Gastric mucosal pH and oxygen delivery and oxygen consumption indices in the assessment of adequacy of resuscitation after trauma: a prospective, randomized study

Resuscitation of critically ill patients based on the results of gastric tonometry: a prospective, randomized, controlled trial

OBJECTIVE

To determine whether additional therapy aimed at correcting low gastric intramucosal pH (pHi) improves outcome in conventionally resuscitated, critically ill patients.

DESIGN

Prospective, randomized, controlled study.

SETTING

General intensive care unit (ICU) of a university teaching hospital.

PATIENTS

A total of 210 adult patients, with a median Acute Physiology and Chronic Health Evaluation II score of 24 (range, 8-51).

INTERVENTIONS

All patients were resuscitated according to standard guidelines. After resuscitation, those patients in the intervention group with a pHi of <7.35 were treated with additional colloid and then dobutamine (5 microg/kg/min then 10 microg/kg min) until 24 hrs after enrollment.

MEASUREMENTS AND MAIN RESULTS

There were no significant differences (p > .05) in ICU mortality (39.6% in the control group vs. 38.5% in the intervention group), hospital mortality (45.3% in the control group vs. 42.3% in the intervention group), and 30-day mortality (43.7% in the control group vs. 40.2 in the intervention group); survival curves; median modified maximal multiorgan dysfunction score (10 points in the control group vs. 13 points in the intervention group); median modified duration of ICU stay (12 days in the control group vs. 11.5 days in the intervention group); or median modified duration of hospital stay (60 days in the control group vs. 42 days in the intervention group). A subgroup analysis of those patients with gastric mucosal pH of > or =7.35 at admission revealed no difference in ICU mortality (10.3% in the control group vs. 14.8% in the intervention group), hospital mortality (13.8% in the control group vs. 29.6% in the intervention group), or 30-day mortality (10.3% in the control group vs. 26.9% in the intervention group).

CONCLUSIONS

The routine use of treatment titrated against pHi in the management of critically ill patients cannot be supported. Failure to improve outcome may be caused by an inability to produce a clinically significant change in pHi or because pHi is simply a marker of disease rather than a factor in the pathogenesis of multiorgan failure.

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.

Prevention of multiple organ failure

Physicians are still largely ignorant of the underlying biology of SIRS and multiple organ failure. Nonetheless, strategies to prevent multiple organ failure are possible. These include aggressive resuscitation of hemodynamically unstable patients, careful assessment to avoid missing clinically significant injuries, early operative treatment of all possible injuries with debridement of all nonviable tissue, early nutritional support, and the early diagnosis and prompt treatment of infectious complications. Treatment of patients with established multiple organ failure is still largely supportive and has made little impact on the patient mortality rate over the past 20 years. Future treatment strategies must focus on multimodality combination therapy aimed at specifically suppressing excessive activation of the inflammatory response while preserving immune competence and normal antimicrobial defenses. Only then are physicians likely to begin to see a reduction in the mortality rate of patients with this complex and challenging condition.

Tonometry to estimate intestinal perfusion in newborn piglets

AIM

To determine the correlation between gastric intramucosal pH and superior mesenteric artery (SMA) flow in newborn piglets.

METHODS

Fourteen newborn piglets were randomly assigned to either a control or to an epinephrine group which received 0,1,2,4,0 microg/kg/min of epinephrine for 60 minutes, each dose. Gastric tonometry was performed, SMA flow was measured, and intramucosal pH and the ratio of tonometer pCO(2) over arterial pCO(2) (rCO(2)) were calculated.

RESULTS

Intramucosal pH decreased over time in both groups, but tended to be lower in the epinephrine group. With increasing dose of epinephrine, SMA flow decreased; this in turn increased rCO(2) (p = 0.04) with a tendency to decrease intramucosal pH (p = 0.06).

CONCLUSIONS

Gastric tonometry may be useful in human neonates to evaluate gut ischaemia.

Serial pHi Measurement as a Predictor of Mortality, Organ Failure, and Hospital Stay in Surgical Patients

Intestinal ischemia is a common condition in critically ill patients and has been postulated to play a role in the development of organ failure and death. This has resulted in the recent interest in monitoring gastric intramucosal pH (pHi) in critically ill patients to provide earlier evidence of inadequate resuscitation, cardiogenic dysfunction, or sepsis. Several reports have indicated that low pHi values obtained during the initial 24 to 48 hours of intensive care unit (ICU) admission were associated with the development of organ failure and death. The purpose of this study was to assess the predictive value of serial pHi measurements obtained throughout the entire ICU admission. A retrospective analysis of critically ill trauma, burn, and surgical patients who had frequent pHi determinations during ICU treatment was performed. When stratified by pHi values, there were no significant differences in length of stay, organ dysfunction, or mortality. Our findings suggest that serial pHi determinations obtained beyond the early critical care period are less reliable predictors of poor outcome.

Direct effects of dopamine on colonic mucosal pH: implications for tonometry

Tonometric measurements of colonic and gastric mucosa pH are used as indirect determinants of splanchnic perfusion in shocked patients or those undergoing aortic cross-clamp. Mucosal acidification in response to splanchnic vasodilators such as dopamine has been assumed to signify ischemia. However, cellular acidification may occur independent of oxygenation and the direct effects of dopamine on mucosal acid-base are unknown. We examined the effects of dopamine on cellular pH (independent of oxygenation) of intestinal mucosa in vitro. Crypts isolated from the distal colon of Sprague-Dawley rats were loaded with a pH-sensitive fluorescent probe, perfused with a Hepes-buffered Ringers solution, and imaged with confocal laser scanning microscopy. In separate experiments, crypts were loaded with a calcium-sensitive probe (Fura-2) and concentrations of free cytosolic calcium were measured with fluorescence imaging. Dopamine perfusion produced a reversible cytosolic acidification of crypts which was not significantly affected by (i) the nominal absence of bicarbonate, (ii) alpha- and beta-adrenergic receptor blockade, or (iii) protein kinase C inhibition. Dopamine did not significantly affect intracellular calcium concentrations. However, dopamine-induced acidification was inhibited by (a) blocking sodium-hydrogen exchange with amiloride, (b) prior exposure to adenosine 3', 5'-cyclic monophosphate (cAMP), or (c) protein kinase A blockade (all P < 0.01). Dopamine directly acidifies mucosal crypt cells in a mechanism that involves a cAMP-mediated inhibition of sodium-hydrogen exchange. This finding accounts for the acidification of intestinal mucosa during low-dose dopamine infusion despite a demonstrable improvement in splanchnic perfusion. Direct mucosal effects of pharmacological agents must be considered in the evaluation of perfusion parameters based on tonometric data.

Persistent gastric intramucosal ischemia in patients with sepsis following resuscitation from shock

STUDY OBJECTIVES

(1) To determine the effects of resuscitation of patients with severe sepsis to conventional hemodynamic end points and normal blood lactate levels on postresuscitation sequential assessments of gastric intramucosal pH (pHi). (2) To determine whether trends in pHi are reflected in trends in systemic hemodynamic, oxygen utilization, and acid-base assessments.

DESIGN

Prospective cohort study.

SETTING

Medical ICU in an inner-city, university-based medical center.

PATIENTS

Twelve recently admitted patients with severe sepsis and signs of circulatory shock who were successfully resuscitated to normal hemodynamic end points and lactate levels and who were also monitored with pulmonary artery catheters and gastric tonometers.

INTERVENTIONS

Because of the observational nature of this study, no specific interventions were employed. The physician staff administered i.v. fluids and pharmacologic agents, during and after the resuscitative period, to treat infection and to achieve and maintain hemodynamic stability. Mechanical ventilation and supplemental oxygen were provided as needed. The hemodynamic and physiologic monitoring employed was determined by the managing physicians and established medical ICU routines.

MEASUREMENTS AND RESULTS

A total of 12 patients were studied. Systemic hemodynamic, oxygen utilization, and acid-base assessments and pHi were recorded following resuscitation, and every 12 h thereafter. pHi decreased from 7.33 +/- 0.08 (mean +/- SD) following resuscitation to 7.26 +/- 0.04 at 24 h, 7.20 +/- 0.07 at 36 h (p < 0.05), and 7.24 +/- 0.08 at 48 h. Corresponding statistically significant and clinically relevant changes in systemic hemodynamic, oxygen utilization, and acid-base variables were not observed. The hospital mortality of this patient group was high (10 of 12; 83%).

CONCLUSIONS

Gastric intramucosal acidosis develops and persists for at least 48 h in patients resuscitated from septic shock to conventional resuscitative end points, including the normalization of lactate levels. These regional changes were not reflected in corresponding changes in systemic acid-base and oxygen utilization variables. Direct determinations of pHi and therapy directed toward the resolution of splanchnic ischemia may be required to improve the outcome in these patients.

Continuous cardiac output and mixed venous oxygen saturation monitoring

Continuous assessment of cardiac output and SVO2 in the critically ill may be helpful in both the monitoring variations in the patient's cardiovascular state and in determining the efficacy of therapy. Commercially available continuous cardiac output (CCO) monitoring systems are based on the pulsed warm thermodilution technique. In vitro validation studies have demonstrated that this method provides higher accuracy and greater resistance to thermal noise than standard bolus thermodilution techniques. Numerous clinical studies comparing bolus with continuous thermodilution techniques have shown this technique similarly accurate to track each other and to have negligible bias between them. The comparison between continuous thermal and other cardiac output methods also demonstrates good precision of the continuous thermal technique. Accuracy of continuous oximetry monitoring using reflectance oximetry via fiberoptics has been assessed both in vitro and in vivo. Most of the studies testing agreement between continuous SVO2 measurements and pulmonary arterial blood samples measured by standard oximetry have shown good correlation. Continuous SVO2 monitoring is often used in the management of critically ill patients. The most recently designed pulmonary artery catheters are now able to simultaneously measure either SVO2 and CCO or SVO2 and right ventricular ejection fraction. This ability to view simultaneous trends of SVO2 and right ventricular performance parameters will probably allow the clinician to graphically see the impact of volume loading or inotropic therapy over time, as well as the influence of multiple factors, including right ventricular dysfunction, on SVO2. However, the cost-effectiveness of new pulmonary artery catheters application remains still questionable because no established utility or therapeutic guidelines are available.

Small intestinal production of nitric oxide is decreased following resuscitated hemorrhage

BACKGROUND

Small intestine microvascular vasoconstriction and hypoperfusion develop after resuscitation (RES) from hemorrhage (HEM), despite restoration of central hemodynamics. The responsible mechanisms are unclear. We hypothesized that the microvascular impairment following HEM/RES was due to decreased intestinal microvascular nitric oxide (NO) production.

METHODS

Male Sprague-Dawley rats (195-230 g) were utilized and three experimental groups were studied: (1) SHAM (cannulated but no HEM), (2) HEM only, and (3) HEM/RES. HEM was to 50% of baseline mean arterial pressure for 60 min, and RES was with shed blood and an equivalent volume of saline. Ex vivo isolated intestinal perfusion and a fluorometric modification of the Greiss reaction were used to quantify production of NO metabolites (NOx). Perfusate von Willebrand factor (vWF) was used as an indirect marker of endothelial cell activation or injury. To assess the degree of NO scavenging by oxygen-derived free radicals, immunohistochemistry was used to detect nitrotyrosine formation in the intestine.

RESULTS

Intestinal NOx decreased following HEM/RES (SHAM 1.35 +/- 0.2 mM vs HEM/RES 0.60 +/- 0.1 mM, P < 0.05), but not with HEM alone (1.09 +/- 0.3 mM). There were no differences in serum NOx levels between the three groups. Release of vWF was increased during the HEM period (SHAM 0.18 +/- 0.1 g/dl vs HEM 1.66 +/- 0.6 g/dl, P < 0.05). There was no detectable nitrotyrosine formation in any group.

CONCLUSIONS

Intestinal NO metabolites decrease following HEM/RES. Elevated vWF levels during HEM and the lack of detectable nitrotyrosine suggest that this is due to decreased endothelial cell production of NO. HEM/RES-induced endothelial cell dysfunction may contribute to persistent small intestine post-RES hypoperfusion and vasoconstriction.

Low-volume resuscitation with a hemoglobin-based oxygen carrier after hemorrhage improves gut microvascular oxygenation in swine

Using palladium-porphyrin quenching of phosphorescence, we investigated the influence of diaspirin cross-linked hemoglobin (DCLHb) on gut microvascular oxygen pressure (microPO2) in anesthetized pigs. Values of gut microPO2 were studied in correlation with regional intestinal as well as global metabolic and circulatory parameters. A controlled hemorrhagic shock (blood withdrawal of 40 mL/kg) was followed by resuscitation with either a combination of lactated Ringer's solution (75 mL/kg) and modified gelatin (15 mL/kg)(lactR/Gel) or 10% DCLHb (5 mL/kg). After resuscitation, gut microPO2 was similarly improved in the lactR/Gel group (from 25 +/- 10 mm Hg to 53 +/- 8 mm Hg) and the DCLHb group (from 23 +/- 9 mm Hg to 46 +/- 6 mm Hg), which was associated with increased gut oxygen delivery. However, the improvement after resuscitation with DCLHb was sustained for longer periods of time (75 vs 30 min). Mesenteric venous PO2 was increased after resuscitation with lactated Ringer's solution and modified gelatin but not with DCLHb, which was associated with an increased gut oxygen consumption in the latter group. We conclude that measurement of microPO2 by the palladium-porphyrin phosphorescence technique revealed DCLHb to be an effective carrier of oxygen to the microcirculation of the gut. Also, this effect can be achieved with a lower volume than is currently used in resuscitation procedures.

Threshold values of intramucosal pH and mucosal-arterial CO2 gap during shock resuscitation

BACKGROUND

The gastric intramucosal pH (pHi) and gastric mucosal-arterial CO2 gap (GAP) estimate visceral perfusion and predict outcome. Threshold values of these variables for use during resuscitation, however, remain poorly defined. The purpose of this study was to develop clinically derived cutoffs for both pHi and GAP for predicting death and multiple organ failure (MOF) in trauma patients.

METHODS

This was a cohort study of 114 consecutive trauma patients who had pHi determined at 24 hours after intensive care unit admission. The corresponding GAP for each of these values of pHi was obtained through chart review. Receiver operating characteristic curves were constructed for both pHi and GAP with respect to death and MOF. These curves were used to determine the value of each variable that maximized the sum of sensitivity and specificity in predicting outcome. chi2 tests and odds ratios were used to determine if significant differences in outcome occurred above and below these cutoff values.

RESULTS

Of 114 patients who had pHi determined at 24 hours after admission, 108 had corresponding GAP values available. The values of pHi and GAP that maximized sensitivity and specificity were 7.25 and 18 mm Hg, respectively. The odds ratio for pHi versus death was 4.6 and for pHi versus MOF was 4.3. The odds ratios for GAP versus death and MOF were 2.9 and 3.3, respectively.

CONCLUSION

In trauma patients, the ability to predict death and MOF is maximized at values of pHi less than 7.25 and GAP greater than 18 mm Hg. These values represent clinically derived cutoffs that should be useful for evaluating the adequacy of intestinal perfusion during resuscitation.

Gastric intramucosal pH-guided therapy in patients after elective repair of infrarenal abdominal aneurysms: is it beneficial?

OBJECTIVE

To determine if gastric intramucosal pH (pHi)-guided therapy reduces the number of complications and length of stay in the intensive care unit (ICU) or the hospital after elective repair of infrarenal abdominal aortic aneurysms.

DESIGN

Prospective, randomized study.

SETTING

Surgical intensive care unit (SICU) of a University Hospital.

PATIENTS

Fifty-five consecutive patients randomized to group 1 (pHi-guided therapy) or to group 2 (control).

INTERVENTIONS

Patients of group 1 with a pHi of lower than 7.32 were treated by means of a prospective protocol in order to increase their pHi to 7.32 or more.

MEASUREMENTS AND RESULTS

pHi was determined in both groups on admission to the SICU and thereafter at 6-h intervals. In group 2, the treating physicians were blinded for the pHi values. Complications, APACHE II scores, duration of endotracheal intubation, fluid and vasoactive drug treatment, treatment with vasoactive drugs, length of stay in the SICU and in the hospital and hospital mortality were recorded. There were no differences between groups in terms of the incidence of complications. We found no differences in APACHE II scores on admission, the duration of intubation, SICU or hospital stay, or hospital mortality. In the two groups the incidence of pHi values lower than 7.32 on admission to the SICU was comparable (41% and 42% in groups 1 and 2, respectively). Patients with pHi lower than 7.32 had more major complications during SICU stay (p < 0.05), and periods more than 10 h of persistently low pHi values (< 7.32) were associated with a higher incidence of SICU complications (p < 0.01).

CONCLUSIONS

Low pHi values (< 7.32) and their persistence are predictors of major complications. Treatment to elevate low pHi values does not improve postoperative outcome. Based on these data, we cannot recommend the routine use of gastric tonometers for pHi-guided therapy in these patients. Further studies are warranted to determine adequate treatment of low pHi values that results in beneficial effects on the patient's postoperative course and outcome.

Tissue hypercarbic acidosis as a marker of acute circulatory failure (shock)

Measurement of pH of the stomach wall (gastric intramural pH) by the tonometric method has been utilized both experimentally and clinically as an indicator of the capability of the stomach to extract and utilize oxygen. As such, it serves as a metabolic marker of acute perfusion failure (circulatory shock). More recently, researchers have found that increases in the PCO2 accounted for the decline in pH; this was documented in tissues other than the stomach wall, including the esophageal and sublingual mucosa. In this review, tissue PCO2 is identified as a universal indicator of impaired perfusion and contrasted with conventional hemodynamic and metabolic markers of perfusion failure.

Intra-abdominal hypertension after life-threatening penetrating abdominal trauma: prophylaxis, incidence, and clinical relevance to gastric mucosal pH and abdominal compartment syndrome

OBJECTIVE

To define the incidence, prophylaxis, and treatment of intra-abdominal hypertension (IAH) and its relevance to gut mucosal pH (pHi), multiorgan dysfunction syndrome, and the abdominal compartment syndrome (ACS).

METHODS

Seventy patients in the SICU at a Level I trauma center (1992-1996) with life threatening penetrating abdominal trauma had intra-abdominal pressure estimated by bladder pressure. pHi was measured by gastric tonometry every 4 to 6 hours. IAH (intra-abdominal pressure> 25 cm of H2O) was treated by bedside or operating room laparotomy.

RESULTS

Injury severity was comparable between patients who had mesh closure as prophylaxis for IAH (n = 45) and those who had fascial suture (n = 25). IAH was seen in 10 (22.2%) in the mesh group versus 13 (52%) in the fascial suture group (p = 0.012) for an overall incidence of 32.9%. Forty-two patients had pHi monitoring, and 11 of them had IAH. Of the 11 patients, eight patients (72.7%) had acidotic pHi (7.10 +/- 0.2) with IAH without exhibiting the classic signs of ACS. The pHi improved after abdominal decompression in six and none developed ACS. Only two patients with IAH and low pHi went on to develop ACS, despite abdominal decompression. Multiorgan dysfunction syndrome points and death were less in patients without IAH than those with IAH and in patients who had mesh closure.

CONCLUSIONS

IAH is frequent after major abdominal trauma. It may cause gut mucosal acidosis at lower bladder pressures, long before the onset of clinical ACS. Uncorrected, it may lead to splanchnic hypoperfusion, ACS, distant organ failure, and death. Prophylactic mesh closure of the abdomen may facilitate the prevention and bedside treatment of IAH and reduce these complications.

Oxygen delivery and outcome

Perioperative haemodynamic optimization of high-risk surgical patients seems to be associated with a reduction in morbidity and mortality. There is, however, no evidence to support the use of treatment directed at achieving survivor values of oxygen delivery and consumption in critically ill patients after admission to intensive care. Mitochondrial dysfunction may be responsible for the inability of patients dying of sepsis to increase oxygen consumption and thus may explain why therapies directed at reducing mortality through increasing oxygen delivery have not been successful. In response to the recent controversy surrounding the risks versus benefits of pulmonary artery catheterization, current research is focusing on the development and evaluation of noninvasive methods to assess the adequacy of resuscitation.

Gastric and esophageal intramucosal PCO2 (PiCO2) during endotoxemia: assessment of raw PiCO2 and PCO2 gradients as indicators of hypoperfusion in a canine model of septic shock

STUDY OBJECTIVES

To validate capnometric recirculating gas tonometry (CRGT) for continuously monitoring gut intramucosal PCO2 (PiCO2) in a septic shock model, and to compare gastric vs esophageal PCO2 vs intramucosal-arterial PCO2 gradients.

INTERVENTIONS

CRTG catheters were placed in the stomach and esophagus of six anesthetized dogs. A saline solution filled balloon tonometry (ST) catheter was also placed in the stomach. After equilibration, 3 mg/kg Escherichia coli lipopolysaccharide (LPS) was administered IV. PiCO2 measurements were made at 0, 45, and 90 min post-LPS by ST and continuously by CRGT.

RESULTS

Baseline PiCO2 was 41.5+/-1.9 (+/-SE) in the stomach by CRGT, 38.0+/-1.0 by ST, and 43.0+/-4.4 mm Hg in the esophagus (p=not significant). Gastric PiCO2 by CRGT increased to 47.0+/-2.4 mm Hg by 25 min post-LPS (p<0.05), whereas gastric (ST) and esophageal PiCO2 increased significantly by 45 min post-LPS. Good agreement was observed between gastric CRGT and ST measurements (mean bias, 1.3 mm Hg). The PiCO2-PaCO2 gradient increased post-LPS, but was significant only for gastric CRGT measurements 90 min post-LPS infusion.

CONCLUSION

CRGT provided continuous gastric PiCO2 measurements that were in close agreement with ST but detected changes earlier than the conventional technique. Continuous esophageal PiCO2 represents a valid alternative for assessing gastric PiCO2.

Relationship between systemic oxygen supply dependency and gastric intramucosal PCO2 during progressive hemorrhage

BACKGROUND

As systemic oxygen delivery (DO2) is reduced, oxygen consumption (VO2) is maintained until a critical level is reached (DO2crit) below which VO2 becomes supply-dependent and anaerobic metabolism ensues. We examined the relationship between gastric intramucosal PCO2 (PiCO2) and the onset of systemic supply dependency. We also compared PiCO2 to mixed venous and portal venous blood PCO2 (PmvCO2 and PpvCO2) to assess their utility as premonitory indicators of supply dependency.

METHODS

Six dogs were subjected to stepwise hemorrhage to effect a progressive decrease in DO2. Inflection points for changes in VO2, PiCO2, PmvCO2, and PpvCO2 versus DO2 were determined.

RESULTS

Mean DO2crit was 6.0 +/- 0.7 mL x kg(-1) x min(-1), whereas the DO2 at which inflection points occurred for PiCO2 and PpvCO2 were 13.2 +/- 1.4 and 11.2 +/- 1.5 mL x kg(-1) x min(-1), respectively (p < 0.05 for both).

CONCLUSION

Continuous monitoring of PiCO2 using capnometric recirculating gas tonometry can serve as an early indicator of systemic hypoperfusion before the onset of systemic supply dependency.

Failure of splanchnic resuscitation in the acutely injured trauma patient correlates with multiple organ system failure and length of stay in the ICU

INTRODUCTION

The purpose of our study was to evaluate the relationship between the state of splanchnic perfusion and morbidity and mortality in the hemodynamically unstable trauma patient acutely resuscitated in the ICU.

METHODS

Gastric intramucosal pH (pHi) was monitored in a blinded fashion in 19 consecutive critically ill trauma patients with evidence of systemic hypoperfusion (arterial pH [pHa] <7.35, base excess >2.3 mmol/L, lactic acid >2.3 mEq/L) who received right heart catheters to guide resuscitation and subsequent hemodynamic monitoring.

DESIGN

Prospective randomized consecutive series with retrospective analysis of data.

SETTING

University hospital, surgical ICU.

RESULTS

The mean values of APACHE II (acute physiology and chronic health evaluation) Injury Severity Score, pHa, arterial base excess, cardiac index, oxygen delivery index, and oxygen consumption index by 24 h were similar (Student's t test, p>0.1) between survivors and nonsurvivors and between those who developed at most a single (SOF) vs multiple organ system failure (MOSF). Supranormal oxygen delivery and utilization parameters were evenly distributed among survivors and nonsurvivors and patients with SOF and MOSF (chi2, p>0.5). Ten patients had a pHi <7.32 and nine patients had a pHi > or = 7.32 by 24 h. Fifty percent of patients with a pHi <7.32 died, compared with 11% of patients with a pH > or = 7.32 (chi2, p=0.07). Sixty percent of patients with a pHi <7.32 developed MOSF compared with 11% of patients with a pHi > or = 7.32 (chi2, p=0.03). The one patient who developed MOSF and died in the pHi > or = 7.32 cohort suffered from massive head trauma and had all futile medical interventions halted. No other patients who achieved a pH > or = 7.32 by hour 24 developed MOSF. Survivors with a pHi <7.32 at hour 24 had an increased ICU stay (pHi <7.32=46+/-15 days, pHi > or = 7.32=13+/-9 days; p<0.01). A pHi <7.32 carried a relative risk of 4.5 for death and 5.4 for the occurrence of MOSF.

CONCLUSION

Attainment of a pHi > or = 7.32 at hour 24 carried a significantly reduced likelihood of MOSF. Being an inference of the state of regional perfusion, in a high-risk microvascular bed, gastric intraluminal tonometry should identify perfusion states of compensated or uncompensated shock during hemodynamic resuscitation of the critically ill injury patient. A low pHi appears to be a marker of postresuscitative morbidity and subsequent increased length of stay.

Effects of abdominal decompression on cardiopulmonary function and visceral perfusion in patients with intra-abdominal hypertension

OBJECTIVE

Increased intra-abdominal pressure (IAP) compromises cardiopulmonary function and visceral perfusion. Our goal was to characterize acute changes in these subsystems associated with operative abdominal decompression.

PATIENT POPULATION

A series of 11 consecutive injured patients monitored with a pulmonary artery catheter and nasogastric tonometer in whom operative decompression was performed. Indications for decompression included oliguria or progressive acidosis despite aggressive resuscitation in the presence of elevated IAP (>25 mm Hg).

MAIN OUTCOME MEASURES

Studied hemodynamic variables included pulmonary artery occlusion pressure (PAOP), right ventricular end-diastolic volume index (RVEDVI), and cardiac index (CI). Pulmonary variables included shunt fraction (Qs/Qt) and dynamic compliance (Cdyn). Visceral perfusion was assessed using hourly urine output 4 hours before and after decompression (UOP) and gastric intramucosal pH (pHi). Mean values before and after decompression were compared using the paired t test. Linear regression and Fisher's z transformation were used to evaluate the relationships between RVEDVI, PAOP, CI, and IAP. IAP was transduced via bladder pressures. Significance was defined as p < 0.05. Data are expressed as means+/-SD.

RESULTS

IAP decreased with decompression (49+/-11 to 19+/-6.8 mm Hg; p < 0.0001). RVEDVI improved independent of CI and correlated better (p < 0.01) with CI (r =0.49, p=0.04) than PAOP did (r=-0.36, p=0.09). PAOP correlated significantly with IAP (r=0.45, p=0.04). Decompression resulted in significant improvements in Qs/Qt, Cdyn, UOP, and pHi.

CONCLUSION

Abdominal decompression in patients with increased IAP improves preload, pulmonary function, and visceral perfusion. Elevated IAP has important effects on PAOP, which makes the PAOP an unreliable index of preload in these patients.

Gastric intramucosal pH predicts death in severe acute pancreatitis

BACKGROUND

This study tested the hypothesis that gastric intramucosal pH (pHi) can predict death in severe acute pancreatitis.

METHODS

Seventeen consecutive patients with predicted severe acute pancreatitis were studied prospectively. Four died from complications related to pancreatitis. Gastric pHi was measured by nasogastric tonometry at least every 12 h for the first 48 h after admission and then on a daily basis during the first week.

RESULTS

The lowest pHi recorded during the first 48 h was significantly less in those admitted to the intensive care unit than that in those who remained on the surgical ward (P = 0.0015) and in nonsurvivors compared with the survivors (P = 0.009). A receiver-operator characteristic curve defined a pHi of 7.25 as the optimal cut-off point to predict death (sensitivity 100 per cent, specificity 77 per cent, overall predictive value 82 per cent).

CONCLUSION

These results suggest that splanchnic ischaemia may be an important determinant of outcome in patients with severe acute pancreatitis.

Gastric intramucosal pH predicts death in severe acute pancreatitis

BACKGROUND

This study tested the hypothesis that gastric intramucosal pH (pHi) can predict death in severe acute pancreatitis.

METHODS

Seventeen consecutive patients with predicted severe acute pancreatitis were studied prospectively. Four died from complications related to pancreatitis. Gastric pHi was measured by nasogastric tonometry at least every 12 h for the first 48 h after admission and then on a daily basis during the first week.

RESULTS

The lowest pHi recorded during the first 48 h was significantly less in those admitted to the intensive care unit than that in those who remained on the surgical ward (P = 0.0015) and in nonsurvivors compared with the survivors (P = 0.009). A receiver-operator characteristic curve defined a pHi of 7.25 as the optimal cut-off point to predict death (sensitivity 100 per cent, specificity 77 per cent, overall predictive value 82 per cent).

CONCLUSION

These results suggest that splanchnic ischaemia may be an important determinant of outcome in patients with severe acute pancreatitis.

The impact of antioxidant and splanchnic-directed therapy on persistent uncorrected gastric mucosal pH in the critically injured trauma patient

BACKGROUND

Critically ill trauma patients with gastric intramucosal acidosis, as measured by gastric tonometry, have an increased incidence of multiple organ dysfunction syndrome despite supranormal O2 delivery. We altered our resuscitation protocol to maximize splanchnic blood flow and decrease oxygen-derived free radical damage.

DESIGN

Prospective clinical trial with historical controls.

METHODS

The protocol differed from control by including administration of folate, mannitol, and low-dose isoproterenol. All patients had gastric tonometers and pulmonary artery catheters. If the intramucosal pH (pHi) was less than 7.25, splanchnic-sparing inotropic and vasodilatory agents were used to optimize systemic cardiac output. Two groups of trauma patients with persistent intramucosal acidosis at 24 hours (pHi < 7.25) were compared: a control group (n = 7), and patients who received the splanchnic/antioxidant protocol (n = 13).

RESULTS

The two groups were similar based on Acute Physiology and Chronic Health Evaluation II score, Injury Severity Score, age, cardiac index, oxygen delivery, and oxygen consumption. The "splanchnic therapy" group had fewer organ system failures as well as shortened length of intensive care unit and hospital stay. Three of 7 patients in the control group and 2 of 13 patients in the splanchnic therapy group had a final pHi < 7.25.

CONCLUSION

Gastric tonometry-guided resuscitation and antioxidant/splanchnic therapy in critically ill trauma patients with persistent gastric mucosal acidosis may decrease multiple organ dysfunction syndrome.

Randomized, prospective comparison of increased preload versus inotropes in the resuscitation of trauma patients: effects on cardiopulmonary function and visceral perfusion

OBJECTIVE

To evaluate the effects of maintaining increased levels of preload on cardiopulmonary function and visceral perfusion during resuscitation.

METHODS

Randomized, prospective study of 39 consecutive trauma patients with a low right ventricular ejection fraction (<40%) admitted to a university Level I trauma center during a 10-month period. Patients were randomized to one of two groups: increased preload (PL), or normal preload with inotropes (INO). The PL group received fluid administration to maintain a target right ventricular end-diastolic volume index (RVEDVI) > or = 120 mL/m2 during resuscitation. The INO group had inotropes added according to a prospectively determined protocol and was maintained at a RVEDVI of 90 to 100 mL/m2. Systemic perfusion was assessed using oxygen transport and acid-base parameters, and pulmonary function was evaluated with PaO2/FiO2 ratio, dynamic compliance, ventilator days, and incidence of adult respiratory distress syndrome. Gut perfusion was assessed by measuring gastric intramucosal pH (pHi). Data are expressed as means +/- SD.

RESULTS

The mean RVEDVI was significantly higher in the PL group (n = 19) than in the INO group (n = 20) during resuscitation (119+/-18 vs. 103+/-22 mL/m2, p = 0.01). There was no difference in oxygen delivery, mixed venous oxygen saturation, lactate, PaO2/FiO2 ratio, dynamic compliance, or ventilator days between the groups. The incidence of adult respiratory distress syndrome was not significantly different (PL 31% vs. INO 50%, p > 0.1). In the patients who had pHi measured sequentially during resuscitation (PL = 13, INO = 17), the final pHi was significantly higher in the PL group (7.31+/-0.1 vs. 7.16+/-0.2, p = 0.03).

CONCLUSION

Patients resuscitated at higher levels of preload have significantly better visceral perfusion than those resuscitated at normal preload with addition of inotropes. This higher preload does not adversely affect pulmonary function.

Continuous measurement of gut luminal PCO2 in the rat: responses to transient episodes of graded aortic hypotension

OBJECTIVES

To test the rapidity of a continuous PCO2 measurement system response to brief reductions in gut perfusion from transient episodes of graded aortic hypotension, and to investigate the relationship between the increase in ileal luminal PCO2 and mean aortic pressure during the episodes.

DESIGN

Prospective, experimental animal study.

SETTING

University research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats, weighing 430 to 510 g.

INTERVENTIONS

Five Sprague-Dawley rats were anesthetized with intraperitoneal sodium phenobarbital and ventilated with 100% oxygen via tracheostomy to a PaCO2 of 30 to 50 torr (4.0 to 6.7 kPa). Distal aortic pressure was monitored invasively, and a sensor was inserted into the ileal lumen. Luminal PCO2 measurements were recorded every 2 secs. Normal saline was infused at 3 mL/hr, and isoflurane was titrated to a mean aortic pressure of 80 to 100 mm Hg. In each rat, paired 2-min inductions of distal aortic hypotension were induced by digital elevation of an aortic silk sling above the celiac artery to as many as possible of the following pressures (mm Hg): 60, 50, 40, 30, 20, and 10. The experiment was stopped if instability of luminal PCO2 or hypotension persisted through the intervening 8-min recovery periods.

MEASUREMENTS AND MAIN RESULTS

One rat completed paired inductions of all six goal aortic pressures. Two rats completed five inductions. One rat completed four inductions, and one rat completed three inductions. The times to onset of luminal hypercapnia and to peak luminal hypercapnia were highly consistent and independent of the degree of hypotension. Onset of hypercapnia was usually detected < 1 min after aortic elevation, but peak luminal hypercapnia occurred approximately 1 min after release of the aortic sling. Regression analysis showed an inverse linear relationship between the maximum increase in luminal PCO2 above baseline and mean aortic pressure during induced hypotension (r2 = .6; p < .001).

CONCLUSIONS

Continuous ileal luminal PCO2 measurement by the sensor is rapidly responsive to brief reductions in aortic pressure in a rat model. Maximum luminal PCO2 increase during such perturbations is inversely related to mean aortic pressure.

Intra-abdominal hypertension and the abdominal compartment syndrome

IAH causes multiple and profound physiologic abnormalities both within and outside the abdomen. IAP monitoring is easily performed by bladder measurements. Careful monitoring and prompt recognition and treatment of IAP are critical in patients after damage control surgery because IAH is extremely common in these patients. Use of mesh fascial prostheses at the initial celiotomy in high-risk patients may prevent the deleterious effects of IAH. IAH should be considered an earlier manifestation of ACS. Surgical intervention should be indicated by IAH and not delayed until ACS is clinically apparent.

Cardiac preload, splanchnic perfusion, and their relationship during resuscitation in trauma patients

INTRODUCTION

Low gastric intramucosal pH (pHi) after shock resuscitation is associated with organ dysfunction and death in trauma patients. However, the relationship between hemodynamic performance, global oxygen transport, and pHi is unclear. Our purpose was to evaluate the relationship between intravascular volume status, splanchnic hypoperfusion, and outcome after shock resuscitation in trauma patients.

DESIGN/SETTING

Cohort study of 79 consecutive critically ill patients at a Level I trauma center stratified by normal (NORM, > or = 7.32) or low (LOW, < 7.32) pHi when lactate normalized (< 2.2 mmol/L).

MAIN OUTCOME MEASURES

Differences during resuscitation in mean values of right ventricular end-diastolic volume index (RVEDVI), pulmonary artery occlusion pressure, cardiac index, oxygen delivery index, and oxygen consumption index. The incidence of multiple organ failure and death in the NORM and LOW groups were analyzed via odds ratio and chi 2.

RESULTS

Patients in the NORM group (n = 45) had a lower incidence of multiple organ failure (4 of 45 vs. 11 of 34, odds ratio 5.0, p < 0.01) and death (5 of 45 vs. 11 of 34, odds ratio 3.8, p < 0.05) than patients in the LOW group (n = 34). NORM patients had a higher initial RVEDVI (116 +/- 31 vs. 95 +/- 25 mL/m2, p < 0.001) and maintained a significantly higher RVEDVI (114 +/- 27 vs. 97 +/- 17 mL/m2, p = 0.003) throughout resuscitation than the LOW group did. There were no differences in the other studied variables.

CONCLUSIONS

Supranormal levels of preload during shock resuscitation are associated with better outcome. Maintaining a RVEDVI higher than 100 mL/m2 during shock resuscitation may be of benefit in critically injured patients.

Use of tissue oxygen tension measurements during resuscitation from hemorrhagic shock

BACKGROUND

Tissue oxygen tension can be measured directly in selected organ beds, and these measurements may be more sensitive in assessing the adequacy of resuscitation than global physiologic parameters. We hypothesized that heart tissue oxygen tension would be an important marker for the severity of ischemic insult to the heart during hemorrhagic shock. We further hypothesized that gut oxygen tension measured in the jejunum would prove to be a better measure of splanchnic hypoperfusion than intramucosal pH (pHi).

METHODS

Tissue oxygen probes were inserted directly into the myocardium of the left ventricle and into the lumen of the proximal jejunum in 10 anesthetized swine. A pHi catheter was introduced into the stomach. The animals were subjected to a controlled hemorrhage of 50% of estimated blood volume. Gut and cardiac oxygen were monitored continuously during hemorrhage and resuscitation, which was performed with shed blood and crystalloid.

RESULTS

While gut O2 and pHi trended together, we were unable to establish a correlation between changes in these two variables during hemorrhage and resuscitation. Heart PO2 decreased significantly during hemorrhage, but surpassed baseline values after resuscitation, a finding not seen in gut PO2. No standard physiologic variables reliably predicted changes in heart PO2 during these experiments.

CONCLUSIONS

Tissue oxygen tensions measurements are highly responsive to changes induced during graded hemorrhagic shock and resuscitation. Gut PO2 and pHi appear to be measuring different physiologic processes in the gastrointestinal tract. The compensatory ability of the heart far exceeds that of the gut after ischemic insult. This hemorrhagic shock model appears feasible for the study of various methods of resuscitation.

Continuous assessment of gastric intramucosal PCO2 and pH in hemorrhagic shock using capnometric recirculating gas tonometry

OBJECTIVES

To test a novel device for continuous monitoring of gut intramucosal PCO2 and pH and to compare its use with conventional intermittent saline balloon-tonometry in a model of hemorrhagic shock.

DESIGN

A prospective animal study.

SETTINGS

A university research laboratory.

SUBJECTS

Eight anesthetized, mechanically ventilated mongrel dogs.

INTERVENTIONS

Two balloon-tip tonometry catheters, one conventional and one modified for continuous recirculating gas tonometry, were inserted into each animal's stomach by the oral route. Gastric intramucosal PCO2 was recorded continuously by capnometric recirculating gas tonometry throughout the experiment. After a baseline period of 90 mins, vital signs, arterial and mixed venous blood gases, and intramucosal PCO2 values were obtained by recirculating gas tonometry and by the conventional method. Using a modified Wiggers' model, the animals were then subjected to hemorrhage of up to 45 mL/kg, or the volume required to effect a decrease in mean arterial pressure to < 30 mm Hg. After 30 mins, the shed blood was reinfused and the experiment continued for an additional 30 mins. Vital signs, arterial and mixed venous blood samples, saline tonometry samples, and recirculating gas tonometry readings were obtained immediately before and 30 mins after reinfusion of blood.

MEASUREMENTS AND MAIN RESULTS

Mean +/- SD baseline intramucosal PCO2 was 47.6 +/- 9.5 torr (6.3 +/- 1.3 kPa) by capnometric recirculating gas tonometry and 45.8 +/- 3.4 torr (6.1 +/- 0.5 kPa) by conventional saline tonometry (p = NS). By 5 mins after inducing hemorrhage, intramucosal PCO2 by recirculating gas tonometry had increased significantly (49.3 +/- 9.7 torr [6.6 +/- 1.3 kPa]; p < .05), and by 30 mins, it had increased to 59.7 +/- 11.3 torr (8.0 +/- 1.5 kPa; p < .001 compared with baseline). After 30 mins of hemorrhage, the conventional method showed an increase in intramucosal PCO2 to 63.0 +/- 20.9 torr (8.4 kPa +/- 2.8 kPa; p = NS vs. baseline by conventional method; p = NS vs. corresponding recirculating gas tonometry values). Gastric intramucosal pH, as determined by recirculating gas tonometry, decreased significantly at 5 mins after starting hemorrhage (7.13 +/- 0.10 to 7.10 +/- 0.10, p < .02). After 30 mins of hemorrhage, intramucosal pH decreased to 6.88 +/- 0.14 (from 7.10 +/- 0.10) by the conventional saline tonometry technique (p < .01) and to 6.89 +/- 0.10 by recirculating gas tonometry (p < .001 vs. baseline). Intramucosal PCO2 by both techniques remained significantly increased above baseline values 30 mins after reinfusion of the shed blood.

CONCLUSIONS

Capnometric recirculating gas tonometry allows continuous and automated assessment of gastrointestinal tract perfusion by providing on-line measurements of intramucosal PCO2, which can also be used to derive intramucosal pH. The technique is able to detect changes in intramucosal PCO2 in response to an induced insult over intervals as short as 5 mins.

The use of oxygen consumption and delivery as endpoints for resuscitation in critically ill patients

OBJECTIVE

Oxygen consumption (VO2I) and delivery (DO2I) indices have been stated to be superior to conventional parameters as endpoints for resuscitation. However, another interpretation of published data is that inability to increase VO2I/DO2I given adequate volume resuscitation reflects inadequate physiologic reserve and poor outcome.

DESIGN

Fifty-eight critically ill patients were randomized to two groups. In group 1 (27 patients) attempts were made to maintain VO2I > or = 150 or DO2I > or = 600 mL/min/m2. If DO2I was > 600, no attempt was made to increase VO2I even if it was < 150. Group 2 (31 patients) was resuscitated based on conventional parameters. Volume resuscitation protocols and goals for pulmonary capillary wedge pressure were the same in both groups. VO2I/DO2I were recorded in group 2, but physicians were blinded to this data. Age, Injury Severity Score, and Acute Physiology and Chronic Health Evaluation (APACHE II) score were not different between groups.

MAIN RESULTS

Three patients in group 1 and two patients in group 2 died of organ failure (OF). One additional patient in group 2 died of refractory shock within 24 hours. Two of the patients in group 1 who died failed to meet VO2I/DO2I goals within 24 hours despite maximal resuscitation. Mortality was not different between the groups even with exclusion of the group 1 patients who failed to meet VO2I/DO2I goals (p = 0.66). After exclusion of the patient in group 2 who died of refractory shock, OF occurred in 18 of 27 (67%) in group 1 and in 22 of 30 (73%) in group 2 (p = 0.58). Length of ventilator support, intensive care unit stay, and hospital stay were not different between groups. When all patients were assessed, no difference was found in the incidence of OF between patients who attained the VO2I goal and those who did not. OF occurred in 20 of 34 (59%) patients who maintained a mean DO2I > or = 600 during the first 24 hours of the study and in 21 of 24 (88%) of those who did not (p < 0.02).

CONCLUSIONS

No difference was found in the incidence of OF or death in patients resuscitated based on oxygen transport parameters compared to conventional parameters. These data suggest that given adequate volume resuscitation, oxygen-based parameters are more useful as predictors of outcome than as endpoints for resuscitation.

Does increasing oxygen delivery improve outcome in the critically ill? No

The strategy of treating critically ill patients by increasing oxygen delivery and consumption to values previously observed among survivors of critical illness (supranormal values) is based on the belief that (1) tissue hypoxia may persist in critically ill patients despite aggressive early resuscitation to traditional endpoints of adequate tissue perfusion and (2) that increasing oxygen delivery can reverse tissue hypoxia. This article addresses the question of whether increasing oxygen delivery improves outcomes in critically ill patients by reviewing the relationship between whole-body oxygen delivery and consumption and by critically examining the randomized controlled trials that have increased oxygen delivery to supranormal values.

Rectal pH measurement in tracking cardiac performance in a hemorrhagic shock model

OBJECTIVE AND DESIGN

We evaluated the utility of rectal mucosal pH measurement for tracking cardiac performance in hemorrhagic shock as compared with gastric tonometry.

MATERIALS AND METHODS

Hemorrhagic shock was induced in five adult swine to a mean arterial pressure of 45-65 mm Hg. Hypotension was maintained for 30 minutes, resuscitation was accomplished with the shed blood and lactated Ringer's solution (3x blood volume). Gastric tonometry, rectal pH, and oxygen transport data were obtained at baseline, 0, and 30 minutes after onset of hypotension and after resuscitation.

RESULTS

Intramucosal pH readings from gastric tonometry and rectal mucosal pH both showed a significant change from baseline to 0 and 30 minutes after onset of hypotension. Data after resuscitation were found to be statistically the same as baseline values.

CONCLUSIONS

Rectal mucosal pH tracks cardiac performance as well as does gastric tonometry in hemorrhagic shock without as many limitations.