# Pulmonary Artery Catheterisation > Pulmonary artery catheter for Cardiac Technology: flotation depths and waveforms, wedge measurement, thermodilution and balloon-volume safety rules. - Canonical URL: https://prepelephant.com/topics/allied/cardiac-technology/pulmonary-artery-catheter - Exam / course: Allied Health · Subject: Cardiac Technology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Pulmonary Artery Catheterisation", PrepElephant, https://prepelephant.com/topics/allied/cardiac-technology/pulmonary-artery-catheter ## Direct answer Threading a balloon-tipped Swan-Ganz catheter through a large-bore introducer sheath lets it float with the blood from right atrium to wedge position, reading every chamber it passes and pausing at the pulmonary capillary bed to report left-heart filling pressure. From the internal jugular vein the distances are roughly 20-25 cm to the right atrium, 30-35 to the right ventricle, 40-45 to the pulmonary artery and 45-50 to wedge (about 10 cm further from the femoral route), with the balloon inflated with no more than 1.5 mL of air and only during advancement and wedge measurement. The catheter carries a distal lumen (PA pressure), a proximal lumen about 30 cm back (right atrial pressure and injectate port) and a thermistor for thermodilution cardiac output. Wedge readings are brief by design — minutes, never left wedged — because the pulmonary artery rupture it prevents is catastrophic. ## What you must remember - **Catheter anatomy:** distal lumen at the tip measures PA pressure and wedge; proximal lumen sits about 30 cm back in the RA; thermistor just proximal to the tip for thermodilution; balloon at the tip, 1.5 mL air maximum. - **Flotation ladder with waveforms:** RA (low undulating a and v waves) → RV (sharp systolic rise to 15-30, low diastolic) → PA (systolic similar, higher diastolic 4-12, dicrotic notch) → wedge (mean 4-12, trace resembles an atrial pressure). - **Wedge rules:** inflate slowly only to the volume that abolishes the PA waveform, never against resistance; read the mean at end-expiration; deflate and confirm the PA trace returns; never wedge for more than a few respiratory cycles. - **Complications in exam order:** ectopy during RV passage (transient), PA rupture or infarction (rare, about 0.1-0.2 per cent, catastrophic — haemoptysis is the sign, pulmonary hypertension and over-wedging the risks), knotting, infection, thrombosis, and balloon rupture. - **Thermodilution technique:** 10 mL saline injected smoothly through the proximal port, three curves averaged; tricuspid regurgitation and intracardiac shunts invalidate the method. - **Indications that survive modern scrutiny:** pulmonary hypertension work-up (with vasoreactivity testing), diagnostically uncertain heart failure, infarct complications, and shunt quantification by saturation run — routine use in uncomplicated cases has been abandoned for good reason. - **Mixed venous saturation:** sampled from the PA port, normal about 60-80 per cent; below about 50 per cent signals inadequate oxygen delivery. ## The floatation, narrated waveform by waveform The trace on the monitor is the navigation instrument. At 25 cm the screen shows a lazy line with small a and v humps — right atrium; the balloon is inflated with 1 mL of air and the catheter advanced. Suddenly sharp spikes to 28 mmHg with a diastole near 5 — right ventricle, with ventricular ectopics the operator rides through. A few centimetres more and the trace morphs: the systolic peak stays but the diastolic pressure climbs and a dicrotic notch appears — pulmonary artery. Advance again and the trace dampens into a wedge pattern (mean near 10) — a branch occluded, a static column stretching to the left atrium. The mean is recorded at end-expiration, the balloon deflated, the PA trace confirmed to return. The journey is the exam question "describe the waveforms as the catheter advances", graded station by station. ## Where students slip Safety slips dominate. The balloon volume rule is misquoted as "inflate to 2-3 mL" — the standard adult balloon holds 1.5 mL, and the rule is inflate slowly, stop when the trace wedges. The catheter is never left wedged between readings — continuous wedging causes pulmonary infarction; the resting place is the main PA. PA diastolic and wedge are conflated: they approximate only at normal heart rate and resistance, and the wedge — not the PA diastolic — is the left-heart number. The 30 cm proximal port is called "the CVP line", though its RA position is what makes thermodilution possible. And the complication list needs the examiner's discriminator: rupture risk rises with pulmonary hypertension, anticoagulation, elderly patients and over-wedging — which is precisely why wedge readings stay brief and gentle. ## Frequently asked questions ### What is the maximum balloon inflation volume for a pulmonary artery catheter? About 1.5 mL of air in adults, inflated slowly only during advancement and wedge measurement, stopping the moment the pulmonary artery trace wedges. Inflation against resistance risks pulmonary artery rupture. ### What waveforms mark each stage of catheter floatation? A low atrial trace with a and v waves; sharp systolic spikes to 15-30 mmHg in the right ventricle; higher diastolic pressure with a dicrotic notch in the pulmonary artery; a damped wedge trace at the wedge position. ### Why does the wedge pressure reflect left ventricular filling? The inflated balloon stops flow, creating a static column from catheter tip through the pulmonary capillaries to the left atrium, so the transmitted pressure approximates left atrial and hence LV end-diastolic pressure — except in mitral stenosis or over-wedging. ### What are the major complications of pulmonary artery catheterisation? Ventricular ectopy during passage, pulmonary artery rupture or infarction (rare but often fatal, heralded by haemoptysis), catheter knotting, thrombosis and infection. Risks rise with pulmonary hypertension and over-wedging. ### What is a normal mixed venous oxygen saturation and what does a low value mean? Sampled from the pulmonary artery, normal is roughly 60-80 per cent. Values below about 50 per cent indicate inadequate oxygen delivery or excessive extraction — as in low cardiac output, severe anaemia or hypoxaemia.