Tissue hemoglobin O2 saturation during resuscitation of traumatic shock monitored using near infrared spectrometry

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Muscle perfusion and oxygen consumption by near-infrared spectroscopy in septic-shock and non-septic-shock patients

OBJECTIVE

To measure muscle blood flow (Qtis) and oxygen consumption (VO(2)tis) in septic and non-septic critically ill patients by near-infrared spectroscopy (NIRS).

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS AND PARTICIPANTS

Four patients with septic shock, eight post-surgical critically ill patients and ten healthy volunteers.

MEASUREMENTS AND RESULTS

Oxyhaemoglobin (HbO(2)) and deoxyhaemoglobin (HbH) variations after venous occlusion were measured by NIRS in the brachioradialis muscle. We calculated Qtis by the rate of HbO(2) and HbH increase in the first 30 s of venous occlusion divided by haemoglobin blood concentration. VO(2)tis was calculated by subtraction of the arterial HbH from the initial increase of HbH after venous occlusion extrapolated to 1 min. Tissue oxygenation index [TOI = HbO(2)/(HbO(2)+HbH)] was also measured before venous occlusion. Two measurements in patients with septic shock, and one measurement in non-septic-shock patients and healthy subjects, were obtained. Of the measurements, 35% were repeated because of low-quality NIRS signal. VO(2)tis and Qtis were two times larger ( P<0.05) in patients with septic shock than in patients without and in healthy subjects. The TOI was very similar among the three groups.

CONCLUSION

In septic-shock patients the increase in VO(2)tis was associated with an equivalent increase in Qtis. Therefore, tissue O(2) supply does not seem to be a limiting factor for muscle O(2) consumption. NIRS combined with venous occlusion allows a rapid, non-invasive and simultaneous assessment of regional perfusion and oxygen consumption. In case of microcirculatory shunt occurrence, the TOI should be cautiously used to assess tissue oxygenation state.

Near-Infrared Spectrometry of Abdominal Aortic Aneurysm in the ApoE-/- Mouse

Abdominal aortic aneurysms (AAAs) occur in 5-7% of people over age 60 in the United States. Early intervention in the disease process could have a significant impact on the incidence of complications and on patient survival, but identifying incipient aneurysms can be difficult. ApoE knockout mice develop AAAs following infusion of angiotensin II (AngII) by osmotic minipump into the subcutaneous space of mice at doses ranging from 500 to 1000 ng kg(-1) min(-1) for 7-28 days. These mice are used as models of AAA development. This study tested the hypothesis that near-IR spectrometry and PCR can determine AngII dose (SEE = 26 ng kg(-1) min(-1), SEP = 37 ng kg(-1) min(-1), r2 = 0.99) and collagen/elastin (C/E) ratio (SEE = 0.38, SEP = 0.39, r2 = 0.85) in mouse aortas.

Detection of high-risk atherosclerotic coronary plaques by intravascular spectroscopy

Multiple technologies are under development to identify plaque composition and vulnerability. This review article is intended to provide basic knowledge to the interventional cardiologist and the clinician about spectroscopy. The concept of light, the wavelength unit and the electromagnetic spectrum are discussed. Different types of spectra analysis including nuclear magnetic resonance, Raman, fluorescence and diffuse reflectance near-infrared spectroscopy are then carefully reviewed. Experimental data to identify atherosclerotic plaque composition for each of these techniques is provided. Potential benefits and challenges are addressed. Finally, diffuse reflectance near-infrared spectroscopy is discussed in more detail as a promising technique to characterize plaque vulnerability in humans.

Tissue oxygen monitoring during hemorrhagic shock and resuscitation: a comparison of lactated Ringer's solution, hypertonic saline dextran, and HBOC-201

BACKGROUND

The ideal resuscitation fluid for the trauma patient would be readily available to prehospital personnel, universally compatible, effective when given in small volumes, and capable of reversing tissue hypoxia in critical organ beds. Recently developed hemoglobin-based oxygen-carrying solutions possess many of these properties, but their ability to restore tissue oxygen after hemorrhagic shock has not been established. We postulated that a small-volume resuscitation with HBOC-201 (Biopure) would be more effective than either lactated Ringer's (LR) solution or hypertonic saline dextran (HSD) in restoring baseline tissue oxygen tension levels in selected tissue beds after hemorrhagic shock. We further hypothesized that changes in tissue oxygen tension measurements in the deltoid muscle would reflect the changes seen in the liver and could thus be used as a monitor of splanchnic resuscitation.

METHODS

This study was a prospective, blinded, randomized resuscitation protocol using anesthetized swine (n = 30), and was modeled to approximate an urban prehospital clinical time course. After instrumentation and splenectomy, polarographic tissue oxygen probes were placed into the liver (liver PO2) and deltoid muscle (muscle PO2) for continuous tissue oxygen monitoring. Swine were hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg over 20 minutes, shock was maintained for another 20 minutes, and then 100% oxygen was administered. Animals were then randomized to receive one of three solutions: LR (12 mL/kg), HSD (4 mL/kg), or HBOC-201 (6 mL/kg). Physiologic variables were monitored continuously during all phases of the experiment and for 2 hours postresuscitation.

RESULTS

At a MAP of 40 mm Hg, tissue PO2 was 20 mm Hg or less in both the liver and muscle beds. There were no significant differences in measured liver or muscle PO2 values after resuscitation with any of the three solutions in this model of hemorrhagic shock. When comparing the hemodynamic effects of resuscitation, the cardiac output was increased from shock values in all three animal groups with resuscitation, but was significantly higher in the animals resuscitated with HSD. Similarly, MAP was increased by all solutions during resuscitation, but remained significantly below baseline except in the group of animals receiving HBOC-201 (p < 0.01). HBOC-201 was most effective in both restoring and sustaining MAP and systolic blood pressure. There was excellent correlation between liver and deltoid muscle tissue oxygen values (r = 0.8, p < 0.0001).

CONCLUSION

HBOC-201 can be administered safely in small doses and compared favorably to resuscitation with HSD and LR solution in this prehospital model of hemorrhagic shock. HBOC-201 is significantly more effective than HSD and LR solution in restoring MAP and systolic blood pressure to normal values. Deltoid muscle PO2 reflects liver PO2 and thus may serve as an index of the adequacy of resuscitation in critical tissue beds.

Normal versus supranormal oxygen delivery goals in shock resuscitation: the response is the same

BACKGROUND

Shock resuscitation is integral to early management of severely injured patients. Our standardized shock resuscitation protocol, developed in 1997 and implemented as a computerized intensive care unit (ICU) bedside decision support tool in 2000, used oxygen delivery index (Do I) > or = 600 mL/min/m as the intervention endpoint. In a recent publication, Shoemaker et al. refuted positive outcome effect of early supranormal Do (i.e., Do I > or = 600) resuscitation. In response to and because of ongoing concern for excessive volume loading, we decreased our Do I endpoint from 600 to 500. Our hypothesis was that by decreasing the Do I endpoint, less crystalloid would be administered. We compare resuscitation responses to the protocol with goals of Do I > or = 600 versus 500 in two patient cohorts.

METHODS

A standardized protocol was used to direct bedside decisions for resuscitation of patients with major injury (Injury Severity Score > 15), blood loss (> or = 6 units of packed red blood cells), metabolic stress (base deficit > or = 6 mEq/L), and no severe brain injury. The protocol logic is to attain and maintain Do I > or = a specified goal for the first 24 ICU hours using primarily blood and volume loading. Two cohorts were compared: Do I > or = 500 (18 patients admitted February-August 2001) versus Do I > or = 600 (18 patients admitted during 2000 age and gender matched with the Do I > or = 500 group). Data were analyzed using analysis of variance, chi, and t tests (p < 0.05).

RESULTS

Both groups had similar demographics (age 30 +/- 3 years; 78% men; Injury Severity Score 27 +/- 3), hemodynamics, and severity of shock at start of resuscitation in the ICU. Resuscitation response was Do I increase to > or = 600 for both cohorts within approximately 12 hours. Throughout the 24-hour ICU process, the Do I > or = 500 cohort received less lactated Ringer's volume than the Do I > or = 600 cohort (total of 8 +/- 1 vs. 12 +/- 2 L; p < 0.05) and tended to receive less blood transfusion (total of 3 +/- 1 vs. 5 +/- 1 units of packed red blood cells).

CONCLUSION

Shock resuscitation using Do I > or = 500 was indistinguishable from Do I > or = 600 mL/min/m. Less volume loading was required to attain and maintain Do I > or = 500 than 600 using computerized protocol technology to standardize resuscitation during the first 24 ICU hours.

Detection of lipid pool, thin fibrous cap, and inflammatory cells in human aortic atherosclerotic plaques by near-infrared spectroscopy

BACKGROUND

A method is needed to identify nonstenotic, lipid-rich coronary plaques that are likely to cause acute coronary events. Near-infrared (NIR) spectroscopy can provide information on the chemical composition of tissue. We tested the hypothesis that NIR spectroscopy can identify plaque composition and features associated with plaque vulnerability in human aortic atherosclerotic plaques obtained at the time of autopsy.

METHODS AND RESULTS

A total of 199 samples from 5 human aortic specimens were analyzed by NIR spectroscopy. Features of plaque vulnerability were defined by histology as presence of lipid pool, thin fibrous cap (<65 microm by ocular micrometry), and inflammatory cell infiltration. An InfraAlyzer 500 spectrophotometer was used. Spectral absorbance values were obtained as log (1/R) data from 1100 to 2200 nm at 10-nm intervals. Principal component regression was used for analysis. An algorithm was constructed with 50% of the samples used as a reference set; blinded predictions of plaque composition were then performed on the remaining samples. NIR spectroscopy sensitivity and specificity for histological features of plaque vulnerability were 90% and 93% for lipid pool, 77% and 93% for thin cap, and 84% and 89% for inflammatory cells, respectively.

CONCLUSIONS

NIR spectroscopy can identify plaque composition and features associated with plaque vulnerability in postmortem human aortic specimens. These results support efforts to develop an NIR spectroscopy catheter system to detect vulnerable coronary plaques in living patients.

End points of resuscitation: choosing the right parameters to monitor

Determining when resuscitation is complete can be challenging, as tissue hypoperfusion can persist despite normal vital signs. This article discusses the limitations of traditional parameters used as resuscitation guidelines and describes new technologies that aid in assessing resuscitation efforts, including advances in hemodynamic monitoring and methods for obtaining global and organ-specific indexes.

A current concept of trauma-induced multiorgan failure

Trauma deaths continue to show a trimodal distribution: immediately at the scene, within the first 24 hours during initial resuscitation, and in the next 3 to 4 weeks as a result of multiple organ failure.(1) Failure to resuscitate adequately in the emergency department can lead to acidosis, hypothermia, and coagulopathy, which can result in multiple organ failure and cause death in these patients. Our current understanding of the initial response to shock and trauma and the development of the systemic inflammatory response syndrome and progressive organ failure is one of a continuum initiated and perpetuated by inflammation and inflammatory mediators. The pathophysiologic character, diagnosis, prevention, and treatment of traumatic injury-induced multiple organ failure are discussed.

Resuscitation from traumatic shock

Shock is the body's response to decreased cellular perfusion. It can begin with hemorrhage, mechanical obstruction of the circulation, cardiac dysfunction, central nervous system injury, or sepsis. Once triggered, shock is perpetuated by the release of toxic compounds from ischemic cells. The treatment of shock consists of the removal or correction of the triggering pathology, followed by resuscitation back to the normal state. Clinical research in shock resuscitation in the past year has focused on recognizing the presence of shock in patients at risk, particularly those with normal vital signs but ongoing, occult hypoperfusion. In the laboratory, the emphasis has been on minimizing the initial hemorrhagic insult, minimizing the release of toxins from ischemic cells, and blocking the response to the toxins that are released.

Near-infrared spectroscopy reflects changes in mesenteric and systemic perfusion during abdominal compartment syndrome

BACKGROUND

Continuous and minimally invasive near-infrared spectroscopy (NIRS)-derived gastric tissue oxygen saturation (GStO(2)) and muscle tissue oxygen saturation (MStO(2)) were evaluated in a clinically relevant porcine model of hemorrhagic shock and abdominal compartment syndrome (ACS).

METHODS

Phenobarbital-anesthetized swine underwent pulmonary artery catheter insertion for mixed venous oxygen saturation (SvO(2)) measurement and midline laparotomy to permit placement of a gastric NIRS probe, a jejunal (regional carbon dioxide [PrCO(2)]) tonometer, superior mesenteric artery (SMA) flow probe, and a portal vein oxygen saturation (SpvO(2)) catheter. A muscle NIRS probe was placed on the front limb. After randomization, Group 1 underwent hemorrhage and resuscitation. Group 2 had no hemorrhage or resuscitation. ACS was induced by peritoneal fluid infusion in both groups. A significant decrease in SMA flow, SpvO(2), GStO(2), SvO(2), and MStO(2) was observed after hemorrhage in Group 1 and with abdominal hypertension in both groups.

RESULTS

GStO(2) significantly correlated with SMA flow (Group 1: r(2) = 0.90; Group 2: r(2) = 0.83) and mesenteric oxygen delivery (mesenteric oxygen delivery, Group 1: r(2) = 0.73; Group 2: r(2) = 0.89). MStO(2) significantly correlated with SvO(2) (Group 1: r(2) = 0.99; Group 2: r(2) = 0.65) and systemic oxygen delivery (SDO2, Group 1: r(2) = 0.60; Group 2: r(2) = 0.88). Tonometer-derived PrCO(2) values did not change at any time point in either group.

CONCLUSIONS

NIRS measurement of GStO(2) and MStO(2) reflected changes in mesenteric and systemic perfusion respectively during hemorrhage and ACS.

Nitroprusside in resuscitation of major torso trauma

OBJECTIVE

Patients with thoracic aortic injury (TAI) usually have sustained other major trauma, and may require aggressive shock resuscitation. In the 24 hours after aortic repair and during resuscitation, our cardiothoracic surgeons request intravenous nitroprusside to maintain mean arterial pressure (MAP) less than 90 mm Hg to minimize bleeding at the repair. We compared the resuscitation response of patients who sustained major torso trauma (MTT) and TAI with that of patients who had MTT with no TAI to determine whether nitroprusside can effectively control MAP during resuscitation and whether use of nitroprusside, because of its peripheral vasodilatory effects, is associated with a favorable resuscitation response.

METHODS

During the 9-month study period, 11 patients who sustained TAI and 38 patients who sustained MTT with no TAI met multiple organ failure risk/shock criteria and were resuscitated by a standardized protocol emphasizing volume loading and hemoglobin replacement to maintain systemic oxygen delivery index (DO2I) > or = 600 mL O2/min-m2 for the first 24 intensive care unit hours. For TAI patients, postoperative management included intravenous nitroprusside infusion titrated by the bedside nurse to maintain mean arterial pressure (MAP) less than 90 mm Hg during the same 24 hours. Data were obtained prospectively during resuscitation. Retrospectively, the resuscitation response of TAI and non-TAI patients was compared.

RESULTS

For the TAI group, nitroprusside effectively controlled MAP (range, 77-87 mm Hg); for the non-TAI group, mean MAP exceeded 95 mm Hg within 5 hours. During the first 8 hours, MAP, pulmonary capillary wedge pressure, and systemic vascular resistance index were less, and DO2I was greater for the TAI than for the non-TAI group. The resuscitation goal of DO2I > or = 600 mL O2/ min-m2 was attained at 4 hours for the TAI group, and was attained at 12 hours for the non-TAI group. No revisions of aortic repairs were required during or as a result of resuscitation.

CONCLUSION

During aggressive shock resuscitation, control of MAP using nitroprusside is feasible and is associated with a favorable resuscitation response. Nitroprusside may be a useful adjunct during shock resuscitation of MTT as a vasoactive agent that promotes peripheral tissue perfusion.