Impedance pneumograph and magnetometer methods for monitoring tidal volume.

The vexatious vital: Neither clinical measurements by nurses nor an electronic monitor provides accurate measurements of respiratory rate in triage

“…There is a long list of proposed alternatives: capnography by mask, nasal prongs, or mouthpiece [30][31][32] ; pneumotachography (direct flow measurement) by mask or mouthpiece 33,34 ; acoustic monitoring by nasal microphones 30,35 ; nasal thermistors (temperature) 18,34,36 ; fiberoptic nasal sensors that gauge condensation during exhalation 30,37,38 ; inductive plethysmography, which measures chest wall and abdominal movement by bands encircling the trunk (extensometry) 26,33 ; single-compartment and multicompartment air mattresses that measure and compare chest and abdominal volumes [39][40][41] ; mask-mounted pyroelectric polymer strips, which detect temperature variations 32,42 ; transdermal fiberoptic photoplethysmography 30,43,44 ; and transthoracic impedance plethysmography. 13,18,26,30,32,37,[45][46][47] All of the above-mentioned modalities have been reported to correlate well with ''criterion standard'' clinical measurement of respiratory rate. We chose to use transthoracic impedance plethysmography in this study because it is noninvasive and can be applied quickly in triage, with minimal removal of attire.…”

“…Transthoracic impedance plethysmography suffers from artifact, as seen in shivering, tremors, talking, crying, and agitation and with other movement. There is also potential for transthoracic impedance plethysmography to produce higher respiratory rate measure- Despite these potential drawbacks, many investigators 13,18,26,30,32,37,[45][46][47] have reported that transthoracic impedance plethysmography correlates well with reference standard clinical measurement of respiratory rate. However, these studies were performed on subjects who were lying down at rest for prolonged periods.…”

Critical review of non-invasive respiratory monitoring in medical care

“…Although transthoracic impedance is believed to be more strongly influenced by the air filling the lungs than actual volume variations (BROWN et al, 1999b), tidal volume determinations from impedance measurements can differ from those obtained using spirometry by more than 100ml (ASHUTOSH et al, 1974).…”

“…For calibration, a co-operative patient is necessary, which excludes many clinical situations. Other problems are sensitivity to body movements and positional changes (ASHUTOSH et al, 1974;ERIKSSON et al, 1986;NAKAJIMA et al, 1996).…”

Ventilation.

“…Other factors such as pulmonary blood volume and lung water also affect thoracic impedance but these do not show regular oscillations in time with breathing and the ventilatory signal can be recognized easily. Although changes in impedance can be calibrated against tidal volume measured spirometrically at the mouth the method is difficult to use quantitatively since changes in posture and chest wall configuration may cause large changes in impedance (Ashutosh, Gilbert, Auchincloss, Erlebacher & Peppi, 1974). Thus although the method has the advantage of being 'non-invasive', it has proved disappointing in terms of quantitative long term monitoring of ventilation, though like the thermistor it can give a good guide to ventilatory frequency and timing.…”