Surgical Physiology Flashcards

A patient loses 1500 ml of blood acutely. According to the ATLS classification, this represents which class of haemorrhagic shock?

Answer: Class III

Class III haemorrhage represents 30-40% blood volume loss (approximately 1500-2000 ml in a 70 kg adult). It is characterised by tachycardia, hypotension, tachypnoea, reduced urine output, and altered mental status. Crystalloid and blood transfusion are typically required.

In the fasting state, which organ is the primary consumer of ketone bodies for energy?

Answer: Brain

During prolonged fasting, the brain adapts to utilise ketone bodies (beta-hydroxybutyrate and acetoacetate) for up to 70% of its energy needs. The liver produces ketone bodies but cannot utilise them as it lacks the enzyme succinyl-CoA:3-ketoacid CoA transferase. Red blood cells lack mitochondria and rely solely on glycolysis.

A patient with a large bowel obstruction develops metabolic acidosis. Which acid-base disturbance is most likely if the patient also has persistent vomiting?

Answer: Mixed metabolic acidosis and metabolic alkalosis

Large bowel obstruction causes metabolic acidosis from ischaemia, bacterial translocation, and lactate production. Concurrent vomiting causes loss of gastric hydrochloric acid, producing metabolic alkalosis. The combination results in a mixed acid-base disturbance. Arterial blood gas analysis and calculation of the anion gap help differentiate the components.

Which of the following is the most important buffer system in the extracellular fluid?

Answer: Bicarbonate-carbonic acid system

The bicarbonate-carbonic acid (HCO3-/H2CO3) system is the principal extracellular buffer. It is an open system: CO2 is regulated by the lungs and HCO3- by the kidneys, giving it enormous buffering capacity. Although the phosphate system is important intracellularly and in renal tubular fluid, and haemoglobin is the main intracellular buffer of red blood cells, bicarbonate dominates extracellularly.

Following major abdominal surgery, a patient develops oliguria with a urine sodium concentration of 8 mmol/L. What is the most likely cause?

Answer: Appropriate physiological response to surgery (ADH and aldosterone secretion)

A low urine sodium (40 mmol/L as the damaged tubules lose their ability to reabsorb sodium.

During the systemic inflammatory response syndrome (SIRS), which cytokine is primarily responsible for inducing fever?

Answer: Interleukin-1 (IL-1)

IL-1 (along with TNF-alpha and IL-6) is a key pyrogenic cytokine. It acts on the hypothalamic thermoregulatory centre via prostaglandin E2 synthesis, resetting the temperature set-point upwards. IL-10 and TGF-beta are anti-inflammatory, while IL-4 promotes Th2 responses.