propofol at other native neuronal ligand-gated ion channels is unclear. 2. To gain some insight into the effects of propofol at a range of native neuronal receptors, the present study has used an extracellular recording technique and determined its effects at GABA(A), 5-HT3, P2X and nicotinic acetylcholine (nACh) receptors of the rat isolated vagus nerve and the GABA(A) and strychnine-sensitive glycine receptor of the rat isolated optic nerve. In addition, we have used patch-clamp recording techniques to further investigate the effects of propofol at the GABA(A) and strychnine-sensitive glycine receptors in rat cultured hippocampal neurons. 3. Propofol (0.3-100 micromol/L) concentration-dependently potentiated submaximal GABA-evoked responses in the vagus nerve and shifted the GABA concentration-response curve to the left. In contrast, propofol at concentrations ranging from 1 to 10 micromol/L had little or no effect on 5-HT3, P2X or nACh receptor-mediated responses in the vagus nerve but, at 100 micromol/L, propofol inhibited these responses to approximately 50% of control. In the optic nerve, EC20 GABA-evoked responses were also potentiated by propofol (10 micromol/L), while EC20 glycine-evoked responses were minimally enhanced. 4. Further investigations using cultured hippocampal neurons showed that submaximal (10 micromol/L) GABA-evoked currents were potentiated by propofol (1-10 micromol/L), in a non-voltage-dependent manner, whereas submaximal (100 micromol/L) glycine-evoked currents were unaffected. 5. These data suggest that propofol, at therapeutic concentrations, exerts its principle pharmacological actions at GABA(A) receptors with relatively little effect at other neuronal ligand-gated ion channels.

Propofol vs midazolam for ICU sedation : a Canadian multicenter randomized trial

STUDY OBJECTIVES

To determine whether sedation with propofol would lead to shorter times to tracheal extubation and ICU length of stay than sedation with midazolam.

DESIGN

Multicenter, randomized, open label.

SETTING

Four academic tertiary-care ICUs in Canada.

PATIENTS

Critically ill patients requiring continuous sedation while receiving mechanical ventilation.

INTERVENTIONS

Random allocation by predicted requirement for mechanical ventilation (short sedation stratum, < 24 h; medium sedation stratum, > or = 24 and < 72 h; and long sedation stratum, > or = 72 h) to sedation regimens utilizing propofol or midazolam.

MEASUREMENTS AND RESULTS

Using an intention-to-treat analysis, patients randomized to receive propofol in the short sedation stratum (propofol, 21 patients; midazolam, 26 patients) and the long sedation stratum (propofol, 4 patients; midazolam, 10 patients) were extubated earlier (short sedation stratum: propofol, 5.6 h; midazolam, 11.9 h; long sedation stratum: propofol, 8.4 h; midazolam, 46.8 h; p < 0.05). Pooled results showed that patients treated with propofol (n = 46) were extubated earlier than those treated with midazolam (n = 53) (6.7 vs 24.7 h, respectively; p < 0.05) following discontinuation of the sedation but were not discharged from ICU earlier (94.0 vs 63.7 h, respectively; p = 0.26). Propofol-treated patients spent a larger percentage of time at the target Ramsay sedation level than midazolam-treated patients (60.2% vs 44.0%, respectively; p < 0.05). Using a treatment-received analysis, propofol sedation either did not differ from midazolam sedation in time to tracheal extubation or ICU discharge (sedation duration, < 24 h) or was associated with earlier tracheal extubation but longer time to ICU discharge (sedation duration, > or = 24 h, < 72 h, or > or = 72 h).

CONCLUSIONS

The use of propofol sedation allowed for more rapid tracheal extubation than when midazolam sedation was employed. This did not result in earlier ICU discharge.

A lack of evidence of superiority of propofol versus midazolam for sedation in mechanically ventilated critically ill patients: a qualitative and quantitative systematic review

Propofol and midazolam are often used for sedation in the intensive care unit. The aim of this systematic review was to estimate the efficacy and harm of propofol versus midazolam in mechanically ventilated patients. A systematic search (Medline, Cochrane Library, Embase, bibliographies), any language, up to June 1999 was performed for reports of randomized comparisons of propofol with midazolam. Data from 27 trials (1624 adults) were analyzed. The average duration of sedation varied between 4 and 339 h. In 10 trials, the duration of adequate sedation was longer with propofol (weighted mean difference 2.9 h; 95% confidence interval [CI], 0.2-5.6 h). In 13 trials (mostly postoperative), sedation lasted 4 to 35 h; in 9 of those, average weaning time from mechanical ventilation with propofol was 0.8-4.3 h; with midazolam it was 1.5-7.2 h (weighted mean difference 2.2 h [95% CI, 0.8 to 3.7 h]). In 8 trials, sedation lasted 54 to 339 h; there was a lack of evidence for difference in weaning times. Arterial hypotension (relative risk 2.5 [95% CI, 1.3 to 4.5]; number-needed-to-treat, 12), and hypertriglyceridemia (relative risk 12.1 [95%CI, 2.9 to 49.7]; number-needed-to-treat, 6) occurred more often with propofol. The duration of adequate sedation time is longer with propofol compared with midazolam. In postoperative patients with sedation <36 h, weaning is faster with propofol.

IMPLICATIONS

The duration of adequate sedation time is longer with propofol compared with midazolam. In postoperative patients with sedation < 36 h, weaning is faster with propofol.

Midazolam and 2% propofol in long-term sedation of traumatized critically ill patients: efficacy and safety comparison

OBJECTIVE

We proposed to compare the efficacy and safety of midazolam and propofol in its new preparation (2% propofol) when used for prolonged, deep sedation in traumatized, critically ill patients. We also retrospectively compared 2% propofol with its original preparation, 1% propofol, used in a previous study in a similar and contemporary set of patients.

DESIGN

A prospective, randomized, unblinded trial (midazolam and 2% propofol) and a retrospective, contemporary trial (2% propofol and 1% propofol).

SETTINGS

A trauma intensive care unit in a tertiary university hospital.

PATIENTS

A total of 63 consecutive trauma patients, admitted within a period of 5 months and requiring mechanical ventilatory support for >48 hrs, 43 of whom (73%) suffered severe head trauma. We also retrospectively compared the 2% propofol group with a series of patients in whom 1% propofol was used.

INTERVENTIONS

For the prospective trial, we randomized two groups--a midazolam group with continuous administration of midazolam at dosages 0.1-0.35 mg/kg/hr, and a 2% propofol group with continuous infusion at dosages 1.5-6 mg/kg/hr. Equal dosages of analgesics were administered. Similar management protocols were applied in the 1% propofol group, used in the retrospective analysis with 2% propofol.

MEASUREMENTS AND MAIN RESULTS

Epidemiologic and efficacy variables were recorded. Hemodynamic and biochemical variables were also monitored on a regular basis. Neuromonitoring was also performed on those patients with head trauma. Sedation adequacy was similar and patient behavior after drug discontinuation was not different in either prospective group (midazolam and 2% propofol). Hemodynamic or neuromonitoring variables were also similar for both groups. Triglyceride levels were significantly higher in the 2% propofol group compared with the midazolam group. A higher number of therapeutic failures because of sedative inefficacy was seen in the 2% propofol group compared with the midazolam group, especially during the first sedation days. When comparing 2% propofol and 1% propofol, a significantly higher number of therapeutic failures because of hypertriglyceridemia were found in the 1% propofol group, as opposed to a major number of therapeutic failures because of inefficacy, found in the 2% propofol group.

CONCLUSIONS

Propofol's new preparation is safe when used in severely traumatized patients. Its more concentrated formula improves the lipid overload problem seen with the prolonged use of the previous preparation. Nevertheless, a major number of therapeutic failures were detected with 2% propofol because of the need for dosage increase. This fact could be caused by a different disposition and tissue distribution pattern of both propofol preparations. New studies will be needed to confirm these results.

Bisulfite-containing propofol: is it a cost-effective alternative to Diprivan for induction of anesthesia?

Propofol (Diprivan(TM); AstraZeneca, Wilmington, DE) is a commonly used drug for the induction of general anesthesia in the ambulatory setting. With the availability of a new bisulfite-containing generic formulation of propofol, questions have arisen regarding its cost effectiveness and safety compared with Diprivan(TM). Two hundred healthy outpatients were randomly assigned, according to a double-blinded protocol, to receive either Diprivan(TM) or bisulfite-containing propofol 1.5 mg/kg IV as part of a standardized induction sequence. Maintenance of anesthesia consisted of either desflurane (4%-8% end-tidal) or sevoflurane (1%-2% end-tidal) in combination with a remifentanil infusion (0.125 microg x kg(-1) x min(-1) IV). Patient assessments included pain on injection, induction time, hemodynamic and bispectral electroencephalographic changes during induction, emergence time, and incidence of postoperative nausea and vomiting. The two propofol groups were comparable demographically, and the induction times and bispectral index values during the induction were also similar. However, the bisulfite-containing formulation was associated with less severe pain on injection (5% vs 11%), with fewer patients recalling pain on injection after surgery (38% vs. 51%, P<0.05). None of the patients manifested allergic-type reactions after the induction of anesthesia. The acquisition cost (average wholesale price in US dollars) of a 20-mL ampoule of Diprivan(TM) was $15 compared with $13 for the bisulfite-containing propofol formulation. Therefore, we concluded that the bisulfite-containing formulation of propofol is a cost-effective alternative to Diprivan(TM) for the induction of outpatient anesthesia.

IMPLICATIONS

Bisulfite-containing propofol and Diprivan(TM) (AstraZeneca, Wilmington, DE) were similar with respect to their induction characteristics; however, the generic formulation was associated with a smaller incidence of injection pain. Assuming that the drug costs are similar, these data suggest that the bisulfite-containing formulation of propofol is a cost-effective alternative to Diprivan(TM).

Clinical significance of rare and benign side effects: propofol and green urine

A 55-year-old man requiring airway protection for esophagogastroduodenoscopy was sedated with propofol. On the third day of propofol infusion his urine was dark green. Although he was afebrile and his white blood cell count was within normal limits, the green urine was suspected to be of infectious etiology. Laboratory tests were ordered and broad-spectrum antibiotics were considered. Antibiotics were avoided when propofol was recognized as a rare and benign potential cause of the green urine. Earlier recognition of this side effect may have averted unnecessary laboratory monitoring. Prompt recognition of such side effects is important in limiting medical expenditures, inordinate drug exposure, and distress among patients and clinicians.

Death related to propofol use in an adult patient

OBJECTIVE

To report an adult trauma patient fatality related to propofol administration.

DESIGN

Retrospective case review.

SETTING

Trauma intensive care unit (ICU) in a level one trauma center.

PATIENT

An 18-yr-old man involved in a motor vehicle crash.

INTERVENTIONS

Treatment for multiple trauma injuries and propofol sedation.

MEASUREMENTS AND MAIN RESULTS

Posttrauma ICU monitoring was performed. The patient developed cardiac arrhythmia, metabolic acidosis, and cardiac failure, which resulted in death.

CONCLUSION

Death related to propofol infusion can occur in adults as well as in pediatric patients.

Intravenous propofol: unique effectiveness in treating intractable migraine

OBJECTIVE

To report the unique effectiveness of propofol, an intravenous anesthetic agent, in treating refractory migraines and other headaches in the setting of an outpatient headache center.

BACKGROUND

We initially observed the dramatic abolition of ongoing migraine in patients (n=6) being treated with propofol in preparation for epidural and other nerve blocks in the headache and pain clinic. The reduction of headache severity was virtually 100%. We decided to treat an additional cohort of patients with intravenous propofol in the headache clinic; these patients had intractable migraines that were refractory to the usual abortive treatments. Subanesthetic doses of propofol were employed in this study. This is the first known report of the utility of this agent specifically for the treatment of intractable headache.

METHODS

Seventy-seven patients were treated for intractable headache in the clinic with intravenous propofol, for both migraine and nonmigrainous headache refractory to the usual methods of abortive treatment.

RESULTS

The average reduction in headache intensity was 95.4% after an average of 20 to 30 minutes of intravenous propofol treatment, using a patient-rated visual analog scale of 0 to 10. Sixty-three of 77 patients reported complete abolition of their headache. The average dose of propofol was 110 mg, which is well within the usual range of preanesthetic doses and is clearly subanesthetic. Moreover, only three of the treated patients reported a return of the headache on the day following treatment. The neuropharmacology of propofol and the putative multiple mechanisms of action upon various neurotransmitter systems in the brain, particularly gamma aminobutyric acid A receptor subtypes, are discussed to explain the results in our patients.

CONCLUSIONS

The use of intravenous propofol may represent a new, rapid, and highly effective form of abortive headache treatment in the headache clinic or emergency room setting and may offer an alternative to other treatment modalities for acute migraine and other severe intractable headaches. The effectiveness of propofol raises many new questions about the pathophysiology of migraine and other headaches.

Sedation in the intensive care unit

OBJECTIVE

To describe the goals of sedative use in the intensive care unit and review the pharmacology of commonly used sedative drugs as well as to review pertinent publications in the literature concerning the comparative pharmacology of these drugs, with emphasis on outcomes related to sedation and comparative pharmacoeconomics.

DATA SOURCES

Publications in the scientific literature.

DATA EXTRACTION

Computer search of the literature with selection of representative articles.

SYNTHESIS

Proper choice and use of sedative drugs is based on knowledge of the pharmacology of commonly used agents and is an essential component of caring for patients in the intensive care unit. The large variability in pharmacokinetics and pharmacodynamics in the critically ill make it difficult to directly compare agents. Midazolam provides rapid and reliable amnesia, even when administered for low levels of sedation. Propofol may be useful when deeper levels of sedation and more rapid awakening are required. Lorazepam can be used for long-term sedation in more stable patients if rapidity of effect is not required. Further investigation in assessment of depth of sedation in the critically ill is needed. Continued study of costs, side effects, and appropriate dosing strategies of all sedative agents is needed to answer questions not sufficiently addressed in the current literature.

CONCLUSION

An individualized approach to sedation based on knowledge of drug pharmacology is needed because of confounding variables including concurrent patient illness, depth of sedation, and concomitant use of analgesic agents. (Crit Care Med 2000; 28:854-866)

Plasma and cerebrospinal fluid concentrations of neuropeptide Y, serotonin, and catecholamines in patients under propofol or isoflurane anesthesia

Propofol is a widely used anesthetic for both induction and maintenance of anesthesia during surgery. A strong feeling of hunger has been reported during the early recovery period after propofol anesthesia. We have investigated the effect of propofol on appetite in 10 patients undergoing a craniotomy and in parallel measured neuropeptide Y (NPY), catecholamines, and serotonin levels in the cerebrospinal fluid and plasma during anesthesia. Ten patients anesthetized with a volatile agent (isoflurane) served as a control group. Plasma NPY and catecholamines levels were not affected by surgery at any time. We observed a strong increase in NPY concentrations in the cerebrospinal fluid independently of the anesthetic technique agent used, whereas catecholamines were unchanged. We found that serotonin concentrations decreased significantly in the plasma (but not in the cerebrospinal fluid) of patients treated by propofol when compared with the control group; this decrease was associated with an increase of hunger early postoperatively. We concluded that the proappetite effect of propofol is mediated through a decrease of serotonin at the peripheral level.Key words: catecholamines, serotonin, neuropeptide Y (NPY), cerebrospinal fluid, serum, appetite.

Activation of rat locus coeruleus neuron GABA(A) receptors by propofol and its potentiation by pentobarbital or alphaxalone

The action of propofol on the rat locus coeruleus was examined using intracellular recording from in vitro brain slice preparations. Concentrations of propofol between 3 and 300 microM were tested. At 100 microM, propofol completely inhibited the firing of all neurons tested (n=34); this was associated with a 5.7-mV hyperpolarization (range 0-16 mV, n=33) and a 35.6% reduction in input resistance (range 7.3-66.1%, n=33). The propofol-induced responses were not affected by 2-hydroxysaclofen (50 microM) or BaCl(2) (300 microM), but were completely blocked by bicuculline methiodide (100 microM) or picrotoxin (100 microM), indicating that propofol acts on GABA(A) receptors. As assessed by inhibition of the spontaneous firing rate, propofol was 5.6-fold more potent than GABA (gamma-aminobutyric acid). Potentiation of the propofol effect by other general anesthetics or other drugs was also investigated. When pentobarbital (100 microM) was tested alone on locus coeruleus cells, no change in membrane potential or input resistance was seen and there was only a 20.3+/-7.2% (n=8) inhibition of firing rate; however, in combination with 30 microM propofol, it caused a 6.1-fold greater increase in membrane hyperpolarization and a 9.7-fold greater reduction in input resistance than 30 microM propofol alone. A relatively low concentration of alphaxalone (10 microM), when tested alone, had little effect on the membrane potential or input resistance and only produced a 46.0+/-8.9% (n=8) inhibition of firing rate; however, in combination with 30 microM propofol, it caused a 9.3-fold greater hyperpolarization and an 8.6-fold greater reduction in input resistance compared with 30 microM propofol alone. In contrast, diazepam caused no potentiation of either propofol- or GABA-induced responses. Our data also indicate that locus coeruleus neuron GABA(A) receptors possess distinctive pharmacologic characteristics, such as blocking of the propofol effects by zinc and insensitivity to diazepam and the direct action of pentobarbital. On the basis of these pharmacologic properties, we suggest that locus coeruleus neuron GABA(A) receptors do not contain the gamma subunit.

Low-dose midazolam infusion for oculoplastic surgery under local anesthesia

PURPOSE

Oculoplastic surgery with infiltration of local anaesthesia at the operative site performed as a day-case procedure is both efficient and cost-effective. Patients considered unsuitable for this because of fear or apprehension may, however, benefit from per-operative conscious sedation. We sought to study the efficacy and safety of this using midazolam, a water-soluble benzodiazepine.

METHOD

We have performed a controlled clinical trial comparing the effect of a low-dose intravenous infusion of midazolam (0.2 mg/ml of normal saline at a rate of 1 mg/h) with saline placebo on 48 subjects undergoing oculoplastic surgery with local anaesthesia. Patients were given pre- and post-operative questionnaires assessing, amongst other factors, anxiety levels, pain, degree of reported amnesia and psychomotor recovery.

RESULTS

Using the low-dose midazolam infusion no adverse cardiorespiratory reactions occurred. Patients receiving midazolam reported remembering significantly less about their operation than controls (p = 0.04) and showed significantly lower state-anxiety after their operation than before (p < 0.02). This change was not noted in the placebo group. There was no significant difference in the psychomotor performance of patients given midazolam compared with controls 2 h after surgery.

CONCLUSIONS

A low-dose continuous infusion of midazolam can be used to safely provide effective anxiolysis and conscious sedation with good psychomotor recovery during oculoplastic procedures in a day-case setting.

Ondansetron pretreatment to alleviate pain on propofol injection: a randomized, controlled, double-blinded study

We used a randomized, controlled, double-blinded design to study the effect of ondansetron (OND) pretreatment on the pain produced by the IV injection of propofol. Eighty patients were randomly assigned to one of two groups: Group I received 2 mL of IV 0.9% saline pretreatment, and Group II received OND (4 mg in 2 mg/mL solution) pretreatment in the dorsum of the hand, followed by propofol 1 min later. Pain was reduced significantly in the OND group (P<0.05). Approximately one third of the patients in each group had myoclonic movements or skin rashes in the limb that received propofol. We conclude that the OND pretreatment may be used to reduce the incidence of pain on injection of propofol and to prevent postoperative nausea and vomiting.

IMPLICATIONS

In a double-blinded, controlled study, IV ondansetron (4 mg) pretreatment was used to alleviate pain on injection of propofol. Ondansetron was successful in relieving pain without any adverse effect in a significant number of patients.

Rats show unimpaired learning within minutes after recovery from single bolus propofol anesthesia

PURPOSE

To examine the learning ability of rats shortly after recovery from a bolus dose of propofol by assessing learning on a swim-to-platform task. Also, muscarinic blockade was used as a pharmacological test of whether learning shortly after propofol anesthesia resembles normal learning.

METHODS

Propofol anesthetized rats (15-20 mg x kg(-1) i.v.) were trained on a swim-to-platform task five to seven minutes after recovering from surgical anesthesia and tested two to three hours later In addition, the muscarinic antagonist scopolamine hydrobromide (5 mg x kg(-1) s.c.) was given to a subgroup of rats before testing. During 10 trials, the number of times a given rat took 10 sec or longer to locate and climb onto a visible platform was tabulated and counted as errors.

RESULTS

When trained shortly after recovery from the anesthetic, propofol anesthetized rats made 3.2 +/- 0.4 compared with 1.0 +/- 0.1 errors in controls (P < 0.0001). Two to three hours later both groups performed equally well. Rats trained after propofol anesthesia and given scopolamine before testing made 0.7 +/- 0.5 errors and performed as well as normal controls, 1.2 +/- 0.2 errors when subjected to the same procedures without propofol anesthesia, and better than scopolamine-treated untrained rats, 5.5 +/- 0.7 errors, (P < 0.05).

CONCLUSION

Training five to seven minutes after recovery from propofol anesthesia resulted in normal retention of the swim- to-platform task. It also produced the same resistance to the disruptive effects of scopolamine as did training in rats that were not anesthetized. Thus, the ability to learn recovers rapidly after propofol anesthesia induced by a single intravenous bolus dose.

Pharmacokinetics, induction of anaesthesia and safety characteristics of propofol 6% SAZN vs propofol 1% SAZN and Diprivan-10 after bolus injection

AIMS

In order to avoid the potential for elevated serum lipid levels as a consequence of long term sedation with propofol, a formulation of propofol 6% in Lipofundin(R) MCT/LCT 10% (Propofol 6% SAZN) has been developed. The pharmacokinetics, induction of anaesthesia and safety characteristics of this new formulation were investigated after bolus injection and were compared with the commercially available product (propofol 1% in Intralipid(R) 10%, Diprivan-10) and propofol 1% in Lipofundin(R) MCT/LCT 10% (Propofol 1% SAZN).

METHODS

In a randomised double-blind study, 24 unpremedicated female patients received an induction dose of propofol of 2.5 mg kg-1 over 60 s which was followed by standardized balanced anaesthesia. The patients were randomized to receive propofol as Propofol 6% SAZN, Propofol 1% SAZN or Diprivan-10.

RESULTS

For all formulations the pharmacokinetics were adequately described by a tri-exponential equation, as the propofol concentrations collected early after the injection suggested an additional initial more rapid phase. The average values for clearance (CL), volume of distribution at steady-state (Vd,ss ), elimination half-life (t1/2,z ) and distribution half-life (t1/2, lambda2) observed in the three groups were 32+/-1.5 ml kg-1 min-1, 2. 0+/-0.18 l kg-1, 95+/-5.6 min and 3.4+/-0.20 min, respectively (mean+/-s.e.mean, n=24) and no significant differences were noted between the three formulations (P >0.05). The half-life of the additional initial distribution phase (t1/2,lambda1 ) in all subjects ranged from 0.1 to 0.6 min. Anaesthesia was induced successfully and uneventfully in all cases, and the quality of induction was adequate in all 24 patients. The induction time did not vary between the three formulations and the average induction time observed in the three groups was 51+/-1.3 s which corresponded to an induction dose of propofol of 2.1+/-0.06 mg kg-1 (mean+/-s.e. mean, n=24). The percentage of patients reporting any pain on injection did not vary between the formulations and was 17% for the three groups. No postoperative phlebitis or other venous sequelae of the vein used for injection occurred in any of the patients at recovery of anaesthesia nor after 24 h.

CONCLUSIONS

From the above results, we conclude that the alteration of the type of emulsion and the higher concentration of propofol in the new parenteral formulation of propofol does not affect the pharmacokinetics and induction characteristics of propofol, compared with the currently available product. Propofol 6% SAZN can be administered safely and has the advantage of a reduction of the load of fat and emulsifier which may be preferable when long term administration of propofol is required.

Propofol in the treatment of moderate and severe head injury: a randomized, prospective double-blinded pilot trial

OBJECT

Sedation regimens for head-injured patients are quite variable. The short-acting sedative-anesthetic agent propofol is being increasingly used in such patients, yet little is known regarding its safety and efficacy. In this multicenter double-blind trial, a titratable infusion of 2% propofol accompanied by low-dose morphine for analgesia was compared with a regimen of morphine sulfate in intubated head-injured patients. In both groups, other standard measures of controlling intracranial pressure (ICP) were also used.

METHODS

Forty-two patients from 11 centers were evaluated to assess both the safety and efficacy of propofol: 23 patients in the propofol group (mean time of propofol usage 95+/-87 hours) and 19 patients in the morphine group (mean time of morphine usage 70+/-54 hours). There was a higher incidence of poor prognostic indicators in the propofol group than in the morphine group: patient age older than 55 years (30.4% compared with 10.5%, p < 0.05), initial Glasgow Coma Scale scores of 3 to 5 (39.1% compared with 15.8%, p < 0.05), compressed or absent cisterns on initial computerized tomography scanning (78.3% compared with 57.9%, p < 0.05), early hypotension and/or hypoxia (26.1% compared with 10.5%, p = 0.07). During treatment there was a trend toward greater use of vasopressors in the propofol group. However, the mean daily ICP and cerebral perfusion pressure were generally similar between groups and, on therapy Day 3, ICP was lower in the propofol group compared with the morphine group (p < 0.05). Additionally, there was less use of neuromuscular blocking agents, benzodiazepines, pentobarbital, and cerebrospinal fluid drainage in the propofol group (p < 0.05). At 6 months postinjury, a favorable outcome (good recovery or moderate disability) was observed in 52.1% of patients receiving propofol and in 47.4% receiving morphine; the mortality rates were 17.4% and 21.1%, respectively. Patients who received the highest doses of propofol for the longest duration tended to have the best outcomes. There were no significant differences between groups in terms of adverse events.

CONCLUSIONS

Despite a higher incidence of poor prognostic indicators in the propofol group, ICP therapy was less intensive, ICP was lower on therapy Day 3, and long-term outcome was similar to that of the morphine group. These results suggest that a propofol-based sedation and an ICP control regimen is a safe, acceptable, and, possibly, desirable alternative to an opiate-based sedation regimen in intubated head-injured patients.

The influence of anesthetic choice, PaCO2, and other factors on osmotic blood-brain barrier disruption in rats with brain tumor xenografts

Increasing the delivery of therapeutic drugs to the brain improves outcome for patients with brain tumors. Osmotic opening of the blood-brain barrier (BBB) can markedly increase drug delivery, but achieving consistent, good quality BBB disruption (BBBD) is essential. We evaluated four experiments compared with our standard isoflurane/O2 protocol to improve the quality and consistency of BBBD and drug delivery to brain tumor and normal brain in a rat model. Success of BBBD was assessed qualitatively with the large molecular weight marker Evans blue albumin and quantitatively by measuring delivery of the low molecular weight marker [3H]-methotrexate. With isoflurane/O2 anesthesia, the effects of two BBBD drugs of different osmolalities were evaluated at two different infusion rates and infusion durations. Arabinose was superior to saline (P = 0.006) in obtaining consistent Evans blue staining in 16 of 24 animals, and it significantly increased [3H]-methotrexate delivery compared with saline in the tumor (0.388 +/- 0.03 vs 0.135 +/-0.04; P = 0.0001), brain around the tumor (0.269 +/- 0.03 vs 0.035 +/- 0.03; P = 0.0001), brain distant to the tumor (0.445 +/- 0.05 vs 0.034 +/- 0.07; P = 0.001), and opposite hemisphere (0.024 +/- 0.00 vs 0.016 +/- 0.00; P = 0.0452). Forty seconds was better than 30 s (P = 0.0372) for drug delivery to the tumor. Under isoflurane/O2 anesthesia (n = 30), maintaining hypocarbia was better than hypercarbia (P = 0.025) for attaining good BBBD. A propofol/ N2O regimen was compared with the isoflurane/O2 regimen, altering blood pressure, heart rate, and PaCO2 as covariates (n = 48). Propofol/N2O was superior to isoflurane/O2 by both qualitative and quantitative measures (P < 0.0001). Neurotoxicity and neuropathology with the propofol/N2O regimen was evaluated, and none was found. These data support the use of propofol/N2O along with maintaining hypocarbia to optimize BBBD in animals with tumors.

IMPLICATIONS

Propofol/N2O anesthesia may be better than isoflurane/O2 for optimizing osmotic blood-brain barrier disruption for delivery of chemotherapeutic drugs to brain tumor and normal brain.

Adjuncts to analgesia. Sedation and neuromuscular blockade

This article provides an overview of some of the current issues involved in sedation and anxiolysis in the intensive care unit. The problems involved in trying to monitor sedation levels are discussed, as are some of the newer options available for physiologic monitoring of the central nervous system. The problem of abnormal mental states in the intensive care unit and the range of antidepressant therapy now available are also covered. The importance of sleep deprivation and the properties of the neuromuscular blockers are also discussed.

The significance of lipoproteins in serum binding variations of propofol

The protein binding of propofol was investigated in vitro in isolated lipoprotein fractions (very low-density lipoprotein [VLDL], low-density lipoprotein [LDL], and high-density lipoprotein [HDL]) and in serum samples from the following subjects: healthy normolipemic volunteers (n = 16), hyperlipidemic subjects diagnosed with familiar polygenic hypercholesterolemia (n = 26) showing high levels of cholesterol, and elderly subjects (n = 15). Protein binding was determined by using ultrafiltration, and the concentration of unbound propofol was measured by using liquid chromatography. Levels of total cholesterol, triglycerides, VLDL cholesterol, LDL cholesterol, HDL cholesterol, albumin, and alpha1-acid glycoprotein were also measured. Propofol was extensively bound to the three lipoprotein fractions (88%+/-2% to VLDL, 93%+/-1% to LDL, and 91%+/-4% to HDL). The percentage of unbound propofol was significantly decreased (P < 0.0001) in hyperlipidemic (0.88%+/-0.20%) individuals whose levels of cholesterol and triglycerides were increased versus healthy subjects (1.26%+/-0.22%), whereas no significant difference was found in the elderly group (1.12%+/-0.23%). A positive relationship was found between serum protein binding of propofol and lipid levels. Multiple regression analysis, including all subjects, showed that changes in the levels of total cholesterol and triglycerides explained approximately 62% of the variability in the serum protein binding of propofol. These results stress the importance of triglycerides and cholesterol in the serum protein binding of propofol. We therefore suggest that these variations in lipid levels, and consequently in protein binding, may influence anesthetic practice with propofol.

IMPLICATIONS

We investigated the effect of serum lipids in the protein binding of propofol. We found that propofol binds extensively to all lipoprotein fractions. Propofol binding showed a significant relationship with the serum levels of cholesterol and triglycerides.

Effect of enteral versus parenteral feeding on hepatic blood flow and steady state propofol pharmacokinetics in ICU patients

OBJECTIVE

The main objective of this study was to evaluate the effect of switching from parenteral to enteral feeding on liver blood flow and propofol steady-state blood concentrations in patients in the intensive care unit (ICU).

DESIGN AND PATIENTS

Steady-state blood concentrations of propofol were measured in eight ICU patients before (on days D -3, D -2, and D -1) and after (on days D + 1, D + 2, and D + 3) switching from parenteral to enteral feeding (on day DO). All patients received a continuous intravenous infusion of propofol (4.5 mg x kg(-1) x h(-1)) from several days before the start of the study, continuing throughout the experimental period. Hepatic blood flow was estimated by measuring steady-state D-sorbitol hepatic clearance.

RESULTS

Hepatic blood flow was high and was not affected by switching from parenteral to enteral feeding: 33 +/- 8 ml x min(-1) x kg(-1) (mean +/- SD) and 33 +/- 10 ml min(-1) x kg(-1) on D -3 and D -1, respectively, as compared to 37 +/- 11 ml x min(-1) kg(-1) and 34 +/- 8 ml x min(-1) x kg(-1) on days D + 1 and D + 3, respectively. Systemic clearance of propofol was much higher than liver blood flow with average values on the six observation days ranging from 74.0 to 81.2 ml x min(-1) x kg(-1) and was not affected by switching from parenteral to enteral feeding.

CONCLUSIONS

Liver blood flow and systemic clearance of propofol were not affected by switching from parenteral to enteral feeding in the eight ICU patients studied. Extrahepatic clearance accounted for at least two thirds of the overall systemic clearance of propofol.

Propofol versus midazolam: safety and efficacy for sedating the severe trauma patient

Previous studies have compared sedation profiles with midazolam (Mz) and propofol (Pf), particularly in heterogeneous populations of patients. Decreases in blood pressure and heart rate have been reported after the administration of propofol. These side effects are potentially deleterious in severe trauma patients, particularly in patients with head trauma. To assess the safety and efficacy of Mz and Pf, alone or in combination, in the prolonged sedation of severe trauma patients, we designed a prospective, controlled, randomized, study. One hundred consecutively admitted trauma patients requiring mechanical ventilation and sedation for more than 48 h were studied. Patients were sedated according to three different protocols based on the continuous i.v. administration of Mz alone, Pf alone, and Mz in combination with Pf. All patients received morphine chloride. Safety and efficacy were assessed during the sedation and wake-up periods according to clinical and laboratory variables. Cerebral hemodynamics were also studied in patients with head trauma. Patients were sedated for 6.3 +/- 4.0 days (mean +/- SD). All three sedation regimens were equally efficacious in achieving the desired sedation goal. The incidence of adverse events during the sedation period was also similar. In head trauma patients with intracranial pressure (ICP) monitoring, we did not find differences in ICP, cerebral perfusion pressure, or jugular venous oxygen saturation among the three groups. The serum triglyceride concentration was significantly higher in the Pf group. Wake-up time was significantly shorter in the Pf group. We conclude that both Mz and Pf are safe and efficacious in the sedation of severe trauma patients. The use of Pf in these patients is associated with a high incidence of hypertriglyceridemia and a shorter wake-up time.

IMPLICATIONS

In a prospective, controlled, randomized study, we confirmed the safety and efficacy of midazolam and propofol, alone or in combination, in the prolonged sedation of a homogeneous group of severe trauma patients, particularly in patients with head trauma. The propofol group had shorter wake-up times and higher triglyceride levels.

Complications of sedation with midazolam in the intensive care unit and a comparison with other sedative regimens

OBJECTIVE

To describe the various complications that have been reported with use of midazolam for sedation in the intensive care unit (ICU).

DATA SOURCES

Publications in scientific literature.

DATA EXTRACTION

Computer search of the literature.

SYNTHESIS

Sedation is required in the ICU in order for patients to tolerate noxious stimuli, particularly mechanical ventilation. Under- and oversedation can lead to complications. To sedate patients in the ICU, midazolam is commonly administered via titrated, continuous infusions. Cardiorespiratory effects tend to be minimal; however, hypotension can occur in hypovolemic patients. Prolonged sedation after cessation of the midazolam infusion may be caused by altered kinetics of the drug in critically ill patients or by accumulation of active metabolites. In addition, paradoxical and psychotic reactions have been rarely reported. Tolerance and tachyphylaxis may occur, particularly with longer-term infusions (> or = 3 days). Benzodiazepine withdrawal syndrome has also been associated with high dose/long-term midazolam infusions. Compared with propofol infusions, midazolam infusions have been associated with a decreased occurrence of hypotension but a more variable time course for recovery of function after the cessation of the infusion. Lorazepam is a more cost-effective choice for long-term (> 24 hrs) sedation.

CONCLUSION

Continuous infusion midazolam provides effective sedation in the ICU with few complications overall, especially when the dose is titrated.

Influence of different fat emulsion-based intravenous formulations on the pharmacokinetics and pharmacodynamics of propofol

PURPOSE

The influence of different intravenous formulations on the pharmacokinetics and pharmacodynamics of propofol was investigated using the effect on the EEG (11.5-30 Hz) as pharmacodynamic endpoint.

METHODS

Propofol was administered as an intravenous bolus infusion (30 mg/kg in 5 min) or as a continuous infusion (150 mg/kg in 5 hours) in chronically instrumented male rats. Propofol was formulated as a 1% emulsion in an Intralipid 10%-like fat emulsion (Diprivan-10, D) or as a 1%- or 6% emulsion in Lipofundin MCT/LCT-10% (P1% and P6%, respectively). EEG was recorded continuously and arterial blood samples were collected serially for the determination of propofol concentrations using HPLC.

RESULTS

Following bolus infusion, the pharmacokinetics of the various propofol emulsions could adequately be described by a two-compartmental pharmacokinetic model. The average values for clearance (Cl), volume of distribution at steady-state (Vd,ss) and terminal half-life (t1/2, lambda 2) were 107 +/- 4 ml/min/kg, 1.38 +/- 0.06 l/kg and 16 +/- 1 min, respectively (mean +/- S.E. n = 22). No significant differences were observed between the three propofol formulations. After continuous infusion these values were 112 +/- 11 ml/min/kg, 5.19 +/- 0.41 l/kg and 45 +/- 3 min, respectively (mean +/- S.E., n = 20) with again no statistically significant differences between the three propofol formulations. Comparison between the bolus- and the continuous infusion revealed a statistically significant difference for both Vd,ss and t1/2, lambda 2 (p < 0.05), whereas Cl remained unchanged. In all treatment groups infusion of propofol resulted in a burst-suppression type of EEG. A profound hysteresis loop was observed between blood concentrations and EEG effect for all formulations. The hysteresis was minimized by a semi-parametric method and resulted in a biphasic concentration-effect relationship of propofol that was described non-parametrically. For P6% a larger rate constant onset of drug effect (t1/2,keo) was observed compared to the other propofol formulations (p < 0.05).

CONCLUSIONS

The pharmacokinetics and pharmacodynamics of propofol are not affected by to a large extent the type of emulsion nor by the concentration of propofol in the intravenous formulation.

Pharmacokinetics and pharmacodynamics of propofol in a new solvent

Pain on injection is the most commonly reported adverse event after propofol injection. In a randomized, cross-over study in two groups of 12 healthy male volunteers (24-42 yr), we compared the pharmacokinetics and pharmacodynamics of two new propofol formulations (1% and 2% concentrations) in a fat emulsion consisting of medium- and long-chain triglycerides with the standard propofol formulation. After a single intravenous bolus injection of 2 mg/kg, propofol blood levels were measured for 24 h and evaluated according to an open three-compartment model. The derived pharmacokinetic variables were not different among formulations. Additionally, electroencephalographic recordings of the onset and duration of hypnotic action were comparable with all formulations. After propofol 1% in the new formulation, fewer volunteers reported severe or moderate pain on injection (9%) than after the standard formulation (59%) (P < 0.05). We attribute this result to a lower concentration of free propofol in the aqueous phase of the new formulation.

IMPLICATIONS

Changing the composition of the carrier fat emulsion for propofol does not have an impact on the pharmacokinetics and efficacy of propofol, but it promises to provide better patient acceptance by lowering the incidence of moderate and severe pain on injection.

Light versus heavy sedation after cardiac surgery: myocardial ischemia and the stress response. Maritime Heart Centre and Dalhousie University

The influence of light versus heavy sedation after coronary artery bypass graft (CABG) surgery on the development of postoperative myocardial ischemia has not been described. After uncomplicated CABG surgery, 50 patients were randomly assigned to receive LOW (n = 24; target Ramsay Sedation Score [RSS] = 2) or HIGH (n = 26; target RSS = 4) sedation with propofol. Analgesia was provided to maintain a visual analog scale (VAS) pain score <7. Myocardial ischemia was identified perioperatively using continuous 3-lead Holter monitoring. By measuring creatine kinase (CK) MB levels preoperatively, at entry to the intensive care unit (ICU), and every 12 h for 48 h; and by obtaining serial 12-lead electrocardiograms (ECG) (preoperatively; 2, 4, 12, 24, and 48 h after ICU admission, 8:00 AM the morning after surgery; and 5 min pre- and postextubation), myocardial infarction was identified. Endocrine stress response was assessed by measuring serum cortisol levels preoperatively, on admission to the ICU, and 24 h postoperatively. In a subset of patients (LOW n = 10, HIGH n = 11), plasma and urinary catecholamine levels were also measured. There were no between-group differences in demographics, operative course, hemodynamic variables, or cortisol levels while in the ICU. The VAS pain score and target RSS were achieved and sustained, and they differed between groups. There were three myocardial infarctions in each group by CKMB criteria alone. No ECG-identifiable myocardial infarction occurred. The ST segment versus time curve (LOW 187 +/- 295 versus HIGH 1071 +/- 2137 mm/min) differed between groups. Urinary and plasma catecholamine levels were similar between groups over the observation period. We conclude that the use of a reduced sedation regimen in combination with adequate analgesia did not result in an increased endocrine stress response or risk of myocardial ischemia.

IMPLICATIONS

This randomized study of patients after coronary artery bypass surgery examined whether light (versus heavy) sedation with propofol in the intensive care unit was associated with an increased degree of myocardial ischemia. Using techniques to detect myocardial ischemia, including Holter monitoring, electrocardiogram, and myocardial enzyme measurements, no differences were found. We conclude that light sedation does not increase the endocrine stress response or the risk of myocardial infarction.