Effect of nasogastric suction and ranitidine on the calculated gastric intramucosal pH

Effects of levosimendan on indocyanine green plasma disappearance rate and the gastric mucosal-arterial pCO2 gradient in abdominal aortic aneurysm surgery

BACKGROUND

Levosimendan has a dual mechanism of action: it improves myocardial contractility and causes vasodilatation without increasing myocardial oxygen demand. In a laboratory setting, it selectively increases gastric mucosal oxygenation in particular and splanchnic perfusion in general. The aim of our study was to describe the effects of levosimendan on systemic and splanchnic circulation during and after abdominal aortic surgery.

METHODS

Twenty abdominal aortic aneurysm surgery patients were randomized to receive either levosimendan (n=10) or placebo (n=10) in a double-blinded manner. Both the mode of anaesthesia and the surgical procedures were performed according to the local guidelines. Automatic gas tonometry was used to measure the gastric mucosal partial pressure of carbon dioxide. Systemic indocyanine green clearance plasma disappearance rate (ICG-PDR) was used to estimate the total splanchnic blood flow.

RESULTS

The immediate post-operative recovery was uneventful in the two groups with a comparable, overnight length of stay in the intensive care unit. Cumulative doses of additional vasoactive drugs were comparable between the groups, with a tendency towards a higher cumulative dose of noradrenaline in the levosimendan group. After aortic clamping, the cardiac index was higher [4(3.8-4.7) l/min/m(2) vs. 2.6(2.3-3.6) l/min/m(2); P<0.05] and the gastric mucosal-arterial pCO(2) gradient was lower in levosimendan-treated patients [0.9(0.6-1.2) kPa vs. 1.7(1.2-2.1) kPa; (P<0.05)]. However, the total splanchnic blood flow, estimated by ICG-PDR, was comparable [29(21-29)% vs. 20(19-25)%; NS]. Organ dysfunction scores (sequential organ dysfunction assessment) were similar between the groups on the fifth post-operative day.

CONCLUSION

Levosimendan favours gastric perfusion but appears not to have a major effect on total splanchnic perfusion in patients undergoing an elective aortic aneurysm operation.

Tonometry revisited: perfusion-related, metabolic, and respiratory components of gastric mucosal acidosis in acute cardiorespiratory failure

Mucosal pH (pHi) is influenced by local perfusion and metabolism (mucosal-arterial pCO2 gradient, DeltapCO2), systemic metabolic acidosis (arterial bicarbonate), and respiration (arterial pCO2). We determined these components of pHi and their relation to outcome during the first 24 h of intensive care. We studied 103 patients with acute respiratory or circulatory failure (age, 63+/-2 [mean+/-SEM]; Acute Physiology and Chronic Health Evaluation II score, 20+/-1; Sequential Organ Failure Assessment score, 8+/-0). pHi, and the effects of bicarbonate and arterial and mucosal pCO2 on pHi, were assessed at admission, 6, and 24 h. pHi was reduced (at admission, 7.27+/-0.01) due to low arterial bicarbonate and increased DeltapCO2. Low pHi (<7.32) at admission (n=58; mortality, 29% vs. 13% in those with pHi>or=7.32 at admission; P=0.061) was associated with an increased DeltapCO2 in 59% of patients (mortality, 47% vs. 4% for patients with low pHi and normal DeltapCO2; P=0.0003). An increased versus normal DeltapCO2, regardless of pHi, was associated with increased mortality at admission (51% vs. 5%; P<0.0001; n=39) and at 6 h (34% vs. 13%; P=0.016; n=45). A delayed normalization or persistently low pHi (n=47) or high DeltapCO2 (n=25) was associated with high mortality (low pHi [34%] vs. high DeltapCO2 [60%]; P=0.046). In nonsurvivors, hypocapnia increased pHi at baseline, 6, and 24 h (all P<or=0.001). In patients with initially normal pHi or DeltapCO2, outcome was not related to subsequent changes in pHi or DeltapCO2. Increased DeltapCO2 during early resuscitation suggests poor tissue perfusion and is associated with high mortality. Arterial bicarbonate contributes more to pHi than the DeltapCO2 but is not associated with mortality. Hyperventilation partly masks mucosal acidosis. Inadequate tissue perfusion may persist despite stable hemodynamics and contributes to poor outcome.

Effects of simulated hypovolaemia on haemodynamics, left ventricular function, mesenteric blood flow and gastric Pco2

BACKGROUND

Compensated clinically silent hypovolaemia may lead to low cardiac output, hypoperfusion and ischaemia. We investigated the cardiovascular effects of simulated hypovolaemia to determine whether it caused mesenteric ischaemia detectable by gastric tonometry.

METHODS

Thirteen healthy volunteers, aged 21-36 years, were investigated. Lower body negative pressure (LBNP) was used to simulate normotensive hypovolaemia. Cardiovascular parameters were measured using echocardiography. Mesenteric blood flow was investigated using Doppler sonography of the superior mesenteric artery (SMA). Gastric Pco(2) (P(g)co(2)) was measured using gas tonometry. Data were collected at baseline, LBNP and during a recovery period.

RESULTS

Normotensive hypovolaemia was induced successfully in 11 volunteers. There were no significant differences in mean arterial pressure between the three data points (91 +/- 6, 93 +/- 10 and 95 +/- 9 mmHg, respectively). With the induction of LBNP, the heart rate increased from 64 +/- 16 to 73 +/- 16 beats/min (P < 0.001), the cardiac index decreased from 2.7 +/- 1.0 to 1.8 +/- 0.6 l/min/m(2) (P= 0.002) and the systemic vascular resistance increased from 1535 +/- 445 to 2270 +/- 550 dyn s/cm(5) (P < 0.001). The SMA mean flow velocity decreased from 53 +/- 18 to 37 +/- 20 cm/s (69 +/- 20%) (P= 0.007), and increased to 56 +/- 34 cm/s (106 +/- 38%) (P= 0.001) during reperfusion. The SMA resistance increased from 92 +/- 30 to 174 +/- 110 mmHg/l/min (P= 0.004). These changes were reversible after termination of LBNP. By contrast, there were no significant differences in P(g)co(2) between the three data points.

CONCLUSIONS

In these volunteers, the mesenteric vascular bed contributed importantly to the maintenance of arterial pressure during normotensive hypovolaemia. However, this compensated hypovolaemia did not compromise the mesenteric perfusion sufficiently to increase P(g)co(2) and to allow detection by tonometry.

Prolonged intestinal mucosal acidosis is associated with multiple organ failure in human acute pancreatitis: Gastric tonometry revisited

AIM: To evaluate whether multiple determinations of intramucosal pH (pHi) in acute pancreatitis (AP) patients could provide additional information of the disease severity during early hospitalization.

METHODS: Twenty-one patients suffering from acute pancreatitis were monitored by gastric tonometry in the first 72 h after hospital admission.

RESULTS: In the survivor group (n = 15) the initially low pHi values returned to normal level (pHi ≥ 7.32) within 48 h (median pHi: d 1: 7.21; d 2: 7.32; d 3: 7.33). In contrast, pHi values in the non-survivor group n = 6) were persistently either below or in the low normal range (median pHi 7.12; 7.12; 7.07 respectively), but pHi differences between the two groups reached significance only after 24 h (P < 0.01). Mucosal acidosis detected at any time during the monitored period was associated with the emergence of single or multiple organ dysfunction (P < 0.01).

CONCLUSION: Prolonged gastric mucosal acidosis was associated with remote organ dysfunction and failure in Acute Pancreatitis, however, correlation with the fatal outcome became significant only 24 h after admission. Due to its non-invasive nature gastric tonometry may supplement the pro-inflammatory markers to achieve a multi-faceted monitoring of the disease.

Equipment review: the success of early goal-directed therapy for septic shock prompts evaluation of current approaches for monitoring the adequacy of resuscitation

A recent trial utilizing central venous oxygen saturation (SCVO₂) as a resuscitation marker in patients with sepsis has resulted in its inclusion in the Surviving Sepsis Campaign guidelines. We review the evidence behind SCVO₂ and its relationship to previous trials of goal-directed therapy. We compare SCVO₂ to other tools for assessing the adequacy of resuscitation including physical examination, biochemical markers, pulmonary artery catheterization, esophageal Doppler, pulse contour analysis, echocardiography, pulse pressure variation, and tissue capnometry. It is unlikely that any single technology can improve outcome if isolated from an organized pattern of early recognition, algorithmic resuscitation, and frequent reassessment. This article includes a response to the journal's Health Technology Assessment questionnaire by the manufacturer of the SCVO₂ catheter.

Gastric tonometry and monitoring gastrointestinal perfusion: using research to support nursing practice

The principles and physiological underpinnings of gastric tonometry are reviewed. Tonometric variables, including the PtCO2, pHi and CO2 gap, are described and critiqued as measurements of gastrointestinal perfusion. Increases in gastrointestinal CO2 unrelated to gastrointestinal hypoperfusion are discussed within different clinical contexts. The technical limitations of gastric tonometry, including procedural errors and PtCO2 measurement are discussed in relation to the accuracy of tonometric measurements. Tonometric measurement using semi-continuous air tonometry is introduced as a strategy to minimize technical limitations.

Effects of terlipressin on systemic and regional haemodynamics in catecholamine-treated hyperkinetic septic shock

OBJECTIVES

To determine the effects of an intravenous bolus dose of a vasopressin analogue, terlipressin (1 mg), on systemic haemodynamic parameters and gastric mucosal perfusion (GMP) in patients with catecholamine-treated septic shock using a gastric tonometry and laser-Doppler flowmetry technique.

DESIGN

Prospective open label study.

SETTINGS

Two multidisciplinary intensive care units.

PATIENTS

Fifteen patients with norepinephrine-treated septic shock.

INTERVENTIONS

Every patient with mean arterial pressure between 50 and 55 mmHg treated with high dose norepinephrine received an intravenous bolus dose of terlipressin as last resort therapy. A laser-Doppler probe and tonometer were introduced into the gastric lumen.

MEASUREMENTS AND MAIN RESULTS

Terlipressin produced a decrease in cardiac output ( p<0.05), a progressive increase in mean arterial pressure ( p<0.05) and in GMP, detected by laser-Doppler flowmetry ( p<0.05) over 30 min and sustained for at least 24 h. The ratio of GMP to systemic oxygen delivery increased after terlipressin bolus dose ( p<0.05). The gradient between gastric mucosal and arterial PCO(2) tended to be lower after terlipressin, and the difference was statistically significant ( p<0.05) after 8 h. Terlipressin administration significantly increased ( p<0.05) urine output compared to baseline and higher values were found at each set of measurement. The terlipressin-induced increase in urine output was associated with a significantly increased creatinine clearance ( p<0.05). Reduction of the high-dose norepinephrine was observed in all patients ( p<0.05).

CONCLUSIONS

Our findings showed that, in patients with norepinephrine-treated septic shock, terlipressin increased GMP, urine output and creatinine clearance by an increase in mean arterial pressure.

Measuring intramucosal pH in very low birth weight infants

Maintenance of adequate perfusion is essential for health of the intestinal mucosa. Methods available to assess intestinal perfusion provide information on mesenteric blood flow, which may differ from mucosal flow. Intramucosal pH (pH(i)) is influenced by tissue oxygenation and perfusion. Gastric pH(i) can be measured using the technique of tonometry. A prospective observational clinical study was performed to examine relationships between measured gastric pH(i) and mucosal CO(2) (mCO(2)), and acid-base balance, gastrointestinal complications (necrotizing enterocolitis and perforation), and death in infants <1500 g birth weight. A nasogastric tonometry catheter (size 5F) was inserted into the stomach of infants, and pH(i) was calculated from mCO(2) levels measured using saline tonometry. Measurements were performed at 3, 12, 24, and 48 h, then daily until arterial access was unavailable. Two hundred eleven sets of measurements were performed on 38 infants [birth weight (mean +/-SD), 863 +/- 241 g; gestation, 26.5 +/- 1.8 wk; and median Clinical Risk Index for Babies score, 8.0 (interquartile range, 5.0-10.75)]. Mean pH(i) was 7.27 (95% confidence interval, 7.26-7.28) and mean mCO(2) was 47.0 mm Hg (95% confidence interval, 45.7-48.3 mm Hg). pH(i) and mCO(2) correlated significantly with arterial pH (pH(a)), arterial PCO(2) (PaCO(2)), and arterial base excess. There were no significant relationships between pH(a) and pH gap (pH(a)-pH(i)) or CO(2) gap (mCO(2)-PaCO(2)). Recurrent low pH(i) (<7.2 on more than one occasion) and an mCO(2)/PaCO(2) ratio of > or =1.29 were significantly associated with an increase in gastrointestinal complications. There were no statistically significant associations with death. In conclusion, changes in pH gap and CO(2) gap can occur without alteration in pH(a). Abnormalities in pH(i) might predict gastrointestinal complications in infants <1500 g.

Splanchnic perfusion during hemodialysis: evidence for marginal tissue perfusion

OBJECTIVE

Splanchnic perfusion may be compromised during hemodialysis because of hypovolemia, inflammatory response, and blood flow redistribution. The aim of this study was to assess the response of splanchnic blood flow and oxygen transport to hemodialysis.

DESIGN

A prospective clinical study.

SETTING

A mixed medical-surgical intensive care unit in a university hospital.

PATIENTS

Nine patients with acute renal failure.

INTERVENTIONS

A 4-hr period of hemodialysis.

MEASUREMENTS AND MAIN RESULTS

Systemic (via a pulmonary artery catheter), hepatosplanchnic, and femoral (via dye dilution) blood flow and gastric mucosal Pco2 were measured before, during, and 2 hrs after hemodialysis. During hemodialysis, despite unchanged arterial blood pressure, cardiac output and stroke volume decreased from 3.0 +/- 1.0 L/m2/min (mean +/- sd) to 2.3 +/- 0.7 L/m2/min (p =.02), and from 38 +/- 16 mL/m2/min to 28 +/- 12 mL/m2/min (p =.01), respectively. Splanchnic but not femoral blood flow decreased from 0.9 +/- 0.3 L/m2/min to 0.7 +/- 0.2 L/m2/min (p =.02). The blood flows returned to baseline values after dialysis without need for therapeutic interventions. Gastric mucosal-arterial Pco2 gradients were high before dialysis (35 +/- 23 torr [4.6 +/- 3.1 kPa]) and did not change. Renin but not atrial natriuretic peptide concentration increased during hemodialysis from 13 +/- 13 microg/L to 35 +/- 40 microg/L and decreased afterward to baseline values (13 +/- 13 microg/L; p =.01). Whereas interleukin 6 tended to decrease, tumor necrosis factor alpha increased during hemodialysis from 74 +/- 24 pg/mL to 86 +/- 31 pg/mL and continued to increase after hemodialysis to 108 +/- 66 pg/mL (p =.022).

CONCLUSION

Hemodialysis and fluid removal in normotensive patients with acute renal failure may result in a reduction of systemic and splanchnic blood flow that is undetectable using traditional clinical signs. In contrast to what is observed in hypovolemia, the changes in regional blood flow are rapidly reversible after hemodialysis.

Impact of enteral feeding on gastric tonometry in healthy volunteers and critically ill patients

BACKGROUND

Enteral feeding may interfere with gastric tonometry measurement. The effect of enteral nutrition on gastric tonometry has not been fully documented.

METHODS

Seven healthy volunteers and nine stable intensive care unit (ICU) patients with poor tolerance of gastric feeding were investigated. Consecutive continuous postpyloric and gastric feeding, both at two different rates (40 and 100 ml. h-1, respectively), and an intragastric 200 ml nutrition bolus were studied. Gastric intramucosal PCO2 (PiCO2) was measured by air tonometry and in patients a gastric intramucosal-arterial PCO2 difference (PCO2 gap) was calculated. Hemodynamics and blood gases were also measured.

RESULTS

In volunteers, PiCO2 remained stable during the postpyloric phase. During continuous gastric feeding PiCO2 did not change significantly, although in 4 volunteers PiCO2 increased >0.5 kPa. PiCO2 decreased significantly after gastric bolus from 6.9+/-0.4 to 6.1+/-0.5 kPa (P<0.05). Eight patients had an increased PCO2 gap (>1 kPa) at baseline (1.8+/-0.6 kPa). PCO2 gap changes during the whole study were not statistically significant. However, during the postpyloric phase (or immediately afterwards), the PCO2 gap increased by more than 0.5 kPa in 5 patients. After gastric bolus, a decrease in PCO2 gap >0.5 kPa was seen in 5 patients.

CONCLUSION

In volunteers, postpyloric feeding does not interfere with gastric tonometry measurement and gastric bolus leads to a PiCO2 decrease. The impact of postpyloric and gastric feeding on gastric tonometry in ICU patients with compromised gut is variable.

Gastric intramucosal PCO2 and pH variability in ventilated critically ill patients

OBJECTIVE

Gastric intramucosal PCO2 (PiCO2) and pH (pHi) are currently used as indices of the adequacy of splanchnic perfusion and as end points to guide therapeutic intervention. However, little is known about their spontaneous variability over time. The present study was designed to define the magnitude of spontaneous variability of PiCO2 and pHi in sedated medical intensive care unit (ICU) patients using an automated recirculating air tonometer and to test whether high-level positive end-expiratory pressure (PEEP) or inverse inspiratory/expiratory (I:E) ratio ventilation resulted in a greater variability than low PEEP with conventional I:E ratio ventilation.

DESIGN

Prospective study.

SETTING

Medical ICU in a tertiary medical center.

PATIENTS

Twenty-three acute respiratory failure patients.

INTERVENTIONS

After being sedated, patients were randomized to undergo pressure control ventilation at the following three settings: A, high PEEP (15 cm H2O) with conventional I:E ratio (1:2), and B, low PEEP (5 cm H2O) with inverse I:E ratio (2:1) alternately, and then C, low PEEP (5 cm H2O) with conventional I:E ratio (1:2). Each ventilation setting period lasted 1 hr.

MEASUREMENTS AND MAIN RESULTS

The PiCO2 and pHi were measured at baseline (time 0), and at 15, 30, 45, and 60 mins thereafter. The corresponding coefficients of variation (CVs) of PiCO2 for overall pooled group and settings A, B, and C were 4.0%, 4.4%, 3.4%, and 4.2%, respectively. The corresponding CVs of pHi for overall pooled group and settings A, B, and C were 0.36%, 0.37%, 0.33%, and 0.4%, respectively. Analysis of variance showed no significant difference in the CVs of PiCO2 or pHi between the three settings. The 95% confidence interval is approximately +/-8% variability for PiCO2 and +/-0.7% variability for pHi.

CONCLUSIONS

In critically ill medical ICU patients with stable hemodynamics, the spontaneous variability of PiCO2 or pHi are not substantial. High PEEP (15 cm H2O) and inverse ratio ventilation (2:1), which does not change the cardiac output or hemodynamics, does not contribute to increased spontaneous variability in PiCO2 or pHi.

Jejunal and gastric mucosal perfusion versus splanchnic blood flow and metabolism: an observational study on postcardiac surgical patients

OBJECTIVES

To evaluate the association between changes in total splanchnic and mucosal perfusion, assessed either by gastric tonometry or jejunal laser Doppler flowmetry in postcardiac surgical patients.

DESIGN

A prospective, observational study.

SETTINGS

A general intensive care unit in a tertiary care center.

PATIENTS

Twelve, postoperative cardiac surgery patients were studied.

INTERVENTIONS

Patients were treated according to clinical routine. Total splanchnic blood flow (indocyanine green extraction), jejunal mucosal perfusion (laser Doppler flowmetry), gastric mucosal-arterial PCO2 gradients, and splanchnic lactate uptake were studied during four 30-min measurements periods, each separated by a period of 1 hr.

MEASUREMENTS AND MAIN RESULTS

There was no consistent association between either total splanchnic and local mucosal perfusion or between gastric and jejunal perfusion as assessed by two different techniques. The PCO2 gradient increased from 0.73+/-0.21 kPa to 1.15+/-0.30 kPa (p < .05), and splanchnic oxygen extraction increased from 40%+/-9% to 49%+/-14% (p < .01).

CONCLUSIONS

In this observational study on postcardiac surgical patients, local mucosal perfusion did not reflect total splanchnic blood flow and vice versa. Either changes in gastric and jejunal mucosal perfusion were different or increasing tissue metabolism was responsible for the observed lack of association between tonometry, laser Doppler flowmetry, and total splanchnic blood flow. Increasing mucosal arterial PCO2 gradient and splanchnic oxygen extraction may reflect a mismatch between splanchnic perfusion and metabolic demands.

Rectosigmoid pHi monitoring during experimental necrotizing enterocolitis

BACKGROUND/PURPOSE

Gastric or rectosigmoid intramural pH (pHi) is considered a reliable indicator of splanchnic perfusion. The aim of this study was to evaluate whether rectosigmoid pHi reflects the severity of bowel damage in experimental necrotizing enterocolitis (NEC).

METHODS

A total of 36 neonatal piglets, (median age, 3; range, 1 to 11 days; median weight, 2.5; range, 1.2 to 3.8 kg), were anesthetized, ventilated mechanically, and had invasive monitoring of hemodynamics. A sigmoid tonometer was inserted into the rectosigmoid colon. Enterocolitis was induced in 27 piglets by intraluminal injection of casein-d-gluconate (16.0 mL/kg) into terminal 100 cm of the ileum. Nine control piglets received an equal amount of intraluminal saline. NEC was graded macroscopically as follows: 0, no changes; 1, mild; 2, moderate; and 3, severe. Histology was evaluated according to Chiu scale from 0 to 5.

RESULTS

The macroscopical bowel injury in caseine-injected piglets was as follows: grade 3 (n = 6), grade 2 (n = 9), grade 1 (n = 12). All control piglets showed macroscopically normal bowel (grade 0). All affected bowels showed histologic changes (Chiu's scale 2 to 4). All study animals had an initial drop of pHi after injection of casein or saline. In control piglets and those with mild NEC (grade 1) pHi tended to return to preinjection level. In animals with moderate or severe NEC (grade 2 to 3) the initial drop was deeper and the pHi continued to decrease significantly throughout the experiment (P < .05). In the arterial pH and mean blood pressure there were no statistically significant differences between piglets with no NEC and mild NEC, and these with moderate or severe NEC.

CONCLUSION

Drop in rectosigmoid pHi was the most sensitive and earliest sign of severe mucosal necrosis of ileum in this experimental NEC model.

Gastric mucosal end-tidal PCO2 difference as a continuous indicator of splanchnic perfusion

Gastric mucosal and arterial blood PCO2 must be known to assess mucosal perfusion by means of gastric tonometry. As end-tidal PCO2 (PE'CO2) is a function of arterial PCO2, the gradient between PE'CO2 and gastric mucosal PCO2 may reflect mucosal perfusion. We studied the agreement between two methods to monitor gut perfusion. We measured the difference between gastric mucosal PCO2 (air tonometry) and PE'CO2 (= DPCO2gas) and the difference between gastric mucosal PCO2 (saline tonometry) and arterial blood PCO2 (= DPCO2sal) in 20 patients with or without lung injury. DPCO2gas was greater than DPCO2sal but changes in DPCO2gas reflected changes in DPCO2sal. The bias between DPCO2gas and DPCO2sal was 0.85 kPa and precision 1.25 kPa. The disagreement between DPCO2gas and DPCO2sal increased with increasing dead space. We propose that the disagreement between the two methods studied may not be clinically important and that DPCO2gas may be a method for continuous estimation of splanchnic perfusion.

A comparison of opiate- and epidural-induced alterations in splanchnic blood flow using intra-operative gastric tonometry

Several methods are available to measure splanchnic blood flow and gut ischaemia. Tonometry is most practical for peri-operative use. Epidural blockade from T5 to T11 causes mesenteric arteriovenous vasodilation and may increase splanchnic blood flow. This study assesses the ability of tonometry to measure differential effects of opiate and epidural analgesia on splanchnic blood flow. Forty patients for elective colorectal surgery were randomly allocated to receive epidural infusion or intravenous morphine. Gastric mucosal PCO2, pHi, standard pHi, PCO2 gap and pH gap were measured after induction and on termination of surgery. These parameters were within normal limits at the end in most cases and there was no significant difference between the groups. The complication rate was similar in both groups and was not correlated with low pHi, but was correlated with blood loss. We were unable to demonstrate a difference in splanchnic perfusion, as assessed by gastric tonometry, between the two groups.

Stress test and gastric-arterial PCO2 measurement improve prediction of successful extubation

OBJECTIVE

Correct early prediction of successful extubation decreases morbidity and mortality. The use of single time point measurements and surrogate markers of true extubation success limits weaning studies. Our aim was to determine whether a "stress test" improves prediction of extubation outcome and to determine the most predictive variables.

DESIGN

Observational study.

SETTING

Intensive care unit of a teaching hospital.

PATIENTS

A convenience sample of 68 patients judged to be ready for extubation.

INTERVENTIONS

We decreased pressure support from 5 to 0 cm H2O for 1 hr before extubation (stress test) while patients were on 5 cm H2O continuous positive airway pressure.

MEASUREMENTS AND MAIN RESULTS

We measured respiratory frequency, tidal volume, ratio of respiratory frequency to tidal volume (f/VT), airway occlusion pressure after onset of inspiration (P0.1), and gastric-arterial PCO2 (deltaPg-aCO2 both on 5 cm H2O and 0 cm H2O pressure support. Then all patients were extubated. Failure of extubation was defined as reintubation within 24 hrs. Seventeen patients (25%) failed extubation. With pressure support of 5 cm H2O and continuous positive airway pressure of 5 cm H2O, most predictors were not different between patients who failed and patients who were successfully extubated. After the stress test, deltaPg-aCO2 was 2 (-5; 15) mm Hg (median; quartiles) in successfully extubated patients vs. 28 (-9; 48) in failures (p = .0003), tidal volume was 473 (387; 558) vs. 400 (323; 435) mL (p = .02), and P0.1 was 2.8 (2; 4.1) vs. 4.1 (2.7; 5.3) mm Hg (p = .03), respectively. The stress test increased specificity of deltaPg-aCO2 from 0.45 to 0.94 and positive predictive value from 0.85 to 0.97. The specificity and positive predictive values for f/VT after the stress test were 0.23 and 0.78.

CONCLUSIONS

A simple stress test improves prediction of extubation outcome. deltaPg-aCO2 has superior specificity and positive predictive value compared with other variables. The use of true clinical outcome (i.e., extubation) instead of the use of surrogate markers (e.g., tachypnea) distinguishes these results from previous studies.

Small bowel tonometry is more accurate than gastric tonometry in detecting gut ischemia

Gastric tonometer PCO2 measurement may help identify gut ischemia in critically ill patients but is frequently associated with large measurement errors. We tested the hypothesis that small bowel tonometer PCO2 measurement yields more accurate information. In 10 anesthetized, mechanically ventilated pigs subject to progressive hemorrhage, we measured gut oxygen delivery and consumption. We also measured tonometer PCO2 minus arterial PCO2 (DeltaPCO2) and calculated the corresponding intracellular pH from tonometers placed in the stomach and jejunum. We found that the correlation coefficient (r2) for biphasic gut oxygen delivery-DeltaPCO2 relationships was 0.29 +/- 0.52 for the gastric tonometer vs. 0.76 +/- 0.25 for the small bowel tonometer (P < 0.05). In addition, the critical gastric tonometer DeltaPCO2 was excessively high and variable (62.9 +/- 39.6) compared with the critical small bowel tonometer DeltaPCO2 (17.0 +/- 15.0, P < 0.01). Small bowel tonometer PCO2 was closely correlated with superior mesenteric vein PCO2 (r2 = 0.81, P < 0.001), whereas gastric tonometer PCO2 was not (r2 = -0.13, P = not significant). We conclude that measurement of gastric tonometer PCO2 yields excessively noisy and inaccurate data on the onset of gut anaerobic metabolism in hemorrhagic shock. Small bowel tonometer PCO2 is less noisy and, as a result, is superior in detecting gut hypoperfusion and the onset of anaerobic metabolism.