Oxygen transport measurements to evaluate tissue perfusion and titrate therapy: dobutamine and dopamine effects

Extracorporeal carbon dioxide removal in heart-beating donor with acute severe asthma: A case report

Status asthmaticus is a life-threatening disorder that can manifest in dangerous levels of hypercapnia and acidosis. The use of extracorporeal carbon dioxide removal (ECCO2R) has been used successfully to control pH and PaCO₂ in patients with acute severe asthma. The present report describes the use of this technology in near-fatal asthma with brain death, and awaiting organ harvest. The ProLUNG® system consists of a veno-venous hemoperfusion circuit with an artificial lung polymethylpentene membrane coated with phosphorylcholine with a surface of 1.81 m². The system can reach a blood flow of 450 ml/min trough a double-lumen central venous catheter (13.0 Fr) placed in femoral, subclavian or jugular vein. The platform is provided with automated management of airflow and VCO₂ monitoring during treatment. The patient was maintained on extracorporeal treatment ensuring stable arterial pH control and PaCO₂ control. In acute status asthmaticus, complicated with cardiac arrest, mini-invasive ECCO2R was an effective method of controlling pH and PaCO₂, for optimizing hemodynamic and aerobic metabolism and for performing protective ventilation for an optimal organ donor preservation until the organ harvest occurs.

Central and Mixed Venous O2 Saturation

Mixed and central venous oxygen saturations are commonly used to ascertain the degree of systemic oxygenation in critically ill patients. This review examines the physiological basis for the use of these variables to determine systemic extraction ration, oxygen consumption and tissue oxygenation, and also understand the role they may play in the early treatment of septic individuals.

The effects of general anaesthesia on oxygen consumption: A meta-analysis guiding future studies on perioperative oxygen transport

BACKGROUND

Increased oxygen extraction, the ratio of consumption to delivery, has been associated with poor outcome after surgery. Oxygen consumption (VO2) can change in several ways in the perioperative period, but is seldom monitored directly in routine care. This study investigates the effects of general anaesthesia on VO2.

METHODS

We searched PubMed, EMBASE, and Cochrane Library 1946-2018 for studies including VO2 measurements before and after anaesthesia induction. Quality was assessed by Cochrane risk of bias tool and NIH Quality Assessment tool for before-and-after studies. Changes in VO2 after anaesthesia induction were pooled in a random effects model meta-analysis with standardized mean differences transformed to absolute changes of VO2. Changes in VO2 after surgical incision and after recovery from anaesthesia were analysed as secondary outcomes in the included studies.

RESULTS

Twenty-four studies including 453 patients were analysed for VO2 changes induced by anaesthesia. Studies were published during 1969-2000 and mean age of patients ranged 28-70 years. VO2 decreased after anaesthesia induction by -65 (-75; -55, 95% CI) mL min^-1 and indexed VO2 (VO2I) by -33 (-38; -28, 95% CI) mL min^-1  m^-2 . After surgical incision and in the post-operative period VO2 increased again. Heterogeneity was considerable among the studies and the overall quality of evidence was very low.

CONCLUSIONS

General anaesthesia probably reduces oxygen consumption but the effect estimate is uncertain. Given the limited generalizability and low quality of the available evidence, new studies in modern perioperative settings and in today's older high-risk surgical patient populations are needed.

A Device for the Quantification of Oxygen Consumption and Caloric Expenditure in the Neonatal Range

BACKGROUND

The accurate measurement of oxygen consumption (VO2) and energy expenditure (EE) may be helpful to optimize the treatment of critically ill patients. However, current techniques are limited in their ability to accurately quantify these end points in infants due to a low VO2, low tidal volume, and rapid respiratory rate. This study describes and validates a new device intended to perform in this size range.

METHODS

We created a customized device that quantifies inspiratory volume using a pneumotachometer and concentrations of oxygen and carbon dioxide gas in the inspiratory and expiratory limbs. We created a customized algorithm to achieve precise time alignment of these measures, incorporating bias flow and compliance factors. The device was validated in 3 ways. First, we infused a certified gas mixture (50% oxygen/50% carbon dioxide) into an artificial lung circuit, comparing measured with simulated VO2 and carbon dioxide production (VCO2) within a matrix of varying tidal volume (4-20 mL), respiratory rate (20-80 bpm), and fraction of inspired oxygen (0.21-0.8). Second, VO2, VCO2, and EE were measured in Sprague Dawley rats under mechanical ventilation and were compared to simultaneous Douglas bag collections. Third, the device was studied on n = 14 intubated, spontaneously breathing neonates and infants, comparing measured values to Douglas measurements. In all cases, we assessed for difference between the device and reference standard by linear regression and Bland-Altman analysis.

RESULTS

In vitro, the mean ± standard deviation difference between the measured and reference standard VO2 was +0.04 ± 1.10 (95% limits of agreement, -2.11 to +2.20) mL/min and VCO2 was +0.26 ± 0.31 (-0.36 to +0.89) mL/min; differences were similar at each respiratory rate and tidal volume measured, but higher at fraction of inspired oxygen of 0.8 than at 0.7 or lower. In rodents, the mean difference was -0.20 ± 0.55 (-1.28 to +0.89) mL/min for VO2, +0.16 ± 0.25 (-0.32 to +0.65) mL/min for VCO2, and -0.84 ± 3.29 (-7.30 to +5.61) kcal/d for EE. In infants, the mean VO2 was 9.0 ± 2.5 mL/kg/min by Douglas method and was accurately measured by the device (bias, +0.22 ± 0.87 [-1.49 to +1.93] mL/kg/min). The average VCO2 was 8.1 ± 2.3 mL/kg/min, and the device exhibited a bias of +0.33 ± 0.82 (-1.27 to +1.94) mL/kg/min. Mean bias was +2.56% ± 11.60% of the reading for VO2 and +4.25% ± 11.20% of the reading for VCO2; among 56 replicates, 6 measurements fell outside of the 20% error range, and no patient had >1 of 4 replicates with a >20% error in either VO2 or VCO2.

CONCLUSIONS

This device can measure VO2, VCO2, and EE with sufficient accuracy for clinical decision-making within the neonatal and pediatric size range, including in the setting of tachypnea or hyperoxia.

Phosphodiesterase Inhibitor-Based Vasodilation Improves Oxygen Delivery and Clinical Outcomes Following Stage 1 Palliation

BACKGROUND

Systemic vasodilation using α-receptor blockade has been shown to decrease the incidence of postoperative cardiac arrest following stage 1 palliation (S1P), primarily when utilizing the modified Blalock-Taussig shunt. We studied the effects of a protocol in which milrinone was primarily used to lower systemic vascular resistance (SVR) following S1P using the right ventricular to pulmonary artery shunt, measuring its effects on oxygen delivery (DO₂) profiles and clinical outcomes. We also correlated Fick-based assessments of DO₂ with commonly used surrogate measures.

METHODS AND RESULTS

Neonates undergoing S1P were treated according to best clinical judgment prior to (n=32) and following (n=24) implementation of a protocol that guided operative, anesthetic, and postoperative management, particularly as it related to SVR. A majority of the subjects (n=51) received a modified right ventricular to pulmonary artery shunt. In a subset of these patients (n=21), oxygen consumption (VO₂) was measured and used to calculate SVR, DO₂, and oxygen debt. Neonates treated with the protocol had significantly lower SVR (P=0.02), serum lactate (P<0.001), and Sa-vO₂ difference (P<0.001) and a lower incidence of CPR requiring extracorporeal membrane oxygenation (E-CPR, P=0.02) within the first 72 postoperative hours. DO₂ was closely associated with SVR (r²=0.78) but correlated poorly with arterial (SaO₂) and venous (SvO₂) oxyhemoglobin concentrations, the Sa-vO₂ difference, and blood pressure.

CONCLUSIONS

A vasodilator protocol utilizing milrinone following S1P effectively decreased SVR, improved serum lactate, and decreased postoperative cardiac arrest. DO₂ correlated more closely with SVR than with Sa-vO₂ difference, highlighting the importance of measuring VO₂ in this population.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02184169.

Update on Vasopressors and Inotropes in Septic Shock

Vasopressors and inotropes are used in septic shock in patients who remain hypotensive despite adequate fluid resuscitation. The goal is to increase blood pressure to optimize perfusion to organs. Generally, goal-directed therapy to supra-normal oxygen transport variables cannot be recommended due to lack of benefit. Traditionally, vasopressors and inotropes in septic shock have been started in a step-wise fashion starting with dopamine. Recent data suggest that there may be true differences among vasopressors and inotropes on local tissue perfusion as measured by regional hemodynamic and oxygen transport. When started early in septic shock, norepinephrine decreases mortality, optimizes hemodynamic variables, and improves systemic and regional (eg, renal, gastric mucosal, splanchnic) perfusion. Epinephrine causes a greater increase in cardiac index (CI) and oxygen delivery (DO2 ) and increases gastric mucosal flow, but increases lactic acid and may not adequately preserve splanchnic circulation owing to its predominant vasoconstrictive alpha (α ) effects. Epinephrine may be particularly useful when used earlier in the course of septic shock in young patients and those who do not have any known cardiac abnormalities. Unlike epinephrine, dopamine does not preferentially increase the proportion of CI that preferentially goes to the splanchnic circulation. Dopamine is further limited because it cannot increase CI by more than 35% and is accompanied by tachycardia or tachydysrhythmias. Dopamine, as opposed to norepinephrine, may worsen splanchnic oxygen consumption (VO2 ) and oxygen extraction ratio (O2 ER). Low-dose dopamine has not been shown to consistently increase the glomerular filtration rate or prevent renal failure, and, indeed, worsens splanchnic tissue oxygen use. Routine use of concurrently administered dopamine with vasopressors is not recommended. Phenylephrine should be used when a pure vasoconstrictor is desired in patients who may not require or do not tolerate the beta (β ) effects of dopamine or norepinephrine with or without dobutamine. Patients with high filling pressure and hypotension may benefit from the combination of phenylephrine and dobutamine. Investigational approaches to vasopressor-refractory hypotension in septic shock include the use of vasopressin and corticosteroids.

Effects of commonly used inotropes on myocardial function and oxygen consumption under constant ventricular loading conditions

Inotropic medications are routinely used to increase cardiac output and arterial blood pressure during critical illness. However, few comparative data exist between these medications, particularly independent of their effects on venous capacitance and systemic vascular resistance. We hypothesized that an isolated working heart model that maintained constant left atrial pressure and aortic blood pressure could identify load-independent differences between inotropic medications. In an isolated heart preparation, the aorta and left atrium of Sprague Dawley rats were cannulated and placed in working mode with fixed left atrial and aortic pressure. Hearts were then exposed to common doses of a catecholamine (dopamine, epinephrine, norepinephrine, or dobutamine), milrinone, or triiodothyronine (n = 10 per dose per combination). Cardiac output, contractility (dP/dtmax), diastolic performance (dP/dtmin and tau), stroke work, heart rate, and myocardial oxygen consumption were compared during each 10-min infusion to an immediately preceding baseline. Of the catecholamines, dobutamine increased cardiac output, contractility, and diastolic performance more than clinically equivalent doses of norepinephrine (second most potent), dopamine, or epinephrine (P < 0.001). The use of triiodothyronine and milrinone was not associated with significant changes in cardiac output, contractility or diastolic function, either alone or added to a baseline catecholamine infusion. Myocardial oxygen consumption was closely related to dP/dtmax (r(2) = 0.72), dP/dtmin (r(2) = 0.70), and stroke work (r(2) = 0.53). In uninjured, isolated working rodent hearts under constant ventricular loading conditions, dobutamine increased contractility and cardiac output more than clinically equivalent doses of norepinephrine, dopamine, and epinephrine; milrinone and triiodothyronine did not have significant effects on contractility.

Maternal caffeine administration leads to adverse effects on adult mice offspring

PURPOSE

This study aimed to evaluate the role of caffeine chronic administration during gestation of C57BL/6 mice on cardiac remodeling and the expression of components of the renin-angiotensin system (RAS) in male offspring as adults.

METHODS

Pregnant C57BL/6 female mice were divided into two groups (n = 10): Control group (C), dams were injected with the vehicle only (saline 0.9% NaCl); Caffeine group (CF), dams received daily a subcutaneous injection of 20 mg/kg of caffeine/day (1 mg/mL saline). Pups had free access to standard chow since weaning to 3 months of age, when they were killed.

RESULTS

CF group showed increased energy expenditure (+7%) with consequent reduction in body mass (BM) gain (-18%), increased blood pressure (+48%), and higher heart rate (+10%) than C group. The ratio between LV mass/BM was greater (+10%), with bigger cardiomyocytes (+40%), and reduced vascularization (-25%) in CF group than in C group. In the LV, the expression of angiotensin-converting enzyme (+30%), Angiotensin II (AngII) (+60%), AngII receptor (ATR)-1 (+77%) were higher, and the expression of ATR-2 was lower (-46%; P < 0.05) in CF group than in C group. In the kidney, the expressions of renin (+128%) and ATR-1 (+88%) were higher in CF group than in C group.

CONCLUSIONS

Chronic administration of caffeine to pregnant dams led to persistent activation of local RAS in the kidney and heart of the offspring, which, in turn, leads to high BP and adverse cardiac remodeling. These findings highlight the urge to encourage pregnant women to avoid food or medicines containing caffeine.

The cardiopulmonary effects of dobutamine and norepinephrine in isoflurane-anesthetized foals

OBJECTIVE

To evaluate the cardiovascular effects of norepinephrine (NE) and dobutamine (DB) in isoflurane-anesthetized foals.

STUDY DESIGN

Prospective laboratory study.

METHODS

Norepinephrine (0.05, 0.10, 0.20, and 0.40 microg kg(-1) minute(-1)) and dobutamine (2.5, 5.0, and 10 microg kg(-1) minute(-1)) were alternately administered to seven healthy, 1- to 2-week-old isoflurane-anesthetized foals. Arterial and pulmonary arterial blood pressure, right atrial pressure, pulmonary artery occlusion pressure, heart rate, body temperature, cardiac output, arterial and mixed venous blood pH, partial pressure of carbon dioxide, partial pressure of oxygen [arterial partial pressure of oxygen (PaO(2)) and mixed venous partial pressure of oxygen (PvO(2))], and packed cell volume were measured. Standard base excess, bicarbonate concentration, systemic and pulmonary vascular resistance, cardiac index (CI), stroke volume, left and right stroke work indices, oxygen delivery (DO(2)), consumption, and extraction were calculated. Results Norepinephrine infusion resulted in significant increases in arterial and pulmonary arterial pressure, systemic and pulmonary vascular resistance indices, and PaO(2); heart rate was decreased. Dobutamine infusion resulted in significant increases in heart rate, stroke volume index, CI, and arterial and pulmonary arterial blood pressure. Systemic and pulmonary vascular resistance indices were decreased while the ventricular stroke work indices increased. The PaO(2) decreased while DO(2) and oxygen consumption increased. Oxygen extraction decreased and PvO(2) increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Norepinephrine primarily augments arterial blood pressure while decreasing CI. Dobutamine primarily augments CI with only modest increases in arterial blood pressure. Both NE and DB could be useful in the hemodynamic management of anesthetized foals.

DYNAMIC NEAR-INFRARED SPECTROSCOPY MEASUREMENTS IN PATIENTS WITH SEVERE SEPSIS

This study evaluated near-infrared spectroscopy (NIRS)-derived measurements in hemodynamically stable patients with severe sepsis, as compared with similar measurements in healthy age-matched volunteers. Prospective, preliminary, observational study in a surgical intensive care unit and clinical research center at a university health center. We enrolled 10 patients with severe sepsis and 9 healthy age-matched volunteers. For patients with severe sepsis, we obtained pulmonary artery catheter and laboratory values three times daily for 3 days and oxygen consumption values via metabolic cart once daily for 3 days. For healthy volunteers, we obtained all noninvasive measurements during a single session. We found lower values in patients with severe sepsis (versus healthy volunteers), in tissue oxygen saturation (StO2), in the StO2 recovery slope, in the tissue hemoglobin index, and in the total tissue hemoglobin increase on venous occlusion. Patients with severe sepsis had longer StO2 recovery times and lower NIRS-derived local oxygen consumption values versus healthy volunteers. In our preliminary study, NIRS provides a noninvasive continuous method to evaluate peripheral tissue oxygen metabolism in hemodynamically stable patients with severe sepsis. Further research is needed to demonstrate whether these values apply to broader populations of patients with systemic inflammatory response syndrome, sepsis, severe sepsis, and septic shock.

Effects of isovolemic resuscitation with hemoglobin-based oxygen carrier Hemoglobin glutamer-200 (bovine) on systemic and mesenteric perfusion and oxygenation in a canine model of hemorrhagic shock: a comparison with 6% hetastarch solution and shed blood

OBJECTIVE

To study Hemoglobin glutamer-200 bovine (Hb-200), 6% hetastarch (HES) and shed whole blood (WB) resuscitation in canine hemorrhagic shock.

STUDY DESIGN

Prospective laboratory investigation. Animals Twelve adult dogs [29 +/- 1 kg (mean +/- SD)].

METHODS

Anesthetized dogs were instrumented for recording systemic and mesenteric hemodynamic parameters and withdrawal of arterial, mixed and mesenteric venous blood, in which hematological, oxygenation, blood gas and acid-bases variables were determined. Recordings were made before [baseline (BL)], after 1 hour of hypovolemia and immediately and 3 hours post-resuscitation with 30 mL kg(-1) of either Hb-200, HES, or WB.

RESULTS

Blood withdrawal (average 34 +/- 2 mL kg(-1)) caused significant hemodynamic changes, metabolic acidosis and hyperlactatemia characteristic for hemorrhagic shock. Only WB transfusion restored all variables. Hemoglobin glutamer-200 bovine infusion returned most hemodynamic parameters including cardiac output and mesenteric arterial blood flow to BL but increased mean arterial pressure above BL (p < 0.05). However, Hb-200 failed to restore total Hb and arterial oxygen content (CaO2), leaving systemic (DO2I) and mesenteric O2 delivery (DO2Im) below BL (p < 0.05). Nevertheless, acid-base variables recovered completely after Hb-200 resuscitation, and met-hemoglobin (Met-Hb) levels increased (p < 0.05). Hetastarch resuscitation returned hemodynamic variables to or above BL but further decreased total Hb and CaO2, preventing recovery of sDO2I and mDO2I (p < 0.05). Thus, systemic and mesenteric O2 extraction stayed above BL (p < 0.05) while acid-base variables recovered to BL, although slower than in Hb-200 and WB groups (p < 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

Resuscitation with Hb-200 seemed to resolve metabolic acidosis and lactatemia more rapidly than HES, but not WB; yet it is not superior to HES in improving DO2I and DO2Im. The hyperoncotic property of solutions like Hb-200 that results in rapid volume expansion with more homogenous microvascular perfusion and the ability to facilitate diffusive O2 transfer accelerating metabolic recovery may be the key mechanisms underlying their beneficial effects as resuscitants.

Tissue oxygenation response to mild hypercapnia during cardiopulmonary bypass with constant pump output

BACKGROUND

Tissue oxygenation is the primary determinant of wound infection risk. Mild hypercapnia markedly improves cutaneous, subcutaneous (s.c.), and muscular tissue oxygenation in volunteers and patients. However, relative contributions of increased cardiac output and peripheral vasodilation to this response remains unknown. We thus tested the hypothesis that increased cardiac output is the dominant mechanism.

METHODS

We recruited 10 ASA III patients, aged 40-65 yr, undergoing cardiopulmonary bypass for this crossover trial. After induction of anaesthesia, a Silastic tonometer was inserted s.c. in the upper arm. S.C. tissue oxygen tension was measured with both polarographic electrode and fluorescence-based systems. Oximeter probes were placed bilaterally on the forehead to monitor cerebral oxygenation. After initiation of cardiopulmonary bypass, in random order patients were exposed to two arterial CO(2) partial pressures for 30 min each: 35 (normocapnia) or 50 mm Hg (hypercapnia). Bypass pump flow was kept constant throughout the measurement periods.

RESULTS

Hypercapnia during bypass had essentially no effect on Pa(CO(2)) , mean arterial pressure, or tissue temperature. Pa(CO(2)) and pH differed significantly. S.C. tissue oxygenation was virtually identical during the two Pa(CO(2)) periods [139 (50-163) vs 145 (38-158), P=0.335] [median (range)]. In contrast, cerebral oxygen saturation (our positive control measurement) was significantly less during normocapnia [57 (28-67)%] than hypercapnia [64 (37-89)%, P=0.025].

CONCLUSIONS

Mild hypercapnia, which normally markedly increases tissue oxygenation, did not do so during cardiopulmonary bypass with fixed pump output. This suggests that hypercapnia normally increases tissue oxygenation by increasing cardiac output rather than direct dilation of peripheral vessels.

Optimizing the intraoperative management of carbon dioxide concentration

PURPOSE OF REVIEW

This review assesses whether there is a carbon dioxide concentration range that provides optimum benefit to the patient intraoperatively. It includes the physiological effects of carbon dioxide on various organ systems in awake and anesthetized individuals and its clinical effects in the ischemia/reperfusion setting. This review will present views on end-tidal or arterial carbon dioxide tension management in the perioperative period.

RECENT FINDINGS

Hypocapnia reduces intracranial pressure and is used by clinicians during acute traumatic brain injury, acute intracranial hemorrhage, and acutely growing brain tumors. There is mounting evidence, however, that hypercapnia improves tissue perfusion and oxygenation. Therefore, clinicians may want to induce mild-to-moderate hypercapnia during reperfusion states such as major vascular surgery, organ transplantation, tissue-graft surgery, and cases managed with low mean arterial pressures to control bleeding. As hypercapnia preserves cerebral blood flow even under relatively low perfusion pressures, it may be beneficial during global reperfusion scenarios. This hypothesis needs to be tested extensively before being considered for clinical applications. From a different perspective, current American Heart Association Guidelines recommend 12-15 breaths/min during cardiopulmonary resuscitation and stress the potential negative role of inadvertent hyperventilation on survival outcome. The importance of this concept is discussed briefly.

SUMMARY

Overall, the benefits of managing carbon dioxide concentration intraoperatively for the maintenance of cardiac output, tissue oxygenation, perfusion, intracranial pressure, and cerebrovascular reactivity are well defined.

Management of septic shock in childhood

OBJECTIVE

The object of this review is to discuss the recognition and treatment of septic shock in children based on principles of resuscitation, antibiotic use and recent therapeutic advances.

METHODS

A comprehensive literature search combining these

METHODS

on-line searches of Ovid, PubMed, and Medline; hand searches of 25 international journals; a trawl of 26 textbooks; searches of reference lists of pertinent articles; and scans of abstracts of recent international meetings. Various national and international units were contacted with regard to current research therapeutic strategies, both published and unpublished.

CONCLUSIONS

Septic shock remains a leading cause of morbidity and mortality in children. Early administration of empirical antibiotic therapy reduces mortality. The keystone of resuscitation is aggressive volume replacement. Adjunctive therapies to modulate the inflammatory response may further enhance outcome, but do not replace principles of resuscitation.

Nonpharmacological prevention of surgical wound infections

Postoperative wound infection is a common and serious complication of surgery. This review will focus on 2 factors known to modulate perioperative immunity: maintenance of perioperative normothermia and provision of supplemental perioperative oxygen. Hypothermia causes numerous adverse outcomes, including morbid myocardial events, increased blood loss and transfusion requirement, postsurgical wound infections, and prolonged hospitalization. Perioperative normothermia should thus be maintained unless therapeutic hypothermia is specifically indicated. Supplemental perioperative oxygen (inspired fraction of 80% instead of 30%) significantly reduces postoperative nausea and vomiting, diminishes the decrease in phagocytosis and bacterial killing usually associated with anesthesia and surgery, and reduces the rate of postoperative wound infection among patients who undergo colon resection. Available data thus suggest that supplemental perioperative oxygen improves surgical outcome with little or no associated risk.

Meta-analysis of hemodynamic optimization in high-risk patients

OBJECTIVE

The aim of this evidence-based report was to review pertinent randomized controlled studies that describe hemodynamic goals in acute, critically ill patients and to evaluate outcome of resuscitation therapy in association with physiologic, clinical, and therapeutic influences.

METHODS

MEDLINE was the source of randomized controlled studies written in English. The inclusion criteria were acutely ill, high-risk elective surgery, trauma, and septic patients. The goals of therapy were to resuscitate to either normal or supranormal values; the latter were described as a cardiac index of >4.5 L x min(-1) x m(-2), pulmonary artery occlusion pressure of <18 mm Hg, oxygen delivery of >600 mL x min(-1) x m(-2), and oxygen consumption of >170 mL x min(-1) x m(-2). The outcome criterion was survival or death. We found 21 randomized clinical trials described in 20 articles. The studies were divided into groups based on the time that goals were implemented (i.e., "early," 8 to 12 hrs postoperatively or before organ failure, vs. "late," or after onset of organ failure) and the severity of illness, determined by the control group mortality as >20% (12 studies) or <15% (nine studies).

RESULTS

In severely ill patients (control mortalities group >20%), six studies had a 23% mortality difference (p <.05) between the control and protocol groups with early optimization, but seven studies optimized after the development of organ failure did not have significantly improved mortality. Moreover, outcome was not significantly improved in less severely ill patients (control mortalities group <15%) and normal values as goals or when therapy did not improve oxygen delivery.

CONCLUSION

Review of 21 randomized controlled trials with various approaches to treatment revealed statistically significant mortality reductions, with hemodynamic optimization, when patients with acute critical illness were treated early to achieve optimal goals before the development of organ failure, when there were control group mortalities of >20% and when therapy produced differences in oxygen delivery between the control and protocol groups.

The oxygen debt during routine cardiac surgery: illusion or reality?

BACKGROUND

Patients undergoing cardiac surgery with the use of cardiopulmonary bypass (CPB) are often thought to have tissue hypoxia and intraoperative oxygen debt accumulation despite the lack of sufficient data to support this assumption.

METHODS AND RESULTS

Oxygen uptake and related parameters, including the plasma lactate and pyruvate concentrations, were studied during the perioperative period in a group of 15 consecutive patients who underwent coronary artery bypass graft surgery. The actual oxygen uptake (VO2) and delivery (DO2) were compared with the individual expected (computed) oxygen transport values. The mean values of DO2 and VO2 were in the range of the expected values. Our results demonstrate a leading role for body temperature in perioperative changes of oxygen consumption rate (r2=0.65, p<0.001). Plasma lactate and pyruvate did not exceed the physiological range in any patient. However, with initiation of CPB, the lactate to pyruvate (LA/PVA) ratio increased (from 9.87 +/- 2.43 at T1 to 12.08 +/- 1.51 at T2, p<0.05). The mean value of the LA/ PVA ratio was elevated during surgery. Later, upon lowering of the plasma lactate concentration in the postoperative period, the LA/PVA ratio decreased to normal values. Without any other evidence of hypoxia, this increase in the LA/PVA ratio could be explained by washout of lactate from previously hypoperfused tissues and intraoperative decrease of lactate clearance.

CONCLUSION

Systemic oxygenation was not impaired during CPB, or during 18 h after surgery in the studied group of patients.

The hemodynamic effects of diaspirin cross-linked hemoglobin in dopamine-resistant endotoxic shock in swine

As the blood substitute Diaspirin Cross-linked Hemoglobin (DCLHb) has potent vasopressor activity, we assessed its hemodynamic effects in a clinically relevant dopamine-resistant endotoxic shock model in swine. In a randomized and controlled study, E. coli LPS was administered to anesthetized and invasively monitored swine. Group I (n = 3) control pigs were not resuscitated. Groups II (n = 5) and III (n = 6) pigs received dopamine (DA) after MAP decreased 30%, and hetastarch and DCLHb, respectively, after dopamine-resistance occurred. Progressive hemodynamic decline occurred in Group I pigs. DA failed to restore MAP to baseline. However, 0% and 67% of pigs also treated with heta-starch and DCLHb, respectively, achieved temporary restoration of baseline MAP (p = 0.03), prompting a reduction in the dose of DA in 0% of hetastarch vs. 50% of DCLHb treated pigs. Except for increased MPAP and decreased heart in DCLHb treated pigs (p<0.001), hemodynamics and survival were not different (p>0.05). In conclusion, although DCLHb exacerbated pulmonary hypertension and did not improve O2 utilization or survival, because DCLHb restored MAP to baseline and had a dopamine sparing effect, further investigation of DCLHb's hemodynamic effects in adrenergic agent-resistant endotoxemia is warranted.

Monitoring tissue oxygenation during resuscitation of major burns

BACKGROUND

Because subcutaneous and splanchnic oxygenation indices are sensitive indicators of evolving hemorrhagic shock and adequacy of resuscitation, we postulated that these indices might have an equivalent role in the monitoring of severely burned patients. This observational study was undertaken to examine changes in tissue oxygenation indices during burn resuscitation.

METHODS

Seven patients with major burns (54 +/- 21% total body surface area) were studied during the first 36 hours of fluid resuscitation. Silastic tubing was placed in the subcutaneous tissue just beneath both normal skin and deep partial thickness burn. Fiberoptic sensors inserted into the tubing measured subcutaneous oxygen and carbon dioxide tensions in the burnt skin (PO2scb and PCO2scb) and normal skin (PO2scn and PCO2scn) continuously. Gastric intramucosal pH (pHi) and the mucosal CO2 (PCO2m) gap were calculated using gastric tonometers. Mean arterial pressure, arterial pH, lactate, and pHi measurements were obtained for 36 hours.

RESULTS

There were no significant differences in mean arterial pressure, arterial pH, or lactate concentrations throughout the study period, whereas indices of tissue oxygenation showed deterioration: pHi decreased from 7.2 +/- 0.1 to 6.7 +/- 0.3 (p = 0.06), the PCO2m gap increased from 12 +/- 17 to 108 +/- 123 mm Hg (p < 0.01), PO2scn decreased from 112 +/- 18 to 50 +/- 11 mm Hg (p < 0.01), PO2scb decreased from 62 +/- 23 to 29 +/- 16 mm Hg (p < 0.01), PCO2scn increased from 42 +/- 4 to 46 +/- 10 mm Hg (p = 0.2), and PCO2scb increased from 42 +/- 10 to 52 +/- 5 mm Hg (p = 0.05).

CONCLUSION

Despite adequate global indices of tissue perfusion after 36 hours of resuscitation, tissue monitoring indicated significant deterioration in the splanchnic circulation and in the normal and burnt skin.

Supportive therapy of the sepsis syndrome

Adequate volume loading may be the most important step in the treatment of patients with septic shock. Techniques allowing us to achieve and tightly control volume loading and regional perfusion are considered to be helpful. An elevated oxygen delivery may be beneficial in some patients but the increase of oxygen delivery should be guided by the measurement of parameters assessing global and regional oxygenation. Forcing an increase in oxygen delivery by the use of very high dosages of catecholamines can be harmful. Vasopressors should be used for achieving an adequate perfusion pressure. For norepinephrine, no negative effects on regional perfusion have been demonstrated. Epinephrine and dopamine should be avoided because they seem to redistribute blood flow away from the splanchnic region. There are no convincing data yet to support the routine use of low dose dopamine or dopexamine in patients with sepsis. Neither low dose dopamine nor dopexamine has been proven to prevent renal failure in septic patients. Furthermore, there is evidence that low dose dopamine may reduce mucosal perfusion in the gut in some patients. There is some suggestion that dopexamine can improve splanchnic perfusion but since these effects remain somewhat controversial, there is no reason for a general recommendation for dopexamine in septic patients.

Maternal oxygen transport variables during the third trimester of normal pregnancy

OBJECTIVE

The aim of this study was to measure and calculate oxygen transport variables in uncomplicated term pregnancies.

STUDY DESIGN

Ten normotensive primiparous women between 36 and 38 weeks' gestation underwent pulmonary and radial arterial catheterization as part of a larger study. Seven women had studies repeated at approximately 12 weeks post partum. Measurements were made with patients in the left lateral recumbent position after a 30-minute stabilization period. Cardiac output was measured with the thermodilution technique. Blood samples were obtained simultaneously from the pulmonary and radial arteries and analyzed in duplicate for oxygen content with a blood gas analyzer.

RESULTS

The oxygen contents of both arterial and mixed venous blood are significantly lower (P <.05) in the third trimester of pregnancy (15.96 and 11.97 mL/dL, respectively) than in the postpartum period (18.00 and 13.54 mL/dL). The fall in oxygen content during pregnancy prevents any significant increase in oxygen delivery in the third trimester (867. 59 mL/min) relative to the postpartum period (806.50 mL/min, P not significant).

CONCLUSION

This is the first report of directly measured oxygen transport variables in healthy pregnant women.

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.

Laser doppler flowmetry in the hyperbaric environment

Continuous monitoring of laser Doppler (LD) flowmetry was performed in eight healthy volunteers (mean age 42.0 + 12.1 yr; range 25-62 yr) before, during and after hyperbaric oxygenation ([HBO at 2.5 and 1.95 ATA (atmosphere absolute)]).Two models of the discrimination analysis are presented which allow classification, resulting from the parameter obtained by the LD flowmetry.The results show that 100% separation of the LD data under HBO at 2.5 and 1.95 ATA including five parameters can be achieved with the first model. The second model for the analysis of four different phases with eight parameters still shows an obvious separation; however, only 75% of the group integration is correct. In addition to transcutaneous P(2) measurements, which are sometimes difficult to obtain perfectly, LD parameters will be of interest to manage HBO treatment, especially when peripheral circulation is reduced.

Continuous home ambulatory intravenous inotropic drug therapy in severe heart failure: safety and cost efficacy

Some patients with dilated cardiomyopathy who are inotrope dependent but remain well by undergoing infusions can be managed by ambulatory infusions at home. We report our results in 20 patients awaiting heart transplantation, unable to be weaned from intravenous inotropic therapy on 2 or more occasions, but who were well while receiving inotropes and received home ambulatory infusions. The patients were treated with ACE inhibitors, digoxin, diuretics, vasodilators, close electrolyte management, and low-dose amiodarone for those with more than four-beat ventricular tachycardia. Infusions were delivered by a tunneled subclavian catheter and syringe driver. Thirteen patients received dopamine, four received dobutamine, and three received both. Mean duration of inotropic therapy was 5 months with 70% of the time spent as an outpatient. Eleven patients received transplants, two remain on the waiting list, and seven died after being removed from the list because of general deterioration or renal dysfunction. There were no sudden deaths. Actuarial survival was 71% at 3 months, which is not less than that expected for an inotrope-dependent population. All patients with idiopathic dilated cardiomyopathy survived to transplantation. In contrast, all three with right heart failure caused by pulmonary vascular disease and four of seven with ischemic cardiomyopathy died. Inpatient days were reduced by 70%, leading to considerable cost savings. Home ambulatory inotropic therapy is safe, cost-effective, best suited to those with idiopathic dilated cardiomyopathy, and dramatically reduces inpatient hospital duration.

Decision support system to assist mechanical ventilation in the adult respiratory distress syndrome

This paper presents a knowledge-based decision support system to assist mechanical ventilation in patients with the Adult Respiratory Distress Syndrome (DSSARDS). The knowledge base uses clinical algorithms developed from interviews and seminars with experts. The system contains 140 rules, applies backward chaining and was built on an IBM-PC compatible microcomputer. Clinical and physiological data and ventilator settings were used for suggestions of ventilatory support mode (VSMODE) and settings (MVSET) and for hemodynamic evaluation and therapy (HEMO). Success rates (s) and kappa coefficient (k) were used to measure agreement between DSSARDS and physicians at 4 decision steps related to: beginning of mechanical ventilation (FIRSTSET), VSMODE, MVSET and HEMO, DSSARDS prototype was evaluated in a development phase with 6 patients aged 48.6 +/- 15.9 years. Agreement results for 142 decision steps were: FIRSTSET k = 0.90, s = 0.93; VSMODE k = 0.76, s = 0.92; HEMO k = 0.58, s = 0.70, MVSET k = 0.86, s = 0.92 (p < 0.05 for all k). Improvements in the knowledge base were performed mainly in HEMO and VSMODE modules. The subsequent test phase studied 5 patients aged 54.8 +/- 11.0 years in a total of 900 decision steps. Results were: FIRSTSET k = 0.93, s = 0.95; VSMODE k = 0.93, s = 0.96; HEMO k = 0.97, s = 0.99, MVSET k = 0.96, s = 0.97 (p < 0.05 for all k). The results indicate significant agreement between DSSARDS and physicians for all decision steps. This suggests that DSSARDS may be used as a support for decision making and a training tool for mechanical ventilation in patients with the adult respiratory distress syndrome.

The effect of oxygen delivery-directed resuscitation on splanchnic and hepatic oxygen transport after hemorrhagic shock

BACKGROUND

Gut and hepatic dysfunction, during and after hypovolemic shock, have been implicated as causative mechanisms in the development of multiple system organ failure in the trauma patient. Current techniques of assessment of perfusion only detect changes in systemic oxygen transport. We designed an animal model that can measure changes in oxygen transport in the liver and gut during hypovolemic shock and resuscitation.

MATERIALS AND METHODS

Animals were hemorrhaged to a mean arterial pressure (MAP) of 60 mm Hg and maintained at 60 mm Hg for 60 min. Animals were then assigned to one of three groups. Group I served as nontreatment controls. Group II received shed blood and saline in sufficient volumes to restore MAP to baseline. Group III animals were resuscitated with shed blood, saline, and donor blood to restore systemic oxygen delivery to the preshock value.

RESULTS

The animals resuscitated to their baseline systemic oxygen delivery, Group III, had significantly higher systemic, hepatic, and splanchnic oxygen delivery than the remaining groups. In addition, Group III had higher oxygen consumption, portal flow, and hepatic artery flow than the blood pressure-directed group, Group II. The decrease in oxygen extraction ratio in the gut and liver was significantly greater in Group III than in Group II.

CONCLUSIONS

These data show that hepatic and gut vascular beds are better perfused when resuscitation from hemorrhage is guided by systemic oxygen transport measurements compared to resuscitation guided by blood pressure.

Epinephrine impairs splanchnic perfusion in septic shock

OBJECTIVE

To assess the effects of epinephrine on splanchnic perfusion and splanchnic oxygen uptake in patients with septic shock.

DESIGN

Prospective, controlled trial.

SETTING

University hospital intensive care unit (ICU).

PATIENTS

Eight patients with septic shock, according to the criteria of the 1992 American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference, requiring treatment with vasopressors.

INTERVENTIONS

We compared in crossover design a 2-hr infusion of epinephrine with dobutamine plus norepinephrine in eight ICU patients with septic shock. Systemic and splanchnic hemodynamics and oxygen transport were measured before and during treatment with epinephrine.

MEASUREMENTS AND MAIN RESULTS

There was essentially no effect of epinephrine on the global parameters, except for increased lactate concentrations. There were marked effects on the regional variables; epinephrine caused lower splanchnic flow and oxygen uptake, lower mucosal pH, and higher hepatic vein lactate.

CONCLUSION

We conclude that undesirable splanchnic effects on patients in whom that region is particularly fragile should be considered when using epinephrine for septic shock treatment.

Oxygen transport and oxygen metabolism in shock and critical illness. Invasive and noninvasive monitoring of circulatory dysfunction and shock

The common underlying physiologic problem in shock is low flow from hypovolemia or maldistributed microcirculatory flow from uneven vasoconstriction, leading to inadequate tissue perfusion (hypoxia), often in the face of increased metabolic demands. Noninvasive monitoring which was found to provide similar information to that of invasive monitoring, was used in the earliest period of time shortly after admission to the emergency department to provide objective physiologic criteria as therapeutic goals for each of the three major circulatory components: cardiac, pulmonary, and tissue perfusion functions. A clinical algorithm or branch-chain decision tree for high-risk surgical patients was developed from decision rules based on survivor and nonsurvivor patterns, outcome predictors, prospective controlled clinical trials of the oxygen delivery/oxygen consumption (DO2/VO2) concept, and the DO2/VO2 responses of a wide variety of therapeutic agents.

The relationship of oxygen consumption measured by indirect calorimetry to oxygen delivery in critically ill patients

OBJECTIVE

The existence of oxygen supply dependency, defined as oxygen consumption (VO2) limited by oxygen delivery (DO2), is still questioned. This study examined the relationship between VO2 and DO2 in two groups of critically ill surgical patients 50 years and older in the first 24 hours of resuscitation after pulmonary artery catheter insertion. Group 1 patients had systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, septic shock, and adult respiratory distress syndrome (ARDS). Group 2 patients had hemorrhagic shock.

METHODOLOGY

Study methodology included (1) augmenting DO2 with fluids, blood, and vasopressors, (2) measuring VO2 by indirect calorimetry to avoid the problem of mathematical coupling with DO2 calculation, and (3) analyzing data during steady states of temperature, sedation, paralyzing agents, and vasopressors.

RESULTS

Six to 18 measurements collected on all study patients during a period within the first 24 hours were analyzed using a linear regression analysis. Statistical significance was set at p < or = 0.05. Seven of nine patients in group 1 demonstrated positive, statistically significant relationships between VO2 and DO2. Of six patients in group 2, one patient demonstrated a positive, significant relationship of VO2 and DO2, three demonstrated inverse relationships, and two patients did not show a DO2/VO2 relationship. Supply dependency did not exist in all patients but was present in seven out of nine patients with systemic inflammatory response syndrome, sepsis, severe sepsis, septic shock, and adult respiratory distress syndrome in the first 24 hours of treatment.

Nociceptive somatic nerve stimulation and skeletal muscle injury modify systemic hemodynamics and oxygen transport and utilization after resuscitation from hemorrhage

OBJECTIVE

To examine if either nociceptive somatic nerve stimulation or skeletal muscle injury modified systemic hemodynamics and oxygen transport and utilization after resuscitation from hemorrhage in anesthetized pigs.

DESIGN

Prospective, randomized, controlled laboratory study.

SETTING

Animal laboratory.

SUBJECTS

Twenty isoflurane-anesthetized and mechanically ventilated large white pigs.

INTERVENTIONS

Three groups of animals were instrumented with femoral arterial and thermodilution pulmonary artery catheters. One group of animals had bilateral brachial nerve electric stimulation before hemorrhage (brachial nerve stimulation + hemorrhage, n = 7). The second group of animals had bilateral hindlimbs skeletal muscle injury induced by firing a captive-bolt handgun with standard charges before hemorrhage (skeletal muscle injury + hemorrhage, n = 6). The third group had neither insult before hemorrhage (control, n = 7). Controlled bleeding was initiated to reduce the cardiac index and systemic oxygen delivery (Do2) by 50% in all animals. Animals were then left for 30 mins before resuscitation. All animals were resuscitated with 4.5% human serum albumin at 45 mL/kg and observed for 2 hrs.

MEASUREMENTS AND MAIN RESULTS

Plasma volume, systemic hemodynamics, and oxygen transport variables were measured and calculated after resuscitation. Similar increases of plasma volume and supranormal cardiac index were observed in all groups immediately after resuscitation. The branchial nerve stimulation and hemorrhage group maintained higher heart rate, cardiac index, Do2, and oxygen consumption (Vo2) than the hemorrhage group. In contrast, the skeletal muscle injury and hemorrhage group had lower systemic mean arterial pressure and vascular resistance, and a tendency for decrease in Vo2, than the hemorrhage group, although heart rate, cardiac index, and Do2 were similar in both groups. Hemorrhage increased the arterial plasma lactate concentration, which was later normalized in all groups 60 mins after resuscitation.

CONCLUSIONS

Neither nociceptive brachial nerve stimulation nor skeletal muscle injury attenuated the increase in plasma volume, cardiac index, or the repayment of systemic oxygen debt after resuscitation from hemorrhage. Brachial nerve stimulation was associated with augmented cardiac index, systemic Do2, and increased Vo2 requirements related to increased sympathetic nervous system activation. Skeletal muscle injury produced early systemic arterial hypotension and vasodilation, and a decrease in Vo2 that was suggestive of pathologic supply dependency on systemic Do2.

Is it time to reposition vasopressors and inotropes in sepsis?

OBJECTIVES

To review the literature on the current use of vasopressors and inotropes in patients with sepsis and sepsis syndrome with respect to the choice of agent, therapeutic end points, and safe and effective doses to be used. To examine the available evidence that supports or refutes goal-directed therapy toward supranormal oxygen transport in optimizing the outcome of critically ill sepsis syndrome patients.

DATA SOURCES

All pertinent English and French articles dealing with hemodynamic support with selected vasopressors and inotropic agents in human sepsis and sepsis syndrome retrieved from a computerized MEDLINE search from 1985 to 1994.

STUDY SELECTION

Clinical studies with norepinephrine, epinephrine, phenylephrine, dopamine, and dobutamine in sepsis syndrome were considered if goal-directed therapy with oxygen transport variables was utilized. Emphasis was placed on prospective, randomized, controlled comparative trials. However, open-label, observational, and comparative studies, or case series, were also evaluated when limited data were available.

DATA EXTRACTION

From the selected studies, information was obtained regarding patient population, dosing regimen, type of therapeutic goals or end points (hemodynamic, or normal vs. supranormal oxygen transport variables) and outcome data (e.g., achievement of goals, resolution of the episode, mortality rate, and development of end-organ dysfunction).

DATA SYNTHESIS

When used in larger than usual doses, epinephrine, norepinephrine, and phenylephrine uniformly increased hemodynamic values. Epinephrine may increase oxygen transport values more reliably than norepinephrine. Dobutamine doses in the range of 2.5 to 6 microgram/kg/min increase oxygen transport variables and hemodynamics to predetermined goals in only 30% to 70% of patients. Larger infusion rates offer no further benefits.

CONCLUSIONS

Insufficient evidence exists to support goal-directed therapy with vasopressors and inotropes in the treatment of sepsis syndrome. No definitive recommendations can be made about the superiority of a vasopressor or inotropic agent due to the lack of data. However, it may be that evaluation of vasopressors earlier in sepsis syndrome will yield more promising results. Large, comparative, controlled trials assessing mortality rate and development of multiple organ system dysfunction are needed.

Triage of critically ill patients: an overview of interventions

The recognition of tissue hypoxia or cumulative oxygen debt is of fundamental importance for triage and resuscitation of critically ill patients during the ¿golden hour¿ in the emergency department (ED). The measurement of central venous blood oxygen saturation, plasma lactate concentration, cardiac output, systemic oxygen transport and use, and non-vital organ oxygenation and function can enhance the detection of systemic and regional hypoperfusion and tissue hypoxia. Systemic and organ-specific oxygenation indices may guide the choice of therapy to optimize resuscitation of the macrocirculation and microcirculation in critically ill ED patients.

Comparison of dopamine to dobutamine and norepinephrine for oxygen delivery and uptake in septic shock

OBJECTIVES

To test whether dopamine infusion improves oxygen delivery (Do2) and oxygen uptake (VO2) in hyperdynamic septic shock patients stabilized by adequate volume and dobutamine alone, or by the combination of dobutamine and norepinephrine.

DESIGN

Prospective clinical trial of two patient groups. Group 1 (n = 15) was stabilized with dobutamine, and group 2 (n = 10) was stabilized with dobutamine and norepinephrine.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Twenty-five postoperative, hyperdynamic septic shock patients.

INTERVENTIONS

The stabilizing catecholamine infusion was replaced in a stepwise manner by dopamine to achieve a similar mean arterial pressure (dopamine doses: group 1, mean 22 +/- 15 micrograms/kg/min [range 6 to 52]; and group 2, mean 57 +/- 41 micrograms/kg/min [range 15 to 130]).

MEASUREMENTS AND MAIN RESULTS

A complete hemodynamic profile was performed with oxygen transport-related variables at baseline, after replacement by dopamine, and after resetting to the original catecholamine infusion. The change to dopamine resulted in increases in cardiac index (group 1: 20% [p < .01]; group 2: 33% [p < .01]), and DO2 (group 1: 19% [p < .01]; group 2: 27% [p < .01]). However, VO2, whether directly measured from the respiratory gases or calculated by the cardiovascular Fick principle, did not change in both groups with dopamine, while the oxygen extraction ratio decreased significantly in both groups with dopamine. Heart rate, pulmonary artery occlusion pressure, and pulmonary shunt fraction all increased with dopamine. PaO2 decreased, but oxygen saturation remained stable in both groups with dopamine.

CONCLUSIONS

Short-term dopamine infusion in hyperdynamic septic shock patients, despite producing higher global DO2, was not superior to dobutamine or the combination of dobutamine and norepinephrine infusion.

Changes in gut intramucosal pH and gut oxygen extraction ratio in a porcine model of peritonitis and hemorrhage

OBJECTIVE

To establish the relationship between gut intramucosal pH and blood flow to the gut, gut oxygen delivery, and gut oxygen extraction ratio in a porcine model of peritonitis and hemorrhage.

DESIGN

Prospective, controlled study.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Thirty pigs of both sexes, weighing 15 to 22 kg.

INTERVENTIONS

Animals were anesthetized, intubated, and mechanically ventilated. A flow probe was placed around the superior mesenteric artery for registration of blood flow. A tonometer was placed in the lumen of midileum for calculation of gut intramucosal pH. Hourly, for 5 hrs, blood samples were taken from mixed venous, mesenteric venous, and arterial blood. Five animals served as controls, ten animals had peritonitis induced by fecal instillation in the abdominal cavity, five were bled stepwise, five were bled rapidly (to a mean arterial pressure of 30 mm Hg), and five were bled rapidly and reinfused after 3 hrs.

MEASUREMENTS AND MAIN RESULTS

Both peritonitis and hemorrhage caused decreases in gut blood flow and intramucosal pH. In mild peritonitis, the intramucosal pH decrease preceded that of blood flow. In all experimental groups, oxygen delivery decreased over time; in both mild and severe peritonitis, this decrease was preceded by a decrease of intramucosal pH. Intramucosal pH correlated well with gut oxygen extraction ratio in peritonitis (r2 = .86). In hemorrhage, there was a correlation of r2 = .66, but in intramucosal pH of < 7.12, a further decrease was accompanied only by minor changes in extraction ratio.

CONCLUSIONS

Since a reduction in blood flow was preceded by a decrease in intramucosal pH, low intramucosal pH in peritonitis cannot be explained by low flow alone. Gut oxygen delivery proved to be a poor indicator of gut acidosis (i.e., low intramucosal pH). In peritonitis, a decreasing intramucosal pH was associated with an increasing oxygen extraction ratio. In hemorrhage, this association had a sharp deflection point below which a further decrease in intramucosal pH occurred concomitantly with an unchanged gut oxygen extraction ratio. Increased extraction ratio was not sufficient, not even initially, to maintain aerobic metabolism (i.e., unchanged intramucosal pH).

Effects of catecholamines on regional perfusion and oxygenation in critically ill patients

Multiple organ failure is the major cause of death in patients with sepsis. Bacterial translocation from the gut is considered to induce and maintain sepsis. Therefore, the splanchnic region plays an important role in the pathogenesis and treatment of sepsis. There is evidence for a very high risk of imbalance between oxygen delivery and oxygen consumption especially in the splanchnic region. Consequently, there is a crucial interest whether it is possible to influence the splanchnic perfusion by specific catecholamines. Unfortunately, only a few, conflicting studies have looked at the effects of the various catecholamines on regional blood flow. Therefore, a clear recommendation for a specific catecholamine regimen in septic shock is impossible. Furthermore, it is unknown whether the choice of a specific catecholamine in the treatment of septic shock affects the patient's outcome. In most patients, the use of vasopressors is indispensable because adequate haemodynamic perfusion pressure is not achieved with fluid therapy alone. The negative effects of vasopressors on splanchnic perfusion are known from studies carried out under non septic conditions. Norepinephrine and dopamine in doses of 10 micrograms/kg/min in septic animals are without negative effects on splanchnic perfusion. Preliminary results show Preliminary results show a decrease in splanchnic oxygenation in patients with septic shock treated with epinephrine. Catecholamines with beta mimetic effects are often used to increase DO2. The question as to whether dobutamine or dopamine should be used first in treatment of septic shock cannot be answered yet. Whether treatment with low dose dopamine or dopexamine actually improves renal function and splanchnic oxygenation is the purpose of ongoing studies.

Management of septic shock

Septic shock due to bacterial and other infections remains an increasing cause of hospital mortality and morbidity. Early recognition and prompt management with diagnostic evaluation, antimicrobial therapy, surgery when indicated and advanced life support undoubtedly saves many lives. Once treatment has been instituted, careful and frequent monitoring is required to optimise therapy and detect complications at an early stage. However, once shock and organ failure have become established the mortality remains high and has changed little in the last few years despite improvements in intensive management. A variety of other approaches to treatment are under investigation but as yet there are insufficient data to recommend their use.