A randomised, controlled trial comparing the Airtraq™ optical laryngoscope with conventional laryngoscopy in infants and children

The Airtraq(™) optical laryngoscope became available in paediatric sizes in the UK in May 2008. We conducted a randomised, controlled trial comparing the Airtraq with conventional laryngoscopy during routine anaesthesia in children. We hypothesised that the Airtraq laryngoscope would perform as well as conventional laryngoscopy. Sixty patients (20 infants and 40 children) were recruited. The mean (SD) intubation time using the Airtraq was longer than conventional laryngoscopy overall (47.3 (32.6) vs 26.3 (11.5) s; p=0.002), though the difference was only significant for children (p=0.003) and not for infants (p=0.29). The Airtraq provided a better view of the larynx compared with conventional laryngoscopy (in infants (percentage of glottic opening scores 100 (95-100 [90-100]) vs 77 (50-90 [40-100]), respectively; p=0.001; visual analogue scores for field of view 9.2 (9.2-9.5 [8.2-10.0]) vs 6.8 (5.1-8.0 [4.7-10.0]), respectively; p=0.001). In children, the Airtraq provided a similar view of the larynx (percentage of glottic opening scores 100 (100-100 [40-100]) vs 100 (90-100 [50-100]), respectively; visual analogue scores for field of view 9.2 (8.6-10.0 [7.0-10.0]) vs 9.2 (8.6-10.0 [5.6-10.0]), respectively; both p>0.05), compared with conventional laryngoscopy.

Frank-starling control of a left ventricular assist device

A physiological control system was developed for a rotary left ventricular assist device (LVAD) in which the target pump flow rate (LVADQ) was set as a function of left atrial pressure (LAP), mimicking the Frank-Starling mechanism. The control strategy was implemented using linear PID control and was evaluated in a pulsatile mock circulation loop using a prototyped centrifugal pump by varying pulmonary vascular resistance to alter venous return. The control strategy automatically varied pump speed (2460 to 1740 to 2700 RPM) in response to a decrease and subsequent increase in venous return. In contrast, a fixed-speed pump caused a simulated ventricular suction event during low venous return and higher ventricular volumes during high venous return. The preload sensitivity was increased from 0.011 L/min/mmHg in fixed speed mode to 0.47L/min/mmHg, a value similar to that of the native healthy heart. The sensitivity varied automatically to maintain the LAP and LVADQ within a predefined zone. This control strategy requires the implantation of a pressure sensor in the left atrium and a flow sensor around the outflow cannula of the LVAD. However, appropriate pressure sensor technology is not yet commercially available and so an alternative measure of preload such as pulsatility of pump signals should be investigated.

GPU accelerated FDTD solver and its application in MRI

The finite difference time domain (FDTD) method is a popular technique for computational electromagnetics (CEM). The large computational power often required, however, has been a limiting factor for its applications. In this paper, we will present a graphics processing unit (GPU)-based parallel FDTD solver and its successful application to the investigation of a novel B1 shimming scheme for high-field magnetic resonance imaging (MRI). The optimized shimming scheme exhibits considerably improved transmit B(1) profiles. The GPU implementation dramatically shortened the runtime of FDTD simulation of electromagnetic field compared with its CPU counterpart. The acceleration in runtime has made such investigation possible, and will pave the way for other studies of large-scale computational electromagnetic problems in modern MRI which were previously impractical.

A comparison of the laryngeal mask airway with facemask and oropharyngeal airway for manual ventilation by critical care nurses in children

The laryngeal mask airway is included as a first line airway device during adult resuscitation by first responders. However, there is little evidence for its role in paediatric resuscitation. Using anaesthetised children as a model for paediatric cardiopulmonary arrest, we compared the ability of critical care nurses to manually ventilate the anaesthetised child via the laryngeal mask airway compared with the facemask and oropharyngeal airway. The airway devices were inserted in random order and chest expansion was measured using an ultrasound distance transducer. The critical care nurses were able to place the laryngeal mask airway and achieve successful ventilation in 82% of children compared to 70% using the facemask and oropharyngeal airway, although the difference was not statistically significant (p = 0.136). The median time to first successful breath using the laryngeal mask airway was 39 s compared to 25 s using the facemask (p < 0.001). In this group of nurses, we did not show a difference in ventilation via a laryngeal mask airway or facemask, although facemask ventilation was achieved more quickly.

Paediatric caudal extradural catheterisation: an evaluation of a purpose designed equipment set

Using a purpose designed set of equipment, the Caudal Extradural Catheter Tray, Oxford Set (B Braun Medical Ltd, Sheffield, UK) we have evaluated the ease of cannulation of the caudal space, and the subsequent success in threading extradural catheters and obtaining satisfactory analgesia via the caudal route. The set was evaluated in 91 children (age range: 1 day to 10 years). Cannulation of the caudal space was achieved in all patients, and catheterisation of the extradural space was successful in 96.7% of patients. Postoperative analgesia was satisfactory in 95% of children who had continuous extradural analgesia. There were no major complications or neurological sequelae associated with using the set. We found the Caudal Extradural Catheter Tray provides the necessary equipment to perform extradural anaesthesia and analgesia safely and successfully in children of a wide age range.

NICE guidelines for central venous catheterization in children. Is the evidence base sufficient?

BACKGROUND

Recent guidelines from the National Institute for Clinical Excellence (NICE) recommend the use of ultrasound guidance for central venous catheterization in children. This study prospectively examined the use of ultrasound guidance for central venous catheterization in children undergoing heart surgery.

METHODS

One hundred and twenty-four infants and children were randomized to either ultrasound-guided or traditional landmark-guided central venous catheterization.

RESULTS

Success rates were significantly greater in the landmark group compared with the ultrasound group (89.3% vs 78%, P<0.002), and arterial puncture rates were significantly lower in the landmark group (6.2% vs 11.9%, P<0.03). There was no significant difference between the two groups in the time taken to perform the catheterization.

CONCLUSIONS

These results are different from the published results on which the NICE guidelines were based; however, the evidence base in children is small. There is currently insufficient evidence to support the use of ultrasound guidance for central venous catheterization in children.

The Newton valve revisited: an in-vitro study of ventilator circuit dead space

A laboratory study was conducted to investigate the volume (length) of the ventilator circuit dead space (VCD) tubing at which dilution of an inspired gas by ventilator driving gas first occurs using three lung models. Various lengths of two VCD tubing materials [Portex (Sims Portex Ltd, Kent, UK) 10 mm bore smooth-walled silicon and Intersurgical (Wokingham, Berks, UK) 22 mm corrugated plastic] were interposed between a T-piece circuit and Nuffield 200 ventilator (Penlon, Abingdon, Oxon, UK) with a Newton valve attached. Dilution of inspired gas by the ventilator driving gas was first detected during ventilation of infant and child lung models when the VCD was 7 ml (6 cm) and 77 ml (102 cm), respectively, using Portex tubing, and 24 ml (6.5 cm) and 105 ml (29 cm), respectively, using Intersurgical tubing. No dilution occurred using the neonatal model. Dilution of the inspired anaesthetic gases by ventilator driving gas may occur in paediatric practice if the VCD volume (length) is inadequate. This risk is greatest in the child.

Self-learning fuzzy control with temporal knowledge for atracurium-induced neuromuscular block during surgery

Self-learning fuzzy logic control has the important property of accommodating uncertain, nonlinear, and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time without the need for detailed process modeling. In this study we utilize temporal knowledge of generated rules to improve control performance. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block of patients in the operating theater where the patient response exhibits high nonlinearity and individual patient dose requirements may vary fivefold during an operating procedure. We developed a computer control system utilizing Relaxograph (Datex) measurements to assess the clinical performance of a self-learning fuzzy controller in this application. Using a T1 setpoint of 10% of baseline in 10 patients undergoing general surgery, we found a mean T1 error of 0.28% (SD = 0.39%) while accommodating a 0.25 to 0.38 mg/kg/h range in the mean atracurium infusion rate. This result compares favorably with more complex and computationally intensive model-based control strategies for atracurium infusion.

Intranasal midazolam for premedication of children undergoing day-case anaesthesia: comparison of two delivery systems with assessment of intra-observer variability

Midazolam is often used for paediatric premedication. We have compared two methods of administering midazolam intranasally in 44 surgical day-case children allocated randomly to receive midazolam 0.2 mg kg-1 as drops or midazolam 0.1 mg kg-1 from an intranasal spray device. Behaviour was recorded on a four-point scale by the parent, nurse and anaesthetist. Coefficients were obtained representing the change in behaviour score. There was no significant difference in method of administration (coefficient 0.13, P = 0.39). Children were significantly more distressed at the time of premedication and at the time of venous cannulation (coefficients 1.31 and 0.70) than at baseline. There was no significant difference in the assessments between observers. Midazolam by either method was equally effective but acceptability of the premedication was poor in both groups. Intranasal midazolam cannot be recommended as a method for routine premedication of young children.

Obstructive sleep apnoea syndrome in children

Obstructive sleep apnoea syndrome in children is a complex disorder characterised by repeated nocturnal episodes of increased upper airway resistive load. It is most commonly associated with adenotonsillar hypertrophy and more children are now presenting for adenotonsillectomy. These children may pose different anaesthetic problems to those having surgery for recurrent infection alone and anaesthetic morbidity and mortality has been reported. In addition, due to the varied symptomatology of the condition, children with unrecognised obstructive sleep apnoea syndrome may present for incidental surgery. This is of importance as patients with undiagnosed obstructive sleep apnoea syndrome may experience additional peri-operative morbidity when undergoing incidental surgery. This article aims to review the aetiology, pathophysiology, clinical presentation and anaesthetic management of children with obstructive sleep apnoea syndrome.

A portable self-learning fuzzy logic control system for muscle relaxation

We have assessed the practicality and performance of the Vital Signs Paragraph neuromuscular blockade monitor as part of a 'self-learning' fuzzy logic control feedback system used to administer atracurium to a required depth of neuromuscular blockade. Fifteen patients undergoing surgery expected to last longer than 90 min entered the study. A Vital Signs Paragraph was used to measure the degree of neuromuscular blockade and control it such that the first twitch of the train-of-four was kept at 10% of its baseline value. The controller instructed a Graseby Medical 3400 infusion pump to administer an atracurium infusion to maintain this level of blockade. Five patients (33%) were withdrawn from the study due to inadequate piezo-electric sensor function. In the remaining 10 patients, the system achieved stable control of neuromuscular blockade with a mean (range) error for the first twitch of the train-of-four of -0.45 (-1.06 to 0.13)%. The mean atracurium infusion rate ranged from 0.13 to 0.67 mg.kg-1.h-1. These results compare reasonably well with previous results using the Datex Relaxograph, whilst the system itself was portable and easy to use. However, the reliability of the system was limited due to variability in the sensitivity of piezoelectric sensors.

Self-learning fuzzy control of atracurium-induced neuromuscular block during surgery

Self-learning fuzzy logic control has the important property of accommodating uncertain, non-linear and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time, without the need for detailed process modelling. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block (NMB) of patients in the operating theatre. Here, the patient response exhibits high non-linearity, and individual patient dose requirements can vary five-fold during an operating procedure. A portable control system was developed to assess the clinical performance of a simplified self-learning fuzzy controller in this application. A Paragraph (Vital Signs) NMB device monitored T1, the height of the first twitch in a train-of-four nerve stimulation mode. Using a T1 setpoint = 10% of baseline in ten patients undergoing general surgery, a mean T1 error of 0.45% (SD = 0.44%) is found while a 0.13-0.70 mg k-1 h-1 range in the mean atracurium infusion rate is accommodated. The result compares favourably with more complex and computationally-intensive model-based control strategies for the infusion of atracurium.

Self-learning fuzzy logic control of neuromuscular block

We have assessed the performance of a "self-learning" fuzzy logic controller to administer atracurium to a required depth of neuromuscular block. We studied 20 ASA I and II patients undergoing surgery anticipated to last longer than 90 min. A Datex Relaxograph was used to measure the degree of neuromuscular block, and control to a T1 twitch height set point of 10% of baseline neuromuscular function was selected. The controller commenced with a blank rule-base and instructed a Graseby 3400 infusion pump to administer an atracurium infusion to maintain this level of block. The system achieved stable control of neuromuscular block with a mean T1 error of -0.52% (SD 0.55%) accommodating a range in mean atracurium infusion rate of 0.25-0.44 mg kg-1 h-1. These results compare favourably with the more computationally intensive and unwieldy adaptive control strategies for atracurium infusion used previously. There was less variation in infusion rates than in our previously studied fixed rules fuzzy controller.

Development of a portable closed-loop atracurium infusion system: systems methodology and safety issues

Safety of closed-loop drug infusion systems is an issue often raised as a matter of concern. As a result, many closed-loop control systems are reported in the literature merely as computer simulation studies and few ever reach the stage of physical realisation and formal clinical evaluation. We address the safety issues involved with such systems by describing the development of a portable closed-loop control system for atracurium-induced muscle relaxation. This is a safety-critical system particularly when applied to brain and eye surgery where movement could have serious deleterious effects. The benefits of closed-loop muscle relaxation in providing stable surgical operating conditions over a wide range of patient sensitivities while infusing the minimum amount of drug makes this a worthwhile aim and serves to demonstrate safety issues which are generally applicable to other closed-loop drug infusion systems. It is hoped that the described methodology will facilitate and encourage the clinical application of closed-loop drug infusion systems so that clinical staff and patients may receive the benefits of closed-loop drug therapy.

Development of a pharmacokinetic model-based infusion system for ketamine analgesia

Model-driven infusion systems in anaesthesia overcome the difficulties in obtaining on-line measurements of controlled variables. A linear pharmacokinetic model for ketamine was used to achieve target blood concentrations and was implemented using a palmtop PC. Although the use of ketamine for analgesia in total intravenous anaesthesia with propofol has been reported, this is the first such application to spontaneously breathing patients. Preliminary results show this to be a useful system, which may easily be applied to other intravenous anaesthetic agents.

National provision of acute pain services

In order to determine the degree to which the recommendations of the report of the joint working party on 'Pain after Surgery' by the Royal College of Surgeons of England and the College of Anaesthetists have been implemented, a postal survey was conducted of all hospitals in the United Kingdom where surgery is performed. The number of hospitals with a multidisciplinary acute pain service had significantly increased from 2.8% before September 1990 to 42.7% at the end of 1994. Over the same period there has been an increase in the number of hospitals with a named clinician responsible for acute pain management, from 20 before 1990 to 230 (65.2%) and the number of hospitals with an acute pain nurse has increased from 8 (2.3%) prior to 1990 to 139 (39.3%). Routine assessment of pain and sedation occurs in 82% of hospitals with established acute pain services and in less than 50% of hospitals without an acute pain service. The use of written protocols, the provision of out-of-hours cover and regular training for all staff have increased with time. Research and audit activity related to acute pain management has also improved since 1990.

Performance assessment of a fuzzy controller for atracurium-induced neuromuscular block

The performance of a fuzzy controller for atracurium-induced neuromuscular block was assessed. Ten ASA I or II patients undergoing surgery anticipated to last at least 120 min were studied. A Datex Relaxograph was used to monitor neuromuscular block. Initially the T1 set point was set at 10% of baseline for at least 30 min (phase I). The T1 set point was then increased to 20% and then returned to 10% for two further periods of at least 30 min duration (phases II and III). The mean (SD) of the mean T1 error in 10 patients for phases I, II and III were 1.1 (1.4)%, -0.43 (1.2)% and 0.28 (0.94)%, respectively. The results show that a simple fuzzy logic controller can provide good accuracy with insensitivity to set point changes despite the considerable inter-individual variation in infusion rate required.

Sequential measurement of the median nerve somatosensory evoked potential during isoflurane anaesthesia in children

We have used sequential measurements of median nerve somatosensory evoked potentials (mnSSEP) in 10 children to estimate the equilibration time of an inhalation anaesthetic agent between alveolar gas, arterial blood and brain. MnSSEP were obtained sequentially every 90-180 s. After control measurements in the absence of isoflurane, the end-tidal concentration was increased stepwise (0.25, 0.5 and 0.75 MAC). Each isoflurane concentration was maintained for 15 min. The point at which the N20 latency reached stability was determined; the mean time between reaching a stable end-tidal isoflurane concentration and this point varied between 5 min 16 s and 7 min 37 s. This technique may be useful in circumstances in which a "steady state" of anaesthesia is important, such as in the determination of MAC or during intraoperative monitoring of evoked potentials.

Effects of isoflurane anaesthesia on the median nerve somatosensory evoked potential in children

Evoked potentials are used to determine the integrity of neural pathways during neurosurgical and orthopaedic procedures, but the extent to which they may be altered by anaesthetic agents has not been studied systematically in children. In this study we have recorded median nerve somatosensory evoked potentials (mnSSEP) in children during isoflurane anaesthesia to determine if there are changes similar to those seen in adults. We studied 10 patients using standardized anaesthetic and clinical neurophysiological techniques. Control mnSSEP were obtained with 70% nitrous oxide in oxygen and isoflurane was then administered at 0.25, 0.50 and 0.75 MAC. The latencies and amplitudes of the mnSSEP were subjected to repeated measures analysis of the variance (ANOVA) and linear regression. There were statistically significant increases in N20, P22 latencies and central conduction time (P < 0.001) and reductions in amplitude of the N20-P22 complex (P < 0.03) with increasing end-tidal isoflurane concentrations. These results are similar to the findings in adults.

The laryngeal mask airway

The laryngeal mask airway (LMA) is a new concept in airway management. A miniature inflatable mask is positioned in the hypopharynx, forming a low-pressure seal around the laryngeal inlet. The mask is attached via a tube to the breathing circuit. It is inserted after induction of anesthesia without the need for muscle relaxants or laryngoscopy. The LMA can be used to facilitate both spontaneous and controlled ventilation in adults and children. The LMA has been used for a wide variety of surgical procedures but is probably best suited to short procedures, especially if a light general anesthetic is used in combination with a regional technique. It may be particularly useful in outpatient anesthesia, as it avoids the need for intubation or muscle relaxants. It can be used as an alternative to mask anesthesia or when an endotracheal tube would have been inserted to allow surgical access. It has been used successfully in cases of difficult or failed intubation, although its role here needs further appraisal. It does not protect against aspiration of stomach contents and should not be used when aspiration is a risk. Controversy exists regarding its use to facilitate positive-pressure ventilation (PPV) due to concern that gases under pressure may be forced into the stomach and predispose the patient to regurgitation. It may be more difficult to use in children. It is now widely used in the United Kingdom; however, it is not yet available for sale in the U.S. It has already had a major effect on practice in Britain and has the potential to do the same in the United States.

Cyclopropane and the Datex Capnomac. Effect of cyclopropane on the single wavelength infrared measurement of volatile anaesthetic agents

We report the effect of cyclopropane used for induction of anaesthesia in children on the subsequent measurement of maintenance volatile anaesthetic agents with the single wavelength infrared absorption technique. After using cyclopropane to induce anaesthesia we have observed that falsely high readings of the expired maintenance agent occur for up to 60 minutes when using the Datex Capnomac. This is because of the effect of low concentrations of cyclopropane expired from the patient.

Clinical evaluation of closed-loop control of blood pressure in seriously ill patients

OBJECTIVE

To compare the effectiveness of a new method of closed-loop (automatic) control of BP with usual manual control.

DESIGN

Within-subject crossover trial.

SETTING

General and open heart ICUs in a university teaching hospital.

PATIENTS

Convenience sample of 74 seriously ill patients aged 17 to 88 yr. Twenty had hypertension: postoperative (n = 7), neurologic damage (n = 6), miscellaneous (n = 7), and were prescribed nitroprusside (n = 11) or nitroglycerin (n = 9). Fifty-four had hypotension: septic (n = 33), other (n = 21), and were prescribed norepinephrine (n = 30), dopamine (n = 11), epinephrine (n = 8), or dobutamine (n = 5). An additional 21 trials were omitted from analysis because of technical (n = 7), clinical (n = 1), or drug-related problems (n = 13).

INTERVENTION

Closed-loop and manual drug administrations 1-hr were studied during periods in each patient. The target and observed mean arterial pressure (MAP) and drug infusion rate were recorded electronically every 30 sec.

MAIN OUTCOME MEASUREMENTS

Time taken to achieve initial control (min); fidelity of control (the integral of size and duration of error from target MAP +/- 10% in mm Hg.hr/hr); and average drug dose administered (microgram/min as % maximum possible per drug).

RESULTS

Compared with manual control, closed-loop achieved faster initial control (log-rank chi 1 = 5.04, p less than .05) and greater fidelity (mean 1.37 vs. 2.36; F = 7.15, p less than .01). There was no difference in average drug dose administered. There was uniformity in the efficacy advantage of closed-loop drug administration across drugs and patient classifications.

CONCLUSION

The new closed-loop system is more effective than the usual manual control in managing acute BP disturbances in the seriously ill patient.

The laryngeal mask airway in children

The laryngeal mask airway was used in 200 children during a variety of surgical procedures. Some problem with the use of the device was encountered in 47 cases (23%), but in only five cases (2.5%) were the problems serious enough to warrant abandonment of its use. A clear airway was ultimately achieved in 191 children. Downfolding of the epiglottis over the laryngeal inlet was identified in eight out of 24 patients where flexible laryngoscopy was performed, clinically all these had unobstructed airways. The mask was used in 16 children with known airway problems. It is concluded that the size 2 laryngeal mask airway can be successfully used within the weight range 6-30 kg.

Unexpected difficult intubation. Asymptomatic epiglottic cysts as a cause of upper airway obstruction during anaesthesia

Two cases of asymptomatic epiglottic cysts which presented as partial upper airway obstruction following induction of anaesthesia are described. The incidence, pathology and anaesthetic management are discussed.

Subaortic stenosis

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Localized Congenital Defects of the Cardiac Interventricular Septum: A Study of Three Cases

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