Patient Monitoring and Testing

Some monitoring is manual (ie, by direct observation and physical examination) and intermittent, with the frequency depending on the patient's illness. This monitoring usually includes measurement of vital signs (temperature, BP, pulse, and respiration rate), quantification of all fluid intake and output, and often daily weight. BP may be recorded by an automated sphygmomanometer; many of these devices also incorporate a transcutaneous sensor for pulse oximetry, which is monitored as well.

Other monitoring is ongoing and continuous, provided by complex devices that require special training and experience. Most such devices generate an alarm if certain physiologic parameters are exceeded. Every ICU should strictly follow protocols for investigating alarms.

Blood Tests

Although frequent blood draws can destroy veins, cause pain, and lead to anemia, ICU patients typically have routine daily blood tests to help detect problems early. Generally, patients need a daily set of electrolytes and a CBC. Patients with arrhythmias should also have Mg, phosphate, and Ca levels. Patients on TPN need weekly liver enzymes and coagulation profiles. Other tests are done as needed (eg, blood culture for fever, CBC after bleeding episode).

Point-of-care testing uses miniaturized, highly automated devices to perform certain blood tests at the patient's bedside or unit (particularly ICU, emergency department, and operating room). Commonly available tests include blood chemistries, glucose, ABGs, CBC, cardiac markers, and coagulation tests. Many are performed in < 2 min and require < 0.5 mL blood.

Cardiac Monitoring

Most critical care patients have cardiac activity monitored by a 3-lead system; signals are usually sent to a central monitoring station by a small radio transmitter worn by the patient. Automated systems generate alarms for abnormal rates and rhythms and store abnormal tracings for subsequent review.

Some specialized cardiac monitors track advanced parameters associated with coronary ischemia, although their clinical benefit is unclear. These include continuous ST segment monitoring and heart rate variability. Loss of normal beat-to-beat variability signals a reduction in autonomic activity and possibly coronary ischemia and increased risk of death.

Pulmonary Artery Catheter Monitoring

Use of a pulmonary artery catheter (PAC) is common in ICU patients. This device is a balloon-tipped, flow-directed catheter that is inserted via central veins through the right side of the heart into the pulmonary artery. The catheter typically contains several ports that can monitor pressure or inject fluids. Some PACs also include a sensor to measure central (mixed) venous O₂ saturation. Data from PACs are used mainly to determine cardiac output and preload. Preload is most commonly estimated by the pulmonary artery occlusion pressure (PAOP)

 However, preload may be more accurately determined by right ventricular end-diastolic volume, which is measured through the use of fast-response thermistors gated to heart rate.

Despite widespread use, PACs have not been shown to reduce morbidity and mortality. Indeed, PAC use has been associated with excess mortality. This finding may be explained by complications of PAC use and misinterpretation of the data obtained. Nevertheless, most physicians believe PACs aid in the management of certain critically ill patients when combined with other objective and clinical data. As with many physiologic measurements, a changing trend is typically more significant than a single abnormal value. Possible indications for PACs are listed in Table 1)

Table 1

Potential Indications for Pulmonary Artery Catheterization Cardiac disorders Acute valvular regurgitation Cardiac tamponade Complicated heart failure Complicated MI Ventricular septal rupture Hemodynamic instability* Assessment of volume status Shock Hemodynamic monitoring Cardiac surgery Postoperative care in critically ill patients Surgery and postoperative care in patients with significant heart disease Pulmonary disorders Complicated pulmonary embolism Pulmonary hypertension *Particularly if inotropic drugs required.

Procedure: The PAC is inserted through the subclavian or internal jugular vein with the balloon deflated. Once the catheter tip reaches the superior vena cava, partial inflation of the balloon permits blood flow to guide the catheter. The position of the catheter tip is usually determined by pressure monitoring (see Table 2) for intracardiac and great vessel pressures) or occasionally by fluoroscopy. Entry into the right ventricle is indicated by a sudden increase in systolic pressure to about 30 mm Hg; diastolic pressure remains unchanged from right atrial or vena caval pressure. When the catheter enters the pulmonary artery, the systolic pressure does not change, but diastolic pressure rises above right ventricular end-diastolic pressure or central venous pressure (CVP), ie, the pulse pressure narrows. Further movement of the catheter wedges the balloon in a distal pulmonary artery. A chest x-ray confirms proper placement.

Table 2

Normal Pressures in the Heart and Great Vessels Type of Pressure Average (mm Hg) Range (mm Hg) Right atrium 3 0–8 Right ventricle     Peak-systolic 25 15–30 End-diastolic 4 0–8 Pulmonary artery     Mean 15 9–16 Peak-systolic 25 15–30 End-diastolic 9 4–14 Pulmonary artery occlusion     Mean 9 2–12 Left atrium     Mean 8 2–12 A wave 10 4–16 V wave 13 6–12 Left ventricle     Peak-systolic 130 90–140 End-diastolic 9 5–12 Brachial artery     Mean 85 70–150 Peak-systolic 130 90–140 End-diastolic 70 60–90 Adapted from Fowler NO: Cardiac Diagnosis and Treatment, ed 3. Philadelphia, JB Lippincott, 1980, p. 11.

The systolic pressure (normal, 15 to 30 mm Hg) and diastolic pressure (normal, 5 to 13 mm Hg) are recorded with the catheter balloon deflated. The diastolic pressure corresponds well to the occlusion pressure, although diastolic pressure can exceed occlusion pressure when pulmonary vascular resistance is elevated secondary to primary pulmonary disease (eg, pulmonary fibrosis, pulmonary hypertension).

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