The laryngeal mask airway (LMA), an alternative to tracheal intubation
in certain situations, has gained popularity in recent years. Initial
ly designed for use in adults it has now become available in suitable
sizes for paediatric anaesthesia. The objectives of this study were to
identify the preferred site of sampling the end-tidal carbon dioxide
(PETCO2) with the LMA and to determine the accuracy of this recording
when compared with arterial CO2 (PaCO2). We studied 30 healthy childre
n, age one to five years and weighing between 10 and 25 kg undergoing
minor surgery requiring mask anaesthesia. In each case, after inductio
n of anaesthesia, the LMA was inserted under direct vision to eliminat
e the possibility of epiglottic air-way obstruction. The fresh gas flo
w was provided by a Jackson Rees modification of an Ayre's T-piece and
was determined according to the following formula: 3 X (1000 + (100 X
body weight)) LPM. Blood pressure, ECG, O2 saturation, temperature an
d end-tidal gas concentrations were recorded The measures of peak PETC
O2 were taken at pre-determined distances from the elbow connector dow
n the LMA shaft. During the sampling sequence an arterial blood sample
was taken for gas analysis. The PaCO2 was 63.5 +/- 9.3 mmHg (mean +/-
SD). At any given sampling site, mean PETCO2 values were less than Pa
CO2 (P < 0.05). However, in eight patients PETCO2 values measured at t
he distal site were higher than the PaCO2 (negative P(a-ET)CO2 gradien
ts). The results of this study suggest that when the LMA is used in ch
ildren undergoing minor surgery who are spontaneously breathing haloth
ane, the PETCO2 values obtained from different sites underestimate the
value of the PaCO2. The preferred site for measuring PETCO2 in these
children is the distal end of the shaft although this value is less th
an paCO2 (p < 0.05). In addition, use of the LMA does not prevent the
hyperrapnia associated with halothane anaesthesia in children breathin
g spontaneously