PiCCO


PiCCO is a method developed by the Munich based company Pulsion Medical Systems to monitor important hemodynamic and circulatory data of patients in intensive care units. The devices also bear the PiCCO brand name. It is used to monitor blood circulation and blood volume in cases of shock, acute respiratory distress syndrome, severe heart failure, polytrauma, burns and during major operations.

Physiological background

The method initially uses transpulmonary thermodilution for calibration to determine cardiac output according to the Stewart-Hamilton method, later the continuous measurement of the cardiac output takes place by means of pulse contour analysis. Compared to the use of a pulmonary catheter, continuous measurement offers additional trend analysis with good control of fluid requirements and the advantages of easier and cheaper handling. A disadvantage is the need for regular recalibration by transpulmonary thermodilution.

Thermodilution

In the thermodilution, a fixed volume of an isotonic saline or glucose solution cooled to below 10 °C is rapidly injected intravenously, preferably central venously. The cold fluid passes as a cold bolus through the right atrium and the right ventricle, then the pulmonary vessels and the left heart, whereupon it flows into the body's circulation. At the measurement point, e.g. in the femoral artery, the temperature of the blood is measured and a so-called thermodilution curve is recorded. It depends on the cardiac output and the amount of fluid in the vasal and extravascular compartments. The preload for the heart can be derived in the form of the global end-diastolic volume or the intrathoracic blood volume ; in addition, the extravascular lung water EVLW, a parameter for impending pulmonary edema, is calculated. In addition, the contractility of the heart muscle can be assessed.
Contractility, preload and afterload are determinants of cardiac output according to the Frank-Starling mechanism.

Pulse contour analysis

After the initial calibration, the cardiac output can then be monitored continuously in real time by pulse contour analysis in addition to arterial blood pressure. The stroke volume is proportional to the area under the systolic part of the pressure curve; multiplied by the stroke rate, the cardiac output is obtained. In addition, it is possible to determine the variation in stroke volume and systemic vascular resistance. The Frank-Starling mechanism was described independently by Frank and Starling in 1899.

Measurement technology

Two catheters are inserted into the patient:
From the transit time and the dilution of a bolus of cold fluid between the two catheter tips, the cardiac output and some volumetric parameters for preload and pulmonary edema can be measured. An additional catheter with pressure sensor in the pulmonary artery is not required.

Interpretation

In addition to the preload parameters ITBV and GEDV, large fluctuations in the arterial pressure curve during ventilation are a further measure of positive volume responsiveness, i.e. the effect of infused fluid on the circulation. A stroke volume variation of more than 10-12 percent measured by the PiCCO in a patient on controlled ventilation without cardiac arrhythmia indicates a volume deficiency.
Compared to pressure-based methods of measuring hemodynamics, such as the pulmonary catheter, "volumetric" parameters are measured here. For example, the preload of the pulmonary catheter is estimated by means of pulmonary artery occlusion pressure and measured by the PiCCO as intrathoracic blood volume index ITBI based on the GEDV. Other parameters, such as cardiac index and systemic vascular resistance index, are given in the same way in both procedures. The determination of a preload parameter, the cardiac index and the systemic resistance allows the differentiation of shock forms and to control appropriate therapeutic interventions. In order to compare the measured parameters, a normalization to the body surface is recommended. Such a parameter is called an index.
Whether the measurement of volumetric parameters offers advantages over the measurement of pressure-based parameters has been proven. The guidelines provide volumetric monitoring via pressure monitoring. Several studies have shown a superiority of volumetric measurements over pressure measurements at least in predicting the effect of fluid administration on cardiac output. Volumetric strategies could also show outcome effects.
The PiCCO measurement represents a supply-side monitoring. However, in the Rivers study on the treatment of early sepsis - one of the few studies to demonstrate survival benefits of hemodynamic monitoring in septic shock - in addition to supply-side monitoring, ScVO2 was used as consumption-side monitoring to optimize therapy in order to ensure a survival benefit. Modern monitoring strategies rely on simultaneous monitoring of the oxygenation balance, i.e. the balance between oxygen supply and oxygen consumption, which is reflected in ScVO2.
Advantages of the PiCCO-System compared to the pulmonary catheter are that the measuring catheter can be in place a longer time and the fact that it is not necessary to pass the heart and heart valves during catheterisation. The reduction of complications during the installation and the economic factor are a great success. Both systems can also be represented in the TISS score.
The pulmonary catheter has a significance in isolated right heart failure, but in any other form of shock PiCCO monitoring is clearly superior.
The calibratability of the PiCCO system primarily provides physiological information about flow, preload, afterload and contractility. Secondly, recalibration adapts the continuous cardiac output measurement to extreme situations. This compensates for effects caused by shock, centralization, vasopressor therapy etc.

Literature