This article was first written during the outbreak of the SARS-CoV-2 pandemic, even though at the time the contagion is decreasing, I still think it’s very important to offer a small summary of the theory and techniques used during the process of prone positioning in patients affected with ARDS (Acute Respiratory Distress Syndrome). The prone position involves positioning the patient ventral side down and dorsal side up.
The main question is: why do we prone position patients that are affected by ARDS?
In the supine position, ARDS shows that the lung parenchyma presents edema homogeneously distributed from the sternum to the vertebrae, causing an increase in weight and the hydrostatic pressures transmitted throughout the lung. The loss of alveolar gas in the dependent regions of the lung is due to the pressure extruded by the gravitational force of the overlying lung parenchyma and the heart. The prone positioning re-distribution of fluids by gravity is the main result: from the dorsal areas, which are subject to squeezing of the lung parenchyma’s gravitational forces, the liquid moves towards the ventral areas which were previously aerated. In addition to this benefit, the back areas are now less subjected to pressure from the heart, because the weight is mainly distributed on the sternum. The prone position exposes the pulmonary section in which perfusion and ventilation are increased, therefore, reducing the shunt. Specifically, the perfusion does not change, but what changes in the distribution of ventilation, which allows the fluids that are moved by gravity to expose the back areas. These back areas are usually the most perfused, and this procedure allows them to re-open.
For several years the main goal was the improvement of oxygenation. Today’s patients who respond to pronation are those whose carbon dioxide levels drop even minimally with equal ventilation. This would mean that in addition to reducing the shunt, the maneuver also helps the distribution of better ventilation. In this condition, there would be an increase in alveolar ventilation with the consequent removal of CO2.
During the prone positioning, the driving pressure can worsen because in some patients there is a reduction in the elasticity of the rib cage. But in many cases, this decrease is compensated by the improvement in the elasticity of the lung.
Pronation is a useful tool to protect against ventilator-induced lung injury (VILI). If the closed areas are those that are the most subjected to the gravitational forces in the pulmonary parenchyma, the pressure to be exerted to overcome cardiac resistance is very high, but by multi-positioning the patient, it can be averted since it is easier to access recruitable areas without subjecting the assisted to pressures that can damage the lungs.
Summing up the effects during prone positioning:
- Improvement of oxygenation due to the recruitment of the dorsal regions, which exceeds the recruitment of the ventral regions, which are now in an unfavourable condition, and the pulmonary profusion is still in good condition in the dorsal regions. These regions have the effect of greater ventilation and greater perfusion thus it reduces the intrapulmonary shunt. The primary goal is the improvement of the redistribution of ventilation.
- VILI prevention. If supine ventilation has reached its limit, it is advisable to pronate the patient in order to prevent damage to the parenchyma. He/she could respond to recruitment maneuvers, which decrease with lower pressure.
- With the prone posture, the ventilation is better distributed, therefore the pulmonary pressure decreases leading to a reduction in the work of the right ventricle. It is, therefore, imperative to monitor the hemodynamic continuously for the reduction of the preload, which will lead to certain consequences and possible right or left ventricular dysfunction. This will then lead to cardiogenic shock. The use of prone positioning, unfortunately, comes with several serious complications.
All guidelines for the management of respiratory failure with the PaO2/FiO2 ratio below 150mmHg include pronation for at least 18 hours a day, if possible, which will likely result in survival benefits. It is recommended that the maneuver be performed with five operators because the relationship between safety and complication is directly related.
Pronation has several side effects, which are attributed to hemodynamic instability, haemoptysis, recent tracheostomy, severe obesity, and recent cardiac arrest. Pronation must be completely excluded in cases of: trauma with the instability of the vertebral column, open abdomen, or abdominal ischemia. Do not overlook the risk of cutaneous compression and integrity, corneal lesions, and dislocation of medical devices such as an endotracheal tube, arterial catheter, peripheral and/or central venous catheters, medical drainages. Proning a patient can expose him/her also to joint injuries, and emesis.
Prior to the Covid-19 era, the execution of correct pronation already required adequate planning with the reprogramming of daily staff organizations (which have been already understaffed for several years) that presupposes the direct involvement and supervision of expert personnel. During the coronavirus pandemic, the staff found itself managing many complex patients, that came with exceptional workloads and not always with experienced staff. Early and periodic treatment with pronation is also included in severe COVID-19 respiratory failure. We are well aware that it is not always possible to involve a certain number of people. The prone positioning can be executed by only three operators, although we have to accept that the consequences and the risks are much higher, and should be taken into account.
The videos show the different methods and have been made available by a colleague and friend (Alberto Lucchini)
Prone positioning executed by 5 operators:
Prone positioning executed by 3 operators:
Thank you and never give up!!!
English version edited by Giulia Azzini
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