The goal of this clinical trial is to learn if nebulized ketamine helps treat moderate to severe asthma attacks in adults in the emergency department. It will also learn about the safety of ketamine when inhaled through a nebulizer.

The main questions it aims to answer are:

• Does nebulized ketamine improve breathing more than standard treatment alone?
• What side effects, if any, do participants experience after receiving nebulized ketamine?

Researchers will compare nebulized ketamine to a placebo (a saltwater mist with no medication) to see how well it works and how safe it is.

Participants will:

• Receive either nebulized ketamine or a placebo mist, along with standard asthma treatment
• Have their breathing checked before and after treatment using a peak flow meter
• Be monitored for 60 minutes and have their symptoms, vital signs, and any side effects recorded

Inclusion Criteria:

1. Adults aged 18 years or older presenting to the Emergency Department with a clinical diagnosis of moderate to severe asthma exacerbation based on SIGN (Scottish Intercollegiate Guidelines Network) criteria.
2. PEFR between 33% and 75% of predicted value or personal best, as measured using a peak flow meter.
3. Stable vital signs as deemed by the treating physician
4. Alert and oriented, able to understand the study purpose and provide informed consent.
5. Not requiring immediate advanced airway intervention, including intubation or emergency non-invasive ventilation.

Exclusion Criteria:

1. Known hypersensitivity or allergy to ketamine or any component of the nebulized solution.

2. History of psychosis, schizophrenia, or other severe uncontrolled psychiatric disorders.

3. Uncontrolled hypertension, defined as systolic BP > 180 mmHg or diastolic BP > 110 mmHg on two consecutive readings at least 5 minutes apart, despite initial ED management.

4. Hemodynamic instability, including persistent hypotension (SBP < 90 mmHg) or tachyarrhythmias requiring urgent treatment.

5. Significant chronic lung disease, including:

   • COPD with frequent exacerbations or baseline FEV₁ < 50% predicted
   • Interstitial lung disease (ILD)
   • Clinically significant bronchiectasis with baseline productive cough or infection

6. Pregnancy or currently breastfeeding.

7. Home BiPAP use or requirement for non-invasive ventilation (e.g., BiPAP/CPAP) during the ED visit (Note: isolated home CPAP for sleep apnea without daytime symptoms is acceptable).

8. Current intubation or imminent need for mechanical ventilation based on clinical judgment.

9. Severe cardiac disease, including decompensated heart failure, recent myocardial infarction (<6 weeks), or known severe valvular disease.

10. Any other medical, surgical, or psychiatric condition that in the opinion of the investigator would place the patient at undue risk from study participation or interfere with the interpretation of study results.

This study uses a double-blind design where all key parties are masked: participants, care providers (administering the nebulization), investigators (overseeing clinical care), and outcomes assessors (recording PEFR and symptom scores). Nebulized ketamine and placebo are prepared in identical-appearing formulations (5 mL clear solution in a nebulizer chamber) to maintain blinding. Randomization codes are securely stored and revealed only after data collection is complete. This design minimizes bias in treatment administration, symptom reporting, and outcome measurement