Hello NAVE crew! In this video lesson of the Vet Anesthesia Unravelled web series, we gonna talk about acid-base status and the most frequent acid-base disorders.
Metabolic processes are essential for energy production, but they also produce volatile and fixed acids that must be neutralised to maintain blood pH. Thus, there are many buffer systems to balance this acid production.
Basically, three different buffer systems work in this way. The first one is composed of blood chemical buffers, which act immediately to control [H+]. The most important are bicarbonate, phosphate and circulating protein buffers. The second one is the respiratory system, which can neutralise in minutes, regulating the concentration of CO2. It is very efficient because it is an open system buffer, that is, excess of CO2 produced by chemical reactions is easily eliminated by expiration. The third group is formed by the kidney buffers, such as bicarbonate, phosphate, and ammonia, which are extremely important but slower acting. It usually takes days to neutralise H+ concentration by these buffers, but they are very effective, not only in balancing H+, but also in eliminating these ions.
*How ​​to access Acid-Base status*
Acid-base disorders are assessed by the blood gas analysis, which should preferably be taken by drawing arterial blood so that it is possible to analyse the respiratory and metabolic components. However, venous blood samples can also be drawn, but only metabolic disorders can be assessed. After the sample is collected, it should be analysed as soon as possible, avoiding changing from cellular metabolism. It is possible to get pH, PaCO2, PaO2, SaO2, HCO3-, Na+, K+, Cl-, H+, ionic range and excess or deficit of bases.
*Acid-base balance disorders*
Acid-base disorders are classified as acidosis and alkalosis, and respiratory, metabolic or mixed. The most commons are:
- Respiratory acidosis: It occurs due to the increase in PaCO2 and is very common in hypoventilation anaesthesia, but it can also happen from lung diseases, airway obstruction, instability of the thorax, heart failure, among other situations in which there is a deficiency in the gas exchange.
- Respiratory Alkalosis: It is not so common and occurs when PaCO2 is lower than 35 mmHg. It usually presents in inadequate mechanical ventilation, with excess in VT or Vm, or in neurological disease, hyperthermia and pain.
- Metabolic acidosis: Indeed, it is the most frequent acid-base disorder in dogs, cats and horses. The main causes are from diarrhoea, azotemia, hemorrhagic shock, ketoacidosis and any other situations that promote lack of tissue oxygenation, excessive consumption of O2 and/or anaerobic catabolism . There is an excess of HCO3- loss or even consumption of this base, and consequently an excess of H+, increasing the anion gap. The base excess should be much more negative than usual.
- Metabolic Alkalosis: It is due to bicarbonate excess, which is usually occurred to the wrong administration of sodium bicarbonate, or excessive loss of H+, which usually happens in cases of hyperemesis, stomach lavage, or prolonged use of loop diuretics.
See the information in detail in the video!
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Additional Material
- Beer KS, Waddell LS. Vet Clin Small Anim, 45:941-952, 2015.
- Corley KTT; Marr CM. Eq Vet Educ, 10:255-265, 1998.
- DiBartola S. Fluid, electrolyte, and acid-base disorders in small animal practice. 4th ed, 744p, 2011.
- Rauserova-Lexmaulova L et al. Topic Co Ani Med, 39:100403, 2020.
- Teixeira-Neto FJ, Garofalo NA. Fluid therapy, acid-base and electrolyte balance in large animals. In: Luna SPL, Carregaro AB. Anesthesia and Analgesia in Equidae, Ruminant and Pigs, 1st ed, 33-52, 2019.
Additional credits
Música Final - Level Up - Quincas Moreira
Meme "The Shining" - Movieclips.com
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