Comparison of two doses of hypobaric bupivacaine in unilateral spinal anesthesia for hip fracture surgery: 5 mg versus 7.5 mg

Introduction Hip fracture is a frequent and severe disease. Its prognosis depends on the perioperative hemodynamic stability which can be preserved by the unilateral spinal anesthesia especially with low doses of local anesthetics. This study aims to compare the efficacy and hemodynamic stability of two doses of hypobaric bupivacaine (7.5 mg vs 5 mg) in unilateral spinal anesthesia. Methods In this prospective, randomized, double-blind study, 108 patients scheduled for hip fracture surgery under unilateral spinal anesthesia were enrolled to receive either 5 mg (group 1) or 7.5 mg (group 2) of hypobaric bupivacaine. Spinal anesthesia was performed in lateral position. Patients’ socio-demographic characteristics, hemodynamic profile, sensory and motor blocks parameters were recorded. Results Both groups were comparable regarding to demographic data. Two cases of failure occurred in group 1 and one case in group 2 corresponding to a comparable efficiency rates (96.29% and 98.14% respectively; p = 0.5). A higher mean onset and lower mean regression times of sensory block were significantly noted in group 1 (7.79±3.76 min vs 5.75±2.35 min, p < 0.001 and 91.29±31.55 min vs 112.77±18.77 min, p <0.001 respectively). Incidence of bilateralization (29.62% vs 87.03%, p < 0.001), incidence of hypotensive episodes (59.25% vs 92.59%, p < 0.001) and vascular loading (1481.48±411.65 ml vs 2111.11±596.10 ml, p < 0.001) were significantly higher in group 2. Conclusion The dosage of 5mg of hypobaric bupivacaine in unilateral spinal anesthesia is as effective as the dosage of 7.5 mg with lower bilateralization incidence and better hemodynamic stability.


Introduction
Hip fracture is a frequent and severe disease that affects mainly old patients with comorbid conditions [1,2]. It represents a major problem of public health because of its high incidence and morbimortality [1][2][3][4]. The prognosis of this disease depends on the comorbidities and the quality of perioperative care [1][2][3][4][5][6][7]. Indeed, any support delay worsens the patient outcome [5][6][7]. In addition, the choice of anesthetic technique is essential as it interferes with the perioperative hemodynamic status and the postoperative rehabilitation quality [8][9][10]. The high incidence of coronary diseases in patients with proximal femur fracture makes them more vulnerable to hypotensive episodes with increased risk of perioperative myocardial ischemia [11]. Overall, both general and regional anesthesia are possible but spinal anesthesia is the most used technique [8,9,12]. The reduced cardiovascular compensation mechanisms in the elderly increase significantly the frequency and severity of hypotensive episodes by sympathetic block in spinal anesthesia [13]. However, despite a better intraoperative hemodynamic stability with general anesthesia, several published studies are rather in favor of regional anesthesia [8,9,12]. In fact, spinal anesthesia may also provide satisfactory hemodynamic stability via sympathetic block reduction. Several solutions have been proposed, such as continuous spinal anesthesia (CSA) and even better, unilateral spinal anesthesia (ULSA) [14][15][16][17] especially when low doses of local anesthetic are used [18][19][20]. This study aims to compare the efficacy and safety of two doses of hypobaric bupivacaine (7.5 mg vs 5 mg) in unilateral spinal anesthesia. The incidence of bilateralization was significantly higher in group 2 (Table 2). Aside from the fifth minute, the incidence of hypotensive episodes was significantly higher in group 2 ( Figure 1). The vascular loading was also significantly higher in group 2 (1481.48 ± 411.65 ml vs 2111.1 ± 596.10 ml; p < 0.001). Ephedrine consumption was higher in group 2 with no significant difference ( Table 2). Patient satisfaction was better in group 1 while that of surgeons were better in group 2 with no significant difference ( Table 2).

Discussion
In our study, we compared the dose of 5 mg hypobaric bupivacaine pathways and spares sympathetic efferent ones [28].
Thereby, opioids have reduced local anesthetics doses in spinal anesthesia, and therefore, the importance of sympathetic block which is dose-dependent, without having specific effects on sympathetic efferent pathways [24][25][26][27][28]. These two mechanisms largely explain the hemodynamic stability with low doses of local anesthetics. This justifies the interest of seeking the lowest possible dose in order to better preserve patient hemodynamic status. The same objective also justifies the use of ULSA, since the unilateral distribution of local anesthetic contributes to the reduction of sympathetic block [15,22,24,29]. Kaya et al found lesser risk of bilateralization with hyperbaric mixture [22]. However, better results were found with hypobaric mixture in the trial of Imbelloni et al [24].
The peroperative hemodynamic instability is related to cardiovascular repercussions of neuraxial blockade and patient compensation mechanisms which are often altered by aging and comorbidities [11]. Its prevention is based essentially on limiting the cardiovascular impact of neuraxial blockade. At least two means are easy and practical: limitation of local anesthetic doses and onesiding sympathetic block. Several studies have confirmed the effectiveness of these techniques either associated or separated.
Thus, the risk of hemodynamic instability ranging from 25 to 69% with conventional spinal anesthesia using ordinary doses decreases significantly with the ULSA in particular with low dosage [15,30,31].
In our study, the probability of having at least one hypotensive episode under hypobaric bupivacaine ULSA was 59. 25 24,32,33]. These thresholds must be interpreted according to the dosage of used opioid and the considered judgment criteria.
In the end, our study which is the first to compare two low doses of hypobaric bupivacaine in ULSA, has some limitations that must be considered in interpreting the results. First, the two doses used had not the same baricity. Second, the risk of bilateralization, interfering with hemodynamic stability regardless of the administered dose, has not been well studied in particular concerning its predictive factors.
Third, the time chosen to declare the failure of the ULSA (15 minutes) was short since the onset time can take up to 30 minutes.

Conclusion
The dosage of 5mg of hypobaric bupivacaine in unilateral spinal anesthesia is as effective as the dosage of 7.5 mg with lower bilateralization incidence and better hemodynamic stability.

Competing interests
The authors declare no competing interests.  Table 1: Demographic characteristics of the two studied groups