Direct Measurement of Intratracheal Pressure in Pediatric Respiratory Monitoring

Abstract

We describe a method based on a Fabry-Perot interferometer at the tip of an optic fiber with a diameter of 0.25 mm for direct measurement of tracheal pressure in pediatric respiratory monitoring. The response time of the pressure transducer and its influence on the resistance of pediatric endotracheal tubes (internal diameter, 2.5 to 5 mm) during constant and dynamic flow at different ventilator settings in a lung model were measured. The transducer was positioned at Ϫ1.5 (inside), 0, and ϩ1.5 cm (outside) relative to the tip of the endotracheal tube and compared with a reference pressure inside the trachea. The clinical application of the transducer was tested in five pediatric patients. The response time of the transducer was 1.3 ms. The influence of the fiberoptic transducer on tube resistance was negligible during constant flow in inspiratory and expiratory directions for all endotracheal tubes tested. There was no difference in pressure measurements with the transducer positioned at or 1.5 cm below or above the tip of the endotracheal tube during dynamic measurements. During clinical circumstances insertion of the fiberoptic transducer was easy, recordings were stable, and the safety of the patient was not jeopardized. The fiberoptic transducer provided a reliable and promising way of monitoring tracheal pressure in intubated pediatric patients. The presence of the probe did not interfere with either pressure-flow relationship or patient care and safety. The technique is proposed for monitoring of respiratory mechanics and calculation of changes in tube resistance caused by kinking and secretions. Respiratory monitoring in pediatric intensive care is currently represented by proximal P/V loops obtained in ventilator software or intensive care monitors using flowmeters placed near the connection between the ventilator system and ETT. This is obviously insufficient as information gained from such P/V loops mainly stems from ETT resistance and performance of ventilator valves. We have previously demonstrated that monitoring respiratory mechanics by direct measurement of tracheal pressure offers considerable advantages compared with monitoring based on either measurements obtained proximal to the tube or tracheal pressures calculated by subtracting pressure needed to overcome flow-dependent tube resistance. In the adult setting tracheal pressure measurement is accomplished by introducing an air-or liquid-filled catheter into the ETT and connecting it to a conventional pressure transducer (1). In the pediatric setting it has generally been held to be impossible to use endotracheal catheters for continuous pressure measurement owing to the encroachment on cross-sectional area of the narrow pediatric tubes (2). Instead hydrodynamic models of varying complexity have been proposed for the calculation of tracheal pressure, i.e. the pressure fall across the ETT because of its resistance, based on measurements above the tube. Guttmann et al. (2)

Nasal Ventilation Alters Mesenchymal Cell Turnover and Improves Alveolarization in Preterm Lambs

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Optical-Fiber Measurement Systems for Medical Applications

“…It consists of a membrane that changes the depth of a microcavity with pressure (Fabry-Perot interferometry). It shows some advantages such as: small size (the silicon sensor chip diameter is equal to 420 µm, the fiber optic diameter is 250 µm or 400 µm), measurement range between -50 cmH 2 O and +350 cmH 2 O, low temperature drift (< 0.2 cmH 2 O/°C), accuracy of 0.5 cmH 2 O or 2.5 % of reading between -50 cmH 2 O to +250 cmH 2 O and 4 % of reading between +250 cmH 2 O to +350 cmH 2 O, short response time (1.3 ms), moreover the introduction of the sensor into the ETT does not significantly increase the fluid-dynamic resistance, therefore the pressure drop across the ETT (Sondergaard et al, 2002). This company produces another FOS, with similar metrological characteristics of the above described sensor, used in urology to monitor bladder pressure and the pressure in the lower urinary tract, especially important in paraplegic patients for the high risk of urinary tract infections.…”

Intermuscular pressure between synergistic muscles correlates with muscle force

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“…Whereas the microcapillary infusion technique was used in earlier investigations on IaMP determination (Styf and Körner, 1986), transducer-tipped semiconductor-based or fibre-optic-based catheter pressure sensors were used in more recent studies (Sondergaard et al, 2002;Kaufman et al, 2003;Cottler et al, 2009;Sezen et al, 2009). Because these methods require a fluid-filled space, which is nonexistent between muscles, they are not suitable to measure the IrMP.…”