Safety, risks, and side effects

Reviewed by Julian Douwes M.D., Chief Medical Officer, Klinik St. Georg

We believe that genuine trust is built through honesty, not reassurance. Whole-body hyperthermia is a real medical procedure with real risks. Here is what you should know—the expected, the uncommon, and the rare—so you can make a truly informed decision.

Editorial disclosure: Lyme Treatment Germany is an educational platform created in partnership with Klinik St. Georg (St. George Hospital) in Bad Aibling, Germany. Our medical content is informed by St. George Hospital's clinical experience. We disclose this relationship transparently. Read our full editorial policy.

Key facts at a glance

Safety record: More than 30,000 hyperthermia sessions performed at St. George Hospital since the early 1990s. Serious adverse events are rare.

Monitoring: Full operating-room-level monitoring including continuous ECG, arterial blood pressure, core temperature sensors, oxygen saturation, and respiratory function. A dedicated anesthesiologist is present throughout.

Expected side effects: Fatigue (3–7 days), flu-like symptoms, Herxheimer reaction, mild skin redness, temporary cognitive fog. These are normal post-procedure responses.

Rare risks: Cardiac arrhythmia, electrolyte imbalances, seizure (extremely rare), anesthesia-related complications. Pre-treatment screening exists specifically to identify and mitigate these risks.

Contraindications: Severe cardiac conditions, uncontrolled seizure disorders, pregnancy, severe organ failure, and other conditions that make hyperthermia medically unsafe. Not every patient is eligible.

Our approach to safety communication

Many medical websites minimize risks to avoid discouraging patients. We take the opposite approach. You are an adult making a significant medical decision. You deserve complete, unvarnished information about what this procedure involves, what can go wrong, and what we do to prevent it.

We have found that patients who understand the real risks—and the real safeguards—make better decisions, have more realistic expectations, and ultimately report higher satisfaction with their treatment experience. Informed consent is not a legal formality. It is an ethical obligation, and we take it seriously.

How safety is maintained during the procedure

Clinical experience

The hyperthermia session is conducted with the same level of monitoring you would expect in an operating room. This is not a wellness procedure overseen by a technician. It is a medical intervention with a full anesthesia team present from start to finish.

Continuous monitoring parameters

Core body temperature — Multiple sensors (rectal and/or esophageal) provide real-time, redundant temperature readings accurate to 0.1°C

Continuous ECG — Heart rhythm is monitored throughout to detect any arrhythmia or cardiac stress immediately

Arterial blood pressure — An arterial line provides beat-by-beat blood pressure readings, far more precise than a standard cuff

Oxygen saturation — Continuous pulse oximetry ensures adequate oxygenation throughout the procedure

Respiratory function — Respiratory rate, tidal volume, and end-tidal CO2 monitoring ensure safe ventilation under sedation

Fluid and electrolytes — IV fluids are administered continuously, and blood draws during the procedure monitor electrolyte balance

This monitoring allows the medical team to respond immediately to any deviation from expected parameters. Temperature elevation is controlled precisely—it is raised gradually at a rate of approximately 1°C per 30–40 minutes. The process can be slowed, paused, or reversed at any point if clinical indicators warrant it.

The medical team

A dedicated team is present throughout the entire procedure, which lasts 6–8 hours:

Anesthesiologist — Responsible for sedation management, airway protection, hemodynamic stability, and rapid response to any adverse event
Hyperthermia physician — Oversees the temperature protocol, monitors the treatment trajectory, and makes clinical decisions about the session
Nursing team — Manages IV medications, fluid administration, patient positioning, monitoring documentation, and direct patient care

This team has collective experience across tens of thousands of hyperthermia sessions. The protocols they follow have been refined over three decades of daily clinical practice. This depth of institutional experience is itself a safety factor—the team has encountered and managed virtually every clinical scenario that can arise during the procedure.

Expected side effects

These are not complications. They are expected physiological responses to the procedure. Understanding them in advance helps you prepare emotionally and practically for the recovery period.

Profound fatigue and exhaustion (3–7 days) The most universal side effect. Your body has undergone a significant physiological event. Most patients describe the first 48–72 hours as the most exhausting period of their treatment. The fatigue gradually resolves, but you should expect to feel significantly depleted for the first week.
Flu-like symptoms (2–5 days) Body aches, headache, chills, and general malaise. These are caused by the immune activation triggered by hyperthermia and by the body's response to bacterial die-off. They typically peak on days 1–2 and gradually subside.
Herxheimer-type reaction (1–5 days) A temporary worsening of your existing Lyme symptoms. This occurs when large numbers of bacteria die and release endotoxins into the bloodstream. The reaction can be intense but is generally interpreted as evidence of bacterial die-off. It is managed with supportive care, IV fluids, and detoxification protocols.
Mild skin redness (hours to days) Superficial redness from the infrared exposure, similar to mild sunburn. This is cosmetic and resolves without treatment.
Temporary cognitive fog (days to weeks) Some patients experience difficulty concentrating, word-finding trouble, or feeling mentally "foggy" during the recovery period. This typically improves over 1–3 weeks.
Emotional sensitivity (days to weeks) Many patients report feeling emotionally vulnerable, tearful, or emotionally heightened during recovery. This is a normal physiological response to the stress of the procedure and typically resolves as the body recovers.
Appetite changes and mild digestive disruption (days) Reduced appetite, mild nausea, or changes in bowel habits are common in the first few days. These resolve with normal dietary resumption.

Uncommon and rare risks

As with any procedure involving general anesthesia and significant physiological stress, serious adverse events are possible. The following risks are uncommon to rare in the context of over 30,000 sessions, but you should be aware of them.

Electrolyte imbalances Prolonged sweating and fluid shifts during the procedure can cause temporary imbalances in sodium, potassium, or other electrolytes. This is monitored during the session and corrected with IV replacement as needed. In most cases it is subclinical and does not cause symptoms.
Prolonged or severe Herxheimer reaction While a Herxheimer reaction is expected, some patients experience a more intense or prolonged version. In rare cases this requires extended IV support, additional detoxification measures, or a longer hospital stay. The medical team monitors for this and adjusts the care plan accordingly.
Transient blood pressure changes Hyperthermia causes vasodilation, which can lower blood pressure. In most patients this is well-tolerated, but some may experience hypotension requiring IV fluid boluses or temporary vasopressor support. Continuous arterial monitoring ensures immediate detection and response.
Mild skin burns Rarely, the infrared exposure may cause localized burns beyond simple redness, particularly in areas of skin contact with the treatment surface. Proper patient positioning and monitoring minimize this risk.

Cardiac arrhythmia The cardiovascular system is under stress during hyperthermia. In rare cases, heart rhythm disturbances may occur. This is why continuous ECG monitoring is maintained and why patients with pre-existing cardiac conditions are screened carefully—and often excluded—before treatment. Resuscitation equipment and medications are immediately available.
Seizure Extremely rare in the context of hyperthermia. Patients with a history of seizure disorders are evaluated carefully, and most are excluded from treatment. When seizure does occur, it is managed immediately by the anesthesia team.
Anesthesia-related complications Any procedure involving sedation or general anesthesia carries inherent risks including airway complications, aspiration, allergic reactions to anesthetic agents, and other anesthesia-specific adverse events. The presence of a dedicated anesthesiologist throughout the procedure is specifically designed to manage these risks.
Thromboembolic events Prolonged immobility during the 6–8 hour procedure, combined with hemodynamic changes, creates a theoretical risk of blood clot formation. Preventive measures including sequential compression devices, hydration, and early mobilization post-procedure are standard practice.

30,000+

Hyperthermia sessions have been performed at St. George Hospital since the early 1990s. This volume represents one of the largest institutional experiences with Lyme-specific whole-body hyperthermia in the world. The safety protocols in use today have been developed and refined across this entire history of clinical practice.

Who should NOT have hyperthermia

Responsible medicine means knowing when to say no. Not every patient is a safe candidate for whole-body hyperthermia, regardless of how much they may benefit from it. The pre-treatment evaluation exists specifically to identify patients for whom the risks outweigh the potential benefits.

Absolute contraindications

Severe cardiac conditions (recent myocardial infarction, unstable angina, significant arrhythmias, severe heart failure)
Active, uncontrolled seizure disorder
Pregnancy or active breastfeeding
Severe uncontrolled hypertension
Active hemorrhagic conditions or severe coagulopathy
Severe anemia (hemoglobin below safe threshold for anesthesia)
Active malignancy under chemotherapy or radiation treatment
Severe hepatic failure (Child-Pugh C)
Severe renal failure requiring dialysis
Inability to tolerate general anesthesia for any reason

Relative contraindications (case-by-case)

Controlled seizure disorder on medication
Moderate cardiac conditions (evaluated individually)
Controlled hypertension on medication
Moderate hepatic or renal impairment
Severe obesity (may affect temperature regulation)
Active autoimmune flare
Recent surgical procedures (within 6–8 weeks)
Metal implants or pacemakers (individually assessed)
Advanced age with significant comorbidities
Severe psychiatric conditions that may affect informed consent

Relative contraindications do not automatically exclude you from treatment. They mean that your case requires careful individual evaluation by the medical team, potentially additional testing, and a clinical judgment about whether treatment can be performed safely with appropriate precautions. Many patients with relative contraindications proceed to treatment after thorough evaluation.

If you are unsure whether a condition you have might affect your eligibility, the best course of action is to request a case review before making any travel arrangements. Our medical team will evaluate your history honestly and tell you whether treatment is a realistic option.

For a detailed discussion of eligibility criteria and how the assessment process works, see our eligibility guide.

Pre-treatment safety measures

Safety does not begin when the hyperthermia session starts. It begins weeks before, with the case review process, and continues throughout the diagnostic workup in the days before the procedure.

Before you arrive

Medical history review. Your complete medical history, current medications, prior surgeries, and existing conditions are evaluated during the initial case review. Patients with clear contraindications are informed before they make any travel commitments.
Physician-to-physician communication. When warranted, our medical team contacts your home physicians to discuss relevant medical details and obtain additional records.

After arrival, before the session

Comprehensive diagnostic workup. The first 2–3 days include extensive blood work, cardiac evaluation (ECG, and echocardiography if indicated), organ function testing, and metabolic assessment. This workup identifies risks that may not have been apparent from the initial case review.
Anesthesiology consultation. A dedicated anesthesiologist evaluates your fitness for sedation, reviews your airway, discusses your medication history, and confirms that you can undergo the procedure safely.
Treatment team conference. Your treating physician, the anesthesiologist, and the hyperthermia team review your case together before the session is scheduled. If any new concerns emerge from the diagnostic workup, the treatment plan is modified or, in some cases, the hyperthermia session is deferred or cancelled.

We do not treat patients who do not meet safety criteria, regardless of how far they have traveled or how much they are hoping for treatment. This is not a business decision. It is a medical and ethical obligation.

An honest assessment

Whole-body hyperthermia is a safe procedure when performed in the right setting, by an experienced team, on appropriately screened patients. The 30,000+ session track record at St. George Hospital supports this. Serious adverse events are rare.

But "rare" is not "impossible." Any procedure involving general anesthesia and sustained core temperature elevation to 41.6–41.8°C carries inherent risk. The question is not "Is this risk-free?" It is: "Is the potential benefit worth the risk, for me, given my specific medical situation?"

That is a question only you can answer, with the guidance of your medical team. Our commitment is to give you the honest, complete information you need to answer it well.

If you are ready to explore whether the potential benefits of hyperthermia justify the risks for your specific case, request a case review. If you want to understand the range of outcomes patients experience, continue to our results and expectations page.

Have questions about your specific situation?

A case review allows our medical team to evaluate your medical history and tell you honestly whether hyperthermia is safe and appropriate for you. No cost, no commitment.

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