How to differentiate between different types of shock, given Cardiac Output, Vascular Resistance, Left End Diastolic Volume (Pulmonary Capillary Wedge Pressure), and Venous Oxygen Saturation
Great vid series, thank you for sharing! Why would mixed venous oxygen saturation drop in dissociative shock? I understand the tissues are starved of oxygen and will pull out any oxygen possible. But, if the left shift of the oxyhemoglobin curve occurs then oxygen is retained on hemoglobin and stays in blood. My understanding is that these highly saturated hemoglobin molecules would then return to the heart with a high oxygen content due to the inability to dissociate. In other words, if the mixed venous oxygen content is low, doesn't that indicate that oxygen is readily dissociating from hemoglobin?
Hi John, that's an excellent question! You are in fact correct, the MVO2 is high, since oxygen remains bound to hemoglobin. What I meant to say is that the oxygen content in the blood that is NOT bound to hemoglobin is low, because that will be pulled out by the tissues. Thank you for pointing this out.
According to UWorld: Obstructive shock has a decreased PCWP but an increased CVP which differentiates it from cardiogenic shock which is increased in both
Thank you for pointing this out! I'm thinking a redo video should come to explain the different types of shock, and to explain why PCWP can be either elevated or low. Just think about where the blood is measured (pulm capillaries) vs. where the obstruction is. If the obstruction is behind the pulm capillaries (like in PE), PCWP is lower. Obstruction after the pulm caps (aortic stenosis) causes build up of pressure upstream to the pulm caps, and thus PCWP is actually higher. Constrictive pericarditis and tamponade prevent blood from even entering into the constricted heart, so generally the PCWP should be low, to even normal (pressure from the pericardium or pericardial space causes pressure on the LV that is transmitted through the walls of the heart, aka transmural pressure). I appreciate the comment! So much of my understanding has improved since I made this video in medical school.
@@LiveLifeMD Okay that makes a lot more sense. So basically, UWorld says CVP is high and PCWP is low because the most common causes of obstructive shock are cardiac tamponade, constrictive pericarditis, tension pneumothorax, and pulmonary HTN all which are going to restrict LV filling making PCWP lower leaving the IVC backlogged making CVP higher. Especially considering that in obstructive shock, the heart is functioning properly, the PCWP should be low or normal. Thank you for responding!
