A prospective infant manikin-based observational study of telephone-cardiopulmonary resuscitation.

INTRODUCTION: Bystander cardiopulmonary resuscitation (CPR) has been shown to significantly improve outcome in sudden cardiac arrest in children. In view of this, most emergency medicine services deliver telephone instructions for carrying out CPR to laypeople who call the emergency services. Little is known as to whether laypeople carrying out these instructions deliver effective CPR. METHODS: Adult volunteers who had no previous experience of CPR were recruited. They were presented with a scenario and asked to perform CPR for 3 min on a training manikin according to the instructions they were given by telephone. Tidal volume, compression rate and depth, time to the beginning of CPR and hand positioning were recorded. RESULTS: Fifty-five volunteers were recruited; three were excluded (two had previous CPR training and one refused to perform CPR). None of the subjects identified correctly that the manikin was not breathing and achieved a level of CPR performance that was consistent with all of the current guidelines. Median tidal volume of rescue breaths was 38 mL. Only 23% of subjects delivered rescue breaths of optimal volume (40-50 mL) and 23% delivered no effective breaths at all. Chest compressions were performed at a median rate of 95 min(-1) with 37% delivering compressions at the optimum rate of 90-110 min(-1). CONCLUSION: None of our volunteers performed telephone-CPR at a level consistent with current guidelines. Further investigation is necessary to determine whether the instructions can be improved to optimise CPR performance.

Simultaneous measurement of force and respiratory profiles during chest physiotherapy in ventilated children.

There are currently no objective means of quantifying chest wall vibrations during manual physiotherapy. The aims of the study were to (i) develop a method to quantify physiotherapy-applied forces and simultaneous changes in respiratory flow and pressure, (ii) assess the feasibility of using this method in ventilated children and (iii) characterize treatment profiles delivered by physiotherapists in the paediatric intensive care unit. Customized sensing mats were designed and used in combination with a respiratory profile monitor. Software was developed to align force and flow data streams. Force and respiratory data were successfully collected in 55 children (median age 1.6 years (range 0.02-13.7 years)). Physiotherapists demonstrated distinctive variations in the pattern of force applied and manual lung inflations. The maximum applied force ranged from 15 to 172 N, and was correlated with the child's age (r = 0.76). Peak expiratory flow increased significantly during manual inflations both with and without chest wall vibrations (p < 0.05). This method provides the basis for objective assessments of the direct and independent effects of vibration forces and manual lung inflations as an essential precursor to developing evidence-based practice.

Bone mineral status in immigrant Indo-Asian women.

BACKGROUND: Indo-Asian immigrants are known to be at high risk of metabolic bone disease, but the prevalence of osteoporosis in this population is unknown. AIM: To compare the bone mineral at the lumbar spine and femoral neck of Indo-Asian immigrant women with that of age-matched Caucasian women. DESIGN: Retrospective analysis. METHODS: Women of Indo-Asian origin referred for bone density scans in the last five years were identified. The skeletal status of each was compared with an age-matched Caucasian control for bone mineral content (BMC), bone mineral density (BMD) and bone mineral apparent density (BMAD) at the lumbar spine and femoral neck, and hip axis length was measured. RESULTS: At the lumbar spine, Indo-Asians had a significantly lower BMD than Caucasians (0.834 vs. 0.913, p = 0.008), but there was no significant difference when BMAD values were calculated (0.123 vs. 0.122). At the femoral neck, there was no difference in BMD (0.728 vs. 0.712, p = 0.5), and BMAD values were significantly higher among Indo-Asians than Caucasians (0.393 vs. 0.319, p = 0.022). Hip axis length was significantly shorter among Indo-Asian women (10.3 vs. 10.7, p = 0.009). DISCUSSION: Although Indo-Asian women appear to have lower spinal BMD than Caucasians, these differences disappear when BMAD values are calculated. While BMD is an areal density, not taking into account the 'depth' of the bone, BMAD is an estimation of volumetric density. Hence lower BMD values in Asians may be a size-related artefact. Longitudinal studies may be required to evaluate the use of BMD as a marker for fracture risk in this population.

Alcohol consumption alters insulin secretion and cardiac autonomic activity.

BACKGROUND: Alcohol may have a cardioprotective effect. One possible mechanism is by modifying insulin resistance/secretion. The aims of this study were: (i) to examine the effect of short-term alcohol consumption on the metabolic control of glucose tolerance; (ii) to study the influence of short-term alcohol consumption on cardiac autonomic activity using spectral analysis of heart rate variability. METHODS: Twenty-one healthy subjects, in a randomized crossover design, either received three units of ethanol daily for 1 week or abstained from ethanol. The control of glucose tolerance was assessed using the intravenous glucose tolerance test with minimal modelling. RESULTS: There was no difference in fasting glucose, fasting insulin or insulin sensitivity between the two groups. Alcohol showed a lower insulin first phase insulin response (no alcohol 659.0 +/- 394.1 SD, alcohol 535.2 +/- 309.1) pmol L-1 min-1, P = 0.027). There was no difference in heart rate or blood pressure but a significant difference in the ratio of high to low frequency spectral power of heart rate variability; (no alcohol 4.55 +/- 3.78, alcohol 8.16 +/- 6.77, P = 0.033). This suggests decreased sympathetic and/or increased vagal modulation of heart rate in the alcohol group. CONCLUSION: The finding of no difference in insulin sensitivity between the two groups contrasts with, but does not entirely contradict, the results of previous epidemiological studies--perhaps suggesting that longer term changes such as liver enzyme induction may be important. The difference in insulin secretion questions the validity of previous studies of the influence of alcohol on insulin sensitivity, where insulin levels were used as a surrogate for insulin resistance.

Evidence-based guidelines for the use of defibrillation pads.

OBJECTIVE: Defibrillation pads are used routinely at both cardiac arrests and cardioversion procedures. There are currently no evidence-based guidelines on how often pads should be replaced, although it has been suggested that they should be changed as often as every three shocks to maintain optimal performance. Previously, we have shown that on exposure to air, pad mass diminishes over time due to evaporation--an effect likely to lead to poorer conduction between skin and paddle. This prospective study was designed to determine if evaporation is accelerated by the passage of a defibrillation current and to formulate evidence-based guidelines for defibrillation pad replacement. MATERIALS AND METHODS: 3M defibrillation pads (2346N) were collected from acute wards and emergency departments in two hospitals in the UK over a 2 month period. The duration of exposure to air, number and energy of shocks, and type of procedure were recorded. When no longer required, pad masses were determined and the loss of pad mass due to evaporation calculated. RESULTS: 26 pairs of pads were collected from 14 cardiac arrests and 12 cardioversions. The total defibrillation energy used ranged from 150 to 5080 J and evaporative drying time from 4 to 38 min. The rate of evaporation from these pads (86.1 mg x min(-1)) was not significantly different from pads previously studied on volunteers in the absence of a defibrillation current (99.4 mg x min(-1)). Of the defibrillation pads exposed to air for less than 30 min, in only one of 49 pads was the loss of mass due to evaporation consistent with a significant increase in transthoracic impedance (TTI). Correspondingly, of two pads used for more than 30 min, both attained a mass consistent with a significant increase in TTI. CONCLUSIONS: Defibrillation pads can be used for up to 30 min without evaporation causing a clinically significant increase in TTI. The passage of a defibrillation current across pads does not further accelerate water loss.

Are European Resuscitation Council recommendations for paddle force achievable during defibrillation?

Transthoracic impedance (TTI) is an important determinant of success in defibrillation. Low TTI increases transmyocardial current and therefore increases the chance of depolarising a critical mass of myocardium. A major component of TTI occurs at the paddle-skin interface and is minimised by pressure applied to the defibrillation paddles. The International Liaison Committee on Resuscitation (ILCOR) 2000 guidelines recommend that 'firm force' should be applied to both paddles, whereas previous European Resuscitation Council (ERC) 1992 guidelines were more precise, recommending that 12 kg of force should to be applied. We assessed whether defibrillator operators are capable of achieving 12 kg paddle force. Fifty advanced life support-trained doctors and nurses attempted to achieve 12 kg paddle force while simulating defibrillation on a resuscitation doll. The median value of the maximum pressures obtainable was 10.1 (max 16.0; min 5.0) kg force. Only 14% could achieve > or =12 kg force on both paddles for defibrillation. Men achieved more force than women (10.7 vs. 8.1 kg force; P<0.01), and there was a correlation between maximum force achieved and operator height (r2=0.27) and dominant hand-grip strength (r2=0.34). The ERC recommendation of 12 kg paddle force is not achievable by the majority of defibrillator operators.

Comparison of calcaneal ultrasound and DXA to assess the risk of corticosteroid-induced osteoporosis: a cross-sectional study.

Patients on long-term oral corticosteroids have an increased risk of low bone mass and fragility fractures. Fracture risk rises soon after commencement of corticosteroid therapy and it is possible that these agents adversely influence bone architecture disproportionately to their effect on bone mass. The best means of assessing bone status in patients using corticosteroids remains uncertain, but quantitative ultrasound of the calcaneus may provide evidence of microarchitectural changes not detected by dual-energy X-ray absorptiometry (DXA). Patients with Crohn's disease have an increased risk of low bone mineral density (BMD), the etiology of which is multifactorial but includes corticosteroid use. We studied 118 consecutive patients with Crohn's disease, 21 of whom used continuous oral corticosteroids, 70 of whom were intermittent users, and 27 who had never used the drug. All patients received DXA of the lumbar spine, hip and calcaneus and quantitative ultrasound (QUS) of the calcaneus. The different techniques were compared using a femoral neck T-score < or = -1.5 as the threshold of corticosteroid-induced osteoporosis. When compared with the femoral neck T-score, there were no significant differences between the predictive values of lumbar spine DXA, calcaneal DXA or calcaneal QUS to identify low femoral neck BMD. However, the absolute T-score required to give similar discriminatory capacity to femoral neck T-score varied substantially (T= -0.81 to -1.5) between the different measurement techniques and sites.

How often should defibrillation pads be changed?: the effect of evaporative drying.

OBJECTIVE: In order to minimise transthoracic impedance (TTI) during defibrillation, water-based pads are used to improve conductivity between metal defibrillation paddles and skin. Subjectively, these pads appear to dry very quickly; an effect that may lead to an increase in TTI due to poorer conduction between paddles and skin. This study was carried out to assess the effect of evaporative drying of defibrillation pads on TTI. MATERIALS AND METHODS: TTI was measured at 5-10 min intervals in 20 adult male volunteers across 3M defibrillation pads (2346N) placed in the anterior-apical position. Measurements of TTI were made at 30 kHz using a Bodystat MultiScan 5000 monitor at end-expiration. A third pad was placed on the left precordium and its mass recorded each time a TTI measurement was made. RESULTS: The median age of subjects was 22 years (range 21-52 years) and their median body mass index was 23.1 kg m(-2) (range 18.4-42.8 kg m(-2)). Median room temperature was 23.0 degrees C (range 19.0-24.0 degrees C) and the median humidity was 31.0% (range 28.0-48.0%). 3M defibrillation pads had an initial mean mass of 25.14 g (S.D. +/- 0.41 g). Changes in defibrillation pad mass due to evaporative loss occurred immediately and rapidly, with all measurements being significantly lower than the baseline value. Mean baseline TTI was 63.6 ohms (S.D. +/- 13.7 ohms). After 30 min a statistically significant (P = 0.012) rise of 1.4 ohms (2.2%), was observed corresponding to a 12.6% decrease in pad mass, after which TTI continued to increase in a linear fashion. CONCLUSION: In the absence of a defibrillation current. 3M defibrillation pads can safely be left on the chest wall for at least 25 min in a typical hospital environment before evaporative drying results in a significant increase in transthoracic impedance.

Does paddle force applied during defibrillation meet advanced life support guidelines of the European Resuscitation Council?

OBJECTIVES: to determine whether paddle force applied during defibrillation meets the 12 kg (approximately 120 N) force recommended by the advanced life support (ALS) guidelines of the European Resuscitation Council (ERC). MATERIALS AND METHODS: an adult mannequin was "defibrillated" using standard defibrillation paddles instrumented to measure paddle force. Paddle force was recorded at the time the discharge buttons on the paddle handles were depressed. RESULTS: 54 doctors and nurses performed simulated defibrillation on a mannequin. Median sternal paddle force was 60.6 N (range 26.1-132.8 N) and median apical paddle force was 59.5 N (range 18.6-118.5 N). Only 3/54 operators (5.6%) applied sternal paddle force equal to or in excess of ERC recommendations. No operator applied apical paddle force equal to or in excess of ERC recommendations. CONCLUSIONS: force applied to defibrillation paddles does not meet guidelines of the European Resuscitation Council. Greater emphasis during advanced life support training should be placed on the importance of firm paddle force during defibrillation.

An investigation of the diagnostic value of bilateral femoral neck bone mineral density measurements.

This paper describes a study to assess the clinical value of bilateral femoral neck bone mineral density (BMD) measurements. Although a range of factors will determine clinical decisions, the classification of the site with the lowest T-score is likely to have significant bearing on the management of a patient. While it is common practice to measure BMD at the lumbar spine and a single neck of femur, knowledge of the BMD of the second femur may also be of diagnostic value. Using dual-energy X-ray absorptiometry, BMD of the lumbar spine and right and left femoral neck was measured in a group of 2372 white, Caucasian women (mean age +/- SD, 56.6 +/- 13.9 years) routinely referred for bone densitometry. Analysis of the measurements showed a significant (p = 0.02) but small difference between the mean BMD of the right (0.840 +/- 0.152 g/cm2) and left (0.837 +/- 0.150 g/cm2) femoral neck. Further investigation of femur scans revealed 79 (3.3%) patients in whom one side was osteoporotic while the other side and spine were normal or osteopenic using the World Health Organization diagnostic criteria in combination with manufacturer's reference data. Patients in whom the femoral neck BMD measurements differed by less than the precision error of the system were then excluded. This left only 51 (2.2%) patients, that is 29 (1.2%) for right femur and spine scan and 22 (0.9%) for left femur and spine scan, in whom knowledge of both femoral neck BMD measurements could have altered the classification of the lowest site assessed to osteoporotic. These data suggest that there is only a small benefit from performing bilateral femoral neck BMD measurements. Since BMD measurements are only one of a range of factors considered as part of a patient's management, it is suggested that the extra time, cost and radiation dose associated with measurement of the second femur may not be justified.

Effects of changes in packed cell volume on the specific heat capacity of blood: implications for studies measuring heat exchange in extracorporeal circuits.

Extracorporeal circuits such as cardiopulmonary bypass (CPB) and renal dialysis machines cause active and/or passive loss of body heat. Attempts to quantify this heat loss are generally based on the Fick principle which requires knowledge of the specific heat capacity (SHC) of blood. As changes in packed cell volume are common, we investigated the effect of these changes on the SHC of blood over a range of packed cell volumes (PCV) from whole blood at 43.1% (3594 J kg-1 degrees C-1) to pure Hartmann's solution (4153 J kg-1 degrees C-1). The SHC of other fluids used during CPB was also measured and found to be 4139 J kg-1 degrees C-1 and 4082 J kg-1 degrees C-1 for normal saline and Gelofusine, respectively. The maximum variability in SHC over the range of PCV values encountered during CPB was calculated to be small (5.5%). We conclude that use of a constant value of SHC for calculation of thermal energy transfer is currently justified.

Ultrasonic propagation in cancellous bone: a new stratified model.

The theoretical modeling of ultrasonic propagation in cancellous bone is pertinent to improving the ultrasonic diagnosis of osteoporosis. First, this paper reviews applications of Biot's theory to this problem. Next, a new approach is presented, based on an idealization of cancellous bone as a periodic array of bone-marrow layers. Schoenberg's theory is applied to this model to predict wave properties. Bovine bone samples were tested in vitro using pulses centered at 1 MHz over various angles relative to the orientated cancellous structure. Two longitudinal modes (fast and slow waves) were observed for propagation parallel to the structure, but only one was observed for propagation normal to the structure. Angular-dependence of velocities was examined, and the fast wave was found to be strongly anisotropic. These results gave qualitative agreement with predictions of Schoenberg's theory. Although this new model is a simplification of the cancellous architecture, it has potential for future research.

The autonomic control of heart rate and insulin resistance in young adults.

The pathophysiology of insulin resistance is unclear. A link between increased heart rate (HR) and insulin resistance suggests an association with sympathetic nervous system activity. To further evaluate this, we examined autonomic activity using spectral analysis of HR variability (HRV), which provides a measure of cardiac sympathovagal modulation, and related this to insulin sensitivity (Si) in 137 men and women (20 yr old). The HRV spectrum displays 2 major peaks: a high-frequency peak, reflecting vagal activity, and a low-frequency peak caused by vagal and sympathetic activity. The high-to-low ratio (HLratio) reflects sympathovagal balance. Si was measured, using the i.v. glucose tolerance test with minimal modeling, and HR data was derived from a 15-min supine electrocardiogram. Women were more insulin resistant than men (Si, 3.94 vs. 5.09 10(4) min(-1)/per pmol x L; P = 0.002), had higher HR (59 vs. 56 beats/min, P = 0.019), but had a higher HLratio (2.04 vs. 1.31, P = 0.001). In men (but not women), Si correlated with HR (r = -0.410, P = 0.001) and measures of HRV: HLratio (r = 0.291, P = 0.002) independently of body mass index. In conclusion, Si correlates with cardiac sympathovagal balance in men, but not women, suggesting gender differences in the autonomic modulation of insulin resistance.

Pharmacological vasodilatation improves efficiency of rewarming from hypothermic cardiopulmonary bypass.

An afterdrop in core temperature after hypothermic cardiopulmonary bypass (CPB) is related to inadequate peripheral rewarming. We proposed that pharmacological vasodilatation during rewarming on bypass would improve peripheral rewarming and reduce the degree of afterdrop. Fifty-nine of 120 patients were randomized to receive a sodium nitroprusside (SNP) infusion during the rewarming stage of hypothermic CPB. Mean systemic vascular resistance (SVR) during the rewarming phase of CPB was 1129 dyne s-1 cm-5 in the control group and 768 dyne s-1 m-5 in the SNP group (P < or = 0.001). Patients receiving SNP rewarmed to 37.0 degrees C faster (299 min vs 376 min; P = 0.003) and were extubated earlier (490 min vs 621 min; P = 0.001). Patients receiving SNP had a warmer mean peripheral temperature (MPT) (32.9 degrees C vs 32.4 degrees C; P = 0.05) on termination of CPB. Postoperative core temperature fell less in the SNP group (35.6 degrees C vs 35.2 degrees C; P = 0.01) as did MPT (31.8 degrees C vs 31.2 degrees C; P = 0.004). SNP-induced vasodilatation during rewarming from hypothermic CPB improves peripheral rewarming, reduces the degree of postoperative core and peripheral hypothermia and reduces time to extubation.

Effects of positive end-expiratory pressure on transthoracic impedance--implications for defibrillation.

The success of defibrillation is determined by trans-myocardial current. This current is inversely proportional to transthoracic impedance (TTI). We proposed that increasing lung volume using positive end-expiratory pressure (PEEP) would increase TTI. 12 healthy subjects aged 21-37 years (6 male) were recruited. TTI between self-adhesive defibrillation pads placed in the standard antero-apical position was measured at 30 kHz at end-expiration using Bodystat MultiScan 5000 equipment. PEEP at 2.5, 5.0, 10.0, 20.0 and 40.0 cm H2O was generated using a standard continuous positive airways pressure (CPAP) circuit. Data were analysed using linear regression and paired t-tests comparing baseline TTI with that at a given PEEP. Mean (+/- S.D.) baseline TTI was 65.7 +/- 6.9 omega. TTI increased linearly with increasing PEEP (r2 = 0.99; P < 0.001). Mean percentage increases in TTI were 0.6% at 2.5 cm H2O PEEP (P = 0.05), 1.5%, at 5.0 cm H2O PEEP (P < 0.001), 3.1% at 10.0 cm H2O PEEP (P < 0.001), 5.6% at 20.0 cm H2O PEEP (P < 0.001) and 10.4% at 40.0 cm H2O PEEP (P < 0.001). PEEP increases TTI, proportionately reducing transthoracic current during defibrillation. Clinically, high levels of PEEP (20-40 cm H2O) may occur during ventilation of patients at cardiac arrest and in acute asthmatics. To maximise peak defibrillation current, PEEP should either be minimised prior to defibrillation or consideration should be given to earlier use of high energy levels for defibrillation.

Development and application of a general purpose ambulatory monitor.

This paper details the development and application of a multi-channel, general purpose, lightweight, portable monitor. The monitor is constructed with separate analogue and digital circuitry so that a dedicated analogue board may be developed for each new application with the same general purpose digital board, the latter requiring only changes to the firmware. At the heart of the digital circuit is an Arizona Microchip PIC 16C64 microcontroller, which can communicate with a computer via a serial port and perform both simple and relatively complex data analysis prior to storing data in memory. The low-power design enables the circuit to operate for potentially longer than a week on one set of batteries. Designed with medical applications in mind, preliminary data from three studies utilising the monitor are described. These include measurements of bladder pressure, personal exposure to pollutant gases and body temperature. The studies demonstrate the system's versatility in a variety of investigations requiring different signal processing and sampling protocols. It is hoped that, in the future, this ambulatory device will contribute to the diagnosis, treatment and understanding of a wide variety of disease conditions.

Effects of respiratory gas composition on transthoracic impedance.

The transthoracic current generated during defibrillation comprises a cardiac and extracardiac component. Changes in impedance of transthoracic pathways will alter the transmyocardial current and may thus affect the outcome from defibrillation. The lungs comprise a large component of extracardiac tissue but the effects of different respiratory gases on transthoracic impedance has not been documented. We therefore measured transthoracic impedance (TTI) using different respiratory gas mixtures. TTI across self-adhesive defibrillation pads placed in the antero-apical position was measured at end-expiration using a 30 kHz low amplitude AC current. Ten healthy subjects aged 22-34 years (eight male) were studied whilst breathing alternate mixtures of air, 100% oxygen. 70% helium in 30% oxygen, and 70% nitrous oxide in 30% oxygen administered in a random sequence. There was no significant difference in TTI between any of the four respiratory gases. Therefore transthoracic current during defibrillation is unlikely to be affected by different respiratory gases. This is the first study to document that these respiratory gases do not change the impedance of transthoracic pathways.

A comparison of transthoracic impedance using standard defibrillation paddles and self-adhesive defibrillation pads.

The success of defibrillation is related to transmyocardial current. This current is inversely proportional to transthoracic impedance (TTI). A similar TTI between different pads and paddles is important to deliver a consistent therapeutic dose to all subjects. Failure to do so may result in either insufficient or excessive transmyocardial current leading to a risk of failed defibrillation or tissue damage respectively. Several different types of defibrillation paddles and self-adhesive defibrillation pads are currently available for clinical use but the TTI achieved with each type has not been established. We measured TTI using two types of commonly used paddles and self-adhesive pads to establish whether any significant differences exist between the products. TTI in 40 adult males was measured using defibrillation paddles and self-adhesive defibrillation pads placed in the antero-apical position. Measurements were made using a 30 kHz low amplitude AC current and taken at end-expiration. Mean TTI (omega)+/-S.D. was 68.2+/-16.1 (Hewlett Packard paddles; A), 62.8+/-13.2 (Hewlett Packard pads; B), 64.6+/-14.3 (PhysioControl paddles; C) and 95.6+/-22.3 (PhysioControl pads; D). Significant differences existed between all groups (P < 0.05) except between B and C. Differences in TTI between A, B and C were small and probably of no clinical significance. TTI in group D is significantly larger. Although transmyocardial current is related to TTI, the relationship is complex and differences in TTI alone cannot predict the outcome from defibrillation.

An optical trigger source for hydrophone-based ultrasound measurement systems: a feasibility study.

Ultrasound is routinely used in many medical applications. Concern for the safety of subjects undergoing investigations has led to the development of systems to quantify the acoustic output of such devices. One system, the NPL ultrasound beam calibrator, uses a multi-element hydrophone to determine rapidly the temporal and spatial characteristics of the acoustic output. When investigating pulsed systems it is necessary to synchronise data acquisition with the launch of the acoustic pulse, a procedure that currently can be both time consuming and difficult. This article examines the feasibility of using an alternative, optical approach, generating a trigger signal in response to the changes in refractive index associated with propagation of the acoustic pulse.