Warning: Lidocaine topical anesthesia can also lead to local anesthetic poisoning!

For every anesthesiologist, local anesthetics are very familiar. It can be said that we have been very cautious and have always landed safely in those years. Although we always think of "local anesthetic poisoning" every time we use this drug, no accidents have occurred under everyone's reasonable use.

Regarding lidocaine local anesthetic poisoning, everyone has their own experience: do not exceed the dosage at one time, pay attention to whether the injection site has rich blood supply, pay attention to the withdrawal, pay attention to the patient's physique...

In short, according to the routine operation, there are indeed very few accidents. As for topical anesthesia, I believe that few anesthesiologists would think that local anesthetic poisoning can occur.

However, topical anesthesia can indeed cause poisoning. Below, we share a case:

The patient's daughter, 8 months old, developed convulsions about 2 hours after applying lidocaine cream (the specific dosage is unknown) to treat moles, which manifested as a generalized seizure. The convulsions stopped after intravenous injection of 2 mg of diazepam and intramuscular injection of 0.1 g of phenobarbital.

The patient was transferred to a higher-level hospital 3 hours after taking the medicine.

Physical examination: body temperature 37℃, pulse 108 times/min, respiration 42 times/min, blood pressure 81/60mmHg, pulse oxygen saturation 90%. He was conscious, with multiple spots and large black moles on the skin, and ulceration and scabs on the left lower limb. Three concave signs (+), coarse breath sounds in both lungs, no dry or wet rales. No abnormalities were found in the heart, abdomen, and nervous system examinations.

Auxiliary examination: Blood gas analysis (venous blood): pH 7.3, PCO2 38 mmHg, PO2 58 mmHg, blood glucose 8.6 mmol/L; methemoglobin 8.1%.

The blood concentration of lidocaine (about 3.5 hours after administration) was 5.1 μg/ml.

Blood routine: white blood cell count 9.3, neutrophil count 73.2%, CRP 44mg/L, liver and kidney function and electrolytes are normal. Chest X-ray shows coarse texture of both lungs. Cardiac ultrasound showed no abnormality, and electrocardiogram and ECG monitoring showed sinus rhythm.

Diagnosis: lidocaine poisoning, skin and soft tissue infection, congenital pigmented nevus.

The patient was given continuous positive airway pressure (CPAP) in the emergency department and admitted to the ICU. After admission, CPAP respiratory support was continued, methylene blue was used to treat methemoglobinemia, and cefoperazone and sulbactam were used to treat infection.

No seizures occurred after admission.

On the second day, breathing became stable and CPAP was stopped.

On the third day, the blood methemoglobin concentration returned to normal and methylene blue was discontinued.

He was hospitalized for 13 days and discharged after the infection was controlled.

Looking back at the entire case, young age is a key factor. After analysis, it may be that children have low weight and thin skin, which is easy to absorb. When applying the same area, the amount of medicine absorbed is significantly more than that of adults, which makes them more susceptible to poisoning.

Someone asked: This child has methemoglobinemia. Is it because of methemoglobinemia that she is prone to local anesthetic poisoning?

No. Some local anesthetics can convert Fe 2+ in the blood into Fe 3+ to form methemoglobin, of which prilocaine is the most abundant, followed by lidocaine and procaine.

In other words, local anesthetics are the "cause" and methemoglobinemia is the "effect."

Since methemoglobin does not have the ability to carry oxygen, the drug actively reverses methemoglobin.

Reversal method : Generally, the reducing agent methylene blue (1-5 mg/kg) or vitamin C 5g is dripped intravenously, and cyanosis disappears within 30 minutes.

This also explains why the child's blood oxygen level is only around 90%.

Let me explain another key question: Why was it confirmed to be lidocaine local anesthetic poisoning?

This is because the plasma elimination half-life of lidocaine is about 100 minutes, and a toxic dose of lidocaine (the toxic dose of lidocaine is 5 μg/ml) was still monitored in this child more than 3 hours after the incident.

Looking back at the whole incident, it is certain that the child suffered from lidocaine local anesthetic poisoning. Whether the amount used at the time or whether the local skin was broken increased the absorption of lidocaine, or whether the child's skin was thin, which made the local anesthetic easy to absorb, these are not important. The key is to make a timely and clear diagnosis. When an incident occurs, we should think of the possibility of local anesthetic poisoning during surface anesthesia.

Finally, let's review the symptoms of lidocaine poisoning:

The manifestations of lidocaine poisoning are mainly excitatory and inhibitory effects on the central nervous system and cardiovascular system.

Central nervous system excitement manifests as irritability, hearing changes, and a metallic taste in the mouth, followed by convulsions and, in severe cases, inhibitory symptoms such as drowsiness, coma, and respiratory arrest.

Cardiovascular system excitement manifests as tachycardia, ventricular arrhythmia, and hypertension, while inhibition manifests as bradycardia, conduction block, and cardiac arrest. The symptoms and treatment of poisoning with other amide local anesthetics are similar to those of lidocaine.

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