This clinical investigation is being undertaken to examine the performance of the CE marked Proxima System - a patient attached blood gas analyser.

The study forms an element of the Post Market surveillance plan for the Proxima system and will also generate method comparison data to allow Sphere Medical to submit the Proxima for FDA regulatory clearance.

The PROX006 study is an open and non-randomised study that will be conducted to assess the performance of the Proxima (a CE marked Medical Device)on a wide range of patients with a variety of conditions. This study will allow the performance of the Proxima and the institution's conventional blood gas analyser to be compared when used in the Intensive Care Unit and Operating Theatre.

The PROX006 investigation is an observational method comparison study - the results obtained from the Proxima will be compared with those obtained on the institution's conventional blood gas analyser (BGA). The potential for bias by the user will be negated in this study by directly comparing the results from the BGA and Proxima.

The data/results documented in the Case Report Form (CRF) will be verified during monitoring visits.

Inclusion Criteria:

• Male and female patients ≥18 years old
• Patients who have (or will have) an arterial line, which was (will be) inserted for clinical need, will be considered for inclusion in this study
• Patients who give informed consent (or their personal/nominated consultee) to participate in the study
• Patients who are likely to have an arterial line for at least 48 hours.

Exclusion Criteria:

• Patients not indicated or contraindicated for an arterial line
• Refusal of consent by a patient or their personal/nominated consultee to participate
• Not for use with patients with uncorrected hyperphosphataemia, hypocalcaemia or hypercalcaemia.
• The patient is considered by the investigator to be unsuitable for the study

Arterial line location/placement is not dictated by this study, however the following criteria should be considered when deciding if arterial catheter placement is suitable, including but not limited to:

• peripheral vascular disease,
• history of placement site neuropathy or chronic pain,
• history of placement extremity coagulopathy or clot formation,
• history of vascular surgery on same extremity as catheter placement (and/or vascular grafts)
• patients with a plan for perioperative anticoagulation. These patients are at increased risk of known complications such as bleeding and arteriospasm and should be excluded in order to mitigate patient study risk.

Patients treated in the Intensive Care Unit, High Dependency Unit or Operating Theatre who require an arterial line to be inserted as standard care