Pressure measurement characteristics of a micro-transducer and balloon catheters.

Respiratory pressure responses to cervical magnetic stimulation are important measurements in monitoring the mechanical function of the respiratory muscles. Pressures can be measured using balloon catheters or a catheter containing integrated micro-transducers. However, no research has provided a comprehensive analysis of their pressure measurement characteristics. Accordingly, the aim of this study was to provide a comparative analysis of these characteristics in two separate experiments: (1) in vitro with a reference pressure transducer following a controlled pressurization; and (2) in vivo following cervical magnetic stimulations. In vitro the micro-transducer catheter recorded pressure amplitudes and areas which were in closer agreement to the reference pressure transducer than the balloon catheter. In vivo there was a main effect for stimulation power and catheter for esophageal (Pes ), gastric (Pga ), and transdiaphragmatic (Pdi ) pressure amplitudes (p < 0.001) with the micro-transducer catheter recording larger pressure amplitudes. There was a main effect of stimulation power (p < 0.001) and no main effect of catheter for esophageal (p = 0.481), gastric (p = 0.923), and transdiaphragmatic (p = 0.964) pressure areas. At 100% stimulator power agreement between catheters for Pdi amplitude (bias =6.9 cmH2 O and LOA -0.61 to 14.27 cmH2 O) and pressure areas (bias = -0.05 cmH2 O·s and LOA -1.22 to 1.11 cmH2 O·s) were assessed. At 100% stimulator power, and compared to the balloon catheters, the micro-transducer catheter displayed a shorter 10-90% rise time, contraction time, latency, and half-relaxation time, alongside greater maximal rates of change in pressure for esophageal, gastric, and transdiaphragmatic pressure amplitudes (p < 0.05). These results suggest that caution is warranted if comparing pressure amplitude results utilizing different catheter systems, or if micro-transducers are used in clinical settings while applying balloon catheter-derived normative values. However, pressure areas could be used as an alternative point of comparison between catheter systems.

Intracranial pressure monitoring in normal dogs using subdural and intraparenchymal miniature strain-gauge transducers.

BACKGROUND: Monitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs. HYPOTHESIS/OBJECTIVE: Assessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects. ANIMALS: Seven adult, bred-for-research dogs. METHODS: In a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia. RESULTS: Baseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement. CONCLUSIONS AND CLINICAL IMPORTANCE: Use of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension.

Overheated and melted intracranial pressure transducer as cause of thermal brain injury during magnetic resonance imaging: case report.

Magnetic resonance imaging is used with increasing frequency to provide accurate clinical information in cases of acute brain injury, and it is important to ensure that intracranial pressure (ICP) monitoring devices are both safe and accurate inside the MRI suite. A rare case of thermal brain injury during MRI associated with an overheated ICP transducer is reported. This 20-year-old man had sustained a severe contusion of the right temporal and parietal lobes during a motor vehicle accident. An MR-compatible ICP transducer was placed in the left frontal lobe. The patient was treated with therapeutic hypothermia, barbiturate therapy, partial right temporal lobectomy, and decompressive craniectomy. Immediately after MRI examination on hospital Day 6, the ICP monitor was found to have stopped working, and the transducer was subsequently removed. The patient developed meningitis after this event, and repeat MRI revealed additional brain injury deep in the white matter on the left side, at the location of the ICP transducer. It is suspected that this new injury was caused by heating due to the radiofrequency radiation used in MRI because it was ascertained that the tip of the transducer had been melted and scorched. Scanning conditions--including configuration of the transducer, MRI parameters such as the type of radiofrequency coil, and the specific absorption rate limit--deviated from the manufacturer's recommendations. In cooperation with the manufacturer, the authors developed a precautionary tag describing guidelines for safe MR scanning to attach to the display unit of the product. Strict adherence to the manufacturer's guidelines is very important for preventing serious complications in patients with ICP monitors undergoing MRI examinations.

The Camino intracranial pressure device in clinical practice. Assessment in a 1000 cases.

BACKGROUND: Intracranial pressure (ICP) monitoring has become standard in the management of neurocritical patients. A variety of monitoring techniques and devices are available, each offering advantages and disadvantages. Analysis of large populations has never been performed. PATIENTS AND METHODS: A prospective study was designed to evaluate the Camino fiberoptic intraparenchymal cerebral pressure monitor for complications and accuracy. RESULTS: Between 1992-2004 one thousand consecutive patients had a fiberoptic ICP monitor placed. The most frequent indication for monitoring was severe head injury (697 cases). The average duration of ICP monitoring was 184.6 +/- 94.3 hours; the range was 16-581 hours. Zero drift (range, -17 to 21 mm Hg; mean 7.3 +/- 5.1) was recorded after the devices were removed from 624 patients. Mechanical complications such as: breakage of the optical fiber (n = 17); dislocations of the fixation screw (n = 15) or the probe (n = 13); and failure of ICP recording for unknown reasons (n = 4) were found in 49 Camino devices. CONCLUSIONS: The Camino ICP sensor remains one of the most popular ICP monitoring devices for use in critical neurosurgical patients. The system offers reliable ICP measurements in an acceptable percentage of device complications and the advantage of in vivo recalibration. The incidence of technical complications was low and similar to others devices.

Clinical evaluation of intraparenchymal Spiegelberg pressure sensor.

OBJECTIVE: The Spiegelberg 3-PN intraparenchymal pressure sensor was clinically evaluated. DESCRIPTION OF INSTRUMENTATION: The Spiegelberg intraparenchymal pressure sensor is a low-cost device that uniquely performs regular automatic zeroing in situ throughout the measurement period. OPERATIVE TECHNIQUE: The Spiegelberg sensor was inserted in 87 patients who required intracranial pressure monitoring as part of their routine management. Complications were assessed by postoperative computed tomographic scanning and clinical investigation. The automated zeroing procedure was assessed after implantation of the sensor and during long-term measurement. In five patients, the "gold standard' of intraventricular pressure was measured simultaneously and compared with the intraparenchymal or subdural Spiegelberg 3-PN pressure. EXPERIENCE AND RESULTS: No complications associated with the Spiegelberg sensor were observed. The duration of monitoring ranged from 3 to 28 days (mean, 10 d). In 3 patients, technical problems occurred, and in 84 patients, the pressure measurement was successful, including the automatic zeroing procedures performed by the monitor after insertion and hourly thereafter. The absolute difference between the Spiegelberg reading and the intraventricular pressure was less than +/-3 mm Hg in 99.6% and less than +/-2 mm Hg in 91.3% of readings. An Altman-Bland bias plot revealed good agreement between the two methods, with an average bias of 0.5 mm Hg, but revealed a significant trend toward 10% lower Spiegelberg readings with increasing intracranial pressure of >25 mm Hg. There was no difference between intraparenchymal and subdural locations. CONCLUSION: The Spiegelberg 3-PN sensor was reliable and simple to use. It can be recommended for routine intraparenchymal and subdural pressure measurement at a considerably lower price compared with other tip transducers and has the unique advantage of automated zeroing in vivo.

Clinical comparison of the Spiegelberg parenchymal transducer and ventricular fluid pressure.

The Spiegelberg brain pressure catheter is a low cost implantable intracranial pressure measuring system which has the unique ability to perform regular automatic zeroing. A new version of the catheter has become available with a subdural bolt fixation to allow insertion of the device into the brain parenchyma. The accuracy of this system has been evaluated in comparison with a ventricular fluid pressure method in a series of patients to determine its accuracy and utility in the clinical environment. Hourly readings from the Spiegelberg system have been compared with those obtained using a standard pressure transducer connected to an external ventricular drain. Measurements continued while there was a clinical need for CSF drainage. Eleven patients were recruited to the study and data were recorded for periods ranging from 40 to 111 hours. A good agreement between the two systems was obtained. In 10 cases the mean difference was less than +/-1.5 mm Hg and the dynamic changes in value were contemporaneous. In one case an intracerebral haemorrhage developed around the tips of the Spiegelberg catheter and significant differences occurred between the two methods of measurement. In conclusion, the Spiegelberg parenchymal transducer provides an accurate measurement of intracranial pressure when compared with ventricular pressure. The transducer was found to be robust in the clinical environment and very popular with the nursing staff. Further studies may determine whether the complication rate of this system is comparable with other available devices.

An outbreak of Pseudomonas aeruginosa infection associated with contaminated urodynamic equipment.

Seven patients developed Pseudomonas aeruginosa urinary tract infections following urodynamic studies, over a two-month period. One patient developed septicaemia and meningitis and died following rupture of a berry aneurysm. Two others required hospital admission for intravenous antibiotic treatment. Pseudomonas aeruginosa was isolated from a pressure dome which covered the pressure transducer of the urodynamic system used for assessing bladder pressure. The device packaging carried the symbol designating this as a 'single use' product, but as an economy measure, a local decision had been taken to change the device monthly.

Clinical evaluation of the InnerSpace fibreoptic intracranial pressure monitoring device.

OBJECTIVE: The aim of this study is the clinical evaluation of the intraparenchymal ICP monitor InnerSpace OPX 100. METHODS: Sixty-four Inner Space OPX 100 transducers in 51 patients with severe head injury (42), intracranial spontaneous bleeding (6) or hypoxia (3) were studied. The transducer was placed in the frontal white matter. Thirty-nine patients received one catheter, eleven patients two catheters and one patient three catheters. The study period ranged from 10 hours-25 days; total study time was 421.5 days (mean duration 6.6 days). RESULTS: In nine cases (14.1%) an inadequate location of the ICP transducer was found, but the accuracy of the measurement was not influenced. Dislocation of the transducer occurred in eight cases (12.5%) due to inadequate handling. A failed transducer was observed in four cases (6.3%) because of a damaged optical fibre (1) or inadequate handling (3). In one patient (1.9%) a minor local infection developed. In eleven cases (17%) a haematoma around the ICP sensor was observed. Six haematomas were small; five haematomas were larger than 1 cm in diameter. In two patients a large frontal haematoma developed after exchange of the transducer. Operative evacuation was necessary in both cases. Zero shift was below 2 mmHg in all catheters. CONCLUSION: It is concluded that the InnerSpace intraparenchymal ICP monitor is a reliable device: the rate of catheter related intracerebral haematomas, however, is not acceptable. This could be improved by a better fixation of the catheter in the burr hole in order to avoid micromovements of the transducer.

Accuracy and reliability of disposable pressure transducers coupled with modern pressure monitors.

OBJECTIVE: To determine the bedside accuracy of direct patient pressure monitoring when used with new and clinically used disposable blood pressure (BP) transducers. DESIGN: Prospective study. SETTING: Laboratory bench and critical care units in an adult and children's hospital. SUBJECTS: Seventy-five bedside patient monitors (25 Marquette Electronics, 25 Spacelab Medical, and 25 Hewlett-Packard), and 100 disposable transducers (50 from Utah Medical Products and 50 from Abbott Critical Care Systems [25 new, 25 clinically used of each manufacturer]) were tested. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A +/- 2% accuracy requirement for bedside monitors and the +/- 3% American National Standards Institute accuracy standard for disposable BP transducers were used. To test the accuracy of the bedside monitors, a certified transducer simulator was used to apply 100 mm Hg to each bedside monitor. To test the accuracy of the disposable BP transducers, a very accurate (+/- 0.05%) pneumatic dead weight tester was used to apply pressures to the transducer. A digital power supply and a 6 1/2 digit voltmeter were used. The average output of the bedside monitors when 100 mm Hg was applied was 99.90 +/- 0.83 mm Hg, with the worst cases being 98 and 103 mm Hg. For all 100 disposable pressure transducers, the average output was 100.03 +/- 0.55 mm Hg, with the worst cases being 98.53 and 101.36 when 100 mm Hg was applied. There was no important difference in the accuracy of the transducers obtained from the two vendors nor whether the transducers had been used clinically. CONCLUSIONS: All disposable BP transducers tested were much more accurate than the American National Standards Institute standard for accuracy. Even the worst case transducers were twice as accurate as required by the American National Standards Institute standard. Only one bedside monitor was outside the +/- 2% accuracy range (103 mm Hg). Based on these findings, this author recommends that fixed calibration disposable transducers and fixed calibration bedside pressure monitoring systems be used. The clinical risks of air embolism and infection from the calibrating mercury manometer and the complexity of the calibration task are the overriding factors for making these recommendations.

Intracranial pressure monitoring techniques.

In patients requiring ICP monitoring, a ventricular catheter connected to an external strain gauge transducer or catheter-tip pressure transducer device is the most accurate and reliable method of monitoring ICP, and enables therapeutic CSF drainage. Clinically significant infections or hemorrhage associated with ICP devices causing patient morbidity are rare and should not deter the decision to monitor ICP. Parenchymal catheter-tip pressure transducer devices measure ICP, similar to ventricular ICP pressure, but have the potential for significant measurement differences and drift due to the inability to recalibrate. These devices are advantageous when ventricular ICP is not obtained or if there is obstruction in the fluid coupling. Subarachnoid or subdural fluid-coupled devices and epidural ICP devices are currently less accurate.

Epidemic bloodstream infections associated with pressure transducers: a persistent problem.

Twenty-four outbreaks of nosocomial bloodstream infection (BSI) were investigated by the Centers for Disease Control from Jan 1, 1977 to Dec 31, 1987. Intravascular pressure monitoring devices (transducers) were the most commonly identified source of bacterial and fungal BSI outbreaks and were implicated as the source of infection in eight (33%) outbreaks. These included outbreaks caused by Candida parapsilosis (2), Serratia marcescens (2), Klebsiella oxytoca (1), Pseudomonas cepacia (1), Acinetobacter calcoaceticus (1), and one polymicrobial bacteremia outbreak due to Acinetobacter, Pseudomonas, Citrobacter, and Enterobacter species. In all eight outbreaks, reusable transducers improperly disinfected or fitted with domes that had been improperly sterilized served as reservoirs for the organism. Compared with nosocomial BSI outbreaks not related to transducers, those in which transducers were implicated as a reservoir involved a larger mean number of patients (24 v 9; P = 0.007), and were significantly more likely to involve intensive care unit patients (23/24 v 3/9; P = 0.025) and to have a longer mean duration (11 v 3 months; P = 0.007). These findings show that the characteristics of transducer- and non-transducer-related BSI outbreaks differ, and that centers using intravascular pressure monitoring devices must be aware of and implement recommended infection control strategies for care and maintenance of these devices.

Outbreak of infection with Achromobacter xylosoxidans from contaminated intravascular pressure transducers.

Achromobacter xylosoxidans contaminating transducers caused 15 cases of hospital infection. In the eight patients with bacteraemia the interval from inoculation to fever was an average of 6.6 days. All the infected patients recovered. Computerization of laboratory records allowed retrieval of previous isolates, and review of clinical records focused the problem on patients with cardiac and aortic diseases. The problem arose from the re-use of disposable equipment after disinfection with a benzalcone.