ATS Pulmonary Function Laboratory Manual

chapter  16

Patient Identification Prior to sample collection, a formal process of ensuring positive identification of the patient is required. At least two unique identifiers (e.g., date of birth, patient’s full name) should be used (5, 6). The patient’s room number or location are not acceptable identifiers. Patient Assessment Urgent blood gas analysis is needed in many situations and these require immediate collection of the specimen. Patients on ventilators may need to achieve a “steady state” before collecting the arterial blood sample. A period of 20–30 minutes may be required to achieve steady state in cases of acute respiratory failure, positive end expira- tory pressure (PEEP) or ventilator modalities intended to promote alveolar patency, postural changes, or post- bronchodilator/airway clearance procedures. Patients with communication deficits or language barriers may need assistance from an interpreter to understand the procedure and provide consent (3). Collection, Labeling, Storage, Transport, and Handling The specimen for blood gas analysis should be collected in a suitable heparinized plastic syringe, or capillary tube ( see Chapter on percutaneous arterial blood sampling). The specimen must be properly labeled with the patient’s full name, a second identifier (e.g., medical record or clinic number, or date of birth) according to the institutional policy, date and time of collection, signature or initials of person collecting the specimen (3). In addition, the following information should be recorded in the medical record: • Age and location of patient If analysis of specimen is expected to occur within 30 minutes the specimen should be stored at room tempera- ture. If analysis is anticipated to be delayed by more than 30 minutes, the specimen should be collected in a glass syringe and placed in an ice water coolant. Blood specimens that will also be analyzed for potassium should not be cooled. Cooling of these samples can hemolyze the red blood cells and produce erroneously high potassium results. Immediate transport of the sample to the blood gas laboratory is essential to avoid variability in analyte results. When the specimen is received in the laboratory, the analysis should be conducted as soon as possible. If air bubbles are not removed from the collection device, vibrations and movement (e.g., those that occur in pneumatic trans- port) of the air within the sample can accelerate gas equilibrium producing erroneous results. The blood sample must be thoroughly mixed immediately prior to analysis to achieve a uniform distribution of red blood cells and plasma. Improperly mixed blood may produce variable results, specifically if hemoglobin and/or hematocrit are measured. The laboratory must have a detailed written procedure for specimen mixing prior to analysis. The specimen should be gently rotated either manually or using a mechanical device that rotates the specimen through two axes for a minimum of one minute immediately prior to analysis (3). Capillary tube samples that contain a stirring bar or rod (“flea”) should be mixed by applying an external magnate and moving the flea from end to end for at least five seconds (3). The manufacturer’s instructions should be followed carefully when introducing samples into blood gas analyzers. Incorrect introduction of blood into the analyzer can result in erroneous results. When blood samples are aspirated into the analyzer, an air bubble may form in the syringe due to fluid displacement, and should be removed immediately in case repeat analysis is necessary. • Body temperature • Time of sampling • Fi O 2 or flow rate and mode of supplemental O 2 delivery, PEEP, or CPAP • Ventilatory status (e.g., assisted or controlled ventilation, spontaneously breathing) • Site of sampling • Position of patient and activity (i.e., rest or exercise)

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