PITFALLS WITHPITFALLS WITH

MECHANICALMECHANICAL

Prof David V. Tuxen Prof David V. Tuxen Dept of Intens Care & Hyperbaric MedDept of Intens Care & Hyperbaric Med

The Alfred HospitalThe Alfred Hospital

he "passed away from an asthma attack" on Monday after paramedics worked to revive him for 50 minutes

Thunderstorm Asthma1. Jul 1983: Birmingham, England2. Nov 1987: Melb, Australia3. Nov 1989: Melb, Australia4. Jul 1994: London, England5. Oct 1997: Wagga Wagga, Australia6. Jun 2004: Naples, Italy7. Nov 2010: Melb, Australia8. Nov 2013: Ahvaz, Iran9. Nov 2016: Melb, Australia10.Dec 2016: Kuwait

Nov 2016: Melb, Australia>8500 ED presents 9 deaths – HC F 20 31 min OM M 18 15died in amb MP M 35

CL M - 70SL M 49

PITFALL 1Patient severe asthma required intubation and mech vent

(FIO2 0.5, RR 18, Vt 700 ml, PaO2 105, PaCO2 55, pH 7.23, Bic 22)

→ BP↓ 80 (CVP 16) → Fluid fill → BP↓ 95 (CVP 18) → Inotropes

What is the problem?

1.Hypovolaemia

2.Pneumothorax

3.Respiratory tamponade

4.LRTI with septic shock

5.Unsuspected cardiac disease

DYNAMIC HYPERINFLATION

GAS TRAPPING

LUNG

VOL.

(L)

Te

Vt

Vei

Normal/Stiff lungs

Obstructed lungs

Vtr

Tuxen & Oh. In Intensive Care Manual1989;192-201

SPONT vs MECH VENTILATION

Tuxen ARRD 1992;146:1136-42Tuxen ARRD 1987; 136: 872-9Spont Ventilation

NORMAL TLC

0

1

2

3

4

5

6

7

8

LUNGVOLUME

(L)

NORMAL FRC

Mech Ventilation

Dynamic HI Apnoea Tidal V.

FRC

Vtr

VT

Auto-PEEP

Pepe & Marini,ARRD 1982;126: 166

EFFECTS

of VE,

VT & R

Tuxen & Lane.Am Rev Respir Dis1987; 136: 872-879

(cm H2O)

10 16 26

0

1

2

3

4V TV EE

VEI

PIP

Pplat

LUNGVOL(L)

FRC

0

20

40

60

80

100

VT

VEVI

0.6 1.0

100

1.6 0.6 1.0

100

1.6 0.6 1.0

100

1.6

ACUTE SEVERE ASTHMA

Ve REQUIREDfor normal PaCO2/pH:

10-25 L/min

Ve SAFEfor VEI < 20ml/kg:

115 ml/kg/min(8 L/min)

HYPOTENSION in mostPNEUMOTHORAX in some >1/3 of MV MORTALITY

HYPOTENSION in mostPNEUMOTHORAX in some >1/3 of MV MORTALITY

PaCO2 50-90 , pH 7.0-7.3BUT NO HYPOTENSION PNEUMOTHORAX MORTALITY

PaCO2 50-90 , pH 7.0-7.3BUT NO HYPOTENSION PNEUMOTHORAX MORTALITY

ASTHMA - VENTILATOR Mx

1. SEDATE & minimal PARALYSE (NMBA)

2. HYPOVENTILATE: VE 115 ml/min/kg, VT <8 ml/kg, R 10-12 VI 80-100 L/min or Te ≥ 4 sec

3. ASSESS DHI (VEI, Pplat, PEEPi ), BP in apnea, blood gases

4. ADJUST VENTILATION BASED ON DHI (not PaCO2 / pH)

(DHI↑ → reduce rate, DHI↓ → increase R)Tuxen. ARRD1992;146 (5): 1136

Same patient, severe asthma, heavy sedation, and ventilated

FIO2 0.4, RR 12, VT 600 ml, VI 80 L/min PaO2 90, PaCO2 60, pH 7.23, Bic 24

BP 110, HR 95, CVP 8, Pplat 25, PEEPi 10

Nursing complain - repeated high pressure alarm (P limit 50 cmH20)

RMO - good air entry both sides, transient P limit ↑ → PIP 58 cmH20

RMO reduces VI to 40 L/min → PIP↓ 40 cmH20 → alarm stops. Calls you.

What should you do 1. Well done! (back to sleep)2. CXR3. VI back to 80 & ↑ PIP limit4. Restore VI to 80 & ↓ RR5. Other

PITFALL 2

EFFECTSEFFECTS

of Vof VEE &V &VII

Tuxen & LaneARRD1987; 136: 872

0

20

40

60

80

PIP

(cm H2O)

Pplat

LUNG

VOL

(L)

0

1

2

3

4VT

VEEVEI

FRCV I

V E

100 70

10

40 100 70

16

40 100 70

26

40

PITFALL 328 yo ♀ admit severe asthma - 2/7 slow improve on neb salbut & IV H’cort

Then deteriorates with increasing dyspnoea & wheeze

RR↑ 28 → 40, PEF↓ 120 → 80, PaO2 75, PaCO2 40, pH 7.42, Bic 25

Rx - contin neb salbut, aminophylline bolus+ 40 mg/hr, IV salbutamol 12 mcg/min, & Tx to ICU.

4 hrs - increasing dyspnoea & distress, RR↑ 50, PEF 200, Chest - minimal wheezeGases: FIO2 0.4, PaO2 85, PaCO2 30, pH 7.36, Bic 16

What is going on?

LACTIC ACIDOSIS

Asthma + IV Salbutamol → LACTIC ACID IN 70 %

Se Lact 5.5 ± 2.5 (2-12)

2 Patterns Ambulance Salb. Bolus (500-750mcg /15-30min)

Hospital Salb. Infus (5-20 mcg/min)

Management Bolus <500 mcg, infus <10 mcg/min

Measure lactate if Bic <22 or decrease >2

Reduce or cease IV Salb. if lact too high

PITFALL 4

A 56 yo female with severe acute on chronic asthma required prolonged MV including high dose asthma Rx and 4 days paralysis.

After 10 days MV, airflow improved considerably BUT patient incapable of weaning - tachypnea & hypercapnia.

O/E: Severe limb weakness, hyporeflexia, sensation intact

What has happened??

Normal MuscleNormal Muscle

Necrotising MyopathyNecrotising Myopathy

EFFECTS OF VENTILATORY STRATEGIES

AdrenalineVentolin (ETT)PancuroniumAdrenaline x 2Bicarb (25 meq)Ca Gluconate

PITFALL 536 yo F - rapid asthma deterioration - emergency intubation & ventilation Vt 600 ml, R 12-14 /min

5 min - P 113, BP unrecordable, ECM commenced

15 min - pH 7.08, PCO2 96, PO2 36, Sat 46%, Bic 27 ECG 60 SR, pulseless, cyanosed, FD pupils, neck veins distended Pericardial tap unrewarding, CXR - no pneumo

25 min - ECM ceased

30 min - HR 120, BP 110, neck viens down

33 min - Re-ventilated : Vt 600 ml, R6-8 /min pH 7.04, PCO2 91, PO2 396, Sat 100%, Bic 27 Pupils reacting, BP maintained. Rosengarten, Tuxen. Anaes & Int Care 1990;19:118

SEVERE HYPOTENSION / EMD

Almost always due to excessive dynamic hyperinflation(May have secondary tension pneumothoraces)

Best management

1. Apnea test

2. Profound hypoventilation (RR 4-6)

3. Colloid fluid loading

MOST DIFFICULT MECH VENT

Eg Hypotension,high PIP despite RR<6, PaCO2 >100, pH <7.00

1. Adenaline, Mg, Ketamine

2. Bicarb, fluid load & more hypoventilation

3. Heliox (50:50)

4. Inhalational anaesthetic (halothane or isofluorane)

5. ECMO (should not be needed)

PITFALL 6

33 yo, 67 kg female with severe asthma – sedated, paralysed & MVRR 12, VT 600 ml, VI 80 L/minFIO2 0.4, PaO2 90, PaCO2 60, pH 7.23, Bic 24

MV stable then: PIP/Pplat↑ 35/20 → 48/33, BP↓105 → 90 , HR↑ 100 → 140O/E Reduced air entry on left, trachea ? shifted to right

What is the most appropriate 1st action (1 only) 1. Reduce RR 2. Urgent CXR3. Inotropes 4. Blind ICC(s)5. Colloid fluid loading 6. IC Jelco

ASTHMA CXR

PNEUMOTHORAX

CAUSES - DHI, CVC, Jelco’s (spontaneous is rare)

EFFECTS - PROPENSITY FOR TENSION due to AO→ Ipsilateral VE↓ → Contralateral VE↑→ Contralateral DHI↑ → RISK B/L PNEUM ↑

MANAGEMENT – Suspected → Reduce RR + urgent CXRSevere BP↓ → BLIND ICCALL ICC’s - BLUNT INSERTION

PNEUMOTHORAX

Most commonly due to excessive dynamic hyperinflation or CVC

Best management when clinically suspected 1. Reduce RR (protect 2nd lung)

2. No intercostal needles (unless in extremis)

3. Urgent CXR

4. Intercostal catheter with blunt dissection

Severe hypotension – urgent ICC (with blunt dissection)

CONCLUSION - Asthma MV

1. DHI – VE <8L/min, low Vt, High VI (↓Ti)

2. Accept high PIP (short Ti) – Pplat<25

3. Avoid Lactic acidosis – salbutamol dose

4. Avoid myopathy – minimize NMBA. Steroid Mx

5. Pneumothorax – reduce RR, avoid needles if poss

6. Hypotens/EMD – Apnea test, RR 4-6