Interpret normal and abnormal arterial blood gas (ABG) results and determine common management strategies for treatment.
Identify indications, complications, and management strategies for artificial airways, oxygen delivery, and monitoring devices.
Identify indications, principles of operation, complications, and management strategies for mechanical ventilation.
Describe the concepts of respiratory muscle fatigue, rest, and conditioning as they relate to the mechanically ventilated weaning patient.
Identify essential components for the successful design and use of weaning predictors, protocols for weaning trials, and multidisciplinary institutional approaches to the care of long-term mechanically ventilated (LTMV) patients.
DIAGNOSTIC TESTS, MONITORING SYSTEMS, AND RESPIRATORY ASSESSMENT TECHNIQUES
Arterial Blood Gas Monitoring
Arterial blood gas (ABG) monitoring is frequently performed in critically ill patients to assess acid-base balance, ventilation, and oxygenation. An arterial blood sample is analyzed for oxygen tension (PaO2), carbon dioxide tension (PaCO2), and pH using a blood gas analyzer. From these measurements, several other parameters are calculated by the blood gas analyzer, including base excess (BE), bicarbonate (HCO3̄ ), and oxygen saturation (SaO2). Fractional arterial SaO2 can be directly measured, if a co-oximeter is available. Normal ABG values are listed in Table 5-1.
TABLE 5-1LABORATORY AND CALCULATED RESPIRATORY VALUES ||Download (.pdf) TABLE 5-1 LABORATORY AND CALCULATED RESPIRATORY VALUES
|Parameter ||Value |
|Arterial Blood Gases |
| ||7.35-7.45 |
| ||35-45 mm Hg |
| ||22-26 mEq/L |
| ||− 2 to 2 mEq/L |
| ||80-100 mm Hg (normals vary with age and altitude) |
| ||> 95% (normals vary with age and altitude) |
|Mixed Venous Blood Gases |
| ||7.32-7.42 |
| ||40-50 mm Hg |
| ||35-45 mm Hg |
| ||60%-80% |
|Respiratory Parameters |
| ||6-8 mL/kg |
| ||8-16/min |
| ||70-100 mL/cm H2O |
| ||≤ − 20 cm H2O |
|Respiratory Calculations |
| || |
| ||Vt/(Plateau pressure − PEEP) |
ABG samples are obtained by direct puncture of an artery, usually the radial artery, or by withdrawing blood through an indwelling arterial catheter system. A heparinized syringe is used to collect the sample to prevent clotting of the blood prior to analysis. Blood gas samples are kept on ice unless there is the ability to immediately analyze to prevent the continued transfer of CO2 and O2 in and out of the red blood cells. ABG analysis equipment is often kept in or near the critical care unit to maximize accuracy and decrease the time for reporting of results. Additionally, portable point-of-care devices are available at many hospitals, which allow measurement at the bedside. Regardless of the method used to obtain the ABG sample, practitioners should wear gloves and follow standard precautions to prevent exposure to blood during ...