Wound Healing and Surgical Drains

The phases of wound healing

Wound healing is a continuous process conventionally divided into four overlapping phases. Knowing the timing matters clinically, because it explains when wounds are most vulnerable and when each complication tends to appear.

Modes of healing

• Primary intention - the edges are clean, apposed and closed with sutures, staples, glue or adhesive strips. There is minimal granulation tissue and a fine scar. Used for clean surgical incisions and clean lacerations.
• Secondary intention - the wound is left open and heals from the base upwards by granulation, contraction and re-epithelialisation. Slower, with a larger scar and more contraction, but appropriate where the wound is contaminated, infected, has tissue loss, or where closure would trap infection - for example a drained abscess cavity, a pilonidal sinus, or a laid-open fistula.
• Tertiary intention (delayed primary closure) - the wound is deliberately left open for a few days to allow inflammation to settle and any infection to declare itself, and is then closed surgically. Used for heavily contaminated traumatic wounds and after some emergency laparotomies.

What impairs healing

Local factors

• Infection - the commonest cause of delayed healing. Bacteria consume oxygen, prolong the inflammatory phase and degrade collagen.
• Ischaemia and hypoxia - peripheral arterial disease, pressure, tight sutures and haematoma all reduce perfusion. Collagen synthesis is oxygen-dependent, so a hypoxic wound cannot lay down matrix.
• Tension across the wound, which both impairs perfusion and mechanically disrupts the healing edge
• Haematoma or seroma, which separates the edges and is an excellent culture medium
• Foreign body, including non-absorbable suture material, prosthetic mesh and contaminated debris
• Previous radiotherapy, which produces endarteritis obliterans and permanently impairs the local blood supply
• Repeated trauma or movement, including across a joint
• Desiccation - a wound that dries out heals more slowly, which is the rationale for moist wound healing

Systemic factors

• Malnutrition - protein deficiency impairs collagen synthesis, vitamin C deficiency prevents hydroxylation of proline and lysine so collagen cannot cross-link (the mechanism of wound breakdown in scurvy), and zinc is a cofactor for numerous enzymes in the proliferative phase
• Diabetes mellitus - through microvascular disease, impaired neutrophil function, glycation of collagen and neuropathy
• Corticosteroids and immunosuppressants - suppress the inflammatory phase, reduce fibroblast proliferation and impair epithelialisation. Vitamin A can partially reverse the steroid effect.
• Smoking - nicotine causes vasoconstriction, carbon monoxide reduces oxygen delivery, and both impair fibroblast function
• Increasing age, with slower epithelialisation and reduced collagen synthesis
• Obesity, through poorly vascularised subcutaneous fat, increased tension and technical difficulty
• Anaemia and hypoxaemia, reducing oxygen delivery to the wound
• Jaundice, uraemia and malignancy
• Chemotherapy and radiotherapy
• Connective tissue disorders such as Ehlers-Danlos syndrome, and hypothyroidism

Abnormal scarring

Wound classification and surgical site infection

Preventing surgical site infection

NICE NG125 sets out measures across the whole pathway, and the important ones are unglamorous.¹

• Do not remove hair routinely; if it must be removed, use electric clippers with a single-use head on the day of surgery - razors increase infection risk
• Antibiotic prophylaxis at induction, timed so tissue concentrations are adequate at incision, for clean-contaminated and contaminated surgery and for clean surgery involving a prosthesis. A single dose is usually sufficient; prolonged post-operative prophylaxis does not reduce infection and drives resistance.
• Alcoholic chlorhexidine skin preparation, allowed to dry fully
• Maintain normothermia intraoperatively, with warmed fluids and forced-air warming
• Maintain adequate tissue oxygenation and perfusion
• Optimise glycaemic control
• Do not use topical antiseptics or antibiotics on the wound to prevent infection
• Cover the wound with an appropriate interactive dressing at the end of the operation, and use an aseptic non-touch technique for dressing changes

A surgical site infection typically presents on day 5 to 7 with erythema, warmth, tenderness, swelling and purulent discharge, sometimes with fever. Management is to open and drain the wound where there is pus, take a swab, debride devitalised tissue, pack the cavity and allow healing by secondary intention. Antibiotics are added for surrounding cellulitis or systemic upset, guided by culture, but they do not substitute for drainage.

Closure materials

• Absorbable sutures are broken down by hydrolysis or enzymatic degradation and do not need removal - polyglactin 910 (Vicryl) braided, poliglecaprone (Monocryl) monofilament, polydioxanone (PDS) monofilament with prolonged strength retention, and catgut, which is now largely obsolete
• Non-absorbable sutures retain strength indefinitely and are removed or left permanently - polypropylene (Prolene), nylon (Ethilon), silk and steel
• Monofilament sutures pass through tissue smoothly and harbour fewer bacteria, so they are preferred in contaminated fields; braided sutures handle and knot better but provide interstices in which organisms can shelter
• Staples are quick and are often used for skin and for bowel anastomoses
• Tissue adhesive (cyanoacrylate glue) and adhesive strips suit small, clean, low-tension wounds, particularly in children
• Mass closure of a laparotomy uses a continuous slowly absorbable monofilament suture with a suture length to wound length ratio of at least 4:1, and small bites of fascia, both of which reduce incisional hernia²

Leave sutures longer where healing is expected to be slow - in diabetes, on steroids, in the malnourished, in irradiated tissue and where there is tension.

Surgical drains

A drain removes fluid, blood, pus or air from a body cavity or wound. Its purpose is either therapeutic, evacuating an existing collection, or prophylactic, preventing one from accumulating and allowing early detection of a leak or bleed.

Indications and the argument against routine drains

• Therapeutic - drainage of an abscess, empyema, pneumothorax, haemothorax, or a large seroma
• Prophylactic - after operations where a collection is likely and would be harmful, or where early detection of a leak matters: axillary clearance and mastectomy, thyroidectomy, pancreatic and some hepatobiliary surgery, and after some anastomoses
• The evidence for routine prophylactic drainage is weak for many operations. Enhanced recovery programmes explicitly recommend avoiding routine drains after colorectal and many other procedures, because they cause pain, restrict mobilisation, prolong stay and do not reliably prevent or detect complications.⁴
• A drain does not compensate for inadequate haemostasis or a poor anastomosis. It is not an insurance policy.

Managing and removing a drain

• Document the type, site, whether it is on suction, and the volume and character of output every shift, and include the losses in the fluid balance
• A sudden change in the character of drainage is a clinical event - fresh blood suggests bleeding, bile suggests a biliary injury, faeculent or turbid fluid suggests an anastomotic leak, and lymphatic-looking milky fluid suggests a chyle leak
• A sudden stop in output may mean the problem has resolved, or that the drain has blocked or fallen out - do not assume the former
• Remove when the output falls below a threshold set by the operating surgeon, commonly around 25 to 50 mL in 24 hours, or when the purpose has been served
• Removal technique - explain the procedure, offer analgesia 30 minutes beforehand, cut any anchoring suture, ask the patient to breathe in and hold (or out and hold for a chest drain), withdraw in one smooth movement, and check that the tip is intact
• Chest drains have their own rules - never clamp a bubbling drain, keep the bottle below the level of the chest, and remove at the end of expiration or during a Valsalva manoeuvre with an immediate occlusive dressing
• Send the tip for culture only if infection is suspected, not routinely

Outcomes

Most surgical wounds heal without incident. Surgical site infection nonetheless remains one of the commonest healthcare-associated infections, affecting around 5% of patients undergoing surgery in the UK, and it accounts for a substantial share of readmissions, prolonged stays and re-operations. Almost all of the interventions that reduce it are cheap and procedural rather than technological.

The longer-term outcome that matters most for abdominal surgery is incisional hernia, which follows 10 to 20% of midline laparotomies and is more common after wound infection. Both are influenced by the same modifiable factors identified before the operation - smoking, obesity, malnutrition, diabetes and anaemia - which is why the pre-operative clinic, the theatre and the ward are all working on the same problem.

For drains, the direction of travel over the last two decades has been towards using fewer of them, for shorter periods, and only where there is a specific reason. The useful habit is to ask, on every ward round, what each drain is for and what would need to happen for it to come out. If neither question has a clear answer, the drain is probably doing more harm than good.