Hemodynamic Monitoring - An Overview

Introduction:

Heme means blood, and dynamic means flow. It measures blood flow, pressure, and oxygenation within the cardiovascular system. Hemodynamic monitoring is required, particularly in critically ill patients. The purpose of hemodynamic monitoring is to ensure there is optimal tissue perfusion and oxygen delivery while maintaining an adequate mean arterial pressure.

What Are the Indications for Hemodynamic Monitoring?

Hemodynamic monitoring is required in the following:

• Any deficit or loss of cardiac function, such as myocardial infarction, congestive heart failure, or cardiomyopathy.

• Any type of shock, such as cardiogenic shock, neurogenic shock, or anaphylactic shock.

• Reduced urine output due to dehydration, hemorrhage, burn, or surgery.

What Are the Methods of Hemodynamic Monitoring?

It can be of two types:

1. Non-Invasive Methods:

• Electrocardiogram.

• Pulse oximetry.

• Kidney function.

2. Invasive Methods:

• Pulmonary artery catheter.

• Central venous pressure.

• Arterial pressure monitoring.

Non-Invasive Methods:

1. Electrocardiogram:

It is a quick, easy, non-invasive method to record the heart's electrical signals. Electrodes are placed at certain points on the body, and these electrodes are connected to the electrocardiogram machine. It is indicated in cases of chest pain, palpitations of the heart, irregular heartbeats, severe tiredness or dizziness, and shortness of breath.

2. Pulse Oximetry:

It is based on the Beer-Lambert law. It measures the oxygen saturation level of the blood.

3. Kidney Function Test:

Urine output is measured quantitatively in a critically ill patient. Whenever there is low production of urine, known as oliguria, it indicates that the heart function is compromised.

Invasive Methods:

1. Pulmonary Artery Catheter:

It is a thin, hollow tube, also known as the Swan-Ganz catheter, that is introduced through a central vein like the femoral, jugular, brachial or antecubital vein, which goes to the right side of the heart and advances into the pulmonary artery. The Swan-Ganz catheter is a quadruple lumen catheter with a thermodilution sensor attached to a transducer which can measure the central venous pressure, right atrial pressure, right ventricular pressure, pulmonary artery pressure, and pulmonary capillary wedge pressure. It has a balloon that can be inflated and helps place the catheter’s tip into the pulmonary artery. It has a key advantage over other methods in that it provides simultaneous measurements of hemodynamic parameters in addition to cardiac output, including pulmonary artery pressure, right, and left-sided filling pressures, and mixed venous oxygen saturation (SvO2).

A pulmonary artery catheter is indicated in the following:

• Pulmonary Hypertension- It is increased blood pressure in the lungs.

• Cardiomyopathy- The enlargement of the heart can ultimately lead to heart failure.

• Congenital Heart Disease- Such as a ventricular septal defect.

• Heart Failure- It is a condition in which the heart cannot produce enough blood for the body.

• Shock- It is a condition in which there is reduced blood flow and oxygen to the tissues.

Risk factors of pulmonary artery catheters include:

• Bruises at the site of insertion of the catheter.

• Excessive bleeding at the site of vein puncture during catheterization.

• Air emboli formation due to entrapment of air from the infusion ports.

• Cardiac tamponade, an accumulation of fluid in the pericardium, can affect the heart to pump blood effectively.

• Pulmonary infarction occurs when the balloon is inflated for an extended period.

• Cardiac wall perforation can also occur.

• Pulmonary artery rupture can occur when balloon inflation damages the pulmonary artery.

• Blood clot formation at the tip of the catheter.

• Infection.

2. Central Venous Pressure:

It is measured by an intravenous catheter placed into the jugular vein and terminates into the vena cava and the right atrium. It is used to estimate the preload and the right atrial pressure. Normally, the central venous pressure ranges between 8 to 12 mmHg. An increase in central venous pressure indicates an increase in the blood volume and impairment in cardiac function due to decreased contractility, valvular abnormalities, and arrhythmias. In contrast, a decrease in central venous pressure indicates a shift in the blood volume or more than 10 % of blood loss.

The central venous pressure is inversely proportional to the venous return to the heart, and indirectly it measures the cardiac output. An increase in the juxta cardiac pressure, pericardial tamponade, right ventricular infarct, and right ventricular outflow obstruction can decrease the venous return of the heart. It is most useful in patients with ascites or edema because an elevated central venous pressure suggests heart or lung disease, whereas a normal central venous pressure suggests chronic liver disease. An elevated central venous pressure is easily appreciated clinically as a pulsation of the internal jugular vein.

3. Arterial Pressure Monitoring:

Most commonly, it is done by cannulation of a peripheral artery. The most common site of arterial cannulation is the radial artery. Cardiac contractility causes mechanical motion of blood flow within the catheter. This motion is transmitted to a transducer which converts the mechanical signals into electrical signals and then transfers them to the monitor.

It is indicated in cases such as:

• Critically ill patients in the intensive care unit.

• Cases in which vasoactive drugs such as Adrenaline, Noradrenaline, Dopamine, and Dobutamine are given.

• Surgical patients with increased risk of morbidity or mortality.

• Patients who require frequent blood draw for arterial blood gas analysis oxygen and carbon dioxide levels in the blood.

However, arterial cannulation is contraindicated in cases like:

• Infection at the site of insertion of the cannula.

• Peripheral arterial vascular insufficiency.

• Peripheral arterial vascular disease.

• Collateral circulation is absent.

Complications include:

• Catheter-related infection and sepsis.

• Absence of collateral circulation.

• Formation of hematoma.

• Formation of arterio-venous fistula.

• Stenosis of the blood vessels.

• Thrombosis.

• Blood loss.

Conclusion:

Hemodynamic monitoring is the study of blood flow through the cardiovascular system and helps monitor critically ill patients in intensive care units. Studying the changes in the blood flow helps in preventing stroke and other complications and thereby preventing it. Echocardiography was the most commonly used method, but the pulmonary artery catheter remains the most reliable method so far. The knowledge of the cardiovascular system function, monitoring of the therapeutic interventions, and the need for differential diagnosis make hemodynamic monitoring an essential component for better outcomes for the patient.