About Shock Index: The Shock Index (heart rate divided by systolic blood pressure) is a simple, rapid measure of physiological compromise. Originally developed in emergency medicine, it is now emerging as a critical tool in maternal health, particularly in LMICs where resources are scarce but the burden of maternal mortality is highest.
New evidence and a recent paper published in eClinical Medicine has demonstrated how impactful the shock index is in predicting risk in pregnant women.
Severe bleeding after birth (postpartum haemorrhage) and maternal sepsis remain the leading causes of preventable maternal deaths worldwide, particularly in low-resource settings. A growing body of evidence now shows that the Shock Index (SI)—a simple measure combining heart rate and blood pressure—can help frontline health workers rapidly identify women at greatest risk of life-threatening complications, where rapid triage and simple treatments can save lives efficiently and effectively.
How this finding was discovered
Professor Andrew Shennan realised that early identification was key to saving lives in maternity, particularly after his experience working in Africa. Time was critical in sepsis and bleeding, yet life-saving interventions are widely available and cost-effective. The pulse will rise long before clinical signs, and a falling blood pressure may only be noticed too late when it is already profound. The team studied retrospective data from Nigeria, Egypt and the UK in sick pregnant women and worked out that by combining both the pulse and the blood pressure (and making it a single reading, a ratio), abnormal vital signs could be identified earlier. A falling blood pressure reading and rising pulse rate indicate shock for either sepsis or haemorrhage.
Traffic light system in CRADLE Vital Signs Alert Device
With this knowledge, the team decided to put the shock index into the CRADLE Vital Signs Alert (VSA) device as an alerting system, in the form of a traffic light. Their data determined that if the shock index is greater than 1.7, it is concerning and is indicated by a red light. If there is an index of less than 0.9, the green light indicates that all is good. Initial studies across Asia and Africa with the VSA looked promising, including reducing referrals in nearly all countries and, in some countries, saving lives.
Initial studies using Shock Index
The CRADLE 2 trial considered what the correct levels were to use. The clinicians in Nigeria put on a form of ‘wetsuit’ on the patients in the study to prevent them from collapsing. In terms of predictions and ruling in and ruling out, the traffic lights needed to prove that using this system was valuable. The Cradle 2 study took place in South Africa in three hospitals: Groote Schuur Hospital, Tygerberg Hospital and Kimberley Hospital.
CRADLE 3 used the outcomes of hysterectomies as an endpoint for sepsis and haemorrhage. The study examined whether shock index impacted hysterectomies and found that it reduced them by 80%. The eight countries involved were India, Haiti, Ethiopia, Sierra Leone, Zambia, Malawi, Zimbabwe and Uganda. Referrals for bleeding were also halved in most countries.
The secondary analysis examined what happened to referrals for bleeding and showed that referrals for bleeding were halved. This resulted in reduced hysterectomies, reducing the resources needed to do these. It also resulted in the ability to target hysterectomies better, thereby improving outcomes.
Landmark Study in Sierra Leone
In one of the largest prospective studies of its kind, conducted across three maternity hospitals in Sierra Leone, researchers demonstrated that the Shock Index consistently predicted serious outcomes, including maternal death, among women presenting with bleeding or sepsis.
Because SI requires no specialised equipment, it offers a practical, low-cost solution for triaging patients in resource-limited environments.
Further Impact Through CRADLE Device
The EMOTIVE study, a large multi-centre LMIC randomised controlled trial, further confirmed the device’s impact. Incorporating CRADLE VSA as part of a bundle of interventions to reduce postpartum haemorrhage led to a 60% reduction in the primary outcome, which included maternal death.
Expanding Applications
Beyond bleeding and sepsis, researchers are exploring new uses for Shock Index, including:
- Antenatal anaemia screening – A study in Karnataka, India found abnormal SI strongly associated with severe anaemia.
- Malaria detection – Work in Bidibidi Refugee Settlement, Uganda showed SI can help identify patients with malaria, a leading cause of death in sub-Saharan Africa and globally.
These findings highlight SI’s potential as a versatile screening tool across multiple maternal and infectious disease contexts.
Next Steps
The research team is now conducting qualitative work to understand how best to integrate CRADLE VSA and Shock Index into existing early warning scores and management pathways. The ultimate goal is to embed SI into routine maternal care, ensuring timely, life-saving interventions for women most at risk.
The latest publication in eClinical Medicine, a high-impact journal, has showcased the impact of the CRADLE VSA and the World Health Organisation (WHO) is putting together a care bundle for managing postpartum haemorrhage. A treatment trolley, including this device, is being recommended by the WHO.
This led to the need for an automated device that records the readings. This has resulted in another project, CRADLE Rapid, which will, for the first time ever, show a number of the shock index. This small desktop device displays shock index with recordable readings.
Shock Index and including this information in the CRADLE VSA device is an exciting, novel and key aid to saving lives through early identification. It provides a powerful means to identifying risk and assists clinicians in their management of risk. It indicates the need for major surgery, severe anaemia or the need for ICU admissions. The contemporary study reflects, in large numbers, a powerful triage system.