Measuring Haemoglobin Non-Invasively

No matter how knowledgeable or well-trained a healthcare professional is, he or she cannot perform effectively without the benefit of INFORMATION which is correct and continuously available. Developments in technology mean that the information available to these healthcare professions is constantly being upgraded, information which, when combined with knowledge, leads to improved care for the patient.

Measurements of the haemoglobin (Hb) in a patient’s fluid system, have been critical to indicate what is happening within the patient. Is the patient anaemic, or is he or she losing blood ? Does he or she need a blood transfusion ? All of the above situations carry their own risks in a clinical setting. For example, blood transfusions have been treated as a matter of course in the past. Recently, however, two studies have shown that the risks associated with blood transfusions are significant. In fact, transfusion of a single unit of blood, increased 30-day mortality by 32% and morbidity (pneumonia, sepsis, or surgical site infection) by 23%. The corresponding figures for a two-unit transfusion are 38% and 40% respectively ! Thus, it has become vital for a clinician to know precisely the status of a patient’s haemoglobin concentration, before authorizing what may become a risky transfusion.

In the very recent past, the only method of measuring the haemoglobin of a patient was via an Invasive Blood Draw technique, followed by a laboratory analysis of the sample taken. This was not only a painfully laborious and costly process, it was also time-consuming, and the results were subject to many variables. These variables are of two classes – those connected to the devices used, and physiological variations in haemoglobin measurements.

Amongst the variations exhibited by the devices used, was the inconsistency shown by CO-oximeters manufactured by different Companies. This fact was amply demonstrated by Gehring, who carried out a series of tests on different devices and found out that Hb measurement varied significantly from manufacturer to manufacturer. CO-oximeters are the gold standard when it comes to measuring haemoglobin concentrations. Thus, if measurements varied so greatly between devices of differing makes, how sure was the clinician that the reading he was taking note of, was correct ? 

In today’s fast-moving world, there has been a move towards Point-Of-Care (POC) devices which, whilst offering faster results with smaller samples, are even less accurate than the conventional method of drawing blood and then testing in the laboratory. The photometric determination of Hb in POC devices, typically uses capillary blood drawn from a pin-prick in the patient’s finger. If the clinician were to press the finger to force more blood out, this may inadvertently cause a greater concentration of blood plasma to be present in the sample, thus distorting the end reading of Hb concentration.

Conductometric Analysis uses the concentration of Hematocrit (Hct) to determine the accompanying concentration of Hb. This method is not very cost-effective, but is acceptable in clinical situations where the patient is physiologically normal. It is, however, subject to the same errors as those experienced when clinicians use POC devices to analyse capillary blood. The accuracy of Hct from this technique is severely compromised by changes in sodium levels and protein concentrations in the blood. The use of plasma volume expanders, added anti-coagulants and the presence of elevated white blood cells also affect readings derived from this method. Conductometric Analysis has been shown to be unreliable at Hb levels of 10 g/dL or less, which means that patients suffering from severe anaemia may not have their condition recognized.

Physiologic variations in Hb measurements are primarily caused by four factors, namely : 

Type of Blood Sample – Blood used can be drawn either from arterial or venous sources. Mokken and ZW Yang have reported that on average, arterial Hb measurements are 0.7 – 1.0 g/dL LESS than those for venous blood drawn from the same patient.

Sample Site – The sample site on the body can also affect Hb measurements. Large discrepancies were found between the values obtained from capillary blood samples from the left and right hands of the same women. There are indications that two samples from different fingers of the same person could have Hb concentrations that differ by up to 2.0 g/dL !

Time – Hb measurements can vary significantly over time, even in stable patients. Research shows that this discrepancy can vary by as much as 2.6 g/dL in male subjects, and 2.3 g/dL in female subjects.

Body Position – Body position before and after the blood draw also affects Hb concentrations due to the normal composition of blood, interstitial fluid shifts, and elevations of protein and white blood cells. Venous Hb concentration shows a significant variation due to the differing concentrations of plasma when a person moves from a reclining position to an upright one.

Taking all of the above into consideration, the development of Masimo Corporation’s first-ever Non-Invasive Continuous Haemoglobin Monitor, has come as a god-send to clinicians the world over. Consider some of the comments below :

Ronald Miller, MD, Chief of Anaesthesia, Professor and Chairman of the Department of Anaesthesia and Perioperative Care at the University of California, San Francisco, who stated : “Masimo SpHb is an impressive new tool that helps us to more safely guide patients in surgery through to recovery. With it, not only can we spot haemoglobin changes as they occur, but we can see where they are heading. This ability to identify an upward or downward haemoglobin trend on a second-by-second basis as it occurs has been of tremendous value”.

Randy Marcel, MD, Medical Director and Chief of Anaesthesiology at the Heart Hospital Baylor Plano in Plano, Texas, stated : “In the past, we’ve only been able to catch a glimpse of patients’ haemoglobin levels from lab measurements, but now, we have complete and real-time haemoglobin visibility. We initially purchased SpHb for use during cardiac surgeries in the OR, but brought in additional units for the ICU, where post-operative monitoring of internal bleeding is critical to patient recovery”.

There are many such attestations to the efficacy of Masimo Corporation’s latest offering, including some from far-flung corners of the globe such as Sri Lanka, Libya and France. 

Masimo Corporation has been at the forefront of innovation and technology ever since 1995, when it debuted Measure-Through Motion and Low-Perfusion pulse oximetry, known as Masimo SET®, which virtually eliminated false alarms and increased pulse oximetry’s ability to detect life-threatening events. In 2005, Masimo introduced Masimo Rainbow SET® Pulse CO-oximetry™, a breakthrough non-invasive blood constituent monitoring platform which can measure many blood constituents which previously required invasive procedures. Founded in 1989, Masimo Corporation has the mission of “Improving Patient Outcomes and Reducing Cost of Care by Taking Non-Invasive Monitoring to New Sites and Applications”.

For more information access : www.masimo.c