Intestinal and gastric tonometry during experimental burn shock.

INTRODUCTION: The occurrence of organ failure following thermal injury, despite restoration of hemodynamic parameters and urine output during resuscitation, has led to efforts to measure end-organ perfusion. The purpose of this 24-h study was to evaluate the utility of gastrointestinal (GI) tonometry during burn shock and resuscitation. METHODS: Male swine (n=11, 23.3+/-0.9 kg) were anesthetized with ketamine and propofol. A 70% full thickness burn was caused by immersion in 97 degrees C water for 30 s. Resuscitation with lactated Ringer's, 4 ml/kg/% burn, was begun at hour 6 and titrated to urine output (UO). Arterial blood gases and pulmonary artery catheter data were measured every 6 h. Gastric and ileal regional PCO(2) (PrCO(2)) were measured continuously by air tonometry, and the gastric and ileal intramucosal pH (pHi) and PCO(2) gap (PrCO(2)-PaCO(2)) were calculated every 6 h. RESULTS: Gastric pHi, ileal PrCO(2), ileal pHi, and ileal PCO(2) gap (but not gastric PrCO(2) or PCO(2) gap) all decreased with shock and were restored to baseline levels by resuscitation. Changes in ileal PrCO(2) were of greater magnitude and demonstrated decreased variability than those in gastric PrCO(2). CONCLUSIONS: In this model, ileal tonometry outperformed gastric tonometry during burn shock and resuscitation.

Use of power Doppler ultrasound to monitor renal perfusion during burn shock.

BACKGROUND: Renal cortical blood flow can be quantified by means of power Doppler ultrasound (PDUS) image analysis. We hypothesized that renal cortical perfusion, estimated by PDUS image intensity (PDUSII), would decrease during burn shock and improve during resuscitation in a porcine model. METHODS: Eight anesthetized swine sustained a 75% scald injury. Resuscitation began 6h postburn. Renal cortical blood flow was measured directly using fluorescent microspheres (CORFLO), and was estimated noninvasively by PDUSII. PDUSII, CORFLO, and cardiopulmonary data were recorded every 2h. RESULTS: PDUSII decreased significantly from preburn to postburn hour 6, and increased with resuscitation by hour 8. CORFLO correlated well with PDUS image intensity (n=48, r(2)=0.696) but poorly with urine output (n=48, r(2)=0.252). CONCLUSION: PDUS in this study was superior to the urine output in assessing renal cortical microvascular blood flow during shock and resuscitation, and may be useful in the care of injured patients.

Evaluation of renal cortical perfusion by noninvasive power Doppler ultrasound during vascular occlusion and reperfusion.

BACKGROUND: Urine output, a frequently used resuscitation end point, is presumed to represent renal cortical perfusion. However, no noninvasive method for direct measurement of renal perfusion exists. Power Doppler ultrasound (PDUS) is a method that reportedly is sensitive to low-velocity and microvascular blood flow and can depict it. This study aimed to develop a quantitative technique for PDUS image analysis, and to evaluate the ability of PDUS to quantify cortical perfusion during renal ischemia induced by vascular occlusion. METHODS: A method was developed to determine the mean gray-scale intensity of PDUS images from within the renal cortex (PDUS image intensity). This index was hypothesized to represent renal cortical microvascular blood flow. Renal cortical blood flow was determined using fluorescent microspheres in five swine. Renal artery flow was measured with an ultrasonic flow probe. Power Doppler ultrasound was performed at baseline; at 75%, 50%, and 25% of baseline renal artery flow; and during reperfusion. RESULTS: Subjectively, PDUS images showed decreases in image intensity corresponding to renal artery occlusion and increases after reperfusion. Cortical blood flow correlated well with renal artery flow (n = 25; r2 = 0.868) and with PDUS image intensity (n = 25; r2 = 0.844). CONCLUSION: Noninvasive power Doppler ultrasound image intensity correlated well with invasively measured renal cortical blood flow, and may be useful during resuscitation of injured and critically ill patients.