Fluids: occult effects. S Magder Department of Critical Care, McGill University Health Centre

Transcription

1 Fluids: occult effects S Magder Department of Critical Care, McGill University Health Centre

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3 Why is volume important? 1. Water is essential to dissolve substances and allow them to diffuse 2. Necessary for bulk flow

4 What does volume do?

5 Volume creates venous elastic recoil force Q = Determinants of flow Stressed Volume Cv x Rv Rv Increase the initial volume Greater flow Cv Stressed volume

6 Heart has a restorative function which refills the veins Volume stretches the veins and creates the recoil pressure that drives flow back to the heart Heart has a permissive function. It lowers the outflow pressure and allows veins to empty

7 Fluid Challenge 1 Assess the value of Pra ( NOT the wedge). Q -ve 2 Give sufficient fluid to raise Pra by ~2mmHg and observe Q. +ve Pra Type of fluid is not of importance if given fast enough

8 Change in CVP of even 1 mmhg should be sufficient to test the Starling response Q (l/min) plateau 5 Slope = 500 ml/min/mmhg 0 10 Pra (mmhg)

9 Non-volume effects +ve 1. Reserves Interstitial unstressed 2. Restore perfusion 3. Non-volume effects Albumin Starch Even saline 1. Filtration -ve 2. Distort the RV 3. Wound healing 4. Liver/renal failure 5. Dilution ScvO 2 Hb INR 6. SID

10 Concept of Stressed and Unstressed Volume SFP MSFP Unstressed volume Unstressed volume provides a reserve that can increase stressed volume Acts like an auto-transfusion Therefore reserves are important

11 MSFP (mmhg) MSFP (mmhg) Change in Capacitance (can recruit ml /kg of unstressed into stressed volume) MCFP (mmhg) MCFP (mmhg) Volume (ml) Volume (ml)

12 Change in Capacitance P MSFP MSFP Q V MSFP MCFP Q MSFP Pra But this volume Can recruit must be restored ~ 10 ml/kg of to provide unstressed to reserves for stressed future needs

13 Importance of interstitial volume 35% 65% 5 L Interstitial IC Provides another important reserve in the system which allows adaption to volume loss

14 Normal Saline in Patient with Large Extra-cellular Volume IC Interstitial IC EC EC The rule that saline distribution is 1/3 vascular 2/3 interstitial is no longer true

15 Non-volume effect of hyperoncotic solution (Albumin 25%, 100 ml) Patients day 1 following cardiac surgery Treating team thought that a fluid bolus would improve cardiac output Patients were 3-5 L positive. Magder & Lagonidis. JCCM 14:164, 1999

16 Albumin vs Saline to Test Volume Responsiveness Pra Cardiac Output delta Pra (mmhg) * * p= ALBUMIN SALINE delta CI (l/min/m 2 ) * p=0.043 ALBUMIN SALINE Magder & Lagonidis. JCCM 14:164, 1999

17 How can cardiac output rise without a rise in Pra? Q Function change It implies a change in both circuit & cardiac function. Volume effect Pra

18 Restore normal perfusion? Restoring cardiac output to normal and improving circulation could turn of cytokine and acute phase response and result in circulatory stabilization.

19 -ve aspects of fluids

20 Starling s Forces Volume increases filtration Pout out Pin in If dialysis can remove 3-4 L without hemodynamic consequences you can loose it into the interstitial space just as fast!

21 Increased back pressure to kidney and liver

22 total time vs Q total time vs HR total time vs CVP total time vs W Q/CVP/Ppao Q=7.1 Q= Time (hours) HR Total fluid removal 8810 L in 3 days

23 Decreased LV function by RV distention RV RV LV LV Can lead to decrease in LV function Decompress Overfill the the right right heart heart

24 Diastolic Ventricular Interaction in Chronic Heart Failure Atherton et al Lancet 1997 Overfilling of the right heart can decrease cardiac function

25 Looks like downward slope to Starling Curve Q Plateau Excess volume decreases cardiac function Volume does not increase cardiac output Pra

26 O 2 Delivery DO 2 = Q x Hb x K x Saturation mlo 2 /min = l/min g/l mlo 2 /g %

27 Increase DO 2 by increase in volume Volume infusion can increase cardiac output if heart not on plateau of the function curve DO 2 = Q x Hb x K x Sat Important consideration in hemorrhagic shock

28 However, 1 l of saline will also dilute [Hb] assuming BV of 4 l (after the bleed) the addition of 1 l of normal saline could decrease [Hb] to 72 g/l DO 2 Q Hb K Sat 369 mlo 2 /min = 3.0 L/min 90 K (1.37) 100% 555 mlo 2 /min = 4.5 L/min 90 K (1.37) 100% 443 mlo 2 /min = 4.5 L/min 72 K (1.37) 100%

29 Amount of H 2 O affects ph 1 Litre 2 Litre Na + Cl meq/l 2 X Na + Cl meq/l SID = 40 meq/l SID = 20 meq/l ph ph 11.66

30 Saline Acidosis SID = 40 Serum Na meq/l Total Body Na + : 140 x 42 = 5880 meq Add 10L of 0.9% saline = /52 = meq/l Serum Cl meq/l Total Body Cl - : 100 x 42 = 4220 meq Add 10L of 0.9% saline = /52 = meq/l SID = 32

31 Occult volume effects +ve 1. Reserves Interstitial unstressed 2. Restore perfusion 3. Non-volume effects Albumin Starch Even saline 1. Filtration -ve 2. Distort the RV 3. Wound healing 4. Liver/renal failure 5. Dilution ScvO 2 Hb INR 6. SID