Consensus is less defined regarding chest tube utilization, tube size selection, and the role of PDUs in nonspontaneous pneumothoraces, but some evidence provides direction.
Key to the selection of a PDC and a PDU in the setting of both spontaneous and nonspontaneous pneumothoraces is the maximal air flow (the volume of air per unit of time) each device accommodates particularly if an air leak (bronchopleural fistula) persists. Gases leaked by a bronchopleural fistula are moist with turbulent flow characteristics. The Fanning equation determines the flow of moist gas with turbulent flow characteristics through a PDC (v = ^2rP/fl; v = flow, r = radius, l = length, P = pressure, f = friction factor). Obviously, the critical factor in chest tube selection is the internal diameter (bore) of the tube and, less so, the tube length. Air flow may be compromised by the presence of viscous fluids such as blood. When considering air drainage alone, tube selection must account not only for removal of existing pleural air, but also the ongoing removal of additional air produced (bronchopleural fistula) and the rate of that air production. Patients with bronchopleural fistulae in the setting of chest trauma, thoracotomy, and ARDS may have air leaks ranging from < 1 L/min up to 16 L/min.
Conceivably, patients with spontaneous pneumothoraces, especially those requiring mechanical ventilation, may also have large air leaks. Practical experience indicates that 16 L/min is not a fixed upper limit for air leak volume, with larger leaks possibly occurring in any patient receiving mechanical ventilation with a persistent bronchopleural fistula. The majority of the minute ventilation in an intubated patient receiving mechanical ventilation can exit a large bronchopleural fistula. This may be the case in a postpneumonectomy stump dehiscence.