Noninvasive physiologic monitoring of high-risk surgical patients

Pre-hospital fluids - when and how much?

When to give intravenous fluids, how much to give and whether intravenous fluids improve patient outcome remain controversial areas. Hypovolaemic shut down patients are difficult to connulate. The on scene is protracted and invariably relatively small volumes of fluid are infused. Those patients who are hypotensive invariably require definitive surgical intervention, therefore, any delay in reaching hospital can worsen outcome. Intravenous fluids given in states of uncontrolled and noncompressible bleeding will enhance blood loss. There is therefore a need to define those patient groups requiring pre-hospital intervention and optimal recusitation objectives in terms of blood pressure in the pre-hospital scene. This paper examines the current evidence base in both animal and human trials and makes recommendations for optimal fluid management in the trauma patient.

The efficacy of noninvasive hemoglobin measurement by pulse CO-oximetry in neonates

OBJECTIVE

To evaluate clinical applicability of noninvasive hemoglobin (Hb) measurement with a pulse CO-oximeter in neonates.

DESIGN

Prospective comparison study.

SETTING

Neonatal ICU.

PATIENTS

Fifty-six preterm and term infants with median age = 20 days (range = 1-98 days) and median weight = 1,440 g (range = 530-4,230 g).

INTERVENTIONS

Hb measurements by Pulse CO-Oximetry (Masimo Radical-7) were recorded immediately prior to venous samplings.

MEASUREMENTS AND MAIN RESULTS

The collected data were compared with the corresponding venous Hb level obtained in laboratory testing, and a total of 137 data pairs were analyzed. Noninvasive Hb values measured with a pulse CO-oximeter were significantly correlated with the venous Hb levels (correlation coefficient, r = 0.758; p < 0.001). Hb values measured with a pulse CO-oximeter were higher than those measured with a laboratory hematology analyzer (13.3 ± 2.6g/dL vs. 12.5 ± 3.1g/dL). In terms of the agreement between the laboratory analyzer and the pulse CO-oximeter, 94.8% of the measurements fell within two standard deviations of the mean difference.

CONCLUSION

Noninvasive Hb measurements with Pulse CO-Oximetry provide clinically acceptable accuracy, and they were significantly correlated with laboratory Hb measurement in neonates. In terms of the clinical applicability, noninvasive Hb monitoring with a pulse CO-oximeter could be useful in the early detection of Hb changes in neonates.

Geriatric care in the surgical intensive care unit

We describe the physiology of aging and its effect on elderly, critically ill, surgical patients. Postoperative age-specific complications and their management will be reviewed. The number of elderly persons, defined as those >65 yrs of age, is the fastest growing segment of the U.S. population. As a result, the frequency of surgery, both elective and emergent, performed on elderly patients will increase. Aging is associated with a decrease in the physiologic reserve; thus, many elderly persons are unable to compensate for the increased metabolic demands that accompany acute illness or injury. This inability to compensate leads to increased rates of postoperative complications and death. Aggressive, goal-directed management in the surgical intensive care unit is beneficial for the geriatric patient. The management of the elderly, surgical, critical care patient is extremely challenging. Understanding age-related physiologic changes will help guide treatment to maximize outcome and prevent complications.

PERIOPERATIVE HIGH-DOSE OXYGEN THERAPY IN VASCULAR SURGERY

BACKGROUND

Patients undergoing infrainguinal bypass surgery have reduced baseline tissue oxygen tension and high rates of wound infections. The hypoxaemia worsens during surgery, potentially reducing the ability to combat bacterial lodgement. We investigated whether high-dose perioperative oxygen administration to patients undergoing infrainguinal arterial surgery results in increased tissue oxygenation.

METHODS

Ten consecutive patients undergoing infrainguinal arterial surgery had transcutaneous partial pressure of oxygen (TcpO(2)) measured preoperatively, intraoperatively after arterial clamps applied, postoperatively and at discharge. Measurements were taken with inspired oxygen concentration (F(i)O(2)) of 30% then 80%. Arterial blood gases were measured at the same times.

RESULTS

Tissue oxygenation showed no difference intraoperatively while arterial clamps were in place, but significantly higher tissue oxygenation was seen with use of high-dose oxygen (F(i)O(2) 80%) postoperatively (P<0.05). Carbon dioxide levels in tissue increased while arterial clamps were in place (P<0.01) and pH fell intraoperatively and following reperfusion (P<0.05).

CONCLUSION

The administration of high-dose oxygen to vascular surgical patients undergoing lower-limb arterial surgery results in increased tissue oxygen concentrations when perfusion is not reduced by the presence of arterial clamps. These results suggest the administration of high-dose oxygen intraoperatively may be beneficial in reducing wound infections, but further research is required.

Survival, Hemodynamics, and Tissue Oxygenation after Head Trauma

BACKGROUND

The aims of this study were to describe the early time course of hemodynamic and tissue perfusion and oxygenation patterns in survivors and nonsurvivors after head injury; to suggest physiologic mechanisms responsible for the observed patterns; and to evaluate postinjury parameters that might be useful for treatment. The hypothesis was that reduced hemodynamics and tissue oxygenation and reduced arterial oxygen saturation affect outcomes.

STUDY DESIGN

Sixty patients with head trauma were noninvasively monitored on arrival in the emergency department to assess the temporal hemodynamic patterns associated with head injury; patients who were brain dead were excluded because they have very different hemodynamic patterns. Cardiac index, mean arterial pressure, and heart rate were monitored to assess cardiac function, pulse oximetry to reflect changes in pulmonary function, and transcutaneous oxygen and carbon dioxide to reflect tissue perfusion function. Patients were stratified by inhospital survival outcomes, the Glasgow Coma Scale, and the presence or absence of associated somatic injuries.

RESULTS

When all head injured patients were considered together, the predominant findings were high cardiac index, hypertension, mild tachycardia, normal pulmonary function, and reduced tissue oxygenation. The subset of survivors and those with high Glasgow Coma Scale had greater than normal cardiac index responses (4.02 +/- 0.01 (SEM) L/min/m2, p < 0.01 versus normal) and better tissue oxygenation (217 +/- 2 mmHg PtcO2/FiO2) than nonsurvivors (70 +/- 3 mmHg, p < 0.01) and those with low Glasgow Coma Scale (160 +/- 2, p < 0.05). Patterns of patients with associated somatic injuries were similar to those with isolated head injury.

CONCLUSIONS

The study suggested that survivors' cardiac index, tissue oxygenation, and arterial oxygen saturation may be considered as markers of resuscitation. Nonsurvivors of head injury had normal blood flow with reduced tissue oxygenation that might have contributed to unfavorable outcomes.

The effect of obesity on bioimpedance cardiac index

BACKGROUND

Cardiac performance may be assessed noninvasively at the patient's bedside by using thoracic bioimpedance. However, it is unclear if this technique can be used reliably in critically injured obese patients because of increased body habitus and chest wall mass.

METHODS

A prospectively maintained database was used to identify all trauma patients admitted to the intensive care unit who underwent simultaneous measurement of cardiac performance by using both thoracic bioimpedance and thermodilution. Patients were divided into 2 groups based on their body mass index (BMI). Patients with a BMI less than 30 kg/m(2) were classified as nonobese, and patients with a BMI of 30 kg/m(2) or greater were categorized as obese.

RESULTS

There were 285 patients who underwent 1,138 simultaneous measurements of cardiac index by using both bioimpedance and thermodilution. There were 211 nonobese patients (BMI = 25 +/- 3 kg/m(2)) and 74 obese patients (BMI = 34 +/- 4 kg/m(2)). Bioimpedance correlated well with thermodilution for the entire population (r = .84, P < .0001), and was reliable equally in obese (r = .85, P < .0001) and nonobese (r = .82, P < .0001) patients. There actually was less test bias in the obese group (-.06 +/- .69) than in the nonobese group (-.16 +/- .75, P = .04).

CONCLUSIONS

Thoracic bioimpedance technology may be used reliably as a noninvasive alternative to pulmonary artery catheterization for assessment of cardiac performance in critically injured obese patients.

Is Noninvasive Hemodynamic Monitoring Appropriate for the Elderly Critically Injured Patient?

BACKGROUND

Noninvasive hemodynamic monitoring in critically ill patients using bioimpedance technology has been shown to be a reliable alternative to invasive thermodilution techniques. However, there have been some concerns that the bioimpedance method may be unreliable in elderly patients with an atherosclerotic and rigid thoracic aorta. The purpose of the present study was to evaluate the effect of age on the reliability of noninvasive bioimpedance technology in measuring cardiac index.

METHODS

This is a retrospective analysis of prospectively collected data in critically injured patients admitted to the surgical intensive care unit. All patients had simultaneous measurement using thermodilution cardiac index (TDCI) and bioimpedance cardiac index (BICI). The population was divided into three age groups (<55 years, 55-70 years, and >70 years). The correlation between TDCI and BICI was calculated for each age group.

RESULTS

There were 1,138 simultaneous measurements of TDCI and BICI in 285 patients. The BICI correlated well with TDCI in all three age groups (r = 0.82 for group <55 years, r = 0.87 for group 55-70 years, and r = 0.80 for group >70 years).

CONCLUSION

Noninvasive cardiac index monitoring in elderly patients is reliable and correlates well with standard thermodilution techniques.

Effect of intra-operative end-tidal carbon dioxide partial pressure on tissue oxygenation

Postsurgical infection risk is correlated with subcutaneous tissue oxygenation. Mild hypercapnia augments cutaneous perfusion. We tested the hypothesis that peripheral tissue oxygenation increases as a function of arterial PCO2 in surgical patients. Twenty patients were randomly assigned to intra-operative end tidal PCO2 of 3.99 (control) or 5.99 kPa (hypercapnia). All other anaesthetic management was per protocol. Tissue oxygen partial pressure, transcutaneous oxygen tension, cerebral oxygen saturation, and cardiac output were measured. Mean (SD) subcutaneous tissue oxygen tension was 8.39 (1.86) kPa in control and 11.84 (2.53) kPa hypercapnia patients (p = 0.014). Cerebral oxygen saturation was 55 (4)% for control vs. 68 (9)% for hypercapnia (p = 0.004). Neither cardiac index nor transcutaneous tissue oxygen tension differed significantly between the groups. Mild intra-operative hypercapnia increased subcutaneous and cerebral oxygenation. Increases in subcutaneous tissue oxygen partial pressure similar to those observed in patients assigned to hypercapnia are associated with substantial reductions in wound infection risk.

Noninvasive hemodynamic monitoring for early warning of adult respiratory distress syndrome in trauma patients

PURPOSE

Traditionally hemodynamic patterns after adult respiratory distress syndrome (ARDS) are described after appropriate diagnostic criteria have been met, but studies begun after the diagnosis of ARDS miss the antecedent circulatory influences that may contribute to its development. This study tests the hypothesis that noninvasive monitoring before the appearance of ARDS may reveal early circulatory deficiencies that lead to this disorder. The aims of this study are as follows: (1) to describe the time course of hemodynamic and tissue perfusion patterns in severely traumatized postoperative patients from the period immediately after admission and during surgical repair to the time that ARDS developed or to hospital discharge in patients who did not develop ARDS, (2) to compare the time course of these patterns in survivors and nonsurvivors of ARDS, and (3) to suggest that reduced flow and perfusion may be early warning signs of ARDS. Prospective descriptive study of severely injured trauma patients noninvasively monitored in the emergency department, operating room, and intensive care unit (ICU). Early hemodynamic pattems were described in the surviving and nonsurviving patients who subsequently developed ARDS. The study was performed in a University-affiliated Level I trauma center and ICU.

PATIENTS AND METHODS

A consecutively monitored series of 60 severely injured patients were prospectively monitored by cardiac output, pulse oximetry (Sapo2), and transcutaneous O2 and co2 (Ptco2 and Ptc(co2)) sensors immediately after emergency admission. Twenty-nine patients developed ARDS in their ICU course, whereas 31 were discharged from the ICU and the hospital without developing ARDS.

RESULTS

Patients who developed ARDS had significantly lower cardiac index and Ptco2 and higher Ptc(co2) values beginning with the early stage compared with those who did not develop ARDS. Nonsurvivors of ARDS had lower Ptco2 values than did the survivors.

CONCLUSION

Early noninvasive monitoring in the emergency department, operating room, and ICU showed reduced cardiac and tissue perfusion functions in patients who subsequently developed ARDS. These patterns were more pronounced in the ARDS patients who died; these patterns may serve as early warning of ARDS.

Transcutaneous oxygen and CO2 as early warning of tissue hypoxia and hemodynamic shock in critically ill emergency patients

BACKGROUND

Although cardiac and pulmonary function can be measured precisely, evaluation of tissue perfusion remains elusive because it usually is inferred from subjective symptoms and imprecise signs of shock. The latter are indirect criteria used to assess the overall circulatory status as well as tissue perfusion but are not direct quantitative measures of perfusion. However, noninvasive transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) tensions, which directly measure skin oxygenation and CO2 retention, may be used to objectively evaluate skin oxygenation and perfusion in emergency patients beginning with resuscitation immediately after hospital admission.

OBJECTIVE

This study was a preliminary evaluation of tissue oxygenation and perfusion by objective PtcO2 and PtcCO2 patterns in severely injured surviving and nonsurviving patients; specifically, the aim was to describe time patterns that may be used as early warning signs of circulatory dysfunction and death.

DESIGN

Prospective descriptive study of a consecutive series of severely injured emergency patients.

SETTING

University-affiliated Level I trauma center and intensive care unit.

PATIENTS AND METHODS

Forty-eight consecutive severely injured patients were prospectively monitored by PtcO2 and PtcCO2 sensors immediately after emergency admission.

RESULTS

Compared with survivors, patients who died had significantly lower PtcO2 and higher PtcCO2 values beginning with the early stage of resuscitation. All patients who maintained PtcO2 >150 torr (19.99 kPa) throughout monitoring survived. Periods of PtcO2 <50 torr (6.66 kPa) for >60 mins or PtcCO2 >60 torr (8.00 kPa) for >30 mins were associated with 90% mortality and 100% morbidity.

CONCLUSION

PtcO2 and PtcCO2 monitoring continuously evaluate tissue perfusion and serve as early warning in critically injured patients during resuscitation immediately after hospital admission.

A critical assessment of endpoints of shock resuscitation

Modern hemodynamic therapy is not only the recognition and treatment of hypotension but also the avoidance and treatment of shock in its broadest sense. The major issues include the recognition of hypoperfusion of the body as a whole or its individual tissues and organ systems and the determination of the best endpoints for the treatment of shock. Even if all of the commonly used clinical indicators of shock are "normal," shock on a cellular, tissue, or organ basis may still be present. Whether "organ-specific" assessments, such as gastric tonometry or tissue oxygen tension measurement, are the ultimate answer to this problem remains to be seen. The determination of adequate intravascular volume (preload) continues to present major difficulties in the care of critically ill or injured patients. Although PCWP is frequently helpful, it is not a gold standard. A bedside ultrasonic technique, such as esophageal Doppler sonography, may replace the Swan-Ganz catheter technique in many patients.

The influence of left lateral position on cardiac output changes after head up tilt measured by impedance cardiography

BACKGROUND

The value of the impedance cardiography (IC) method for measuring cardiac output (CO) with the subject in the left lateral position has not yet been established. We compared the CO after a 30 degrees head-up tilt with the subjects in the supine and left lateral position.

METHODS

Thirty healthy young volunteers were placed in the supine horizontal position. CO, stroke volume (SV) and heart rate (HR) were measured for five minutes using impedance cardiography (NCOMM3, BoMed Medical Manufacturing, Location). Then a 30 degrees head-up tilt was done and the measurements were continued for an additional five minutes. After that the subjects were placed in the left lateral horizontal position and the measuring procedure was repeated.

RESULTS

After the tilt, SV and cardiac index (CI) decreased and HR increased statistically significantly in the supine and in the left lateral position. SV and CI also decreased statistically significantly but HR did not change after the shift from the supine to the left lateral position. Although CI was smaller in the left lateral position, the time course of CI change after the tilt was identical in the supine and in the left lateral position.

CONCLUSION

When using the IC method of SV measurement, the absolute value of the CI changes when moving from the supine to lateral positions. It is not clear whether this change is physiologic or an artifact of the measurement technique. However, changes in CI in response to a 30 degree head up tilt are the same in either position. We conclude that changes in CI can be measured with the IC method in the lateral position.

Prediction of postoperative cardiac surgical morbidity and organ failure within 4 hours of intensive care unit admission using esophageal Doppler ultrasonography

OBJECTIVE

To compare esophageal Doppler ultrasonography with standard hemodynamic variables used in postoperative care for the prediction of postoperative complications after cardiac surgery.

DESIGN

Prospective, observational pilot study.

SETTING

University hospital, multidisciplinary intensive care unit

PATIENTS

Postoperative cardiac surgical patients.

INTERVENTIONS

Standard postoperative management as guided by routinely measured hemodynamic variables.

MEASUREMENTS

An esophageal Doppler ultrasound probe was inserted for measurement of stroke volume (SV), cardiac output (CO), and other flow-related variables. Both these and routine hemodynamic variables (mean arterial pressure, central venous pressure, heart rate, arterial base deficit, urine output, core-toe temperature difference) were recorded at half-hourly intervals for the first 4 postoperative hrs. The incidence of systemic inflammatory response syndrome at 24 hrs, Acute Physiology and Chronic Health Evaluation II, and multiple organ failure scores, postoperative complications, and length of ICU and hospital stays were recorded.

MAIN RESULTS

Twenty consecutively admitted patients were studied: eight after emergency bypass grafting and 12 after elective bypass grafts and/or valve replacement. Of the nine patients who developed postoperative complications, two died. At admission, significant differences were seen between patients with a complicated and those with an uncomplicated surgical procedure for SV, heart rate, and standard base excess, but not for cardiac output. By using receiver operator characteristic curves, SV was the best marker for predicting postoperative complications during the initial postoperative period.

CONCLUSIONS

A low SV and a high heart rate, both at ICU admission and during the subsequent 4 hrs, were the best prognostic factors for development of complications after cardiac surgery. Cardiac output values were not useful. This pilot study suggests that the minimally invasive technique of esophageal Doppler ultrasonography may be a useful tool to assist early prognostication.

A meta-analysis of three decades of validating thoracic impedance cardiography

OBJECTIVE

To provide a meta-analysis of current literature concerning the validation of thoracic impedance cardiography (TIC) and to explain the variations in the reported results from the differences in the studies.

DATA SOURCES

A computer-assisted search of English-language, German, and Dutch literature was performed for the period January 1966 to April 1997. Moreover, references from review articles were obtained.

STUDY SELECTION

A total of 154 studies comparing measurements of cardiac output or related variables obtained from TIC and a reference method were analyzed.

DATA EXTRACTION

Articles were classified by differences in TIC methodology, reference method, and subject characteristics. Fisher's Zf transformed correlation coefficients were used to compare results. Data were pooled using the random-effects method.

DATA SYNTHESIS

An overall pooled r2 value of .67 (95% confidence interval, 0.64-0.71) was found. However, the correlation was higher in repeated-measurement designs than in single-measurement designs (r2 = .53; 95% confidence interval, 0.43-0.62). Further research using analysis of variance revealed a significant influence of the reference method and the subject characteristics on the correlation coefficient. The correlation was significantly better in animals than in cardiac patients. Subgroup analysis revealed that TIC correlated significantly better to the indirect Fick method than to echocardiography in healthy subjects. No significant influence of the applied TIC methodology was found.

DISCUSSION

The overall r2 value of .67 indicates that TIC might be useful for trend analysis of different groups of patients. However, for diagnostic interpretation, a r2 value of .53 might not meet the required accuracy of the study. Great care should be taken when TIC is applied to the cardiac patient. However, because the applied reference method was of significant influence, differences between TIC and the reference method are incorrectly attributed to errors in TIC alone.

Early continuous noninvasive haemodynamic monitoring after severe blunt trauma

BACKGROUND

Invasive haemodynamic parameters obtained by pulmonary artery (PA) catheterization from survivors' patterns were reported to provide criteria for therapeutic goals in high-risk elective surgery and accidental injuries. This approach is limited because PA catheterization requires critical care conditions; however, noninvasive methods can provide early information anywhere in the hospital.

OBJECTIVES

To evaluate the feasibility of using noninvasive haemodynamic monitoring of patients with severe blunt trauma immediately after emergency department (ED) admission and to describe the early time course of haemodynamic events in survivors and nonsurvivors of blunt trauma.

SETTING

A large, academic, level-I trauma centre.

DESIGN

Prospective, descriptive haemodynamic study.

PATIENTS AND METHODS

38 severely injured patients, 22 (58%) survivors and 16 (42%) nonsurvivors, with ISS > 15 were monitored by: (a) an improved thoracic bioelectric impedance device that estimated cardiac output noninvasively and continuously, (b) simultaneous arterial oxygen saturation by pulse oximetry, (c) noninvasive blood pressure measurement and (d) transcutaneous oxygen and carbon dioxide sensors. The patients were monitored as soon as possible upon arrival at the ED and continued during the first 24 h or more after admission. When the patient reached the ICU, monitoring by PA catheterization was undertaken to validate the noninvasive methods and for continued diagnostic evaluations.

RESULTS

Cardiac output estimations by thermodilution and bioimpedance were well correlated; r = 0.91. Survivors started with high cardiac index (CI) values that subsequently rose to over 4 L/min/m2; arterial oxygen saturation (SaO2), transcutaneous oxygen tension and transcutaneous-oxygen-tension-to-inspired-fraction-of-oxygen-concentr ati on (PtcO2/FiO2) values were normal in survivors and higher than those of the nonsurvivors. In the 1st h after admission, nonsurvivors' blood pressures were higher than normal and higher than that of the survivors, but in the 2nd and 3rd h, both groups were in the normal range; thereafter, nonsurvivors' values were lower than survivors' and often lower than normal.

CONCLUSIONS

The noninvasive haemodynamic monitoring system provides reasonably accurate, continuous, on-line, real-time display of haemodynamic data that show marked differences in the early patterns of survivors and nonsurvivors. The study suggests noninvasive monitoring may be used for early detection and correction of posttraumatic circulatory deficits.

Thoracic Electrical Bioimpedance Versus Thermodilution in Patients Post Open-Heart Surgery

Thoracic electrical bioimpedance cardiography is a non-invasive, continuous and low-cost method of estimation of cardiac output and other haemodynamic parameters. Though subject to continuous technological refinement controversial opinions exist on its validity in subsets of critically ill patients, patients with heart disease or after cardiac surgery. A comparison study between thermodilution (TD) and bioimpedance (TEB) was performed in 28 patients undergoing elective cardiac surgery (CABG, aortic or mitral valve replacement or combined procedures). 128 pairs of cardiac index estimates at specific time points during 20 hours at the postoperative ICU were evaluated. A poor correlation (r = 0.26, p<0.05, bias -0.07 l.min-1.m2, precision + 1.1 l.min-1.m-2, 95% limits of agreement -2.27 - 2.13 l.min-1.m-2) between TD and TEB cannot support the routine use of TEB monitoring in early postoperative period after open-heart surgery. Possible reasons of lack of agreement in this population are discussed. Further studies with technically improved bioimpedance cardiographs will be needed.

Multicenter study of noninvasive monitoring systems as alternatives to invasive monitoring of acutely ill emergency patients

BACKGROUND

Recent reports showed lack of effectiveness of pulmonary artery catheterization in critically ill medical patients and relatively late-stage surgical patients with organ failure. Since invasive monitoring requires critical care environments, the early hemodynamic patterns may have been missed. Ideally, early noninvasive hemodynamic monitoring systems, if reliable, could be used as the "front end" of invasive monitoring to supply more complete descriptions of circulatory pathophysiology.

OBJECTIVES

To evaluate the accuracy and reliability of noninvasive hemodynamic monitoring consisting of a new bioimpedance method for estimating cardiac output combined with arterial BP, pulse oximetry, and transcutaneous PO2 and PCO2; we compared this system of noninvasive monitoring with simultaneous invasive measurements to evaluate circulatory deficiencies in acutely ill patients shortly after hospital admission where invasive monitoring was not readily available. We also preliminarily explored early differences in temporal hemodynamic patterns of survivors and nonsurvivors.

DESIGN AND SETTING

Prospective comparison of simultaneous invasive and noninvasive measurements of circulatory function with retrospective analysis of data in university-run county hospitals, university hospitals and affiliated teaching hospitals, and a community private hospital.

PATIENTS

We studied 680 patients, including 139 severely injured or hemorrhaging patients in the emergency department (ED), 129 medical (nontrauma) patients on admission to the ED, 274 high-risk surgical patients intraoperatively, and 138 patients recently admitted to the ICU.

RESULTS

A new noninvasive impedance device provided cardiac output estimations under conditions in which invasive thermodilution measurements were not usually applied. There were 2,192 simultaneous bioimpedance and thermodilution cardiac index measurements; the correlation coefficient, r = 0.85, r2 = 0.73, p < 0.001. The precision and bias was -0.124+/-0.75 L/min/m2. Both invasive and noninvasive monitoring systems provide similar information and identified episodes of hypotension, low cardiac index, arterial hemoglobin desaturation, low transcutaneous O2, high transcutaneous CO2, and low oxygen consumption before and during initial resuscitation. The limitations of noninvasive systems were described.

CONCLUSIONS

Noninvasive monitoring systems gave continuous displays of physiologic data that provided information allowing early recognition of low flow and poor tissue perfusion that were more pronounced in the nonsurvivors. Noninvasive systems may be acceptable alternatives where invasive monitoring is not available.

Benefits, risks and alternatives of pulmonary artery catheterization

Twenty-five years after the introduction of the pulmonary artery catheter in clinical practice, its effectiveness in improving patient outcome is seriously questioned. Experts still recommend to use pulmonary artery catheters in selected critically ill patients, although evidence supporting these recommendations is lacking. The risks and the unclear benefits associated with this procedure should prompt the search for alternative, noninvasive monitoring techniques.

Maximum cardiac output during incremental exercise by first-pass radionuclide ventriculography

STUDY OBJECTIVE

To validate a noninvasive first-pass radionuclide ventriculographic (FPRV) measurement of maximum cardiac output (Qv) during exercise.

DESIGN

Comparison of Qv to that measured by the Fick principle (Qf) at peak exercise.

SETTING

Academic cardiopulmonary exercise laboratory.

PATIENTS

Seventy-eight consecutive patients without a history of septal defect undergoing clinically indicated maximum incremental cardiopulmonary exercise testing with pulmonary arterial catheterization and FPRV.

MEASUREMENTS AND RESULTS

Ventilation and gas exchange were measured breath-by-breath or by a mixing chamber/mass spectrometer system. Arterial and mixed venous O2 content were measured each minute during exercise. When patients without left-to-right ventricular stroke count ratio evidence for left-sided regurgitation were isolated, peak Qv was linearly related to Qf (r=0.75, p=0.0001). To account for a small systematic overestimation (bias) of Qf by Qv, the linear equation for the Qv/Qf relation was derived for patients studied between 1990 and 1993 and applied to those studied subsequently. The resulting corrected peak Qv was tightly related to peak Qf (r=0.90, p<0.001) with confidence intervals for slope and intercept overlapping identity.

CONCLUSION

FPRV can reasonably estimate maximum cardiac output during incremental exercise in patients for whom the technique has ruled out left-sided cardiac regurgitant lesions.

Impedance cardiography. The impact of new technology

The 1990s have witnessed major advances in impedance cardiography technology. Problems existed with the methods used to calculate cardiac output. Excessive lung fluid, as often found in critically ill patients, may also invalidate measurements. The signal processing and measurement techniques used in older systems were deficient. The newer systems, of which there are at least six, incorporate novel and improved signal processing techniques. They also offer analog visual displays, personal computer interfacing, sophisticated analytical software and haemodynamic patient management systems. Evaluation of these systems is difficult because no true 'gold standard' method of cardiac output measurement exists. When compared with thermodilution techniques, limits of agreement of +/- 20-30% seem acceptable. These limits can be achieved in normal subjects but not in critically ill patients. Validation data are available for only half of the new systems. Until recently, the main application for impedance cardiography has been research but improved accuracy should lead to increased clinical usage.

Invasive haemodynamic monitoring: concepts and practical approaches

The goal of haemodynamic care is to ensure adequate organ blood flow and oxygen supply. Clinical signs of organ perfusion have limited value in estimation of tissue perfusion, but invasive haemodynamic monitoring is needed to gain information of the underlying pathological condition and to guide oxygen delivery and haemodynamic therapy. Many of the available haemodynamic measurements involve pulmonary artery (PA) catheterization. Pressure measurements from PA catheters require meticulous attention to the dynamic properties of the transducer-pressure line system and appreciation of pressure variation owing to respiration. New techniques of continuous measurement of mixed venous oxygen saturation and cardiac output provide valuable trend data, allowing immediate diagnosis and treatment of pathological changes. Fast-response thermistor PA catheters are useful tools for estimating right ventricular function. Although clinicians generally regard PA-catheter data as a valuable therapy guide, few studies showing the beneficial influence on overall outcome have been carried out, and some studies have reported suboptimal understanding and utilization of these data. Transoesophageal echocardiography (TEE) is also a valuable monitor of left ventricular systolic and diastolic function and myocardial ischaemia in anaesthetized patients and in intensive care settings, but it requires a trained operator and is time-consuming. Continuously displayed TEE data, obtainable with automatic border detection, will make TEE even more useful in the near future. More effective monitors of perfusion and oxygenation of individual organs are needed. Less invasive techniques are also constantly sought. Combining data from several noninvasive monitors, including measurements of pulse oximetric O2 saturation, transthoracic impedance cardiac output and transcutaneous oxygen tension, has been reported to reflect closely changes obtained with more invasive monitoring.