Prevention and management of spinal anesthesia-induced hypotension is essential for preventing complications in the perioperative/peripartum period. In 2018, an international consensus statement was published that detailed guidelines for managing hypotension related to spinal anesthesia for cesarean sections. In summary, the publication recommended the following: vasopressors should be used routinely and preemptively, alpha-agonist drugs such as phenylephrine are preferred as first-line agent due to abundance of data on their use, left uterine displacement and colloid preloading or crystalloid co-loading should be routinely performed, and systolic blood pressure goal should be kept within 90% of baseline.
Researchers also recommended that a phenylephrine infusion should be started at 25-50mcg/min just after spinal injection (with a lower dosing recommended for pre-eclamptic patients who exhibit less hypotensive response), and tachycardia and bradycardia should be avoided and treated with fluids or beta-agonist respectively. Significant bradycardia with hypotension may warrant use of ephedrine or an anticholinergic, and circulatory collapse should be promptly treated with epinephrine.2
Of note, when compared to physician-controlled infusions, smart pumps and double-drug infusions may yield better hemodynamics. At least three studies have suggested that norepinephrine, when delivered via smart pump, may improve maternal and fetal physiology, but studies comparing phenylephrine and norepinephrine using standard pumps are lacking.3-5 Such modalities perform optimally when combined with continuous non-invasive blood pressure monitoring, however, patient safety in the case of artifactual measurements needs more study as well. Regarding monitoring, standard ASA monitors are required and non-invasive blood pressures are ideally taken every 1-2 minutes as equipment/resources allow. Regarding resource-poor care areas, it is considered unreasonable to proceed with spinal blockade without vasopressor and anticholinergics readily available. For the novice provider, a fixed-rate vasopressor infusion with concurrent boluses as needed has been found to be an effective alternative to provider-managed titration of the infusion.
Patients with cardiac disease should be receive individualized care (choice of vasopressor, monitors, anesthetic technique, etc.) based on the entire clinical picture, taking into account their baseline physiology and expected changes related to surgery/labor, anesthesia, and delivery. Single-shot spinal blocks in the setting of cardiac disease pose increased risk of hemodynamic instability compared to combined low-dose combined spinal/epidural or epidural-only techniques. This is due to the quick-onset of sympathectomy seen with full-dose spinal anesthesia. Controlled titration of neuraxial blockade is recommended for the majority of these types of cases.
Results of a recently published survey from Ireland indicate that phenylephrine is the most widely used vasopressor currently. A concerning finding is that ~80% of the 15 reporting centers did not routinely maintain heart rate at baseline or use the rate as a surrogate for cardiac output. Following publication of the aforementioned consensus statement, two of the reporting centers changed practice to use phenylephrine primarily. Of note, a significant number of centers reported not using phenylephrine infusions due to fear of precipitating bradycardia and/or low cardiac output. Only 3 centers had a departmental protocol for management of spinal anesthesia-induced hypotension and only 2 changed practice based on the consensus statement, heralding a need for more support, resources, and assessment of the barriers to implementation. Furthermore, some aspects of the guideline can be improved when more evidence becomes available, such as the recommendations on ephedrine for bradycardia, smart infusions, or fluid pre/co-loading.1
Potential advances in the management of spinal hypotension include the search for optimal vasopressors or combinations of drugs; advances in monitoring to allow rapid assessment of risk of hypotension, cardiac output, volume status, etc.; and genetic studies to predict individual responses to vasopressors.
References
1. ffrench-O’Carroll R, Tan T. National survey of vasopressor practices for management of spinal anaesthesia-induced hypotension during caesarean section. International Journal of Obstetric Anesthesia. 2020. doi:10.1016/j.ijoa.2020.09.003
2. Kinsella SM, Carvalho B, Dyer RA, et al. International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. Anaesthesia. 2018;73(1):71-92. doi:10.1111/anae.14080
3. Ngan Kee WD. Norepinephrine for maintaining blood pressure during spinal anaesthesia for caesarean section: A 12-month review of individual use. International Journal of Obstetric Anesthesia. 2017;30:73-74. doi:10.1016/j.ijoa.2017.01.004
4. Ngan Kee WD, Khaw KS, Tam Y, Ng FF, Lee SW. Performance of a closed-loop feedback computer-controlled infusion system for maintaining blood pressure during spinal anaesthesia for caesarean section: A randomized controlled comparison of norepinephrine versus phenylephrine. Journal of Clinical Monitoring and Computing. 2017;31(3):617-623. doi:10.1007/s10877-016-9883-z
5. Ngan Kee WD, Lee SWY, Ng FF, Tan PE, Khaw KS. Randomized double-blinded comparison of norepinephrine and phenylephrine for maintenance of blood pressure during spinal anesthesia for cesarean delivery. Anesthesiology. 2015;122(4):736-745. doi:10.1097/ALN.0000000000000601
