Effects of mechanical ventilation on organ function Masterclass ICU nurses
Case Male, 60 - No PMH - L 1.74 m and W 85 kg Pneumococcal pneumonia Stable hemodynamics - No AKI MV in prone position (PEEP 16 - FiO2 60%) Intensivist / fellow / nurses discuss the following questions at the bedside:
Questions What is the effect of mechanical ventilation on right ventricular function? What is the effect of mechanical ventilation on left ventricular function? Besides its effect on the circulation, what are the effects of MV on kidney function What are the effects of MV on cerebral blood flow and intracranial pressure?
Cardiac output = Venous return
What happens with changing metabolic needs Cardiac output 5 L HR 75/min SV 66.7 ml EF 65% Cardiac output 20 L HR 150/min SV 77 ml EF 75% = 11.5 L Large increase in CO mainly explained by in venous return
Venous return curve 6 5 Venous return CO (l/min) 4 3 2 1 0-6 -4-2 0 2 4 6 8 10 12 14 16 18 20 CVP (mm Hg)
It is not arterial pressure that drives venous return MAP (mmhg) and SVI (ml/m2) 100 80 60 40 20 MAP (mmhg) SVI (ml/m2) *** *** *** 0 Baseline 1 Hr 4 Hrs 6 Hrs Terlipressin in septic shock Albanèse J. Crit Care Med 2005;33:1897-1902
SVC Main function of RV is to keep RAP low Towards RV 0 RAP = 0 After fluid challenge Venous resistance IVC VR = MSFP - RAP Venous resistance mm Hg 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 Before After Mean Systemic Filling Pressure Cecconi M. Intensive Care Med 2013;39:1299-1305
VCS Pleura Pericard RA VCI 100 Relative increase compared to airway pressure (%) 75 50 25 70 37 43 0 Pleural pressure Pericardial pressure Central venous pressure Lansdorp B. Crit Care Med 2014;42:1983-1990
Tv 400 ml PEEP 16 MSFP VCS Pleura Pericard MAP 22 cm H20 RA 6.5 RA mmhg VCI
What happens with RV afterload? Extra-alveolar blood vessels - + + + + Alveolar blood vessels Pulmonary vascular resistance Total vascular resistance Alveolar blood vessels Extra-alveolar blood vessels RV FRC TLC
Do you think RV failure is improved by proning?
IAP VR PaO2 Central BV RV preload Recruitment PVR RV afterload LV preload No No CO increase Yes Preload reserve CO increase Jozwiak M. Am J Respir Crit Care Med 2013;188:1428-1433
ARDS (N = 16) 5,5 P < 0.05 800 P < 0.05 CI (l/min/m2) 4,5 3,5 DO2 (ml/min/m2) 700 600 500 2,5 Supine Prone 400 Supine Prone IAP (mmhg) 20 18 16 14 12 10 8 P < 0.05 GFRI (ml/min) 100 80 60 40 20 NS 6 Supine Prone 0 Supine Prone Hering R. Anesth Analg 2001;92:1226-1231
Prone position and RV failure Before PP After 18 h of PP P-value SAP (mm Hg) 115 ± 12 117 ± 14 NS HR (bpm) 107 ± 15 100 ± 13 0,019 CI (l/min/m 2 ) 2.9 ± 0.8 3.4 ± 0.8 0,013 RVEDA/LVEDA 0.91 ± 0.22 0.61 ± 0.21 < 0,001 Septal eccentricity 1.5 ± 0.2 1.1 ± 0.1 < 0,001 TR (n) 20 7 LVEDV (ml) 45 ± 13 64 ± 21 < 0,001 LVEF (%) 58 ± 11 60 ± 9 NS N = 21 Severe ARDS with PF < 100 Veillard-Baron A. Chest 2007;132:1440-1446
What happens with LV afterload? 90 90 0 20 10 30 Spontaneous ventilation LV pressure should increase 80 mmhg to open AV Mechanical ventilation LV pressure should increase 60 mmhg to open AV
What happens with LV afterload? Positive pressure ventilation may decrease LV afterload Alveolar pressure 20 Alveolar pressure 20 14 14
MV for cardiogenic shock IABP IABP + MV P-value UP (ml/uur) 55.1 ± 33 142 ± 38 < 0.001 RRsys (mmhg) 104 ± 17 104 ± 10 NS CI (l/min/m2) 3.2 ± 0.45 3.7 ± 0.7 0.025 PCWP (mmhg) 21 ± 5 16 ± 4 0.025 Heart rate 104 ± 19 93 ± 11 0.102 Dobutamine 6.7 ± 2.3 2.5 ± 3.3 0.002 ph 7.3 ± 0.1 7.42 ± 0.03 0.002 Intensive Care Med 1999;25:835-838
Effects on renal function Hemodynamic Slower loss of fluid from vasculature Normal Rapid vascular refilling with fluid removal Cardiac output Normal oncotic pressure Arterial Venous CVP Normal intersitium Neurohormonal Interstitial oedema Fluid therapy Ultrafiltration Renal blood flow Low oncotic pressure Increased capillary permeability Plasma protein leak Hypoalbuminaemia Decreased GFR Rapid loss of fluid from vasculature Systemic inflammation Slow vascular refilling with fluid removal Fluid retention
PCO2 PO2 Brain metabolism ICP Jugular vein Autonomic centers CVP 1 2 3 4 Resistance vessels Conduit vessels CO SVR MAP
Starling resistor model ICP ICP An increase in ICP raises outflow pressure and capillary fluid flux Thoracic pressure only increases ICP if CVP > ICP
PEEP and ICP increase 35 30 25 ICP (mm Hg) 20 15 10 ** ** 5 0 PEEP 0 PEEP 5 PEEP 10 PEEP 15 ICP normal ICP increased McGuire G, et al. Crit Care Med 1997;25:1059-1062
PEEP and ICP increase mm Hg 90 80 70 60 50 40 30 20 10 0 PEEP 0 tot 5 PEEP 6-10 PEEP 11-15 ICP CPP Huynh T, et al. J Trauma 2002;53:488-493
Conclusions MV decreases RV and LV preload MV has variable effects on RV and LV afterload MV decreases renal function MV decreases cerebral blood flow and has a variable effect on ICP