Severe hypertension and raised haematocrit: unusual presentation of Guillain-Barré syndrome

Benefits of remimazolam as an anesthetic sedative for older patients: A review

Owing to the decreased levels of receptors in the peripheral and central nervous systems, the functions of various organ systems decline in older patients. When administering anesthesia to older patients, it is necessary to consider the effects of medication on the homeostatic balance. Remimazolam, a new benzodiazepine, was recently developed as an anesthetic drug that has shown promise in clinical anesthesia application owing to its molecular structure, targets, pharmacodynamics, and pharmacokinetic characteristics. Remimazolam exhibits a rapid onset and metabolism, with minor effects on liver and kidney functions. Moreover, the drug has a specific antagonist, flumazenil. It is safer to use in older patients than other anesthetic sedatives and has been widely used since its introduction. Comparisons of the pharmacokinetics, metabolic pathways, effects on target organs, and hemodynamics of different drugs with those of commonly used anesthetic sedative drugs are useful to inform clinical practice. This article elaborates on the benefits of remimazolam compared with those of other anesthetic sedatives for sedation in older patients to demonstrate how it offers a new option for anesthetics in older patients. In cases involving older patients with increased clinical complexities or very old patients requiring anesthesia, remimazolam can be selected as the preferred anesthetic sedative, as outlined in this review.

Identification of factors affecting outcomes in patients with Guillain Barre syndrome

Background

Guillain Barre syndrome (GBS) is a rare autoimmune neurological disorder resulting in variable clinical course and outcome. Various factors such as age, symptoms and disease form that influence the outcome of GBS have been previously studied.

Aim

This study aimed at identifying factors affecting the outcomes in patients with GBS.

Methods

A retrospective observational study was conducted on GBS (ICD-G61.0) patients admitted to the hospital between 2014 and 2019. Patient information on demographics, medical and medication history, laboratory parameters, electrophysiological data, type of GBS and therapy received were retrieved from medical records. Univariate and multivariate analysis were conducted to identify factors associated with outcome (improved and not improved) and calculate odds ratio (OR).

Results

A total of 212 GBS patients were included in the study, of which 67% were males and the mean age was 39.9±20.1 years. 168 (79%) patients showed improvement whereas the remaining 44(21%) did not show improvement. Patients with hypertension (OR=4.512; CI=1.309-15.556, p=0.017), alcoholics (OR=5.148; CI=1.234-21.472, p=0.025), sepsis (OR= 9.139; CI=1.102-75.760, p=0.040) and cardiac arrest (OR=17.495; CI=1.249-245.027, p=0.034) were associated with risk of no improvement. Whereas those treated with IVIgG plus Physiotherapy/Occupational therapy (OR=0.062; CI=0.016-0.242, p=0.001) and Plasmapheresis plus Physiotherapy/Occupational therapy (OR=0.007; CI=0.000-0.147, p=0.001) were associated with improvement.

Conclusion

Understanding these factors help to further give a more directed and focused management to improve the condition in patients who are at risk of poor outcome. Further follow-up studies could be done to determine and manage the residual disabilities associated with GBS to improve patient's quality of life.

Metabolic Profiles of Propofol and Fospropofol: Clinical and Forensic Interpretative Aspects

Propofol is an intravenous short-acting anesthetic widely used to induce and maintain general anesthesia and to provide procedural sedation. The potential for propofol dependency and abuse has been recognized, and several cases of accidental overdose and suicide have emerged, mostly among the health professionals. Different studies have demonstrated an unpredictable interindividual variability of propofol pharmacokinetics and pharmacodynamics with forensic and clinical adverse relevant outcomes (e.g., pronounced respiratory and cardiac depression), namely, due to polymorphisms in the UDP-glucuronosyltransferase and cytochrome P450 isoforms and drugs administered concurrently. In this work the pharmacokinetics of propofol and fospropofol with particular focus on metabolic pathways is fully reviewed. It is concluded that knowing the metabolism of propofol may lead to the development of new clues to help further toxicological and clinical interpretations and to reduce serious adverse reactions such as respiratory failure, metabolic acidosis, rhabdomyolysis, cardiac bradyarrhythmias, hypotension and myocardial failure, anaphylaxis, hypertriglyceridemia, renal failure, hepatomegaly, hepatic steatosis, acute pancreatitis, abuse, and death. Particularly, further studies aiming to characterize polymorphic enzymes involved in the metabolic pathway, the development of additional routine forensic toxicological analysis, and the relatively new field of ‘‘omics” technology, namely, metabolomics, can offer more in explaining the unpredictable interindividual variability.

Comparison of propofol and desflurane for postanaesthetic morbidity in patients undergoing surgery for aneurysmal SAH: a randomized clinical trial

PURPOSE

Surgery for aneurysmal clipping after subarachnoid haemorrhage (SAH) poses a unique anaesthetic challenge. However, data on the influence of anaesthetic agents in these patients are lacking. The study aims to evaluate the superiority of propofol over desflurane for postanaesthetic morbidity in patients undergoing surgery following aneurysmal SAH.

METHODS

Seventy World Federation of Neurosurgeons Grade I and II patients were randomized into propofol (n = 35) and desflurane groups (n = 35). Anaesthesia was maintained with propofol/fentanyl in propofol group and desflurane/fentanyl in the desflurane group. Jugular venous oxygen saturation (SjVO₂) and brain relaxation were assessed intraoperatively. Time to eye opening, response to verbal commands, and extubation were noted from the time of discontinuing the anaesthetic agent. Duration of postoperative hospital stay and modified Rankin score (MRS) at discharge were subsequently compared.

RESULTS

Median postoperative hospital stay was 9 (6, 14) days with use of propofol and 9 (7, 12) days in desflurane group (P = 0.671). 18 patients in the propofol group and 14 patients in the desflurane group had good outcome (modified Rankin score 0-1; P = 0.453). Both the anaesthetics were similar in terms of intraoperative haemodynamics, brain relaxation, time to eye opening, response to verbal commands, and extubation time (P > 0.05). Emergence hypertension was more in the desflurane group (P = 0.007). The intraoperative SjVO₂ values were significantly higher in the desflurane group (P < 0.05).

CONCLUSION

Propofol and desflurane are comparable in terms of postoperative morbidity in patients undergoing aneurysm neck clipping following SAH.

Deep Sequencing of Distinct Preparations of the Live Attenuated Varicella-Zoster Virus Vaccine Reveals a Conserved Core of Attenuating Single-Nucleotide Polymorphisms

The continued success of the live attenuated varicella-zoster virus vaccine in preventing varicella-zoster and herpes zoster is well documented, as are many of the mutations that contribute to the attenuation of the vOka virus for replication in skin. At least three different preparations of vOka are marketed. Here, we show using deep sequencing of seven batches of vOka vaccine (including ZostaVax, VariVax, VarilRix, and the Oka/Biken working seed) from three different manufacturers (VariVax, GSK, and Biken) that 137 single-nucleotide polymorphism (SNP) mutations are present in all vaccine batches. This includes six sites at which the vaccine allele is fixed or near fixation, which we speculate are likely to be important for attenuation. We also show that despite differences in the vaccine populations between preparations, batch-to-batch variation is minimal, as is the number and frequency of mutations unique to individual batches. This suggests that the vaccine manufacturing processes are not introducing new mutations and that, notwithstanding the mixture of variants present, VZV live vaccines are extremely stable.

IMPORTANCE

The continued success of vaccinations to prevent chickenpox and shingles, combined with the extremely low incidence of adverse reactions, indicates the quality of these vaccines. The vaccine itself is comprised of a heterogeneous live attenuated virus population and thus requires deep-sequencing technologies to explore the differences and similarities in the virus populations between different preparations and batches of the vaccines. Our data demonstrate minimal variation between batches, an important safety feature, and provide new insights into the extent of the mutations present in this attenuated virus.

Cardiac Sympathetic Hyperactivity in a Patient with Guillain-Barré Syndrome: An Analysis Using Cardiac [(123)I] Metaiodobenzylguanidine (MIBG) Scintigraphy

A 31-year-old woman gradually developed weakness in the lower extremities and gait disturbance. Subsequently, the patient developed severe constipation and hypertension with tachycardia. Nerve conduction studies revealed demyelinating polyneuropathy. Serum anti-GQ1b IgG antibody was detected. The levels of plasma noradrenaline and dopamine and urinary noradrenaline were elevated. Cardiac [(123)I] metaiodobenzylguanidine (MIBG) scintigraphy showed a normal H/M rate at the early phase and an elevated washout rate. According to these findings, the patient was diagnosed with Guillain-Barré syndrome with cardiac sympathetic hyperactivity. During convalescence, the plasma and urine catecholamine levels fell within the reference ranges, and MIBG scintigraphy showed a decreased washout rate.

Molecular studies of the Oka varicella vaccine

Varicella zoster virus (VZV) is one of eight members of the Herpesviridae family for which humans are the primary host; it causes two distinct diseases, varicella (chickenpox) and zoster (shingles). Varicella results from primary infection, during which the virus establishes latency in sensory neurons, a characteristic of all members of the Alphaherpesvirinae subfamily. Zoster is caused by reactivation of latent virus, which typically occurs when cellular immunity is impaired. VZV is the first human herpesvirus for which a vaccine has been licensed. The vaccine preparation, v-Oka, is a live-attenuated virus stock produced by the classic method of tissue culture passage in animal and human cell lines. Over 90 million doses of the vaccine have been administered in countries worldwide, including the USA, where varicella morbidity and mortality has declined dramatically. Over the last decade, several laboratories have been committed to investigating the mechanism by which the Oka vaccine is attenuated. Mutations have accumulated across the genome of the vaccine during the attenuation process; however, studies of the contribution of these changes to vaccine attenuation have been hampered by the lack of a suitable animal model of VZV disease and by the heterogeneity that exists among the viral population within the vaccine preparation. Notwithstanding, a wealth of data has been generated using various laboratory methodologies. Studies of the vaccine virus in human xenografts implanted in severe combined immunodeficiency-hu mice, have enabled analyses of the replication dynamics of the vaccine in dorsal root ganglia, T lymphocytes and skin. In vitro assays have been used to investigate the effect of vaccine mutations on viral gene expression and sequence analysis of vaccine rash viruses has permitted investigations into spread of the vaccine virus in a human host. We present here a review of what has been learned thus far about the molecular and phenotypic characteristics of the Oka vaccine.

The performance of compartmental and physiologically based recirculatory pharmacokinetic models for propofol: a comparison using bolus, continuous, and target-controlled infusion data

BACKGROUND

With the growing use of pharmacokinetic (PK)-driven drug delivery and/or drug advisory displays, identifying the PK model that best characterizes propofol plasma concentration (Cp) across a variety of dosing conditions would be useful. We tested the accuracy of 3 compartmental models and 1 physiologically based recirculatory PK model for propofol to predict the time course of propofol Cp using concentration-time data originated from studies that used different infusion schemes.

METHODS

Three compartmental PK models for propofol, called the "Marsh," the "Schnider," and the "Schüttler" models, and 1 physiologically based recirculatory model called the "Upton" model, were used to simulate the time course of propofol Cp. To test the accuracy of the models, we used published measured plasma concentration data that originated from studies of manual (bolus and short infusion) and computer-controlled (target-controlled infusion [TCI] and long infusion) propofol dosing schemes. Measured/predicted (M/P) propofol Cp plots were constructed for each dataset. Bias and inaccuracy of each model were assessed by median prediction error (MDPE) and median absolute prediction error (MDAPE), respectively.

RESULTS

The M/P propofol Cp in the 4 PK models revealed bias in all 3 compartmental models during the bolus and short infusion regimens. In the long infusion, a worse M/P propofol Cp at higher concentration was seen for the Marsh and the Schüttler models than for the 2 other models. Less biased M/P propofol Cp was found for all models during TCI. In the bolus group, after 1 min, a clear overprediction was seen for all 3 compartmental models for the entire 5 min; however, this initial error resolved after 4 min in the Schnider model. The Upton model did not predict propofol Cp accurately (major overprediction) during the first minute. During the bolus and short infusion, the Marsh model demonstrated worse MDPE and MDAPE compared with the 3 other models. During short infusion, MDAPE for the Schnider and Schüttler models was better than the Upton and the Marsh models. All models showed similar MDPE and MDAPE during TCI simulations. During long infusion, the Marsh and the Schüttler models underestimated the higher plasma concentrations.

CONCLUSION

When combining the performance during various infusion regimens, it seems that the Schnider model, although still not perfect, is the recommended model to be used for TCI and advisory displays.

Complete DNA sequences of two oka strain varicella-zoster virus genomes

Varicella-zoster virus (VZV) is a herpesvirus and is the causative agent of chicken pox (varicella) and shingles (herpes zoster). Active immunization against varicella became possible with the development of live attenuated varicella vaccine. The Oka vaccine strain was isolated in Japan from a child who had typical varicella, and it was then attenuated by serial passages in cell culture. Several manufacturers have obtained this attenuated Oka strain and, following additional passages, have developed their own vaccine strains. Notably, the vaccines Varilrix and Varivax are produced by GlaxoSmithKline Biologicals and Merck & Co., Inc., respectively. Both vaccines have been well studied in terms of safety and immunogenicity. In this study, we report the complete nucleotide sequence of the Varilrix (Oka-V(GSK)) and Varivax (Oka-V(Merck)) vaccine strain genomes. Their genomes are composed of 124,821 and 124,815 bp, respectively. Full genome annotations covering the features of Oka-derived vaccine genomes have been established for the first time. Sequence analysis indicates 36 nucleotide differences between the two vaccine strains throughout the entire genome, among which only 14 are involved in unique amino acid substitutions. These results demonstrate that, although Oka-V(GSK) and Oka-V(Merck) vaccine strains are not identical, they are very similar, which supports the clinical data showing that both vaccines are well tolerated and elicit strong immune responses against varicella.

Status epilepticus secondary to hypertensive encephalopathy as the presenting manifestation of Guillain-Barré syndrome

Malignant hypertension due to autonomic dysfunction is a known complication of Guillain-Barré syndrome. We describe a child who presented with status epilepticus secondary to hypertensive encephalopathy who, in recovery, was found to be areflexic. Nerve conduction studies confirmed the clinical diagnosis of Guillain-Barré syndrome. She was treated with antihypertensive and antiseizure medications and intravenous immune globulin with complete resolution of her autonomic symptoms and improvement in her weakness. Guillain-Barré syndrome may result in hypertensive encephalopathy that can manifest as status epilepticus before the onset of motor symptoms.

Genetic profile of an Oka varicella vaccine virus variant isolated from an infant with zoster

Varicella virus vaccine strain Oka (V-Oka) has in rare cases caused zoster in vaccinated people. Despite broad usage of V-Oka, little is known about varicella-zoster virus genomic sequence variation of strains in vaccine and isolates from patients with vaccine adverse events. Direct sequencing of 20 regions of V-Oka-GSK was compared to the sequences of the original V-Oka-Biken, GlaxoSmithKline Oka vaccine (V-Oka-GSK), and Oka-parental (P-Oka) strains. We analyzed single nucleotide polymorphisms (SNP) differentiating the Oka parental and Oka vaccine strains identified in open reading frames (ORFs) 6, 9A, 10, 21, 31, 39, 50, 51, 52, 54, 55, and 59 and eight base substitutions within ORF 62. Sixteen of these SNP impose an amino acid change in the corresponding gene product. The genotypic analysis revealed that (i) both V-Oka-GSK and V-Oka-Biken comprise mixtures of strains represented in variable proportion from lot to lot; (ii) V-Oka-GSK/zoster isolated from the zoster patient had six wild-type SNP in ORF 9A, 10, 21, 52, 55, and 62 (mutation 108838); (iii) none of the six revertant SNP would reliably discriminate Oka vaccine from the wild type; and (iv) the genomic variation found in V-Oka/zoster might be associated with changes in the biological behavior of the virus. Further studies will be needed to identify potential virulence factors in variant vaccine strains.

Comparative Pharmacokinetics and Pharmacodynamics of the New Propofol Prodrug GPI 15715 and Propofol Emulsion: Retracted

BACKGROUND

GPI 15715 is a new water-soluble prodrug that is hydrolyzed to release propofol. The objectives of this crossover study in volunteers were to investigate the pharmacokinetics and pharmacodynamics of GPI 15715 in comparison with propofol emulsion.

METHODS

In two separate sessions, nine healthy male volunteers (19-35 yr, 70-86 kg) received GPI 15715 and propofol emulsion as a target controlled infusion over 60 min. In the first 20 min, the propofol target concentration increased linearly to 5 microg/ml. Subsequently, the targets were reduced to 3 microg/ml and 1.5 microg/ml for 20 min each. The plasma concentrations of GPI 15715 and propofol were measured from arterial and venous blood samples up to 24 h and pharmacokinetics were analyzed. The pharmacodynamic effect was measured by the median frequency of the power spectrum of the electroencephalogram, and a sigmoid model with effect compartment was fitted to the data.

RESULTS

Compared with propofol emulsion, propofol from GPI 15715 showed a different disposition function and especially larger volumes of distribution. The propofol effect site concentration for half maximum effect was 2.0 +/- 0.5 microg/ml for GPI 15715 and 3.0 +/- 0.7 microg/ml for propofol emulsion (P < 0.05). Propofol from GPI 15715 did not show a hysteresis between plasma concentration and effect.

CONCLUSIONS

Compared with propofol emulsion, propofol from GPI 15715 showed different pharmacokinetics and pharmacodynamics, particularly a higher potency with respect to concentration. These differences may indicate an influence of the formulation.

An evaluation of single nucleotide polymorphisms used to differentiate vaccine and wild type strains of varicella-zoster virus

Rashes following immunization with the vaccine strain (vOka) of varicella-zoster virus (VZV) may occur in up to 5% of children and 10% of adults. In 40% of cases, the causative virus is the vaccine strain and in 60% wild type virus is found. Several reports have identified three restriction site polymorphisms in ORF 62 and the loss of one in ORF 6, which differentiate vOka from wild type VZV, including the parental wild type strain from which vOka, is derived. Using polymerase chain reaction (PCR), restriction enzyme analysis, and sequencing, we analyzed the presence of these markers in the GlaxoSmithKline (GSK, UK) and Merck vaccine preparations as well as in 15 vaccine virus rashes and 15 wild type UK viruses. Our data suggest that a Sma1 positive and an Nae1 positive site in ORF 62 are present in the GSK and Merck vaccine preparations and all vaccine virus rashes. By contrast, a BssHII positive vaccine virus restriction site in ORF 62 and an Alu1 negative site in ORF 6 were mixed in the GSK and Merck vaccines and absent in some of the vaccine rashes. The BssHII site was also present in the European wild type C viruses in UK. The data suggest that unlike the Biken vaccine preparation, the Merck and GSK vaccine preparations are polymorphic for the BssHII and Alu1 restriction sites. These sites are also present variably in the vaccine viruses causing rashes following vaccination, and are therefore unreliable markers for differentiating vOka and wild type VZV strains.

Pharmacokinetics and clinical pharmacodynamics of the new propofol prodrug GPI 15715 in volunteers

BACKGROUND

GPI 15715 (AQUAVAN injection) is a new water-soluble prodrug which is hydrolyzed to release propofol. The objectives of this first study in humans were to investigate the safety, tolerability, pharmacokinetics, and clinical pharmacodynamics of GPI 15715.

METHODS

Three groups of three healthy male volunteers (aged 19-35 y, 67-102 kg) received 290, 580, and 1,160 mg GPI 15715 as a constant rate infusion over 10 min. The plasma concentrations of GPI 15715 and propofol were measured from arterial and venous blood samples up to 24 h. Pharmacokinetics were analyzed with compartment models. Pharmacodynamics were assessed by clinical signs.

RESULTS

GPI 15715 was well tolerated without pain on injection. Two subjects reported a transient unpleasant sensation of burning or tingling at start of infusion. Loss of consciousness was achieved in none with 290 mg and in one subject with 580 mg. After 1,160 mg, all subjects experienced loss of consciousness at propofol concentrations of 2.1 +/- 0.6 microg/ml. A two-compartment model for GPI 15715 (central volume of distribution, 0.07 l/kg; clearance, 7 ml. kg-1 min-1; terminal half-life, 46 min) and a three-compartment model for propofol (half-lives: 2.2, 20, 477 min) best described the data. The maximum decrease of blood pressure was 25%; the heart rate increased by approximately 35%. There were no significant laboratory abnormalities.

CONCLUSIONS

Compared with propofol lipid emulsion, the potency seemed to be higher with respect to plasma concentration but was apparently less with respect to dose. Pharmacokinetic simulations showed a longer time to peak propofol concentration after a bolus dose and a longer context-sensitive half-time.

Safety and immunogenicity of live attenuated varicella vaccine in 9-month-old children

BACKGROUND

The present study was conducted to evaluate the safety and immunogenicity of live attenuated varicella vaccine (Oka-strain) in 9-month-old infants.

METHODS

One hundred and fourteen infants were vaccinated once with live attenuated varicella vaccine (Valrix; SmithKline Beecham Biologicals, Rixensart, Belgium) containing a mean virus titer of 10(4.0) plaque-forming units (p.f.u.) per dose. Signs and/or symptoms after vaccination were followed for 42 days. Home visits were made to detect solicited local reactions (0-3 days) and solicited general reactions (0-21 days), as well as unsolicited reactions. Specific varicella antibodies were determined by an indirect immunofluorescence method. The geometric mean titer and seroconversion rate were calculated.

RESULTS

Signs and/or symptoms were reported in 47.4% (54/114) of cases following vaccination. The only local symptom reported was pain on digital pressure at the injection site and this was reported in 28.1% (32/114) of infants. General symptoms were reported in 38.6% (44/114) of cases. The most frequently reported findings were fever (27.2%), which was mostly mild, restlessness (20.2%) and cough (11.4%). Only four unsolicited symptoms were reported and they were all unrelated to vaccination. No serious adverse event was reported. Of the 109 infants included in the immunogenicity analysis, 105 were seronegative and four were seropositive for antibodies against varicella before vaccination. The vaccine elicited seroconversion in 97.1% of initially seronegative cases. The post-vaccination geometric mean titer for these infants was 30.9 geometric mean titer (GMT).

CONCLUSIONS

The vaccine was found to be safe and immunogenic when given to infants as young as 9 months of age. This may be of clinical significance during outbreaks of varicella and especially for developing countries.

Autonomic dysfunction as the presenting feature of Guillain-Barré syndrome

Autonomic dysfunction has been demonstrated in various conditions associated with peripheral neuropathy such as acute intermittent porphyria, amyloidosis, and Guillain-Barré syndrome (GBS). In the latter, hypertension is an associated complication that typically occurs after neurological signs are already present. We report a case of a patient with autonomic dysfunction as the presenting feature who was admitted to the coronary unit with chest pain and hypertension. Subsequently, he developed progressive symmetric muscle, weakness, sensory changes, and areflexia. GBS was then diagnosed based on the clinical picture, albuminocytologic dissociation in the cerebrospinal fluid, and electrodiagnostic abnormalities suggestive of demyelinative polyneuropathy with conduction block. Few cases in the literature have reported autonomic dysfunction as the presenting feature of GBS, such as in this case. In a previously asymptomatic patient, acute onset of autonomic dysfunction should alert the physician to the possibility of an acute polyneuropathy, such as GBS.

A case of Guillain-Barré syndrome accompanied by sympathetic overactivity and hypertensive encephalopathy

Hypertension has often been observed in patients with Guillain-Barré syndrome, and various underlying mechanisms have been implicated. We report the case of a child with the Guillain-Barré syndrome whose hypertension was associated with increases in both renin activity and circulating catecholamines. This case also appeared to be complicated by hypertensive encephalopathy. Following administration of intravenous regitine, a blood pressure change was observed and cardiac performance was assessed by two-dimensional echocardiography. Results indicated that increased total peripheral resistance may have been responsible for the symptoms and the hypertension. The hypertension was effectively managed by nifedipine, captopril and prazosin without the need for beta-blockade.

Autonomic involvement in Guillain-Barré syndrome: a review

Autonomic neuropathy is an important and common complication of Guillain-Barré syndrome (GBS). Manifestations be present in cardiovascular, sudomotor, gastrointestinal and other systems involving both sympathetic and parasympathetic fibers. Some apparently selective acute autonomic neuropathies may be subvarieties of GBS. Experimental work in animal models, pathological studies of GBS patients, and autonomic function studies have provided some help in the understanding of this complication. In managing GBS patients with autonomic dysfunction there are important practical considerations that can improve their care. In this article we review the literature on autonomic neuropathy in GBS and propose a management scheme to accommodate it in the overall treatment of the neuropathy.

Pharmacokinetic model identification and parameter estimation as an ill-posed problem

For model identification and parameter estimation in the framework of linear pharmacokinetics it is most often assumed that the disposition function is a finite sum of exponential functions with time constants lambda i and associated coefficients Ci. Least-square fitting procedures are used to estimate the coefficients Ci and the corresponding discrete locations lambda i on the lambda-axes. This work presents an alternative approach. It does not assume that the non-zero coefficients are located at sharply defined values of lambda, but that they are represented by a continuous function h(lambda), the spectrum of the disposition function. This turns the non-linear least-square problem into a linear problem, which is known to be as so-called "ill-posed". Regularization methods have been developed in recent years as suitable tools for the treatment of such ill-posed problems. Application of Tikhonov regularization to the case of the bolus kinetics of propofol in 8 volunteers is demonstrated. In 7 of the 8 cases a spectrum with 4 to 5 peaks was found, and in one volunteer there were only 2 peaks. All spectra with more than 2 peaks showed negative values of h(lambda). The method used is described and the results are compared with those of conventional compartment analysis.

Propofol as an induction agent in the goat: a pharmacokinetic study

The pharmacokinetics of propofol, 4 mg/kg, administered as a bolus dose intravenously (i.v.) prior to the maintenance of anaesthesia with halothane in oxygen, were determined in five goats, and a clinical impression of its use as an induction agent was made. Induction of anaesthesia was rapid and smooth, providing satisfactory conditions for intubation in all animals. Post-induction apnoea occurred in one goat and minimal regurgitation of ruminal contents was recorded in two animals. Recovery times were rapid with a mean time to standing after halothane inhalation ceased of 13.7 min. The blood propofol concentration time profile was best described by a bi-exponential decline in all five goats. The mean elimination half-life was short (15.5 min), the volume of distribution at steady state large (2.56 l/kg) and the clearance rapid (275 ml/min.kg). Propofol was shown to be a very satisfactory induction agent in the goat.

Cardiovascular effects of a continuous two-hour propofol infusion in dogs. Comparison with isoflurane anesthesia

The cardiovascular effects during 2 hours of anesthesia with either a continuous propofol infusion or isoflurane were compared in the same six healthy dogs. Dogs were randomly assigned to be anesthesized with either propofol (5 mg/kg, i.v. administered over 30 seconds, immediately followed by a propofol infusion beginning at 0.4 mg/kg/min), or isoflurane (2.0% end-tidal concentration). The propofol infusion was adjusted to maintain a light plane of anesthesia. Dogs anesthetized with propofol had higher values for systemic arterial pressure due to higher systemic vascular resistance. Dogs anesthetized with isoflurane had higher values for heart rate and mean pulmonary artery pressure. Cardiac index was not different between the two groups. Apnea and cyanosis were observed during induction of anesthesia with propofol. At the end of anesthesia the mean time to extubation for dogs anesthetized with either propofol or isoflurane was 13.5 min and 12.7 min, respectively. A continuous infusion of propofol (0.44 mg/kg/min) provided a light plane of anesthesia. Ventilatory support during continuous propofol infusion is recommended.

The effects of halothane and nitrous oxide on the pharmacokinetics of propofol in dogs

The pharmacokinetics of propofol, 6.5 mg/kg, administered as a bolus dose intravenously (i.v.) were studied in six dogs (group 1). The effect of maintaining anaesthesia with halothane and nitrous oxide in oxygen on propofol pharmacokinetics was also investigated in six dogs undergoing routine anaesthesia (group 2). Induction of anaesthesia was rapid in all animals. Post-induction apnoea was a feature in three of the 12 dogs. The blood propofol concentration-time profile was best described by a bi-exponential decline in two dogs in group 1 and in 3 dogs in group 2, and by a tri-exponential decline in four dogs in group 1 and 3 dogs in group 2. The elimination half-life was long in both groups (90.9 min and 75.2 min, respectively), the volume of distribution at steady state large (4889 and 4863 ml/kg) and the clearance rapid (58.6 and 56.3 ml/kg.min). There were no significant differences between the groups, thus indicating that maintenance of anaesthesia with halothane and nitrous oxide had no effect on the pharmacokinetics of propofol in the dog.

Apparent polycythaemia

Patients with apparent polycythaemia are characterised by a raised packed cell volume (PCV; males above 0.51, females above 0.48) but normal red cell mass (RCM; less than 25% greater than predicted). Prediction and interpretation of RCM and PV should be based on height and weight, since the use of body weight alone is misleading. Patients with PCV values up to 0.60 may have apparent polycythaemia but only 18% have a reduced PV (relative polycythaemia). Therefore, the most common cause of the raised PCV is a change in RCM and/or PV within their normal ranges. The clinical associations and possible causes for the RCM/PV changes include male sex, obesity, dehydration, diuretics, smoking, hypertension, alcohol, arterial oxygen desaturation, renal disease and increased catecholamine levels. Retrospective studies of patients with apparent polycythaemia and information from other groups of polycythaemic patients suggest an increased risk of vascular occlusion, although other factors, such as hypertension and smoking, are also involved. Proposed management includes modification of possible underlying causes and examination for risk factors for vascular occlusion. In patients with PCV levels chronically above 0.54 venesection should be used, but patients with PCV values below this level should only be venesected if they are considered to be at risk of vascular occlusion. The suggested target value for PCV for venesected patients is 0.45 or below.

Total intravenous anaesthesia with propofol and buprenorphine

A combination of propofol infusion and two bolus doses of buprenorphine, 2.5 or 5.0 micrograms/kg were evaluated in a total intravenous anaesthesia technique in 36 patients of ASA grade 1 or 2 undergoing cholecystectomy. Additional boluses of propofol were given intravenously if needed. Systolic blood pressure after tracheal intubation increased significantly only in those who received the smaller dose of buprenorphine. Patients in both groups remained haemodynamically stable throughout surgery with minimal side effects. Recovery was fast even with prolonged infusions and without major side effects. No patient reported awareness on postoperative questioning.

Comparison of propofol and thiopentone as anaesthetic agents for electroconvulsive therapy

Propofol and thiopentone were compared as anaesthetic agents for electroconvulsive therapy in 31 patients on four occasions in a repeated measure crossover study. Discomfort on injection was significantly more common with propofol (51.6% of anaesthetics) compared to thiopentone (1.6% of anaesthetics). The duration of seizure was shorter with propofol in both treatments but there was significant drug-time interaction. Propofol gave a milder tonus and clonus during seizure when both treatments were considered together. The increase in systolic and diastolic arterial pressures and heart rate after treatment were significantly higher with thiopentone. Apnoea was significantly longer with propofol. The times to sitting up unaided and opening the eyes on command were the same for both drugs. The ability to walk 10 m 20 minutes after anaesthesia was significantly better with propofol (p less than 0.0001).

Clinical pharmacology of propofol: an intravenous anesthetic agent

Propofol is a 2,6-diisopropylphenol with sedative-hypnotic properties. Because of its slight solubility in water, the drug is formulated as an emulsion for clinical use. It is highly lipophilic and distributes extensively in the body. The blood concentration-time profile of propofol after an iv bolus injection follows a three-compartment model with half-lives of 2-4 min, 30-45 min, and 3-63 h, respectively. Propofol is extensively metabolized by the liver prior to its elimination by the kidney. Following an iv dose of 2-2.5 mg/kg, loss of consciousness occurs in less than one minute and lasts for approximately five minutes. Hypnosis can be maintained by propofol blood concentrations of 1.5-6 micrograms/mL in the presence of N2O/O2 (60:40 ratio) or other anesthetic agents. During induction, propofol decreases the systolic and diastolic blood pressure by approximately 20-30 percent with minimal change in heart rate; apnea is also common. The cardiovascular and respiratory effects of propofol, however, should not cause major concern in otherwise healthy patients. By virtue of its pharmacokinetic profile, the drug lends itself to continuous infusion for maintenance of anesthesia. When used as the main anesthetic agent, it produces satisfactory anesthesia with rapid recovery and without major adverse effects in healthy individuals. In continuous infusion propofol can be used as an alternative to inhalation anesthetics.

Induction dose of propofol in children

In a study of 144 children aged 1-12 years, attempts were made to assess the ED50 and ED90 of the intravenous induction agent, propofol. The doses required for loss of eyelash reflex and tolerance of facemask, in 50% of unpremedicated children, were 1.6 mg/kg and 2.5 mg/kg respectively. In children premedicated with oral trimeprazine the corresponding values of ED50 were 1.1 mg/kg and 2.0 mg/kg. Doses of 2.8 mg/kg in unpremedicated and 2.0 mg/kg for those who received trimeprazine were required for loss of eyelash reflex in 90% of children. This probably corresponds to an effective induction dose. Pain and movement on induction were common; the incidence was 27% and 21.5% respectively.

Total intravenous anaesthesia with propofol and alfentanil by computer-assisted infusion

The combination of propofol and alfentanil was administered to 20 patients for total intravenous anaesthesia during general surgery. The infusion rates for both drugs were controlled by microprocessors in order to institute constant blood levels adapted to the patients' varying needs. The mean blood level of propofol required for adequate hypnosis during anaesthesia was 2.42 micrograms/ml (SD 0.43). Awakening occurred 7.9 minutes (SD 3.4) after the end of the infusion, at a propofol blood level of 1.59 micrograms/ml (SD 0.34). The plasma level of alfentanil was 285 ng/ml (SD 72) during major noxious stimulation and 148 ng/ml (SD 56) during minor stimulation. The computer-assisted infusions showed a measured/predicted ratio of 1.01 (SD 0.28) for alfentanil and 0.88 (SD 0.22) for propofol. This indicates that the administration device used in this study is reasonably reliable. The technique of total intravenous anaesthesia was characterised by a smooth induction without significant haemodynamic alterations, by good control during anaesthesia and by a very fast recovery without major side effects.

Propofol infusion for sedation in intensive care

Ten patients, with a range of illness severity, received a continuous 8-hour infusion of undiluted propofol for sedation while undergoing mechanical ventilation in a general intensive care unit. The level of sedation was assessed hourly and measurements were made of haemodynamic, respiratory, haematological and biochemical variables. Sedation remained satisfactory in most patients throughout the study period, with only occasional alterations in infusion rate, and eight patients required further sedative therapy within 45 minutes of discontinuation of the propofol infusion. Arterial pressure tended to decrease from baseline values; mean and diastolic pressures demonstrated a significant decrease (p less than 0.05) at 4, 7 and 8 hours during the infusion. Adrenal steroidogenesis was not inhibited significantly. Propofol infusion proved to be a useful and readily controllable sedative agent, and discontinuation of the drug was followed by rapid recovery in most cases. The critically ill may be particularly sensitive to the cardiovascular depressant properties of the drug.

The contracted plasma volume syndromes (relative polycythaemias) and their haemorheological significance

Relative polycythaemia is a general term which includes patients with a normal red cell mass but a contraction of the plasma volume as the cause for the polycythaemia. The relative polycythaemias can broadly be divided into two groups. Firstly, relative polycythaemia may be due to a primary loss of plasma volume due to dehydration, capillary leak or hypo-oncotic pressure. Secondly, relative polycythaemia may be due to a primary contraction of the vascular compartment (i.e. reduced venous compliance). It is this second group which is the least understood and is analysed in detail in this review. In general, this group of polycythaemias is secondary to exogenous or endogenous stress and is mediated via the sympathetic nervous system. Hypoxia, smoking, neurological disorders, myocardial infarction and acute psychological stress have all been demonstrated as possible factors. In many cases of chronic stress polycythaemias aetiological factors may be identified, whereas in others the term idiopathic is probably appropriate. There appears to be a relationship between the idiopathic stress polycythaemias, hypertension and psychological stress. Other patients may have primarily a disorder of blood volume control involving the autonomic nervous system and its receptors. The haemorheological significance of relative polycythaemia and its management are discussed. Treatment is generally dictated by the underlying cause. In stress polycythaemias the stimulus should be removed as far as possible. However, in some patients with chronic idiopathic stress polycythaemia, regular venesection may be required to maintain the venous haematocrit at an appropriate level.