Infusion, it's not easy to say I love you

This is the 3825th article of Da Yi Xiao Hu

In the previous article, we talked about oxygen and water being the two most important substances for maintaining life. In recent years, the medical community has not only changed its view on oxygen inhalation for critically ill patients, but has also reflected on fluid therapy for critically ill patients.

Infusion is an important means of treatment in modern medicine, and the understanding of its importance has also gone through a tortuous process. The earliest clinical infusion therapy can be traced back to the cholera pandemic in 1831. In 1832, Scottish doctor Thomas Latta injected boiled saline into the patient's veins to replenish the body fluids lost due to vomiting and diarrhea caused by cholera. He is considered to be the first doctor who successfully established the human intravenous infusion treatment model. During the First and Second World Wars, people realized that post-traumatic shock was mainly caused by the loss of blood volume, so they actively used blood and plasma to treat the wounded, and thus saved many soldiers' lives. However, because the need for water and electrolytes was ignored, the incidence of post-traumatic renal failure was very high. During the Vietnam War, a large amount of crystalloid fluid was used to treat shock, resulting in a decrease in the incidence of renal failure in the wounded, but problems such as edema and acute respiratory distress syndrome (ARDS) occurred.

In 1961, American scholar Shires and others used isotopes to measure the circulating blood volume before and after major surgery and found that in addition to the patient's blood volume, blood loss and extracellular fluid, a part of the fluid was missing. Subsequent studies have shown that the circulating blood volume and extracellular fluid of patients undergoing major surgery and trauma have partially entered the "third space". Therefore, in addition to replenishing the exogenous loss, the patient's fluid replacement should also replenish the additional fluid loss that enters the "third space". In the 1970s and 1980s, some scholars proposed that resuscitation should be achieved by infusion to achieve an "extraordinary state" of circulatory function. Actively rehydrating patients with trauma, shock and other critical illnesses has become a consensus in the academic community and is widely used in clinical practice, known as the open fluid therapy strategy.

However, this also brings many problems. Large amounts of fluid replacement cause tissue edema, aggravate microcirculatory disorders, and poor wound healing; pulmonary edema is more obvious, especially for ARDS patients; renal congestion affects renal perfusion, leading to acute kidney injury; liver congestion, impaired synthesis function; intestinal edema affects absorption function and leads to increased intra-abdominal pressure; myocardial edema, impaired cardiac function; cerebral edema, increased intracranial pressure; endocrine disorders, metabolic disorders. Infusion may lead to neutrophil activation and aggravate inflammatory response. There is a layer of viscous substance composed of polysaccharide protein complexes on the surface of vascular endothelial cells, called glycocalyx, which has multiple protective effects on cells. Infusion may aggravate the degradation of glycocalyx and increase vascular permeability. In the early 1990s, some scholars found that most patients in surgical ICUs had excessive fluid in their bodies, and patients with excessive fluid load had increased perioperative complication rates and mortality.

In 2002, Lobo and other scholars proposed the concept of restrictive infusion. Restrictive fluid replacement can maintain good microcirculatory perfusion, facilitate tissue growth and healing, reduce lesion edema, and reduce ischemia-reperfusion injury. In the past decade, researchers have conducted a series of clinical studies to compare the advantages and disadvantages of restrictive and open fluid therapy. The results showed that patients treated with restrictive fluid therapy had reduced acute kidney injury, shorter mechanical ventilation and ICU stay, lower mortality, and positive fluid balance was closely related to the patient's mortality. Recognizing that fluid overload is associated with increased morbidity and mortality, modern fluid replacement strategies place more emphasis on the risks rather than the benefits of intravenous fluid replacement.

Today's ICU doctors are more cautious about giving intravenous fluids to critically ill patients. They use ultrasound and other modern methods to carefully assess the amount of fluid in the patient's body and determine whether fluid infusion is needed by measuring the patient's fluid responsiveness and biochemical tests. Fluid itself is also a "drug" and should only be used carefully when needed.

The National Institute for Health and Care Excellence (NICE) guidelines in the UK stipulate that fluid therapy is suitable for patients who cannot meet their fluid needs through oral or enteral administration, and intravenous fluid therapy should be stopped immediately if there is an indication. This principle applies not only to outpatients but also to critically ill patients in the ICU.

Author: Emergency and Critical Care Department, Songjiang District Central Hospital, Shanghai

Sheng Ruanmei Wang Xuemin