Oxidative injury in ICU

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1 Oxygen Therapy and Mechanical Ventilation

2 Goals of Oxygen Therapy Correct hypoxemia or suspected tissue hypoxia Decrease work of breathing Decrease the symptoms associated with chronic hypoxemia Prevent or minimizes the increased cardiopulmonary work load

3 Indications (1)In room air, PaO2<60 mmhg or SaO2<90% (2)In new lives, Pa O2<50 mmhg or SaO2<88%.

5 Oxygen delivery Oxygen delivery (DO2) = Cardiac output (CO) x oxygen content of the blood(cao2) ml/min CaO2 = [(Hb x SaO2 x 1.3)+(0.003 x PaO2)] x 10 ml/l

6 Four Types of Hypoxia 1.Hypoxemic hypoxia (1)Lowered FiO2 or PiO2 (2)Hypoventilation (3)V/Q mismatch: e.g. pneumonia or COPD (4)Diffusion defect: e.g. ARDS (5)Shunt: intrapulmonary or extrapulmonary 2.Anemic hypoxia 3.Circulatory hypoxia 4.Histotoxic hypoxia : e.g. cyanide poisoning

7 Complications of Oxygen Therapy Respiratory depression :COPD patient respiratory drive depend on hypoxemia Absorption atelectasis Oxygen toxicity FiO2 too high lead to oxygen free radicals increase Surfactant production

8 Oxygen administration system Low flow equipment FiO2 is variable High flow equipment FiO2 is fixed. 給予病人大於三倍 minute ventilation 量的氧氣

9 Low flow equipment Nasal cannula: FiO2= 20% + O2 L/min (1~5 L/min) 4% 優點缺點方便便宜患者可進食舒服無 CO2 retention 問題引起耳與鼻壓力傷害引起鼻黏膜乾燥與刺激氧氣濃度最高約 40%

10 Low flow equipment Simple Mask: FiO2: 30~50% ; O2: 5~10L/min 優點較高氧氣濃度與溼度適用予以口呼吸或鼻子不適之患者氧氣流量須大於 5 L/min 以避免 CO2 滯留缺點言語不便咳痰不便顏面受傷者不宜妨礙進食眼睛乾燥

Low flow equipment Reservoir bag Exhaled gas Open Vents Oxygen 5-7 L/min----- FiO2: 0.35-0.

11 Low flow equipment Reservoir bag Exhaled gas Open Vents Oxygen 5-7 L/min----- FiO2: Reservoir bag Exhaled gas One way Flap One way Valve Oxygen 4-10 L/min---- FiO2: Partial rebreathing system Non- rebreathing system

12 High flow equipment Venturi system: 利用 venturi valve, 在氧氣通過時, 將 room air 吸入, 以稀釋成所需的 FiO2 優點提供正確氧氣濃度可避免氧氣太高造成之呼吸抑制不同接頭有不同氧氣濃度 (24,28,31,35,40, 50%) 缺點面罩太緊會不舒服患者產生恐怖感妨礙進食吐痰眼睛乾燥與刺激

13 Mechanical Ventilation NIPPV Non-invasive Positive Pressure Ventilation CPAP or BiPAP Conventional Mechanical Ventilation Volume cycled ventilation and Pressure cycled ventilation Others

14 Indications (1) 肺泡換氣不足 :type II respiratory failure (2) 肺擴張不足 :flail chest (3) 呼吸肌力不足 : COPD patient (4) 呼吸作功太大 : 如病人已喘至三四十次 (5) 呼吸驅動不穩 :intracerebral hemorrhage (6) 嚴重低血氧症 : 尤其當病人 FiO2/PaO2 小於 200 (7) 預防性使用 :post-operation

15 四大要素 FLOW PRESSURE TIME VOLUME

16 名詞解釋 Trigger: 設定結束吐氣動作的條件 ( 開始吸氣 ) Limit: 設定某一個值不能超過該 limit Cycle: 設定結束吸氣動作的條件 ( 開始吐氣 )

17 Trigger Time trigger: 先設定一個 rate, 時間到了就啟動 Pressure trigger: 先設定一個 pressure sensitivity (e.g. 2 cmh2o) 當 P AW 降到 baseline 以下的預設值時就啟動 Flow trigger: 機器必需是 continuous flow(e.g. 6L/min) 再設定一個 flow sensitivity (e.g. 3L/min) 當 airway flow 降到 baseline 以下的預設值 ) 時就啟動

18 Cycle Time cycle 時間到了就切換成吐氣, 最常用 Flow cycle 當 flow 降到 initial flow 的某個 % 時切換成吐氣 (e.g. PSV=25%) Volume cycle 當 volume 達到預先設定的值時切換成吐氣 (e.g. Assist volume ventilation) E.g. VCV, IMV

19 Volume cycled ventilation (1) Full support: a) VCV (Volume control ventilation):time trigger mode b) ACMV (assist-control mandatory ventilation): 此為 time or patient trigger mode 假設呼吸速率 set 12 breaths/min, 當病人有自呼時 (patient trigger), 呼吸器將完成此一呼吸達到一固定的換氣量, 若病人沒有自呼, 則五秒後 time trigger) 呼吸器將自動打入一固定的換氣量

20 Volume cycled ventilation (2) Partial support: a) IMV (intermittent mandatory ventilation): 病人本身有自呼, 而 ventilator 所設定的時間一到, 又會打入一固定換氣量的 ventilatory breath b) SIMV (synchronized intermittent mandatory ventilation): 與 IMV 不同處, 在於 ventilator 可 sense 到病人的呼氣, 而把要打入的 ventilator breath 延後至病人吸氣時再給予

21 Volume control ventilation Preset Peak Flow Flow (L/min) Dependent on C l & R aw Pressure (cm H 2 O) Preset V t Volume (ml) Time (sec)

22 Pressure cycled ventilation (1) Full support: PCV (pressure control ventilation) 當 preset 的 respiratory rate 一固定, 時間一到 (time trigger),ventilator 便將氣體打入, 直至 airway pressure 到達設定值才停止 (2) Partial support: PSV (pressure support ventilation) 當病人一發生自呼時 (patient trigger),ventilator 即接手打入一氣體以達到設定的 airway pressure

23 Pressure Control Ventilation Flow (L/min) Set PC level Pressure (cm H 2 O) C l Time (sec) C l Volume (ml)

24 Lung Compliance The ease with which lungs can be expanded Dynamic Compliance: Cdyna=Tidal Volume/PIP-PEEP Static Compliance: Cstat= Tidal Volume/Pplat-PEEP

25 Plateus Pressure (Pplat) Volume control ventilation with a 0.8 second inspiratory hold

26 Positive End-Expiratory Pressure (PEEP) 當吐氣終了時, 呼吸器提供一個正壓避免肺泡塌陷可減少吸氣時所作的功增加 FRC, 保持肺泡擴張或避免塌陷改善氧合

27 BiPAP and CPAP (1) BiPAP: 類似 PSV mode, 在病人吸氣時給予一個 ipap, 在病人吐氣時給予一 epap, 如此可減少病人呼吸時所作的工 (2) CPAP: continuous positive airway pressure 在整個呼吸過程中持續給予病人一個正壓, 如此可改善病人的 hypoxemia

28 Other modes Dual mode: Volume support, PRVC (Pressure regulated volume control ) and Pressure augmentation/vaps (Volumeassured pressure support) 同時保障潮氣量及避免氣道壓過高, 融合了 volume ventilation 和 pressure ventilation 的優點並改善了它們的缺點 APRV (Airway pressure release ventilation) and Proportional assist ventilation (PAV)

29 呼吸器設定 Tidal volume: 6-15 ml/kg of IBW R.R: breaths/minute FiO 2 : 100% I/E: 1/1.5 PEEP: 5 cmh2o Flow rate: 50l/minute

30 呼吸器設定 COPD: VT = 8-12ml/kg,f=6-10/min, flow > 60L/min Lung fibrosis: VT 8-10 ml/kg, f = 12-20/min ARDS: VT =6ml/kg, Keep P Plat < 30cmH 2 O, High PEEP, keep SaO %,FiO 2 盡可能不要 > 0.6

31 Trouble Shooting 基本動作 : 拿掉呼吸器先用 ambui 擠壓, 並同時聽有沒有呼吸音, 或兩邊的呼吸音是否一樣檢查 endotracheal tube 有無阻塞或 cuff balloon 有沒有漏氣檢查呼吸器上哪些數字或燈在閃當病人一切都正常時, 再來檢查呼吸器是否有問題

32 常見的突發性問題病人問題 : Airway (increased Ppeak-Pplat) Endotracheal tube 阻塞 - 痰堵住, 咬管, 滑入, 漏氣 Bronchospasm Pulmonary parenchymal disease ( Ppeak-Pplat unchanged or decreased) Pneumonia Atelectasis Pulmonary edema Extrapulmonary causes Pneumothorax Pleural effusion Abdominal distension (eg, ascites) Delerium, anxiety, pain, acute neurological event

33 常見的突發性問題機器問題漏氣管路脫落 FI O2 不夠呼吸器設定錯誤 Trigger sensitivity 不夠敏感或太敏感呼吸器的 flow 開的不夠 (volume ventilation)

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untitled : SARS (RAPHAEL) 5 SCMV SIMV+PCV PSIMV+ SPONT : 1 1.1 20 4050 Bennett PR-1A Bird mark 6070 Bennett MAEngstrom200 Servo900 (PEEP)(CPAP)(IMV) (SIMV) T 80 Servo900cBennett7200Bennett7200aeBear1000 Bear1000T/se