Arterial line

"Arterial line" is a topic from Section 2.1.19 in the second edition of the CICM Syllabus for the Second Part Examination. Looking back through countless SAQs, one cannot find a single mention of this ever coming up as the sole subject of any written paper question, which is frankly incomprehensible. The last time it appeared in the oral section appears to be OSCE 7 from the first sitting of 2003, where  "candidates were expected to demonstrate a safe technique for radial artery cannulation.  Additional requested information included local anatomy and performance characteristics of the monitoring system."   These devices exist on the same level of mundane routine as the ABG, the ECG, and the fluid bolus; but whereas the latter are widely used in the CICM exams, the humble art line has rarely appeared, except as a source of waveform information (eg.Question 30.2 from the second paper of 2013 and Question 11.2 from the first paper of 2021). Moreover there is no specific competency document describing these devices (whereas for CVCs and pleural drains, an observable work-based competency assessment is in place). 

What follows is something of a link directory because most of the detailed knowledge related to arterial line insertion has been migrated to the First Part Exam section, where it forms a part of the annotations for Section G6(ii) of the 2023 CICM Primary Syllabus, "describe the invasive and non-invasive measurement of blood pressure, including limitations, potential sources of error and the need for calibration". The rationale for keeping everything in that area is mostly related to the recognition that  the skill of inserting and troubleshooting arterial lines is acquired very early in one's training as an intensivist, and it seemed to make logical sense to include the practical components of that craft together with all the exam-relevant theoretical content involving things like resonance, damping and frequency response. 

• Description
  • A rigid kink-resistant catheter with a winged hub for suture fixation, usually of a width no greater than 18-20G (see Arterial cannulation equipment)
• Safety features
  • Inert material (FEP, fluorinated ethylene propylene), rigid to prevent kinking and waveform damping, with atraumatic bevels at the tip to minimise vessel injury.
• Indications

  • Haemodynamic monitoring:

    • Where blood pressure is labile
    • Where haemodynamic instability is anticipated (eg. major surgery)
    • Where haemodynamic therapy is being titrated (eg. vasoactive drugs such as noradrenaline)
    • Where non-invasive blood pressure monitoring would be inaccurate or unreliable, for example in the context of arrhythmia or morbid obesity

  • Blood sampling:

    • Where respiratory therapy such as mechanical ventilation is being titrated
    • Where frequent biochemistry testing is required and venous sampling is difficult

  • Diagnostic or interventional procedure:

    • Intra-arterial drugs
    • Endovascular procedures
    • Intra-aortic balloon counterpulsation
    • Arterial embolisation
  • Continuous cardiac output monitoring (eg. the purpose of pulse contour analysis)
• Relative/absolute contraindications

  • Absolute contraindications

    • Absence of collateral circulation (abnormal modified Allen's test gets mentioned here, though most people would agree it is basically meaningless)
    • Local infection
    • Distorted anatomy (eg, previous surgical interventions, congenital malformations)
    • Active Raynauds Disease
    • Thromboangitis obliterans (Buerger disease)
    • Burns
    • Aneurysm
    • Stent or synthetic vascular graft
    • Arteriovenous malformation or AV fistula

  • Relative contraindications

    • Severe peripheral vascular disease
    • Severe coagulopathy (INR > 3.0, APTT > 100sec as suggested by UpToDate)
    • Severe thrombocytopenia (platelet count 50 x 109/L, as suggested by UpToDate)
    • Recent use of thrombolytic agents
  • (see Indications and contraindications for arterial line insertion)
• Alternative options
  • Non-invasive measurement of blood pressure
  • Clinical assessment of pulse character and amplitude
  • Ultrasound estimation of MAP from Doppler flow measurements
• Consent
  • Complication rates listed below should be mentioned
  • Reassurance re. the use of local anaesthetic
  • Assessment for coagulopathy and previous surgery at the site (eg. fem pop bypass?)
  • Confirmation of allergy information (latex of gloves, dressing glue, chlorhexidine cleaning solution, local anaesthetic agent)
• Complications (early, late, etc)
  • Complications can be grouped as generic and site-specific (see Complications of arterial cannulation).
  • Scheer et al (2002) found that the risk of major complications was roughly 1 % for all sites.
  • Common complications include:
    • Pain and swelling
    • Accidental dislodgement
    • Thrombosis
    • Embolization
    • Haematoma
    • Haemorrhage
    • Pressure injury from hub, tubing or immobilisation device
    • Limb ischemia (very rare: Nuttall et al (2016) found a very low overall vascular complication rate, 3.4 per 10,000).
  • Durie et al (2002) and Bhananker et al (2009), from different perspectives (quality assurance and litigation), note that incident reports for arterial catheters are generally benign and related to dislodgement and haematoma. They are also comparatively few, contrasted with IV access devices (9% of the total closed claims analysed by Bhananker et al). 
• Advantages
  • Precise and immediately responsive blood pressure monitoring
  • Avoidance of the sources of error for noninvasive blood pressure monitoring
  • Improved convenience and comfort of blood sampling 
• Disadvantages
  • Reduced mobility, including reduced limb dexterity for the cannulated limb
  • Risks mentioned in the complications
  • Iatrogenic blood loss from a more frivolous approach to blood sampling
• Positioning and anatomy
  • Depends on site
  • The usual radial arterial puncture technique calls for the wrist to be 
• Site selection
  • Balance of risk and benefit favours the radial artery as the first choice for arterial catheterisation.
  • Other sites can be considered under circumstances where this first choice is not available (see factors involved in site selection for arterial cannulation)
• Environment, monitoring
  • The minimum expectation from the monitoring equipment, at the bedside is a capability to monitor the arterial line transducer and display the measured pressure, as well as the capacity to zero and level the transducer.
  • A non invasive blood pressure monitoring device is a desirable cross-calibration adjunct
• Staff, team, roles
  • An assistant is usually required to help coordinate the connection of the transducer line, but this can also be accomplished by a well-organised solo operator.
• Procedure technique
  • Blind or ultrasound-guided
  • Seldinger vs. cannula-over-needle (see Arterial cannulation technique)
• Technical procedural caveats
  • The superficial position of the radial artery does not require a deep cannulation; a common cause of error is through-and-through puncture
  • Hyperextension of the wrist can lead to a narrower target vessel because of stretch over the radial styloid
• Confirmation of success, correct placement, or correct function
  • A transduced arterial waveform, and flow of blood into the access line when the counterpressure bag line is interrupted and the pressure is released
• Safe maintenance of the device or process
  • A well secured device (eg. with skin sutures) guards against dislodgement
  • Minimising access to the line reduces the risk of infection
  • Attention to dressing changes and hygiene
  • Stabilisation of the wrist in the slightly extended position using an arm board should prevent some of the vessel injury associated with excessive catheter excursion
  • Hanrahan et al (2022) and Xiao et al (2022) also list practices related to the frequency of line and bag changes, transducer flushes, continuous infusions of fluid or heparin, and other methods of maintaing patency of the catheters.
• Safe removal
  • Direct pressure on the site of insertion needs to be continued for a time beyond the point where exterior bleeding has ceased, as the possibility of haematoma or pseudoaneurysm formation is not trivial
  • The risk increases with femoral arterial lines, where the site of arterial puncture may be some distance from the site of the skin puncture.
• Interpretation of data/output
  • Information derived from the arterial pressure waveform
  • Arterial line dynamic response testing
  • Normal arterial line waveforms
  • Interpretation of abnormal arterial line waveforms
  • Discrepancy between invasive and non-invasive arterial blood pressure measurement
• Strategies for risk mitigation
  • Experience of the proceduralist is important
  • Assessment of the collateral circulation (beyond the largely non-predictive Allen's test) may be useful in higher risk category patients (eg. those with peripheral vascular disease or multiple previous arterial line cannulations)
  • Minimising the number of puncture attempts seems to be the most important determinant of the most serious complications
  • Ultrasound guidance for insertion seems to be a promising method of reducing puncture-related complications (Spencer et al, 2024)
  • Limb immobilisation and device securement is the most effective method of preventing displodgement-related complications

Abide & Meissen (2021), a chapter from Interventional critical care, is the highest yield reference for the time-poor exam candidate.