Acute Kidney Injury
By the end of this chapter, you will be able to:
- Explain the consequences of fluid overload, caused by AKI, in the cardiovascular and pulmonary systems
- Describe the outcomes of excessive circulating nitrogenous wastes, caused by AKI, on the GI and nervous systems
- Explain how pH imbalances, due to AKI, will affect electrically excitable tissues and rate/depth of breathing
As mentioned, the effects of rising blood levels of wastes and the inability to excrete said wastes and fluid will have profound effects on almost every system in the body.
Fluid overload (because volume can’t be excreted) will cause problems with
- Cardiovascular: increased blood volume will increase blood pressure and work for the heart. This can push a heart into failure if it can not maintain pumping this excessive volume.
- Pulmonary: increased blood volume may increase blood pressure in pulmonary circulation. As a result, some plasma-like fluid leaks out of the pulmonary capillaries and into alveolar space, manifesting as pulmonary edema which can be heard upon auscultation of the chest
Excessive circulating nitrogenous wastes will cause problems with
- Gastrointestinal: nitrogenous wastes like urea and ammonia are very irritating to tissues that have fluid, given their ability to dissolve in water easily. Thus, the entire GI tract will be irritated, manifesting in nausea and vomiting.
- Nervous: Similarly, excessive nitrogenous wastes will dissolve in the cerebrospinal fluid and thus irritate the CNS, manifesting as confusion and CNS depression (i.e. reduced level of consciousness, altered cognition)
Imbalance of pH and electrolyte imbalances (because excretion/absorption is impaired) will cause problems with
- Cardiovascular: disturbances in electrolytes – especially potassium – will have effects on all electrically excitable cells: especially the heart. Thus electrolyte imbalances due to AKI can cause arrhythmias
- Nervous: similarly, electrolyte disturbances will affect the CNS – manifesting in altered cognition, CNS depression, and possibly seizures.
- Pulmonary: pH imbalances will affect the rate and depth of breathing as the respiratory system tries to maintain pH balance. AKI prevents acid from being excreted – so a faster breathing rate (tachypnea) will occur causing the body to work harder to breathe.
As kidneys fail, wastes accumulate in the blood causing direct damage to the CNS and GI systems. This presents as CNS depression (altered consciousness and cognition) and GI distress (e.g. nausea, vomiting. Impaired kidney function will lead to problems with both fluid and electrolyte balance with an overload of fluid in vasculature and tissues. This fluid overload will have consequences on the heart (increased workload) and vessels (high blood pressure) with excess fluid wanting to enter third spaces (e.g. alveoli) causing complications in other systems. Electrolyte disturbances will affect anything that is electrically excitable such as the heart (e.g. arrhythmias) and CNS (e.g. cognition). Kidneys also help maintain pH homeostasis by excreting acid; hence loss of kidney function will lead to acidosis which the respiratory system will work faster and harder to compensate to maintain pH homeostasis.