Introduction

Operating theatres (OTs) are highly controlled environments where biomedical engineering, infection control, and clinical expertise converge to enable safe anesthesia and surgery. The air-conditioning (AC) system—part of heating, ventilation, and air conditioning (HVAC)—is central to this environment by maintaining:

• Temperature: 20–24°C
• Humidity: 40–60%
• Ventilation: Positive pressure to prevent ingress of contaminated air
• Air changes: 15–20 per hour (laminar flow in specialized theatres)
• Filtration: HEPA systems capturing >99.97% of particles ≥0.3 µm

Failure of the AC system due to mechanical breakdown, power disruption, or lack of redundancy triggers physiological, pharmacological, and infection control risks, while also impairing surgical team performance.

The Science of Thermal and Airflow Control in the OTThermodynamics of Heat Transfer

Heat exchange occurs in four primary ways:

• Radiation: Heat transfer from surgical lamps onto the patient
• Conduction: Direct heat transfer from patient to operating table
• Convection: Primary cooling mechanism provided by air movement
• Evaporation: Heat loss via sweating and wound evaporation

Impact of AC failure:

• Loss of convection
• Radiation dominance
• Impaired evaporation
• Ambient temperatures can exceed 28°C within 30–60 minutes, leading to hyperthermia and staff heat stress

Humidity Control

• Normal range: 40–60%
• Below 30%: Risk of static electricity
• Above 70%: Condensation and bacterial growth
• Failure of AC: Increased humidity due to lack of dehumidification and perspiration → increased infection risk

Airflow Dynamics

• Normal: Positive pressure and laminar flow (0.3–0.5 m/s) to protect the sterile field
• AC failure results in:
• Loss of positive pressure
• Cessation of laminar flow
• Increased airborne particulate counts (>200 CFU/m³ within 1 hour)

Heat Load in the OT

• Surgical lights: 500–1000 W
• Anesthesia machines/monitors: 200–400 W
• Human metabolic heat: ~100 W per person
• With 8–10 staff, total heat load = 1.5–2 kW
• Without AC, temperature rises by 1–2°C every 15–20 minutes

Environmental Standards

• Temperature: 20–24°C
• Humidity: 40–60%
• Air exchanges: ≥15 per hour (laminar: ≥300 per hour)
• Pressure differential: +2.5 Pa

Chain Reaction of AC Failure

• Within minutes: Loss of laminar flow, rising temperature
• 30–60 minutes: Temperature >28°C, humidity increases, vaporizers lose calibration accuracy
• 1–2 hours: Loss of positive pressure, microbial contamination increases
• Beyond 2 hours: Unsafe for elective surgery, infection control breaches, staff fatigue

Thermoregulatory Physiology in the Anesthetized PatientHeat Balance Equation

ΔS = M ± R ± C ± K – E

• ΔS: Change in body heat content
• M: Metabolic heat
• R: Radiation
• C: Convection
• K: Conduction
• E: Evaporation

Impact of AC failure: Convection reduced, radiation increased, evaporation impaired → hyperthermia

Effect of Anesthesia

• General anesthetics: Lower vasoconstriction and shivering thresholds by 2–3°C
• Volatile agents: Dose-dependent vasodilation
• IV agents (e.g., propofol): Impair hypothalamic regulation
• Neuraxial anesthesia: Blocks sympathetic vasomotor tone

Special Populations at Higher Risk

• Neonates/infants: High surface area-to-volume ratio, immature regulation
• Elderly: Reduced vasomotor and sweating responses
• Obese patients: Insulation by adipose tissue, high metabolic rate
• Cardiac patients: Heat stress increases cardiac workload
• Burns patients: Increased evaporative losses

Physiological Consequences of Hyperthermia

• Cardiovascular: Tachycardia, arrhythmias
• Respiratory: Increased CO₂ production, ventilatory demand
• Metabolic: Increased O₂ consumption, lactate accumulation
• Neurological: Worsened ischemic injury
• Renal: Dehydration, electrolyte disturbances

Pharmacological Consequences of AC FailureVolatile Agents

• Higher temperature increases vapor pressure → risk of overdose, hypotension, delayed emergence

Neuromuscular Blocking Agents

• Succinylcholine: Faster breakdown, shorter duration
• Atracurium: Faster metabolism
• All NMBAs: Increased volume of distribution due to vasodilation

Intravenous Anesthetic Agents

• Propofol: Reduced stability, risk of bacterial contamination
• Remifentanil: Faster metabolism, reduced potency
• Insulin: Heat-induced denaturation, critical for diabetics

Other Drugs

• Local anesthetics: Shorter block duration
• Antibiotics: Faster degradation, possible subtherapeutic dosing

Biochemistry of Heat Stress

• Heat shock proteins protect against protein denaturation
• Oxidative stress increases ROS → cellular damage
• Electrolyte disturbances → sodium and potassium loss
• Respiratory alkalosis may develop

Anesthetic Management StrategiesIntraoperative Monitoring

• Core temperature: Esophageal or nasopharyngeal probes
• Hemodynamics: Watch for vasodilation
• Neuromuscular function: Train-of-four monitoring

Environmental and Cooling Measures

• Portable cooling units
• Ice packs or cooling blankets
• Fans to increase air exchanges

Clinical, Ethical, and Systems-Level ManagementClinical Scenarios

• Elective surgery: Postpone if HVAC not restored in 30–60 minutes
• Emergency surgery: Proceed with cooling and enhanced monitoring
• Pediatric cases: Minimize draping, active cooling
• Complex surgery: Cancel unless HVAC restored

Infection Control Risks

• Staphylococcus aureus: Higher SSI risk
• Aspergillus: Proliferates in humid, stagnant conditions

Ethical Responsibilities

• Patient safety takes priority
• Risks should be documented and informed consent obtained

Engineering Solutions

• Dual power supplies for redundancy
• Sensor-based real-time monitoring of OT climate
• Portable HEPA filters to maintain air quality during downtime

Conclusion

Air-conditioning failure in the operating theatre is a complex crisis with systemic implications. Anesthesiologists must:

• Prioritize patient safety above all else
• Monitor physiology and drug pharmacokinetics closely
• Collaborate with surgeons, engineers, and infection-control teams
• Advocate for resilient HVAC systems with built-in redundancy