The Evolution of the Fluid in the Muir Barclay Formula
The Muir Barclay formula, a historical but significant protocol for fluid resuscitation in major burn patients, has seen its primary fluid component change over the decades. The original formula, popularized in the United Kingdom in the early 1960s, stipulated the use of freeze-dried plasma, a colloid solution, as the main fluid for restoring intravascular volume. This was combined with a 5% dextrose solution, a crystalloid, to fulfill the patient's metabolic water requirements. The rationale for using a colloid like plasma was to increase plasma osmotic pressure, thereby retaining fluid within the circulatory system.
By the late 1980s, medical practices and available products evolved. The fluid component for the Muir Barclay formula was updated, and 4.5% human albumin solution (HAS) became the replacement for the earlier plasma solutions. Albumin, a key protein in plasma, serves the same core purpose of providing oncotic pressure to prevent fluid from leaking out of the blood vessels. This transition was part of a larger shift in clinical practice toward safer, more standardized blood products and away from less reliable sources like freeze-dried plasma. Today, while superseded by other methods in most burns units, the Muir Barclay protocol is still a valuable historical and educational example of fluid resuscitation strategies.
Historical Context of Burn Resuscitation
The development of fluid resuscitation protocols for burn patients is a story of continuous refinement based on clinical experience and scientific understanding. Before formulas like Muir Barclay, burn treatment was less systematic, leading to inconsistent outcomes. The Muir Barclay formula was a major step forward, providing a structured approach to a life-threatening condition known as burn shock. This condition is characterized by massive fluid shifts from the intravascular space into burned and unburned tissues due to increased capillary permeability, leading to severe hypovolemia. The formula addressed this directly by administering a colloid-rich fluid to counteract this osmotic shift.
Contemporaneous with or subsequent to Muir and Barclay's work, other resuscitation protocols emerged. In the United States, the Parkland formula, developed by Baxter and Shires in 1968, gained prominence. The key pharmacological difference lies in the choice of fluid: Parkland primarily uses Ringer's lactate, a crystalloid solution, rather than a colloid. The debate over the optimal use of colloids versus crystalloids in burn resuscitation has continued for decades, and the Muir Barclay formula represents a strong early advocate for colloid-based strategies. Some modern burn units have even used a hybrid approach, combining elements of both Parkland and Muir Barclay protocols.
Composition and Administration Details
As previously mentioned, the fluids in the Muir Barclay formula were either the original freeze-dried plasma plus dextrose or, later, 4.5% human albumin solution. The calculation for the total fluid volume needed over the initial 36 hours is based on the patient's weight and the total body surface area (TBSA) affected by the burn. Specifically, the formula was often expressed as: (patient weight in kilograms) x (% TBSA burn) / 2. This total volume is then divided and administered over a series of time periods, with equal volumes given in each period, but with progressively longer intervals between infusions.
This schedule differs significantly from the more commonly used Parkland formula, which administers half of the total 24-hour volume in the first 8 hours. The Muir Barclay protocol was typically structured into six periods:
- First 12 hours: Three infusions given at 4-hour intervals.
- Second 12 hours: Two infusions given at 6-hour intervals.
- Third 12 hours: A single, final infusion.
This schedule aimed to manage the changing fluid requirements over the critical initial 36 hours following a major burn injury, a period during which capillary permeability gradually normalizes.
Muir Barclay vs. Parkland Formulas
| Feature | Muir Barclay Formula | Parkland Formula |
|---|---|---|
| Primary Fluid | Plasma (originally), then 4.5% Human Albumin Solution | Lactated Ringer's Solution (crystalloid) |
| Fluid Type | Colloid-based | Crystalloid-based |
| Time Period | 36 hours, broken into six staggered periods | 24 hours, with half given in the first 8 hours |
| Calculation | (kg x % TBSA) / 2 for each period | 4 mL x kg x % TBSA for first 24 hours |
| Key Mechanism | Increases plasma oncotic pressure to retain fluid intravascularly | Replaces lost electrolytes and water, with some fluid leaving the intravascular space |
| Modern Usage | Largely historical, though sometimes used in modified or hybrid regimens | Widely used worldwide as a standard protocol |
The Pharmacological Rationale
The fundamental pharmacology behind the Muir Barclay formula lies in the properties of colloids. When a severe burn occurs, the body's capillary walls become more permeable, allowing water and small electrolytes to leak out into the interstitial space. This leads to profound edema and a drop in blood volume, a condition known as burn shock. Colloid solutions like plasma and albumin contain large protein molecules that cannot easily cross these permeable capillaries. By infusing these large molecules, the plasma osmotic pressure is increased. This helps to pull and hold fluid within the blood vessels, effectively restoring and maintaining circulating blood volume and blood pressure. The use of a small amount of dextrose in the original formula was simply to ensure adequate metabolic water supply, not as a primary fluid for resuscitation.
Conclusion
In conclusion, the fluid used in the Muir Barclay formula evolved from freeze-dried plasma and 5% dextrose to a 4.5% human albumin solution, reflecting changes in medical safety and practice. This colloid-based resuscitation protocol was a significant development in burn care, providing a structured method for replenishing lost intravascular volume in the critical hours following a major burn. While largely replaced by crystalloid-based approaches like the Parkland formula, understanding the Muir Barclay formula provides valuable insight into the history of burn management and the pharmacological strategies used to combat burn shock.
Note: Modern burn care protocols may differ significantly. For current best practices, consult contemporary medical guidelines such as those from the American Burn Association or local burns units.
For a detailed look at the evolution of fluid resuscitation in burns, consider resources published by medical journals and societies, such as those cataloged on the National Institutes of Health website.
