Nursing care
Arterial line complications: bleeding, distal ischaemia, damping and levelling errors
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
An arterial line can bleed rapidly if it disconnects, can reduce blood flow to the hand, and can give misleading pressures when the waveform is damped or the transducer is not level with the phlebostatic axis. The nurse keeps the site visible, alarms on and connections locked, checks distal perfusion, and troubleshoots the system before acting on a number.
Bleeding and disconnection
An arterial catheter sits in a high-pressure vessel, so a loose connection, open stopcock or dislodged catheter can cause substantial blood loss within minutes. Risk is higher in patients receiving anticoagulants or with coagulopathy. Use locking connections, keep the insertion site and tubing visible rather than buried under blankets, and keep monitor alarms active with appropriate limits.
If you find a disconnection, close the system or apply firm direct pressure at the site at once, then assess the patient and call for help. A sudden fall in displayed pressure with a flat trace may reflect disconnection rather than true hypotension, so look at the patient and the line together. Document the event and estimated blood loss, and report it.
Distal ischaemia, thrombosis and infection
The catheter can cause arterial spasm or thrombus, reducing flow to the hand or foot beyond the site. Check colour, temperature, capillary refill, sensation, movement and pain in the limb against the opposite side, at the frequency your unit requires. Pallor, coolness, mottling, numbness or new pain distal to the line are concerning findings.
Report suspected ischaemia promptly; the provider may decide to remove the catheter. Infection is also possible, so use aseptic technique for sampling and dressing changes and inspect for redness, tenderness or discharge. Do not inject medicines into an arterial line, because intra-arterial injection can damage the vessel and tissue beyond it.
Damped and underdamped waveforms
An overdamped waveform looks flattened and sluggish, with a lost dicrotic notch, and tends to underestimate systolic pressure. Causes include air bubbles, clots, kinked or overly long tubing, loose connections, catheter against the vessel wall, or a flush bag that has lost pressure. An underdamped trace shows exaggerated spikes and ringing, overestimating systolic pressure.
A fast-flush or square-wave test helps judge the system: a correctly responding system shows about one or two oscillations before returning to baseline, while fewer suggests overdamping and more suggests underdamping. Work from patient to transducer: check the limb position, look for kinks, bubbles and clots, confirm the pressure bag, then retest before trusting the reading.
Levelling and zeroing errors
The transducer must be level with the phlebostatic axis, at the fourth intercostal space in the mid-axillary line, which approximates the right atrium. If the transducer sits below this point, readings are falsely high; if it sits above, they are falsely low. A height error of about ten centimetres produces an error of roughly seven to eight mmHg.
Re-level whenever the bed height or patient position changes, and zero the system by opening the transducer to air according to your protocol, for example at set-up, after monitor changes or when readings look doubtful. Many apparent haemodynamic changes after repositioning are levelling problems. Correct the system first, then compare with a cuff pressure if uncertainty remains.
Original scenario and documentation
In a hypothetical item, a client's arterial pressure jumps after the bed is lowered for a procedure, while the client looks unchanged. Options include giving a prescribed antihypertensive, removing the line, re-levelling and zeroing the transducer, or doubling the flush rate. Re-levelling is the right first step because the transducer is now below the phlebostatic axis.
Acting on an artefactual number could cause harm, while removing the line or altering the flush does not address the cause. Document waveform quality, site appearance, distal perfusion checks, levelling and zeroing, and any interventions. Escalate true pressure changes, bleeding or ischaemia promptly through the unit's escalation pathway.
Sources and further reading
OpenAnesthesia: Arterial line complications. Vascular, infectious and mechanical complications, vasospasm and thrombosis, bleeding and exsanguination risk from disconnection, and waveform problems.
OpenAnesthesia: Arterial blood pressure monitoring. Transducer levelling to the right atrium, hydrostatic error per height difference, zeroing, overdamping and underdamping, and square-wave testing.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our cardiovascular practice questions are the closest set to what this page covers.
Common questions
What happens if the transducer is below the phlebostatic axis?
Readings will be falsely high, because the extra column of fluid adds hydrostatic pressure. Re-level to the fourth intercostal space at the mid-axillary line and zero according to protocol.
What does an overdamped arterial waveform look like?
It looks flattened, with a rounded peak and loss of the dicrotic notch. Systolic pressure is usually underestimated. Look for bubbles, clots, kinks, loose connections or a soft pressure bag.
What signs suggest ischaemia distal to an arterial line?
Pallor, coolness, mottling, slow capillary refill, numbness, weakness or new pain in the hand or foot beyond the site. Report promptly so the provider can assess and decide on removal.
More on cardiovascular
Guides on this