Q: Why not just use hypotension (SBP <90) as the threshold?

Hypotension is a late sign of shock. The SI detects compensated shock where HR rises before BP falls (due to endogenous catecholamines). A patient with BP 110/70 but HR 120 has SI 1.09 and is haemodynamically compromised despite non-hypotensive BP. The SI identifies these patients earlier.

Q: Can the Shock Index be used in patients on beta-blockers?

Beta-blockers blunt the heart rate response to hypovolaemia, which may result in a falsely low SI in a shocked patient. In these patients, the SI is less sensitive; alternative markers of tissue hypoperfusion (lactate, base deficit, skin mottling) become more important.

Q: What is the role of the Shock Index in paediatric patients?

In children, the SI varies with age (higher normal values in younger children). Age-adjusted SI percentiles have been published. SI >90th percentile for age has been associated with poor outcomes in febrile children and injured children. Age-specific thresholds should be used.

Question 1

Why not just use hypotension (SBP <90) as the threshold?

Accepted Answer

Hypotension is a late sign of shock. The SI detects compensated shock where HR rises before BP falls (due to endogenous catecholamines). A patient with BP 110/70 but HR 120 has SI 1.09 and is haemodynamically compromised despite non-hypotensive BP. The SI identifies these patients earlier.

Question 2

Can the Shock Index be used in patients on beta-blockers?

Accepted Answer

Beta-blockers blunt the heart rate response to hypovolaemia, which may result in a falsely low SI in a shocked patient. In these patients, the SI is less sensitive; alternative markers of tissue hypoperfusion (lactate, base deficit, skin mottling) become more important.

Question 3

What is the role of the Shock Index in paediatric patients?

Accepted Answer

In children, the SI varies with age (higher normal values in younger children). Age-adjusted SI percentiles have been published. SI >90th percentile for age has been associated with poor outcomes in febrile children and injured children. Age-specific thresholds should be used.

Question 4

What is a 'reversed' Shock Index (rSI)?

Accepted Answer

The reversed Shock Index is SBP/HR. A rSI <1 is equivalent to SI >1. Some clinicians prefer rSI because higher values are reassuring (rSI >1 = stable) aligning with conventional thinking (higher BP and lower HR are better). Both provide identical information.