Anesthesiologists are adjusting induction doses of fentanyl, propofol and midazolam in older patients to account for age, but the reduced doses nonetheless have a tendency to hover at the upper end of recommended limits for these often-fragile patients, leaving the door ajar to a host of potential complications.
“It is well known that elderly patients require 25% to 50% less IV induction dose than younger patients,” said Shamsuddin Akhtar, MD, associate professor of anesthesiology and director of medical studies at Yale University School of Medicine, New Haven, Conn. “In addition, there’s some older literature showing that elderly patients with lower intraoperative BIS [bispectral index] levels have worse outcomes than their counterparts. This suggests that deeper anesthesia may have some longer-term morbidity and mortality.
“So we decided to investigate the current practice in the field,” Dr. Akhtar said. “Are practitioners generally following recommendations by reducing IV induction doses for the elderly?”
To that end, Dr. Akhtar and his colleagues reviewed the intraoperative electronic anesthetic records of 1,868 adults (≥18 years) receiving general anesthesia for gastrointestinal surgeries between February 2013 and January 2014. Patients undergoing multiple procedures, those requiring temporary abdominal closure, and/or those undergoing rapid sequence induction were excluded from the analysis. Post-induction mean arterial pressure (MAP) was measured within the first 10 minutes of induction.
Table. Anesthesia Dosing by Age
18-70 y >70 y P Value
Midazolam, mg/kg 0.018 0.006 <0.01
Fentanyl, mcg/kg 1.30 1.18 <0.01
ASA I/II 1.36 1.17 0.06
ASA III/IV 1.27 1.17 0.15
Propofol, mg/kg 2.20 1.70 <0.01
ASA I/II 2.34 1.88 <0.01
ASA III/IV 1.96 1.65 <0.01
ASA, American Society of Anesthesiologists
There was a significant decrease in the dosing of fentanyl, propofol and midazolam with increasing age (Table).
Despite this age-based dosing reduction, the researchers still found a significantly larger drop in MAP following induction in patients older than 70 years. Indeed, those younger than 70 had a mean MAP decrease of 17 mm Hg, whereas those older than 70 had a 23 mm Hg MAP decrease.
The investigators also found a significant decrease in fentanyl and propofol dosing with increasing American Society of Anesthesiologists (ASA) classification (P<0.01). There was no significant difference in midazolam dosing based on ASA classification, however (P=0.47). Additionally, patients classified as ASA III and IV (n=792) did not exhibit a significant fentanyl dose change with increasing age.
Although he was encouraged by the age-based decrease in dosing revealed by the study, Dr. Akhtar was still concerned that older patients are receiving more induction agent than necessary (Figure). “For example, one article gave a propofol range of 1 to 2 mg/kg in elderly patients,” he said. “In our study, patients received doses at the upper end of that range. The same article gave a fentanyl range between 0.5 and 1 mcg/kg in elderly patients, and in our study patients received greater than 1 mcg/kg.
“So we are potentially overdosing these patients, and we could be using much less. So the question is what kind of impact might that have? If the blood pressure drops, then you might need to give other medications in response,” he continued. “But you’re not always able to do that quite as easily in elderly patients as in younger patients.”
Dr. Akhtar, who is presenting his findings at the ASA’s 2014 annual meeting (abstract A1243), recognized that some clinicians might be hesitant to administer lower doses than they are otherwise comfortable with. “I think people might be afraid they’re not anesthetizing the patient completely and afraid of possible recall at the lower dose, especially if they’re not using a depth-of-anesthesia monitor. I think that’s what makes people give more drug rather than less. Remember we can always start with less and give more if necessary.
“My recommendation is that we should aim more for the lower end of the recommended dose rather than the higher end,” he concluded.