Research and clinical interest in POD, particularly in cardiac surgery patients, has increased tremendously. Delirium, a disabling condition, is likely to cause prolonged cognitive impairment. The postoperative phase is a critical period for patients during which complications such as POD can significantly affect recovery.

In the context of cardiac surgery, the prevalence of POD poses challenges to the quality of postoperative care, specifically in the aging population, in whom major cardiac surgeries are being increasingly performed. This study aimed to investigate the relationship between POH and delirium in patients who underwent cardiac surgery.

In the current adult patient study, an independent association was observed between POH and early-onset delirium, which aligns with our initial hypothesis and differs from the findings of previous studies. However, no correlation was observed, and no relationship between hypertension and POD [19]. Based on our findings, the adjusted models demonstrated a significant association between delirium and POH. The odds ratios exceeded 5 (p < 0.006), indicating that individuals who developed POH were highly prone to POD.

Similar to our previous and other published reports, we found that most patients with delirium were older adults [20,21,22].

The explanation lies in the physiological processes linked to aging, as advanced-age individuals tend to become frail [22]. Therefore, any disabling condition or comorbidity could affect the individual’s cognition and overall health. We also observed a higher prevalence of delirium in patients undergoing emergency surgery. This observation is supported by a previous report [23]. Our study found that delirium was associated with increased morbidity, consistent with findings from previous research [24]. In this investigation, we observed an increased occurrence of delirium in on-pump CABG and other non-coronary cardiac surgeries compared with off-pump CABG. This finding is consistent with that of a previous study, which independently linked the type of surgery operation to delirium [25].

Intraoperative hypotension or fluctuations in blood pressure independently pose a risk for the development of POH, POD, and various complications [26,27,28]. Individuals who experienced intraoperative hypotension were excluded from the study. The exclusion of patients with intraoperative hypotension aimed to ensure a focused investigation into the specific impact of hypotension on delirium in the ICU setting, thus contributing to the rigor of our study design. Contrary to earlier findings that indicated a correlation between extended operative time and increased risk of POD, our study did not find an association between the two [29].

Statistical differences between the groups regarding ICU stay duration and postoperative complications were noted. Importantly, these results align with those reported in a previous study [30].

Shirvani et al. reported that delirium occurring in the postoperative period after CABG is associated with electrolyte imbalances and metabolic disturbances. One potential rationale for this is that patients undergoing major cardiac surgery often experience blood loss and oxygen saturation fluctuations during the operation, which may account for the onset of hypotension during the postoperative period [31]. Maintaining a baseline regional cerebral oxygen saturation level > 50% is recommended to decrease the likelihood of POD development [32].

POH and POD are significant complications associated with surgical procedures, particularly in older adults. Several mechanisms link POH with POD. Cerebral hypoperfusion due to reduced blood pressure impairs brain oxygen and nutrient delivery and increases delirium risk, particularly in vulnerable populations [33]. Hypotension also triggers inflammatory responses, releasing cytokines like IL-6 and TNF-α, contributing to delirium. Metabolic disturbances, such as hypoxia and acidosis, disrupt neuronal function, whereas sustained hypotension compromises the blood–brain barrier, allowing toxins to affect the brain. Additionally, hypotension alters the neurotransmitter balance, affects cognitive function, and leads to delirium [34, 35].

In our study, all patients underwent major cardiac surgeries under general anesthesia, and delirious patients were treated postoperatively using a standardized protocol for delirium. The use of dexmedetomidine has been identified as being linked to decreased occurrence of POD in the early days after the procedure [36].

Furthermore, our findings also indicate a substantial influence of delirium on postoperative outcomes. Individuals who experienced delirium during their hospital stay experienced more severe postoperative complications than those who did not, which is similar to that of previous studies [37].

Moreover, our study revealed that patients experiencing delirium were more likely to be transferred to other healthcare facilities for ongoing treatment, in contrast to patients without delirium.

Our study had some limitations. First, the timing, duration, and frequency of blood pressure measurement during the postoperative days were not reported in this investigation; however, they were reported for any exposure. Second, hypotension management was beyond the scope of this investigation. Third, the etiology of delirium in the late postoperative period may differ from that in the early postoperative period, and extending the measurements beyond ICU discharge is unlikely to alter our findings. Fourth, its single-center design might have limited the generalizability of our findings to healthcare settings with different protocols and patient demographics. Considering the sample size of 307 patients, excluding 16 participants may have affected the statistical power. A larger sample size would have enhanced the reliability and precision of this study. The variety of surgeries and the use of on-pump versus off-pump techniques.

Finally, our study reported a standardized delirium management protocol without specific anesthesia and medication administration details, introducing variability in treatment approaches that may influence the observed outcomes.