Hello! Thank you for asking on HCM! I understand your concern and would like to explain that the risk of pulmonary embolism or a brain stroke is high from the coagulation changes induced by the renal failure. Staying in sitting position for 6 hours, taking into consideration the atmospheric pressure changes, would face him with a higher risk for acute complications. If this flight is extremely necessary, I recommend performing some tests like: - resting ECG - complete blood count - coagulation tests (INR, PT) - kidney and liver function tests - fasting glucose - blood electrolytes, etc. An injection of enoxaparine or fraxiparine before the flight may be helpful in preventing possible emboli (or just aspirin if no contraindications). Hope to have been helpful! Best wishes, Dr. Iliri