Management of Shock After Spinal Anesthesia
For shock after spinal anesthesia, immediately administer vasopressors (phenylephrine or ephedrine) to restore blood pressure while avoiding aggressive fluid resuscitation, which is ineffective and potentially harmful in this neurogenic shock state. 1, 2, 3
Immediate Hemodynamic Support
First-Line Vasopressor Therapy
Phenylephrine is the preferred vasopressor for spinal anesthesia-induced hypotension, administered as 50-250 mcg IV boluses or continuous infusion at 0.5-1.4 mcg/kg/minute titrated to effect. 2
Ephedrine 3-6 mg IV boluses represents an alternative first-line agent, particularly when bradycardia accompanies hypotension. 1, 4
Norepinephrine should be added if systolic blood pressure remains <90 mmHg despite initial vasopressor therapy, as it is the recommended agent for maintaining adequate mean arterial pressure in refractory hypotension. 1
Fluid Management Strategy
Crystalloid preloading (500-1000 mL) administered BEFORE spinal anesthesia does NOT prevent hypotension in elderly patients or those with comorbidities and should not be relied upon. 4, 5
If crystalloids are used, administer 20 mL/kg at the TIME of spinal block rather than before, which reduces cardiovascular side effects from 9.9% to 2.3% (NNT = 13). 6
Avoid D5W entirely in this setting - it cannot expand intravascular volume because dextrose rapidly extravasates from intravascular to interstitial space and is contraindicated in hypotension. 7
Use 0.9% normal saline or isotonic crystalloids if fluid administration is deemed necessary, as these are appropriate for acute resuscitation. 7
Special Considerations for High-Risk Patients
Patients with Cardiac Disease
Exercise extreme caution with fluid loading in patients with underlying heart disease, as the fixed afterload-dependent states (aortic stenosis, mitral stenosis) can precipitate pulmonary edema with aggressive volume resuscitation. 8
For patients with cardiac disease, appropriate fluid loading and vasoconstrictor use should be tailored individually, with increased vigilance for the more unpredictable onset of cardiovascular compromise. 1
Dobutamine 5-20 mcg/kg/min may be added if myocardial dysfunction contributes to persistent hypotension, though this is uncommon in pure neurogenic shock from spinal anesthesia. 1
Avoid beta-blockers or calcium channel blockers acutely in the shock state despite their role in chronic cardiac management. 8
Patients with Diabetes
Spinal anesthesia actually protects against perioperative hyperglycemia compared to general anesthesia by attenuating the surgical stress response, with glucose levels remaining stable throughout the procedure. 9
Standard glucose monitoring protocols apply, but insulin requirements are typically reduced compared to general anesthesia. 9
Patients with diabetes insipidus require special attention to fluid balance, though low spinal anesthesia can be performed safely with appropriate perioperative desmopressin administration and careful circulatory management. 10
Monitoring and Assessment
Block Height Surveillance
Assess sensory block height at least every 5 minutes until no further extension is observed, as the risk of high or total spinal block increases dramatically with cephalad spread. 1
When sensory block reaches T7 or above, hypotension incidence increases to 60%, and at T4 or higher, all patients require vasopressor therapy. 5
Increasing agitation, significant hypotension, bradycardia, upper limb weakness, dyspnoea, or difficulty speaking indicate developing high block requiring immediate intervention. 1
Hemodynamic Targets
Maintain mean arterial pressure ≥65 mmHg as the initial target, though this should be adjusted based on patient comorbidities and baseline blood pressure. 1
Establish invasive arterial blood pressure monitoring if hypotension does not rapidly respond to initial vasopressor therapy. 8
Monitor for end-organ perfusion including mental status, urine output (target >30 mL/h), and lactate clearance. 1
Critical Pitfalls to Avoid
The most dangerous error is assuming standard hypovolemic shock management applies - aggressive fluid resuscitation is ineffective because spinal anesthesia causes distributive shock from sympathetic blockade, not true hypovolemia. 1, 4, 5
Failure to aspirate CSF from an intrathecal catheter does NOT exclude subarachnoid positioning, and assuming epidural placement can lead to catastrophic overdosing with epidural-dose local anesthetics causing high or total spinal block. 1
Vasopressors should be used with appropriate caution but NOT withheld - the interim analysis suggesting early vasopressor use may be deleterious applies to hemorrhagic shock, not neurogenic shock from spinal anesthesia. 1
In patients with underlying cardiac disease, the balance between maintaining perfusion pressure and avoiding excessive afterload is critical - phenylephrine's pure alpha-agonist effects may increase cardiac afterload in vulnerable patients. 1
Bradycardia accompanying hypotension requires ephedrine or atropine rather than pure alpha-agonists, as phenylephrine can worsen bradycardia through baroreceptor reflex. 1, 3