Surgery - Choice of fluids Flashcards
Colloids and crystalloids
- A CRYSTALLOID will dissolve in water and form a true solution which can pass through a semi permeable membrane eg dialysis
- In dialysis solute molecules go from a region of higher concentration to lower, across a semipermeable membrane
- A COLLOID is a solution containing particles of 1-1000nm which do not settle out under gravity.
- These particles cannot pass across a semi permeable membrane
The choice of fluid-1
- Much debate
- Reviews show no difference between crystalloid resuscitation in
- Mortality
- Overall length of stay
- Incidence of Pulmonary oedema
Choice of fluid -2
- Crystalloid fluids-H20 and electrolytes and best for replenishment of ECF depletion
- For blood volume replacement, 3-4 times vol. lost is needed because it is distributed in a ratio of 1:4 intravascular:extravascular
- No incidence of allergic reactions
- Cheap
- Plasma oncotic pressure reduced because of dilutional effect on plasma proteins- thus fluid passes out leading to oedema
- Don’t forget Starlings forces-the balance of hydrostatic and colloid pressures
Choice of fluids 3
- Colloids are large molecules that stay in the circulation
- They exert colloid oncotic pressure and stay in the circulation so less volume is needed in hypovolemia
- They have electrolytes added to achieve iso-osmolality
Crystalloids
- NaCl- all Na stays extracellular and osmolality of ECF unaltered ( water stays put )
- Glucose 5% iso-osmotic-behaves as free water (body metabolises glucose ), osmolality of ECF decreases and water shifts from ECF to ICF in a ratio of 1:2 ( because 66% TBW is ICF )
- Ringers soln. has electrolytes needed for cellular function
- Hartmanns was formulated to treat acidosis in sick children
- Lactate is metabolised by gluconeogenesis in the liver consuming H+ and producing excess HCO3-
- Care in pts with renal disease or liver dysfunction
Colloids-2
1.Semi-synthetics ( HES, gelatins and dextrans )
2.Plasma derivatives-albumin
- Gelofusine- 4% soln gelatine in saline. t1/2 2-4 hrs
- Haemaccel-3.5% polygelin containing NaCl, KCl and Ca Cl2 .t1/2, 6hrs
- Hespan-6% starch in NaCl. 60% remains in body for 24 hrs-bound to tissues
- Starch-a large molecule similar to glycogen
Colloids-3
- Colloids do not easily cross capillary membrane-thus use in resus.
- Volume expanding effect less than expected in critically ill patients who have capillary leak, esp. burns and sepsis
- Renal dysfunction, coagulopathy and anaphylaxis
- Licences for all HES products suspended in 6.2013
- European Medicines Agency revised that in 2014 to allow use in pts with acute blood loss but further studies into trauma cases and surgical safety
- Addition of albumin finds no advantage in survival of sepsis pts over crystalloid alone
Peri-operative issues-1
- Pre-op fasting. Fluid restriction /starvation separate issues. May be significant in emergency cases
- Emergency patients may suffer from d&v in 60% cases .Most could be resuscitated pre-operatively.Rarely works like this. Care needed with those with prolonged symptoms, sepsis and organ failure-invasive monitoring, HDU. Hartmanns solution useful
- Intra-operative losses may be 10ml/kg/hr with an open chest/abdomen. Evaporation, sero-sanguinous fluid in wounds and 3rd space losses ( loss in ileus ). Use Hartmanns and a colloid
- Post-operatively-pts often fluid depleted-inadequate measurement of loss and replacementand. Remember the shifts of fluid and electolytes that take place. Poor analgesia may mask the CV signs ( epidural analgesia )
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Post-op fluid replacement
- Care with fluids-D/Saline often used with resulting hyponatraemia
- K is omitted ( may predispose to ileus ) and overcautious infusion of fluid/Na esp. to the elderly leads to hyponatraemia and hypovolaemia
- Third space losses underestimated
- Include intra-operative fluids ( and losses ) on 1st day chart
- Insensible loss may be 1-1.5 litres
- Patients with bowel obstruction may pose difficulty-dehydrated due to 3rd space losses, N/G tube aspirate and decreased oral intake
Bowel obstruction-1
- Patients with bowel obstruction may pose difficulty-
- Dehydrated due to 3rd space losses, N/G tube aspirate and decreased oral intake
- Often septic and lose protein into the bowel/peritoneum leading to hypo-albuminaemia
- Goals are restore vascular and interstitial fluids,
- Correct electrolytes and acid/base status and optimise O2 delivery
- Vasoconstriction limits rate at which ECF can be replenished
- Frequent monitoring of BP, HR,urine output, U&Es, Hb and CVP
- Give Hartmanns and albumin if COP is less than 15mmHg
- Maintenance with saline and dextrose with K supps and albumin prn
*
Water balance /24 hrs
Input Output
Source Volume (mL) Site of loss Volume (mL)
Water 1000 Urine 1000
Food 650 Skin 500
Metabolism 350 Lungs 400
Faeces 100
Total =2000 =2000
Daily requirements Water-30ml/kg/24hrs, Glucose-100 gm/24hrs
Na, K, 1 mmol/24hrs
Composition of commonly used crystalloids
Fluid Na Cl− K+ Mg2 Ca HC03 Glucose Osm
Normal plasma 142 103 4.5 1.25 2.5 24 0.08 291
0.9 % saline 154 154 308
5% glucose 5 278
0.18% sal. 4% dex 30 30 4 284
Hartmann’s soln 131 111 5 2 29 (lac) 278
NaHCO3 8.4% 1000 1000 pH 82000
NB sodium bicarbonate very dangerous, huge sodium load and huge local dehydration causing necrosis
*Constituent measurements are in mmol/L, except for glucose, which is in g/dL.
Composition of colloids
Na K Ca Cl What else pH
Haemaccel mw30k 145 5 6 145 Gelatine 35g 7.3
Gelofusine mw 30k 154 0.4 0.4 125 Gelatine 40 g 7.4
Hespan mw 200k 154 154 Starch 6og 5
Dextrans
Haemaccel also has Mg
Dextrans are glucose polymers and available as solutions with either sodium chloride 0.9% or dextrose 5% in different molecular weight preparationsand concentrations and are used to reduce plasma viscosity and as a vol expander
Indicators for urgent fluid resuscitation
- Systolic BP < 100mm Hg ( care )
- HR >90bpm
- Capillary refill time>2 secs
- Peripheries are cold
- RR >20 bpm
- NEWS is 5 or more
- Improvement with passive leg raising suggests fluid responsiveness ( may worsen situation )
National Early Warning System-NEWS
- *Parameter** 3 2 1 0 1 2 3
- *RR** ≤8 9-11 12-20 21-24 ≥25
- *SpO2** ≤91 92-93 94-95 ≥96
- *Added O2** Yes No
- *Temp** ≤35 35.1-36 36.1-38 38.1-39 ≥39
- *Syst. BP** ≤90 91-100 101-110 111-219 220
- *HR** ≤40 41-50 51-90 91-110 111-130 ≥130
- *Conc.level** A VPU
