Retinal arterial blood flow and retinal changes in patients with sepsis: preliminary study using fluorescein angiography

The retina is considered to be one of the most metabolically active tissues in the body [1]; hence, hypoperfusion might lead to a higher probability of microcirculatory and structural retinal changes. Methods such as advanced retinal photographic imaging techniques and computer-assisted image analysis might be used to characterize, measure, and quantify even subtle variations and abnormalities in the retinal microvasculature [2]. Retinal fluorescein angiography has been used to study microvascular changes during and after cardiac bypass [3] and could be a new instrument for noninvasive observation of retinal microcirculatory changes in association with cerebral microemboli [4, 5].

Microcirculatory alterations are common in sepsis. Sublingual and gastric mucosal microcirculatory abnormalities in animal models with septic shock have been well described [6]. Severe microcirculatory sublingual derangements measured by orthogonal polarization spectral or sidestream dark-field imaging techniques are proposed to be better predictors of outcome than global hemodynamic variables [7, 8]. Furthermore, the cerebral microcirculation was impaired in animal models of sepsis [9]. In humans, proinflammatory and anti-inflammatory cytokines are released after microbial invasion with excessive sympathetic outflow. The proinflammatory response is responsible for the hemodynamic consequences of sepsis, namely vasodilation and hyperdynamic state or even myocardial depression [10, 11]. Patients have low resistance, high cardiac output circulation, tachycardia, and hypotension.

In this single-center preliminary study of sepsis in an intensive care unit (ICU) population, we measured retinal blood flow using retinal fluorescein angiography. We hypothesized that alterations in retinal blood flow visualized by angiography may relate to macrohemodynamics, levels of inflammatory mediators, and retinal microvascular pathologies and reflect brain dysfunction or the clinical severity of sepsis.

During the 2012–2015 study period, a total of 667 patients with sepsis were screened for the present study. Of those, 342 patients met the study criteria, and 309 were admitted outside office hours or during times when there was no possibility for retinal angiography to be performed, leaving 33 patients who were included in the study. Two patients later refused to participate, leaving 31 patients for the final analysis.

Patients with arterial PRAFT had higher APACHE II scores (22.5 [21.2–29.5] vs. 20 [15–21], P = 0.049), and their IOP was higher (17.8 [14.7–22.1] mmHg vs. 14 [12.5–15.5] mmHg, P = 0.029). Retinal abnormalities were more frequent in those with PRAFT (81% vs. 20%, P = 0.001) (Table 1).

Cardiac index measured with a thermodilution technique using a pulmonary catheter was lower in those with PRAFT before angiography (2.1 [1.7–2.5] vs. 3.1 [2.5–3.2], P = 0.042) and at angiography (2.1 [1.7–2.4] vs. 2.6 [2.2–3.1], P = 0.039). There were no differences in the doses of vasopressors, mean arterial pressures, or serum lactate levels between the PRAFT and SRAFT groups during angiography (Table 2, Fig. 1).

	All patients (N = 31)	Patients with short arterial filling time <8.28 seconds (n = 15)	Patients with prolonged arterial filling time >8.28 seconds (n = 16)	P value
Intraocular pressure at angiography, mmHg	15.7 [13.3–19.5]	14.0 [12.5–15.5]	17.8 [14.7–22.1]	0.031
Retinal changes, n (%)	16 (51.6)	3 (20)	13 (81.3)	0.001
Mean blood glucose level, mmol/L	7.8 [6.8–10.4]	8.9 [7.7–10.2]	8.1 [7.2–9.4]	0.36
CRP at angiography, mg/L	160 [114–316]	254 [146–366]	139 [77.7–224.5]	0.011
CRP, highest before angiography, mg/L	264 [149–380]	307 [161.7–435.7]	187 [99.5–363.5]	0.104
PCT at angiography, μg/L	3.87 [1.96–12.2]	0.387 [1.96–12.2]	7.06 [1.9–31.8]	0.28
PCT, maximum before angiography, μg/L	9.4 [2.4–36.6]	11.6 [6.7–30.3]	6.7 [0.96–61.9]	0.669
Platelets, lowest before angiography, ×109/L	170 [124–219]	184.5 [166–270.7]	146 [98.5–202.3]	0.056
Platelets, lowest at angiography, ×109/L	149 [90–185]	167 [123–209]	96 [84–178]	0.07
PT-INR, highest before angiography	1.3 [1.15–1.9]	1.2 [1.1–1.6]	1.45 [1.27–2.2]	0.025
PT-INR, highest at angiography	1.35 [1.2–1.67]	1.25 [1.17–1.45]	1.45 [1.2–2.1]	0.09
Noradrenaline dose, highest before angiography, μg/kg/minute	0.2 [0.06–0.53]	0.23 [0.073–0.64]	0.167 [0–0.38]	0.47
Noradrenaline dose during angiography, μg/kg/minute	0.04 [0–0.24]	0.0242 [0–0.61]	0.050 [0.005–0.23]	0.71
Cardiac index, lowest before angiography, L/minute/m2	2.4 [1.7–3]	3.1 [2.5–3.2]	2.1 [1.7–2.5]	0.042
Cardiac index, during angiography, L/minute/m2	2.3 [1.9–2.7]	2.6 [2.2–3.1]	2.1 [1.7–2.4]	0.039
MAP at angiography, mmHg	73.9 [68–88]	78.5 [69.5–88.8]	69.6 [65.5–89.2]	0.49
MAP below 65 mmHg before angiography, minutes	13.6 [8–33]	11 [4.5–37.5]	23 [8–33]	0.470
Lactate angiography, mmol/L	1.9 [1.3–2.5]	1.75 [1.31–2.5]	1.98 [1.34–2.54]	0.62
Lactate, highest before angiography, mmol/L	3.4 [1.9–8.6]	2.97 [2.2–6.7]	6.05 [1.87–10.03]	0.61
BE lowest before angiography, mmol/L	−7.8 [−13.5 to −4.8]	−7.8 [−12.9 to −3.3]	−7.9 [−14.1 to −7]	0.467
BE during angiography, mmol/L	−4.3 [−7.9 to 0.375]	−3.2 [−7.5 to 0]	−4.9 [−11.1 to 0.9]	0.57
PaO2, mmHg	12.3 [11.4–14.5]	11.4 [10.3–13.8]	12.2 [9.9–13]	0.66
PaCO2, mmHg	4.9 [4.5–6]	5.2 [4.6–6]	5.1 [4.2–5.9]	0.77
PaO2/FiO2 ratio, mmHg	31.5 [23.6–37.1]	34.6 [23.8–47.9]	34.2 [23.8–43.7]	0.95

Abbreviations: CRP, C-reactive protein, PCT, Procalcitonin, PT-INR, Prothrombin time international normalized ratio, MAP, Mean arterial pressure, BE, Base excess, PaCO ₂ , Partial pressure of carbon dioxide in arterial blood, PaO ₂ /FiO ₂ ratio Ratio of partial pressure of oxygen in arterial blood to fraction of inspired oxygen

Pathological retinal findings were present in 16 patients (51.2%) (Fig. 2). The most common retinal abnormality was fluorescein-leaking retinal microaneurysm (56%), followed by vitreous hemorrhage (13%) and other retinal hemorrhages (6.5%). The abnormal retinal findings were present in 13 (81.3%) of 16 patients in the PRAFT group and 3 (20.0%) of 15 patients in the SRAFT group (P = 0.001). In surviving patients, the abnormal retinal findings were found to have resolved in control angiography.

The IOP was higher in the prolonged RAFT group (18 mmHg vs. 14 mmHg, P = 0.031). Interestingly, 16% of all the patients with sepsis studied had ocular hypertensive pressures (IOP >21 mmHg). There were no differences in ICU, 30-day, or 365-day mortality rates between the two patient groups with different arterial filling times (Table 1). In the control angiography of the survivors performed 3–6 months following ICU discharge, the median RAFT was 12.56 (12.1–14.9) seconds, and there were no differences between the PRAFT and SRAFT groups.

In the present preliminary prospective study, we found that, first, patients with sepsis and PRAFT had retinal abnormalities and experienced higher IOPs more frequently than those with sepsis and SRAFT. Second, patients in the PRAFT group had a significantly lower cardiac index and lower IL-6 and CRP levels. Third, these patients had higher APACHE II scores upon admission.

To the best of our knowledge, this is the first study involving measurement of retinal blood flow in human patients with sepsis and exploration of the feasibility of this measurement to reflect the macro- and microcirculation. The decision to use median time as the cutpoint value for prolonged RAFT could be considered a limitation of the present study. Because there are no reference values for RAFT, and owing to the limited sample size, we decided to use the median in this pilot study. Patients with SRAFT had higher cardiac indexes and more elevated levels of inflammatory markers. This is in line with the hyperdynamic hemodynamic state often seen in early sepsis with a proinflammatory phase [15]. In contrast, the relationship between the cardiac index and microcirculatory perfusion has not been demonstrated using sublingual techniques [16, 17]. However, in another study with an early goal-directed fluid therapy and vasoactive medication protocol, sublingual microcirculation flow velocity correlated with mean arterial pressure and mixed venous oxygen saturation [18]. According to an animal model of hyperdynamic septic shock, arterial flow is increased in the mesenterial artery, whereas ileal microcirculation is decreased. Taken together, human organ blood flow distribution varies between different organs in patients with sepsis, and according to our results, it follows changes in cardiac output.

Our results suggest that retinal angiography may be used to estimate the macrocirculation and could provide a new technique for noninvasive monitoring of the central nervous system. These findings generate ideas for future studies on the applicability of retinal blood flow as a tool for the assessment of microcirculation and cerebral circulation in particular. In our series, prolonged retinal blood flow was related to retinal microcirculatory abnormalities. Further studies are needed to evaluate whether retinal blood flow changes are related to systemic microhemodynamics. It may be possible to evaluate the severity of illness by simply looking into the patient’s eye with a fundus camera, which is accessible and also easily affordable for the ICU clinician.

In the present series, the IOP was higher among patients with PRAFT. Similarly, correlation between increased IOP and delayed filling time of the retinal veins was suggested in an earlier study in patients with glaucoma [19, 20]. Decreased IOP was previously reported in patients with Puumala virus infections, with a mean IOP of 4.5 mmHg [21]. To our knowledge, intraocular hypertension has not previously been documented in patients with sepsis. In our series, 16% had IOP >21 mmHg.

In our study, retinal abnormalities were observed in half of the patients with sepsis and were more common in patients in the PRAFT group (81%). Microvascular changes in the retina are usually associated with diabetes and hypertension [22]. In our series of patients admitted to the ICU with sepsis, we found fluorescein-leaking retinal microaneurysms and retinal hemorrhages. In harmony with our results, intra- and periretinal hemorrhages were observed in a previous study of patients with severe acute pancreatitis [23]. In that study, retinal changes were associated with multiple organ failure syndrome. In our series, patients with retinal changes were more severely ill on admission (APACHE II score 22.5 [21.2–29.5] vs. 20 [15–21], P = 0.049).

A novel finding of the present study is the fluorescein-leaking retinal microaneurysms. Pathological processes such as inflammation or ischemia may upset the normal retina-blood barrier in the retinal capillaries, thereby allowing extravascular leakage of fluorescein. Even transient hypoxia, for example, can increase the permeability of the retinal arterioles even with normal intraluminal blood pressure and may also later involve the venous side [24]. These permeability changes are thought to be related to changes in the vascular endothelial cells. In our patients, sepsis-related lower cardiac indexes and elevated IOPs with altered, prolonged retinal blood flow may have produced transient retinal hypoxia and may have resulted in the development of retinal microvascular abnormalities. In our study, inflammatory parameters measured (IL-6, CRP) at the same time as retinal blood flow were significantly higher in those with shortened retinal filling time. In our series, the rapid retinal blood flow could thus be linked with the hyperdynamic hemodynamic and proinflammatory responses.

This preliminary study demonstrates that retinal angiography could be a feasible monitoring technique for the ICU. The retinal blood flow, IOP, and microvascular angiopathies were linked in the patients with sepsis. Patients with RAFTs more than 8.3 seconds had a lower cardiac index and more frequently had retinal angiopathies, higher IOP, and lower levels of inflammatory markers, indicating an impaired inflammatory response.