Practical Prescription and Monitoring in Critical Patients

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The 4 "D"s of Fluid Therapy

💊 Drug (The Fluid Solution)

Select the appropriate crystalloid or colloid solution tailored to the patient's biochemical profile. Avoid the indiscriminate, routine administration of 0.9% Normal Saline in states of primary tissue acidosis.

⚖ Dose (dose / rate)

Determine the exact volume required, titrating the infusion rate in milliliters per hour according to baseline hemodynamic indices and dynamic perfusion targets.

⏳ Duration

Define explicit time frames to stop fluid administration, monitoring resolution of circulatory shock to prevent adverse interstitial edema and volume overload.

🔄 De-escalation

Actively remove accumulated interstitial fluid, facilitating a negative fluid balance using diuretics or ultrafiltration once cardiovascular stability is restored.

Conceptual Four-Phase Approach (The R.O.S.E. Model)

Resuscitation fluid management in septic or critical shock progresses dynamically across four distinct clinical stages:

R Phase (Resuscitation)

• Clinical objective: Save the patient's life by immediately correcting extreme arterial hypotension and refractory circulatory shock.
• Fluid strategy: Rapid bolus administration of balanced isotonic crystalloids (30 mL/kg of weight in the first 3 hours since onset).
• Fluid balance state: Strongly positive on purpose.

O Phase (Optimization)

• Clinical objective: Stabilize cell perfusion, closely monitoring that overload does not compromise tissue oxygenation.
• Fluid strategy: Rigorous evaluation of fluid responsiveness using dynamic parameters, minimizing the use of blind continuous basal infusions.
• Fluid balance state: Moderately positive, controlled.

S Phase (Stabilization)

• Clinical objective: Maintain tissue homeostasis and perfusion of vital organs upon remission of the acute phase of shock.
• Fluid strategy: Exclusive contribution to cover basal requirements for insensible losses and ongoing diuresis, providing minimal basal electrolytes.
• Fluid balance state: Neutral or stable maintenance.

E Phase (Evacuation)

• Clinical objective: Promote active de-escalation and removal of excess body water accumulated in the interstitium during the resuscitation phases.
• Fluid strategy: Targeted use of loop diuretics (continuous infusion furosemide) or renal clearance support with targeted negative balance.
• Fluid balance state: Strongly negative, reducing damage due to pulmonary and visceral interstitial edema.

Evaluation of Response to Fluids: Dynamic vs. Static Indices

It is a clinical error in contemporary practice to guide fluid administration based exclusively on traditional static parameters such as Central Venous Pressure (CVP) or pulmonary artery occlusion pressure. These values only measure atrial or ventricular filling pressures and do not predict in any way whether a ventricle is capable of increasing its ejection cardiac output in the face of an additional volume load.

The use of dynamic parameters of fluid responsiveness based on the cardiopulmonary physiological interactions of positive pressure mechanical ventilation should be prioritized:

• Pulse Pressure Variation (PPV) or Stroke Volume Variation (SVV): A value of PPV > 12% or SVV > 10% in a patient under controlled mechanical ventilation, in sinus rhythm, with tidal volume ≥ 8 mL/kg of weight, predicts with high diagnostic sensitivity an increase in cardiac output after the infusion of a volume bolus.
• Passive Leg Raise (PLR) Test: Reversible dynamic maneuver that simulates an immediate internal autotransfusion of approximately 300 mL of blood from the venous territory of the lower extremities to the right atrium. If measurement by transthoracic echocardiography or pulse contour reveals an stroke volume increase > 10% during the maneuver, the patient is classified as a fluid responder, allowing volume to be prescribed with minimal risk of irreversible iatrogenic overload.