Relation between mean arterial pressure and renal function in the early phase of shock: a prospective, explorative cohort study

Abstract

Introduction: Because of disturbed renal autoregulation, patients experiencing hypotension-induced renal insult might need higher levels of mean arterial pressure (MAP) than the 65 mmHg recommended level in order to avoid the progression of acute kidney insufficiency (AKI).

Methods: In 217 patients with sustained hypotension, enrolled and followed prospectively, we compared the evolution of the mean arterial pressure (MAP) during the first 24 hours between patients who will show AKI 72 hours after inclusion (AKIh72) and patients who will not. AKIh72 was defined as the need of renal replacement therapy or "Injury" or "Failure" classes of the 5-stage RIFLE classification (Risk, Injury, Failure, Loss of kidney function, End-stage renal disease) for acute kidney insufficiency using the creatinine and urine output criteria. This comparison was performed in four different subgroups of patients according to the presence or not of AKI at the sixth hour after inclusion (AKIh6 as defined as a serum creatinine level above 1.5 times baseline value within the first six hours) and the presence or not of septic shock at inclusion.The ability of MAP averaged over H6 to H24 to predict AKIh72 was assessed by the area under the receiver operating characteristic curve (AUC) and compared between groups.

Results: The MAP averaged over H6 to H24 or over H12 to H24 was significantly lower in patients who showed AKIh72 than in those who did not, only in septic shock patients with AKIh6, whereas no link was found between MAP and AKIh72 in the three others subgroups of patients. In patients with septic shock plus AKIh6, MAP averaged over H6 to H24 or over H12 to H24 had an AUC of 0.83 (0.72 to 0.92) or 0.84 (0.72 to 0.92), respectively, to predict AKIh72 . In these patients, the best level of MAP to prevent AKIh72 was between 72 and 82 mmHg.

Conclusions: MAP about 72 to 82 mmHg could be necessary to avoid acute kidney insufficiency in patients with septic shock and initial renal function impairment.

Figure 1

Flow diagram. RRT: renal replacement therapy.

Figure 2

Evolution of mean arterial pressure (MAP) during the first 24 hours. The evolution of hourly MAP (left panels) and of MAP time-averaged MAP (right panels) compared between patients who will have acute kidney insufficiency (AKI) at H72 (black squares) and those who will not (open squares), is shown for the whole population (top panels), for the group of patients with no AKI at H6 (middle panels) and for the group of patients with AKI at H6 (bottom panels). The significant differences observed in MAP (from H10 to H24 for hourly MAP and from H12 to H24 for time-averaged MAP, as indicated by an asterisk upon each time point) between patients who will or will not have AKI at H72 in the whole population (top panels) were mainly due to the patients with AKI at H6 (bottom panels). Asterisks upon time points indicate a significant difference (P < 0.05) between patients who will have AKI at H72 (black squares) and those who will not (open squares) (post hoc comparison after analysis of variance). Error bars represent standard errors.

Figure 3

Mean arterial pressure (MAP) according to the presence or not of septic shock. The MAP (from H6 to H24 for hourly MAP and for time-averaged MAP) was significantly lower in patients who will than in those who will not have AKI at H72 in the septic shock population (as indicated by an asterisk upon each time point) (bottom panels), while no difference was found in the non septic shock patients (top panels). Asterisks upon time points indicate a significant difference (P < 0.05) between patients who will have AKI at H72 (black squares) and those who will not (open squares) (post hoc comparison after analysis of variance). Error bars represent standard errors.

Figure 4

Mean arterial pressure (MAP) according to the presence of septic shock or acute kidney insufficiency. The MAP (from H6 to H24 for hourly MAP and for time-averaged MAP) was significantly lower in patients who will than in those who will not have AKI at H72 only in the sub-group of patients with septic shock and AKI at H6 (as indicated by an asterisk upon each time point in the bottom panels). Asterisks upon time points indicate a significant difference (P < 0.05) between patients who will have AKI at H72 (black squares) and those who will not (open squares) (post hoc comparison after analysis of variance). Error bars represent standard errors.

Figure 5

Performance of mean arterial pressure to predict acute kidney insufficiency (AKI) at H72. The areas under the receiver operating characteristics curves (AUC) of time-averaged MAP over H6 to H24 (left panel) and over H12 to H24 (right panel) to predict acute kidney insufficiency (AKI) at H72 was examined in four subgroups of patients: patients with no AKI at H6 and non septic shock (black thin line), patients with no AKI at H6 and septic shock (dashed thick line), patients with AKI at H6 and non septic shock (dashed thin line), and patients with AKI at H6 and septic shock (black thick line). In this latter subgroup, the AUC (see values in Table 3) was significantly higher than in the three others subgroups for time-averaged MAP over H6 to H24 (left panel) (P = 0.0037 vs the no AKI at H6 and septic shock patients; P = 0.0037 vs the no AKI at H6 and non septic shock patients; P = 0.02 vs the AKI at H6 and non septic shock patients) and over H12 to H24 (right panel) ((P = 0.0065 vs the no AKI at H6 and septic shock patients; P = 0.002 vs the no AKI at H6 and non septic shock patients; P = 0.036 vs the AKI at H6 and non septic shock patients). MAP: mean arterial pressure.

Figure 6

Vasopressors doses administered during the first 72 hours. To draw this figure we summed the hourly doses of norepinephrine and epinephrine (μg/kg/min.) administered continuously by iv infusion, considering these two catecholamines as equipotent in term of vasopressor activity. It shows that the doses of vasopressor administered were higher in patients who will show acute kidney insufficiency at H72 (squares) compared to those who will not (circles), particularly during the first 24 hours, and that this difference was retrieved in septic shock (black squares and circles) and in non septic shock patients (open squares and circles).