A10 Life support

Topic

Life support temporarily replaces a physiological function that the body can no longer maintain on its own, sustaining the patient while the affected organ recovers or an alternative treatment is determined. It can replace respiratory, renal, cardiovascular, or digestive functions, with the ultimate goal of progressively reducing assistance as the body regains the ability to perform these functions itself.

In cases of respiratory failure, mechanical ventilation takes over the work of the diaphragm and respiratory muscles, delivering the necessary volume of air. To achieve this, the ventilator must generate sufficient pressure to overcome both the stiffness of the respiratory system and airway resistance. The stiffer the lung or the higher the flow resistance, the greater the pressure required to deliver the same volume.

The pressure required to maintain air in the lung at the end of inspiration allows for the assessment of lung distension. Particular attention is also paid to the difference between this pressure and the pressure remaining at the end of expiration. Protective ventilation strategies aim to keep this difference below approximately 15 centimeters of water, thereby reducing the risk of ventilator-induced lung injury.

When renal function fails, dialysis replaces the elimination of waste products by passing blood through an artificial membrane. The efficacy of a session depends on the filter's capacity to remove a reference substance, the duration of the procedure, and the body volume in which the substance is distributed. These factors are combined into an index representing the effective dialysis dose received. If the value falls below a specific minimum, the clearance is considered insufficient.

When the heart, lungs, or both suffer from severe failure, extracorporeal membrane oxygenation (ECMO) may be used. This system draws blood from the patient, passes it through a membrane to oxygenate it, and returns it to the circulation. Its configuration depends on whether it is intended primarily to replace lung function or to provide circulatory support as well. The oxygen supply provided by this system depends on the blood flow passing through the membrane and the extent to which oxygen content is increased. The higher the extracorporeal flow, the greater the proportion of the body's needs that can be met artificially. As the heart or lungs regain function, the proportion supplied by the system decreases, allowing for gradual withdrawal or weaning.

When the digestive tract cannot be used effectively, total parenteral nutrition delivers necessary macronutrients and micronutrients directly into a central vein. In critically ill patients, metabolic status can be assessed via nitrogen balance by comparing nitrogen intake from proteins with nitrogen excretion by the body. A markedly negative balance indicates the breakdown of body proteins and catabolism. Nutritional therapy aims to bring this balance close to zero and, during recovery, to make it slightly positive.

Weaning is also crucial in mechanical ventilation. It involves progressively shifting the work of breathing from the ventilator to the patient's own muscles. To determine whether weaning can begin, clinicians consider respiratory rate and the volume of air moved with each breath. Very rapid, shallow breathing indicates a high likelihood of failure.

During weaning, pressure support is gradually reduced while the patient's response is monitored. If the respiratory rate rises excessively, oxygenation drops, or agitation develops, the attempt may be deemed unsuccessful, and a higher level of support is reinstated.

Collectively, mechanical ventilation, dialysis, extracorporeal support, and parenteral nutrition temporarily replace essential bodily functions. Each technique requires assessing whether the support provided is adequate while simultaneously ensuring the intervention itself does not cause harm. The goal of intensive care medicine is not to maintain these substitutions indefinitely, but to sustain the patient through the critical phase and—once recovery permits—progressively return each function to the body through controlled weaning.

ID:2273