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...

There is increasing interest in the use of cuffed paediatric tracheal tubes, these tubes have a number of advantages and disadvantages. One disadvantage is the decreased margin of safety associated with the use of cuffed tracheal tubes. When using an uncuffed tube, the margin of safety is approximately the length of the trachea, however, for a cuffed tube, this margin is reduced and is the length of the trachea minus the distance between the proximal edge of the cuff and the and the tip of the tube. We have found that, compared with traditional uncuffed tubes, cuffed tubes may be associated with a reduced margin of safety of approximately 50% or more.

We compared the systemic absorption of ropivacaine (0.2%) and bupivacaine (0.2%) after caudal epidural injection of 2 mg/kg in children aged 1-7 yr. Our results show that ropivacaine undergoes slower systemic absorption from the caudal epidural space in children than does bupivacaine.

We have compared the haemodynamic responses to i.v. propofol 2.5 mg kg-1 with those to thiopentone 5.0 mg kg-1 in 41 healthy Chinese children at induction of anaesthesia. They were allocated to four groups according to their age and induction agent received: group 1 < 2 yr, propofol, n = 9; group II < 2 yr, thiopentone, n = 9; group III 2-12 yr, propofol, n = 12; group IV 2-12 yr, thiopentone, n = 11. Anaesthesia was maintained by spontaneous ventilation with 70% nitrous oxide and 0.5% halothane in oxygen. Arterial pressure and heart rate were monitored by automatic oscillotonometer. Stroke volume was measured by two-dimensional echocardiography and pulse Doppler. Measurements were made before induction and at 1-min intervals for 5 min after induction. The reduction in mean arterial pressure was significantly greater after propofol (28-31%) than after thiopentone (14-21%) (P = 0.001). The reduction in cardiac index (10-15%) after induction was not significantly different between the two agents (P = 0.122). Baroreflex mediated increases in heart rate and systemic vascular resistance were less after propofol than after thiopentone. The baroreceptor reflex was more attenuated in children aged less than 2 yr than in older children.