Abstract
The purpose of this study was to extend previous observations of a greater decrease in tidal volume in infants than in children during halothane anaesthesia. We analyzed the inspiratory flow waveform recorded during spontaneous ventilation in: infants, two to six months of age, and children, one to five years of age. In addition we analyzed the CO2 signal and the pressure waveform during an occluded inspiration. The pressure generated during the initial 100 msec of inspiratory occlusion, an index of respiratory drive, was analyzed to give some insight into the aetiology of the age-related differences. In 15 infants and 15 children, Flow (V), pressure (Pao) and PCO2 were recorded at three concentrations of inspired halothane (FiH): 0%, 1% and 2% which correspond to an endtidal halothane concentration of about 0.3%, 0.9% and 1.3% respectively. Data were analyzed for minute ventilation (Vi) and parameters of timing (Total time (Ttot), Inspiratory time (Ti)), the amplitude of the neural output (mean inspiratory flow (Vt/Ti), tidal volume (Vt)) and the shape of the inspiratory breath profile (the inspiratory centroid flow (Ci/ Ti), the inspiratory duty cycle (Til Ttot)). In some, the airway was occluded at end expiration and the slope of the initial 100 msec of occlusion (dP/dt) together with the maximal negative pressure (PMAX) were measured. Estimates of respiratory mechanics E’rs (PMAX/ Vt) and (Vt/Ti)/(dP/dt) were obtained. The Vt and Ttot decreased with increasing FiH in both infants and children (P < 0.05). The PetCO2 increased in both groups and the % increase was greater in infants. The parameters of breath shape were unchanged. Infants experienced a decrease in Vi as FiH increased (P < 0.01). In children the parameters of breath amplitude Vt/ Ti and dP/dt did not change with halothane administration but, in infants, Vt/ Ti and dP/dt showed opposite dependencies on FiH; VT/Ti decreased whereas the dP/dt increased with increasing FiH. The E’rs was higher in infants (P < 0.05). The (Vt/Ti)/(dP/dt) decreased as FiH increased in infants (P < 0.05). We conclude that there are age-related changes in the ventilatory response to halothane.
Résumé
Cette étude vise à parachever des observations précédentes selon lesquelles, sous anesthésie à l’halothane, le volume courant du nourrisson diminue plus que celui de l’enfant. Nous avons analysé la forme d’onde du débit inspiratoire enregistrée pendant la respiration spontanée chez des nourrissons âgées de deux à six mois et chez des enfants âgés d’un à cinq ans. En outre, nous avons analysé le tracé du CO2 et la forme de d’onde de la pression pendant l’occlusion des voies respiratoires en inspiration. La pression générée pendant 100 msec d’occlusion représentant un index de l’effort respiratoire, a été analysée dans le but d’obtenir un aperçu de l’étiologie de la variation causée par l’âge. Chez 15 nourrissons et 15 enfants, le débit V, la pression (Pao) et la PCO2 sont enregistrés à trois différentes concentrations d’halothane inspiré (FiH): 0%, 1% et 2%, correspondant respectivement à une concentration téléexpiratoire d’halothane d’environ 0,3%, 0,9% et 1,3%. Sont mesurés la ventilation minute (Vi), les paramètres temporels (durée totale (Ttot), durée inspiratoire (Ti)), l’amplitude de la décharge neuronale (débit inspiratoire moyen (Vt/Ti), le volume courant (Vt)) et la forme du profil inspiratoire (le débit moyen centroïde (Ci/ Ti), le cycle inspiratoire (Ti/ Ttot)). Chez certains, les voies aériennes sont occluses en fin d’expiration et la courbe des 100 msec initiales qui suivent l’occlusion (dP/dt) de même que la pression négative maximale (PMAX) sont mesurées. On évalue la mécanique par l’élastance du système respiratoire (E’rs) avec le rapport (PMAX/Vt) et son efficacité par le (Vt/Ti)/(dP/ dt). Le Vt et le Ttot diminuent avec l’augmentation de la FiH tant chez les nourrissons que chez les enfants (P < 0,05). La PetCO2 augmente dans les deux groupes mais cette augmentation est plus importante chez les nourrissons. Les paramètres de la courbe respiratoire sont inchangés. Les nourrissons subissent une baisse de Vi avec l’augmentation de la FiH (P < 0,01). Chez les enfants les paramètres de l’amplitude Vt/ Tét le dP/dt ne changent pas avec l’administration de l’halothane, mais chez les nourrissons, le Vt/ Ti et le dP/dt ont une dépendance à la FiH opposée. L’E’rs est plus élevée chez les nourrissons (P < 0,05). Le (Vt/Ti)/(dP/dt) diminue chez le nourrisson avec l’augmentation de la FiH (P < 0,05). Nous concluons qu’il existe, sous halothane, des changements de la réponse ventilatoire en relation avec l’âge.
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Brown, K.A., Reich, O. & Bates, J.H.T. Ventilatory depression by halothane in infants and children. Can J Anaesth 42, 588–596 (1995). https://doi.org/10.1007/BF03011875
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DOI: https://doi.org/10.1007/BF03011875