•In circulatory shock, the ScvO2 is generally greater than SvO2 with a difference of 5–18%.

•The goal of early resuscitation, within 6 h of septic shock, is to keep SvO2 more than 65% or ScvO2 more than 70%.

•A fiberoptic central venous and a pulmonary artery (PA) catheter is available for

continuous measurement of ScVO2 and SvO2, respectively, by reflection spectrophotometry for continuous monitoring.

Step 11: Interpret lactate levels

•Lactate levels often reflect anaerobic metabolism due to tissue hypoxia.

•High and rising levels (>2 mmol/L) has adverse prognosis, while falling lactate levels indicate an adequate response to resuscitation of the shocked patient.

•Lactate levels may increase due to increased production due to global or local tissue hypoxia but also due to stimulation of glycolysis and metabolic pathways that accelerate lactate formation in sepsis. Adrenaline infusions can increase lactate levels by accelerating glycolysis.

•High lactate levels may also represent decreased clearance due to reduced liver blood flow or hepatic dysfunction.

•Thus, interpretation of lactate levels may be complicated.

•Also, arterial lactate levels are a global measure, and regional hypoperfusion of some vascular beds may exist even in the presence of normal lactate levels.

Step 12: Integrate findings (see Appendix 2)

•The aim is to use hemodynamic monitoring to optimize preload using either CVP or fluid challenges, dynamic indices such as SVV or PPV, or passive leg raising.

•The cardiac output should be monitored, and oxygen delivery variables should be optimized.

•Determine improvement of oxygen delivery and demand ratio by noting increase in ScvO2 and decrease in lactate levels.

•Clinical improvement in mentation, heart rate, blood pressure, and hourly urine output should be checked.

•Calculated hemodynamic and oxygenation parameters (see Appendix 2).

Suggested Reading

1.Antonelli M, Levy M, Andrews PJF, et al. Hemodynamic monitoring in shock and implications for management. International Consensus Conference, Paris, France, April 27–28, 2006. Intensive Care Med. 2006;33:575–90.

One of the most important recommendations is that hypotension is not required to define shock, and as a result, importance is assigned to the presence of inadequate tissue perfusion on physical examination. Given the current evidence, the only biomarker recommended for diagnosis or staging of shock is blood lactate. It was also recommended against the routine use of (1) the pulmonary artery catheter in shock and (2) static preload measurements used alone to predict fluid responsiveness.

2.Jardin F. Cyclic changes in arterial pressure during mechanical ventilation. Intensive Care Med. 2004; 30:1047–50.

3.Reinhart K, Kuhn HJ, Hartog C, Bredle DL. Continuous central venous and pulmonary artery oxygen saturation monitoring in the critically ill. Intens Care Med. 2004;30:1572–8.

Continuous fiberoptic measurement of central vein O2 saturation has potential to be a reliable and convenient tool which could rapidly warn of acute change in the oxygen supply/demand ratio of critically ill patients.

4.De Backer D. Lactic acidosis. Intens Care Med. 2003;29:699–702.

5.Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, Peterson E, Tomlanovich M. Early goal directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med. 2001;345:1368–77.

Websites

1.Lane.stanford.edu

Basic guideline on interpretation of vascular waveform

2.www.edward.com

An industry website with nice illustrations

3.www.covidien

An industry website with advanced monitoring technology

4.Clinicalcenter.nih.gov

NIH guideline on basic hemodynamic monitoring