Cross-Synaptic Learning for USMLE: Shock, Swanz Ganz Catheters, and pH Derrangements

Summary: Episode 86:  Four categories of shock intuitively with respiratory and metabolic acidoses.<br> <br> Shock<br> A. Causes of hypovolemic shock <br> Diarrhea, blood loss, cholera, sweating, not DI (b/c losing pure water, and not losing Na, total body Na is NORMAL! Losing water from ICF; no signs of dehydration; when you lose salt, show signs of dehydration).<br> Cross-Synaptic Learning Principle = Epidemiology. Other examples include most common causes of death by age group (MC genetic cause of MR = Down Syndrome, MCC of MR = Fetal Alcohol Syndrome, MCC death in youth = accidents).<br> [ad#300×250]<br> Example: lady with hypovolemic shock – when she was lying down, her BP and pulse were normal; when they sat her up, the BP decreased and pulse went up. What does this indicate? That she is volume depleted. This is called the TILT test. Normal BP when lying down b/c there is no effective gravity, therefore normal blood returning to the right side of the heart, and normal CO. However, when you sit the patient up, and impose gravity, you decrease the venous return to right heart. So, if you are hypovolemic, it will show up by a decrease in BP and an increase in pulse. Cardiac output is decreased, and the catecholamine effect causes this scenario. How would you Rx? Normal saline.<br> Example: pt collapses, and you do a tilt test: 100/80 and pulse of 120 while lying down. Sitting up, it was 70/60 and pulse of 150. The pt is severely hypovolemic, therefore Rx is normal saline. Treatment: One liter in, showed no signs, put another liter and the BP becomes normal, and is feeling better, but still signs of volume depletion (dry mouth). We have the BP stabilized, but the pt lost hypotonic salt solution, therefore we need to replace this. So on IV, give hypotonic salt sol’n (b/c was losing hypotonic salt solution). We do not give 5% dextrose and water b/c there’s not any salt in it. Therefore, we will give ½ normal saline. The treatment protocol is: when a pt loses something, you replace what they lost. And when pt is hypovolemic, always give isotonic saline.<br> Example: DKA, have osmotic diuresis; tonicity of fluid in the  urine that has excess glucose is hypotonic. Hypotonic fluid has a little more fluid than salt. So the pt is severely hypovolemic; therefore the first step in management is correction of volume depletion. Some  people are in hypovolemic shock from all that salt and water loss. Therefore need to correct hypovolemia and then correct the blood sugar levels (DKA pts lose hypotonic solution). Therefore, first step for DKA pt is to give normal saline b/c you want to make them normotensive. Do not put the pt on insulin b/c it’s worthless unless you correct the hypovolemia. It can take 6-8 liters of isotonic saline before the blood pressure starts to stabilize. After pt is feeling better and the pt is fine volume wise. Now what are we going to do? The pt is still losing more water than salt in urine, therefore still losing a hypotonic salt solution, therefore need to hang up an IV with ½ normal saline (ie the ratio of solutes to water) and insulin (b/c the pt is loosing glucose).<br> So, first thing to do always in a pt with hypovolemic shock is normal saline, to get the BP normal. Then to correct the problem that caused the hypovolemia. It depends on what is causing the hypovolemia (ie if pt is sweating, give hypotonic salt solution, if diarrhea in an adult give isotonic salt sol’n (ie normal saline), if pt with DI (ie stable BP, pt is lucid) give water (they are losing water, therefore give 5% dextrose (ie 50% glucose) and water).<br> B. Four kinds of shock:<br> 1. Hypovolemic shock:<br> Blood loss, diarrhea (adult or child), basically whenever you are lose salt, you could end up with hypovolemic shock. Give volume.<br> 2. Cardiogenic shock:<br> MC due to MI. Right Ventricular Assist Device and await transplant.<br> 3. Neurogenic shock:<br> Assoc. with spinal cord injuries.