| Is there a role for prone ventilation in the
management of ARDS ? Dr N Bailey Ipswich Hospital Return To Tutorial Table Of Contents Acute Respiratory Distress Syndrome Acute severe respiratory failure of noncardiac origin. Characterised by severe hypoxia and pulmonary oedema. Typically associated with very poor lung compliance and associated with a known precipitating event.
Incidence: Overall incidence 4.0-75 per 100 000 per year (Scandinavia 94 ALI 17/100,000 ARDS 13/100,000) Outcome: Mortality varies 40 to 60% Most die of non respiratory complications during the supportive phase of ARDS rather than hypoxia Survivors relatively good quality of life.
Diagnostic Criteria Acute Onset CXR: Bilateral infiltrates No apparent cardiogenic cause - pulmonary capillary wedge pressure of < 18mmHg - or lack of clinical evidence of L Atrial Hypertension Known trigger or risk factor Hypoxia Acute Lung Injury: Pa02/FiO2 <300 ARDS Pa02/FiO2 < 200 Bernard et al 1994
Case Study 57 year-old male. Presented with Hx inc SOB right sided pleuritic chest pain, fevers, rigors and anorexia. Unwell for one week pre-presentation. Unremarkable medical history Smoker 40 /day smoking Hx 40+ pkt yrs Case Study- Presentation Arrival A&E HR-130 BP-95/40 RR-40. SaO2 80% O2 @ 15 litres – reservoir mask. Auscultation widespread bronchial breathing. Intubated in A&E Post intubation inotropic infusion & drug paralysed.
ICU Admission Ventilated:- Press. Controlled Ventilation PEEP 15 + 20 Press support RR 15 FiO2=1 Resulting in T.Vol approx 600 ml & SaO2 of 90 percent. Bronchoscopy bilaterally inflamed bronchi and brown mucinous material present. Antibiotic therapy erythromycin, ceftriaxone and gentamicin initiated. Diagnosis septic shock 20 to Community Acquired Pneumonia. Case Study- Day 1 Difficult ventilation – persisting hypoxemia Bld Gases pH 7.2 Pa02 52 PaC02 66 ABE -4 HC03 25 FiO2=1 (PaO2/FiO2 = 52) Trialled various ventilation strategies Various PEEP Recruitment manoeuvres Trialled Prone ventilation – minimal improvement.
Case Study – Day 2 Patient hypotensive minimal response to inotropes. Hypoxic- Sa02 of 80 percent with P. Controlled ventilation Fi02 of 1. Failing to improve with modification of ventilatory modes Demise in the early hours of the morning despite aggressive therapy.
Management of ARDS Removal of the precipitating/underlying cause Ventilatory support Oxygenation with min. ventilatory trauma Low tidal volumes of 5 to 7 mls / kg Limit inspiratory press PIP <35 cmH20 Permissive hypercapnia ?? Permissive hypoxia p02 55-65 mmHg Management- Techniques Alveolar Recruitment PEEP inc. PaO2 with min. Fi02.(10 to 20 cm) Ventilator facilitated recruitment techniques Physiotherapy Ventilation strategies Inverse ratio / newer modes. Nitric Oxide Prone Ventilation
Other management options Steroids (Meduri et. al.) Surfactant PDE inhibitors ECMO Ketoconazole Prostaglandin Inhibitors
Question ? Does prone ventilation help improve clinical outcomes ?
Prone Ventilation- Method Does not require a special bed Requires special care & supportive staff Support for shoulders, upper chest, pelvis (Free movement of chest ) Extreme care of ETT & lines Rotated in 2 step procedure – Side then prone Pressure care – esp. eyes
Prone Ventilation- Problems Adequate staff numbers Pressure care Free movement of chest wall / neck / Face & eyes ETT & Line displacement Obese patient Presence of other injuries Need for increased sedation Transient desaturation Facial oedema
Extensive literature confirms the positive effect on PaO2
Limited outcome studies Does prone ventilation reduce mortality in ARDS ? EFFECT OF PRONE POSITIONING ON THE SURVIVAL OF PATIENTS WITH ACUTE RESPIRATORY FAILURE
NEJM 2001;345:568-73. Multicentre randomised study over three years involving 304 patients with acute lung injury or ARDS. Patients were assigned to either supine ventilation or prone ventilation for a period of six (or more) hrs/day for 10 days
Prone Ventilation- Study Aim Primary:-Determine if prone ventilation improved survival in patients with Acute lung injury or ARDS. End Pt: Death:- 10/7, ICU Discharge, 6/12 Secondary:- Improvements in respiratory failure & organ dysfunction at 10 days
Prone Ventilation- Methods Ventilator settings pre rotation to continue for duration of prone ventilation. Ventilated as per American-European Consensus Conference on mech. ventilation. No other aspects of the management controlled by the study.
Prone Ventilation- population Patients were randomised & list was concealed Study sample – Criteria 20 percent decrease in 10 day mortality at a power of 80 percent if the total number of deaths at this time was at least 95. Trial stopped after the enrollment of 304 patients and 70 deaths Stopped early in part because of difficulty in persuading units to omit prone ventilation as a care protocol
Prone Ventilation Study - Patient Profile
Prone Ventilation- variations Supine group:- 12 patients (43 manoeuvres) treated in the prone position 20 severity hypoxia. Prone group: 91 missed periods of pronation in 41 patients Prone Ventilation- Results Mortality (Prone vs Supine):
10 days: 21.1% vs 25.0% [32 vs 38 deaths] Rel risk death (prone) 0.84 - confid Interval 0.56-1.27
ICU Discharge: 50.7% vs 48.0% [77 vs 73 deaths] Rel risk death (prone) 1.05 - confid Interval 0.84-1.32
6 months: 62.5% vs 58.6% [95 vs 89 deaths] Rel risk death (prone) 1.06 - confid interval 0.88-1.28
That is no statistically significant difference
Prone Ventilation- Respiratory Variables
Prone Ventilation-Post Hoc Results Groups showing significantly lower mortality at 10 days Quartile with lowest PaO2/FiO2 ratio (<88) 23.1% vs 47.2% Rel. risk of death (prone) 0.46 95% confid. Interval 0.25-0.95 Quartile with highest SAP II score. 19.4% vs 48.5% Rel. risk of death (prone) 0.40 - 95% confid. interval. 0.19-0.85 Quartile with highest tidal vol. (>12ml/kg) 18.2% vs 41.0% Rel. risk of death (prone) 0.44 - 95% confid. interval. 0.20-1.00
Prone Ventilation- Results Main study reported no significant benefit from prone ventilation Post Hoc Analysis showed some sub groups had significantly lower mortalities in the first 10 days. (Differences in mortality rate did not persist beyond discharge from ICU) Prone Ventilation Secondary results: Oxygenation improved in prone ventilation. In 73% of pronation procedures PaO2/FiO2 increased by more than 10. No difference in incidence of organ dysfunction. No. of days without non pulmonary organ failure similar (2.7±3.7 days-prone group & 2.8 ±3.6 days-supine group, P=0.83).
Prone Ventilation - Complications
Prone Ventilation- Discussion Study size – the power analysis is confusing – If criteria of 20% decrease in mortality at a power of 80% with death rate 60% you need 270 cases Numbers recruited sufficient for analysis 6/12 (death rate 60%) Numbers insufficient for analysis at 10/7 (death rate 23%) where a power analysis suggest population of 1200 Stopped early in part due to difficulty in persuading units to omit prone ventilation as a care protocol – ?? strong proponents of prone ventilation
Post Hoc Analysis Are the results valid – Post Hoc Analysis Identifies benefit in severe disease Further study of prone ventilation in severe ARDS
IMPRESSION Negative mortality study ? Sample size May require more specific population A sub group with resistant hypoxia Complications do occur ? Underplayed in this study. Prone Ventilation – Our conclusions Still no supportive outcome evidence for its use Proponents in some centres – as per study Need motivated staff at all levels Probably worth using if persistent hypoxia. |
