Paeds SAQs · investigations-procedures-and-technology
Umbilical venous and arterial catheterisation — formative SAQs
Two MedVellum formative short-answer questions on umbilical venous and arterial catheterisation in newborns: the two vessel types and courses with the high and low arterial positions, the venous target at the diaphragm, and the Shukla birth-weight depth formula; and the recognition and management of complications including malposition, lower-limb ischaemia, renal artery thrombosis with hypertension, portal vein thrombosis, and line sepsis, with the dwell-time limits of five days for arterial and fourteen days for venous catheters. The marks and timing support transparent self-assessment. They are not an official board format or pass standard.
On this page & tools
Target exams
SAQ 1 — The two lines, the positions, and the depth formula
Question 1 — 10 formative marks; suggested time 15 minutes [1]
A 28-week preterm infant weighing 1000 grams needs an umbilical arterial catheter for blood-gas and blood-pressure monitoring and an umbilical venous catheter for central access and parenteral nutrition. You are asked to describe how you would place the lines, calculate the depth, and confirm the position. [1] [9]
- Describe the umbilical vessel anatomy and the two catheter courses, and state where each tip should lie. (3 marks)
- State the Shukla birth-weight depth formula, and calculate the insertion length for each line for this 1000-gram infant. (3 marks)
- State the preferred arterial position and why, and the venous target on radiograph. (2 marks)
- State the catheter French sizing for this infant and how you confirm the tip before use. (2 marks)
Full-credit answer — SAQ 1
Reveal full-credit answer for SAQ 1
1. Vessel anatomy and catheter courses
The umbilical stump carries two thick-walled, small-lumen arteries and one thin-walled, large-lumen vein. The umbilical venous catheter enters the umbilical vein, passes through the left branch of the portal vein and the ductus venosus, and emerges in the inferior vena cava just beneath the right atrium; its tip belongs at the inferior vena cava and right atrium junction at the diaphragm, around the eighth to ninth thoracic vertebra. The umbilical arterial catheter enters the umbilical artery, runs down the internal iliac (hypogastric) artery to the common iliac artery, and ascends the descending aorta; its tip belongs high, between the sixth and ninth thoracic vertebrae, with a low position at the third to fourth lumbar vertebra used only when a high position is unattainable. [9]
2. The Shukla formula and the calculation
The Shukla and Ferrara birth-weight formula estimates both depths. The umbilical arterial catheter length equals three times the birth weight in kilograms plus nine centimetres, and the umbilical venous catheter length equals half of that value plus one centimetre. For a 1000-gram infant, the weight is 1.0 kg, so the arterial length is 3 × 1 + 9 = 12 cm, and the venous length is half of 12, which is 6, plus 1 = 7 cm. Body-measurement and surface-anatomy methods — such as the umbilicus-to-nipple distance minus one centimetre for the venous line — can improve first-attempt accuracy, but the Shukla formula is the examination answer and the bedside starting point. [1]
3. The preferred arterial position and the venous target
The high arterial position between T6 and T9 is preferred because it sits in a wide segment of the descending aorta above the origin of the celiac, superior mesenteric, and renal arteries, where the catheter is bathed in fast flow and the risk of occluding a branch artery is low. The Cochrane review of high versus low position found no evidence to support a low position and concluded that high catheters should be used, because the high position carries a lower incidence of vascular complications without any rise in death, intraventricular haemorrhage, or necrotising enterocolitis. The venous target on radiograph is the diaphragm at T8 to T9 — above the ninth thoracic vertebra is too high and below the tenth is too low. [7]
4. Catheter sizing and tip confirmation
A 1000-gram infant is under 1500 grams, so the arterial catheter is 3.5 French (a 5 French catheter is used over 1500 grams); the venous catheter is usually 5 French, with a double-lumen line chosen if two lumens are needed at once. The tip is confirmed on an anteroposterior chest and abdomen radiograph (with a lateral view when the AP leaves doubt) before any use, and any malposition — a venous tip in the portal system or the heart, or an arterial tip in a branch or low position — is repositioned. Bedside ultrasound or echocardiography resolves the venous tip when the radiograph is uncertain, and reduces the rate of complications when used routinely. [9] [11]
SAQ 2 — Recognising and managing complications
Question 2 — 10 formative marks; suggested time 15 minutes [6]
A baby on the neonatal unit has an umbilical arterial catheter that has been in situ for six days and an umbilical venous catheter in situ for nine days. The nursing team reports that the baby's right foot is pale and cold, the blood pressure has risen, and the stump looks red with a small amount of discharge. [6]
- What is the likely cause of the pale, cold foot, and what is your immediate management? (3 marks)
- What is the likely cause of the rising blood pressure, and how would you investigate and manage it? (3 marks)
- What does the red, discharging stump indicate, and what is your management? (2 marks)
- State the dwell-time limits for umbilical catheters, and explain the principle that underpins them. (2 marks)
Full-credit answer — SAQ 2
Reveal full-credit answer for SAQ 2
1. The pale, cold foot
A pale, cold, or cyanosed lower limb after umbilical arterial catheter insertion is arterial vasospasm or thromboembolism until proven otherwise, and the line is removed immediately. The mechanism is compromise of the iliac arterial supply by a low-sitting tip, a thrombus, or an embolus, and waiting is the wrong response. The limb is rewarmed and the perfusion reassessed, and the catheter tip and any thrombus are imaged with specialist input guiding vasodilator or thrombolytic therapy if the ischaemia does not resolve. The same principle governs every arterial-line assessment: check the lower limbs every shift, and act on blanching or cyanosis without delay. [6]
2. The rising blood pressure
Persistent hypertension in a baby with an umbilical arterial catheter is renal artery thrombosis until proven otherwise. The thrombus compromises the renal arterial supply, driving renin release and hypertension. The line is removed, the blood pressure is managed with antihypertensive therapy, and the renal vasculature is imaged with ultrasound or Doppler to confirm the thrombus. The hypertension may persist after the line is removed, so monitoring continues and the specialist team guides ongoing anticoagulation and blood-pressure management. Recognising the link between the arterial line and the hypertension is the step that protects the kidneys. [6]
3. The red, discharging stump
A red, swollen, or discharging umbilical stump is omphalitis, which is both a contraindication to insertion and an indication for removal of any line present. The picture may progress to catheter-related bloodstream infection, so blood cultures are taken — paired peripheral and line cultures aid interpretation — and broad-spectrum antibiotic therapy is started. The line is removed, the stump is cultured and cleaned, and the baby is observed for progression to sepsis or necrotising fasciitis. Topical antibiotic ointment is not applied to umbilical stumps because it promotes fungal colonisation and resistance. [9]
4. The dwell-time limits and the principle
The umbilical arterial catheter is removed by five days and the umbilical venous catheter by fourteen days, or sooner whenever the line is no longer needed or any sign of sepsis or vascular insufficiency appears. The principle is that dwell time is the single biggest driver of complications — the level-four cohort data showed the cumulative incidence of complications climbing most steeply after about ten days for arterial and sixteen days for venous catheters, and the dwell limits are set conservatively below those thresholds. Early planning of definitive peripheral or central access ensures the umbilical line comes out on time rather than staying in by default. [6]
References
- [1]Shukla H; Ferrara A Rapid estimation of insertional length of umbilical catheters in newborns American journal of diseases of children (1960), 1986.PMID 3728405
- [6]Levit OL; Shabanova V; Bizzarro MJ Umbilical catheter-associated complications in a level IV neonatal intensive care unit Journal of perinatology, 2020.PMID 31911645
- [7]Barrington KJ Umbilical artery catheters in the newborn: effects of position of the catheter tip The Cochrane database of systematic reviews, 2000.PMID 10796375
- [9]Marshall M Radiographic assessment of umbilical venous and arterial catheter tip location Neonatal network, 2014.PMID 24985114
- [11]Lin YJ; Liu YC; Huang HC; et al Echocardiographic determination of umbilical catheter tip location mitigates complications: a randomised controlled trial Children (Basel, Switzerland), 2025.PMID 41300627