Anesthesia for the Elderly

Aging is a process related to several biological changes that may influence the anesthesia experience. In old age, there is a decrease in nervous system tissue mass, particularly a decline in grey matter brain volume, neuronal density, and concentration of neurotransmitters [1, 2]. These changes mean that older patients, particularly those above 65 years old, are more sensitive to anesthesia and may have more complications following anesthesia than younger patients [1]. The increased sensitivity to anesthesia in elderly patients means that anesthesiologists may be able to use less anesthesia to achieve proper sedation in older patients compared to younger ones [1].

Depending on anesthesia type, the amount of drug needed for the desired effect changes. For inhalation anesthesia, the amount of drug needed decreases by about 6% each decade of life [1]. For certain opioids, such as fentanyl, the potency of the drug increases almost two-fold in an elderly patient, making the correct dosage of pre- and post-surgery pain medicine much lower compared to that needed in younger patients [1]. Another result of aging on the anesthesia experience is a greater susceptibility to experiencing post-operative cognitive dysfunction and delirium.

Post-operative cognitive dysfunction (POCD) is defined as an impairment in cognitive abilities, such as memory, perception, and attention, following surgery [3]. In patients above 60 years old, the risk of developing POCD a week after major surgery is 25% [4]. Three months post-surgery, POCD incidence in patients above 60 years old is about 10% [4]. Furthermore, the risk of developing POCD is nearly three times higher in patients above 80 years old compared to middle-aged patients [5]. However, anesthesia type may relate to this risk of development. Silvert et al. (2014) found that the incidence of POCD in elderly patients 1 week after surgery with general anesthesia was 4.1% compared to 11.9% after surgery with regional anesthesia and without sedation or post-operative opioids [6]. Three months post-surgery, the incidence of POCD was 6.8% in the group that received general anesthesia and 19.6% in the group that received regional anesthesia [6]. Nonetheless, the authors did not conclude that general anesthesia lowers the incidence of POCD, instead they argued that the surgery type may have more to do with the development of POCD in the elderly patients than the anesthesia type [6].

Post-operative delirium (POD), in contrast, refers to a state following surgery where the patient has “reduced awareness of the environment and a disturbance in attention,” typically 1-3 days post-surgery [3]. The incidence of POD in elderly patients ranges between 5-15% [3]. One randomized double-blind study found that elderly patients (>65 years old) who received deep sedation had a greater incidence of POD than elderly patients who received light sedation [2]. In addition to these increased risks of POCD and POD, elderly patients may also take a longer amount of time to recover from anesthesia compared to their younger counterparts [1, 2]. Despite evidence of these negative post-operative effects, there is also some evidence to suggest that elderly patients may be almost four times less likely to experience any adverse event during surgery or develop post-operative nausea and vomiting and drowsiness than younger patients [7].

Overall, there is no conclusive evidence that anesthesia should not be used in elderly patients and most patients recover to their peers’ cognitive ability shortly after surgery. Instead, anesthesiologists should carefully monitor the amount of anesthetic given to limit the risk of POCD and POD in elderly patients who are highly sensitive to anesthesia.

References:

1. Kanonidou, Z. & Karystianou, G. (2007). Anesthesia for the Elderly. Hippokratia, 11(4), 175-177.
2. Strøm, C., Rasmussen, L.S., & Sieber, F.E. (2014). Should general anesthesia be avoided in the elderly? Anaesthesia, 69(Supp1), 35-44. doi:10.1111/anae.12493.
3. Deiner, S. & Silverstein, J.H. (2009). Postoperative delirium and cognitive dysfunction. BJA: British Journal of Anaesthesia, 103(Supp1), i41-i46. doi: 10.1093/bja/aep291
4. Moller, J.T. et al. (1998). Long-term postoperative cognitive dysfunction in the elderly ISPOCD1 study. Lancet, 351(9106), 857-61. doi: 10.1016/s0140-6736(97)07382-0
5. Johnson T., et al. (2002) Postoperative cognitive dysfunction in middle-aged patients. Anesthesiology, 96, 1351–7
6. Silbert BS, Evered LA, Scott DA. (2014). Incidence of postoperative cognitive dysfunction after general or spinal anaesthesia for extracorporeal shock wave lithotripsy. Br J Anaesth; 113(5), 784-791. doi: 10.1093/bja/aeu163
7. Chung, F., Mezei, G., & Tong, D. (1999). Adverse events in ambulatory surgery. A comparison between elderly and younger patients. Canadian Journal of Anaesthesia, 46, 309-321. doi: 10.1007/BF03013221