M. G. Irwin

Patient-maintained propofol sedation. Assessment of a target-controlled infusion system.

We have developed a system which allows patients to operate a target‐controlled infusion of propofol to provide sedation and we have studied its use in 36 unpremedicated patients undergoing local and regional anaesthetic procedures lasting 10–280 min. An intravenous propofol infusion was started at a target plasma level of 1 μg.ml−1. The patient was able to increase the target propofol concentration in 0.2‐μg.ml−1 increments by pressing a demand button. There was a lockout interval of 2 min and a maximum permissible target concentration of 3 μg.ml−1. There was considerable interindividual variability in propofol consumption (mean 39.3 μg.kg−1.min−1, range 3–131 μg.kg−1.min−1), no cardiovascular instability and little oversedation. Eight patients required supplementary oxygen. Optimal sedation was provided at median target concentrations of 0.8–0.9 μg.ml−1. The target‐controlled infusion system bias was − 47% and the inaccuracy was 48%. Patient satisfaction was high and 89% said that they would definitely use the technique again. This technique combines the benefits of target‐controlled infusion with patient‐controlled feedback and produces safe intra‐operative sedation.

Propofol effective concentration 50 and its relationship to bispectral index

Sixty unpremedicated healthy adult patients were studied during induction of anaesthesia with intravenous propofol delivered by a ‘Diprifusor’ target‐controlled infusion. Bispectral index (BIS) and spectral edge frequency (SEF95) were measured concurrently with the predicted blood and effect site propofol concentrations. Logistic regression was used to calculate the predicted propofol blood and effect site concentrations required to produce unconsciousness and no response to a noxious stimulus in 50% and 95% of patients and to correlate BIS with these end‐points. The Diprifusor TCI software produces anaesthesia at consistent target concentrations. Bispectral index correlates well with clinical end‐points and may be useful during propofol anaesthesia.

Remifentanil post-conditioning attenuates cardiac ischemia–reperfusion injury via κ or δ opioid receptor activation

Background: Ischemic pre‐ or post‐conditioning of the heart has been shown to involve opioid receptors. Remifentanil, an ultra‐short‐acting selective μ opioid receptor agonist in clinical use, pre‐conditions the rat heart against ischemia–reperfusion injury. This study investigates whether remifentanil post‐conditioning is also cardioprotective.

Incidence of diaphragmatic paralysis following supraclavicular brachial plexus block and its effect on pulmonary function

Thirty unpremedicated ASA physical status 1–3 patients aged between 18 and 69 years, scheduled for upper limb surgery, received a conventional supraclavicular brachial plexus block using a nerve stimulator and bupivacaine 0.375% 0.5 ml.kg−1. Spirometric measurements of pulmonary function and ultrasonographic assessments of diaphragmatic function were made before the block and at 10‐min intervals after injection until full motor block of the brachial plexus had developed. Complete paralysis of the ipsilateral hemidiaphragm occurred in 50% of patients. Seventeen per cent of patients had reduced diaphragmatic movement and the rest (33%) had no change in diaphragmatic movement. Those with complete paralysis all showed significant decreases in pulmonary function, whereas those with reduced or normal movement had minimal change. All patients remained asymptomatic throughout, with normal oxygen saturation on room air.

Optimal timing for the administration of intranasal dexmedetomidine for premedication in children.

Previous studies have shown that 1 μg.kg−1 intranasal dexmedetomidine produces significant sedation in children aged between 2 and 12 years. This investigation was designed to evaluate the onset time. One hundred children aged 1–12 years of ASA physical status 1–2 undergoing elective surgery were randomly allocated to five groups. Patients in groups A to D received intranasal dexmedetomidine 1 μg.kg−1. Patients in Group E received intranasal placebo (0.9% saline). Children from groups A, B, C, D and E had intravenous cannulation attempted at 30, 45, 60, 75 and 45 min respectively after intranasal drug or placebo administration. Vital signs, behaviour and sedation status of the children were assessed regularly until induction of anaesthesia. More children from groups A to D achieved satisfactory sedation at the time of cannulation when compared to group E (p < 0.001). The proportion of children who achieved satisfactory sedation was not significantly different among groups A to D. Overall 62% of the children who received intranasal dexmedetomidine had satisfactory sedation at the time of cannulation. The median (95% CI) time for onset of sedation was 25 (25–30) min. The median (95% CI) duration of sedation was 85 (55–100) min.

ORIGINAL ARTICLE: Optimal timing for the administration of intranasal dexmedetomidine for premedication in children

Previous studies have shown that 1 μg.kg−1 intranasal dexmedetomidine produces significant sedation in children aged between 2 and 12 years. This investigation was designed to evaluate the onset time. One hundred children aged 1–12 years of ASA physical status 1–2 undergoing elective surgery were randomly allocated to five groups. Patients in groups A to D received intranasal dexmedetomidine 1 μg.kg−1. Patients in Group E received intranasal placebo (0.9% saline). Children from groups A, B, C, D and E had intravenous cannulation attempted at 30, 45, 60, 75 and 45 min respectively after intranasal drug or placebo administration. Vital signs, behaviour and sedation status of the children were assessed regularly until induction of anaesthesia. More children from groups A to D achieved satisfactory sedation at the time of cannulation when compared to group E (p < 0.001). The proportion of children who achieved satisfactory sedation was not significantly different among groups A to D. Overall 62% of the children who received intranasal dexmedetomidine had satisfactory sedation at the time of cannulation. The median (95% CI) time for onset of sedation was 25 (25–30) min. The median (95% CI) duration of sedation was 85 (55–100) min.

Changes in airway configuration with different head and neck positions using magnetic resonance imaging of normal airways: a new concept with possible clinical applications

BACKGROUND The sniffing position is often considered optimal for direct laryngoscopy. Another concept of airway configuration involving a laryngeal vestibule axis and two curves has also been suggested. We investigated whether this theory can be supported mathematically and if it supports the sniffing position as being optimal for direct laryngoscopy. METHODS Magnetic resonance imaging scans were performed in 42 normal adult volunteers. The airway passage was divided into two curves-primary (oro-pharyngeal curve) and secondary (pharyngo-glotto-tracheal curve). Airway configuration was evaluated in the neutral, extension, head lift, and sniffing positions. The airway passage, point of inflection (where the two curves meet), its tangent, and the line of sight were plotted on each scan. RESULTS The point of inflection lay within the laryngeal vestibule in all positions. The head lift and sniffing positions caused the tangent to the point of inflection to approximate the horizontal plane. The sniffing, extension, and head lift positions caused a reduction in the area between the line of sight and the airway curve compared with the neutral position. CONCLUSIONS A two-curve theory is proposed as a basis for explaining airway configuration. The changes in these curves with head and neck positioning support the sniffing position as optimal for direct laryngoscopy. Application of this new concept to other forms of laryngoscopy should be investigated.

Intranasal dexmedetomidine following failed chloral hydrate sedation in children.

Chloral hydrate is the most commonly used sedative for paediatric diagnostic procedures in China with a success rate of around 80%. Intranasal dexmedetomidine is used for rescue sedation in our centre. This prospective investigation evaluated 213 children aged one month to 10 years who were not adequately sedated following administration of chloral hydrate. Children were randomly assigned to receive rescue intranasal dexmedetomidine at 1 μg.kg−1 (group 1), 1.5 μg.kg−1 (group 2) or 2 μg.kg−1 (group 3). The sedation level was assessed every 10 min using a modified observers assessment of alertness/sedation scale. Successful rescue sedation in groups 1, 2 and 3 were 56 (83.6%), 66 (89.2%) and 51 (96.2%), respectively. Increasing the rescue dose was associated with an increased success rate with an odds ratio of 4.12 (95% CI 1.13–14.98), p = 0.032. We conclude that intranasal dexmedetomidine is effective for sedation in children who do not respond to chloral hydrate.

Persistent pain in patients following scoliosis surgery

Chronic or persistent pain is increasingly recognised as a consequence of surgery in a number of different disciplines. The pain often exhibit qualities that differ from the acute post-operative pain and may represent changes in the central nervous system. There is lack of information regarding the incidence of persistent pain in patients following spinal surgery for scoliosis. This study aims to estimate the incidence of persistent pain following spinal surgery for scoliosis in a group of mainly adolescent patients. Questionnaires were distributed to consecutive patients attending the outpatient clinic of a hospital with specialist services in paediatric orthopaedics and spinal surgery. One hundred and five patients out of 122 eligible patients completed the survey. Fifty-two percent had ongoing pain upon hospital discharge either in the primary surgical site and/or in the iliac bone graft site. Approximately 10 and 7% of all patients had back and pelvic pain persisting beyond 12 months, respectively. A small proportion described elements of neuropathic pain. There was a trend suggesting that those who experienced more severe post-operative pain were more likely to develop persistent pain. These data are consistent with those reports that implicate surgery as the trigger for chronic pain.

The Finapres 2300e finger cuff. The influence of cuff application on the accuracy of blood pressure measurement

Blood pressure measurements associated with malapplication of a finger cuff were compared with contemporaneous intra‐arterial pressure data in seven volunteers to determine the influence of cuff application on the accuracy of the Finapres 2300e. Systolic readings in all cuff positions differed from arterial line data by more than the recommended standard and tight and loose cuff applications under and over‐read respectively, in all subjects. The results show the Finapres to be sensitive to small degrees of finger cuff malapplication which contribute to the bias on direct arterial comparison and limit the reliability of the instrument in clinical practice.