Effect of anesthetics on heart rate

The most basic examination before surgery in the hospital is to check the heart and blood pressure. If the blood pressure is too high or the heart beats too fast, the surgery will need to be delayed. During surgery, anesthesia is also a necessary option, but the doctor will recommend local anesthesia, partial anesthesia or general anesthesia based on the patient's condition. During the anesthesia process, heart rate, blood oxygen saturation, and blood pressure need to be monitored throughout the process to ensure that any discomfort can be detected at the first time. This article introduces some situations of heart rate, let’s take a look.

1 Heart rate and life expectancy

Under anesthesia, the patient's heart rate is at a resting rate, and after falling asleep, metabolism is low and oxygen consumption is low. If oxygen is given during surgery, lower blood pressure and heart rate can meet the body's oxygen supply and demand balance. Among mammals, the heart rate of elephants is only 30~35bpm, while that of mice is as high as 600~700bpm. The heart rate of elephants is 20 times slower than that of mice. Their average lifespan is 30 years, which is 20 times longer than that of mice. Heart rate is closely related to life expectancy.

The normal human heart rate is 60~100bpm, more than twice as fast as that of an elephant, but the average lifespan in the early days was similar to that of an elephant, thus breaking the above relationship between heart rate and lifespan. A human heart rate can beat 3×109 (3 billion) times in a lifetime, which is also the highest among mammals. Why is this happening? Because humans have evolved, their physiology and biochemistry are very different from other mammals, it is possible for them to live long lives.

According to statistics, the average life expectancy in the United States in 1900 was 50 years old, but by 2004 it was close to 80 years old. Because developed countries have good medical care and disease control centers, the average life expectancy continues to increase, while in underdeveloped countries it still hovers around 40 to 50 years old. China is a developing country, but its living standards and medical conditions are constantly improving. By 2013, the number of people aged 60 and over will exceed 200 million, making it the only country in the world with over 100 million elderly people. The current average life expectancy in China has reached 72.71 years, including 72.9 years for men and 74.45 years for women.

People spend one-third of their time sleeping. Good sleep is essential for relieving stress, slowing down heart rate (<50bpm), and prolonging life. It can also save 3 billion of our precious heart rates.

2 Heart rate and cardiovascular disease

Although people can live to be a hundred years old, the adverse effects of heart rate on cardiovascular system cannot be ignored. Long-term fast heart rate accelerates heart, artery, brain and kidney damage mainly through mechanical, biochemical metabolism and neurohormonal factors, including free radical production, protein oxidation and telomere shortening, leading to cardiovascular accidents such as hypertension, atherosclerosis, hyperlipidemia, coronary heart disease and sudden death.

Athletes generally have a slower heart rate, about 50-60 bpm. It has been reported that patients with a heart rate of 83 bpm have a higher cardiovascular mortality rate than those with a heart rate of < 62 bpm. The mortality rate for a heart rate of 90-100 bpm is three times that of a heart rate < 62 bpm. Therefore, heart rate is a strong independent predictor of cardiovascular and all-cause mortality.

Beta-blockers can antagonize the overactivation of sympathetic nerves (sympathetic storm), produce negative chronotropic effects, lower heart rate and blood pressure, and improve ejection fraction. Studies in the past 20 years have shown that standard treatment with beta-blockers can reduce morbidity and mortality, which is a major breakthrough in the treatment of chronic heart failure and hypertension, and can reduce the heart rate to 60bpm. There are more than 11 types of beta-blockers, and we should choose those that are beta-1 selective (cardioselective), lipid soluble (can pass the blood-brain barrier), and long-acting, such as metoprolol or bisoprolol. An average dose of 76 mg/d of metoprolol can achieve good results. Do not stop taking the medication before surgery in order to obtain intraoperative cardiac protection.

3 Heart rate and blood pressure

Both heart rate and blood pressure are important in anesthesia management. Under resting anesthesia, as long as the systolic blood pressure is not lower than 90~100 mmHg and the heart rate is 50~60bpm, it will not have any adverse effect on the patient, especially for patients with ischemic heart disease, as it can improve myocardial oxygen consumption, cardiac energy reserves and oxygen supply and demand balance.

During anesthesia surgery, if the heart rate increases to more than 100~120bpm, it may indicate three situations: shallow anesthesia or patient pain, insufficient volume or excessive blood loss or heart failure, etc., which need to be actively identified and treated. If the intraoperative systolic blood pressure is >90 mmHg and the heart rate is <50 bpm <60 bpm, it means that the patient's anesthesia is stable, there is no sign of volume depletion or heart failure, and do not rush to use atropine to increase the heart rate.