Replacement fluids

Replacement fluids

Signs of extracellular fluid depletion

·        Symptoms: oliguria (min 0.5 ml/kg/hr), thirst, tachycardia, dry tongue, weakness, confusion

·        Signs: weight change, ¯tissue turgor, postural hypotension, cool peripheries, dry axilla and mucous membranes, ¯JVP

·        Common in surgical patients due to: vomiting, ileus, stomal losses, etc. Not always naso-gastric losses. Frusemide is a flogging offence! It‟s due to intravascular hypovolaemia

·        Investigations: 

o   Bloods: ­Hb, ­Urea/Creatinine, Na/K

o   Urine Na

o   Maybe ABG for acid/base balance

·        Replace deficit quickly over 30 minutes – 1 ½ hours, not by increasing hourly rate

·        Give boluses of 200-250 mls N/saline, Hartmanns or plasma expander

·        Take care in older patients/CHD: don‟t tolerate large Na loads (® pulmonary oedema)

·         If on IPPV, this pushes up intra-thoracic pressure to 10 – 15 cm H2O (0 – 5 cm H2O is normal), so when using central venous pressure need to adjust for this before determining whether hypovolaemic

Depletion in children

·        Can be rapid and profound.  Described as:

o   Mild: loss of 4 – 5 % body mass.  History of diarrhoea/vomiting but few signs

o   Moderate: loss of 6 – 9 % body mass.  Sunken eyes & fontanelle.  Urine output < 0.5 mls/kg/hour

o   Severe: 10% loss of body mass.  Very ill.  Hypotension and rapid weak pulse

Types of Replacement Fluids

·        Crystalloids: isotonic, short intravascular T½ . For replacement of extra-cellular loss. To replace blood give 3 times blood loss

o  0.9 % saline: 154 mmol/L NaCl (isotonic)

o  Hartmanns and Lactated Ringers: electrolyte mixture similar to plasma 

o  Excessive replacement of plasma losses acutely with saline may ® hyperchloraemic acidosis

·        Dextrose containing solutions: not for replacing blood loss (hypertonic). For treatment of water loss or when sodium restrictions are present:

o  Barts: 4% dextrose/0.18% saline – 30 mmol/L NaCl + 168 Kcal/L

o  5% dextrose: 200 Kcal/L (calories and water only)

·        Synthetic Colloids: isotonic, long intravascular T½, for blood volume replacement. More readily available than blood and no infection risk, don‟t require cross matching. Give 1:1 ratio with blood lost. If > 1 L required, consider albumin and/or blood. Kidneys take time to excrete, so watch for fluid overload, especially in renal impairment and kids 

o  Haemaccel: polygeline (degraded gelatine) plus electrolytes (145 mmol/L NaCl + 5.1 mmol/L K + 6.25 mmol./L Ca). T½ = 4 hours, hypersensitivity rare 

o  Dextran 40, 70: dextran with molecular weight 40K (T½ = 2 – 4 hours) or 70K (T½ = 6 hours), hypersensitivity reactions, impairs coagulation and cross match

o  Hetastarch (Hespan), Pentaspan: starch solution, MR = 70K, T½ = 17 hours, hypersensitivity rare

·        Blood products: reserved for > 20% blood loss or continuing bleeding or Hb acutely < 70 g/L

·        If fluids not hypo-osmotic compared with blood, then red cell would swell ® haemolysis

·        Warm fluids, especially if refrigerated.  Haemaccel and crystalloids can be microwaved

Child Requirements

·        Maintenance fluid: 4% dextrose + 0.18% saline + 20 mmol KCl/L at:

§  Per hour Per day

o   First 10 kg          4 mls/kg        100 mls/kg

o   Second 10 kgs   2 mls/kg        50 mls/kg

o   All subsequent kgs       1 ml/kg          25 mls/kg

·         Losses (e.g. nasogastric tube, fever, diarrhoea) replaced with an equal volume of 0.45% NaCl + 20 mmol KCl/L. Give as boluses of 20 ml/kg over 15 – 30 mins. Losses decrease with renal failure 

·        Admit or observe in a short stay facility for several hours

·        Don‟t use homemade solutions – use Gastrolyte

·        Orally, of by NG tube if necessary: 

o   Replace calculated losses over 6 hours (don‟t worry about maintenance requirements). Hourly observations and reassess and reweigh after 6 hours

o   Give the remainder of the daily fluid maintenance over the next 18 hours

·        Resume breast feeding as soon as rehydration is complete or sooner if this takes longer than 6-hours

·        If after 4 – 6 hours the child remains dehydrated, then IV

Adult requirements

·        Adult daily requirements:

o  2.5 - 3 litres of fluid

o  100 mmol Na (60 mmol/day in elderly)

o  60 mmol of K+ (max of 10 mmol per hour)

·        Can be given as: 

o  2.5 – 3 litres of dextrose/saline (=0.18% saline + 4% dextrose) per day with 20 mmol/L KCl in each bag, or

o  2 litres of 5% dextrose and 500 mls of saline

o  Run in at 50 – 100 mls per hour (NB, smaller daily requirements for a small person)

o  If concerned about heart failure/pulmonary oedema than monitor saturation

·        Intraoperative fluid replacement:

o  Oral intake withheld before surgery 

o  In major surgery, half the estimated 24 hour maintenance requirement should be given initially (600 – 1000 ml saline), followed by maintenance requirements plus loses 

o  K is usually excluded for first few post-operative days: due to ­ liberation from cells

o  Excess use of low Na fluids post-operatively may cause hyponatraemia given ­ ADH

Abdominal losses

·        GIT has huge internal economy of fluid secretion & absorption

·        Losses through surgical intervention (stoma, leaking viscous, etc) replaced with iv solution of similar composition 

·        Saliva       1500

·        Gastric     1500

·        Pancreatic          700

·        Bilary       500

·        Jejunostomy      2-3000

·        Ileostomy           500

·        Colostomy          300

·        Diarrhoea           0.5 – 15,000 (Normal ileum delivers 1200 – 1500 per day)

·        Diarrhoea and Vomiting

o   Leads to dehydration, hyponatraemia, hypokalaemia, hypochloraemia 

o   Replace ½ calculated losses in first 24 hours with saline plus potassium. Maximum rate of potassium replacement is 20 mmol/hr

Burns

·        Burns ® rapid loss ® secondary organ damage (e.g. renal)

·        Give 2-4 mls/kg * %burned area of Hartmanns: half over first 8 hours, rest over next 16, in addition to maintenance requirements. Consider blood transfusion

Monitoring adequacy of Fluid Replacement

·        Monitor pulse, BP, respiratory rate and urine output (i.e. put in catheter):

·        Na to K ratio in urine should be > 1.  If < 1 then body frantically reabsorbing Na Þ not in balance

Postoperative Hyponatraemia

·        Normal value of Na: 135 – 145 mmol/L 

·        Hyponatraemia is not a diagnosis – it is found in diverse conditions. Body Na may be low, normal or high. Relative water retention is a common factor 

·        Condition and treatment can be hazardous.  If correct too fast then pontine demyelination 

·        Treatment must be slow and monitored closely. Treatment can range from water restriction or diuresis to sodium restriction or normal saline. Need to know underlying cause 

·        Don‟t use hypotonic fluids post-op unless Na is high. Eg dextrose saline – glucose absorbed very quickly post surgery ® hypotonic 

Symptoms:  

·        The big boogie is underlying cerebral oedema. Bigger problem if abrupt onset. Rapid correction can cause central pontine melanosis

·        Symptoms don‟t correlate well with [Na]

·        Early: anorexia, headache, nausea, vomiting, muscle cramps, weakness

·        Advanced: mutism, dysarthria, impaired response to verbal or painful stimuli, bizarre behaviour, hallucinations, asterixis, incontinence, respiratory insufficiency, spastic quadriparesis in 90%

·        Far advanced: (too late to do much) decorticate or decerebrate posturing, bradycardia, hypo or hypertension, dilated pupils, seizures, respiratory arrest, coma, polyuria (central diabetes insipidous)

·        Should always be a differential in post-operative coma