Effect of hemorrhage and resuscitation on subcutaneous, conjunctival, and transcutaneous oxygen tension in relation to hemodynamic variables

Endpoints of Resuscitation for the Victim of Trauma

Useful resuscitation endpoints must serve both to diagnose the need for and to ensure the ongoing adequacy of resuscitation. To this end, traditional measures of organ perfusion are now widely appreciated to be grossly inadequate. Useful endpoints or milestones range from the global, to the regional, to the cellular specific. Understanding the basic principles of perfusion-related dysoxia in trauma and hemorrhage and its potential rapid transition to involve inflammatory and immune responses on cellular oxygen utilization will aid the clinician in choosing and appropriately interpreting endpoint monitoring data. There also appears to be an optimal window of opportunity for monitoring to help mitigate the development of more complicated inflammatory states. This article reviews the underlying need for endpoint selection (both global and regional, biochemical and functional) and monitoring during resuscitation of the polytrauma patient. At this juncture it appears that early use of a blend of global markers such as lactate and base deficit coupled with an available sensitive regional monitor such as gastric tonometry may offer the best combination of current technology to guard against early perfusion-related dysoxia. Future techniques involving optical spectroscopy offer the exciting potential to assess oxygenation at the cellular level. This may aid in ultra-early detection and resolution of perfusion-related dysoxia in addition to recognizing its transition to more complex inflammatory-mediated circulatory and metabolic failure.

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.

Tissue oxygenation monitoring using resonance Raman spectroscopy during hemorrhage

BACKGROUND

The ability to monitor the patient of hemorrhage noninvasively remains a challenge. We examined the ability of resonance Raman spectroscopy to monitor tissue hemoglobin oxygenation (RRS-StO2) during hemorrhage and compared its performance with conventional invasive mixed venous (SmvO2) and central venous (ScvO2) hemoglobin oxygen saturation as well as with near-infrared spectroscopy tissue hemoglobin oxygenation (NIRS-StO2).

METHODS

Five male swine were anesthetized and instrumented followed by hemorrhage at a rate of 30 mL/min for 60 minutes. RRS-StO2 was continuously measured from the buccal mucosa, and NIRS-StO2 was continuously measured from the forelimb. Paired interval measures of SmvO2, ScvO2, and lactate were made. Pearson correlation was used to quantify the degree to which any two variables are related. Receiver operating characteristic (ROC) area under the curve values were used for pooled data for RRS-StO2, NIRS-StO2, SmvO2, and ScvO2 to compare performance in the ability of tissue oxygenation methods to predict the presence of an elevated arterial blood lactate level.

RESULTS

Sequential RRS-StO2 changes tracked changes in SmvO2 (r = 0.917; 95% confidence interval [CI], 0.867-0.949) and ScvO2 (r = 0.901; 95% CI, 0.828-0.944) during hemorrhage, while NIRS-StO2 failed to do so for SmvO2 (r = 0.283; 95% CI, 0.04919-0.4984) and ScvO2 (r = 0.142; 95% CI, -0.151 to 0.412). ROC curve performance of oxygenation measured to indicate lactate less than or greater than 3 mM yielded the following ROC area under the curve values: SmvO2 (1.0), ScvO2 (0.994), RRS-StO2 (0.972), and NIRS-StO2 (0.611).

CONCLUSION

RRS-StO2 seems to have significantly better ability to track central oxygenation measures during hemorrhage as well as to predict shock based on elevated lactate levels when compared with NIRS-StO2.

Bladder tissue oxygen tension monitoring in pigs subjected to a range of cardiorespiratory and pharmacological challenges

PURPOSE

A fall in tissue oxygen tension (tPO(2)) is an early indicator of organ hypoxia in both patients and animal models. We previously demonstrated the utility of bladder tPO(2) in various rodent shock models. As a prelude to clinical testing, we aimed to provide further validation of bladder tPO(2) monitoring in a large animal model undergoing a range of cardiorespiratory insults and vasoactive drug interventions.

METHODS

Anaesthetized, mechanically ventilated, instrumented female pigs (n = 8) were subjected to a range of short-term cardiorespiratory (changes in inspired oxygen concentration (FiO(2)), haemorrhage, positive end-expiratory pressure) and pharmacologic (inotrope, pressor) challenges. Global haemodynamics, arterial and pulmonary blood gases and bladder tPO(2) were measured before and after each challenge.

RESULTS

Bladder tPO(2) values fell in line with increasing degrees of hypoxaemia and haemorrhage, and were restored during resuscitation. These changes often preceded those seen in global haemodynamics, arterial base excess and lactate. The rise in bladder tPO(2) with hyperoxia, performed as an oxygen challenge test, was incrementally blunted by progressive haemorrhage. Dobutamine and norepinephrine both increased cardiac output and global O(2) delivery, but had no effect on bladder tPO(2) or lactataemia in these healthy pigs.

CONCLUSIONS

In this pig model bladder tPO(2) provides a sensitive indicator of organ hypoxia compared to traditional biochemical markers during various cardiorespiratory challenges. This technique offers a potentially useful tool for clinical monitoring.

Tissue oxygen tension monitoring: will it fill the void?

PURPOSE OF REVIEW

The holy grail of circulatory monitoring is an accurate, continuous and relatively noninvasive means of assessing the adequacy of organ perfusion. This could be then advantageously used to direct therapeutic interventions to prevent both under-treatment and over-treatment and thus improve outcomes. However, in view of the heterogeneous response (adaptive or maladaptive) of different organs to various shock states, any monitor of perfusion adequacy cannot reflect every organ system, but should at least detect early deterioration in a 'canary' organ. Tissue oxygen tension reflects the balance between local oxygen supply and demand, and could thus be a potentially useful monitoring modality. This article examines the different technologies available and reviews the current literature regarding its utility as a monitor.

RECENT FINDINGS

Tissue oxygen tension, measured at a variety of sites in both human and laboratory studies, does appear to be a sensitive indicator of organ perfusion in different shock states. However, responses can vary not only between organs and between different shock states, but also over time. These changes reflect the particular oxygen supply-demand balance present in that tissue bed at that specific time point in the disease process. The response to a dynamic oxygen challenge test provides further information that allows severity to be more readily differentiated.

SUMMARY

Monitoring of tissue oxygen tension may offer a potentially useful tool for clinical management though significant validation needs to be first performed to confirm its promise.

Tissue oxygen monitoring in rodent models of shock

Tissue Po2 (tPo2) reflects the balance between local O2 supply and demand and, thus, could be a useful monitoring modality. However, the consistency and amplitude of the tPo2 response in different organs during different cardiorespiratory insults is unknown. Therefore, we investigated the effects of endotoxemia, hemorrhage, and hypoxemia on tPo2 measured in deep and peripheral organ beds. We compared arterial pressure, blood gas and lactate levels, descending aortic and renal blood flow, and tPo2 in skeletal muscle, bladder epithelium, liver, and renal cortex during 1) LPS infusion (10 mg/kg), 2) sequential removal of 10% of circulating blood volume, and 3) reductions in inspired O2 concentration in an anesthetized Wistar rat model with values measured in sham-operated animals. Different patterns were seen in each of the shock states, with condition-specific variations in the degree of acidemia, lactatemia, and tissue O2 responses between organs. Endotoxemia resulted in a rise in bladder tPo2 and an early fall in liver tPo2 but no significant change in muscle and renal cortical tPo2. Progressive hemorrhage, however, produced proportional declines in liver, muscle, and bladder tPo2, but renal cortical tPo2 was maintained until profound blood loss had occurred. By contrast, progressive hypoxemia resulted in proportional decreases in tPo2 in all organ beds. This study highlights the heterogeneity of responses in different organ beds during different shock states that are likely related to local changes in O2 supply and utilization. Whole body monitoring is not generally reflective of these changes.

Transcutaneous pressure of oxygen: a noninvasive and early detector of peripheral shock and outcome

A noninvasive tool to recognize early shock would improve outcome by providing prompt recognition of tissue ischemia and precise resuscitation endpoint. The skin is the first tissue bed to vasoconstrict in shock states. Studies have demonstrated that transcutaneous partial pressure of oxygen (PtCO2) increases with higher FiO2 in nonshock states as arterial pressure of oxygen (PaO2) increases, but in shock situations, PtCO2 mirrors changes in cardiac output and oxygen delivery with minimum response to increasing FiO2 and PaO2. This study examined the relationship of hemodynamic variables and the degree of PtCO2 response to FiO2 of 1.0 (identified as the "oxygen challenge test") to mortality and organ failure. This prospective observational study examined 38 patients requiring at least 24 h of cardiac output monitoring for shock resuscitation in the Surgical Intensive Care Unit. Patients were resuscitated to the standard protocol of blood pressure, urine output, oxygen delivery (DO2), and mixed venous O2 (SvO2). Seventy-nine percent of the patients (30/38) with a mean age of 59 +/- 21 years had septic shock or severe sepsis with a 26% mortality (10/38). Measurements included hemodynamic variables, PtCO2, and outcome (mortality and organ failure). In this study, the ability of PtCO2 value to increase by 21 mmHg on a FiO2 of 1.0, at 24 h of resuscitation, divided survivors from nonsurvivors, P <.001. The PtCO2 response to FiO2 may provide an additional noninvasive method of detecting early shock as well as a specific endpoint of resuscitation.

Near infrared spectroscopy for evaluation of the trauma patient: a technology review

Clinicians now realize the limitations of the physical examination in detecting compensated shock states, the severity of uncompensated states, and in determining the adequacy of resuscitation in order to prevent subsequent post-traumatic multisystem organ failure and death. A renewed interest has developed in interrogating the state of oxygen transport at the end-organ level in the trauma patient. Although used as a research tool and now clinically to monitor cerebral oxygenation during complex cardiovascular and neurosurgery, near infrared absorption spectroscopy (NIRS) is being more aggressively investigated and now marketed clinically as a noninvasive means to assess tissue oxygenation in the trauma patient at the end organ level. This paper will describe the principles of NIRS and the basis for its proposed use in the trauma patient to assess tissue oxygenation. This includes its known limitations, current controversies, and what will be needed in the future to make this technology a part of the initial and ongoing assessment of the trauma patient. The ultimate goal of such techniques is to prevent misassessment of patients and inadequate resuscitation, which are believed to be major initiators in the development of multisystem organ failure and death.

Molecular diagnostics of injury and repair responses in critical illness: what is the future of "monitoring" in the intensive care unit?

OBJECTIVE

To identify potential future means of monitoring injury and repair in critical illness.

DESIGN

Review of the literature.

RESULTS

Critically ill patients are monitored extensively and intensively by such means as hemodynamics, laboratory values, and radiologic studies. In general, however, the goal of monitoring has been to measure the degree of injury and to prevent further injury, rather than to measure repair. Measures of repair have been limited to phenotypic end points such as return of organ function, as measured by blood chemistry. In this article, I examine how it may be possible in the future to monitor the progress of repair using genomic and proteomic biomarkers. These types of monitors would enable clinicians to control the healing environment using real time, rapid biomarkers, and sophisticated techniques to target therapy to the patient's current inflammatory state, taking into account the genetic makeup of the patient and his or her likely response to a given drug.

CONCLUSIONS

The rapidly evolving sciences of genomics, proteomics, computational biology, and complex system theory can be used a) to model critical illness; b) to model adaptive and maladaptive responses to critical illness; c) to tailor treatments to create an ideal inflammatory environment for repair and regeneration, taking into account the individual genetic contribution; and d) to monitor the progress of repair. The major obstacles to reaching these goals are technological, and experience suggests that they will be overcome.

Gut intramucosal pH as an early indicator of effectiveness of therapy for hemorrhagic shock

OBJECTIVE

To determine the value of intramucosal pH for evaluating the effectiveness of treatment for hemorrhagic shock.

DESIGN

Randomized, controlled trial.

SETTING

University center, animal laboratory.

SUBJECTS

Eighteen piglets, weighing 17 to 23 kg.

INTERVENTIONS

Anesthetized animals were bled to a mean arterial pressure (MAP) of 40 to 50 mm Hg and a 70% reduction in cardiac output during a 1-hr period. This state was maintained for the next hour. The piglets were treated with crystalloid solution to restore cardiac output and MAP during the subsequent 80 mins of the experiment. Some animals were given vasoactive drugs during volume therapy to modulate splanchnic perfusion and increase the diversity of values of various variables.

MEASUREMENTS AND MAIN RESULTS

Systemic hemodynamic and oxygen transport variables were monitored. Tissue oxygen tensions were measured in the liver and abdominal subcutaneous tissue layer. Gut intramucosal pH (pHi) was determined, using a balloon tonometer. The animals were divided into responders (n=9) and nonresponders (n=9) according to whether pHi increased or decreased during resuscitation. Hemodynamic and oxygen transport variables improved in the group of responders. In the group of nonresponders, values decreased. Liver and subcutaneous oxygen tensions increased during the initial phase of resuscitation in both groups but decreased after 30 mins in the nonresponder group.

CONCLUSIONS

The change in pHi during the first hour of resuscitation could be used to divide animals treated uniformly from a hemodynamic point of view into two distinct groups with seemingly different outcome. The minimally invasive method could be of value for early evaluation of the results of treatment of hemorrhagic shock.

Dopexamine improves liver oxygenation during crystalloid resuscitation from experimental hemorrhagic shock

OBJECTIVE

To evaluate the effects of dopexamine administration on hemodynamic variables and tissue oxygen tensions during crystalloid resuscitation from hemorrhagic shock.

DESIGN

Randomized, control trial.

SETTING

An animal laboratory at a university center.

SUBJECTS

Twelve piglets, mean weight 22 kg.

INTERVENTIONS

The animals were anesthetized and bled to a state of hemorrhagic shock and resuscitated, using a crystalloid solution infused at a rate of approximately 2.6 mL/min/kg (total amount 208 mL/kg). Cardiac output and mean arterial pressure (MAP were measured as indicators of volume filling during the 20- to 30-min resuscitation period and during the follow-up period until 80 mins from the start of resuscitation. Dopexamine was administered by infusion at 6 micrograms/kg-min from the start of volume replacement (dopexamine group, n = 6). The rest of the animals (control group, n = 6) were given volume replacement only.

MEASUREMENTS AND MAIN RESULTS

Systemic oxygen transport variables were calculated. Tissue oxygen tensions were continuously recorded from the liver, conjunctival layer, and via subcutaneous and transcutaneous electrodes in the abdominal region. MAP decreased from 119 +/- 2 (SEM) to 44 +/- 2 mm Hg and cardiac output decreased by 77% during the shock period. During resuscitation, cardiac output was restored in both groups. MAP increased close to the baseline during the early resuscitation period and decreased slowly during follow-up. Oxygen delivery remained at 46% of baseline, whereas systemic oxygen consumption was restored during resuscitation in both groups. Liver tissue oxygen tension increased well above baseline during resuscitation in the dopexamine group, and liver tissue oxygen tension was significantly higher than in the control group. After 60 mins of resuscitation, the liver oxygen tension decreased to control group values. None of the other tissue oxygen tensions showed any differences between groups.

CONCLUSIONS

Dopexamine administration during crystalloid resuscitation from hemorrhagic shock was well tolerated and resulted in significant and specific, although transient, improvement in liver oxygenation.

Measurements of tissue oxygen tension in vascularised jejunal autografts in pigs

Tissue oxygen measurements were evaluated as a monitor of the jejunal flap in seven female landrace pigs. A small polarographic sensor (diameter 0.55 mm) was used in which interstitial tissue oxygen tension was measured continuously in a jejunal flap and a muscle flap (rectus abdominis) during arterial and venous occlusion. Mean (SEM) tissue oxygen tension in the two types of flap were 44(9) mmHg (jejunal flap) and 47(8) mmHg (rectus flap). After arterial occlusion for 30 minutes the values dropped to 17(4) mmHg for the jejunal flap and 12(2) mmHg for the muscle flap. The decline became significant after five minutes. During venous occlusion (30 minutes) the values fell to 20(4) mmHg and 14(1) mmHg. The arterial occlusion was undetectable by the naked eye, but the enteric tissue after venous occlusion became severely congested and blue-black in colour. The condition returned to normal after release of the clamp. We conclude that direct measurement of tissue oxygen tension in a jejunal flap is a reliable method of detecting impaired perfusion. This method may in the future be used to monitor vascularised jejunal autografts.

The effect of norepinephrine and dobutamine on bladder epithelial oxygen tension

STUDY OBJECTIVES

To assess the effects of two contrasting vasoactive agents (dobutamine [DOB] and norepinephrine [NE]) on (1) global and regional cardiorespiratory variables, (2) acid base status, and (3) bladder epithelial oxygen tension (BEOT), a putative marker of organ perfusion.

DESIGN

Measurement of aortic blood flow (ABF) and renal blood flow (RBF), mean arterial blood pressure, arterial blood gases, and BEOT were made during infusion of placebo and varying doses of DOB and NE.

SETTING

Medical school laboratory.

SUBJECTS

Eighteen anesthetized, spontaneously breathing, male Sprague-Dawley rats divided into three groups.

INTERVENTIONS

Two groups were allocated to receive escalating doses of DOB (to 40 micrograms/kg/min) or NE (to achieve a 50% change in any hemodynamic variable). The drug therapy was then discontinued for 15 min and restarted at the previous maximum dose. A third group received 0.9% saline solution at the same infusion rate (16 mL/kg/h).

MEASUREMENTS AND RESULTS

There was a dose-related increase in mean blood pressure with NE and fall with DOB. Compared with control values, NE had no effect on ABF but decreased RBF significantly whereas DOB significantly increased ABF but had no effect on RBF. Base excess and BEOT decreased significantly and in parallel with both agents, more so with NE.

CONCLUSIONS

Despite their different macrocirculatory effects, DOB and NE both produced a significant but reversible fall in BEOT and a metabolic acidosis. BEOT shows potential as a monitor of the effectiveness of organ perfusion.

Critical tissue oxygen tension defines tissue oxygen debt in the isolated hindlimb of the pig during progressive ischemia

OBJECTIVE

To determine a critical skeletal muscle oxygen tension (PO2) value below which a tissue oxygen debt develops.

DESIGN

Descriptive study of oxygen transport values in relation to skeletal muscle PO2 throughout progressive ischemia by means of arterial blood flow reductions in an isolated hindlimb model in the pig.

SETTING

Surgical Research department of the University of Amsterdam.

SUBJECTS

Six female Yorkshire pigs weighing 26 to 35 kg (average 33).

INTERVENTIONS

Controlled blood flow to the isolated hindlimb was achieved by means of extracorporeal circulation. The hindlimb was studied during progressive flow reduction.

MEASUREMENTS AND MAIN RESULTS

Oxygen delivery (DO2) and oxygen consumption were calculated as the product of extracorporeal blood flow and, respectively, arterial oxygen content and arterial-venous oxygen content difference. In this fashion, an oxygen supply dependency could be determined in all animals. A critical DO2 value was determined below which a tissue oxygen debt developed. Skeletal muscle PO2 was measured continuously, using a Clark-type polarographic oxygen sensor. Combining the critical DO2 value with the corresponding skeletal muscle PO2 value resulted in a critical skeletal muscle PO2 value of 15.2 +/- 0.4 torr (2.0 +/- 0.1 kPa).

CONCLUSION

In this pig model, a critical skeletal muscle PO2 value could be determined below which a tissue oxygen debt presumably developed.

Subcutaneous oxygen tension: a useful adjunct in assessment of perfusion status

OBJECTIVES

Using a new fluorescence-quenching optode which, unlike earlier oximeters, neither consumes oxygen nor generates heat, we sought to determine the effects of hemorrhage and resuscitation on subcutaneous PO2. Additionally, we compared the effects of resuscitation with diaspirin crosslinked hemoglobin, an oxygen-carrying solution, on subcutaneous PO2 to that of traditional resuscitative fluids. We also compared mean arterial pressure and central venous oxygen saturation, indirect indices of perfusion, to subcutaneous PO2, a direct index of perfusion.

DESIGN

Prospective trial, randomized for selection of treatment regimen.

SETTING

Shock-trauma laboratory of a medical university.

SUBJECTS

Male Sprague-Dawley rats, weighing 260 to 380 g.

INTERVENTIONS

Rats were bled 22 mL/kg and resuscitated, 1 min later, with either 66 mL/kg of lactated Ringer's solution, 22 mL/kg of human serum albumin, 22 mL/kg of blood, or 22 mL/kg of diaspirin crosslinked hemoglobin. A fifth group of animals was not resuscitated after hemorrhage. Subcutaneous PO2 and mean arterial pressure were monitored continuously throughout the experiment, while central venous oxygen saturation was measured intermittently.

MEASUREMENTS AND MAIN RESULTS

Subcutaneous PO2 decreased in response to hemorrhage and, although it did increase after resuscitation with each fluid, no treatment was able to restore subcutaneous PO2 to baseline within 2 hrs postresuscitation. Subcutaneous PO2 continued to decrease after hemorrhage in the unresuscitated animals. In contrast, mean arterial pressure was restored to baseline values in only blood- and diaspirin crosslinked hemoglobin-treated animals, although this effect was lost within 30 mins in the blood-treated group. Only blood restored the central venous oxygen saturation to baseline values in the early postresuscitation period.

CONCLUSIONS

The fluorescence-quenching optode consistently followed changes in subcutaneous PO2 during hemorrhage and after resuscitation. Diaspirin crosslinked hemoglobin performed as well as blood in restoring peripheral perfusion, as measured by subcutaneous PO2, while both of these fluids were superior to either lactated Ringer's solution or albumin. Both whole blood and diaspirin crosslinked hemoglobin restored mean arterial pressure to baseline, although the effect of the latter was of a longer duration. The pressor effect of the crosslinked hemoglobin did not affect peripheral perfusion, as reflected by the values for subcutaneous PO2. Subcutaneous PO2 is a useful adjunct in assessment of the adequacy of peripheral perfusion and may help redefine targets for resuscitation.

The influence of different levels of PEEP on peripheral tissue perfusion measured by subcutaneous and transcutaneous oxygen tension

OBJECTIVE

To compare subcutaneous (PscO2) and transcutaneous (PtcO2) oxygen tension measurements in relation to hemodynamic variables at different levels of PEEP, and to evaluate the usefulness of these measurements as monitors of peripheral tissue perfusion.

DESIGN

Prospective trial.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Seven patients with gastric cancer who where undergoing total gastrectomy.

INTERVENTIONS

Silicone catheter was placed in the upper arm and transcutaneous oxygen monitor was placed on the upper part of the chest. A pulmonary artery catheter was placed in the right pulmonary artery.

MEASUREMENTS AND RESULTS

PscO2 and PtcO2 together with hemodynamic variables were measured at different levels of PEEP. Progressive increase of PEEP reduced cardiac index (CI) (p < 0.05) with a concomitant decrease of PscO2 (p < 0.05) and oxygen delivery (DO2) (p < 0.05). Changes in PtcO2 paralleled changes in arterial oxygen tension (PaO2), but no correlation was found between PtcO2, CI and DO2.

CONCLUSION

PscO2 is a sensitive indicator of subcutaneous tissue perfusion, which can be used to identify the PEEP level, with optimum peripheral perfusion. PscO2 seems to be a more reliable indicator of tissue perfusion than PtcO2.

Evaluation of tissue oximetry in perioperative monitoring of colorectal surgery

Twenty patients undergoing elective colorectal surgery were studied during and after operation by means of tissue oximetry measuring the subcutaneous partial pressure of oxygen (PscO2) and by gastric intramural pH measurement. Mean(s.d.) PscO2 recorded 24 h after surgery was significantly lower than the peroperative value: 14(10) versus 24(14) mmHg, P less than 0.02. The postoperative PscO2 was also significantly lower than that measured in a control group of ten healthy volunteers: 14(10) versus 34(18) mmHg, P less than 0.001. The peroperative PscO2 of the patients who developed a postoperative complication was significantly lower than that of those who had an uneventful postoperative clinical outcome: 16(9) versus 32(14) mmHg, P less than 0.02. The peroperative PscO2 of the patient group with complications was also significantly lower than that of the control group: 16(9) versus 34(18) mmHg, P less than 0.02. The peroperative PscO2 of the group of patients without complications was almost identical to that of the control group. During operation only one patient developed gastric intramural acidosis. Perioperative oxygen debt and the response of subcutaneous tissue oxygen tension to oxygen breathing seemed to correlate better with clinical outcome than gastric wall pH values and the conventional parameters of tissue perfusion.

Assessment of the perfusion in peripheral tissue beds by subcutaneous oximetry and gastric intramucosal pH-metry in elective colorectal surgery

Gastric intramucosal pH (pHi) and subcutaneous oxygen tension (PscO2) were compared with traditional perfusion parameters in patients undergoing elective colorectal surgery and were related to clinical outcome. Ten patients were studied per- and postoperatively and tissue oximetry studies were also performed in a group of 10 healthy volunteers. The response of PSCO2 to oxygen breathing proved to be the most sensitive predictor of clinical outcome. Of the 10 patients 8 failed to respond to an O2 challenge, while all 10 volunteers in the control group did so. Out of those 8 patients 6 presented with mainly infectious complications while only 3 had an inadequate perioperative urine output and none presented with signs of arterial or of gastric intramural acidosis. The present study suggests a possible relationship between clinical outcome and oxymetric signs of tissue hypoperfusion after O2 challenge in surgical patients, even in the presence of an adequate urine output and a normal gastric wall pH.