The patient developed VAP during deep sedation, following ventilation, to allow recovery for 48 h after surgery. The patient’s oxygenation also decreased. Thus, we used the iASV mode as there was a shortage of manpower in the hospital. Antibiotic treatment was effective, and the respiratory condition of the patient improved.
Amato et al. reported improvement of outcomes using low tidal volume ventilation (LTVV) ; therefore, the importance of limiting the tidal volume (VT), as a lung protective strategy, has been emphasized. Several randomized control trials on LTVV have been conducted to date. In a systematic review of these reports, the safety of LTVV and the risk of an excessive plateau pressure have been pointed out [6, 7].
The Berlin definition , which was announced as an alternative to the definition of acute respiratory distress syndrome (ARDS) set out by the American–European Consensus Conference and used since 1992, includes the evaluation of oxygenation performance by adding a certain PEEP load to the diagnostic criteria, suggesting the importance of an appropriate PEEP load. Bellani et al.  investigated the real-life practice of treating ARDS in an ICU in 459 countries across 5 continents using the Berlin definition. In total, 2377 patients were diagnosed with ARDS within 48 h and were intubated; however, in one-third of these cases, a ventilation limit of VT < 8 ml/kg was not used, and the plateau pressure measurement remained at 40.1%. In addition, PEEP was set at less than 12 cm H2O in 82.6% of cases; the PEEP setting did not reach this level, even with inhalation of a high concentration of oxygen. Therefore, ARDS patients were not considered to have received adequate ventilation. Furthermore, Bellani et al. also predicted a shortage of medical staff to cope with the increase in ventilation patients , and thus, that it would become challenging to ensure appropriate ventilation management on a continuous basis.
It has been reported that iASV can facilitate more appropriate ventilation management  than that which is achieved with the conventional facility protocol, without burdening the medical personnel . The closed-loop mechanism of the iASV reduces the work of medical staff, and thus, it is expected that this treatment will become a standard of treatment. Additionally, iASV can improve oxygenation capacity while maintaining lung protective ventilation  comparable to conventional management. The protocols proposed in the ARMA study  and the ALVEOLI study  were incorporated in the closed-loop setting algorithms related to oxygenation by the INTELLiVENT (i.e., implementation of FiO2 and PEEP settings), based on an open lung strategy, in the presented case.
To date, no report has detailed the progression of automatically changing the ventilation settings in iASV for patients who developed VAP during the observation period, as in our case. In this case, we noted that FiO2 and PEEP gradually increased while the oxygenation capacity declined; there was a predominant decline in FiO2 after recovery of oxygenation capacity and that PEEP gradually decreased after FiO2 reached 0.3. During this period, the tidal volume could be limited to 8–10 ml kg, and the plateau pressure could be limited to 15 cm H2O or less. In this case, PEEP increased automatically to up to 14 cm H2O, but in cases of sepsis from VAP and further septic shock, an automatic increment in PEEP leads to significant circulatory suppression, possibly due to impaired venous return.
iASV has a feedback mechanism that evaluates circulatory dynamics from respiratory fluctuation of a pulse oximeter waveform called the heart lung index (HLI), and the PEEP was changed automatically by the ventilator. This safety mechanism did not operate in our case because of change in the circulation dynamics. In this case, it is possible that fluctuation in the circulation dynamics due to the sepsis accompanying VAP and duplication of the circulating blood volume by transfusion after the surgery functioned synergistically to maintain the cardiac function. This may have prevented circulation suppression due to the increase in PEEP.
The use of iASV has certain limitations. It is unknown whether iASV can always be used in all patients with VAP or whether the HLI is effective. In iASV, we checked arterial blood gas analysis as previously mentioned, and continuous observation of respiration and circulation remains necessary. Furthermore, iASV automatically increases the set values of FiO2 and PEEP when the oxygen levels are low, which may delay the awareness of ventilator-associated events by the medical staff; therefore, warning alerts at this stage and improvement of the display function may be necessary.
In summary, we experienced a case in which the use of iASV was effective following the onset of VAP after surgery. While the closed-loop mechanism of iASV may contribute to the implementation of a lung protective strategy and reduce the labor of medical staff, it still needs improvement. Furthermore, when using iASV, it is also important to understand the mode of ventilation and to observe respiration and circulation conventionally.