Intravenous fluids may be used for:
provide daily fluid requirement in patients unable to take in adequate fluids or losing increased amounts and correct dehydration
Use crystalloids to maintain volume.
A common regime (for an average 70kg man) to give 3 L fluid with 150 mmol sodium and 60 mmol potassium is:
Other common regimes are:
The replacement of intravascular volume in hypovolemic patients
Use colloids to replace the intravascular volume fast and effectively. These fluids (such as gelofusin and dextran) are contain large particles osmotically active and remain in the intravascular space. These are often used initially in patient who are hypotensive.
Use crystalloids to expand volume over longer periods of time. These contain smaller molecules and will distribute over time into the interstitial and interacellular spaces.
There is no clear benefit in outcome from initial resuscitation with colloids versus crystalloids and either can be justified. Current ATLS guidelines recommend an initial 2L of crystalloid (specifically hartmanns) to restore volume in acute haemorrhage. the amount of crystalloid required to restore circulating volume is roughly 3-4 times the volume lost.
A common regime to replace fluid loss requires several adjustments and close monitoring is:
Severe hemorrhage requires packed red blood cell infusion.
Hartmann’s solution at 20-30 ml/kg/hr can also be used for fluid resuscitation
70 kg man has ~42 L (%60) body fluids. Distribution of fluid in the body is:
1/3 in extracellular fluid
2/3 in intracellular fluid
Transcellular fluids include cerebrospinal fluid, synovial fluid, pleural fluid, ocular fluid, etc.
Fluid movement between these compartments are governed by osmotic and Starling forces:
Osmotic equilibrium at the cell membrane regulates the water balance between ECF and ICF. Osmotic forces depend on osmolality (Osmoles of solute per kilogram of solvent). Main solutes include charged (Na+, K+, Cl-, HCO3‑) and uncharged (urea, glucose) molecules.
Starling equation illustrates movement of fluid across capillaries depending on three factors:
On the arterial side of capillary bed, intravascular fluid moves into interstitial space (higher intravascular hydrostatic force). On the venous side, fluid is reabsorbed into plasma (lower intravascular hydrostatic force).
When fluid is infused into plasma, hydrostatic forces increase and oncotic pressure decrease (dilution effect) until fluid is evenly distributed in ECF and Starling forces are in equilibrium.
History: Patient history, observation and fluid charts, patient notes, etc.
Examination: Blood pressure, pulse, respiratory rate, skin turgor and capillary refilll time, temperature
Investigations: urine output (<30 ml/hr for 70kg man), central venous pressure readings, blood tests, chest x-ray
Response to fluid challenge: Give a 500 ml 0.9% saline or 250 ml colloid through large bore 14G (brown) or 16G (grey) cannula over 5 minutes. Measure response: CVP monitoring, pulse or BP increase and reduction of respiratory stress. Repeat as necessary. Fluid challenge is safe is lungs are clear.
Nil-by-mouth, increased fluid loss (diarrhea ot vomiting), thirst and dry mouth
Low CVP, low BP, tachycardia, weight several kg below pre-op weight
Decreased urine output
Bloods: urea disproportionately raised to creatinine, high sodium and potassium levels
Fluid challenge may not be sufficient to raise CVP initially
Fluid intake > output
Raised CVP, pulmonary oedema, weight several kg above pre-op weight
Blood sodium level may be low
X-ray may show pulmonary oedema and effusion
CVP rises and plateaus with fluid challange
Daily fluid balance of 70 kg man:
Intake: ~2500 ml
Output: ~ 2500 ml
* Minimal volume of urine a healthy person needs to produce is 0.5 – 1 ml/kg/hr
Maintenance fluid requirement for healthy nil-by-mouth patient:
A 70 kg man will require 2650 ml fluid per day: 40 + 20 + 50 = 110 ml/hr --> 2640 ml/day + 100 mM Na+ and 60 mM K+
A 40 kg woman will require 2160 ml fluid per day: 40 + 20 + 20 = 80 ml/hr --> 1920 ml/day + 100 mM Na+ and 60 mM K+
Daily fluid requirements increase in illness:
Fluid requirements in resuscitation depends on stages of hypovolemic shock:
Stage 1 (< 15% or <750ml loss): Normal blood pressure as compensated by increased systemic vascular resistance --> give Crystalloid
Stage 2 (15-30% or 750-1500ml): Tachycardia, postural hypotension, +/- sweating and anxiety – partially compensated by increased systemic vascular resistance --> give Colloid
Stage 3 (30-40% or 1500-2000ml): Systolic blood pressure <100 mmHg, tachycardia, tachypnoea, altered mental state (confusion) --> give Colloid + Blood
Stage 4 (>40% or >2000ml): Very low blood pressure, bradycardia, weak pulse pressure, depressed mental state, urine output negligible --> give Colloid + Blood
Fluid overload risk is high in:
Post-operation fluid maintenance
Crystalloids are water with electrolytes, which form a true solution and are able to pass through a semipermeable membrane. Crystalloids are lost rapidly from intravascular space into interstitial space (depending on the osmolality), and they remain in extracellular compartment for about 45 minutes. Therefore they require larger volumes than colloids for fluid resuscitation. Eventually water from crystalloids diffuse through intracellular fluid as well (membrane pumps and metabolism alter crystalloid distribution and osmotic forces)
Colloids: Water with large molecules or microscopic particles, which are dispersed through water and do not form a true solution. These particles do not pass through semipermeable membranes. Therefore colloid solutions remain in intravascular space longer depending on molecular weight of colloids.
This man most likely has injured his spleen and losing blood into abdominal cavity. He is probably in stage II hypovolemic shock and can progress to stage III. Sympathetic response to bleeding causes hypertension, tachycardia, tachypnea and sweating. He needs colloids (Gelofusine) to replace intravascular fluid and achieve adequate hemodynamic response for a long period. Adequate amount of colloids can be determined by series of fluid challenges. Crystalloids (0.9% saline or 5% dextrose) can later be added to further increase fluid input.
- Intake: nil by mouth, 3000 ml IV normal saline
- Output: 500 ml urine, 3500 ml from nasogastric tube
Last blood results show low potassium. She weighs 60 kg, is apyrexial and has normal BP and heart rate. She complains of a dry mouth. Which fluids are required for the next day before surgery?
First we need to calculate her current water deficit. Her total fluid output is 5000 ml (another 1 L from insensible losses) and total input is 3000 ml. This leaves a deficit of 2000ml. For the next 24 hours she needs IV fluids to replace this 2000 ml on top of her normal needs.
Her normal daily fluid requirement is 2400 ml (calculated using her weight: (4*10+2*10+1*40)*24ml). Since she is nil-by-mouth, her only water input is ~250 ml metabolic water. Adding all her requirements, she needs minimum of 4000 ml fluids(2000+2400-250). Replacement fluids for anticipated losses from nasogastric tube can be prescribed as well, but caution must be taken to avoid overloading. Possible regimes are:
- 4 L Hartmann’s solution over 24 hours
- 2 L 5% dextrose (replace deficit) and 2 L Hartmann’s solution over 24 hours
In this scenario preferring Hartmann’s solution over 0.9% saline is important to correct hypokalemia. Blood tests should be repeated to re-check electrolyte levels.
This is a reference section for those interested in numbers
1. McLatchie GR, Borley NR, Chikwe J, Ovid Technologies Inc. Oxford handbook of clinical surgery. Oxford ; New York: Oxford University Press; 2007.
2. Cooper N, Forrest K, Cramp P. Essential guide to acute care. 2nd ed. Malden, Mass.: Blackwell BMJ Books; 2006.
3. Kumar PJ, Clark ML. Kumar & Clark's clinical medicine. 7th ed. Edinburgh ; New York: Saunders Elsevier; 2009.
4. Goldberg A, Stansby G. Surgical talk : revision in surgery. 2nd ed. London, Singapore ; Hackensack, NJ: Imperial College Press ; Distributed by World Scientific; 2005.
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