[Aventilatory mass flow during apnea : investigations on quantification].

BACKGROUND: Aventilatory mass flow (AVMF) is routinely used for apneic oxygenation in various clinical procedures but no data exist to quantitatively describe the gas flow. This study was designed to determine the amount of AVMF during the clinical situation of apnea to force spontaneous respiration at the end of anaesthesia with controlled ventilation.

MATERIALS AND METHODS: A total of 200 patients undergoing anesthesia for routine surgery were examined. AVMF was analyzed with a high resolution, low gas stream, thermal mass flow analyzer. The intended recording time was 3 min.

RESULTS: Measurement was reliably successful and suitable for evaluation in only 23 patients. AVMF-induced gas flow started on average 17.9 + or - 9.4 s after onset of apnea. Maximum flow was reached within 158 + or - 20 s and determined to be 135 + or - 32 ml/min. The slope of increase of gas flow showed a rapid oscillation corresponding to the heart rate in all patients and in 14 out of 23 patients a slow oscillation with a frequency of 8.9 + or - 1.8/min.

CONCLUSIONS: During apnea AVMF develops in a non-linear fashion. The maximum flow observed is closely related to the estimated oxygen consumption. Heart rate synchronous flow variations are probably caused by intrathoracic volume variations due to heart action. The low frequency oscillations correspond to the frequency of Traube-Hering-Mayer waves.