Modern narcotic devices provide to the anesthesiologist a wide choice of the IVL various modes, unlike earlier models where all range of the modes was most often provided one and only – ventilation with control on volume. The choice of the correct mode during an operative measure is very important for ventilation of the patient as it in addition to convenience to the anesthesiologist has considerable influence on the frequency of postoperative complications. In this article we will consistently sort all main modes of ventilation provided in modern narcotic devices and we will make recommendations about the choice of each of them.
Carrying out the general anesthesia begins, as a rule, with the patient's preoksigenation. At the same time the APL valve is opened and use a stream of 100% of oxygen which has to be more minute ventilation of the patient. For example, the stream of oxygen of 7 l/min is sufficient for the patient's preoksigenation with minute ventilation of 5.5 l/min. Duration of a preoksigenation is 3–5 minutes and is estimated on an oxygen concentration indicator on an exhalation – it has to become more than 70% or be stabilized. Further carry out induction, in process of backfilling of the patient close the APL valve and switch over to the mode manual IVL by means of a respiratory bag and a front mask. It is not recommended to close the APL valve on values more than 20 cm w.g. (at adult patients) as it can lead to disclosure of an esophageal sphincter and inflating of a stomach. After an intubation of the patient or installation of a laryngeal mask provisions of an endotracheal tube (a laryngeal mask) and only exercise kapnografichesky and auskultativny control then pass to automatic IVL.
The ventilation mode with control on the volume (VCV) is the most traditional for use. Its pluses are that the established minute volume of ventilation is guaranteed to the patient. Minuses of this mode are also essential as the safe value of peak pressure on a breath is not guaranteed. Nevertheless, this mode is very well familiar to most of anesthesiologists in view of what it is used most often at the intubated patients. Also this mode is recommended in thoracic surgery when the thorax of the patient is open and use of the modes with control on pressure is capable to lead to reinflating of lungs.
The ventilation mode with control on pressure (PCV) unfairly finds considerably smaller application, especially for us in the country. At the same time, it allows to control more precisely peak pressure on a breath, is more physiologic and safe. There are many works confirming that PCV is more preferable at patients with the increased body weight as it allows to achieve the same minute volume of ventilation at much smaller figures of peak pressure on a breath, in comparison with ventilation with control on volume. The mode is also good the fact that it allows to notice quickly decline in quality of a muscular relaxation, a thorax compression, obstruction of respiratory tracts and other troubles.
The modes of the alternating compulsory ventilation with control on pressure or on the volume (SIMV and PSIMV) are preferable at preservation at the patient of spontaneous ventilation in a varying degree, for example, when using a laryngeal mask. They allow the patient to breathe in intervals between compulsory breaths. Support of independent breaths of the patient can be solved connection of an option support by pressure (PSV) or supports by the volume (VSV).
Support of independent breath by pressure or volume (PSV and VSV) as the separate modes, are applied at preservation or restoration of spontaneous breath at the patient. Are often applied when using a laryngeal mask and also at an anesthesia termination stage. It is group of purely auxiliary modes which will work only in case of preservation for the patient of spontaneous breath of adequate frequency. The SPONT mode when completely spontaneous breath of the patient can be supported by pressure also also belongs to group of the auxiliary modes.
In conclusion it is necessary to tell several words about use during operation of function of positive pressure at the end of an exhalation (PEEP), than often unreasonably neglect. This option is in all modern narcotic devices, and in some of them certain basic PEEP cannot be disconnected. Use of positive pressure at the end of an exhalation allows to prevent development of postoperative atelectases and also to avoid considerable decrease in functional residual capacity of lungs at laparoscopic interventions. Basic PEEP values at adults – 3-5 cm w.g., and if necessary this parameter can reach 10 cm w.g. and more.