seanrowley1

Hi Guys, I will do my best to explain Stroke Volume Variance (SVV). It is easier to discuss verbally but I will give it a try here. SVV is a value given in % and it measures the ave variation of the beat to beat stroke volumes through out the respiratory cycle. If a patient is fluid responsive, i.e. more volume will improve stroke volume and thus improve cardiac output then you will see a high variation. This happens because the patients great vessels cant withstand the intra thoracic pressure changes caused by the vent. If the patient is adequetely volume recusitated then the vessals will be be more full and then able to withstand those pressure changes better. Think of a firehose.........if you have the water running through a firehose at full blast then it is really tough to squeeze the hose and slow down the flow. However, if you cut the amount of water going through the hose way down then you will find it's easier to squeeze and then you can slow down and speed up flow depending on how hard you squeeze it. Now apply this idea to what is happening intra thoracicly (sp?) If your patient is not adequetely volume resucitated then as the pressure increases from the vent pushing a breath of air in it will put pressure on your great vessels which will impede venous return back to the heart. If venous return is decreased then your stroke volume will decrease. Then when the intra thoracic pressure drops as the vent backs off the vessels open up and venous return is increased which now causes an increase in stroke volume. SVV is measuring the difference between the largest stroke volume and the smallest stroke volume over that respiratory cycle. If the patient is adequetely volume resucitated then their vessels will able to withstand those changes in intra thoracic pressure much better and your variation will be lower. I hope this helps and doesn't confuse things more. Have a great weekend.