Mechanical ventilation in COPD Asthma drtrc

Conventional Mechanical Ventilation for Respiratory Failure in COPD Dr.T.R.Chandrashekar M.D Director critical care K.R.Hospital, Bangalore .

COPD It is defined as a preventable and treatable disease state characterized by airflow limitation that is not fully reversible The airflow limitation is in most cases is both progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases . Although COPD affects the lungs, it also produces significant systemic consequences

Systemic effects of COPD Effects Mechanism

Why COPD is Important ? COPD is the only chronic disease that is showing progressive upward trend in both mortality and morbidity It is expected to be the third leading cause of death by 2020 Approximately 14 million Indians are currently suffering form COPD* Currently there are 94 million smokers in India 10 lacs Indians die in a year due to smoking related diseases * The Indian J Chest Dis & Allied Sciences 2001; 43:139-47

In COPD limitation is EF No conventional ventilator supports expiration actively How does MV help ? Although the load is expiratory the failure is inspiratory Inspiratory muscle loading and fatigue is of central pathophysiological importance in the development of acute respiratory failure

Pathophysiology of COPD Expiratory flow limitation is the primary problem

Lung Capacity and Disease Space for fresh air TLC

The Vicious Cycle Increased resistance Airtrapping Decreased Compliance ↑ PVR >DH >DH  WOB FATIGUE ↑ PCO2/↓Pao2 ↓ PH V/Q mismatch

Worsening EFL Gas Exchange Vd/Vt increase Neuromechanical Uncoupling Dyspnea COPD Exacerbation Increased ventilatory drive Hypoxia Hypercarbia Acidosis Tachypnea DH EELV, IC Mechanical Disadvantage PEEPi Cdyn Elastic/threshold loading of insp muscles Insp muscle dysfn CVS effects Pulm MAP RV preload LV afterload

Identify & Measure Complications Manage COPD Key factor is DH Auto PEEP PEEPi EELV

Concept of DH It is a adaptive mechanism which leads to increased elastic recoil force and keeps airways patent to force out air but…. Due to use of accessory muscle usage increased force is also applied to airways which lead to collapse & exaggerate the EFL

Concept of Auto PEEP, DH AUTO PEEP is defined as the difference between PEEP set by the clinician and the PEEP as measured by the ventilator with an expiratory hold.

Identification of Auto PEEP Inspiration Expiration Time (sec) Flow (L/min) } Normal Patient Air Trapping Auto-PEEP

Measurement of Auto PEEP Reduce set PEEP to zero before measuring Auto PEEP Paralysed patient only AT HE END OF EXPIRATION 2 -3 SEC OCCULSION

Auto-PEEP and Volume of Trapped Gas Tuxen, Am Rev Respir Dis 1989; 140:5

WHAT ARE EFFECTS OF AUTO PEEP? Hemodynamic compromise. Due to increase in FRC, respiration starts in the flatter portion of the P/V curve, where change in volume for a change in pressure is less –Increased WOB. Trigger will have to cross the auto PEEP level before inspiration is initiated. Missed breaths

Mechanical Effects of AECOPD Thorax 2006;61:354-61

AUTOPEEP AND TRIGGER Time (sec) Pressure (cmH 2 0) AUTOPEEP BASELINE BASELINE SHIFTS

Missed breath Auto PEEP Wasted effort, increased WOB

There are only 3 factors that determine auto-PEEP. Minute ventilation. (It doesn’t matter whether it’s from respiratory rate or VT). I: E [inspiratory: expiratory] ratio. Expiratory time constants. Let us learn how to manipulate these parameters To prevent Auto PEEP

CO2 removal is inversely proportional to Minute Ventilation CO2 removal is inversely proportional to Effective Alveolar Ventilation Effective Alveolar Ventilation = Minute Ventilation – Dead Space Ventilation

COPD on ventilator on VC Vt 500ml, Fio2 40%, PEEP 4cms H2o RR10/mt, I:E 1:2 Po2 is 60, PCo2 is 68 Increase Vt to 500ml Increase RR 15 After one hr repeat ABG shows PO2 of 58 PCO2 of 83 Minute ventilation of 500x10=5000 Minute ventilation of 500x15=7500

Effective Alveolar ventilation Vt=500ml RR=10 MV=5l EAV=MV-Dead space Dead space ventilation =150x10=1.5l EAV=5l-1.5l=3.5l Vt-500ml RR= 15 MV=7.5l EAV=MV-Dead space Dead space ventilation =300x15=4.5l EAV=7.5l-4.5l=3.0l

FRC EELV/DH COPD compliance Resistance PVR

Respiratory rate RR 10breaths/ min, If I:E ratio 1:2 Total cycle time 60 sec/10 = 6 sec Inspiration = 2seconds Expiration 4 seconds RR 20 breaths/ mt, I:E Ratio 1:2, TCT=60/20=3 sec Inspiration = 1seconds Expiration 2 seconds 3 sec 1sec 2 sec

Minute ventilation Tidal volume=6-7ml/kg Rate 12/mt, IC is reduced Low minute ventilation leads to ↑ PCO2 which is the price we pay for preventing DH, In fact current literature suggests that risk of dynamic hyperinflation is much larger than those of permissive hypercapnia. Provide enough ventilation to keep a normal PH, not a normal PCO2.

Manipulate - I:E Ratio Pressure T ime Gives more time for expiration and reduces DH T insp . . I : E = 1 : 2 I : E = 1: 3 PEEP PIP PIP PEEP T insp . T exp Total cycle time

Peak flow Normally in adults it is set between 40-60l/min, or can be calculated as follows Ins time Tidal volume PEAK FLOW = X 60 A peak flow of around 80-90l/mt

RISE TIME 40 P CIRC cmH 2 O INSP EXP 30 20 10 0 10 -20 80 60 40 20 0 20 -80 40 60 0 4 8 12s 2 6 10 Slow rise Moderate rise Fast rise TE TE TE TI L min V .

PEAK FLOW Peak Flow 30l/mt Peak Flow 90 l/mt

Addition of external PEEP “The Paradox “

+6 +6 +7 Pleural Alveolus Mouth start of Inspiration Airway Pressures with Auto-PEEP Auto-PEEP = +6 Wilson et al, U of Iowa

Can PEEP be used in all COPD pts? Whenever accessory muscles are in use to counter act them PEEP can be used when patients are on partial/ supported modes In asthmatics and when patients are paralysed the response can be variable and unpredictable… Then the question arises how to be sure it is not harmful?

Monitoring the response to external PEEP

0 cm H 2 O PEEP 8 cm H 2 O PEEP Auto peep

Calculation of Exp time constants Compliance x Resistance 0.1l/cmH2O x 5 cmH2O/l/sec= o.5 sec 0.5 x3= 1.5 sec Increased resistance 0.1 x 20 = 2sec 2x3=6sec

Management of Auto PEEP. 1) low tidal volume Decrease the RR 2) Increase expiratory time. 3) Increase peak flow 4) Addition of Extrinsic PEEP Sedation/Control of Fever 6) Bronchodilatation }}} Low MINUTE VENTILATION

Ventilatory support in COPD……

ARF-COPD ABG PH-7.45 PO2-57mmHg PCO2-65mmHg Spo2-89% HCo3-34mmoles Patient is 60 yr old has COPD on room air Comfortable RR-25/mt HR-100/mt

ARF-COPD ABG PH-7.30 PO2-57mmHg PCO2-65mmHg Spo2-89% HCo3-23mmoles Patient is restless Disoriented Accessory muscle used RR-35/mt Paradoxical breathing 0n 4l of oxygen on resv bag. Baseline Pco2, PH, WOB, Hemodynamic stability, FIO2,Mentation Should be kept in mind while interpreting ABG’s and decision to ventilate

Spontaneous Weaning Controlled Conventional ventilation NIV Mechanical ventilation

Ventilation difficulties in COPD Ventilating a COPD patient is difficult because the disease may not have a reversible component, Quantifying dynamic hyper inflation at bedside is very difficult COPD patients are difficult to wean. Co morbidities & systemic effects

60 yr old COPD patient is Drowsy, disoriented RR-40/mt, accessory muscle+, BP-80/50mmHg, ABG –PH-7.08, PCO2-85mmHg,Pao2-49mmHg, SPo2-83% on 5l of oxygen or COPD pt on NIV after 2hrs restless , not synchronizing, PH,PCO2,PO2 deteriorated Case scenario

Indications for Invasive Mechanical Ventilation. NIPPV failure. Severe dyspnea with use of accessory muscles+. RR> 35 breaths per minute. Life-threatening hypoxemia (PaO2, 50-40 mm Hg). Severe acidosis (pH < 7.25) and hypercapnia ( >60 mm Hg). Respiratory arrest. Somnolence, impaired mental status. Cardiovascular complications (hypotension, shock, heart failure).

Intubation and MV Decision to intubate if the patient is not a candidate for NIV or has not done well on NIV- has to be made decisively and if delayed both morbidity and mortality are higher. Post intubation bagging has to be low tidal volume and low rate 6-7/mt. If paralysed keep them on relaxants for a day or two. Fill them adequately before induction , Add a small dose of a inotrope in a corpulmonale patient

Ventilatory settings in passive pt Set a moderate FIO2, usually 40%, target a SPO2 of 90% Mode –Volume controlled, square wave. Tidal volume = RR= I: E ratio = Flow 7ml/kg 12/mt =80-100l/mt 1:3 or more depending on expiratory time constants

Ventilation in a passive patient External-PEEP application has a variable and unpredictable response Due to no contribution of the expiratory muscles, the reason how external PEEP helps to reduce DH Reducing the lung heterogeneity. Opening up previously closed units it could help in mucus clearance and bronchodilator therapy.

Paw (cm H 2 O) Normal P Plat (Normal Compliance) Increased PIP } Increased P TA (increased Airway Resistance ) Increased Airway Resistance Begin Inspiration Begin Expiration P aw (cm H 2 O) Time (sec) Airway Resistance Distending (Alveolar) Pressure Expiration PIP Normal Inflation Hold (seconds)

A PIP = 40-45 cmH2O. Ppl pressure < 30cmH2O. Minimal sensitivity- Pressure or Flow trigger. PEEP setting- Start at 5 cmH2O, any further increase always look at PIP and plateau pressure. Any increase in these pressures, decrease PEEP. (Keep a close watch on hemodynamics)

Ventilating a spontaneous patient PS /PC mode/PAV Pressure support to generate 7ml/Kg VT Minimal trigger setting- flow or pressure Peak flow -80-100l/min PEEP can be added starting at 5cmH2O in an increments of 2cmH2O

Ventilating a spontaneous patient You rarely require more than 10cmH2O PEEP. Expiratory sensitivity (PS) can be set much above the default setting of 25%.( 40%) If the patient is not synchronizing, increasing PS could lead to increased VT, DH, and missed breaths. In such a situation other causes like fever, pain etc have to be looked for. In case no other cause can be found, sedation can be used .

CYCLING AT 40% OF FLOW CYCLING AT 25% 0F PEAK FLOW PRESSURE SUPPORT Flow cycling Flow Time Peak flow 40% 25%

Weaning Weaning begins when the precipitating factor of the respiratory failure is partially or totally reversed. Marginal respiratory mechanics. Factors which increase resistance like size of the tube, deposition of secretions in the tube, kinking/curvature of the tube, presence of elbow-shaped parts, HME in the circuit Steroids + Relaxants Myopathy

Weaning Role of tracheostmy is uncertain, but due to marginal respiratory mechanics it is thought it may help in weaning. Weaning can be done with PS mode to SBT. In very difficult cases extubation on to NIV is a option Corpulmonale may warrant small dose of inotrope, a dose of diuretic & low fluid strategy during weaning.

IN COPD Preventing VILI is not the primary objective here; Avoiding barotrauma, improving airway clearance, and reducing the consequences of hyperinflation have been the motivators. Yet, use of small VT for avoidance of high plateau pressure, Acceptance of permissive hypercapnia, Judicious use of PEEP to lessen effort and perhaps to reopen compromised airways in some patients now guide the care of obstructed patients as well.

Mechanical ventilation in COPD Asthma drtrc

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