The Effect of Anaesthesia and Intermittent Positive Pressure Ventilation With Different Frequencieson the Anatomical and Alveolar Deadspace

Abstract

Deadspace was measured in nine healthy subjects in the supine position, premedicated but awake and breathing spontaneously at a rate of 12 b.p.m. and subsequently under anaesthesia with artificial ventilation with frequencies of 12 and 24 b.p.m. The minute volume was kept at a relatively constant value. The physiological deadspace was calculated using the Bohr equation and the division into anatomical and alveolar deadspace was made with the aid of capnography. Physiological deadspace was increased by anaesthesia and IPPV, mainly as a consequence of increased rebreathing in the apparatus deadspace. There was no significant change in the anatomical deadspace. Thus, the expected reduction in deadspace brought about by endotracheal intubation was nullified by an increase in the anatomical deadspace distal to the carina. The VDanat/VT ratio remained constant on changing the respiratory frequency. A significant alveolar deadspace was measured during spontaneous breathing. This was unchanged by the induction of anaesthesia and the institution of artifical ventilation. On changing the frequency, the VDalv/VT ratio remained constant. It is concluded that both the anatomical and the alveolar deadspaces increasing with increasing tidal volume, but are unaffected by the breathing rate.

Acute Effects of Intermittent Positive Pressure Breathing in Patients with Chronic Obstructive Lung Disease

“…The overall efficiency of ventilation was improved by IPPB, as judged by the ventilation volume required to reduce end-tidal nitrogen to 2%, and the distribution of inspired gas was more (21,23), while the effect of IPPB has, obviously, not been studied. Any change in FRC will also affect the demands on ventilation volumes.…”

Dead space during one-lung ventilation

“…These are valid and simple therapeutic options to control mild hypercapnia during OLV but their effect on the elimination of CO 2 is limited compared with the increase in alveolar ventilation brought about by increasing the respiratory rate. This is why dead space typically increases in response to increases in PEEP [29] (Fig. Figure 2c shows how adding an inspiratory pause of 35% to prolong inspiratory time (same tidal volume and a PEEP of 5 cmH 2 O during OLV) decreases dead space compared with a breath without such a pause (dotted line).…”

“…positive pressure ventilation and the other is related to the systematic increases in VD aw with age and pulmonary diseases such as chronic obstructive pulmonary disease [10,29,30]. This explains why during thoracic surgery in the lateral position VD aw may double when compared with healthy patients in the supine position ventilated through standard endotracheal tubes [15,28,31 && ] ( Table 1).…”

“…We believe that this tidal volume is still excessively high during OLV due to obvious anatomical and physiological reasons [32]. Data were taken during two-lung ventilation and one-lung ventilation, before and after a lung recruitment [29]. The gray row shows the baseline reference values of dead space and its components of healthy patients submitted to general anesthesia using standard endotracheal tubes and ventilator settings [15].…”

Capnography in the Intensive Care Unit

“…Elevated mean air- way pressure can result in wasted ventilation, or reductions in cardiac output, both of which may alter PETC02. It should be noted that anatomical and alveolar dead space increase with larger tidal vol-umes, and this could also decrease PETCOZ of mechanical breaths [90]. The following sections of this paper will review the uses of capnography during mechanical ventilation.…”