Monitorización de los gases de la vía aérea en anestesia pediátrica. Presentación de un modelo experimental de medición endotraqueal de gases

Resumen

Introducción

Diseñamos una sonda endotraqueal para medir fracciones inspiradas y espiradas de los gases de la mezcla durante anestesia general pediátrica.

Objetivos

Comparar los gases analizados en el circuito, mediante monitorización intra y extratraqueal, y comprobar sus posibles diferencias.

Material y métodos

Pacientes de 7 a 12 años; ASA I; bajo anestesia inhalatoria en ventilación mecánica. Se analizan dentro y fuera de la tráquea, fracciones inspiradas (Fi) y espiradas (Fe) de O₂/N₂O/Sevoflurano; la relación Fe/Fi; presión arterial de CO₂ (PaCO₂); y end tidal CO₂ (E_TCO₂); mediante medición previa al tubo endotraqueal (TET) desde pedilite, y mediante sonda en tráquea, anterior a la carina y posterior al TET. Ambos dispositivos fueron conectados al mismo monitor. Se realizaron mediciones en inicio, 5’, 10’, 15’, 20’, 30’, 40’, 50’ y 60 minutos tras intubación, y de PaCO₂ en los mismos tiempos. Se compararon valores medios (T Student), coeficiente correlación de Pearson (r), y se determinaron modelos de regresión (ANOVA).

Resultados

Incluimos 71 pacientes. La diferencia media (DE) de E_TCO₂ fue 5(±3) mmHg superior para la medición endotraqueal (p < 0,005), casi coincidente (±1,3 mmHg) con la PaCO₂ (p ≤ 0,5). Los gradientes (DE) de Fi-Fe O₂/N₂O fueron 3 (±2) puntos superiores en la medición endotraqueal (p < 0,05). Sin embargo, sevoflurano presentó diferencia media extratraqueal superior 0,6 (±0,2) puntos (p < 0,05). Conforme avanza el tiempo anestésico, los gradientes Fi-Fe O₂/N₂O, se equiparan transcurridos 18 (±3) minutos, para sevoflurano esto sucede en 8 (±2) minutos.

Conclusiones

Las fracciones inspiradas y espiradas de los gases de la mezcla son distintos, según se realice la medición intra o extratraqueal.

Summary

Background

We designed an endotracheal probe for measuring inspired and expired gas fractions during pediatric general anesthesia.

Objective

To compare the gas fractions measured by means of intratracheal and extratracheal monitoring.

Material and methods

The study included ASA 1 patients between the ages of 7 and 12 years under inhaled anesthesia with mechanical ventilation. The following para-meters were recorded inside and outside the trachea: inspired and expired oxygen, nitric oxide (N₂O) and sevoflurane fractions; the expired and inspired fraction gradients; PaCO₂; and end-tidal carbon dioxide (ETCO2). Measurements were taken by an airflow sensor (Pedi-Lite) in the circuit before the point of connection to the endotracheal tube and by an intratracheal probe placed between the tube and the carina. Both sensors were connected to the same monitor. Measurements were taken on intubation and 5, 10, 15, 20, 30, 40, 50, and 60 minutes thereafter. PaCO₂ was recorded at the same time. The recorded values were analyzed using the t test and the Pearson product moment correlation coefficient (r), and regression models were constructed using analysis of variance.

Results

Seventy-one patients were enrolled in the study. The mean difference (SD) ETCO₂ was 5 (3) mm Hg higher according to endotracheal measurement (P < .005), and that measurement was almost identical (±1.3 mm Hg) to the PaCO₂ (P ≤ .5). The inspired/expired gradients of endotracheal measurement of oxygen and N₂O were 3 (2) points higher (P < .05) than the gradients of extratracheal measurements. In the case of sevoflurane gradients, however, the extratracheal values were higher (mean difference, 0.6 [0.2] points, P < .05). The inspired/expired oxygen and N₂O gradients became equal after 18 (3) minutes; the sevoflurane gradients became equal after 8 (2) minutes.

Conclusions

Intratracheal and extratracheal measurements of the inspired and expired fractions of mixed gases provide different results.