The CO 2 production is therefore low and minute ventilation around 100 ml/kg/min PBW as shown by Radford in 1955, is still adequate. In the operating room for planned surgery, the patient’s metabolism is usually low, and the body temperature is frequently below or equal to 36☌. The targeted minute ventilations are very different as well as tidal volume and respiratory rate based on the category of patients. Usual respiratory rates and tidal volumes are represented for surgical patients (planned surgery and one lung surgery with protective ventilation) and critically ill patients (non ARDS, ARDS with protective and ultraprotective ventilation, and CARDS (COVID-19 ARDS) patients). These are two different worlds in terms of patient’s needs.įigure 1: This figure is a schematic representation of the findings based on the analysis of more than 30 studies providing respiratory rate and tidal volumes in different settings (ICU and OR) for more than 40,000 patients. Ventilator settings in the operating room or in critically ill patients (in the emergency department and in the ICU) are very different, leading to minute ventilation around 100 ml/kg/min PBW in the operating room (OR) and at least 150 ml/kg/min PBW in critically ill patients. The dots represent isopleth curves illustrating the levels of 100 and 150 ml/kg/min PBW of minute ventilation. We show on Figure 1 the values of minute ventilation, tidal volume and respiratory rate (when available) in several studies conducted in patients managed in the operating room (9 studies) and in critically ill patients in the ICU (25 studies). We have developed a free educational SmartPhone application, VentilO, to facilitate the initial settings of protective mechanical ventilation. A classical recommendation for minute ventilation is 100 ml/kg/min PBW (for instance used to set the ASV mode and recommended since 1955)= in order to get a reasonable level of PaCO 2, it is not appropriate for most critically ill patients. This may be more a habit or intuitions and by experience: RR is set around 10 in the operating room, around 20 in newly intubated critically ill patients, and sometimes increased to 25 or 30 in ARDS patients. However, there is no clear recommendation and clues for the initial setting of the respiratory rate and therefore minute ventilation. It is easy to provide charts for the tidal volume based on gender and height and predicted body weight (PBW). We will also discuss the impact of these settings for the specific situation of COVID-19 patients. However, protective ventilation does not just mean tidal volume reduction and we would like to focus here on the respiratory rate and the instrumental dead space.īased on the recently published paper “Impact of Respiratory Rate and Dead Space in the Current Era of Lung Protective Mechanical Ventilation”, we will discuss here how to set the initial respiratory rate in mechanically ventilated patients and the determinants of alveolar ventilation (CO 2 elimination) other than tidal volume: the respiratory rate will be discussed in part 1 and dead space in part 2 (published next week). Protective mechanical ventilation should be implemented after intubation in ARDS and in non ARDS patients, and in COVID-19 patients with pneumonia.
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