Validation of respiratory inductive plethysmography using the Qualitative Diagnostic Calibration method in anaesthetized infants

Abstract

During recent years there has been renewed interest in noninvasive methods of assessing respiratory function in infants, since the use of face masks and pneumotachographs (PNT) have both been shown to affect breathing pattern [1]. Respiratory inductive plethysmography (RIP) is a means of measuring breathing movements without any connections at the airway opening, and therefore has numerous potential applications in infants, including prolonged respiratory monitoring in the intensive care unit or postoperatively. RIP uses inductance coils within elasticated bands to measure the respiratory excursion of the ribcage (rc) and abdomen (abd). The respiratory system is assumed to move with two "degrees of freedom", so that changes in inductance are proportional to changes in ribcage and abdominal volume. The weighted sum of the rc and abd is therefore proportional to the tidal volume (VT). Studies using RIP have increased our understanding of respiratory control and mechanics [2,3], including the fact that infancy is characterized by abdominal breathing [4], and that halothane anaesthesia is associated with a loss of ribcage recruitment [5].Whereas uncalibrated RIP is a valuable means of assessing both respiratory timing and various qualitative aspects of rc and abd asynchrony [6][7][8], calibration is essential if quantitative changes in ventilation are to be assessed. Such calibration, which involves a two-stage process of determining the relative contributions of rc and abd to each breath and then ascertaining a proportionality coefficient in order to scale the weighted sum to actual tidal volume, has, however, proved to be a major challenge when using RIP in infants. Three main methods of calibration have been proposed, as outlined below.1) The rc and abd signals are compared with simultaneous recordings of VT from a PNT, according to the equation:where Vrc is the inductance (voltage) of the rc signal and Vabd is that of the abd signal. Providing VT is measured over a large enough number of breaths, a proportionality coefficient K can then be derived using a least squares or graphical solution to the equation. However, since this always requires the simultaneous use of a PNT, the advantages of RIP are at least partially lost.2) In 1987, KONNO and MEAD [9] described the isovolume manoeuvre, as a means of determining the relative contribution of rc and abd without a PNT. This requires the subject to shift gas gently between the rc and abd during a breath hold or airway occlusion, thereby producing paradoxical movements of the two compartments. Since VT does not change, equation (1) Measurements were made during spontaneous (SV) and intermittent positive pressure (IPPV) ventilation, sighs and airway occlusions. The VT,DIF was the difference between VT,QDC and VT,PNT (%VT). The contribution of the ribcage (rc) to VT,QDC (%rc) and the thoracoabdominal phase lag were also derived. Twenty-eight infants, mean (SD) age 14.0 (6.2) months were studied.VT,QDC represented VT,PNT most closely when Š20 breaths were analysed. The...

Measurement of Total and Compartmental Lung Volume Changes in Newborns by Optoelectronic Plethysmography

“…Unfortunately, the calibration procedure is critical and patient-dependent. In addition, measurements are not reliable if the position and condition of the patient differ from those assumed during calibration (3). Moreover, the use of RIP for tracking longterm changes in EELV is still questioned (4,5).…”

“…Connecting to the airway opening may introduce leaks, annoy the infant, and affect the breathing pattern (1,2), while the use of patient-dependent calibration procedures can lead to inaccurate measurements when a patient's condition or posture changes with respect to the baseline state (3). Moreover, none of the existing techniques have proved to be reliable in tracking long-term changes in endexpiratory lung volume (EELV) due to integration drift or problems in the measurements stability (4,5).…”

Automated respiratory inductive plethysmography to evaluate breathing in infants at risk for postoperative apnea

“…They do not rely on a calibrated RIP system. The calibration routines which assign proportionality constants to the ribcage and abdomen signals, thereby allowing their summation to give a tidal volume, 13,[34][35][36] assume a fixed spinal angle, an assumption that is problematic with mobile infants, postanesthesia. The algorithms do not require segmentation of the data record into individual breaths.…”

Pletismografia respiratória por indutância: estudo comparativo entre calibração por manobra de isovolume e calibração qualitativa diagnóstica em voluntários saudáveis avaliados em diferentes posturas

“…(11) According to the authors, the contributions of the rib cages and abdomens of anesthetized children were insufficient to derive K. One of the findings of the present study was the contribution of the rib the gold standard method (ISOCAL), various studies have suggested the use of the QDC method. (11)(12)(13)(14) One of the major advantages of the QDC method is that it is easy to perform, given that, for QDC, individuals need only maintain baseline breathing for 5 min, and calibration is performed on the basis of the variation in the results obtained for each compartment. This method is questionable in view of the RIP calibration principle, i.e., variation in calibration because of volume shifts between the rib cage and abdomen.…”

“…(4,8,9) Although ISOCAL is considered the gold standard for RIP calibration, the vast majority of studies employ QDC because the method requires no specific respiratory maneuvers. (10)(11)(12)(13) We are unaware of any studies comparing the two methods of RIP calibration regarding the values of the constant K when different positions are employed. …”