Anesthesia causes marked changes to the cardiovascular system, including changes in heart rate and blood pressure. A common concern is whether the heart actually stops beating during anesthesia. Understanding the effects of anesthesia on the heart can help ease worries about undergoing surgery.
Does the heart stop beating under anesthesia?
The heart does not typically stop beating completely during routine anesthesia. However, anesthesia does cause changes in heart rate and rhythm that may give the impression that the heart has stopped. Here are some key points about the effects of anesthesia on heart function:
- General anesthesia causes a decrease in sympathetic nervous system activity. This leads to lower blood pressure and a slower heart rate.
- The heart continues beating during anesthesia, but the slower heart rate and lower blood pressure can make the pulse harder to detect.
- Some anesthetic medications can cause short pauses in heart rhythm or transient drops in blood pressure. This is normal and not dangerous.
- In very rare cases, anesthesia can trigger serious heart rhythm problems leading to cardiac arrest. However, anesthesia providers are well trained to rapidly recognize and treat such events.
So in summary, the heart does keep beating during routine anesthesia, but often at a slower rate that can be harder to perceive. Short pauses in rhythm or drops in blood pressure may occur, but the heart quickly recovers. Cardiac arrest under anesthesia is extremely rare when performed by a qualified anesthesiologist.
Why does the heart rate decrease under anesthesia?
The slower heart rate under anesthesia is due to effects on the autonomic nervous system. The autonomic nervous system controls involuntary functions like heart rate, blood pressure, and breathing.
The two main branches of the autonomic nervous system are:
- Sympathetic nervous system – activates the “fight or flight” response, increasing heart rate, blood pressure, and breathing rate.
- Parasympathetic nervous system – activates “rest and digest”, slowing heart rate and breathing.
Anesthetic drugs suppress sympathetic activity while enhancing parasympathetic activity. This shifts the autonomic balance towards the parasympathetic system, leading to slower heart rate, lower blood pressure, and slower breathing.
Specific anesthetic drugs have some additional effects:
- Propofol directly suppresses sympathetic activity to the heart, slowing heart rate.
- Inhalational anesthetics like sevoflurane also inhibit sympathetic activity.
- Opioids relieve pain but also release hormones that slow heart rate.
The combined sympatholytic and parasympathomimetic effects of anesthesia account for the slower heart rate. Despite the slower rate,studies show heart function is actually well preserved during routine anesthesia.
What about changes in heart rhythm?
Anesthesia can affect electrical conduction in the heart, leading to short-term changes in heart rhythm:
- Transient arrhythmias – Brief periods of irregular heartbeats may happen, but resolve on their own.
- Heart blocks – Delayed or blocked conduction of electrical signals through the heart.
- Asystole – Prolonged pauses between heartbeats for 4-8 seconds. The heart soon resumes a normal rhythm.
These rhythm changes are due to anesthetic effects on heart electrical activity and sympathetic/parasympathetic balance. The irregular rhythms are transient and typically not harmful. Anesthesia providers monitor the EKG and are prepared to treat any persistent arrhythmias.
Are vital signs closely monitored under anesthesia?
Vital signs including heart rate, blood pressure, and oxygen levels are continuously monitored during anesthesia. This allows the anesthesia care team to rapidly detect and treat any abnormal changes.
Monitoring includes:
- Electrocardiogram (EKG) – monitors heart rhythm and rate.
- Blood pressure cuff – periodically records blood pressure.
- Pulse oximeter – measures oxygen saturation of blood.
- Capnography – monitors carbon dioxide levels reflecting respiratory status.
In addition, an anesthesia provider is present throughout surgery to watch vital signs and make adjustments to anesthesia as needed. The combination of close monitoring and real-time adjustments enables early detection and management of cardiac issues.
When does the heart actually stop under anesthesia?
Cardiac arrest, where the heart stops beating, is an extremely rare anesthesia complication. The estimated incidence is only 1.1 to 2.9 per 10,000 anesthetics.
Risk factors for cardiac arrest during anesthesia include:
- Advanced age
- Severe illness affecting heart function
- Emergency surgery
- Trauma patient
- Insertion of central vein catheter
Cardiac arrest may be triggered by:
- Severe allergic reaction (anaphylaxis)
- Lack of oxygen to the heart
- Imbalance of electrolytes like potassium
- Extreme surgical stress
With close monitoring and prompt cardiopulmonary resuscitation, survival rates from anesthesia-related cardiac arrest are around 60-70%.
What stops the heart during euthanasia anesthesia?
In euthanasia procedures performed under heavy anesthesia, drugs are administered to intentionally stop the heart and cause death. This is different than routine anesthesia where the goal is to maintain normal heart function.
Drugs used to intentionally stop the heart during euthanasia include:
- Potassium chloride – Stops electrical activity and causes cardiac arrest.
- Propofol – At very high doses, profoundly suppresses heart function.
These drugs are given at doses sufficient to cause complete circulatory collapse. This is necessary to achieve the intent of euthanasia to end life.
Does the heart temporarily stop during CPR?
Yes, the purpose of chest compressions during CPR is to temporarily substitute for the heart’s pumping action. Chest compressions squeeze the heart between the breastbone and spine, forcibly ejecting blood from the heart.
During CPR:
- Natural heart contractions cease.
- Chest compressions artificially pump blood for about 10-20% of normal cardiac output.
- This low blood flow aims to buy time until the heart can resume beating on its own or defibrillation can restore normal rhythm.
So in short, the heart does stop beating during CPR. However, chest compressions provide some temporary circulatory support until efforts to restart the heart succeed.
Does anesthetic gas stop the heart?
Anesthetic gases like sevoflurane, isoflurane, and desflurane do not normally cause the heart to stop beating. However, at very high concentrations, anesthetic gases can suppress heart function.
Normally only about 1-2% concentration of anesthetic gas is required during surgery. But at concentrations above 10-15%, anesthetic gases can:
- Depress myocardial contractility, reducing heart pumping ability.
- Dilate blood vessels, decreasing blood pressure.
- Suppress electrical conduction in the heart.
This can potentially progress to complete cardiac standstill. Such high anesthetic gas levels are never required during surgery and only encountered with anesthetic gas leaks or equipment misuse.
Prolonged exposure to very high anesthetic concentrations led to rare gas poisoning deaths historically. But current anesthetic equipment includes exhaust scavenging to prevent gas accumulation and alerts to detect leaks.
At normal surgical levels, anesthetic gases do not stop the heart. Their impact is limited to reducing heart rate and blood pressure.
Can a Pacemaker keep the heart beating under anesthesia?
Yes, a permanent pacemaker can help maintain adequate heart rate and cardiac rhythm under anesthesia by electrically pacing the heart.
Benefits of pacemakers during anesthesia:
- Prevents severe bradycardia (slow heart rate)
- Treats heart block by maintaining electrical conduction
- Corrects anesthesia-induced arrhythmias
- Provides backup pacing if heart stops unexpectedly
The external EKG monitors used during surgery allow the anesthesiologist to confirm the pacemaker is functioning properly. The pacemaker may be adjusted as needed if arrhythmias occur.
Having a pacemaker can provide reassurance to patients prone to anesthesia-related cardiac side effects. However, most patients still do well under anesthesia even without a pacemaker in place.
Conclusion
In summary, the heart generally continues beating during routine anesthesia, albeit at a slower rate. Transient rhythm abnormalities may occur, but are quickly corrected. Cardiac arrest under anesthesia is extremely rare in healthy patients.
Continuous monitoring allows anesthesia teams to promptly detect and manage any cardiac issues. While anesthesia does markedly affect heart function, catastrophic events like asystole or cardiac arrest almost never happen under the care of a qualified anesthesiologist.