How many times can blood be safely drawn from an arterial line, and what is the proper sampling technique?

Arterial Line Blood Sampling: Frequency and Technique

There is no specific limit on how many times blood can be safely drawn from an arterial line—sampling frequency should be determined by clinical need—but proper technique is critical to prevent fatal complications from sample contamination. 1

Core Safety Principle

The primary concern with arterial line sampling is not the number of draws, but rather preventing sample contamination that can lead to fatal hypoglycemic brain injury. 1 Drawing samples from an indwelling arterial line is the method of choice for frequent blood analysis in adult critical care areas. 1

Mandatory Flush Solution Requirements

Only sodium chloride 0.9% (with or without heparin) should be used for arterial line flush solutions. 1, 2, 3 This is non-negotiable because:

• Glucose-containing solutions have caused fatal neuroglycopenic brain injury when mistakenly used as flush solutions 1
• Even minimal contamination with glucose solutions can conceal true hypoglycemia or create falsely elevated readings 2, 3
• Fatal brain injury can occur within two hours of hypoglycemia onset 1, 2
• Blood sampling from cannula lumens carrying other solutions is explicitly not recommended 1, 3

Proper Sampling Technique

System Selection

Closed arterial line sampling systems are strongly recommended over open systems. 1, 3 When open systems must be used, minimize dead space volume between the sampling port and arterial lumen. 1

Discard Volume Requirements

The evidence on discard volumes shows important nuances:

• For heparinized lines (1 unit/mL): Minimum discard of dead space plus 2 mL is required for accurate coagulation studies 4
• For heparinized lines (2 units/mL): Minimum discard of dead space plus 5 mL is required 5
• Samples from heparinized arterial lines cannot be reliably used for APTT ratio results even with adequate discard volumes 6
• Blood-conserving arterial line systems can reduce blood loss by approximately 157 mL over 7 days compared to conventional systems 7

Critical Technique Points

• Use distinguishable syringes for discard versus sampling 1
• Prevent flush solution from entering the dead space, sample, or three-way taps during the entire sampling process 1
• Maintain closed system integrity whenever possible 3

Mandatory Safety Checks

Before Setup

The flush solution must be independently double-checked by a second practitioner before connecting to the arterial line. 1, 2, 3 This independent validation requires two clinicians to separately check, alone and apart from each other, then compare results. 1

During Use

Double-check the flush infusion bag at least once per nursing shift and at every patient handover. 1, 3 This check must include physically removing the bag from its pressurizing device to verify contents. 1, 3

Storage Requirements

• Store sodium chloride 0.9% bags for arterial line use separately from IV fluids 1
• Do not store glucose-containing solutions in areas where they might be confused with flush solutions 1, 2
• Use pressurizing devices with fully transparent front panels to permit unimpaired inspection 1

Response to Abnormal Results

Unexpectedly High Glucose Values

Any unexpectedly high glucose reading from an arterial line must trigger immediate medical review and verification of the sampling system. 1, 3 Draw a confirmatory sample from an alternative site if contamination cannot be ruled out. 1, 3

Before Insulin Administration

Before starting insulin in a non-diabetic patient or increasing insulin infusion above 6 units/hour based on arterial line samples, conduct a medical review and verify no possibility of sample contamination. 1 If verification is impossible, obtain a confirmatory sample from an alternative site. 1

Any Unexpected Abnormality

Any blood test showing unexpected abnormality or unusual variation from previous results should prompt checking the sample source for possible contamination. 1, 3 If contamination cannot be excluded, draw confirmatory samples from alternative sites. 1, 3

Training and Policy Requirements

All staff involved in arterial line insertion, management, or sampling must be appropriately trained and competent in these standards. 1, 2 Hospitals must have policies defining local procedures for arterial line use, including prescribing, administering, and monitoring flush solutions and blood sampling technique. 1, 2

Critical Pitfalls to Avoid

• Never use glucose-containing solutions as flush solutions—this has caused fatal outcomes 1, 2
• Never assume adequate discard volume without knowing the heparin concentration in your flush solution 5, 6, 4
• Never skip the independent double-check of flush solutions—contamination errors remain common with one event reported weekly to national safety systems 1
• Never rely on arterial line samples for APTT results in post-cardiac surgery patients—heparin contamination persists despite adequate discard volumes 6