General surgery 2 Flashcards
How is sodium and water controlled?
RAAS
Decreased effective arterial blood volume leads to decreased renal blood flow at JGA
This stimulates RENIN: At1–>AT2 via ACE
ATII leads to efferent renal artery constriction (increasing GFR), peripheral vasoconstriction, proximal Na+ reabsorption, sympathetic activation and release of aldosterone
Thirst + ADH release
Aldosterone = distal Na+ absorption
What is the net result of RAAS?
Increased EABV
Leads to increased stretch of atrial myocardium and release of ANP
ANP vasodilator renal arterioles and decrease RAAS activity - sodium and water excretion
What are the symptoms of dehydration?
Mild: headache, lack of energy, tiredness
Moderate: dry mouth, decreased alertness, sunken eyes and muscle cramps
Severe: confusion, disorientation, tachycardia, tachypnoea, low BP
How should dehydration be monitored?
Fluid balance chart
Urine output: <1ml/kg/hour = dehydration
Bloods = increased electrolytes, with raised urea
What electrolyte abnormalities can be seen with excessive vomiting
Hypochloraemic, hypokalaemic metabolic alkalosis (as gastric acid is lost)
Sodium depleted
What is the treatment of excessive vomiting?
0.9% salne to replace the ECF volume as well as KCL (20mmol) to restore potassium levels
metabolic alkalosis will self-correct with restoration of fluid and potassium balance, but U+Es should be frequently checked during treatment
What electrolyte abnormality will a high volume pancreatic/ileal/jejunal/bile fistula show?
Fistulas: likely to contain a high bicarbonate level due to their alkaline nature, and thus fluid and bicarbonate replacement is required
Bowel contents after Ampulla of Vater are alkaline in nature
Acidosis displaces potassium from teh cell, so plasma potassium levels may seem elevated when in fact, total body potassium is depleted
What electrolyte abnormality will be seen with diarrhoea?
Acute: hyperchloraemia metabolic acidosis with hypokalaemia if profuse
Chronic diarrhoea can cause a metabolic alkalosis
Treatment: ORS or 0.9% saline and 20mmol potassium
How should fluids be prescribed in a closed head injury?
General goal in cerebral oedema = maintain a state of euvolaemia to reduce the risk of a secondary brain injury
If patient = haemodynamically stable, 2/3 of maintenance with isotonic fluid is best.
Hypotonic best avoided as they may decrease serum osmolality and increase cerebral oedema
What electrolyte abnormality is seen in acute tubular necrosis?
Hyperkalaemia
Hyperphosphataemia
Hypermagnesia
Hyponatraemia
hypocalcaemia
metabolic acidosis
What electrolyte abnormality is seen in dehydration?
Isonatraemia, but can be hyponatraemic if hypertonic fluid is being lost, or hypernatraemic if hypotonic fluid is being lost
What is SIADH?
Non-physiologic release of ADH which results in decreased water excretion and normal sodium excretion leading to a dilutional hyponatraemia
Investigations show hyponatraemia with normal urea/creatinine.
There is increased urinary sodium giving aaa increased specific gravity of urine
What are the causes of SIADH?
Malignancy: small cell lung, pancreas, prostate
CNS disorders: meningoencephalitis, haemorrhage, head injury
Chest disease: TB, pneumonia, abscess
Endocrine disease: hypothyroidism
Drugs: Opiates, psychotropics
Other: Major surgery, trauma, symptomatic HIV
What is diabetes insipidus?
Passage of large volumes of dilute urine (>3L/day) due to impaired water resorption by the kidney collecting ducts
Reduced ADH secretion from the posterior pituitary (cranial DI) or impaired response of the kidneys
pathology: hypernatraemia and raised plasma osmolality
What is the effect of congestive cardiac failure on electrolyte abnormalities?
neurohormonal adaptation process - activation of the adrenergic and RAAS - salt and water retention
Can get dilutional hyponatreamia due to dietary sodium restriction and inability to excrete water
Hypokalaemia can result from prolonged administration of diuretics, or hyperkalaemia can occur in severe heart failure leading to reductions in GFR, particularly if they are on potassium sparing diuretics / ACEi
What is shock?
Acute circulatory failure that compromises tissue perfusion
What are the different types of shock?
Hypovolaemia: haemorrhage/dehydration
Distributive: sepsis, anaphylaxis, neurogenic
Cardiogenic: Mi, arrhythmia, valve
Obstructive: passive PE, tamponade, tension pneumothorax
What is Cardiac output?
Stroke volume x heart rate
What is BP?
Cardiac output x SVR
What is MAP?
diastolic BP + (systolic-diastolic)/3
What are the essential features of any kind of shock?
Fall in BP by at least 40mmHg (SPB <90)
Tachycardia
Tachypnoea
Hypovolaemic/cardiogenic: cold, pale, clammy with rapid thready pulse and narrow pulse pressure
Septic: hot, flushed, sweaty with a rapid bounding pulse. pulse pressure wide due to vasodilation
What is the effect of shock on the Brain and cerebrum?
Autoregulation over MAP of 50-150mmHg
below - patient = agitated, confused, drowsy and eventually unresponsive
What is the effect of shock on the CVS?
reduced diastolic pressure leads to inadequate myocardial perfusion, leading to ischaemic calf pain, arrhythmias and eventually infarction
What is the effect of shock to the resp system?
increased respiratory rate due to metabolic acidosis
What is the effect of shock to the kidneys
Autoregulation over 70-170 but below this - oliguria
impaired renal function
What is the effect of shock on the GI system?
Decreased gut motility and nutrient absorption, and decreased ability to sustain normal flora, leading to infection susceptibility
What is the effect of shock on the skin?
Blood supply is centralised, giving cool/clammy/mottled peripheral skin