Renal
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Fluid balance disordersFluid balance disorders include hypovolaemia (oligaemia), dehydration/acute fluid depletion, and hypervolaemia/fluid overload. Careful attention to fluid balance is essential in ICU. Patients are likely to require ‘maintenance’ fluids in addition to any fluid resuscitation.
Causes
Hypovolaemia (see also Shock, 
p.104) occurs when there is a decrease in the volume of circulating blood. It can be accompanied by a decrease in total body water (dehydration/acute fluid depletion); but can also occur where there is an overall increase in total body water, due to fluid leaking out of the intravascular space (e.g. in sepsis). Causes include:
p.104) occurs when there is a decrease in the volume of circulating blood. It can be accompanied by a decrease in total body water (dehydration/acute fluid depletion); but can also occur where there is an overall increase in total body water, due to fluid leaking out of the intravascular space (e.g. in sepsis). Causes include:
Haemorrhage (see
p.112), or burns (transdermal fluid loss).
‘Third-space’ losses (e.g. fluid leaking into the interstitial compartment, or oedema caused by diseases such as sepsis or pancreatitis):
This may occur rapidly, especially where surgical/radiological drainage of large amounts of ascites or pleural fluid (especially transudate) promotes rapid reaccumulation of fluid
Severe dehydration.
Aggressive negative balance with RRT.
Dehydration/acute fluid depletion
Inadequate intake or inadequate fluid resuscitation.
↑Increased fluid losses:
GI: diarrhoea, vomiting
Other: severe burn injury, hyperpyrexia/heatstroke
Aggressive negative balance with RRT.
Hypervolaemia/fluid overload
Iatrogenic.
Renal failure (acute kidney injury or chronic kidney disease).
Polydipsia.
Chronic heart failure.
Cirrhosis.
Nephrotic syndrome.
Presentation and assessment
Fluid balance/volume status assessment will include:
The patient’s fluid charts (and anaesthetic charts).
Any history of diarrhoea, vomiting, diuresis.
Hypovolaemia may present as shock (see Shock, 
p.104, and Haemorrhage, 
p.114). Signs and symptoms of fluid depletion may include:
p.104, and Haemorrhage, p.114). Signs and symptoms of fluid depletion may include:
General: thirst, skin turgor, dry mucous membranes, sunken eyes:
Pyrexia may be present if it is associated with the cause of fluid loss
Neurological: altered mental state, ↓consciousness, syncope.
Cardiovascular: tachycardia, normotension or hypotension:
↑ capillary refill time
Cold peripheries, mottling
↑cardiac output or CVP (if monitored) in response to straight leg raising (45° for 4 minutes) or a fluid bolus
Renal: anuria/oliguria, raised urea and creatinine:
Polyuria may be present if it is associated with the cause (i.e. DKA)
Metabolic acidosis
GI: vomiting or diarrhoea may be present.
Other: hypernatraemia, raised serum osmolality, raised serum lactate.
Acute fluid overload signs and symptoms may include:
General: peripheral/dependent oedema, or enlarged and tender liver, ascites may be present if there is acute-on-chronic overload.
Respiratory: pulmonary oedema may occur.
Cardiovascular: tachycardia, raised JVP (>4 cm from sternal angle), CVP (>15 cmH2O), or PAOP (>18 mmHg):
Gallop rhythm, S3 may be present
Hypotension may be present if cardiogenic shock is present
Renal: pre-existing renal failure or oliguria may be present, polyuria may also be present.
Other: hyponatraemia, ↓serum osmolality ( ↑ serum chloride and or sodium may be present in iatrogenic hypervolaemia).
Investigations
ABGs (hypoxia, acidaemia).
FBC, coagulation screen.
Serum lactate.
Serum magnesium, calcium, and phosphate.
Serum glucose (to exclude hyperglycaemic states), capillary ketones.
Serum osmolality.
TFTs, serum cortisol (if hypoadrenalism or hypothyroidism suspected).
Serum CRP.
Septic screen (blood, urine, sputum cultures, if infection is suspected).
Stool culture and CDT testing, if diarrhoea present.
Cardiac enzymes (if a myocardial infarct is suspected).
12-lead ECG and echocardiography (if cardiogenic shock suspected).
CXR (if pulmonary oedema or infection suspected).
CVP or cardiac output measurement, or echocardiography may help define intravascular fluid balance status.
Urinalysis (both dipstick and urinary U&Es/osmolality).
Differential diagnoses
Dehydration/acute fluid depletion
Hyperosmolar hyperglycaemic state.
Meningitis.
Adrenal insufficiency or hypothyroidism.
Acute fluid overload
Cardiac failure.
TUR syndrome.
Immediate management
Give O2 as required, support airway, breathing, and circulation.
Manage shock/hypotension as required (
p.104).
Manage major haemorrhage if required (
p.112).
Dehydration/acute fluid depletion
Assess patient fully, including age, weight, working diagnosis, co-morbidities, and volume status (CRT, HR, BP, C/JVP, UOP):
Urinary catheterization is likely to be required
Prescribe appropriate fluid challenge:
250-500 ml IV gelatin colloid (e.g. Gelofusine®) over 15-60 minutes
In patients who are very small, elderly with IHD, or known to have poor LV function consider reducing fluid challenge to 200 ml over 30-60 minutes
In fit healthy severely dehydrated patients (e.g. patients with severe DKA) consider speeding initial fluid challenges up to 1000 ml over 15-30 minutes
Review patient following fluid challenge noting changes in haemodynamic and urinary variables.
Prescribe further fluid challenges as appropriate, and review again.
Prescribe maintenance fluids (usually crystalloids) and resuscitation fluids (crystalloids or colloids) separately.
Acute fluid overload
Treat pulmonary oedema if present (
p.86).
Consider monitoring degree of overload using CVP measurement.
Potential therapies include:
Diuresis: furosemide IV 20-40 mg (requires functioning kidneys)
Vasodilatation using GTN IV infusion if patient is normo- or hypertensive (1 mg/ml at 0-15 ml/hour) and/or morphine IV 2-10 mg (repeated doses may accumulate in renal failure)
Fluid removal using renal replacement therapy
If in extremis consider venesecting 200-400 ml of blood whilst preparing other treatments
Further management
Electrolyte abnormalities associated with acute fluid balance problems:
Hyponatraemia/hypernatraemia; hypokalaemia/hyperkalaemia.
Calcium (hypocalcaemia in massive blood transfusion, pancreatitis).
Phosphate (hypophosphataemia; hyperphosphataemia in acute renal failure 2° to tubular obstruction, e.g. tumour lysis syndrome).
Magnesium (hypomagnesaemia 2° to marked diuresis).
Acid-base problems associated with fluid balance problems include:
Hyperchloraemic metabolic acidosis 2° to excessive replacement with 0.9% sodium chloride
Hypochloraemic hypokalaemic metabolic alkalosis 2° to HCl loss with persistent vomiting, or excess NG aspirates
Metabolic acidosis 2° to diabetic ketoacidosis
Metabolic acidosis 2° to excess bicarbonate loss from small bowel fistula, or ureteroenterostomy.
Pitfalls/difficult situations
The optimal degree of fluid resuscitation in acute hypovolaemia, and the point at which to initiate inotropes/vasopressors is unclear.
Glucose containing fluids such as 5% glucose spread into interstitial and intracellular fluid spaces, whilst the oncotic pressure generated by colloids keeps fluid within the intravascular space for longer; as an approximation regarding intravascular fluid replacement 1 L of colloid is equivalent to 2-3 L of saline 0.9% is equivalent to 8-9 L of 5% glucose:
There is very little evidence to advocate the use of colloids (including human albumin solution) over crystalloids, or vice-versa
‘Balanced’ solutions may avoid hyperchloraemic acidosis
Hypotonic fluids may exacerbate cerebral oedema and increase ICP in head-injured patients; human albumin solution is not recommended in cases of TBI.
Salt loading should be avoided in hepatic failure.
Fluid accumulation during critical care management may be associated with ↑ length of time weaning from mechanical ventilation.
Prescribing maintenance fluids
(See also Tables 7.1 and 7.2.)
Daily fluid requirements: ˜40 ml/kg/day or 1.5 ml/kg/hour:
Increase if there are large losses from urine, diarrhoea, vomiting, or skin (e.g. burns losses)
In practice, U&Es should be regularly checked and potassium supplementation given as required. Maintenance fluids may be adjusted according to plasma sodium, for example:
Na+ <135 mmol/L: 0.9% saline.
Na+ 135-145 mmol/L: Hartmann’s or glucose 4%/saline 0.18%.
Na+ >145 mmol/L: 5% glucose.
Maintenance fluids may also be provided in the form of enteral feed or PN.
1Larger daily amounts of sodium are regularly given to critically ill patients, especially during acute resuscitation. Hyponatraemic/hypo-osmolar fluids should be avoided in head injuries; sodium-containing fluids should be avoided if possible in liver failure.
Further reading
Antonelli M, et al. Hemodynamic monitoring in shock and implications for management. Intensive Care Med 2007; 33: 575-90.
National Heart, Lung, and Blood Institute ARDS Clinical Trials Network, et al. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med 2006; 354: 2564-75.
Powel-Tuck J, et al. British consensus guidelines on intravenous fluid therapy for adult surgical patients. (GIFTASUP). London: NHS National Library of Health, 2008.
Perel P, et al. Colloids versus crystalloids for fluid resuscitation in critically ill patients. Cochrane Database Syst Rev 2011; 3: CD000567. DOI: 10.1002/14651858.CD000567.pub4.
SAFE study Investigators. A comparison of albumin and saline for fluid resuscitation in the intensive care unit. N Engl J Med 2004; 350: 2247-56.
SAFE study Investigators. Saline or albumin for fluid resuscitation in patients with traumatic brain injury. N Engl J Med 2007; 357: 874-84.
Table 7.1 Commonly available IV fluids | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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