The most important finding of this research is PPI can predict hypotension happened on surgical patients in the first 1 hour and is associated with length of ICU stay. If PPI can reach 1.15 in the first hour in ICU, it predicts patients could discharge from ICU within 48 h, with 73.8% sensitivity and 90.0% specificity.
Patients undergoing long time surgeries tend to manifest high level of lactate. This is a multifactorial phenomenon. Slow lactate clearance rate, inadequate perfusion, massive blood transfusion and application of anaesthetic drugs, all of these can lead to increased serum lactate after surgery[9–11]. It is known to us all that hyperlactacidemia is a strong indictor of poor prognosis[12, 13], because it will deteriorate internal environment and lead to multiple organ dysfunction. We should minimize the length of hyperlactacidemia as much as possible. In regard to surgical patients, especially who are transferred to ICU after surgeries, going through big operations is a challenge. On top of that, they are at risk of increased blood lactate[1–3]. So, it is essential to ensure adequate perfusion to accelerate lactate clearance and shorten the length of hyperlactacidemia. If we can recognize hypotension in the early phase, we can take measures to improve perfusion more quickly and the shorten length of hyperlactacidemia.
We need indicators to guide clinic interventions to ensure perfusion. Despite that a lot of indexes have been proved useful in directing treatment, many of them are invasive or not real-time, which would weaken their significance in guiding therapies or predicting prognoses in the early phase. Compared to other indicators that are used in guiding shock treatment, PPI is non-invasive and real-time. Studies on PPI have confirmed its significance on reflecting tissue perfusion in critically ill patients[6, 15, 16].
Based on many previous researches, we carried out this retrospective study and confirmed that in the first hour in ICU, PPI has its role in predicting whether the patients would discharge within 48 hours or not, with a reasonable accuracy (73.8% sensitivity and 90.0% specificity). If we look forward, after 6 hours in ICU, for patients with PPI ≥ 1.35,they have 96.7% possibility of discharging from in the first 2 days. As time went by, after 12 hours, PPI of both groups could reach 1.2(1.23 ± 0.28 vs 1.22 ± 0.34), a value indicating an acceptable regional prefusion. No association was found between PPIT1 and LOS ICU.
Lactate and LCR are widely regarded as prognostic indexes for shock patients[2, 4, 12, 13]. Although in this study, both lactate (T1, T2) and LCR(T0 − 1) still have their significances, compared to PPI, which could be used to predict outcomes in the first hour in ICU, their shortcomings are obvious, not to mention that they’re invasive and not real-time.
It’s known to us all that at the initial period of hypoperfusion, peripheral vessels contract in order to supply enough blood returning to heart[17, 18]. In this phase, macro vital signs, like HR and BP, are normal. Because macro circulation is stable, lactate doesn’t increase. But PPI, which reflects regional perfusion, will decrease for the vessels contraction. This makes PPI superior to other macro parameters in indicating potential hypoperfusion.
Different to other studies, our research not only proved PPI’s predictive role in hypoperfusion, but also found its association with length of ICU stay. These findings help physicians to take measures more quickly, which may be helpful in improving patients’ outcomes.
Low temperature and vascular diseases are the two main confounding factors which could affect value of PPI. In this study, we excluded all patients with diseases affecting blood flow of upper limbs. In our routine nursing, we give warm-keeping service to all the patients, for example covering blankets. If necessary, we provide warm blower to keep patients warm. Besides, by comparing temperature between the 2 groups, no significant difference was found. Above all could exclude the confounding effects on PPI.