Why Normal Saline is Preferred Over DNS in Post-Operative NPO Patients
Balanced crystalloids are generally preferred over normal saline (NS) for most surgical patients, but when comparing NS to dextrose-containing solutions like DNS in NPO post-operative patients, NS is preferred because it avoids unnecessary hyperglycemia while maintaining intravascular volume. 1, 2
Rationale for Avoiding Dextrose in Post-Operative Patients
- A randomized controlled trial in non-diabetic elective surgery patients showed that even a relatively small volume (500 ml) of dextrose-containing solution caused significant hyperglycemia, with plasma glucose exceeding 10 mmol/L in 72% of patients receiving dextrose saline 2
- Perioperative hyperglycemia is strongly associated with increased postoperative morbidity and mortality, making avoidance of unnecessary glucose administration important 3
- Post-operative patients are already in a state of stress-induced insulin resistance, and adding dextrose can exacerbate hyperglycemia 1
- Hypoglycemia is rarely an issue in adult post-operative patients despite average fasting times of almost 13 hours, eliminating the need for routine dextrose administration 2
Fluid Management Recommendations for Post-Operative Patients
- Balanced crystalloids (like Ringer's Lactate or Plasmalyte) are actually preferred over NS for most surgical patients due to their lower risk of hyperchloremic metabolic acidosis and adverse renal events 3, 1
- However, when comparing specifically between NS and DNS for NPO post-operative patients, NS is preferred to avoid unnecessary hyperglycemia 2
- A mildly positive fluid balance is recommended to protect kidney function, which can be achieved with either balanced crystalloids or NS 3
- Intraoperative fluid administration rates of 1-2 ml/kg/h are recommended to minimize the risk of postoperative complications 1
Potential Complications of NS vs. DNS
Normal Saline (NS) Concerns:
- Large volumes of NS can cause hyperchloremic metabolic acidosis 3, 4
- NS administration is associated with a higher incidence of major adverse kidney events compared to balanced solutions when used in large volumes 3, 5
- NS can lead to hypernatremia and hyperchloremia, especially when used as a drug diluent in significant volumes 6
Dextrose Normal Saline (DNS) Concerns:
- Causes significant, albeit transient, hyperglycemia even in non-diabetic patients 2
- Hyperglycemia is associated with increased postoperative morbidity and mortality 3
- Provides unnecessary calories in patients who are typically not at risk for hypoglycemia 2
Special Considerations
- In patients with traumatic brain injury, 0.9% saline is specifically recommended as first-line fluid therapy 1
- For patients with diabetic ketoacidosis, recent evidence suggests balanced fluids may be superior to NS for resolution of metabolic derangements 7
- In patients with sickle cell disease vaso-occlusive episodes, lactated Ringer's solution has shown better outcomes compared to NS 5
- For kidney transplant recipients, buffered crystalloid solutions are recommended over 0.9% saline 3
Practical Approach to Post-Operative Fluid Selection
- For routine post-operative NPO patients: Use balanced crystalloids (preferred) or NS rather than dextrose-containing solutions 1, 2
- For patients requiring large volume resuscitation: Balanced crystalloids are preferred over NS to avoid hyperchloremic metabolic acidosis 3
- For patients with pre-existing hyperglycemia or diabetes: Absolutely avoid dextrose-containing solutions like DNS 3, 2
- For neurosurgical patients: NS may be preferred over balanced solutions 3, 1
In conclusion, while balanced crystalloids are generally preferred over NS for most surgical patients, when specifically comparing NS to DNS in post-operative NPO patients, NS is the better choice to avoid unnecessary hyperglycemia while maintaining intravascular volume.