Heart bypass surgery: Mannitol reduces the risk of postoperative delirium

A randomized study examined the potential role of mannitol in preventing delirium during heart bypass surgery. But how much is the risk reduced?

Mannitol for delirium prophylaxis after cardiac bypass surgery

This small study showed a significantly reduced risk of delirium in the mannitol group (22.2% vs. 42.2%, p = 0.035). Larger studies are needed to confirm these results.
No significant differences were found between the groups regarding mortality rate, length of stay in the intensive care unit, or reoperation rate. The same applies to mechanical ventilation time, aortic clamp time, and cardiopulmonary bypass interval.

In the double-blind study, 90 adult patients undergoing cardiac surgery with cardiopulmonary bypass were randomized. Different primer solutions were used to prepare the heart-lung machine:

Intervention group: Ringer's lactate supplemented with 200 ml of 20% mannitol, plus sodium bicarbonate and sodium heparin.
Control group: Ringer's lactate with sodium bicarbonate and sodium heparin, but without mannitol.

The following endpoints were examined in both groups:

Occurrence of postoperative delirium, diagnosed using the Delirium Observation Screening Scale
Duration of mechanical ventilation
Length of intensive care unit stay
30-day mortality

Results: Mannitol significantly reduces the risk of delirium

Overall, 32.2% of surgical patients experienced postoperative delirium. However, the incidence differed significantly between the two study groups:

Control group: delirium in 42.2% of patients
Mannitol group: delirium in only 22.2% of patients (p = 0.035)

No significant differences were observed between the two groups for the other endpoints. This also applied to the reoperation rate, aortic clamp time, and cardiopulmonary bypass interval, which were also analyzed. Furthermore, no significant adverse effects related to mannitol were observed.

Causes of Postoperative Delirium

But why does acute confusional syndrome occur after surgery? It is known to be a multifactorial pathogenesis. Various factors are involved, including:

Neuroinflammation
Neurotransmitter alterations
Subclinical cerebral vascular events
Increased intracranial pressure
Reduced cerebral blood flow due to hemodilution

In cardiac surgery, cardiopulmonary bypass and its duration are considered risk factors for the occurrence of postoperative confusion. Rapid changes in temperature, intravascular pH, and arterial blood pressure during cardiopulmonary bypass can trigger a pronounced inflammatory response. This affects cerebral perfusion, oxygen consumption, and oxygen supply to the affected brain area. As a result, hypoxia and ischemia of the brain tissue can occur, which significantly increases the risk of postoperative delirium.

Why does mannitol have a preventative effect?

The beneficial effects of using mannitol in the primer solution of the heart-lung machine are based on several mechanisms:

The osmotic effect of mannitol reduces intracranial pressure by removing water from the tissue.
Mannitol improves cerebral perfusion and prevents the formation of cerebral edema.
Mannitol has antioxidant effects. It can reduce oxidative stress, which is considered a key factor in the pathogenesis of postoperative delirium.

Conclusion: Mannitol as a promising strategy against postoperative delirium

This randomized controlled trial demonstrates a significant reduction in the risk of delirium with mannitol. Due to the limited sample size, larger studies are needed to confirm these results. Neither mortality nor length of intensive care stay were higher in the mannitol arm than in the control group. These results provide initial evidence that mannitol may contribute to delirium prevention. Further studies are needed to evaluate its clinical benefit.

Source

Hemmati Maslakpak M, Negargar S, Farbod A, et al. Effect of mannitol on postoperative delirium in patients undergoing coronary artery bypass graft: a randomised controlled trial. Open Heart 2024;11:e002743. doi:10.1136/ openhrt-2024-002743