Pathophysiology of Acid Base Balance

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Intensive and Critical Care Nursing (2008) 24, 28—40


Pathophysiology of acid base balance: The theory practice relationship Sharon L. Edwards ∗
Buckinghamshire Chilterns University College, Chalfont Campus, Newland Park, Gorelands Lane, Chalfont St. Giles, Buckinghamshire HP8 4AD, United Kingdom Accepted 13 May 2007

Acid base balance; Arterial blood gases; Acidosis; Alkalosis

Summary There are many disorders/diseases that lead to changes in acid base balance. These conditions are not rare or uncommon in clinical practice, but everyday occurrences on the ward or in critical care. Conditions such as asthma, chronic obstructive pulmonary disease (bronchitis or emphasaemia), diabetic ketoacidosis, renal disease or failure, any type of shock (sepsis, anaphylaxsis, neurogenic, cardiogenic, hypovolaemia), stress or anxiety which can lead to hyperventilation, and some drugs (sedatives, opoids) leading to reduced ventilation. In addition, some symptoms of disease can cause vomiting and diarrhoea, which effects acid base balance. It is imperative that critical care nurses are aware of changes that occur in relation to altered physiology, leading to an understanding of the changes in patients’ condition that are observed, and why the administration of some immediate therapies such as oxygen is imperative. © 2007 Elsevier Ltd. All rights reserved.

The implications for practice with regards to acid base physiology are separated into respiratory acidosis and alkalosis, metabolic acidosis and alkalosis, observed in patients with differing aetiologies. By understanding normal physiological principles and how they relate to clinical situations can enhance patient care. A good understanding of Present address: Department of Pre-registration Nursing, Faculty of Health Studies, Buckinghamshire Chilterns University College, United Kingdom. Tel.: +44 1494 522141x2123 (Off.)/1442 876772 (Res.); fax: +44 1494 603182. E-mail address: ∗

the essential concepts of acid base physiology is necessary so that quick and correct diagnosis can be determined and appropriate treatment implemented. The homeostatic imbalances of acid base are examined as the body attempts to maintain pH balance within normal parameters.

General principles of acid base balance
The primary function of the respiratory system is to supply an adequate amount of oxygen (O2 ) to tissues and remove carbon dioxide (CO2 ). The kidneys

0964-3397/$ — see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.iccn.2007.05.003

Pathophysiology of acid base balance
Table 1 Site Interstitial fluid (ISF) Blood The major body buffer systems Buffer system Bicarbonate Phosphate and protein Bicarbonate Haemoglobin Plasma proteins Phosphate Proteins Phosphates Phosphate Ammonia Calcium carbonate Description For metabolic acids Not important because concentration is too low Important for metabolic acids Important for buffering CO2 and H+ Minor buffer Concentration too low Important buffer of extracellular H+ Important buffer


Intracellular fluid Urine Bone

Responsible for most of titratable acidity Important—–formation of NH4 + and hence excretion of H+ In prolonged metabolic acidosis

will excrete any excess acids or alkali. The respiratory and renal organs together with the buffering effects of blood maintain hydrogen ion (H+ ) concentration. H+ concentration is one of the most important aspects of acid base homeostasis. When there is an increase or decrease in acid production, blood bicarbonate (HCO3 − ), proteins, and phosphate buffer body fluids (Table 1). However, there comes a point in the disease process when these buffers can no longer maintain appropriate concentrations of H+ . Patients admitted to hospital can have life threatening situations such as diabetic ketoacidosis, asthma, severe vomiting, which alter pH balance and exacerbate their problems. To maintain homeostasis...
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