Background: The clinical effects of chronic amphetamine use in patients undergoing general anesthesia have been evaluated in various case studies dating back more than 40 years. However, most of these studies involved prescription stimulants for narcolepsy, ADHD, and depression with only scant case reports regarding illicit IV methamphetamine use. The goal of this retrospective cohort study was to evaluate the hemodynamic effects and vasopressor requirements within the first hour of general anesthesia in patients testing positive for methamphetamine use.
Methods: After obtaining IRB approval, medical records from Jan 1, 2014 to Dec 31, 2015 were examined and patients testing positive for methamphetamine within 10 days of surgery were identified and placed into an acute (positive within 48 hours of surgery) vs subacute group (positive within 10 days but negative prior to surgery). Exclusion criteria included age > 65 years old, age < 15 years old, polytraumas, ICU patients, and patients with medical history including HTN, IDDM, ESRD, CVAs, CAD, CHF, and ASA III-V patients if they would remain ASA III without the methamphetamine use. A control group was created using patients of statistically similar age, sex, ASA status, and surgical category. Hemodynamic instability, defined in our study as a MAP drop > 40% for at least five minutes or requiring phenylephrine>300µg or ephedrine>15mg or any amount of epinephrine or vasopressin within the first hour of anesthesia. Chi-square analysis was conducted to identify the proportions of Hemodynamic instability among the three groups. P-value<0.05 was considered to be statistically significant.
Results: Among the 363 patients included in the final analysis, 139 (38.3%) were found to be methamphetamine acutely positive, 74 (20.4%) were methamphetamine subacute, compared to 150 (41.3%) control patients. Almost half (62 or 44.6%) of methamphetamine acutely positive patients were found to meet the hemodynamic instability criteria compared to 9 (6%) of control patients and 21 (28.4%) for methamphetamine subacutely positive(p<0.001). Furthermore, acutely positive patients had higher phenylephrine requirements; the acutely positive, subacutely positive, and control groups required 357.6, 292.2, and 58.7 µg phenylephrine on average.
Conclusions: Patients undergoing general anesthesia who tested positive for methamphetamine within 10 days of surgery were found to experience hypotension during the first hour of general anesthesia more frequently and severely than a negative control group. Furthermore, methamphetamine users experienced higher phenylephrine requirements than the control group, particularly if they were positive within 48 hours of surgery compared to positive within 10 days of surgery. Awareness of the increased incidence of intraoperative hypotension is beneficial to anesthesiologists and allows for adequate preparation of the frequent hypotension. Further studies evaluating the effects of methamphetamine on postoperative outcomes including acute kidney injury, cardiac ischemia, ICU admissions, and length of stay are recommended.
