“Critical care evolved from anesthetic approaches and postoperative practice. In elective cases, the sudden trauma of surgery interrupts resting physiology and is addressed by an attempt to restore a normal baseline. In the critical care setting, however, the price of maintaining normality may be injury inflicted by the therapy itself (ventilator-induced lung injury, drug toxicity, consequences of sedation, and so forth). Equally plausible is that our enforcing of normal indicators and protracted use of excessive support may impede the patient’s potential to adapt to the abnormal physiology that characterizes chronic critical illness.

Health is characterized by gradual transitions between physiological states, by variation of cardiorespiratory indices, and by continual adaptation to biochemical, environmental, and mechanical stressors. Acute disease, on the contrary, is often characterized by abrupt transitions, failure to adapt to the stressor, and monotonously inflexible physiological patterns. Currently, our treatments rescue very effectively, but when sustained for too long they may frustrate the patient’s innate adaptability to stressful but potentially survivable illness. For example, early use of short-term muscle relaxants enables lung-protective strategies and may reduce mortality risk in acute respiratory distress syndrome, but when sustained for too long muscle relaxants can cause muscular atrophy and sustained weakness. Because evolution did not provide for appropriate responses to severe acute injuries, an argument can be made that we must moderate the initial assault and response, and then build our capability to respond to lingering challenges over time.

During health, tolerable stresses above the resting baseline that are applied and released build strength, promote tolerance, and remodel tissues. Endurance athletes are a good example of what can be achieved with intermittent exposure to challenging stress. Stress-induced adaptations include enhanced pulmonary oxygen exchange, increased blood volume and hemoglobin concentration, enriched blood flow to skeletal muscle, improved thermal regulation, increased mitochondrial size and density, and increased capillarization of muscular beds. The healthy individual is also extremely adaptable when the physiologic milieu is gradually changed. Important lessons regarding adaptation to abnormal physiology have been learned from protracted exposure to hypoxic inspired gas, both in mountain climbing and in the experimental laboratory.”

Read the entire piece here at Critical Care v. 17 suppl. 1.