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A New Tool for Monitoring Oxygen in Immobilised Rhinos

Male white rhinoceros with intact horns in Hluhluwe-iMfolozi Park, South Africa
Research · Physiology

Potent opioids used to immobilise white rhinoceroses (Ceratotherium simum) can cause hypoxaemia — abnormally low oxygen levels in arterial blood. Veterinarians therefore need to monitor how well the blood is taking up oxygen. A South African study shows that a relatively simple calculation based on blood samples can give them a useful additional tool.

Researchers studied 16 wild-caught males, aged four to five years, at a facility in Kruger National Park. The animals were immobilised with drug combinations based on the opioid etorphine. Researchers collected blood from an ear artery and compared three ways of calculating oxygen saturation with direct measurements from a laboratory instrument called a co-oximeter.

How much oxygen is the blood carrying?

Most oxygen in the blood is carried by haemoglobin in red blood cells. Oxygen saturation describes how much of haemoglobin’s carrying capacity is being used. Low saturation means less oxygen is available to be transported to the body’s tissues.

A pulse oximeter estimates saturation using a light sensor attached to the animal. In rhinos, these readings can become unreliable when saturation is very low. Direct measurement of blood samples, meanwhile, requires laboratory equipment that is harder to use in the field.

Portable blood-gas analysers are easier to carry. They can measure oxygen partial pressure and acidity, or pH, in a blood sample. The researchers used these measurements to calculate how much oxygen was bound to haemoglobin. Acidity matters because it changes how strongly haemoglobin holds onto oxygen.

The simpler calculation worked best

The most useful approach used the Hill equation, which describes oxygen binding to haemoglobin. The researchers adapted the calculation to the rhinos’ body mass and blood pH. Its results agreed well with laboratory measurements when actual oxygen saturation was between 70 and 100%.

A more complicated version that also accounted for temperature and additional aspects of the blood’s acid–base balance offered no improvement. The third calculation method was sufficiently reliable only between 90 and 100% saturation.

Below 70%, none of the methods met the study’s reliability criterion. Even so, the simpler Hill calculation came closer to direct measurements than previously investigated pulse-oximeter readings at such low saturation.

The researchers have developed a calculator that converts blood-gas measurements into estimated oxygen saturation. It could be particularly useful during prolonged or complex procedures. Each blood sample provides a snapshot, however, so the calculation is intended to complement continuous pulse-oximeter monitoring.

Sources and image credit

  1. Mtetwa, T. K., Meyer, L. C. R., Buss, P. E., Donaldson, A. C., & Snelling, E. P. (2026). Reliability of calculated arterial oxygen-haemoglobin saturation in determining blood oxygenation of immobilised white rhinoceros (Ceratotherium simum). BMC Veterinary Research.Primary open-access research article, published 16 September 2026. Full text checked. Sixteen wild-caught male white rhinoceroses aged 4–5 years were studied at Veterinary Wildlife Services in Kruger National Park, South Africa. The pH-adjusted Hill equation reliably estimated arterial oxygen-haemoglobin saturation from 70–100%, but none of the tested calculation methods met the reliability threshold below 70%.

Image: Male white rhinoceros (Ceratotherium simum) in Hluhluwe Game Reserve, Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa, photographed 8 January 2019. Photo: Bernard DUPONT. Source: Wikimedia Commons. CC BY-SA 2.0. Representative male; not an identified animal from the 2026 study. · CC BY-SA 2.0 · Source

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