Place the right line at the right depth — umbilical venous and arterial catheterisation

Station status

This is one MedVellum formative structured clinical encounter. The scoring, prompts and performance descriptions are educational feedback tools. They are not an official college station, timing, mark allocation, pass score or reproduced examination format. The encounter assesses the vessel anatomy and courses, the Shukla birth-weight depth formula with the calculation for a 1000-gram infant, the high and low arterial positions with the high preferred and the reason, the venous target at the diaphragm, the radiographic confirmation of the tip, and the recognition and immediate management of a white limb, persistent hypertension, and line sepsis, with the dwell-time limits. [1] [9]

Candidate instructions

You are the paediatric registrar in the neonatal unit caring for a sick preterm infant who needs umbilical venous and arterial catheters. Decide which lines are needed, calculate the depth, state how you confirm the position, and then respond to the complications as they unfold. Speak directly to the nursing team and the family. State what you would assess, calculate, or give; do not perform the procedure on the actor. [1] [7]

Room setup and observable starting state

The encounter. The infant, Baby Rao, is a 28-week preterm baby weighing 1000 grams, admitted to the neonatal unit on respiratory support. The team has asked you to place an umbilical arterial catheter for blood-gas and blood-pressure monitoring and an umbilical venous catheter for central access and parenteral nutrition. As the encounter unfolds, the radiograph is returned, then a limb goes pale, the blood pressure rises, and the stump becomes red and discharging. The candidate is asked to manage the lines safely across each stage. [1]

Simulation safety. The infant is represented by a manikin or a card with the weight and the radiograph images. The procedure is described, not performed, on any actor. The nursing team and the family respond to questions without obstructing the encounter. [9]

Actor cues

Neonatal nurse actor

• Begin with, "Baby Rao needs lines — the arterial for monitoring and the venous for the TPN. How deep do we go?" If asked about the weight, answer: "One kilo exactly, twenty-eight weeks." [1]
• When the radiograph is returned: "The films are up — where should the tips be?" [9]
• When the limb goes pale: "The right foot's gone white — what do you want me to do?" [6]

Parent actor

• Asks, "Why does my baby need these lines, and when can they come out?" A strong candidate explains the indication, the dwell-time limits, and the plan for definitive access. [6]

Assessor cues and clinical data

Release findings as the candidate reaches each step. Reward the anatomy, the formula and calculation, the high position as preferred, the radiographic confirmation, and the immediate recognition of each complication. [1]

Step 1 — The lines and the depth calculation

Expected strong behaviour: state that the infant needs an umbilical arterial catheter and an umbilical venous catheter; describe the two thick-walled arteries and one thin-walled vein; state the Shukla formula with the arterial length as three times weight in kilograms plus nine centimetres and the venous as half that plus one; calculate the arterial length as twelve centimetres and the venous as seven centimetres for a 1000-gram infant; and choose a 3.5 French arterial catheter and a 5 French venous catheter. [1]

Step 2 — The position and the confirmation

Expected strong behaviour: state the high arterial position between T6 and T9 as preferred because it sits above the visceral and renal arteries and carries fewer vascular complications, and the venous target at the diaphragm at T8 to T9; order an anteroposterior chest and abdomen radiograph (with a lateral view if uncertain) before any use; and reposition any malposition, with ultrasound or echocardiography when the venous tip is uncertain. [7] [9]

Step 3 — The white limb

Expected strong behaviour: recognise the pale, cold right foot as arterial vasospasm or thromboembolism; remove the arterial line immediately; rewarm the limb and reassess perfusion; involve the specialist team for vasodilator or thrombolytic therapy if the ischaemia does not resolve; and state that the lower limbs are checked every shift with an arterial line. [6]

Step 4 — Persistent hypertension

Expected strong behaviour: recognise the rising blood pressure as renal artery thrombosis until proven otherwise; remove the line if still present; manage the blood pressure with antihypertensive therapy; image the renal vasculature with ultrasound; and arrange specialist guidance on anticoagulation and ongoing monitoring. [6]

Step 5 — The red, discharging stump

Expected strong behaviour: recognise the red, discharging stump as omphalitis, which contraindicates further insertion and demands removal of any line present; take blood cultures (paired peripheral and line cultures); start broad-spectrum antibiotics; remove the line; and observe for progression to sepsis. State the dwell-time limits — five days for arterial and fourteen days for venous — and explain that dwell time is the biggest driver of complications, with definitive access planned early. [6]

Mark allocation

This encounter uses a formative seven-point global judgement: excellent, clear pass, pass, borderline, fail, clear fail, unacceptable. The four anchor behaviours are the Shukla formula with the calculation, the high arterial position as preferred, the immediate removal of a line for a white limb, and the recognition of omphalitis as a contraindication. A candidate who states all four anchors and the dwell-time limits passes comfortably. [1] [6]

Feedback summary

A candidate who has named the two vessels and their courses, calculated the depth with the Shukla formula for a 1000-gram infant, placed the arterial tip high at T6 to T9 and the venous tip at the diaphragm at T8 to T9, confirmed both on radiograph, removed the line at once for a white limb, recognised renal artery thrombosis as the cause of persistent hypertension, and identified omphalitis as a contraindication with the dwell-time limits, has demonstrated the full procedural and safety depth of the topic. [1] [9]