Noninvasive Hb monitoring device informs blood transfusion decisions during surgery

Continuous total haemoglobin (SpHb) monitoring with a noninvasive device facilitates effective blood management during a major surgery, helping to avoid unnecessary or a delay in transfusions, according to a study.

Compared with conventional blood gas sampling, noninvasive Hb monitoring resulted in less postoperative blood transfusion, shorter stay in the intensive care unit (ICU), and decreased mortality in a cohort of 120 adult patients expected to lose >20 percent of their total blood volume during their elective major surgery, the investigators said. [J Coll Physicians Surg Pak 2022;32:1242-1248]

The noninvasive Hb monitoring device used in the study, a pulse CO-oximeter, uses light-absorbing diode sensors of different wavelengths. This method is similar to the one used when measuring oxyhaemoglobin with conventional pulse oximetry.

An advantage of continuous and noninvasive measurement of Hb over intermittent blood sampling, according to the investigators, is the ability to quickly assess a patient's condition in case of acute blood loss and, therefore, facilitate more appropriate blood management. After all, while monitoring of the patients’ vital signs and tissue oxygenation indicators is necessary, it is the measurement of Hb concentration in the blood that informs whether to perform transfusion or not. [Langmuir 2021;37:11561-11572; Clin Biochem Rev 2007;28:179-194]

“Delays in blood transfusion may result in impaired tissue perfusion. However, unnecessary blood transfusion should be always kept in mind due to potential reactions and complications related to transfusion. Besides increased cost, unnecessary blood transfusions are also associated with an increase in the duration of hospital stay, the incidence of pneumonia, and mortality,” they added. [Health Sci Rep 2021;4:e448; Front Cardiovasc Med 2022;9:874133; Transfus Med Hemother 2022;49:143-157]

Better blood management

Of the 120 patients (mean age 54 years, 57.5 percent male) included in the study, 60 underwent noninvasive Hb monitoring (SpHb group) and 60 did conventional blood gas sampling (control group). The mean duration of anaesthesia was 5.94 hours, and the average time was 5.12 hours.

Haemoglobin, platelet, creatinine levels; the amount of fresh frozen plasma or platelet suspension transfused intraoperatively and postoperatively; and the amount of blood units transfused intraoperatively were similar in the SpHB and control groups. However, the postoperative blood transfusion rate in the SpHb group was significantly lower (median 0 vs 2 international units [IUs]; p=0.020).

Furthermore, postoperative haemoglobin levels of ICU patients in SpHb group were also significantly higher than those of their counterparts in the control group (8.41 vs 7.75 g/dL; p=0.033).

The intraoperative, postoperative, total transfusion rates were positively correlated with postoperative ICU stay (p<0.001, p<0.001, and p<0.001, respectively). On multivariable analysis, factors such as cranial surgery, postoperative transfusion, pH, and SpO₂ had a significant effect on ICU stay (p<0.001, p<0.001, p=0.002, and p=0.017, respectively).

“[The device] was also used for the assessment of volume and perfusion status. Perfusion Index (PI) and Pleth variability index (PVI) were continuously monitored. In this way, the clinicians became aware of any possible discordance between the Hb level and the volume … [a method that allows evaluation of] the fluid response intraoperatively,” according to the investigators.

However, they acknowledged that the device may not replace conventional methods. Instead, it can be used as an auxiliary monitoring technique.

“SpHb measurement in major surgical cases can accompany conventional Hb measurement methods, allowing effective patient blood management practice. It prevents unnecessary blood transfusions by ensuring that the decision of blood transfusion is made at the appropriate time during the surgical intervention and that the appropriate amount of blood and blood products are given to patients,” the investigators said.

Given that mortality and morbidity may be lowered by reducing postoperative blood transfusion, the use of a noninvasive Hb monitoring method in major surgeries may increase patient safety.