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Central Venous and Arterial Lines and Pulmonary Artery Catheters (Swan-Ganz) - Lecture Notes

Central Venous Access: Overview and Terminology

  • Central lines and peripheral equivalents discussed: central venous catheter (CVC), peripherally inserted central catheter (PICC), Hickman line (tunneled long-term), internal jugular (IJ), subclavian (SC), femoral venous access.
  • PICC line: placed in the arm; used for IV therapy, CVP monitoring, SCVO₂ monitoring, distal port sampling, and drug infusion.
  • Hickman line: long-term tunneled catheter; placed under the skin and then into the vein; designed to reduce infection risk compared with non-tunneled lines; not commonly seen in acute discussions but important historically and test-worthy.
  • Why femoral lines are avoided: higher infection risk and patient may pull line out easily.
  • Thoracic/near-thoracic lines require chest imaging (chest X-ray) to confirm placement and rule out complications.

Central Line Insertion and Placement Details

  • Insertion sites: Internal jugular (IJ), Subclavian (SC), Femoral. PICCs are peripherally inserted (arm).
  • In many settings, ultrasound is used by nurses to aid placement of peripheral/central lines; physicians typically place central lines.
  • Distal ports in a central line can be used for drug infusion and venous blood sampling; emphasis on correct port use is essential.
  • Cardiac positioning check: tip should terminate in the superior vena cava (SVC) or just outside the right atrium (RA). If it travels into the RA or right ventricle (RV), this is problematic and must be corrected immediately.
  • If a line tip enters the RV, rapid adverse effects can occur (e.g., stimulation of ventricular tachycardia). If new VT is observed, withdraw the catheter until RA waveform is achieved and notify the physician immediately.

Signs, Placement, and Imaging

  • Any line that enters the thoracic cavity requires a chest X-ray to confirm placement and rule out complications.
  • If the line is misplaced into the RA or RV, or if the waveform changes (e.g., VT on EKG), action is required to reposition or remove the line.
  • Be aware of line dysfunction signals: damped waveform, kinks, or occlusions; if the waveform degrades, do not record readings and troubleshoot.

Arterial Lines vs Central Lines

  • Arterial line (A-line): a catheter placed in an artery (commonly radial) for continuous real-time blood pressure monitoring and arterial blood sampling for ABGs.
  • Insertion considerations: arterial lines require meticulous technique; improper placement increases risk of infection and bleeding.
  • Real-time data: arterial lines provide continuous BP; crucial when using vasoactive drips (highly sensitive to dose changes).
  • ABG sampling is painful; arterial lines allow easier access for repeated sampling.
  • Important caution: do not leave a patient on a vasoactive drip and rely on noninvasive BP alone; monitor pressure continuously and correlate with cuff BP.

Mean Arterial Pressure (MAP) and Waveforms

  • MAP is a key perfusion metric; typical target range is
    \text{MAP} \in [70, \ 110] \ \text{mmHg}
  • MAP is calculated as
    \text{MAP} = \frac{2 \cdot \text{Diastolic} + \text{Systolic}}{3}
  • Arterial waveform features (for line integrity):
    • The dicrotic notch (diacrotic notch) is the small notch after the arterial upstroke; loss of the notch or a flattening waveform suggests line issues or deteriorating cardiac function.
    • If the pulse oximeter waveform disappears along with the arterial waveform, suspect a non-perfusing rhythm (e.g., pulseless electrical activity); immediate assessment and intervention required.
  • Ensure arterial line zeroing and leveling to atmospheric pressure at the start of shift or after patient repositioning; if zeroed to the patient waveform, readings will be inaccurate.

Transducers, Leveling, and Calibration

  • Transducer height must be appropriate relative to patient anatomy; head of bed typically kept at 15°–30° for most measurements to maintain accuracy.
  • Zeroing and leveling: perform zeroing at atmospheric pressure and level the transducer at the phlebostatic axis (approximately mid-chest, level with RA)
  • Re-level after repositioning or bed adjustments; lines tend to drift and readings can drift off by several mmHg.

Line Interactions with Blood Pressure Readings

  • Arterial line readings should be correlated with cuff BP measurements on the opposite arm; cuff should be on the arm opposite the arterial line.
  • Pulse oximetry should be on the same side as the arterial line to avoid alarm conflicts.
  • Flush sequences: flush lines approximately every 4 hours to prevent clot formation and maintain patency; there is usually a pigtail valve in the transducer to allow flushing.
  • Dressing checks: line dressings should be checked at every assessment in ICU settings; typical practice is every 4 hours; dressing changes may be required every 72 hours or as needed.
  • Maintain line cleanliness to minimize infection risk; promptly address any corner of the dressing that begins to lift.

Central Venous Pressure (CVP) and Right-Sided Hemodynamics

  • CVP reflects right ventricular preload (the venous return to the heart) and is a measure of the volume status.
  • Normal CVP range: approximately CVP \approx 2 \text{ to } 6 \ \text{mmHg}
  • Measurement site: SVC near the RA; use the distal lumen for CVP measurement because the tip is near the SVC/RA junction.
  • Low CVP suggests hypovolemia; used as an index during resuscitation (historically termed the “tank” analogy).
  • High CVP suggests fluid overload or problems hindering venous return (e.g., right-sided failure, tamponade). Cardiac tamponade may elevate CVP; note that specific testing on tamponade is not included in this session.
  • CVP waveform components: a, c, x, b, y waves; absence of expected waves suggests line misplacement or obstruction.
  • Central venous oxygen saturation (ScvO2):
    • Normal range: ScvO2 \in [70\%, 85\%]
    • Used in sepsis management and shock monitoring; low values indicate increased tissue oxygen extraction or poor delivery.
    • High values may indicate decreased oxygen extraction, mitochondrial dysfunction, or shunting.
    • Central venous oxygen saturation is measured from venous blood returned to the heart (via a central venous line), whereas mixed venous saturation (SvO2) reflects blood from the entire venous system after circulation through the body.

Mixed Venous Oxygen Saturation (SvO2) and Central Venous Oxygen Saturation (ScvO2)

  • SvO2 is measured further down in the pulmonary circulation (via Swan-Ganz catheter) and reflects oxygen extraction from the entire body.
  • SvO2 is typically slightly different from ScvO2 due to sampling location:
    • SvO2 provides a comprehensive view of systemic oxygenation after the mixed venous blood has returned to the RA via the right heart and pulmonary circulation.
    • SvO2 is generally considered a more global measure of oxygen delivery and utilization; ScvO2 is a surrogate measured in the SVC/RA region.
  • Both low and high values have clinical implications similar to ScvO2, but SvO2 is more representative of whole-body oxygen balance.

Pulmonary Artery Catheters (Swan-Ganz Catheters)

  • What they are: pulmonary artery catheters (Swan-Ganz) used for hemodynamic monitoring in select patients.
  • Indications (as discussed in class and common NCLEX context): to infuse, sample venous blood, and measure cardiac outputs, RA pressures, PA pressures, and PAWP (wedge pressure).
  • Insertion pathway: RA -> RV -> PA; chest X-ray is required to confirm final placement in the pulmonary artery.
  • Lines and ports:
    • Thermistor/temperature sensor port (used for thermodilution CO measurements).
    • Multiple lumens with ports for injectate and samples; the red port is used for wedge pressure workflow; the blue port is near the end of the catheter for sampling.
    • Balloon port: used to inflate the balloon for temporarily occluding the PA to obtain the wedge pressure (PAWP).
    • Venous oximetry port: central venous oximetry connector; acts similarly to pulse oximetry but in the venous system.
    • Some Swan-Ganz catheters include pacing wires (pacing swans) and a “bloom” port.
  • Thermodilution cardiac output (CO) measurement:
    • Technique: inject a small volume (commonly 10 mL) of saline or D5W through the distal port; the thermistor detects the temperature change as the injectate passes the sensor.
    • The CO is calculated from the change in temperature over time; typically performed in triplicate and the results are averaged: usually three injections are performed and the averaged value is reported.
  • Pressures obtained with Swan:
    • Right atrial pressure (RAP)
    • Right ventricular systolic/diastolic pressures
    • Pulmonary artery systolic/diastolic/mean pressures
    • Pulmonary artery wedge pressure (PAWP), also called PA occlusion pressure (PAOP) or left atrial pressure surrogate
    • Mixed venous oxygen saturation (SvO2) can be measured from the distal lumen, reflecting mixed venous blood after passage through the lungs.
  • Pressure relationships and physiology:
    • Right-sided preload is reflected by RAP and CVP (central venous pressure).
    • Right-sided afterload is reflected by pulmonary vascular resistance (PVR).
    • Left-sided preload is approximated by PAWP (PA occlusion pressure), and correlates with left atrial pressure.
    • Systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) reflect afterload in systemic and pulmonary circuits, respectively.
  • Balloon inflation and safety:
    • The balloon should be inflated with a limited amount of air (approximately up to 1.5 mL) using a 3 mL syringe with an explicit limiter to prevent overinflation.
    • The syringe that comes with the catheter has a 1.5 mL limiter; do not exceed this value, else balloon rupture or dangerous embolic events can occur.
    • If air is introduced into the pulmonary artery via balloon overinflation, it can cause a pulmonary embolism (PE) or infarction.
    • After obtaining wedge pressure, the balloon must be deflated and the catheter repositioned as needed; never leave the balloon inflated.
  • Wedge pressure and measurement considerations:
    • The wedge pressure reading approximates left-sided filling pressure and correlates with left atrial pressure; the balloon occlusion isolates the line from the right heart so the pressure reflects the left side.
    • If the catheter loops into the right ventricle and triggers VT on the monitor, you must pull the catheter back to the RA and call the provider; inserting or advancing the catheter is a physician responsibility.
  • SvO2 vs ScvO2 specifics:
    • SvO2 provides mixed venous oxygen saturation; SvO2 generally reflects end-organ oxygen delivery/utilization balance across the entire body; ScvO2 is a central venous oxygen saturation, a proxy with values usually similar but slightly different due to sampling location.

Practical Management and Troubleshooting

  • Troubleshooting lines:
    • Dampened waveform indicates reduced amplitude; could be kinked line, air bubble, or catheter defect.
    • If you lose all waveforms, suspect line disconnection or pump failure; assess patient first.
    • Common causes of reading errors: loose stopcocks, disconnected hubs, malfunctioning cables, or line becoming wet or damaged.
    • If a line becomes nonfunctional, do not push medications through it; notify the team and consider alternative access.
  • Infections and contamination:
    • The most serious complication is infection; monitor dressings and site integrity at every assessment.
    • If signs of infection arise (e.g., fever, redness, drainage), obtain two blood cultures and remove the line if infection is suspected; send the catheter tip in a sterile culture cup if removed.
    • Catheters are not indefinitely long-lasting; typical lines are functional for about a week in many ICU settings before higher risk of dysfunction or infection.
  • Clotting and occlusion:
    • Clots can form on lines; regular flushing helps prevent this.
    • Keep the line well-maintained; avoid manipulating the catheter in ways that could kink or injure it.
  • Catheter migration and dislodgement:
    • Lines may move with patient repositioning; this can alter readings and placement.
    • If you suspect dislodgement, obtain imaging or adjust per protocol and notify the physician.

Nursing Priorities and Patient Care Protocols

  • Chest imaging is required to verify thoracic catheter placement (CVCs and Swan-Ganz catheters).
  • Zeroing and leveling the transducer is a routine, critical step at shift start and after repositioning.
  • Align invasive monitoring with other monitoring: cuff BP on the arm opposite the line; pulse oximeter on the same side as the line to avoid alarm conflicts.
  • Regular line assessment every assessment, with dressings checked; line dressings may require changes every 72 hours or as needed.
  • Infection prevention is paramount: promptly address any dressing integrity issues, use sterile technique, and monitor for signs of infection.
  • Clinical interpretation should consider the patient as a whole (respiratory status, cardiac status, perfusion), not just one value in isolation.
  • When communicating with physicians:
    • Be prepared to discuss MAP, CVP, wedge pressure, SvO2, ScvO2, and CO when related to patient status.
    • If there are concerns about device function or patient stability, escalate promptly.

Quick Reference: Key Values, Concepts, and Formulas

  • MAP target: \text{MAP} \in [70,\;110]\ \text{mmHg}
  • MAP = \frac{2 \cdot \text{Diastolic} + \text{Systolic}}{3}
  • CVP normal range: CVP \approx 2 \text{ to } 6\ \text{mmHg}
  • ScvO2 normal range: ScvO2 \in [70\%, 85\%]
  • SvO2 provides mixed venous oxygen saturation, measured in the pulmonary circulation; different from ScvO2 due to sampling site, but both reflect systemic oxygen balance.
  • PAWP/PAOP (wedge pressure) approximates left atrial pressure; PAWP is obtained by balloon occlusion in the PA.
  • PA pressures: systolic/diastolic/mean (in the PA); used to assess pulmonary hemodynamics and right heart function.
  • ROLES of venous pressures:
    • CVP/RAP reflect right-sided preload.
    • PAWP reflects left-sided preload.
    • PVR and SVR reflect afterload in pulmonary and systemic circuits, respectively.
  • Thermodilution CO measurement (Swan): inject ~10 mL saline; measure temperature change with the thermistor; perform three injections and average the results.
  • Balloon safety for PA catheter: limit inflation to ~1.5 mL; deflate promptly after wedge reading to avoid balloon rupture or embolism.
  • Line maintenance: flush every ~4 hours; check for line patency; ensure stopcocks are on and hubs are tight; correlate with noninvasive BP.
  • Signs of trouble requiring action: loss of waveform, signs of infection at the site, sudden reading changes, or suspected catheter misplacement; escalate to the physician.

Final Notes and Exam-Oriented Concepts

  • Always consider the patient holistically; do not rely on a single numeric value to drive interventions.
  • Be aware of the specific risks and indications for different access types (e.g., femoral lines higher infection risk; PICC for longer-term access; IJ vs SC choice depends on anatomy and risk of pneumothorax).
  • Recognize the major hemodynamic relationships:
    • RAP/RAP-like CVP = right-sided preload; PAWP = left-sided preload.
    • PVR and SVR describe afterload in respective circulations.
    • SvO2 and ScvO2 provide information about oxygen delivery/consumption balance, with SvO2 reflecting global venous return.
  • In Swan-Ganz scenarios, expect potential arrhythmias when crossing the right heart; know the protocol to withdraw to RA and contact the clinician if VT occurs.
  • Practice calculating MAP and understanding when readings indicate adequate perfusion versus risk of shock or poor perfusion.

Practice Prompts (conceptual checks)

  • If CVP is low, what are the likely causes and initial management considerations?
  • How would you interpret a high ScvO2 in a septic patient?
  • Why is a chest X-ray required after placing a catheter that enters the thoracic cavity?
  • What actions should you take if the Swan-Ganz catheter shows VT on the monitor?
  • How would you verify wedge pressure using a Swan-Ganz catheter, and what does a high wedge pressure suggest?