Fluid Requirements

Question 1

What are the causes of High anion gap metabolic acidosis (HAGMA)?

Answer 1

• G – glycols (ethylene glycol, propylene glycol)
• O – oxoproline (pyroglutamic acid) (product of disordered glutathione metabolism, following paracetamol overdose)
• L – L-lactate
• D – D-lactate (unusual, occurs in short bowel syndrome)
• M – methanol
• A – aspirin
• R – renal failure (uraemia)
• K – ketoacidosis (e.g. diabetic ketoacidosis [DKA], starvation, alcohol)

Question 2

What are the causes of Normal anion gap metabolic acidosis (NAGMA)?

Answer 2

• Hyperalimentation (e.g. starting TPN)
• Acetazolamide use
• Renal tubular acidosis (RTA)
• Diarrhoea
• Ureteroenterostomy (colon wastes HCO3-)
• Pancreatic fistula (enterocutaneous fistula) (pancreatic secretes HCO3- rich fluid)

Rapid volume expansion with N/S, e.g. surgery, traumatic blood loss

Question 3

Class 1 haemorrhage

• definition
• symptoms
• management

Answer 3

< 15% blood volume loss:

The clinical symptoms of volume loss with class I haemorrhage are minimal. In uncomplicated situations, minimal tachycardia occurs. No measurable changes occur in blood pressure, pulse pressure, or respiratory rate.

For otherwise healthy patients, this amount of blood loss does not require replacement, because transcapillary refill and other compensatory mechanisms will restore blood volume within 24 hours, usually without the need for blood transfusion.

Question 4

Class 2 haemorrhage

• definition
• symptoms
• management

Answer 4

15% to 30% blood volume loss

Clinical signs of class II haemorrhage include

• tachycardia
• tachypnoea, and
• decreased pulse pressure: related primarily to a rise in diastolic blood pressure due to an increase in circulating catecholamines, which produce an increase in peripheral vascular tone and resistance. Systolic pressure changes minimally in early haemorrhagic shock; therefore, it is important to evaluate pulse pressure rather than systolic pressure.
• Other pertinent clinical findings associated with this amount of blood loss include subtle central nervous system (CNS) changes, such as anxiety, fear, and hostility.
• Despite the significant blood loss and cardiovascular changes, urinary output is only mildly affected.
• The measured urine flow is usually 20 to 30 mL/hour in an adult with class II haemorrhage.

Accompanying fluid losses can exaggerate the clinical manifestations of class II haemorrhage. Some patients in this category may eventually require blood transfusion, but most are stabilized initially with crystalloid solutions.

Question 5

Class 3 haemorrhage

• definition
• symptoms
• management

Answer 5

Class III haemorrhage: 31% to 40% blood volume loss:

Symptoms: classic signs of inadequate perfusion, including marked tachycardia and tachypnoea, significant changes in mental status, and a measurable fall in systolic blood pressure.

The priority of initial management is to stop the haemorrhage, by emergency operation or embolization, if necessary. Most patients in this category will require packed red blood cells (pRBCs) and blood products to reverse the shock state.

Question 6

Class 4 haemorrhage

• definition
• symptoms
• management

Answer 6

Class IV haemorrhage: > 40% blood volume loss.

The degree of exsanguination with class IV haemorrhage is immediately life-threatening. Symptoms include marked tachycardia, a significant decrease in systolic blood pressure, and a very narrow pulse pressure or unmeasurable diastolic blood pressure. (Bradycardia may develop preterminally.) Urinary output is negligible, and mental status is markedly depressed. The skin is cold and pale.

Patients with class IV haemorrhage frequently require rapid transfusion and immediate surgical intervention.