Hypotension, also known as low blood pressure, can occur during or after anesthesia and must be watched closely by anesthesia providers. The post-anesthesia induction period may see increased risk for hypotension 1. Post-anesthesia induction hypotension (PAIH) can significantly impact surgical outcomes and remains one of the factors most closely associated with anesthesia-related morbidity 2. It is therefore critical to understand, predict and treat it as best as possible.
Hypotension is roughly defined as a > 30% decrease in mean arterial pressure as compared to the first measurement in the operating theater prior to general anesthesia induction 3.
In addition to heightened morbidity postoperatively, PAIH is associated with increased risk of renal injury and postoperative intensive care admission. It is also significantly linked to postoperative myocardial injury 2. Research has identified several risk factors: age, hypertension, diabetes, and being male.
A recent multicenter observational study assessed the data of subjects receiving general anesthesia with propofol and sufentanil, demonstrating that that the likelihood of PAIH increased with age 1. Another study found that being over 30 years of age in particular was linked to PAIH 2. The degree of hypertension at time of arrival to the operating theater has also been found to be associated with PAIH 3, in addition to the presence of diabetes 3 and being male 1.
Furthermore, PAIH has been clearly linked to the physical well-being of patients. One study found that it was linked to American Society of Anesthesiologists (ASA) physical status (PS) class IV patients, i.e. patients “with severe systemic disease that is a constant threat to life” 1,4. A more recent study found that patients with an ASA PS class II and above were more likely to experience PAIH 2.
Different research has pointed to different links to the type of anesthesia used and the mode of delivery. First, early intraoperative hypotension in particular has been associated with neuraxial anesthesia 1. Second, although one study found that the type of volatile anesthetic was not linked to the occurrence of PAIH 3, another found that the administration of propofol and thiopental contributed to a greater incidence of PAIH 2. In addition, the type of surgery is also a relevant factor: orthopedic surgery in particular is associated with a greater incidence of PAIH 2.
It remains unknown whether interventions to improve or maintain blood pressure would improve outcomes in patients with various risk factors. However, most clinicians err on the side of caution and try to avoid hypotension all together 6. A number of interventions exist to correct hypotension to this end, the overall efficacy of which exceed 94% 3. Bolus fluids are the most frequently used intervention, with an established effectiveness of 96% 3.
Naturally, however, any factor linked to PAIH should be avoided when possible in order to minimize risk proactively. As such, one study suggests that alternatives to propofol anesthetic induction (such as etomidate) should be used in patients with an ASA PS of 3 or above and over 50 years of age 7.
References
1. Südfeld, S. et al. Post-induction hypotension and early intraoperative hypotension associated with general anaesthesia. Br. J. Anaesth. (2017). doi:10.1093/bja/aex127
2. Nega, M. H., Ahmed, S. A., Tawuye, H. Y. & Mustofa, S. Y. Incidence and factors associated with post-induction hypotension among adult surgical patients: Prospective follow-up study. Int. J. Surg. Open 49, 100565 (2022). doi: 10.1016/j.amsu.2022.103321.
3. Jor, O. et al. Hypotension after induction of general anesthesia: occurrence, risk factors, and therapy. A prospective multicentre observational study. J. Anesth. (2018). doi:10.1007/s00540-018-2532-6
4. ASA Physical Status Classification System | American Society of Anesthesiologists (ASA). Available at: https://www.asahq.org/standards-and-guidelines/asa-physical-status-classification-system. (Accessed: 8th December 2022)
5. Saugel, B. et al. Mechanisms contributing to hypotension after anesthetic induction with sufentanil, propofol, and rocuronium: a prospective observational study. J. Clin. Monit. Comput. (2022). doi:10.1007/s10877-021-00653-9
6. Wong, G. T. C. & Irwin, M. G. Post-induction hypotension: a fluid relationship? Anaesthesia (2021). doi:10.1111/anae.15065
7. Reich, D. L. et al. Predictors of hypotension after induction of general anesthesia. Anesth. Analg. (2005). doi:10.1213/01.ANE.0000175214.38450.91