The relationship of oxygen consumption measured by indirect calorimetry to oxygen delivery in critically ill patients

Is reduction of pocket probing depth correlated with the baseline value or is it "mathematical coupling"?

Previous studies using correlation or regression analysis have showed that treatment effects measured by the change in clinical parameters are often associated with baseline values of the same parameters. These studies, however, have a methodological weakness. Correlation/regression between baseline measures and the derived change variable invalidates the statistical procedures of testing the null hypothesis: that the coefficient of correlation/regression is zero. This is due to the phenomenon of mathematical coupling. To investigate the impact that this has on the observed correlation/regression coefficient when in reality this is zero, we used random simulations of hypothetical data to model the treatment of periodontal pockets. Results showed a strong probability of obtaining statistically significant correlation/regression coefficients. To separate this artificial effect of mathematical coupling from the true underlying biological relationship, one must apply appropriate analytical strategies to re-evaluate previous evidence within the periodontal literature.

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.

Energy expenditure after 2- to 3-hour elective surgical operations

Energy expenditure was measured by indirect calorimetry in 17 adult patients (8 women and 9 men) before surgery, 4 hours immediately after surgery, and 24 hours late after surgery in patients undergoing elective surgery of small-to-medium scope.

MATERIAL AND METHODS

The total duration of surgery ranged from 2 to 3 hours. Repeated measures were performed on the same patient, so that each patient was considered to be his/her own control. All patients received a 5% dextrose solution (2000 mL/day) throughout the postoperative period.

RESULTS

Men showed a reduction in CO2 production during the immediately after surgery period (257+/-42 mL/min) compared to before surgery (306+/-48 mL/min) and late after surgery (301+/-45 mL/min); this reduction was not observed in women. Energy expenditure was also lower in men during immediately after surgery (6.6 kJ/min). None of the other measurements, including substrate oxidation, showed significant differences.

CONCLUSION

Therefore, elective surgery itself cannot be considered an important trauma that would result in increased energy expenditure. According to this study, it is not necessary to prescribe an energy supply exceeding basal expenditure during the immediate after-surgery period. The present results suggest that the energy supply prescribed during the postoperative period after elective surgery of small-to-medium scope should not exceed 5-7 kJ/min, so the patient does not receive a carbohydrate overload from energy supplementation.

Haemodynamic and oxygen transport responses in survivors and non-survivors following thermal injury

Resuscitation from shock based on invasive hemodynamic monitoring has been widely used in trauma and surgical patients, but has been only sparsely evaluated in thermally injured patients, probably due to fear of invasive monitoring in this group of patients. However, end-point resuscitation to fixed circulatory and oxygen transport values has been proposed to be associated with an improved survival rate following trauma and high-risk surgery. Furthermore, the early circulatory response to resuscitation has been shown to be predictive of survival in these patients. In this study the early hemodynamic and oxygen transport profile following thermal injury was analysed with the aim to detect possible differences in the response of survivors and non-survivors. The transpulmonary thermodilution technique was used for hemodynamic monitoring of 21 patients, who were admitted to our burn unit with severe burns. Six patients died and 15 patients survived to leave the intensive care unit. Survivors were found to have a significantly higher cardiac index and oxygen delivery rate during the early postburn period than non-survivors. Furthermore, initial serum lactate levels as well as the ability to clear elevated lactate were found to be significantly associated with survival. Blood pressure and heart rate were not significantly different between the two groups of patients. All patients received significantly higher volumes of crystalloids during the first 24 h than predicted from the Baxter formula, independent of outcome. We concluded that standard vital signs such as blood pressure and heart rate may be invalid as outcome related resuscitation goals, and too insensitive to ensure appropriate fluid replacement. The response to fluid therapy may be significantly associated with outcome; survivors responding with an augmentation of cardiac output and oxygen delivery not seen in non-survivors. Lactate levels seem to correlate with organ failure and death and appear a suitable end-point for resuscitation of severely burned patients.

Intraoperative evaluation of tissue perfusion in high-risk patients by invasive and noninvasive hemodynamic monitoring

OBJECTIVE

Although invasive monitoring has not been effective in late stages after organ failure has occurred, early postoperative monitoring revealed differences in survivor and nonsurvivor patterns and provided goals for improving outcome. We searched for the earliest divergence of survivor and nonsurvivor circulatory changes as an approach to earlier preventive therapy. The aim was to describe the intraoperative time course of circulatory dysfunction in survivors and nonsurvivors among high-risk elective surgery patients using both the thermodilution pulmonary artery catheter (PAC) and multicomponent noninvasive monitoring.

DESIGN

Prospective intraoperative description of circulatory dysfunction.

SETTING

University-run county hospital.

PATIENTS

Two hundred nine consecutively monitored high-risk elective surgery patients.

MEASUREMENTS AND MAIN RESULTS

We evaluated the data of high-risk elective surgery patients using both PAC and multicomponent noninvasive monitoring. The latter consisted of the following: a) an improved bioimpedance method for estimating cardiac output; b) the standard pulse oximetry to screen for pulmonary problems; c) transcutaneous oxygen and carbon dioxide tension sensors to evaluate tissue perfusion; and d) routine noninvasive blood pressure and heart rate. The current noninvasive impedance cardiac output estimations closely approximated those of the thermodilution method; r2 = .74, p < .001; the precision and bias was -0.124 +/- 0.75 L/min/m2. Outcome measures included intraoperative description of circulatory patterns of high-risk surgical patients who survived compared with nonsurvivors. Hypotension, low cardiac index, arterial hemoglobin desaturation, low transcutaneous oxygen, high transcutaneous carbon dioxide tensions, low oxygen delivery, and low oxygen consumption developed intraoperatively gradually over time; the abnormalities were more pronounced in the nonsurvivors than in the survivors.

CONCLUSIONS

The survivors had slightly higher mean arterial pressure, cardiac index, and mixed venous oxygen saturation, as well as significantly higher oxygen delivery, oxygen consumption, transcutaneous oxygen tension, and transcutaneous oxygen tension/FIO2 ratios, than did the nonsurvivors. The data suggest that blood flow, oxygen delivery, and tissue oxygenation of the nonsurvivors became inadequate toward the end of the operation. Noninvasive monitoring provides similar information to that of the PAC; both approaches revealed low-flow and poor tissue perfusion that were worse in the nonsurvivors. The continuous on-line real-time displays of hemodynamic trends facilitate early recognition of acute circulatory dysfunction.

Relationship of mortality to increasing oxygen delivery in patients > or = 50 years of age: a prospective, randomized trial

OBJECTIVE

To investigate the relationship of mortality to early resuscitation using two levels of oxygen delivery (DO2) in critically ill surgical patients > or =50 yrs of age who were stratified into groups: age < or =75 yrs (age 50 to 75 yrs group); and age >75 yrs (age >75 yrs group).

DESIGN

A prospective, randomized trial, continued from a previous project.

SETTING

Surgical intensive care unit, university affiliated.

PATIENTS

Consecutive patients, >50 yrs of age, unable to generate a DO2 of > or =600 mL/min/m2 with fluid resuscitation alone, with a diagnosis of systemic inflammatory response syndrome, sepsis, severe sepsis, septic shock, and/or acute respiratory distress syndrome.

INTERVENTIONS

During the first 24 hrs of resuscitation, patients were randomized to receive fluids, blood transfusions, and vasoactive agents in order to achieve DO2 treatment goals of > or =600 mL/ min/m2 in the protocol group and 450 to 550 mL/min/m2 in the control group.

MEASUREMENTS AND MAIN RESULTS

One hundred five patients completed the study. In patients aged 50 to 75 yrs, the mortality rate was 21% (9/43) in the protocol group and 52% (12/23) in the control group (p=.01, 95% confidence interval of -58% to -4%). In patients >75 yrs of age, the mortality rate was 57% (12/21) in the protocol group and 61% (11/18) in the control group. Oxygen extraction ratios (O2ER) and oxygen consumption values were significantly (p=.02) lower in the age >75 yrs group compared with the age 50 to 75 yrs group.

CONCLUSIONS

Patients 50 to 75 yrs of age receiving a DO2 of > or =600 mL/min/m2 demonstrated a statistically significant (p=.01) improved survival rate over patients in the control group. Patients >75 yrs of age demonstrated no benefit from attempts to increase DO2 to >600 mL/min/m2, and they may have been overtreated as reflected by the lower O2ER values in this age group. Treating to an O2ER that reflects a balance between oxygen consumption and DO2 may be an alternative goal that allows individual titration.

In search of the optimal end points of resuscitation in trauma patients: a review

Complete resuscitation from shock is one of the primary concerns of the surgeon taking care of injured patients. Traditionally, the return to normalcy of blood pressure, heart rate, and urine output has been the end point of resuscitation. Using these end points may leave a substantial number of patients, up to 50 to 85% in some series, in "compensated" shock, which if it persists may ultimately lead to the death of the patient. Because of this potential other end points are being used and include supernormal values for oxygen transport variables (cardiac index, oxygen delivery, and oxygen consumption), lactate, base deficit, and gastric intramucosal pH. We believe that the current data support the use of lactate, base deficit, and/or gastric intramucosal pH as the appropriate end points of resuscitation of trauma patients. The goal should be to correct one or all of three of these markers of tissue perfusion to normal within the initial 24 hours after injury.