Malignant Hyperthermia Susceptibility (MHS)
Malignant Hyperthermia Susceptibility (MHS) is a genetic disorder of skeletal muscle that, while dormant in daily life, can trigger a dangerous reaction upon exposure to certain anesthetic agents. In susceptible individuals, exposure to volatile anesthetic gases (such as sevoflurane, isoflurane) or the muscle relaxant succinylcholine causes an abnormal and rapid release of calcium within muscle cells. This uncontrolled release leads to a hypermetabolic state, characterized by:
- Rapid increase in body temperature: Often one of the most prominent and severe signs.
- Muscle rigidity or spasms: Especially noticeable in the jaw and neck initially, then spreading throughout the body.
- Elevated heart rate (tachycardia): A common early indicator of a problem.
- Abnormally fast breathing and increased carbon dioxide levels: Reflecting the body's accelerated metabolism.
- Breakdown of muscle tissue (rhabdomyolysis): Can lead to dangerous electrolyte imbalances and kidney damage.
MHS is most commonly inherited in an autosomal dominant pattern, meaning a person only needs to inherit the altered gene from one parent to be susceptible. It's crucial for individuals with a family history of MH to inform their anesthesiologist. Anesthesiologists can prepare a non-triggering anesthetic plan and have the antidote, dantrolene, ready to treat a reaction if one occurs.
Pseudocholinesterase Deficiency
Pseudocholinesterase deficiency is a rare condition that affects how the body breaks down certain muscle relaxants used during general anesthesia, particularly succinylcholine and mivacurium. For most people, the enzyme pseudocholinesterase quickly metabolizes these drugs within minutes. However, in individuals with a deficiency, the drugs remain active much longer than expected. This leads to extended muscle paralysis, preventing the patient from moving or breathing on their own for several hours after surgery. The patient requires continued mechanical ventilation until the medication wears off naturally.
Genetic vs. Acquired Deficiency
Pseudocholinesterase deficiency can be inherited or acquired.
- Inherited: Caused by a mutation in the BCHE gene, which is responsible for producing the pseudocholinesterase enzyme. A person can have a deficiency if they inherit a copy of the gene from one or both parents.
- Acquired: Certain health conditions and medications can cause a person to produce less of the enzyme over time. These can include:
- Severe burns or malnutrition
- Chronic infections
- Kidney or liver disease (like cirrhosis or hepatitis)
- Cancer
- Certain medications, including some oral contraceptives
Severe Allergic Reactions and Anaphylaxis
While MH and pseudocholinesterase deficiency are specific medical conditions, severe allergic reactions (anaphylaxis) to anesthetic medications are another critical reason certain drugs cannot be used. True allergies to anesthetic agents are rare, but can be life-threatening. The most common triggers are:
- Neuromuscular blocking agents (NMBAs): Used to induce muscle paralysis for intubation and surgery.
- Antibiotics: Administered to prevent infection.
- Latex: A common allergen, once widely used in surgical gloves and other equipment.
Unlike the conditions above, an allergy doesn't prevent anesthesia entirely, but requires the anesthesiologist to avoid the specific triggering agent. Careful pre-operative screening for allergies is essential to prevent a reaction during surgery. For more information, consult the Anesthesia Patient Safety Foundation's resources on this topic. Anaphylaxis During Anesthesia
Medical Conditions that Increase Anesthesia Risk
Beyond genetic disorders and allergies, a range of serious medical conditions can pose heightened risks and require a carefully tailored anesthetic approach. These are often considered relative contraindications, meaning the condition doesn't prohibit anesthesia but requires specific precautions. Risk factors include:
- Severe heart disease (heart failure, unstable angina)
- Significant lung disease (COPD, severe asthma)
- Obesity
- Obstructive sleep apnea
- Diabetes
- Kidney or liver problems
In such cases, the anesthesiologist focuses on optimizing the patient's health before the procedure and choosing anesthetic agents and techniques that minimize physiological stress.
Understanding Your Anesthetic Plan
Risk Assessment for a Safe Procedure
The anesthesia team will conduct a thorough pre-operative evaluation to assess your risk and develop a safe plan. Key steps include:
- Detailed Medical History: A comprehensive review of all personal and family medical issues, particularly any past reactions to anesthesia.
- Medication Review: Discussing all prescription and over-the-counter drugs, and any herbal supplements, to prevent drug interactions.
- Physical Examination: Assessing heart, lung, and airway health to anticipate any potential difficulties.
Alternatives to General Anesthesia
In high-risk scenarios, or for certain procedures, alternative forms of anesthesia may be safer:
- Local Anesthesia: Numbing a small, specific area (e.g., for stitches).
- Regional Anesthesia: Numbing a larger part of the body, such as an arm or the lower half of the body (e.g., spinal or epidural anesthesia).
- Monitored Anesthesia Care (MAC) or Sedation: Patients are relaxed and comfortable but remain conscious and able to respond.
Comparison of Standard vs. High-Risk Anesthesia
| Characteristic | Standard Anesthetic | High-Risk Anesthetic |
|---|---|---|
| Triggering Drugs | Commonly used volatile agents & succinylcholine are options. | Non-triggering drugs only are used for conditions like MHS. |
| Patient Monitoring | Standard monitoring of vital signs and oxygen levels. | Intensive, continuous monitoring for specific physiological changes. |
| Emergency Protocol | Standard emergency protocols. | MH-specific protocol or other specialized response plan. |
| Pre-operative Screening | Standard medical history review. | In-depth review of family and personal history of anesthesia reactions. |
| Follow-up | Standard post-procedure care. | Often includes genetic testing and counseling for family members. |
Conclusion
No single condition absolutely prevents a person from having any form of anesthesia. However, specific and rare genetic disorders like Malignant Hyperthermia Susceptibility and Pseudocholinesterase Deficiency render certain anesthetic drugs unsafe. Other conditions and allergies also require careful planning and medication selection. The good news is that modern anesthesiology offers a wide range of alternative medications and techniques, allowing a safe procedure for most individuals. The key to mitigating these risks is providing your anesthesia care team with a complete and honest medical history, including any family history of adverse reactions.
