Does the size of the ventilator tidal volume affect the incidence of post operative pneumonia?

After major abdominal or thoracic surgery, the patient may develop rapid shallow ventilation because of splinting, pain or heavy sedation. This may lead to the development of post operative atelectasis and pneumonia. Hence, it seems reasonable to expect that the administration of large tidal volumes (VT) during post operative mechanical ventilation will prevent or decrease the incidence of post operative pulmonary complications including that of pneumonia. Whether or not this is true is yet to be determined. Therefore, we performed the following prospective study. We hypothesized that large VT mechanical ventilation after major operations resulted in a lower incidence of post operative pneumonia.

Adults admitted to the surgical intensive care unit for post operative mechanical ventilation after major abdominal or thoracic surgery were placed on one of two VT regimens: 9 ml/kg (group 1) or 14 ml/kg up to a maximum of 1000 ml (group 2). Patients who were not placed on the correct VT regimen and those whose tidal volumes were changed during the study were excluded. Standard ICU monitoring was instituted. In addition, ventilator performance, peak inspiratory pressures, blood gases and daily chest X-rays were monitored. The incidence of post operative pneumonia was recorded. Results were analyzed by SPSS statistical software. Results: Forty-nine patients completed the study, 29 in group 1 and 20 in group 2. Their mean age was 52.7 years. There were 28 males and 21 females. Thirteen of 49 patients (26.5%) developed post operative pneumonia. A comparison of the two groups is shown below:

Conclusion

Post operative ventilation with large tidal volumes does not reduce the incidence of pneumonia.

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