Hemorrhagic Shock: Diagnosis

00:01 So let’s talk about the path of physiology of hemorrhagic shock.

00:04 Very simply, hemorrhage means blood loss.

00:07 Shock means tissue level hypoxia.

00:10 So hemorrhagic shock refers to inadequate blood flow in order to oxygenate tissues.

00:16 The tissues aren’t getting enough blood supply to get the oxygen supply that they need to meet their metabolic demands.

00:24 Physiologic compensation can mask the effects of blood loss.

00:28 So especially early in the course of blood loss, patients are very good at increasing their cardiac output, increasing their heart rate, increasing their vascular resistance in order to maintain tissue level perfusion.

00:41 And this can make it difficult to identify shock in the early stages.

00:45 So we have to really be vigilant in looking for signs of hemorrhagic shock in our patients.

00:50 The hemorrhagic shock is divided up into different classes.

00:53 And it’s not so much important to memorize all of the features of every class of shock.

00:58 But it is important to understand how shock progresses clinically and to note that it’s a non-linear progression.

01:04 So different classes of shock are divided up according to how much blood you lose.

01:09 You’ll note that in class 1 shock, you’re losing under 15% of your blood supply.

01:15 In class 2 shock, you’re losing up to 30% of your blood supply which is quite a lot.

01:20 In class 3 up to 40% and in class 4 more than 40%.

01:25 But here’s a really interesting stuff.

01:27 So in class 1 shock, you typically are not even gonna be tachycardic.

01:31 You’re gonna have a normal blood pressure, normal respirations, normal urine output and a normal mental status.

01:38 So you can loss 750 CCs of blood which if you saw that strewn around the room would be quite impressive to you.

01:44 That is a lot of blood loss.

01:47 Yet you’re gonna have almost no physiologic derangement from that.

01:50 Now, when you get up into class two shock, you’re gonna start to see, maybe development of a little bit of tachycardia and maybe some narrowing of the pulse pressure.

01:59 So now, our sympathetic nervous system has started to kick in.

02:03 We’re responding to blood loss by raising the heart rate, raising the vascular tone which is gonna increase our pulse and increase our diastolic blood pressure to narrow our overall pulse pressure.

02:17 However, we’re still really not gonna have not much in the way of tachypnea, maybe a little bit.

02:23 We should have reasonably normal urine output.

02:26 And while the patient might feel anxious, they’re not necessarily gonna be confused or altered.

02:32 However, when you get up over 1.500 CCs we begin to really significantly decompensate.

02:37 So this is where we begin to see significant tachycardia.

02:42 And this is the first place where we see the hypotension.

02:45 Patients also will be uniformly tachypnic.

02:47 They’re gonna begin to lose their urine output.

02:50 And they’re gonna be confused or lethargic in terms of their mental status 'cause they’re not getting great cerebral perfusion.

02:56 So as we lose more and more blood, our physiologic derangements get worse.

03:00 But it’s important to recognize that it happens in a non-linear fashion.

03:04 So when we lose 500 to 1.000 CCs of blood, our overall clinical status is really pretty good.

03:11 But we start to sort of deteriorate a little bit around 1.500 CCs, but then when we get over that level, we actually deteriorate quite rapidly.

03:21 So you can see this is a non-linear progression and up at the higher ends of the blood loss curve, you’ll have more significant clinical manifestations with relatively less blood loss.

03:32 This is all the product of compensation.

03:35 So small amounts of blood loss or really moderate amounts of blood loss, we compensate for very well.

03:41 But once we exceed our ability to physiologically compensate, really, everything starts to deteriorate and we start to see these life threatening signs and symptoms that we are all familiar with.

03:53 So one of the things to remember about hemorrhagic shock is that the clinical signs, at least up until the bitter end are relatively unreliable.

04:02 Now, vital signs correlate pretty well with how much acute blood loss the patient has, but other kinds of things like capillary refill and skin turgor, and pallor and those kind of things.

04:15 They’re not necessarily terribly reliable, especially in adults.

04:19 Vital signs are more useful but there are exceptions to these rules.

04:24 So at extremes of age, you’ll see differences in how patients physiologically compensate.

04:32 Kids are notorious for compensating extremely well up until the very bitter end at which point they will begin to deteriorate extremely rapidly.

04:41 Older people might not have much capacity to compensate at all and might show signs of shock with relatively less blood loss.

04:49 There is also the consideration of medications.

04:52 So patients who are on beta blockers, calcium channel blockers, other kinds of drugs that blunt the physiologic response to blood loss can make it more difficult to assess the clinical degree of blood loss the patient has.

05:04 And lastly, healthy young people will often have low resting heart rates.

05:10 It’s not uncommon for young people, especially trained athletes to have heart rates in the 40s or 50s.

05:15 So they might have significant blood loss with the heart rate of 80.

05:19 That’s not technically tachycardic for the overall population but it is for that person.

05:25 So you always wanna interpret vital signs in the context of the patient’s baseline physiologic state, especially in as much as you know what it is.

05:35 So really important thing to remember on hemorrhagic shock is that any vital sign abnormality should be taken seriously.

05:41 Remember, when we looked at the classes of shock, the first vital sign to change is gonna be the heart rate.

05:48 So tachycardia is gonna occur once the patient has lost between 750 and 1.500 CCs of blood.

05:57 We don’t wanna wait until the patient becomes grossly tachycardic or hypotensive to start considering the possibility of blood loss, because you don’t develop those findings until very late in the process of hemorrhagic shock.

06:11 You have to lose more than 1.500 or 2.000 CCs to clinically appear frankly shocky.

06:19 So the bottom line is if your patient is tachycardic, if their pulse pressure is narrowing, if they have any early finding suggestive of hemorrhagic shock, you wanna take it seriously, you wanna identify the source of bleeding and you wanna reverse it.

06:33 Because if you wait until your patient is hypotensive, they would have already loss a significant amount of blood and their outcomes are gonna be bad.

06:41 To identify hemorrhagic shock in a trauma patient, it is recommended to take into account laboratory testing in addition to vital signs. Heart rate and blood pressure alone are not reliable. The following tests are to be ordered in every patient you suspect of having hemorrhagic shock: Arterial blood gases, hemoglobin level, lactate and hematocrit. These tests are useful only if performed periodically. A single-time testing is not useful in this setting.