Critically ill patients in the emergency department commonly require arterial line placement for continuous direct blood pressure monitoring, frequent arterial blood gas sampling, and frequent blood sampling. Trans-radial catheterization has been shown to reduce access site complications and increase patient comfort compared to trans-femoral access. Radial artery access on the first attempt is optimal; attempts at reentry delay care and increase the risk of vascular spasm, hematoma, infection, neurovascular injury, and pain. The traditional pulse palpation method of radial artery cannulation can be challenging, especially in patients with weak pulses (i.e. morbidly obese or hypotensive individuals).

A review of literature suggests that ultrasound guided trans-radial catheterization compared to standard pulse palpation reduces access time and increases rate of first-entry success when performed by physicians trained in ultrasound. Thus, complications ascribed to reentry are prevented and timely care is provided.

To the investigator's knowledge, only one other prospective study has been conducted to assess the utility of ultrasound guided radial artery cannulation in the emergency department. Due to the paucity of literature to support the use of ultrasound guided trans-radial catheterization in critically ill patients, the study will aim to provide further data on the topic. Both techniques are considered standard of care.

Patients presenting to the Emergency Department 18 years old or greater, who do not belong to a vulnerable group, requiring arterial line placement will be included in this trial. The investigators will randomize each patient into LM vs US. Data collected will include number of attempts, success rate, and time for procedure to be completed. PGY-1 residents will perform the arterial line placement.

Inclusion Criteria:

• Patients requiring arterial line placement.

Exclusion Criteria:

• Adults Unable to Consent
• Members of Vulnerable Populations