What is the significance of minimizing pump time and cross clamp time in cardiac surgery?

Significance of Minimizing Pump Time and Cross-Clamp Time in Cardiac Surgery

Minimizing aortic cross-clamp time and cardiopulmonary bypass time is critical in cardiac surgery as they are independent predictors of mortality, morbidity, and adverse outcomes including myocardial injury, stroke, renal dysfunction, and prolonged hospital stays.

Impact on Mortality and Morbidity

Prolonged aortic cross-clamp time (XCT) and cardiopulmonary bypass time (CPBT) directly correlate with increased surgical risk:

• Each 1-minute increase in cross-clamp time is associated with a 2% increase in mortality in both low and high-risk patients 1
• Cross-clamp times >60 minutes independently predict:
  • Low cardiac output
  • Prolonged ventilation
  • Renal complications
  • Increased blood transfusion requirements
  • Higher mortality rates
  • Extended hospital stays 1

The most recent evidence from the mini-mitral international registry (2023) confirms that aortic cross-clamp time is significantly associated with mortality, low cardiac output syndrome, and acute kidney injury (all P<0.001) 2.

Safe Time Limits

Research has established threshold values beyond which risks increase substantially:

• XCT >150 minutes: 3.07 times higher adjusted odds of 30-day mortality (12.2% vs 1.8%)
• CPBT >240 minutes: 8.78 times higher adjusted odds of 30-day mortality (31.5% vs 1.9%) 3

Myocardial Protection Considerations

The impact of prolonged cross-clamp time varies based on myocardial protection strategy:

• For patients requiring extended cross-clamp times (≥75 minutes), intermittent cold blood cardioplegia (ICC) provides superior protection compared to intermittent warm cardioplegia (IWC) 4
• ICC results in:
  • Less myocardial damage
  • Reduced postoperative cardiac mortality
  • Lower incidence of perioperative myocardial injury (6% vs 17%)
  • Fewer major adverse cardiac events (25% vs 37%) 4

Patient-Specific Considerations

The impact of cross-clamp time varies based on left ventricular function:

• In patients with preserved LV function (LVEF >40%), XCT is an independent predictor of mortality (OR 1.014 per minute)
• Surprisingly, in patients with poor LV function (LVEF <40%), very short XCT (1-30 minutes) may be associated with similar or higher mortality than longer XCT (91-120 minutes) 5

Minimizing Cross-Clamp Time in Different Surgical Approaches

Off-Pump Techniques

Off-pump CABG can potentially reduce morbidity and mortality by avoiding cardiopulmonary bypass:

• Meta-analyses show a 30% relative risk reduction for stroke in off-pump vs on-pump CABG
• However, concerns exist regarding graft patency (82.6% in off-pump vs 87.8% in on-pump) and incomplete revascularization 6

Clampless/Anaortic Techniques

When performing off-pump CABG, minimizing aortic manipulation is crucial:

• Clampless techniques significantly reduce neurological complications (OR = 0.46,95% CI: 0.29–0.72) 6
• Endoaortic balloon occlusion can shorten pump and clamp times compared to traditional cross-clamping 6

Minimally Invasive Approaches

While minimally invasive techniques offer benefits, they often involve longer cross-clamp times:

• The International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS) noted prolonged cross-clamp times as a limitation of minimally invasive mitral valve repair 6
• For robotic-assisted procedures, surgeons should consider imposing a hard stop after predetermined times (recommended clamp times no longer than 2 hours, and even shorter with impaired ventricular function) 6

Practical Recommendations

1. Optimize surgical planning and team coordination to minimize unnecessary time on bypass and cross-clamp
2. Select appropriate myocardial protection strategy based on anticipated cross-clamp time and patient risk factors
3. Consider off-pump techniques for appropriate cases, especially in patients with high risk of stroke
4. Implement clampless/anaortic techniques when feasible to reduce neurological complications
5. Set predetermined time limits for cross-clamping based on patient risk factors
6. Develop proficiency with minimally invasive techniques before attempting complex or concurrent procedures
7. Be prepared to convert to alternative approaches when cross-clamp or bypass times become excessively prolonged

Pitfalls to Avoid

• Underestimating the impact of prolonged cross-clamp time in seemingly low-risk patients
• Prioritizing minimally invasive approaches at the expense of significantly longer cross-clamp times, especially early in the learning curve
• Failing to adjust cross-clamp time thresholds based on patient-specific factors like ventricular function
• Continuing with a challenging approach when cross-clamp time is becoming excessive

By understanding the significance of minimizing pump and cross-clamp times and implementing strategies to reduce them, cardiac surgeons can significantly improve patient outcomes.