Systemic Arterial Catheters
Arterial catheter placement is indicated in those patients who require frequent blood pressure monitoring and in those who require more than 2 or 3 blood gas samples per day. The most common arterial access site utilized in non-neonates is the radial artery (70%), followed by the posterior tibial and femoral artery. Peripheral arteries are best used because of the low complication rate should thrombosis occur. However, the femoral artery has frequently been cannulated using the Seldinger technique in children, with few complications. The superficial temporal artery is easily identified and cannulated in neonates. However, because of concern for retrograde flow of air or debris into the carotid artery circulation, it should be used only if extreme care is taken during flushing of the catheter.
Arterial cannulations in children are performed via either the percutaneous or cutdown methods. Percutaneous insertion should be attempted primarily in most cases. Typical catheter sizes for arterial cannulation include 24- or 22-gauge in neonates, 22-gauge in large infants and children, and 20-gauge in older children and adolescents. Two methods of percutaneous cannulation are commonly used: (1) the direct cannulation method and (2) the transfixion technique. I prefer the transfixion technique in which the catheter and needle are advanced through the artery as the pulse is palpated (Fig. 7-3). The needle frequently abuts the head of the radius, which is directly under the artery. Withdrawal of the catheter and needle may demonstrate a flash of blood, at which point the needle and catheter are advanced once again. The needle is then removed, the catheter withdrawn until blood return is visualized, and the catheter advanced down the lumen of the artery. The catheter is sutured in place and secured with tape as a sterile dressing is placed over the cannulation site. At times a wire, such as a 0.0015-inch diameter wire, which fits through a 24-French catheter, may be used to advance the catheter into the artery when difficulties are encountered with placement.
Percutaneous insertion of a catheter into the radial artery. The hand is taped securely to an arm board with a roll placed under the wrist (A). The radial pulse is palpated, and the needle/catheter guided at approximately a 30° angle through the artery (B). As the needle/catheter is withdrawn and passes into the artery, blood may be observed to flow into the hub. The needle/catheter is then advanced a second time, the needle removed (C), the catheter withdrawn until blood return is observed (D), and the catheter advanced down the lumen of the artery (E).
The technique of arterial cut-down of the radial or posterior tibial artery is most often utilized in neonates and infants. A 6- to 8-mm transverse incision is performed over the arterial site, and blunt dissection is used to identify the artery (Fig. 7-4). The radial artery is often located deeper than one might expect, frequently lying directly on the head of the radius. It is unusual to observe or palpate pulsations in the artery. An appropriately sized over-the-needle catheter is introduced directly down the lumen of the artery. The needle is removed. The catheter is advanced into the artery only if blood flow returns from the catheter. Otherwise, the catheter is slowly removed until blood flow return is noted, at which point the catheter is advanced. It is rare that artery ligation is required.
Insertion of a catheter into the radial artery by the cut-down technique. A 1-cm incision is performed over the area of the radial artery just proximal to the wrist (A). The artery is identified on the head of the radius and retracted distally with a suture as a needle/catheter is advanced into the lumen of the artery (B). Ligation of the artery is usually not necessary.
The umbilical artery provides an excellent site for arterial access in neonates who are less than 10 days of age, with umbilical artery catheters being placed in up to 30% of neonates who are admitted to the neonatal ICU. Umbilical tape or a heavy suture may be placed around the base of the umbilical cord to reduce bleeding. An incision on the inferior aspect of the umbilicus, approximately 1 to 2 cm above skin level, should allow identification of one of the 2 ventrally located umbilical arteries (Fig. 7-5). If the artery cannot be located or cannulated in the umbilical stump, another option is to perform an infraumbilical curvilinear incision with identification of the umbilical artery in the space of Retzius, which exists posterior to the linea alba and anterior to the peritoneum. After a 4-0 suture is placed around the artery for retraction, the artery is partially transected, and a 3.5-French (preterm or small neonate) or 5-French catheter is advanced into the artery after being flushed with heparinized saline. The catheter is advanced gently, as resistance is often met at a point approximately 5 to 6 cm from the umbilicus as the catheter passes from the hypogastric artery into the femoral artery. The final catheter position should be either above the mesenteric vessels (T-9 to T-11) or below the renal vessels (L-4). The data from Fig. 7-6 may be used to determine the insertion length of the umbilical artery catheter. Advancing the catheter a length equivalent to 0.65 times the distance between the umbilicus and the shoulder plus the length of the umbilical stump will place the catheter in the L-4 vertebral region. A radiograph should be performed to document catheter position following placement.
Insertion of a catheter into the umbilical artery. An incision is performed on the inferior aspect of the umbilicus 1 to 2 cm above the base (A). One of the 2 arteries is identified, surrounded with a suture (B), incised, and cannulated (C). If an artery cannot be identified in the umbilical cord, an infraumbilical incision will allow access to (D) and cannulation of (E) an umbilical artery in the space of Retzius.
Umbilical artery catheter insertion length as a function of patient total body length. (Adapted from Klaus MH, Fanodroff AA. Case of the High-Risk Neonate, 4th ed. Philadelphia: W.B. Sanders; 1993.)
A transducer is connected to the arterial catheter via noncompliant tubing, and a continuous-flow system is used to provide flushing of the catheter with heparinized saline or dextrose water. At no time should the catheter be flushed in a bolus fashion because large amounts of fluid may be incidentally introduced. Studies have demonstrated that flush may appear in the carotid artery distribution after injection of only 0.3 to 0.75 mL of flush into the radial artery of a neonate. Care should be taken to minimize blood waste, especially in small neonates. Systems that provide on-line information with regard to PaO2, PaCO2, and pH have been developed and are becoming more reliable. Other devices avoid blood waste by aspirating the blood into proximal tubing for later reinfusion after sample withdrawal.
Systolic and diastolic blood pressures may be artificially elevated as a result of catheter whip in a large artery and artificially decreased if dampening of the signal occurs from air or clot in the connecting tubing or if the tubing is too narrow, too long, too compliant, or kinked. Systolic and diastolic arterial pressure data obtained from a peripheral systemic arterial catheter often are greater and less, respectively, than those measured in the aorta. The mean arterial pressure, however, is the same in both. The mean arterial pressure may be estimated by adding the diastolic blood pressure plus one-third of the difference between the systolic and diastolic blood pressure and is the most reliable parameter of blood pressure.
Complications of arterial catheter placement are surprisingly low. Distal embolization or ischemia is rare, and tissue loss even more so. Thrombosis of the vessel most frequently occurs in the radial artery in small newborns and infants after prolonged catheterization. Follow-up ultrasound evaluation has demonstrated that the majority of obstructed arteries recanalize following catheter removal. If the pulse is lost in an extremity following attempted or successful arterial catheter placement, the catheter should be removed, and systemic anticoagulation considered. If the limb is nonviable, then surgical exploration should be entertained. Although acute vascular injury may lead to chronic ischemia and limb length discrepancy, arterial exploration is technically difficult and often unrewarding in neonates and infants. In those cases, consideration for heparin anticoagulation, administration of streptokinase or urokinase, and observation will often result in improvement in limb perfusion.
The incidence of clinically significant aortic thrombus formation in patients with umbilical artery catheters is between 3% and 6%. The incidence of adverse thromboembolic events appears to be greater in those patients with a low (L-4 or lower) abdominal umbilical artery catheter. Overt aortoiliac thrombosis accompanied by decreased lower extremity blood flow, and hypertension may be managed with supportive care and antihypertensive therapy. More severe sequelae should be treated with systemic heparinization and/or fibrinolytic therapy with surgical thrombectomy performed if limb-threatening ischemia, renal failure, visceral compromise, or systemic acidosis is present. If unilateral lower extremity ischemia occurs in a patient with an umbilical artery catheter in place, consideration should be given to angiography and/or thrombolytic therapy via the catheter before it is removed.
Sepsis related to arterial catheters occurs in fewer than 1% and in 2% to 5% of cases with radial and umbilical artery catheters, respectively. No medications, except for heparin and papavarin, should be administered via any arterial line.
The central venous pressure (CVP, right atrial pressure) serves as an excellent monitor of volume status, especially in children. In the pediatric population, the central venous pressure is as reliable as pulmonary artery or pulmonary capillary wedge pressure assessment in patients who have normal cardiac function and in whom high positive end-expiratory pressures (PEEP) are not being applied.
Central venous access may be obtained by cut-down or by percutaneous means (see Chapter 9: Vascular Access Procedures). Most commonly, access by cut-down is obtained via the external jugular vein, the common facial vein, or the saphenous vein at the saphenofemoral junction with placement of either a tunneled broviac silastic or a standard polyurethane catheter. The external jugular vein has a more direct, straight path to the superior vena cava (SVC) in neonates and infants than in children and adolescents. The common facial vein should be traced back to the internal jugular vein before cannulation to ensure proper identification. The femoral vein may be cannulated via the saphenous vein, which is easily identified in the anteromedial subcutaneous tissues of the upper thigh/groin. In newborns, the umbilical vein may be used to gain access to the central venous circulation. A 5- or 8-French catheter may be advanced via the umbilical vein to the left portal vein through the ductus venosus and into the right atrium. Difficulty with incidental passage into the portal venous system is frequent and may be recognized by the development of resistance before the predicted catheter insertion length. When this problem is encountered, the catheter should be removed a short distance, twisted, and gently reinserted. The catheter should be removed if radiography demonstrates placement in the portal venous system.
Percutaneous access to the central veins is most commonly performed via the subclavian, internal jugular, or femoral veins. In children, a 21-gauge needle is used to access the subclavian vein. The patient should be placed in the Trendelenburg position, and a roll placed under the back. Placement can be done “blindly” following anatomical landmarks, or the assistance of bedside fluoroscopy or ultrasound guidance may be a useful adjunct. The needle is advanced at a point approximately 5 mm below the clavicle in the area of the midclavicular line until the clavicle is encountered. The needle is then walked down and advanced underneath the clavicle just lateral to the point where the first rib and the clavicle come into approximation. The hub of the needle is then brought in an inferior and lateral direction. The needle is advanced in a superior and medial direction under the clavicle toward the sternal notch as the vein is encountered. Once the needle is within the lumen of the vein, as evidenced by free return of blood during aspiration, a “J”- wire is passed through the needle, the needle is removed, and the catheter is placed over the wire into the central venous position in the SVC or right atrium.
The internal jugular vein is most frequently accessed from a point one fingerbreadth above the clavicle between the heads of the sternocleidomastoid muscle (SCM). The needle is oriented toward the ipsilateral nipple and enters the vein at a 45° angle. An alternative approach is posterior to the sternocleidomastoid with the needle entering the skin at the junction of the lower and middle thirds of the posterior margin of the SCM while the needle is oriented toward the sternal notch. The femoral vein is located medial to the artery in the groin. The vein may be identified by aspiration with a 21-gauge needle at a 45° angle approximately one fingerbreadth medial to the palpated femoral artery pulse and 1 to 2 fingerbreadths below the inguinal ligament. Ultrasound guidance is advised during central venous access, especially during internal jugular cannulation.
Assessment of central venous pressure should be performed at end-expiration because it is at this point that the CVP is least affected by the patient's ventilatory status. Pressure measurements should be performed using a transducer placed at the level of the right atrium. Variation in central venous pressure with the cardiac cycle should be documented. Normal right atrial pressure is 5 to 10 mm Hg.
The central venous oxygen saturation (ScvO2), as determined via a central venous pressure catheter, may be used to guide treatment in patients with sepsis. Such goal-directed therapy may decrease the mortality of adult patients with severe sepsis and septic shock.
The most common complication of central venous catheter placement is sepsis, which occurs with an incidence of from 5% to 10%. Sepsis is most often managed with antibiotic therapy and catheter removal or replacement, although in the pediatric population central venous catheter sepsis may, if necessary, be treated successfully with antibiotics and maintenance of the catheter in situ. Vascular thrombus formation likely occurs in all patients with central venous catheters. However, these thromboses are clinically significant in only 5% to 10% of patients. Catheter-induced superior vena caval occlusion may result in hydrocephalus, pulmonary lymphangiectasia, and chylothorax, with the majority of such cases occurring in patients under 1 year of age. Other complications associated with placement and maintenance of a central venous catheter include catheter breakage, catheter dislodgment and embolization, pneumothorax in 6% of cases, hydrothorax following malposition of the catheter into the thoracic cavity, subclavian artery puncture leading to hemorrhage, brachial plexus injury, and thoracic duct injury when a left subclavian or internal jugular vein catheterization is attempted. Wire breakage with embolization may occur if the wire is withdrawn inappropriately through the introducing needle.
Measurement of Abdominal Pressure
Recognition of elevated intraabdominal pressure (IAP) is important in ICU patients with shock. The abdominal physical examination provides general assessment of whether the abdomen is distended and taut and thus concerning for abdominal compartment syndrome (ACS). Other signs of ACS include decreased urine output or anuria, reduced venous return, cyanosis of the lower extremities, high ventilator pressure requirements, and development of metabolic acidosis. Cardiac output may be reduced by as much as 30% due to compression of the diaphragm and heart. While pathologic IAP has not been well-defined in pediatric patients, any pressure greater than 20 mm Hg is considered to be consistent with ACS and potentially physiologically compromising in adult patients. IAP is most effectively assessed via a liquid-filled bladder catheter with a manometer placed through the access port of the bladder catheter drainage system. Emergent decompression of the abdomen via exploratory laparotomy should be performed following recognition of ACS. The abdomen should be decompressed by enlargement of the abdominal wall by placement of a synthetic mesh or through use of a silo or by open abdominal wall packing. Placement of such a pressure-monitoring balloon catheter via the oral or nasal route into the stomach has also been used for such measurements.
Pulmonary Arterial Catheters
The use of pulmonary artery (PA) catheters has been largely replaced by central venous pressure monitoring since, as mentioned previously, CVP assessment is accurate in most infants and children. In addition, prospective, randomized, controlled trials in adults have shown that mortality is increased in patients in whom a pulmonary artery catheter is used for central pressure monitoring. Thus, the rate of use of PA catheters in the ICU has decreased dramatically. Even so, there are times when right atrial catheter assessment of cardiopulmonary status may be inadequate in patients with pulmonary, renal, or cardiac insufficiency, those who remain hypotensive or hypoperfused despite apparently adequate volume resuscitation, and those who require pharmacologic intervention to enhance cardiac output. Such patients may benefit from the additional information provided by a pulmonary arterial catheter. A 5-French catheter is appropriate for patients approximately 25 to 30 kg in weight, and a 7-French catheter is appropriate for older patients. Most catheters have 5 lumina: (1) a port for injection of either 0.5 or 1.5 mL of air into an inflatable balloon at the tip of the catheter; (2) a thermistor probe near the tip, which allows determination of core body temperature and thermodilution cardiac output; (3) a fiberoptic bundle for determination of pulmonary arterial mixed venous oxygen saturation; (4) a port distal to the inflatable balloon that allows assessment of pulmonary arterial pressures when the balloon is deflated and left atrial pressures when inflated; and (5) 1 or 2 additional proximal infusion/pressure-monitoring ports usually placed in the right ventricle and/or right atrium.
Pulmonary arterial catheters are most often placed via a subclavian or internal jugular approach. In young children (less than 2 years old), the femoral venous approach may make transcardiac passage of the catheter easier. Once venous access is established, an introducer catheter is placed; the balloon is inflated and tested; and all monitoring infusion ports are flushed and zeroed. The balloon is inflated as the catheter is gently advanced: right atrial, right ventricular, pulmonary arterial, and, finally, pulmonary wedge waveforms should be observed (Fig. 7-7). The pulmonary arterial catheter may curl in the right heart, or the tip may impinge in the trabeculae of the right ventricle. Catheter placement may be especially difficult in those patients with right ventricular hypertrophy or dysfunction. Counterclockwise rotation while advancing the catheter, placing the patient in the left decubitus position, and raising or lowering the head of the bed may all aid in catheter placement. Occasionally, fluoroscopy or echocardiography may help to guide insertion. The balloon should “wedge” or occlude the pulmonary artery at the end of the 1.5-mL insufflation with rapid return of a pulmonary artery pressure waveform on deflation. The ability to wedge the balloon with <1.0 mL of air may indicate that placement of the catheter is too distal in the pulmonary artery. Chest radiographs should be obtained to document correct placement.
Pulmonary artery catheter placement is illustrated. Vascular pressure waveforms may be used to monitor passage of the catheter through the right atrium (A), right ventricle (B), the pulmonary artery (C), and into the wedged position in the pulmonary artery (D). (Pulmonary capillary occlusion pressure = PAOP and reflects left atrial filling pressure.)
The balloon should remain inflated during passage of the catheter through the right heart in order to reduce the incidence of arrhythmias. Treatment of arrhythmias is rarely required, and lidocaine should be administered only if sustained ventricular tachycardia is induced at the time of placement.
Rupture of the pulmonary artery is a rare but lethal complication. Hemoptysis and/or cardiopulmonary collapse may follow balloon inflation during a wedge pressure measurement. Those patients with pulmonary arterial hypertension and coagulation deficiencies are at highest risk. This complication may be avoided by maintaining the tip of the catheter <2 cm lateral to the spine on chest radiograph; inflating the balloon with the minimal volume necessary to achieve a wedge tracing; and minimizing the frequency of wedge pressure assessment.
The distal port of the catheter should be continuously monitored for permanent wedging, which can lead to pulmonary infarction. If permanent wedging is observed, the catheter should be withdrawn until appropriate pulmonary arterial and wedge tracings are observed during deflation and inflation of the balloon, respectively. A number of other complications of pulmonary artery catheter placement are summarized in Table 7-1. Valvular damage may occur during withdrawal of the catheter with an inflated balloon. Knotting of the catheter in the right ventricle may require manipulation under fluoroscopy.
Complications of Pulmonary Artery Catheter Placement
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Table 7-1 Complications of Pulmonary Artery Catheter Placement
|Pulmonary artery thrombus formation/embolus |
|Pulmonary infarction |
|Ventricular arrhythmias |
|Right bundle branch block |
|Perforation of the right ventricle |
|Pulmonary artery rupture |
|Cardiac valvular damage |
|Knotting of catheter in right ventricle |
Measurement of Pulmonary Artery Pressure
The right atrial pressure may fail to represent the left ventricular preload in the setting of sepsis, acquired respiratory distress syndrome (ARDS) with application of high ventilator pressures, pulmonary hypertension, pulmonary embolus, pulmonary fibrosis, and cardiac dysfunction. In such cases, assessment of the left atrial pressure (LAP), as an approximation of left ventricular end-diastolic volume (LVEDV), may be accomplished during inflation of the pulmonary arterial catheter balloon. A static column of blood, without intervening valves, is then interposed between the distal catheter pressure monitoring site and the left atrium. This pulmonary artery occlusion pressure (PAOP) provides an estimate of LAP and, therefore, pulmonary capillary pressure, which is a determinant of the hydrostatic forces resulting in pulmonary edema. A PAOP greater than 25 mm Hg in normal lungs and greater than 18 mm Hg in the setting of sepsis and ARDS will frequently result in the development of pulmonary edema. The PAOP may also be used to assess LVEDV in order to optimize cardiac contractility. Unless cardiac compliance is altered (sepsis, restrictive pericarditis, cardiomyopathy) or mitral valve disease is present, the PAOP will accurately reflect LVEDV. Accurate assessment of LVEDV is also dependent on the location of the pulmonary arterial catheter tip: unless the tip is posterior to the level of the left atrium in the supine patient, alveolar pressures may exceed those of venous and/or arterial pulmonary vascular pressures, resulting in occlusion of the venous and/or arterial vasculature distal to the pulmonary artery catheter during a variable period of the respiratory cycle. This will preclude accurate assessment of LAP. Fortunately, the flow-directed pulmonary arterial catheter inserts most frequently at or below the left atrium because a predominance of blood flow is distributed to the dependent regions of the lungs.
PAOP should be assessed at end-expiration because the effects of ventilation on intrathoracic pressures and, therefore, PAOP may be significant. It is at this point that intrathoracic pressures are closest to atmospheric pressure. Application of PEEP may result in overestimation of the LAP by the PAOP. This effect is less significant in the injured, noncompliant lung. Under such circumstances, PAOP will exceed the LAP by only 1 mm Hg for every 5 cm H2O increase in applied PEEP. For this reason, and because of the potential for alveolar collapse and deterioration in gas exchange that may accompany even transient periods of ventilator disconnect in the patient with severe respiratory insufficiency, PAOP should be measured and reported without any attempt to reduce the effect of PEEP in such patients. All central pressures should be obtained from a paper tracing, rather than a digital output, so that end-expiratory pressures may be specifically identified and recorded.
Measurement of Cardiac Output
Invasive cardiac output assessment is frequently performed in the ICU using the temperature indicator dilution technique. An indicator of iced or room-temperature saline is injected into any central venous port. It is important to inject the bolus rapidly and at the same point in the respiratory cycle. Room temperature injectate-determined cardiac outputs are no less accurate than those assessed using iced-saline injections. In general, 5-mL injectate volumes are used, except in infants and small children in whom 1-mL iced saline injections are preferred. After mixing of the bolus with blood in the right ventricle, the blood temperature is assessed by a thermistor located at the tip of the pulmonary artery catheter (Fig. 7-8). Once the initial blood temperature, the volume of injectate, the injectate temperature, and the change in blood temperature as a function of time are known, cardiac output can be determined.
This figure illustrates thermodilution cardiac output determination during periods of normal (A), high (B), and low (C) cardiac output. The magnitude and duration of the change in temperature are inversely proportional to the cardiac output.
The accuracy of cardiac output assessment is improved by performance of measurements in triplicate. Any irregular curves or assessments that deviate by more than 10% are discarded. The mean of the remaining 3 individual measurements has an overall accuracy of ±10%.
The Fick equation may also be applied to invasively determine cardiac output
Calculation of the Fick-determined cardiac output requires assessment of the mixed-venous oxygen saturation via a pulmonary arterial catheter, arterial oxygen saturation, and airway oxygen consumption (VO2). Because of the inherent error present in each of the variables incorporated into the calculation, the Fick cardiac output has an overall error of approximately ±5%. In addition, the Fick-calculated cardiac output overestimates the thermodilution cardiac output by approximately 5% to 10%. A number of studies have demonstrated the feasibility of on-line Fick calculation of cardiac output through assimilation of data obtained from continuous oxygen consumption monitoring, arterial pulse oximetry, and mixed-venous oximetry.
Mixed Venous Oximetry Monitoring
The oxygen hemoglobin saturation in mixed venous pulmonary artery blood is referred to as the SvO2. As oxygen delivery (DO2) increases or oxygen consumption (VO2) decreases, more oxygen remains in the venous blood. The result is an increase in SvO2 (Fig. 7-9). In contrast, if DO2 decreases or VO2 increases, relatively more oxygen is extracted from the blood, and, therefore, less oxygen remains in the venous blood. A decrease in SvO2 is the result. The SvO2 serves as an excellent monitor of oxygen kinetics because it specifically assesses the adequacy of oxygen delivery in relation to oxygen consumption (DO2/VO2 ratio Fig. 7-10).
Oxygen consumption (VO2) and delivery (DO2) relationships. (Reprinted with permission from Hirschl RB. Oxygen delivery in the pediatric surgical patient. Can Opin Pediatr 19946:341.)
The relationship of the mixed venous oxygen saturation (SvO2) and the ratio of oxygen delivery to oxygen consumption (DO2/VO2) in normal eumetabolic, hypermetabolic septic, and hypermetabolic exercising canines. (Reprinted with permission from Hirschl RB, Heiss K. Cardiopulmonary critical care and shock. In: Oldham KT, Calambani PM, Foglia RP, eds. Surgery of Infants and Children. Scientific Principles and Practice. Philadelphia: Lippincott-Raven; 1997:149–182.)
Many pulmonary arterial catheters contain fiberoptic bundles that provide continuous mixed-venous oximetry data. Emitted light is reflected from circulating red blood cells and transmitted via the receiving fiberoptic bundle to an analyzer, where the data on the reflected light at 3 wavelengths are assessed to provide accurate determination of hemoglobin oxygen saturation. Continuous SvO2 monitoring provides a means for assessing the adequacy of oxygen delivery, early identification of cardiopulmonary instability, rapid assessment of the response to therapy, and cost savings in critically ill patients because of a diminished need for other data such as sequential blood gas monitoring. A decrease in SvO2 to less than 65% or a change in SvO2 over 5% to 10% should be investigated by assessing the factors that determine the SvO2 cardiac output, SaO2, and hemoglobin level with consideration for variables that might result in an increase in oxygen consumption. The accuracy of SvO2 monitoring may be diminished under certain circumstances where arteriovenous shunting occurs such as in the occasional patient with cirrhosis or sepsis. Importantly, this means that in situations where vasoregulation is altered, the SvO2 may be normal even though the oxygen delivery at the tissue level is inadequate.
Advanced Hemodynamic Monitoring
Algorithms can be developed that noninvasively can predict hemorrhage prior to the initiation of shock.
The components integral to integrated monitoring systems include: a ventilator; 3/5-lead ECG; pulse oximeter; noninvasive blood pressure (NIBP); end-tidal carbon dioxide (etCO2); patient temperature; invasive arterial and intracranial pressure capabilities; Ethernet communications; closed-loop control of oxygenation, ventilation, and IV fluid control; an integrated electronic medical record (data storage/export); alarming, intravenous (IV) pumps along with smart help, connected by powered USB ports. The system should support several external IV pumps and other yet to be developed noninvasive monitors, all connected via powered-USB ports. Other potential modules that could be included are an oxygen concentrator, patient warming, and an anesthesia control module.
Continuous patient monitoring started in the 1960s, when the technology for monitoring astronauts' vital signs was transferred to the bedside. Over the past 50 years patient monitoring systems have incorporated a variety of invasive and noninvasive sensor technologies to derive and display clinically important parameters. Patient monitoring systems are set to evolve once again as new sensing technologies merge with rapid advances in computing technology. Within this context, the application of advanced modeling techniques to standard physiological waveform data is leading to the discovery of several, previously unknown, hemodynamic relationships. The next generation of patient monitoring systems will be noninvasive functional tools that are able to estimate hemodynamic states in real-time, predict physiological reserve, and optimize care of the patient.
The goal of this chapter section is to familiarize the reader with several existing and a number of new sensor technologies for advanced hemodynamic patient monitoring in the setting of acute injury, specifically hemorrhage. The setting of acute blood loss has been chosen because the physiology of hemorrhage is typically rapid and compensatory, without the confounding effects of an insidious medical illness. The application of these new sensing and machine-based technologies will be transferable to many other areas of disease detection and monitoring. By improving our ability to recognize early changes in the pathophysiology of illness or injury we hope to limit disease progression, guide early therapy, and promote rapid recovery, thereby improving patient outcomes.