The evidence for connecting low‐pressure thoracic suction to an underwater‐seal chest‐drain bottle to assist in the management of a pneumothorax is controversial, despite the widespread use of this technique in clinical practice (Havelock et al. [103]). While 70% of pneumothoraces resolve within 3 days after chest drain insertion, up to 30% continue to have an ongoing air leak. Thoracic suction may be indicated for this group of patients (Tschopp et al. [275]).

If indicated, appropriately trained staff should set up the system and advice should be sought from a specialist if required. The addition of suction to the drainage system increases the negative pressure, enhancing lung re‐expansion. A high‐volume, low‐pressure thoracic suction unit (Figure 12.31) should be applied to a single‐chamber chest‐drain bottle, using pressure in the range of 10–20 cmH₂O (1–2 kPa) (Havelock et al. [103], Zisis et al. [295]). Suction should be applied and the pressure increased gradually to prevent lung tear (George and Papagiannopoulos [88]).

When the tubing is attached to the suction port of the chest drain bottle, the suction must remain on at all times. However, the suction tubing can be disconnected from the port to allow the patient to mobilize away from the bed space. Once suction has been discontinued, the tubing must be disconnected from the port before the suction is turned off. Turning off the suction and leaving the tubing attached to the port of the underwater‐seal chest‐drain bottle could potentially cause a tension pneumothorax (Havelock et al. [103]).

Most suction units are fitted with a disposable air filter capsule between the vacuum connector and the filter capsule mount. The filter prevents cross‐infection and should be changed after use in each patient. Direct connection between the chest drain bottle and the high‐flow, low‐pressure suction unit without an intermediate suction jar or canister can lead to patient injury, loss of effective suction, and contamination of the hospital vacuum system, posing an infection control risk. An intermediate suction canister must therefore be attached between the thoracic suction unit and the underwater‐seal chest‐drain bottle to prevent contamination of the thoracic suction unit filter (MHRA [158]) (Figure 12.32).

While ambulatory chest drainage bags with a built‐in Heimlich valve cannot be attached to suction, ambulatory digital chest drainage systems monitor the negative pressure within the thoracic space and adjust the suction pressure accordingly. Multi‐chamber chest drain bottles have a built‐in suction control compartment that is controlled by either an underwater seal or external suction. The manufacturer's instructions must be followed.