Not all hypotension is from hypovolemia. Then why load every hypotensive patient with #fluids? 🤔 An excerpt from a previous lecture. Very basic. Intended for #medicalstudent #MedEd
Experts, stay away 😄
First, what happens when somebody is hypovolemic?
Experts, stay away 😄
First, what happens when somebody is hypovolemic?
The cardiac output drops
Unless doing #POCUS, we are not measuring cardiac output. We are measuring blood pressure. So, why does it drop? because it depends on the cardiac output!
Now, what does cardiac output (CO) depend on? - stroke volume (SV) and heart rate (HR). Stroke volume is the volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction.
But not all hypovolemia causes significant hypotension or shock state (tissue hypoperfusion). It’s because there are compensatory mechanisms that kick in and try to maintain the blood pressure.
Sympathetic activation causes increase in heart rate as well as venoconstriction leading to increased venous return and thereby stroke volume ultimately increasing the cardiac output.
In addition, activation of the renin-angiotensin-aldosterone (RAAS) system and anti-diuretic hormone/vasopressin leads to vasoconstriction thereby increasing the systemic vascular resistance, and accompanying salt and water retention contributes to maintaining the stroke volume.
So as the compensatory mechanisms work to increase the cardiac output and systemic vascular resistance, the blood pressure improves.
But when the volume loss exceeds the capacity of these compensatory mechanisms, hypovolemic #shock occurs.
In these patients, aggressive fluid resuscitation helps; give what they lost (e.g. blood) and try to stop the ongoing losses.
But In day-to-day clinical practice, undifferentiated shock is more common. Hypotension could be secondary to circulatory failure from various causes.
But In day-to-day clinical practice, undifferentiated shock is more common. Hypotension could be secondary to circulatory failure from various causes.
For example, in cardiogenic shock, the problem is the pump failure, which means the heart Is not able to pump enough blood.
Fluids might worsen the situation here. Address the cause of pump failure and give ionotropic agents as needed.
Fluids might worsen the situation here. Address the cause of pump failure and give ionotropic agents as needed.
What is obstructive shock? Here the pump itself is OK but something is obstructing its work. = the heart is not able to pump effectively because of the extrinsic compression or resistance to outflow.E.g. pericardial effusion, constrictive pericarditis,
tension pneumothorax and acute pulmonary embolism.
Treating the cause quickly is important to relieve the obstruction. E.g. Pericardiocentesis for pericardial effusion, needle decompression/tube thoracostomy for pneumothorax etc.
Treating the cause quickly is important to relieve the obstruction. E.g. Pericardiocentesis for pericardial effusion, needle decompression/tube thoracostomy for pneumothorax etc.
In distributive shock, there is severe peripheral vasodilatation and the blood pools there leaving the vital organs under perfused.
Here the pump is fine and actually working hard but the output is being distributed to wrong places. In this case, Typically seen in septic shock.
Here the pump is fine and actually working hard but the output is being distributed to wrong places. In this case, Typically seen in septic shock.
Other examples include anaphylactic shock and neurogenic shock.
While fluids may help initially in this case (septic shock) to stabilize the tissue perfusion, indiscriminate administration may result in venous congestion and manifestations of fluid overload.
While fluids may help initially in this case (septic shock) to stabilize the tissue perfusion, indiscriminate administration may result in venous congestion and manifestations of fluid overload.
Here is the recent tweetorial on pathologic sequelae of fluid overload in various organs
That's it for now. Lets talk about #POCUS findings in these conditions later. For those of you who prefer video format, here it is 👇
