Consistent with other observational studies , our cohort found that frailty was more commonly diagnosed in older (mean age of 71.6 years) and female patients, and they had more limitations in their daily physical performance (MET). Since functional frailty status is not a routine consideration used in pre-anesthesia clinics for perioperative outcome predictions , this study did not find differences in the ASA physical classifications between the frail and non-frail surgical patients.
The prevalence of frailty in patients receiving spinal anesthesia in this study population was 25.8%, which is comparable with the findings of a previous larger-scale study (21.5%) . The higher prevalence rates of frailty in surgical patients receiving neuraxial anesthesia over general anesthesia could simply be an implication that anesthesiologists generally consider regional blocks a safer option, associated with fewer perioperative complications in sicker and elderly patients [4, 9]. In a recent cohort study, the Mayo Clinic study group found that frail patients who had knee arthroplasties done under neuraxial blocks were associated with significantly lower mortality (hazard ratio 0.49; 95% CI 0.27–0.89) and wound complication rates (hazard ratio 0.71; 95% CI 0.55–0.90) in comparison to those who received general anesthesia . With neuraxial anesthesia, it is important to take into consideration whether frail patients are more sensitive to local anesthetics during spinal nerve blocks , and if so, whether local anesthetic dosages should be reduced for spinal anesthesia.
Our study showed that sensory dermatome blockage levels achieved by similar doses of intrathecal bupivacaine were not different between frail and non-frail patients, as the anesthesiologists were blinded to patients’ frailty status. Most importantly, we found that time intervals to pain sensation at the surgical site (sensory recovery) and voluntary movement of lower limbs (motor recovery) also showed no significant difference between the frail and non-frail groups, highlighting that bupivacaine sensitivity for spinal nerve blocks was not significantly affected by frailty. However, we observed more hypotensive events in frail patients and these patients also required more vasopressor therapy after spinal anesthesia. It is known that autonomic dysregulation is the main cause of developing intraoperative hypotension in the frail .
The findings of this study must be interpreted in light of several limitations. Although this was a prospective study, patients in the frail groups were older and consisted of significantly more female, which might have confounded the clinical outcomes observed during spinal anesthesia. After propensity matching, 12 non-frail patients with more identical characteristics (similar in gender, age, educational levels and smokers) were selected from the non-frail patients for matched comparison of the outcome assessments. Our results suggested that the pharmacodynamics of local anesthetics used in spinal nerve blocks are not significantly altered in frail patients even when compared with younger, predominantly male non-frail individuals. Furthermore, we do not expect elderly and frail patients to require higher doses of local anesthetics than younger patients to achieve similar levels of spinal anesthesia. Secondly, we used Fried’s phenotypic criteria to assess frailty, where the frailty index has been recognized as a more comprehensive tool for multiple-domain assessment of frailty . Clinically, measurements using frailty phenotypes require less geriatric expertise and has a shorter assessment time. Nevertheless, the Fried’s criteria employ quantitative evaluation, making it a valid subjective clinical instrument for preoperative assessment of frailty [1, 7]. Thirdly, time to pain sensation at the surgical site was used as a surrogate indicator for sensory recovery after spinal anesthesia instead of precise measurement of spinal dermatomes. However, as patients were cared in the PACU and on the wards after surgery, surgical pain may be considered a more subjective than dermatome measurement; as spinal dermatome measurements will be done by different medical staff in the two units, leading to inconsistent interrater reliability among anesthetic, PACU, and ward personnel. Lastly, this study focused on the effects of bupivacaine and may not be generalizable to other local anesthetics.