ISSN:
1432-055X
Keywords:
Schlüsselwörter: Narkosebeatmung, Säuglinge – Kuhnsystem – Kinderkreissystem – Transkutane PO2/PCO2-Messung
;
Key words: Anaesthesia, infants – Breathing systems – T-piece system, Paediatric circuit system – Ventilation modes – Face mask – Endotracheal tube – Transcutaneous PO2/PCO2
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Description / Table of Contents:
Abstract. Monitoring of ventilation in infants is difficult and often not very reliable. In this study, transcutaneous measurement of blood gas tensions was used to investigate the influence of four different modes of ventilation on oxygenation and ventilation in anaesthetized infants. Methods. In a randomised study, transcutaneously measured PO2 (tcPO2) and PCO2 (tcPCO2) tensions were continuously registered in 42 ASA class I and II infants between 3 and 24 weeks of age undergoing minor surgical procedures (inguinal hernia repair). Two breathing systems combined with different modes of ventilation were evaluated: manual ventilation with Kuhn's T-piece system and face mask (group A; n=11) or endotracheal tube (group B; n=10); manual ventilation with paediatric circuit system and face mask (group C; n=11); and mechanical ventilation with paediatric circle system, endotracheal tube, and positive end-expiratory pressure (PEEP) 3 cm H2O (group D; n=10). Transcutaneous values were measured by a combined tcPO2/PCO2 electrode (E 5277, Radiometer). Anaesthesia was maintained by controlled ventilation with N2O/O2 (67%/33%) and halothane 0.5 – 1.5 vol.%. Surgical and anaesthetic techniques were standardized and the anaesthetist was blinded to the measured values. Results. Preoperative mean tcPO2 values while spontaneously breathing air ranged between 69 and 75 mm Hg in all patients. During anaesthesia and controlled ventilation (FiO2=0.33), there was a significant increase in tcPO2 (P〈0.01) in 3 groups: in groups A and D mean tcPO2 increased to 90 – 100 mm Hg and in group C to 110 – 120 mm Hg. In contrast, tcPO2 in group B reached only 75 – 80 mm Hg, which was not considered significant. Postoperatively, tcPO2 immediately reached baseline values in all patients (Fig. 2). Compared to preoperative values, the alveolar-tcPO2 difference (AtcDO2) significantly increased during anaesthesia in all groups (Fig. 3). The tcPCO2 measurements revealed marked alveolar dysventilation, with hyperventilation supervening in groups A, B, and D; in group C, however, most (7 of 11) infants were normoventilated (Fig. 4). Conclusions. Adverse effects of anaesthesia on pulmonary function in infants are caused by loss of the PEEP effect induced by the physiological subglottic stenosis. Endotracheal intubation and the increase in chest wall compliance during anaesthesia lead to a decrease in functional residual capacity (FRC) associated with premature airway closure and ventilation/perfusion mismatch. These pathophysiological disturbances result in a marked increase in AaDO2 and low arterial PO2 values despite high FiO2, as could be observed when intubated infants had been ventilated with a high-flow T-piece system (group B). Mechanical ventilation with a paediatric circuit system and endotracheal tube allows the use of low PEEP levels (group D), which may replace the lost subglottic function and partially restore the FRC. Ventilation by mask does not disturb the functional subglottic stenosis, and the impairment of pulmonary function will depend solely on the decrease in FRC caused by increased chest wall compliance (group A). If mask ventilation is combined with a paediatric circuit system (group C), the pressure relief valve produces a low PEEP of 2 to 3 cm H2O, which may partially counteract the decrease in FRC. With regard to oxygenation, the paediatric circle system proved to be superior to the high-flow T-piece system independent of whether children were ventilated via a face mask or an endotracheal tube. The group-specific differences in degree of dysventilation with manual ventilation show that the type of breathing system is important with regard to the size of the tidal volume delivered. Thus, tidal volumes will be unintentionally increased by the high fresh gas flow needed when a T-piece system is used. The lower flow and preadjusted pressure limit may prevent the delivery of excessive tidal volumes with the paediatric circuit system. The high incidence of dysventilation with mechanically controlled ventilation might be caused by the limited applicability of ventilation nomograms during anaesthesia for this age group.
Notes:
Zusammenfassung. In einer randomisierten Studie wurden bei 42 Säuglingen im Alter von 3 – 24 Wochen die transkutanen PO2(tcPO2)- und PCO2(tcPCO2)-Werte während kurzer operativer Eingriffe kontinuierlich registriert, wobei unterschiedliche Narkosebeatmungsverfahren zum Einsatz kamen: KUHN-System mit Maske (Gruppe A; n=11), KUHN-System mit Endotrachealtubus (Gruppe B; n=10), Kinderkreissystem mit Maske (Gruppe C; n=11); Kinderkreissystem mit Respirator (Gruppe D; n=10). Es wurde eine Inhalationsanästhesie mit 0,5 – 1,5 Vol% Halothan in N2O/O2 (67/33%) durchgeführt und kontrolliert beatmet. Narkoseverfahren und Rahmenbedingungen waren standardisiert und der ausführende Anästhesist konnte die Meßwerte nicht einsehen. Präoperativ lag der tcPO2 bei Raumluftatmung in allen Gruppen zwischen 69 – 75 mm Hg. Während Narkosebeatmung kam es in den Gruppen A, C und D zu einem signifikanten (p〈0,01) Anstieg des tcPO2 auf 90 bis 120 mm Hg, in Gruppe B ergab sich eine nur geringe, nicht signifikante Zunahme auf 75 – 80 mm Hg. Nach Narkoseende wurden in allen Gruppen wieder die Ausgangswerte erreicht. Allgemein kam es zu einer signifikanten Zunahme der alveolotranskutanen Sauerstoffdruckdifferenz (AtcDO2) während Anästhesie. Die Ergebnisse zeigen, daß die Art des Narkosebeatmungsverfahrens die Oxygenierung unterschiedlich beeinflußt, wobei das Kinderkreissystem dem Spülgassystem überlegen ist. Die tcPCO2-Messung erbrachte eine erhebliche alveoläre Dysventilation, wobei die Hyperventilation überwog. Die gruppenspezifischen Unterschiede im Grad der Dysventilation weisen darauf hin, daß die Art des Narkosesystems eine wesentliche Rolle bei der Generierung des Atemhubvolumens spielt.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s001010050086
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