Hemodynamic Parameters Change Earlier Than Tissue Oxygen Tension in Hemorrhage

Methane Exhalation Can Monitor the Microcirculatory Changes of the Intestinal Mucosa in a Large Animal Model of Hemorrhage and Fluid Resuscitation

Background: Internal hemorrhage is a medical emergency, which requires immediate causal therapy, but the recognition may be difficult. The reactive changes of the mesenteric circulation may be part of the earliest hemodynamic responses to bleeding. Methane is present in the luminal atmosphere; thus, we hypothesized that it can track the intestinal circulatory changes, induced by hemorrhage, non-invasively. Our goal was to validate and compare the sensitivity of this method with an established technique using sublingual microcirculatory monitoring in a large animal model of controlled, graded hemorrhage and the early phase of following fluid resuscitation.

Materials and Methods: The experiments were performed on anesthetized, ventilated Vietnamese minipigs (approval number: V/148/2013; n = 6). The animals were gradually bled seven times consecutively of 5% of their estimated blood volume (BV) each, followed by gradual fluid resuscitation with colloid (hydroxyethyl starch; 5% of the estimated BV/dose) until 80 mmHg mean arterial pressure was achieved. After each step, macrohemodynamic parameters were recorded, and exhaled methane level was monitored continuously with a custom-built photoacoustic laser-spectroscopy unit. The microcirculation of the sublingual area, ileal serosa, and mucosa was examined by intravital videomicroscopy (Cytocam-IDF, Braedius).

Results: Mesenteric perfusion was significantly reduced by a 5% blood loss, whereas microperfusion in the oral cavity deteriorated after a 25% loss. A statistically significant correlation was found between exhaled methane levels, superior mesenteric artery flow (r = 0.93), or microcirculatory changes in the ileal serosa (ρ = 0.78) and mucosa (r = 0.77). After resuscitation, the ileal mucosal microcirculation increased rapidly [De Backer score (DBS): 2.36 ± 0.42 vs. 8.6 ± 2.1 mm⁻¹], whereas serosal perfusion changed gradually and with a lower amplitude (DBS: 2.51 ± 0.48 vs. 5.73 ± 0.75). Sublingual perfusion correlated with mucosal (r = 0.74) and serosal (r = 0.66) mesenteric microperfusion during the hemorrhage phase but not during the resuscitation phase.

Conclusion: Detection of exhaled methane levels is of diagnostic significance during experimental hemorrhage as it indicates blood loss earlier than sublingual microcirculatory changes and in the early phase of fluid resuscitation, the exhaled methane values change in association with the mesenteric perfusion and the microcirculation of the ileum.

Blood Loss Estimation in Small Animals and Assessment of a Pictorial Tool to Improve Accuracy in a Global Population of Veterinary Anesthesia Staff

Visual estimation of blood loss is the most common form of evaluating intraoperative hemorrhage, and is also the most inaccurate. This study investigated the visual estimation accuracy of a global population of anesthesia staff and students as an initial estimation and also with the assistance of a pictorial guide. A voluntary, two-part, online, anonymous survey was distributed to members of two email databases with an interest in anesthesia, including students, nurses, interns, residents, general practitioners, and specialists. The survey consisted of visual and brief descriptive depictions of blood loss scenarios involving small animals, principally including images of common surgical items and receptacles containing a blood-like substance. Each participant estimated the blood volume (in mL) for each scenario twice, initially (Pre-Guide [PGD]) and then with the aid of a pictorial guide (With-Guide [WGD]). The pictorial guide used similar images labeled with corresponding volumes. Data was analyzed for normality with the Shapiro-Wilks test, corrected to absolute error and compared for statistical significance using the Wilcoxon signed-ranks test or the Kruskal-Wallis test as appropriate. The overall raw PGD phase median estimation error was−27 mL (range −99 to 248 mL). The PGD raw median error increased with scenario complexity. There were no differences between role, gender, experience, or country of origin. The overall median raw estimation error for the WGD phase was 13 mL (range −80 ml to 143 mL) (p = 0.0128). Visual blood loss estimation is inaccurate amongst veterinary anesthetists and associated staff, showing decreasing accuracy with increasing complexity. A pictorial guide improves the accuracy generally, and specifically for more complex scenarios which are likely to reflect the clinical situation.

Development and assessment of a pictorial guide to improve accuracy of visual estimation of blood loss of small animals

OBJECTIVE

To investigate the accuracy of visual blood loss estimation from small animals among veterinary staff and final-year veterinary students, and the development and utility of a pictorial guide to improve estimation, in a veterinary hospital.

STUDY DESIGN

Online anonymous voluntary survey.

METHODS

A two-part online survey was circulated to voluntary participants at the University Veterinary Teaching Hospital Sydney, The University of Sydney, including students, nurses, interns, residents, general practitioners and specialists. The survey consisted of visual and brief descriptive depictions of blood loss scenarios involving small animals, principally including images of common surgical items and receptacles containing a bloodlike substance. Each participant estimated the blood volume (in millilitres) for each scenario two times, initially [Pre-Guide (PGD)] and then with the aid of a pictorial guide [With-Guide (WGD)]. The pictorial guide used similar images labelled with corresponding volumes. Data were analysed for normality with the Shapiro-Wilk test, corrected to absolute error and compared for statistical significance using the Wilcoxon signed-rank test or the Kruskal-Wallis test as appropriate (p < 0.05).

RESULTS

A total of 59 participants provided 288 responses. The raw median PGD error was -16 mL (range -105 to 443 mL), indicating a tendency towards underestimation of the actual volume. The WGD median error was 18 mL (range -91 to 191 mL), indicating a tendency towards overestimation when using a pictorial guide (p < 0.0001). Data corrected to absolute error showed a PGD median error of 34 mL (range 0-443 mL) and WGD median error of 23 mL (range 0-191 mL; p < 0.0001). There were differences between the participant roles in the PGD phase but not when using the pictorial guide.

CONCLUSIONS

and clinical relevance Participants generally underestimated surgical blood loss, with a wide variation, when visually estimating scenarios involving small animals. A pictorial guide improved estimation by reducing the absolute median error and narrowing the range.

Tissue oxygen tension monitoring of organ perfusion: rationale, methodologies, and literature review

Tissue oxygen tension is the partial pressure of oxygen within the interstitial space of an organ bed. As it represents the balance between local oxygen delivery and consumption at any given time, it offers a ready monitoring capability to assess the adequacy of tissue perfusion relative to local demands. This review covers the various methodologies used to measure tissue oxygen tension, describes the underlying physiological and pathophysiological principles, and summarizes human and laboratory data published to date.

Effects of a dexmedetomidine constant rate infusion and atropine on changes in global perfusion variables induced by hemorrhage followed by volume replacement in isoflurane-anesthetized dogs

OBJECTIVE

To evaluate the effects of a dexmedetomidine constant rate infusion (CRI) and atropine on changes in global perfusion variables induced by hemorrhage and volume replacement (VR) in isoflurane-anesthetized dogs.

ANIMALS

8 adult dogs.

PROCEDURES

Each dog was anesthetized twice, with a 2-week interval between anesthetic sessions. Anesthesia was maintained with 1.3 times the minimum alveolar concentration of isoflurane with and without dexmedetomidine (1.6 μg/kg, IV bolus, followed by 2 μg/kg/h, CRI). Dogs were mechanically ventilated and received an atracurium neuromuscular blockade during both sessions. During anesthesia with isoflurane and dexmedetomidine, atropine was administered 30 minutes before baseline measurements were obtained. After baseline data were recorded, 30% of the total blood volume was progressively withdrawn and VR was achieved with an equal proportion of autologous blood.

RESULTS

Following hemorrhage, cardiac index, oxygen delivery index, and mixed-venous oxygen saturation were significantly decreased and the oxygen extraction ratio was significantly increased from baseline. The anaerobic threshold was not achieved during either anesthetic session. When dogs were anesthetized with isoflurane and dexmedetomidine, they had a significantly lower heart rate, cardiac index, and mixed-venous oxygen saturation during VR than they did when anesthetized with isoflurane alone. Plasma lactate concentration, mixed venous-to-arterial carbon dioxide difference, base excess, and anion gap were unaltered by hemorrhage and VR and did not differ between anesthetic sessions.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the use of a dexmedetomidine CRI combined with atropine in isoflurane-anesthetized dogs that underwent volume-controlled hemorrhage followed by VR did not compromise global perfusion sufficiently to result in anaerobic metabolism.

A new severity predicting index for hemorrhagic shock using lactate concentration and peripheral perfusion in a rat model

Forty percent of trauma deaths are due to hemorrhage, with 33% to 56% occurring in the prehospital environment. This study proposes a new index (NI) based on the ratio of serum lactate concentration (LC) to peripheral perfusion (PP) as an indicator of hemorrhage-induced mortality during the prehospital stage. Thirty-six anesthetized rats were randomized into three groups according to volume of controlled blood loss. We measured heart rate (HR), systolic and diastolic blood pressures (SBP and DBP), mean arterial pressure (MAP), pulse pressure (PPR), respiration rate (RR), temperature (TEMP), LC, PP, shock index (SI = HR/SBP), and proposed the new hemorrhage-induced mortality index (NI = LC/PP). Peripheral perfusion, defined as peripheral tissue perfusion and skin microcirculation, was continuously monitored by laser Doppler flowmetry. All parameters were analyzed for changes between prehemorrhage and posthemorrhage to investigate the effects of hemorrhage on mortality. Areas under a receiver operating characteristic curve (AUCs) in descending order for NI, SI, PP, SBP, MAP, PPR, DBP, TEMP, LC, RR, and HR were 0.975, 0.941, 0.922, 0.919, 0.903, 0.884, 0.847, 0.816, 0.783, 0.744, and 0.672, respectively. The correlation coefficients with mortality for NI, SI, PP, SBP, MAP, PPR, DBP, TEMP, LC, RR, and HR were -0.818, -0.759, 0.726, 0.721, 0.694, 0.662, 0.597, 0.544, -0.487, 0.420, and -0.296, respectively, with the same order as the AUC. NI was shown to be an optimal independent mortality predictor on multivariable logistic regression analysis. In conclusion, the newly proposed hemorrhage-induced mortality index, based on blood lactate/PP ratio, was a better marker for predicting mortality in rats undergoing acute hemorrhage in comparison to the other parameters evaluated in this study.

A survival prediction model of rats in hemorrhagic shock using the random forest classifier

Hemorrhagic shock is the cause of one third of deaths resulting from injury in the world. Although many studies have tried to diagnose hemorrhagic shock early and accurately, such attempts were inconclusive due to compensatory mechanisms of humans. The objective of this study was to construct a survival prediction model of rats in hemorrhagic shock using a random forest (RF) model, which is a newly emerged classifier acknowledged for its performance. Heart rate (HR), mean arterial pressure (MAP), respiratory rate (RR), lactate concentration (LC), and perfusion (PF) measured in rats were used as input variables for the RF model and its performance was compared with that of a logistic regression (LR) model. Before constructing the models, we performed a 5-fold cross validation for RF variable selection and forward stepwise variable selection for the LR model to see which variables are important for the models. For the LR model, sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (ROC-AUC) were 1, 0.89, 0.94, and 0.98, respectively. For the RF models, sensitivity, specificity, accuracy, and AUC were 0.96, 1, 0.98, and 0.99, respectively. In conclusion, the RF model was superior to the LR model for survival prediction in the rat model.

Crystalloids versus colloids during acute normovolemic anemia: the quest continues

The optimal kind of fluid for fluid resuscitation during acute, severe hemorrhage is still discussed controversially. Of particular interest in this context is the choice of colloids versus crystalloids and their effect on the critical hemoglobin level. In a previous issue of Critical Care, Pape and colleagues describe the effect of four different volume replacement options on the critical hemoglobin concentration, and show marked differences for the different treatments. Even though some important pathophysiological issues remain unsolved, the current manuscript adds interesting evidence to an ongoing quest.

The impact of a regular blood donation on the hematology and EEG of healthy young male blood donors

The aim of this study was to investigate the effect of 400 ml whole blood donation on the human electroencephalogram (EEG) and hematology, not earlier reported in the literature. EEG activity was recorded from ten male blood donors (experiment group) before, during and after blood donation (i.e., 400 ml whole blood withdrawal). EEG topography and regional spectral field powers analyses were carried out via fast Fourier transformation. The venous hemoglobin (Hb) concentration was measured with a hematology analyzer. In the control investigation, 12 male age-matched volunteers (control group) were kept in semi-sitting position for the duration of a blood donation without actually vena puncture. The volunteers had no prior experiences of blood donation. Within the experiment group, post-donation Hb concentration decreased by 3.7% compared with the pre-donation Hb values (P < 0.01). Before blood donation, Hb concentration in control group was significantly higher compared to the experiment group (P < 0.05). For the experiment group, the field power of alpha-1 (7.5-9.5 Hz) EEG during blood withdrawal was significantly lower compared to that after blood withdrawal (P < 0.05). In contrast for the control group, all seven bands of regional spectral field powers showed no significantly discrepancies in the three periods. Blood donation attenuates the alpha-1 at the parietal-frontal area on human EEG-DMN transiently with no lasting effect at post-donation period. The blood donation-related effects on brain function may be of little consequence due to slight hemodynamic change and the results may facilitate the opinion that blood donation is a safe process and that should not discourage volunteers.

Laser Doppler imaging for early detection of hemorrhage

BACKGROUND

Laser Doppler Imaging (LDI) is a noninvasive means to measure blood flow through the superficial skin capillary plexus using flux units. Our objective was to determine the ability of LDI of the skin to detect and quantify rapid, severe hemorrhage.

METHODS

Five Yucatan mini-pigs (25-35 kg) underwent controlled hemorrhage of 25 mL/kg blood for 20 minutes. Median flux of a 10 cm × 10 cm area of the lower abdomen was measured at 2-minute intervals from initiation of hemorrhage to resuscitation with concurrent measurement of heart rate (HR), systolic blood pressure (SBP), and mean arterial pressure (MAP).

RESULTS

Average time to a change of 5 U in flux following start of hemorrhage was 2.4 minutes. This was significantly faster than time to change in HR (19.2 minutes, p < 0.05) and showed a trend toward more rapid identification of hemorrhage relative to changes in SBP (3.2 minutes, p = 0.157) and MAP (3.6 minutes, p = 0.083). Flux changes occurred at smaller % total blood volume lost than HR (3.94% vs. 28.8%, p < 0.05) and trended toward smaller volume identification than SBP (4.88%, p = 0.180) and MAP (5.36%, p = 0.102). Average correlation (ρ) of blood volume lost to flux was -0.974; HR, 0.346; SBP, -0.978; and MAP, -0.975. A change of 5 flux units was significantly more sensitive for hemorrhage than a change of 5 beats per minute in HR or 5 mm Hg in SBP or MAP (0.596 vs. 0.169, 0.438, and 0.287 respectively, all p < 0.05).

CONCLUSION

LDI is a sensitive, specific, and early means to detect and quantify severe hemorrhage.