Question

Acid-base balance (blood gas analysis) Electrolyte imbalance symptoms and EKG changes, normal lab values .Antibiotic resistance .Hypersensitivities (reactions) and symptoms .Antibody production

Answer 1

ANSWER :-

1. ACID BASE BALANCE :-

Arterial blood gas analysis is a common investigation in emergency departments and intensive care units for monitoring patients with acute respiratory failure. It also has some application in general practice, such as assessing the need for domiciliary oxygen therapy in patients with chronic obstructive pulmonary disease. An arterial blood gas result can help in the assessment of a patient's gas exchange, ventilatory control and acid–base balance. However, the investigation does not give a diagnosis and should not be used as a screening test. It is imperative that the results are considered in the context of the patient's symptoms.

While non-invasive monitoring of pulmonary function, such as pulse oximetry, is simple, effective and increasingly widely used, pulse oximetry is no substitute for arterial blood gas analysis. Pulse oximetry is solely a measure of oxygen saturation and gives no indication about blood pH, carbon dioxide or bicarbonate concentrations.

Arterial puncture

Blood is usually withdrawn from the radial artery as it is easy to palpate and has a good collateral supply. The patient's arm is placed palm-up on a flat surface, with the wrist dorsiflexed at 45°. A towel may be placed under the wrist for support. The puncture site should be cleaned with alcohol or iodine, and a local anaesthetic (such as 2% lignocaine) should be infiltrated. Local anaesthetic makes arterial puncture less painful for the patient and does not increase the difficulty of the procedure.¹ The radial artery should be palpated for a pulse, and a pre-heparinised syringe with a 23 or 25 gauge needle should be inserted at an angle just distal to the palpated pulse (Fig. 1). A small quantity of blood is sufficient. After the puncture, sterile gauze should be placed firmly over the site and direct pressure applied for several minutes to obtain haemostasis. If repeated arterial blood gas analysis is required, it is advisable to use a different site (such as the other radial artery) or insert an arterial line.

To ensure accuracy, it is important to deliver the sample for analysis promptly. If there is any delay in processing the sample, the blood can be stored on ice for approximately 30 minutes with little effect on the accuracy of the results.

Complications of arterial puncture are infrequent. They include prolonged bleeding, infection, thrombosis or arteriospasm.

Fig. 1

Performing an arterial puncture

Interpreting a blood gas result

The automated analysers measure the pH and the partial pressures of oxygen (PaO₂) and carbon dioxide (PaCO₂) in arterial blood. Bicarbonate (HCO₃ˉ) is also calculated (Box 1). These measurements should be considered with the patient's clinical features (Table 1).

Box 1
Reference ranges for arterial blood gases
pH PaO2 PaCO2 HCO3ˉ Base excess	7.35 – 7.45 80 – 100* mmHg 35 – 45 mmHg 22 – 26 mmol/L –2 – +2 mmol/L	10.6 – 13.3 kPa 4.7 – 6.0 kPa
Reference ranges for venous blood gases
pH PvO2 PvCO2 HCO3ˉ	7.32 – 7.43 25 – 40 mmHg 41 – 50 mmHg 23 – 27 mmol/L
* age and altitude dependent (see text) Kilopascals: to convert pressures to kPa, divide mmHg by 7.5

Table 1 Correlating arterial blood gas results with clinical features Metabolic imbalances Respiratory imbalances Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis pH ↓ ↑ ↓ ↑ PaCO2 N (uncompensated) ↓ (compensated) N (uncompensated) ↑ (compensated) ↑ ↓ HCO3ˉ ↓ ↑ N (uncompensated) ↑ (compensated) N (uncompensated) ↓ (compensated) Base excess ↓ ↑ N/↑ N/↓ Clinical features Kussmaul-type breathing (deeper, faster respiration), shock, coma Paraesthesia, tetany, weakness Acute: air hunger, disorientation Chronic: hypoventilation, hypoxia, cyanosis Acute: hyperventilation, paraesthesia, light-headedness Chronic: hyperventilation, latent tetany Common causes With raised anion gap: diabetic ketoacidosis, lactic acidosis, poisons (e.g. ethylene glycol), drug overdoses (paracetamol, aspirin, isoniazid, alcohol) With normal anion gap: diarrhoea, secretory adenomas, ammonium chloride poisoning, interstitial nephritis, renal tubular acidosis, acetazolamide administration Vomiting, prolonged therapy with potassium-wasting diuretics or steroids, Cushing's disease, ingestion/overdose of sodium bicarbonate (e.g. antacids) Hypoventilation chronic lung disease with CO2retention, e.g. chronic obstructive pulmonary disease, respiratory depression from drugs (e.g. opioids, sedatives), severe asthma, pulmonary oedema Hyperventilation anxiety, pain, febrile illness, hypoxia, pulmonary embolism, pregnancy, sepsis N = within normal range ↑ = increased ↓ = decreased

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