萬惡肥為首-肥胖肺換氣不足綜合症
今天遇到一位特別的病人，他常常引起他人的注目，不要誤會他是什麼韓式俊男美女，相反他倒像個日本相撲手-差不多兩個振華的身形! 我喜歡叫他肥師傅，不知是否與他做中式點心師傅有關，所以有如此龐大身形。許多年前他是因急性二型呼吸衰歇(acute type II respiratory failure) 入院，當時大家都以為他患有非常嚴重的阻塞性睡眠窒息症(OSA)，但因OSA引起呼吸衰歇的情況是絕無僅有的。所以我的團隊相信他實在是患上肥胖肺換氣不足綜合症(Obesity
Hypoventilation Syndrome, OHS)。
事後亦証明我們的臨床診斷是正確-有30-70% OHS病人會因急性二型呼吸衰歇(acute type II
respiratory failure) 入院(1)。當時大家對處理OHS的經驗甚少，所以借用了處理慢阻肺病急性發作(AECOPD)的方案，使用了高低正氣壓呼吸機(Bi- Level Positive airway pressure, Bilevel Therapy) 來改善肥師傅的呼吸衰歇情況，誤打誤撞下病人的病情穩定下來(2) ，不過相比慢阻肺病病人，肥師傅的反應較遲緩，其實這正是OHS 病人典型的表現(3) 。稍後肥師傅亦可以轉用連續正氣壓機(Continuous Positive Airway Pressure, CPAP) 出院。
大家對肥人患上阻塞性睡眠窒息症不會感到陌生，但什麼是肥胖肺換氣不足綜合症(Obesity Hypoventilation Syndrome, OHS)? 傳統上是指那些: 日間血含二氧化碳(PaCO2 >45mm Hg) ；BMI(BODY MASS INDEX) >30kg/m2 ；又沒有其他明顯病因引起的慢性肺泡換氣不足(chronic alveolar hypoventilation) 的症候(4)。其病理十分複雜: 中央肥胖引致橫隔膜活動受制、肺容量減少、用作呼吸的肌肉功能失調…(5,6)。一般來說病人越肥血中含二氧化碳量越高(7)。另外阻塞性睡眠窒息症亦常見於OHS的病人(8)。內分泌失調(Leptin and insulin like growth
factor-1)也可能扮演一定角色(9,10) 。
OHS 會帶來病人心血管和身陳代謝的改變(11)，OHS病人會比OSA病人更常有肺動脈高壓(pulmonary hypertension)(12)，因而傷害健康及日常活動量(13)。一旦OHS病人需要入院接受治療，他們的病情大多嚴重，甚至要住院多時或入住深切治療部(14)，前景(prognosis)亦不太樂觀(15) 。所以肥師傅上次是死裹逃生。要診斷OHS同樣要經睡眠測試(PSG)及量度病人睡眠時的血含二氧化碳量(16)。
第一線治療OHS的方案是利用正氣壓呼吸機(Positive Airway Pressure, PAP) 來逆轉其病理，連續正氣壓機(CPAP) 大多數已經能改善50-80% OHS病人的病情(17)，但自動連續正氣壓機(auto-titrating CPAP)卻不適用於OHS。若果CPAP 不能令病人的含氧量高於90%，那麼就應轉用高低正氣壓呼吸機(Bi-Level Positive airway pressure, Bilevel Therapy)(18)。幸好有部份病人在病情穩定後可以轉回用較經濟的CPAP(19)，肥師傅的情況就是個好例子。不過有10-20%的OHS病人不肯接受正氣壓呼吸機治療(PAP)，亦有另外10-20% 病人使用PAP的情況不理想(20,21)。單獨使用氧氣治療不單無助醫治OHS，甚至可能加重病人血中二氧化碳量(22,23)，但若果病人使用PAP後，血含氧量仍不達標，那麼這時就要加上氧氣治療(17,19)，不過仍然要小心觀察病人的血中二氧化碳量(20,24) 會否隨之上升。
成功減肥當然可以大大改善OHS(25)的病情，但手術比其他方案更能保持”瘦身” 效果(26)。藥物治療對OHS是起不了大作用的(27,28)。但我嚇然發現肥師傅這些年來從未成功減過肥。他笑笑口說:「下次先至講呢樣! 減肥是終身事業、不用急的。」
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**為保障個人私隱及達到教育效果，因此文中案例可能由真實及/或虛構病例改編而成***
