Laboratory Criteria to Stop CPR in the Emergency Department
The only laboratory criterion with guideline support for terminating CPR in the ER is end-tidal CO2 (ETCO2) ≤10 mmHg after 20 minutes of CPR in intubated patients, but this should never be used alone—it must be part of a multimodal decision-making approach. 1
The ETCO2 Criterion
The 2015 American Heart Association guidelines specifically address this:
- In intubated patients: Failure to achieve ETCO2 >10 mmHg by waveform capnography after 20 minutes of CPR may be considered as one component when deciding to end resuscitation (Class IIb, LOE C-LD) 1, 2
- Critical caveat: This should NOT be used in isolation 1
- In non-intubated patients: A specific ETCO2 cutoff should NOT be used as an indication to end resuscitation (Class III: Harm) 2
The physiologic rationale is that ETCO2 reflects cardiac output and pulmonary blood flow during CPR. Persistently low values suggest inadequate perfusion despite resuscitative efforts.
Post-Arrest Prognostic Markers (Not for Stopping CPR)
Important distinction: The following laboratory values are for prognostication AFTER return of spontaneous circulation (ROSC), not for deciding when to stop CPR:
- Neuron-specific enolase (NSE): High serum values at 48-72 hours after cardiac arrest may support prognosis of poor neurologic outcome when performed with other prognostic tests at ≥72 hours post-arrest 1
- This is explicitly for post-resuscitation care, not intra-arrest decision-making
The Reality: No Validated Lab-Based Stopping Rules for the ER
The evidence reveals a critical gap:
For in-hospital cardiac arrest, the decision to terminate resuscitation rests with the treating physician based on multiple clinical factors, NOT laboratory criteria 3. These factors include:
- Witnessed versus unwitnessed arrest
- Time to CPR initiation
- Initial arrest rhythm
- Time to defibrillation
- Comorbid disease
- Pre-arrest state
- Whether ROSC occurred at any point
The guidelines explicitly state: Clinical decision rules for in-hospital termination have limited evidence for reliability and should be prospectively validated before adoption 3
What the Research Shows
Recent validation studies have developed termination-of-resuscitation rules, but these are based on clinical variables, not laboratory values:
- Modified Goto's TOR rule includes: initial asystole, unwitnessed arrest, EMS-CPR duration >20 minutes, and no prehospital ROSC 4
- A 2025 study identified rules using age, initial rhythm, witnessed status, monitored status, ICU location, and resuscitation duration—again, no lab values 5
Practical Algorithm for ER Termination Decisions
Step 1: Continue CPR for at least 20-30 minutes from time of collapse unless overwhelming reasons suggest futility 6
Step 2: If patient is intubated, check ETCO2:
- If ETCO2 remains ≤10 mmHg after 20 minutes, this supports (but does not mandate) termination
- Never use this alone 1
Step 3: Assess clinical factors:
- Initial rhythm (asystole/PEA vs. VF/VT)
- Witnessed status
- Bystander CPR provided
- Any ROSC achieved during resuscitation
- Reversible causes addressed (H's and T's)
- Duration of resuscitation
Step 4: Consider prolonged efforts for:
- Recurring or refractory VF/VT
- Drug toxicity
- Primary hypothermia
- Potentially reversible causes 3
Critical Pitfalls to Avoid
Never use ETCO2 alone: The guidelines explicitly warn against single-variable decision-making 1, 2
Don't apply out-of-hospital rules in the ER: The BLS and ALS termination rules are designed for field use, not in-hospital settings 1
Avoid premature termination: The 1998 European guidelines recommend at least 20-30 minutes of resuscitation unless futility is overwhelming 6
Don't confuse post-arrest prognostication with intra-arrest termination: NSE and other biomarkers are for predicting neurologic outcomes after ROSC, not for deciding when to stop CPR 1
The Bottom Line
There are essentially no validated laboratory criteria for stopping CPR in the ER. The decision remains primarily clinical, based on arrest characteristics, resuscitation duration, and response to interventions. ETCO2 ≤10 mmHg after 20 minutes in intubated patients is the only lab value mentioned in guidelines, and it must be used only as part of a comprehensive assessment, never in isolation.