Fluid resuscitation in burns patients 1: Using formulas
Williams, C. (2008) Fluid resuscitation in burn patients 1: using formulas. Nursing Times; 104: 14, 28–29.
This is the first in a two-part unit on caring for patients with burns. It focuses on the two main formulas used to produce calculations for fluid resuscitation.
Catherine Williams, PGCE, MSc, BSc, DipN, RNT, RN, is nurse tutor, school of health science, Swansea University.
It is well established that fluid management is fundamental when treating burn patients during the immediate post-trauma period. Through clinical experience, we know that adequate volumes of IV fluids are required to prevent burns shock in those with extensive burn injuries.
The aim of resuscitation is to restore and maintain adequate oxygen delivery to all tissues of the body following the loss of sodium, water and proteins.
Fluid loss starts immediately after the burn occurs, because heat damage increases the permeability of the capillaries, which means that plasma is able to leak out of the blood circulation. This increase disrupts the normal exchange of blood plasma into the extracellular space at the site of injury, which results in rapid fluid loss.
The greatest loss of plasma occurs in the first 12 hours after burn injury. The plasma loss then slowly decreases during the second 12 hours of the post-burn phase, although extensive leakage can continue for up to three days (Ahrns, 2004). Optimal fluid replacement during this period is essential to ensure cardiac output and renal and tissue perfusion. Usually, 36 hours post-burn, capillary permeability returns to normal and fluid is drawn back into the circulation.
There is also visible fluid loss occurring from exudate, blisters and oedema, and evaporative loss at the burn surface. Tissue oedema develops quickly during the first 6–8 hours and continues gradually during the next 18–24 hours post burn.
The body is able to compensate by shutting down the blood supply to the skin, abdominal viscera and kidneys but continued loss overwhelms the system. Blood volume decreases, resulting in intravascular hypovolaemia – sometimes referred to as ‘burns shock’ – which can be fatal if left untreated.
During the initial resuscitation period, an escharotomy (a surgical incision into an eschar, a scab or slough formed on the skin) may be necessary as fluid can accumulate under the eschar and inhibit vascular perfusion, respiratory movement or both.
Aim of fluid resuscitation
The primary function of fluid resuscitation is to:
Prevent burn shock by giving adequate fluid without overloading the vascular system or causing excessive oedema;
Maintain circulatory volume in the face of losses due to the burn – this is essential for cardiac output, renal perfusion and tissue perfusion;
Provide metabolic water;
Maintain tissue perfusion to the zone of stasis and prevent the burn from deepening.
The main function is not to correct depleted intravascular volume.
Criteria for fluid resuscitation
Burns of more than 15% of surface body area in adults and of over 10% in children warrant formal resuscitation.
There is no ideal resuscitation regimen. Many different types are used and have been adapted over the years, such as those recommended by: Brooke (1953); Evans et al (1952); Muir and Barclay (1962); and Parkland (1968). All these formulas can be found in Bosworth (2003).
For many years, there was no consensus on the ideal fluid for preventing burn shock except that the essential ingredients should include water and salt. The formula to be followed is 0.5mmol sodium per kilogram of body weight per percentage of total burn surface area (TBSA).
A variety of fluids have been recommended for use, such as plasma, human albumin solution (HAS), dextran and Hartmann’s solution. However, it would appear that controversy still remains about which fluids should be used (the crystalloid versus colloid debate).
Hypertonic saline achieves much the same results but with less volume than isotonic saline and oedema is less.
Colloids may be extravasated to tissues because of the increased vascular permeability but withholding protein replacement may further decrease plasma oncotic pressure.
A study by Bunn et al (2004) concluded that hypertonic crystalloid is no better than isotonic and near-isotonic crystalloid for the resuscitation of patients with burns. Therefore it could be concluded that the optimal composition of fluid to be used remains unknown.
There is no robust scientific evidence to support the adoption of one particular protocol over any others. To date, no single formula recommendation has been established as the most successful approach to adopt on fluid resuscitation of burn patients who are critically ill. Each burns unit/centre will have its own preference and experienced staff can exercise some discretion regarding their fluid composition of choice.
Lund and Browder (1944) charts are used to calculate the percentage of burn surface area to assess the burn before fluid resuscitation is started. Even though this chart is more than 60 years old, it is still considered the most accurate way to calculate the burn injury.
Erythema should not be counted in the final TBSA as, most of the time, it does not require treatment and does not affect fluid loss.
Historically, fluid management has been as much an art as a science – a fine line must be negotiated between an adequate resuscitation and one of fluid overload.
Predominantly, fluid resuscitation is carried out intravenously and the most commonly used resuscitation formula is the pure crystalloid Parkland formula.
This advocates the guideline for total volume of the first 24 hours of resuscitation at approximately 4ml per kilogram of body weight per percentage burn of TBSA. Half the volume is given in the first eight hours post burn, with the remaining volume delivered over 16 hours.
The Parkland formula has the advantage of being easy to use. It leads to fewer respiratory problems later on, although there may be pronounced general oedema in the first stages of its use as large volumes of fluid are required.
The Parkland formula for the total fluid requirement in 24 hours is as follows:
4ml x TBSA (%) x body weight (kg);
50% given in first eight hours;
50% given in next 16 hours.
Children receive maintenance fluid in addition, at an hourly rate of:
4ml/kg for the first 10kg of body weight plus;
2ml/kg for the second 10kg of body weight plus;
1ml/kg for >20kg of body weight.
Urine – adults: 0.5–1.0 ml/kg/hour;
Urine – children: 1.0–1.5ml/kg/hour.
Note: in order to ensure accurate calculations subtract any fluid that has already been received from the amount that is required for the first eight hours.
Muir And Barclay formula
The other commonly used formula was developed by Muir and Barclay (1962). This uses a colloid resuscitation with plasma and runs over 36 hours.
As the fluid lost from the circulation is plasma, it seems logical to replace it with plasma. With colloid resuscitation, less volume is required and the blood pressure is better supported.
However, both colloid and plasma are expensive. They may also leak out of the circulation and may result in oedema of the lungs.
The 36 hours are divided into six periods of varying length, and an equal volume of plasma is administered in each period. The volume to be transfused in each period is calculated via the formula. This volume is given in each successive period of four, four, four, six, six and 12 hours. At the end of a period, if the assessment shows that the patient’s clinical condition is stable, the transfusion is continued according to the formula. If there is any clinical evidence of under- or overtransfusion then the plasma rations for the next and following periods are altered accordingly.
The Muir and Barclay formula is as follows: % x kg = volume needed.
Total % of burn surface area x body weight in kilograms = volume in millilitres of fluid to be given in each period.
The volume needs to be recalculated at each change in time period:
Every four hours for the first 12 hours;
Every six hours between 12 and 24 hours;
After 36 hours.
Note: areas of erythema should be excluded from TBSA. When using this formula, maintenance fluid is also required.
It is worth noting that the time-dependent variable for all formulas begins from the moment of injury, not from the time that a patient is seen in A&E. The formulas are a starting point. It is important to be aware that the actual amount of fluid infused varies according to each patient’s clinical condition and must be titrated according to their requirements and clinical condition, regardless of the choice of formula.
Part 2 of this unit, to be published in next week’s issue, discusses nursing care during fluid resuscitation.
Ahrns, K.S. (2004) Trends in burn resuscitation: shifting the focus from fluids to adequate endpoint monitoring, edema control and adjuvant therapies. Critical Care Nursing Clinics of North America; 16: 1, 75–98.
Bosworth, C. (2003) Burns Trauma: Management and Nursing Care. London: Bailli貥 Tindall.
Bunn, F. et al (2004) Hypertonic versus near isotonic crystalloid for fluid resuscitation in critically ill patients. Cochrane Database of Systematic Reviews; 3: CD002045.
Evans, E.I. et al (1952) Fluid and electrolyte requirements in severe burns. Annals of Surgery; 135: 6, 804–815.
Lund, C., Browder, N.C. (1944) Estimation of area of burns. Surgery, Gynaecology and Obstetrics; 79: 352–358.