85 LINES

# 86 LINES

Vascular access and drainage tubes are bread-and-butter surgical skills — and high-yield exam material. The MRCS Part A loves to test whether you can match the right line to the right clinical scenario, recognise classical complications, and reason about flow physics. This lesson walks through every line you are likely to meet on the wards and in the SBA paper.

Detailed notes

Peripheral venous cannulae

A peripheral venous cannula (PVC) is the default route for short-term IV access. Cannulae are colour-coded by gauge — and the trap that catches candidates every year is that a higher gauge number means a smaller bore.

Colour	Gauge	Approx flow (ml/min)	Typical use
Blue	22G	36	Paediatrics, fragile elderly veins
Pink	20G	60	Standard fluids, antibiotics
Green	18G	90	Blood transfusion (minimum)
White	17G	145	Major resuscitation
Grey	16G	200	Trauma, major haemorrhage
Orange (Brown)	14G	270+	Fastest — massive transfusion, trauma

Flow rate obeys the Hagen–Poiseuille equation:

> Flow ∝ (radius)⁴ / length × pressure / viscosity

The two practical consequences a candidate must internalise:

- Doubling the radius increases flow 16-fold — bore is everything in resuscitation. A short, wide grey cannula in the antecubital fossa beats any central line for speed of volume delivery.

- Length matters inversely — this is why a short fat peripheral cannula resuscitates faster than a long triple-lumen central line, despite the central line "looking bigger."

👩‍⚕️ Classic SBA trap: a shocked trauma patient needs the biggest, shortest line you can get — two grey or orange peripheral cannulae, not a central line.

Central venous catheter (CVC)

A CVC is a long catheter whose tip sits in the superior vena cava (or SVC–RA junction, ideally at the level of the carina on CXR). It is not a resuscitation line — its lumens are narrow and long, so flow is slow.

Indications:

- ➡ Vasopressors and inotropes (extravasation of noradrenaline peripherally causes necrosis)

- ➡ Hypertonic fluids or TPN (high osmolality damages peripheral veins)

- ➡ Repeated blood sampling and ABGs

- ➡ Failed peripheral access

- ➡ Central venous pressure (CVP) monitoring

- ➡ Renal replacement therapy or plasmapheresis (with appropriate large-bore dialysis catheter)

Sites:

Site	Pros	Cons
Internal jugular (right preferred)	Ultrasound-friendly, straight course to SVC, compressible	Uncomfortable for awake patients, near carotid
Subclavian	Lowest infection rate, comfortable for long use	Highest pneumothorax risk; non-compressible if arterial puncture
Femoral	Easiest in cardiac arrest (away from chest compressions)	Highest infection and DVT rates

The right internal jugular is preferred for elective insertion because the vein runs a straight, vertical course to the SVC and there is no thoracic duct to injure (unlike the left).

Technique — Seldinger:

1. Needle into vein under ultrasound guidance

2. Guidewire passed through the needle

3. Needle removed, dilator railroaded over wire

4. Catheter railroaded over wire

5. Wire removed, lumens aspirated and flushed

6. CXR to confirm tip position and exclude pneumothorax

Complications (a frequent SBA target):

- Arterial puncture (carotid, subclavian, femoral)

- Pneumothorax — especially subclavian; always get a CXR

- Haemothorax, chylothorax (left-sided — thoracic duct)

- Air embolism (keep patient head-down during IJ insertion)

- CLABSI (central line-associated bloodstream infection)

- Catheter-related thrombosis

- Dysrhythmias during guidewire passage — the wire irritates the right atrium; withdraw a few centimetres

- Malposition (azygos vein, contralateral subclavian, looping back)

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Arterial line

An arterial line provides continuous beat-to-beat blood pressure monitoring and a port for frequent ABGs. It is not used for drug or fluid administration — intra-arterial injection of vasoactive drugs can cause limb-threatening ischaemia.

- Radial artery — the commonest site. Allen's test confirms ulnar collateral supply before cannulation: occlude both arteries, ask the patient to clench, release the ulnar — the hand should pink up within ~7 seconds.

- Alternatives: brachial, femoral, dorsalis pedis.

Complications: thrombosis with distal ischaemia, infection, haematoma, and retrograde embolisation into the cerebral circulation if flushed forcefully (a real concern with brachial and femoral lines).

PICC (peripherally inserted central catheter)

A long, fine catheter inserted into a deep arm vein — usually the basilic (preferred over cephalic because it is larger and runs a straighter course to the axillary vein). The tip sits in the SVC, so it is technically a central line despite the peripheral entry.

Used for medium-term IV therapy (weeks to months): chemotherapy, prolonged antibiotics (e.g. endocarditis, osteomyelitis), TPN.

Tunnelled central catheters

The catheter is tunnelled through a subcutaneous track before entering the vein. A Dacron cuff within the tunnel triggers fibrosis, anchoring the line and creating a mechanical and bacteriological barrier — hence lower infection rates than non-tunnelled lines.

- Hickman line — long-term IV access; chemotherapy

- Broviac — smaller-lumen Hickman variant, paediatric

- Permcath / Tesio — tunnelled dialysis catheters (large bore, dual lumen)

Portacath (TIVAS)

A totally implantable venous access system: a catheter attached to a subcutaneous reservoir under the chest wall skin. Accessed percutaneously with a Huber needle through the silicone port.

- No external component — best cosmesis, lowest infection rate of any central line, patient can swim and shower freely.

- Ideal for intermittent outpatient chemotherapy over months to years.

- Downside: more invasive insertion and removal (formal surgical procedure under LA ± sedation).

Dialysis lines

- Vascath — non-tunnelled, large-bore, dual-lumen; inserted urgently for short-term haemodialysis or plasmapheresis (days to weeks).

- Tesio / Permcath — tunnelled equivalent for longer-term dialysis while awaiting fistula maturation.

Arteriovenous (AV) fistula

The gold standard vascular access for chronic haemodialysis. A surgical anastomosis between an artery and a superficial vein arterialises the vein, allowing repeated cannulation with dialysis needles.

- Radio-cephalic (Brescia–Cimino) fistula at the wrist is the classic first choice — distal-first preserves more proximal options for later. Next: brachiocephalic, then brachiobasilic.

- Requires 6–12 weeks of maturation before use.

- Examination: a thrill is palpable, a bruit is audible. Loss of either suggests thrombosis.

- AV graft (synthetic PTFE) is an alternative when the patient's veins are inadequate — usable within 2–3 weeks, no maturation needed, but higher rates of infection and thrombosis.

Complications: thrombosis, stenosis, infection, steal syndrome (distal limb ischaemia from arterial diversion), high-output cardiac failure, aneurysm formation.

Chest drains

Inserted into the pleural cavity to drain air (pneumothorax), blood (haemothorax), pus (empyema), or effusion. Site of insertion is the triangle of safety:

- Anterior border of latissimus dorsi (posteriorly)

- Lateral border of pectoralis major (anteriorly)

- A horizontal line at the level of the 5th intercostal space / nipple inferiorly

- Apex at the base of the axilla

The needle/dilator passes just above the rib to avoid the neurovascular bundle in the subcostal groove (vein–artery–nerve, superior to inferior).

Pigtail drains are smaller-calibre, image-guided drains used for loculated collections and abscesses (intra-abdominal, pelvic, pleural).

Urinary catheters

- Foley (indwelling) — latex or silicone; balloon retains it in the bladder. Latex for short term; silicone for >2 weeks (less encrustation, less allergy).

- Three-way catheter — large bore with an irrigation channel; standard post-TURP to flush clots.

- Suprapubic catheter — inserted through the anterior abdominal wall when urethral catheterisation is impossible (stricture, prostatic disease) or for long-term use. Avoids urethral trauma and is more comfortable.

- Intermittent self-catheterisation (ISC) — periodic clean catheterisation; preferred in neurogenic bladder. Lowest infection rate of any catheter strategy.

Nasogastric (NG) tubes

Used for gastric decompression (bowel obstruction, post-op ileus) or feeding (fine-bore).

Confirmation of position before use:

1. Aspirate pH < 5.5 confirms gastric placement (Trust-mandated first-line check).

2. CXR if pH is equivocal or aspirate cannot be obtained — the tube should bisect the carina and tip below the left hemidiaphragm.

3. Auscultation (the "whoosh test") is no longer accepted — it can be falsely positive with bronchial misplacement.

The catastrophic complication is misplacement into the bronchial tree, with subsequent feeding causing pneumonia or pneumothorax. This is a Never Event.

> Pearl: Spinal and lumbar drains are covered in detail in Lesson 35 (CSF and Spinal Anatomy).


Test yourself

A 24-year-old trauma patient is hypotensive and tachycardic after a road traffic collision. Which is the single most appropriate venous access?

• ((Right internal jugular triple-lumen central line::Long, narrow lumens — slow flow; reserved for vasopressors and monitoring, not resuscitation.))
• ((Two grey (16G) peripheral cannulae in the antecubital fossae::☑️ Short and wide — Poiseuille's law: flow ∝ r⁴/length, so peripheral wins for resuscitation.))
• ((Femoral vascath::Useful in arrest if access is impossible, but slower than two large peripheral lines.))
• ((Pink (20G) cannula in the dorsum of the hand::Far too small for major haemorrhage — standard fluids only.))
• ((PICC line::Long, fine catheter for medium-term therapy; useless for acute resuscitation.))

👩‍⚕️ For massive haemorrhage: think short and fat, not central.

Which colour cannula corresponds to a 14-gauge cannula?

• ((Pink::20G — standard fluids and antibiotics, ~60 ml/min.))
• ((Green::18G — minimum size for blood transfusion, ~90 ml/min.))
• ((Grey::16G — trauma and major transfusion, ~200 ml/min.))
• ((Orange (Brown)::☑️ 14G — the largest standard peripheral cannula; 270+ ml/min.))
• ((Blue::22G — paediatric and fragile veins; the smallest commonly used.))

👩‍⚕️ Remember: bigger number = smaller bore.

A patient develops sudden shortness of breath and reduced breath sounds on the right after a subclavian CVC insertion. What is the most likely complication?

• ((Air embolism::Presents with sudden cardiovascular collapse, not isolated unilateral breath sound loss.))
• ((Pneumothorax::☑️ Classic subclavian complication — the pleural dome lies just deep to the vein.))
• ((Catheter malposition into the azygos vein::Usually asymptomatic; detected on routine post-insertion CXR.))
• ((Haemothorax::Possible but typically presents with hypotension and dullness, not reduced breath sounds alone.))
• ((Cardiac tamponade::Late complication from catheter-tip perforation, not immediate post-insertion.))

👩‍⚕️ Always request a post-insertion CXR after any subclavian or IJ line.

Which site has the lowest infection rate for central venous access?

• ((Internal jugular::Intermediate infection risk; preferred for elective insertion under USS.))
• ((Subclavian::☑️ Lowest infection rate, but highest pneumothorax risk and non-compressible.))
• ((Femoral::Highest infection rate due to groin colonisation; also ↑ DVT.))
• ((PICC via basilic vein::Higher rates of catheter-related thrombosis than subclavian.))
• ((External jugular::Rarely used for definitive central access; tortuous course.))

👩‍⚕️ Subclavian = cleanest but riskiest insertion. Trade-off favours it for long-term lines.

A patient on long-term haemodialysis has a radio-cephalic fistula created. When can it typically be used?

• ((Immediately::Fistulas need vein arterialisation before they can withstand needling.))
• ((2 weeks::Too early — this is the timeframe for an AV graft, not a native fistula.))
• ((6–12 weeks::☑️ Standard maturation period for a native AV fistula.))
• ((6 months::Unnecessarily long — most are ready well before this.))
• ((Only after angiographic confirmation of patency::Clinical thrill and bruit suffice; angiography is reserved for failure.))

👩‍⚕️ Graft = quick but dirty (2–3 weeks, more infection). Fistula = slow but gold standard.

A guidewire is being advanced during a right IJ CVC insertion. The monitor shows sudden ventricular ectopics. What should you do?

• ((Continue advancing and complete insertion::Persistent stimulation can precipitate VT or VF.))
• ((Withdraw the guidewire a few centimetres::☑️ The wire is irritating the right atrium/ventricle — pull back until ectopics resolve.))
• ((Remove the wire completely and restart::Unnecessary — partial withdrawal is sufficient.))
• ((Give IV amiodarone::Treats the arrhythmia but not the cause; address the mechanical trigger first.))
• ((Call cardiac arrest team::Premature — this is a benign, reversible mechanical irritation.))

👩‍⚕️ The wire is too far in. Withdraw, not advance.

Where should the tip of a correctly positioned central venous catheter lie on CXR?

• ((Right atrium::Risk of arrhythmia and perforation; the wire goes here, not the catheter.))
• ((SVC at the level of the carina::☑️ Just above the SVC–RA junction; the carina is the radiographic landmark.))
• ((Right ventricle::Catastrophic — can cause perforation and tamponade.))
• ((Brachiocephalic vein::Too proximal; risks thrombosis and inadequate dilution of hypertonic infusions.))
• ((Azygos vein::Malposition; line should be repositioned.))

👩‍⚕️ Carina ≈ SVC–RA junction on a frontal CXR. Use it.

A 6-year-old requires long-term IV drug therapy for a genetic disorder. He pulls at his Hickman line, and his parents request an alternative. What is the best option?

• ((Triple lumen subclavian line::Non-tunnelled — even higher infection risk and still external.))
• ((PortaCath::Implanted under the skin with no external component — ideal for an active child who pulls at lines. ☑️))
• ((Intermittent peripheral cannulation::Avoids central access but impractical for long-term genetic-disorder therapy with poor veins.))
• ((PICC line::External catheter on the arm — same pulling risk as Hickman.))
• ((Broviac line::Tunnelled paediatric Hickman variant — still has an external component.))

👩‍⚕️ Totally implanted port = nothing to grab, best cosmesis, lowest infection.

A radial arterial line is inserted for continuous BP monitoring. Which test should be performed beforehand?

• ((Buerger's test::Assesses lower limb arterial insufficiency, not hand collateral supply.))
• ((Allen's test::☑️ Confirms adequate ulnar collateral flow before sacrificing radial patency.))
• ((Trendelenburg test::Tests saphenofemoral valve competence in varicose veins.))
• ((Tinel's test::Reproduces paraesthesia by tapping a nerve — used in carpal tunnel syndrome.))
• ((Phalen's test::Also for carpal tunnel; flexion of the wrist.))

👩‍⚕️ Allen's: occlude both arteries → clench → release ulnar → hand should pink up in ~7 s.

An NG tube has been inserted for decompression. Aspirate pH is 6.5 and no further fluid can be obtained. What is the next step?

• ((Begin feeding — the position is fine::Dangerous — pH > 5.5 does not confirm gastric placement.))
• ((Auscultate over the epigastrium while injecting air::The "whoosh test" is unreliable and no longer recommended.))
• ((Request a CXR to confirm position::☑️ When pH is equivocal, radiographic confirmation is mandatory before use.))
• ((Remove and reinsert::Premature; confirm position first.))
• ((Inject contrast and re-image::Unnecessary — a plain CXR is sufficient.))

👩‍⚕️ pH < 5.5 = safe to use. Anything else = CXR.

Which is the correct triangle of safety for chest drain insertion?

• ((Bounded by sternocleidomastoid, clavicle and trapezius::This is the posterior triangle of the neck.))
• ((Anterior to mid-axillary line, lateral to nipple, above 5th ICS, apex at base of axilla::☑️ Standard landmarks — avoids long thoracic nerve, diaphragm and internal mammary vessels.))
• ((Below the 8th rib in the mid-clavicular line::Risks diaphragm and intra-abdominal injury.))
• ((2nd intercostal space, mid-clavicular line::Old needle-decompression site for tension pneumothorax — not for drain insertion.))
• ((Posterior to mid-axillary line at the 7th space::Risks long thoracic nerve and diaphragm.))

👩‍⚕️ Always insert just above the rib to avoid the neurovascular bundle.

Revision summary

- Cannula colours (high → low gauge): Blue 22 · Pink 20 · Green 18 · White 17 · Grey 16 · Orange/Brown 14. Higher number = smaller bore.

- Poiseuille: flow ∝ r⁴ / length. For resuscitation choose short and fat peripheral cannulae, not central lines.

- Minimum cannula for blood: green 18G.

- CVC sites: IJ (USS, right preferred) · subclavian (low infection, ↑ pneumothorax, non-compressible) · femoral (easy in arrest, ↑ infection/DVT).

- CVC insertion: Seldinger (needle → wire → dilator → catheter) under USS. Post-procedure CXR mandatory — tip at SVC/carina.

- CVC complications: pneumothorax, arterial puncture, air embolism, dysrhythmia (wire in RA → withdraw), CLABSI, thrombosis, malposition.

- Arterial line: radial commonest, do Allen's test first; never inject drugs.

- PICC: basilic > cephalic; tip in SVC; weeks–months of therapy.

- Tunnelled lines (Hickman, Broviac, Permcath, Tesio): subcutaneous tunnel + Dacron cuff → lower infection; months–years.

- Portacath: totally implanted, best cosmesis, intermittent chemo.

- Dialysis: Vascath (temporary, non-tunnelled) vs Tesio/Permcath (long-term, tunnelled).

- AV fistula: radio-cephalic (Brescia–Cimino) first; matures in 6–12 weeks; gold standard for HD. AV graft = PTFE, usable in 2–3 weeks, ↑ infection/thrombosis.

- Chest drain: triangle of safety — pec major (ant), lat dorsi (post), 5th ICS / nipple line (inf), apex of axilla. Insert above the rib.

- Urinary catheters: Foley · 3-way (post-TURP irrigation) · suprapubic · ISC.

- NG tube: pH < 5.5 confirms gastric position; otherwise CXR. Never auscultate.