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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

Çϸ鼭 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¿¡ À־ÀÇ 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.