In our observational study, we found that preoperative moderate to severe anemia in hip fracture surgical patients over 80 years old was associated with more MACCE and PPCs. In addition, preoperative moderate to severe anemic patients had higher in-hospital mortality than those with normal to mild anemia. However, according to the study, the patients had similar rates of delirium, ICU admission, gastrointestinal complications, and DVT between cohorts.

The prevalence of preoperative anemia in our study was much higher than reported. One reason was that the target population in our study was hip fracture patients, and another reason was that the research focused on patients over 80 years old. The concept of anemia is defined by the WHO as a hemoglobin level less than 12 g/dl in women and 13 g/dl in men. It was recommended by the blood management in hip fracture patients the preoperative hemoglobin level should be kept above 8 g/dl, and 10 g/dl was suggested for frail patients with serious comorbidities. However, the threshold for blood management in hip fracture patients over 80 years old is unknown. A higher hemoglobin level of 11 g/dl was cautiously chosen for hip fracture patients over 80 years old because it is a clinically implicated level that could compromise both men and women. It was hypothesized that anemia-induced tissue hypoxia may contribute to the pathophysiology associated with clinical anemia (Hare et al. 2018). Acute kidney injury, stroke, and myocardial injury may occur because of anemia (Hare Gregory 2021).

Perioperative anemia has long been an issue that captures both surgeons’ and anaesthethiologists’ attention. Several original studies and reviews have reported increased postoperative morbidity and mortality in both cardiac and noncardiac surgery patients with abnormal preoperative hemoglobin concentrations. Padmanabhan and colleagues observed anemic impacts on morbidity and mortality after surgery with less improvement, and preoperative correction of anemia could improve outcomes of cardiac surgery (Padmanabhan et al. 2016). Moreover, Burton and colleagues suggested that preoperative anemia might be associated with a higher comorbidity burden and the likelihood of postoperative morbidity and mortality (Burton et al. 2019). Another study by Fowler and colleagues included 38,770 patients from 474 hospitals in 27 countries, and 30% were anemic. They found an increased risk of complications and death (Fowler et al. 2018).

Anemia was associated with vital organ injury. Musallam and colleagues (Musallam et al. 2011) collected data from a prospective registry from 211 hospitals for a 30-day mortality and morbidity. This was a retrospective cohort study with 227,425 patients and 30.4% preoperative anemia compared with 64.7% preoperative anemia of hemoglobin < 11 g/dl in our study. In agreement with the study, we also reported higher in-hospital mortality in anemic patients than in patients over 80 years old with preoperative Hb concentrations greater than 11 g/dl. Both studies were retrospective studies, but their research was a multicenter study with more patients. Noncardiac surgery was included, but our study focused on hip fracture surgery, with more elderly patients over 80 years old. Multivariate logistic regression was used to assess the adjusted effect of anemia, but our study was conducted with a propensity score-matched analysis to confirm the strength of the results. They also found that preoperative anemia was associated with increased postoperative morbidity and mortality, as in our study. Patients over 80 years old accounted for less than 3% in the study, and orthopedics surgery accounted for less than 5% of the surgeries. As pointed out by the authors, 7% of the preoperative hematocrit concentrations were obtained more than 4 weeks before surgery and might not accurately predict the concentrations at the time of surgery. However, in our study of hip fracture surgery and in elderly patients over 80 years old, all hemoglobin values were obtained within 3 days before surgery and were more strongly associated with patient outcomes. Sameed and colleagues (Sameed et al. 2021) reported that postoperative pulmonary complications contributed substantially to perioperative morbidity, mortality, and health care costs. Compared to advanced age, physical condition, specific comorbidities, and surgery type, preoperative anemia when treated decreases the risk of adverse outcomes in surgical patients. It was reported that in noncardiac surgery, the prevalence of anemia might be over 30% with an increased prevalence in elderly patients, which was over 65% in our study. Carson and colleagues (Boyd-Carson et al. 2020) reported preoperative anemia (hemoglobin < 11 g/dl) with morbidity and mortality after emergency surgery and concluded that anemia was associated with increased a 90-day and a 30-day mortality, prolonged hospital stay, and risk of return to the operating theater.

It is paradoxical that transfusion and anemia are associated with organ injury and increased morbidity and mortality in surgical interventions (Shander et al. 2011). The transfusion rate (> 2 U) was similar in both cohorts, but the timeline of the treatment was not analyzed in the study. It was reported that preoperative blood management with acute therapy near the time of surgery decreased the intraoperative transfusion rate and increased the postoperative hemoglobin level (Hare Gregory 2021). Several studies have focused on the relationship of postoperative transfusion and mobility and mortality with different conclusions. Smeets and colleagues found no effect of erythrocyte blood transfusion on mortality for hip fracture (Smeets et al. 2018). Bolliger and colleagues suggested a beneficial effect of perioperative transfusion for gastrectomy for cancer (Kouyoumdjian et al. 2021). However, Dukleska and colleagues reported increased morbidity and mortality with preoperative blood transfusions in neonates undergoing surgery (Dukleska et al. 2020). Although timely diagnosis and preoperative anemia treatment are necessary for surgical patients, implementation of anemia therapy is challenging partly because of limited evidence (Bolliger et al. 2022) (Table 4).

This study has several limitations. First, it is a retrospective single-center study; thus, the cause and effect relationship cannot be confirmed in our study. Second, the time span of the study period was approximately 5 years. The clinical practice guidelines were updated, and the threshold of the transfusion was revised by year, especially for cardiac, orthopedic, and critically ill patients. However, transfusion was also analyzed in our practice, and multiple statistical analyses were used to lessen the effect of the unknown confounders. In addition, all the known factors that affected the outcomes of hip fractures were included.