Mechanical Ventilation
1. ÀûÀÀÁõ - 2 types of respiratory failure
1) Hypoxic respiratory failure
FiO2 > 0.6¿¡¼ SaO2<90%ÀÏ ¶§
2) Hypercarbic respiratory failure
minute ventilationÀÌ °¨¼ÒÇϰųª physiologic dead space°¡ Áõ°¡µÇ´Â »óÅÂ
¿¹> neuromuscular disease(myasthenia gravis, myopathy)
respiratory muscle fatigue(asthma, COPD, restrictive lung disease·Î ÀÎÇØ
workload°¡ Áõ°¡ÇÏ´Â °æ¿ì)
* acute hypercarbic respiratory failure
PaO2 > 50mmHg & pH < 7.30 => mechanical ventilationÇÊ¿ä
hypercarbic respiratory failure¿¡¼ ventilator txÀÇ ¸ñÀûÀº CO2 tensionÀ»
º¯È½ÃÄÑ arterial pH¸¦ Á¤»óÈÇÏ´Â °ÍÀÌ´Ù.
* Permissive hypercapnia
severe obstructive or restrictive lung diseaseȯÀÚ¿¡¼ airway pressure°¡ Áõ°¡ÇØÀÖ¾î
tidal volumeÀÌ Á¦Çѵɼö ÀÖ°í pH normalizationÀÌ ¾î´ÀÁ¤µµ ºÒ°¡´ÉÇѵ¥ ÀÌ·± »óŸ¦
permissive hypercapnia¶ó ÇÑ´Ù.
2. Modes - triggered, cycled & limited (Tab 266-1)
¨ç triggered : cycleÀ» ½ÃÀÛÇÒ ¶§ inspiratory effert¿¡ ÀÇÇØ triggerµÇ´À³Ä, ¾Æ´Ï¸é time-based
signal¿¡ ÀÇÇØ triggerµÇ´À³Ä¸¦ °áÁ¤
¨è cycle : inspiration ³¡À» °áÁ¤
i) volume cycled ventilation : ƯÁ¤ tidal volumeÀÌ È¯ÀÚ¿¡°Ô Àü´ÞµÇ¸é inspirationÁ¾·á
ii) pressure cycled
iii) time cycling
iv) flow cycling
¨é limiting fator : operator-specified value
¿¹> airway pressure¸¦ limiting factor·Î Á¤ÇÑ °æ¿ì ÁÖ¾îÁø ƯÁ¤ ¾Ð·ÂÀ» ³Ñ¾î¼¸é
inspiratory flow°¡ ÁߴܵÊ.
1) ACMV(Assist Control Mode Ventilation)
- inspiratory effort or timer signal¿¡ ÀÇÇØ trigger
- volume-cycled
- rate : operator-specified backup rate
- rate´Â ¿ì¼¼ÇÑÂÊÀÌ ¼±ÅõÊ
- ventilation½ÃÀÛ¶§ ÃßõµÇ¸ç weaning¶§´Â ºÎÀûÇÕ
(¡ñ ȯÀÚ°¡ È£ÈíÀÌ ÀÖÀ» ¶§ full assistanceÇϱ⠶§¹®¿¡)
tachypnea°¡ ÀÖÀ» ¶§ nonrespiratory or nonmetabolic factor(anxiety or pain or airway
irritation)°¡ ÀÖÀ¸¸é respiratory alkalemia¹ß»ý°¡´É(-> myoclonus or seizure)
- cycleµ¿¾È ÃæºÐÈ÷ exhalationÇÒ ½Ã°£ÀÌ ¾ø´Ù¸é dynamic hyperinflation(=auto-PEEP)¹ß»ý
°¡´É
2) SIMV(Synchronized intermittent mandatory ventilation)
* ACMV¿ÍÀÇ ÁÖ¿äÇÑ Â÷ÀÌÁ¡Àº
i) ÀÚ¹ßÈ£Èí Çã¿ë
ii) ¹Ì¸® Á¤ÇØÁø Ƚ¼ö¸¸Å µµ¿ÍÁÜ
tachypneaȯÀÚ¿¡¼ »ç¿ëÇÏ±ä ¾î·Æ´Ù. ¸¸¾à tachypnea°¡ resp or metabolic acidosis¿¡
´ëÇÑ ¹ÝÀÀÀ¸·Î »ý°å´Ù¸é ACMV·Î changeÇÏ¿© minute ventilationÀ» Áõ°¡ÇÏ¿© pH¸¦ Á¤»óÈ
ÇÏ¸é¼ underlying process¸¦ ´õ evaluationÇÑ´Ù.
3) CPAP(Continuous positive airway pressure)
fresh gas¸¸ Á¦°ø
operator-specified pressure : 0-20 cmH2O
extubation potentialÀ» Æò°¡Çϱâ À§ÇØ »ç¿ë
4) PCV(Pressure-control ventilation)
time-triggered, time-cycled, pressure limited(-> operator°¡ °áÁ¤)
tidal volume, inspiratory rate´Â Á¾¼ÓÀû
barotraumaȯÀÚ¿¡¼ ÀûÇÕ(¡ñairway pressure°¡ Á¦ÇѵǹǷÎ)
postop thoracic surgical patient
minute ventilation & TVÀ» monitorÇØ¾ß ÇÑ´Ù.
(¡ñ rate¿¡ µû¶ó minute ventilationÀÌ º¯ÇϹǷÎ)
* ÁÖ¹®Á¦´Â patient-ventilator asynchrony(time-cycled, time-triggered¶§¹®)
±×·¯¹Ç·Î ´ëºÎºÐÀÇ È¯ÀÚ´Â heavy sedationÀÌ ÇÊ¿äÇϹǷΠhemodynamically unstableÇÑ
ȯÀÚ¿¡¼± ÇØ·Ó´Ù.
5) PSV(Pressure-support ventilation)
- patient-triggered, flow cylced, pressure limited.
- weaningÀ» À§ÇØ ¼³°èµÊ
- PSV + SIMV combinationÇÏ¿© »ç¿ë°¡´É
- weaning pt¿¡¼ ´ëºÎºÐ tolerable
3. Ventilated ptÄ¡·á¿¡ ÀÖ¾î¼ÀÇ Guidelines
respiratory functionÀÌ È£ÀüµÇ¸é °¡Àå ¸ÕÀú PEEP°ú supplemental O2¸¦ ÁÙÀδÙ.
FiO2¡Â0.5, PEEP ¡Â5 cmH2O¿¡¼ ÀûÀýÇÑ SaO2°¡ À¯ÁöµÇ¸é mechanical ventilatory support
levelÀ» ÁÙÀÏ·Á°í ½ÃµµÇØ¾ß ÇÑ´Ù.
full ventilatory support¸¦ ¹Þ¾Ò´Ù¸é weaning¿¡ µé¾î°¡µµ·Ï ÇÑ´Ù.
(SIMV, PSV or SIMV+PSV)
4. General support in the ventilated patient
¨ç immobilized pt : DVT risk
=> subcutaneous heparin and/or pneumatic compression bouts
¨è diffuse GI mucosal injury¿¡ ´ëÇÑ prophylaxis
H2 blocker, antacid, cytoprotective agent(carafate) : È¿°úÀû
¨é nutrition support : 72½Ã°£³»¿¡ ½ÃÀÛÇØ¾ß ÇÑ´Ù.
¨ê dealyed gastric emptying : promotility agent(cisapride or metoclopramide)¸¦ »ç¿ëÇÑ´Ù.
5. Complications of mechanical ventilation
1) Pulmonary Cx - barotrauma, nosocomial pneumonia, oxygen toxicity
tracheal stenosis, resp. deconditioning
¨ç Barotrauma > 50 cmH2O ÀÏ ¶§ ¹ß»ý
interstitial emphysema, pneumomediastinum, subcutaneous emphysema
- airway pressure°¡ °¨¼ÒÇϸé ȸº¹
pneumothorax - thoracostomyÇÊ¿ä
¨è nosocomial pneumonia
72½Ã°£ÀÌ»ó intubation½Ã high risk
endotracheal tube cuffÁÖÀ§·Î small leakµÇ¾î aspirationµÊ.
*mc organisms : GNB, S. aureus, anaerobic bacteria
mechanical ventilation½Ã E-tube, upper airway¿¡ bacteria°¡ colonizationÇϹǷÎ
nosocomial pneumonia¸¦ Áø´ÜÇϱâ À§Çؼ´Â
airway secretionÀÇ "protected brush" bronchoscopic samplingÀÌ ÇÊ¿äÇÏ´Ù.
=> colonization°ú infectionÀ» °¨º°ÇϱâÀ§ÇØ quantitative microbiologic techniqueÀ»
½ÃÇàÇÑ´Ù.
¨é Oxygen toxicity
72½Ã°£ÀÌ»ó FiO2 ¡Ã 0.6 À϶§
free radical¶§¹®
* ¿¹¹æ : PEEP»ç¿ëÀ¸·Î FiO2¸¦ 0.6ÀÌÇÏ·Î ³·Ãá´Ù.
antioxidentÀÇ »ç¿ëÀº ½ÇÇèÁß
¨ê Hypotension
intrathoracic pressure¡è -> venous return ¡é
2) GI effect
positive-pressure ventilation
-> stress ulceration : H2 blocker, sucralfate prophylaxis
mild to moderate cholestasis
¡ñ intrathoracic pr¡è -> PV pr¡è, self limited.
6. Weaning
1) Suction½Ã cough
good indicator of a patient's ability to mobilize secretion
2) Weaning index(ȸ/min/L)
: È£ÈíȽ¼ö/Tidal volume
mechanical assistance¾øÀÌ 105¹Ì¸¸À̸é successful extubation°¡´ÉÇÔ.
3) Acceptable chest wall & diaphragm functionÀ» ³ªÅ¸³»´Â indicator
i) inspiratory pressure > -30 mmH2O
ii) Vital capacity > 10 mL/kg
4) alveolar ventilationÀÇ ÀûÀý¼º
pH 7.35-7.40¿¡¼ CO2Á¦°Å°¡ ÃæºÐÇϸç,
FiO2 < 0.5, PEEP ¡Â 5 cmH2O¿¡¼ SaO2 > 90%ÀÏ ¶§ alveolar ventilationÀº ÀûÀýÇÏ´Ù°í
º»´Ù.
5)* T-piece & CPAP weaning
: ªÀº±â°£ mechanical ventilationÀ» ½ÃÇàÇÏ¿´°Å³ª respiratory muscle reconditioningÀÌ
ÇÊ¿ä¾øÀ» ¶§
* SIMV & PSV
: ¿À·£ ±â°£ intubationÇÏ¿´°Å³ª Á¡Â÷ÀûÀÎ respiratory muscle reconditioningÀÌ ÇÊ¿äÇÑ °æ¿ì
(1) T-piece weaning
brief spontaneous breathing trial with supplemental O2
5 min/hr -> 1hr rest(interval) -> 5min/hr
5->10 ºÐÀ¸·Î Á¡Â÷ Áõ°¡½ÃÄÑ °á±¹ ȯÀÚ°¡ ¼ö½Ã°£µ¿¾È ventilator independent»óŰ¡
µÇ¸é extubationÀ» ½ÃµµÇÒ¼ö ÀÖ´Ù.
(2) CPAP weaning
T-piece¿Í À¯»çÇϳª spontaneous breathing½Ã CPAP mode°¡ Àü´ÞµÈ´Ù´Â Â÷À̰¡ ÀÖ´Ù.
(3) SIMV weaning
È£ÈíȽ¼ö°¡ 25ȸ/ºÐ ÀÌ»óÀ̸é ÀϹÝÀûÀ¸·Î resp. muscle fatigue¸¦ ÀǹÌÇϸç
exercise & rest period¸¦ combineÇÏ´Â °ÍÀÌ ÇÊ¿äÇÏ´Ù.
ȯÀÚ°¡ 4ȸ¹Ì¸¸¿¡¼ stableÇÒ¶§±îÁö exercise period¸¦ Á¡Â÷ Áõ°¡½ÃŲ´Ù.
(4) PSV weaning
volume-cycled ventilation¿¡¼ ȯÀÚ°¡ ÇÊ¿ä·ÎÇÏ´Â peak insp. pressureº¸´Ù ¾à°£ ¾Æ·¡¿¡
settingÇÑ´Ù.
resp. rate°¡ ºÐ´ç 25ȸ°¡ µÉ ¶§±îÁö pressure support levelÀ» Á¡Â÷ 5cmH2O¾¿ °¨¼Ò½ÃŲ´Ù.
support°¡ ÇÊ¿ä¾øÀ» ¶§ extubationÇÑ´Ù.