Haemorrhagic shock

Blood volume is normally 7% body weight (5 litres in a 70 kg man). Acute loss of circulating blood leads to compensatory

Albumin

Albumin

Figure 5.3 Capillary leak after major surgery or in critical illness. Electron microscopy in rats with severe sepsis shows holes that appear in the endothelium

Pre-operative Surgery 24-hour

Figure 5.4 Microalbuminuria as a measure of capillary leak during surgery and in systemic inflammatory response syndrome (SIRS)

Pre-operative Surgery 24-hour

Figure 5.4 Microalbuminuria as a measure of capillary leak during surgery and in systemic inflammatory response syndrome (SIRS)

responses. Tachycardia is the first measurable sign. At the cellular level, inadequately perfused cells compensate initially by anaerobic metabolism producing a lactic acidosis. Mild metabolic acidosis is common following major surgery for this

Table 5.3 Estimated fluid and blood losses based on patient's initial presentation (for a 70 kg man)

Losses

Class 1

Class 2

Class 3

Class 4

Blood loss (ml)

Up to 750

750-1500

1500-2000

Over 2000

Blood loss or

Up to 15%

15-30%

30-40%

Over 40%

tennis score

loss

loss

loss

loss

(% blood vol)

Pulse rate

< 100

> 100

> 120

> 140

Blood pressure

Normal

Normal

Reduced

Reduced

Pulse pressure*

Normal

Reduced

Reduced

Reduced

Respiratory rate

14-20

20-30

30-40

> 35

Urine output

(ml h-1)

> 30

20-30

5-15

Negligible

CNS

Alert

Mild

Anxious and

Confused and

anxiety

confused

lethargic

*Pulse pressure is the difference between systolic and diastolic blood pressure. (Adapted with permission from the American College of Surgeons: Committee on Trauma. Advanced Trauma Life Support for Doctors. Student course manual. 6th edn. Chicago: American College of Surgeons, 1997.)

*Pulse pressure is the difference between systolic and diastolic blood pressure. (Adapted with permission from the American College of Surgeons: Committee on Trauma. Advanced Trauma Life Support for Doctors. Student course manual. 6th edn. Chicago: American College of Surgeons, 1997.)

reason and a persistent metabolic acidosis in some patients may indicate inadequate fluid resuscitation. Eventually cell membrane damage and cell swelling occurs which leads to fluid shifts. The best way to think of haemorrhage is by using tennis scores (Table 5.3).

By the time blood pressure has dropped in a healthy patient because of bleeding, at least 30% of circulating blood volume has been lost. Certain groups do not manifest the usual signs of hypovolaemia: athletes can compensate for blood loss very well, patients on beta blockers or calcium antagonists may not generate a tachycardia, and patients with permanent pacemakers and the elderly also have altered responses. Therefore a 30% loss of blood volume (nearly 2 litres in an average adult) is the smallest amount of blood loss that consistently causes a drop in systolic blood pressure - classical haemorrhagic shock.

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