Isoflurane for resection of pheochromocytomas

The most proximal and accurate site for sampling end-tidal CO2 in infants

The most proximal site to sample end-tidal CO2 with reasonable accuracy in infants during pulmonary ventilation using a Mapleson D circuit remains controversial. The utilisation of high fresh gas flow near the site of gas sampling dilutes the expired gas and causes an underestimation of end-tidal CO2. In this study a laboratory model was used to identify, qualitatively and quantitatively, the most proximal site in the Mapleson D circuit where the measurement of end-tidal CO2 is not influenced by mixing with fresh gas. A fresh gas flow rate of between 2 and 15 L.min-1 with a respiratory rate of 20-30.min-1 and a tidal volume of 30-100 ml.min-1 was evaluated. This experiment was divided into two parts. Firstly, an infant lung model was used to visualize the site of mixing between fresh gas and smoke-labelled exhaled gas. Secondly, fresh gas flow and expired gas flow were controlled and the end-tidal CO2 concentration was measured along the length of the anaesthetic circuit to identify the site of mixing of fresh gas and expired gas during steady-state conditions. Three expired gas flows were studied at six fresh gas flows. In all our studies, the rate of fresh gas flow and expired gas flow influenced the site of mixing and degree of dilution but no mixing was observed distal to the point at which the endotracheal tube connector narrows to the diameter of the endotracheal tube (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Capnometry and the paediatric laryngeal mask airway

The laryngeal mask airway (LMA), an alternative to tracheal intubation in certain situations, has gained popularity in recent years. Initially 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 children, age one to five years and weighing between 10 and 25 kg undergoing minor surgery requiring mask anaesthesia. In each case, after induction of anaesthesia, the LMA was inserted under direct vision to eliminate the possibility of epiglottic airway obstruction. The fresh gas flow 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 and end-tidal gas concentrations were recorded. The measures of peak PETCO2 were taken at pre-determined distances from the elbow connector down 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 PaCO2 (P < 0.05). However, in eight patients PETCO2 values measured at the distal site were higher than the PaCO2 (negative P(a-ET)CO2 gradients).(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of end-tidal PCO2 measurements using a sidestream capnometer in infants and children ventilated with the Sechrist infant ventilator

To determine the accuracy of end-tidal PCO2 (PETCO2) measurements analyzed with a sidestream capnometer in infants and children whose lungs were ventilated with a Sechrist infant ventilator and an Ayre's t-piece, we compared PETCO2 measurements obtained from the proximal (PETCO2-p) and distal (PETCO2-d) ends of the tracheal tube to arterial PCO2 (PaCO2) in 37 healthy infants and children between 1.3 and 24.5 kg. Both PETCO2-p and PETCO2-d accurately approximated PaCO2, however, the mean (+/- SD) arterial to end-tidal PCO2 difference (delta(a-ET)PCO2) was significantly greater with proximal (1.27 +/- 1.54 mmHg) than with distal sampling (0.64 +/- 1.64 mmHg) (P less than 0.01). In the subgroup of patients who weighted less than 12 kg, the delta(a-ET)PCO2 using proximal gas sampling (1.94 +/- 1.29 mmHg) was also significantly greater than it was using distal sampling (0.74 +/- 1.31 mmHg) (P less than 0.001). We conclude that although statistically different, both proximal and distal estimates of PETCO2 provide acceptable estimates of PaCO2 in healthy infants and children who are ventilated with a Sechrist infant ventilator and an Ayre's t-piece system.

Single breath end-tidal CO2 estimates of arterial PCO2 in infants and children

To determine whether single breath end-tidal carbon dioxide (PE'CO2) measurements accurately estimate arterial PCO2 (PaCO2) in infants and children, 68 healthy infants and children, ASA physical status I or II scheduled for peripheral and lower abdominal surgery requiring endotracheal intubation were studied. A 3 ml single breath sample was obtained with a 23-gauge needle which was inserted through the wall of the endotracheal tube below the connector. The mean +/- SD PE'CO2 33.6 +/- 6.9 mmHg did not differ significantly from the corresponding mean +/- SD PaCO2 33.6 +/- 5.6 mmHg. The coefficient of determination, r2, was 0.97. The authors conclude that single breath PE'CO2 measurements from the proximal end of the endotracheal tube accurately estimate the PaCO2 in infants and children.

Vecuronium and phaeochromocytoma. A report of two cases using different modes of administration

Two patients presenting for removal of phaeochromocytoma are described. Vecuronium was used to provide neuromuscular blockade by two different methods of administration: an infusion and a large bolus dose. Both gave satisfactory results and we suggest that vecuronium may be the neuromuscular blocking agent of choice for patients with phaeochromocytoma.

Factors influencing capnography in the Bain circuit

The Bain circuit provides continuous fresh gas flow near the airway. The potential mixing of this fresh gas with expired gas may prevent reliable analysis of expired gas. We therefore investigated the interaction of sampling site, fresh gas flow rate, expiratory flow rate, and sampling flow rate on expiratory capnography. Sampling near the fresh gas outlet yielded inaccurate results under several of these conditions. The magnitude of the error was related to the fresh gas and expiratory flow rates. A reliable sampling region near the endotracheal tube was identified.