Rapid monitoring of gastrointestinal intraluminal PCO2 as an end-organ perfusion index

Esophageal capnometry during hemorrhagic shock and after resuscitation in rats

BACKGROUND

Splanchnic perfusion following hypovolemic shock is an important marker of adequate resuscitation. We tested whether the gap between esophageal partial carbon dioxide tension (PeCO2) and arterial partial carbon dioxide tension (PaCO2) is increased during graded hemorrhagic hypotension and reversed after blood reinfusion, using a fiberoptic carbon dioxide sensor.

MATERIALS AND METHOD

Ten Sprague-Dawley rats were anesthetized, tracheotomized, and cannulated in one femoral artery and vein. A calibrated fiberoptic PCO2 probe was inserted into the distal third of the esophagus for determination of luminal PeCO2 during maintained anesthesia (pentobarbital 15 mg/kg per hour), normothermia (38 +/- 0.5 degrees C), and fluid balance (saline 5 ml/kg per hour). Three out of 10 rats were used to determine the limits of hemodynamic stability during gradual hemorrhage. Seven of the 10 rats were then subjected to mild and severe hemorrhage (15 and 20-25 ml/kg, respectively). Thirty minutes after severe hemorrhage, these rats were resuscitated by reinfusion of the shed blood. Arterial gas exchange, hemodynamic variables, and PeCO2 were recorded at each steady-state level of hemorrhage (at 30 and 60 min) and after resuscitation.

RESULTS

The PeCO2-PaCO2 gap was significantly increased after mild and severe hemorrhage and returned to baseline (prehemorrhagic) values following blood reinfusion. Base deficit increased significantly following severe hemorrhage and remained significantly elevated after blood reinfusion. Significant correlations were found between base deficit and PeCO2-PaCO2 (P < 0.002) and PeCO2 (P < 0.022). Blood bicarbonate concentration decreased significantly following mild and severe hemorrhage, but its recovery was not complete at 60 min after blood reinfusion.

CONCLUSION

Esophageal-arterial PCO2 gap increases during graded hemorrhagic hypotension and returns to baseline value after resuscitation without complete reversal of the base deficit. These data suggest that esophageal capnometry could be used as an alternative for gastric tonometry during management of hypovolemic shock.

Acute phase response to nitroprusside-induced controlled hypotension in patients undergoing radical prostatectomy

This study evaluated the effects of sodium nitroprusside-induced controlled hypotension on the acute phase response in patients undergoing radical prostatectomy. Thirty patients were randomly allocated to two groups, a hypotension group (mean arterial blood pressure was adjusted to 50 mmHg) and a control group (mean arterial blood pressure > 70 mmHg). C-reactive protein increased significantly in the hypotension group from 0.13 (0.23) to 9.85 (2.84) microg x ml-1 and in the control group from 0.15 (0.27) to 7.38 (3.02) microg x ml-1. In both groups, serum amyloid A increased significantly, but levels were higher in the hypotension group [585 (125) microg x l-1] than in the control group [460 (187) microg x l-1]. Interleukin-6 increased significantly in both groups, but was higher in the hypotension group [139 (124) pg x ml-1] than the control group [56 (27) pg x ml-1]. Elastase showed no significant changes in the control group but in the hypotension group there was a significant increase from 65 (51) to 122 (75) ng x ml-1. Sodium nitroprusside-induced hypotension was associated with a more pronounced acute phase reaction.

A novel approach to monitor tissue perfusion: bladder mucosal PCO2, PO2, and pHi during ischemia and reperfusion

PURPOSE

The purpose of this study is to determine if monitoring urinary bladder PCO2, PO2, and calculated intramucosal pH would be a reliable index of tissue perfusion.

MATERIALS AND METHODS

This nonrandomized controlled study was conducted in a laboratory at a university medical center. Eight immature female Yorkshire pigs were studied with T-9 aortic cross-clamping for 30 minutes followed by a 60-minute period of reperfusion. Cystotomy was performed for placement of a Foley catheter and Paratrend 7 O2/CO2 sensor.

RESULTS

Baseline hemodynamic and metabolic measurements were obtained along with measurements of bladder mucosal PO2 and PCO2 (mean+/-SEM). Blood flow measured with microspheres confirmed absence of blood flow during occlusion and hyperemia during reperfusion. Bladder mucosal PO2 decreased from 42+/-14.0 mm Hg (5.6 kPa) to 1.3+/-1.3 mm Hg (1.4 kPa) during the 30-minute interval of ischemia. This was followed by an increase of bladder PO2 to greater than baseline values at the end of the reperfusion period. Bladder mucosal Pco2 increased from 57+/-4.7 mm Hg (7.6 kPa) to 117+/-7.1 mm Hg (15.6 kPa) (P < .05) during ischemia. During reperfusion the Pco2 returned to baseline levels (55+/-4.0 mm Hg [7.3 kPa]). Calculated bladder mucosal pHi declined from 7.31+/-0.04 to 7.08+/-0.05 (P < .05) during the ischemic period and after reperfusion pHi was 7.17+/-0.03.

CONCLUSIONS

Monitoring urinary bladder PO2, PCO2, or calculating pHi may provide a simple and reliable means of monitoring tissue perfusion.