Fluid therapy in acute myocardial infarction: evaluation of predictors of volume responsiveness

Background: Static vascular filling pressures suffer from poor predictive power in identifying the volume-responsive heart. The use of dynamic arterial pressure variables, including pulse pressure variation (PPV) has instead been suggested to guide volume therapy. The aim of the present study was to evaluate the performance of several clinically applicable haemodynamic parameters to predict volume responsiveness in a pig closed chest model of acute left ventricular myocardial infarction.
Methods: Fifteen anaesthetized, mechanically ventilated pigs were studied following acute left myocardial infarction by temporary coronary occlusion. Animals were instrumented to monitor central venous (CVP) and pulmonary artery occlusion (PAOP) pressures and arterial systolic variations (SPV) and PPV. Cardiac output (CO) was measured using the pulmonary artery catheter and by using the PiCCO^® monitor also giving stroke volume variation (SVV). Variations in the velocity time integral by pulsed-wave Doppler echocardiography were determined in the left (ΔVTI_LV) and right (ΔVTI_RV) ventricular outflow tracts. Consecutive boluses of 4 ml/kg hydroxyethyl starch were administered and volume responsiveness was defined as a 10% increase in CO.
Results: Receiver–operator characteristics (ROC) demonstrated the largest area under the curve for ΔVTI_RV [0.81 (0.70–0.93)] followed by PPV [0.76 (0.64–0.88)] [mean (and 95% CI)]. SPV, ΔVTI_LV and SVV did not change significantly during volume loading. CVP and PAOP increased but did not demonstrate significant ROC.
Conclusion: PPV may be used to predict the response to volume administration in the setting of acute left ventricular myocardial infarction.     

Automated pre‐ejection period variation predicts fluid responsiveness in low tidal volume ventilated pigs

Introduction: The respiratory variation in the pre‐ejection period (ΔPEP) has been used to predict fluid responsiveness in mechanically ventilated patients. Recently, we automated this parameter and indexed it to tidal volume (PEPV) and showed that it was a reliable predictor for post‐cardiac surgery, mainly paced, patients ventilated with low tidal volumes. The aims of the present animal study were to investigate PEPV's ability to predict fluid responsiveness under different fluid loading conditions and natural heart rates during low tidal volume ventilation (6 ml/kg) and to compare the performance of PEPV with other markers of fluid responsiveness. Methods: Eight prone, anesthetized piglets (23–27 kg) ventilated with tidal volumes of 6 ml/kg were subjected to a sequence of 25% hypovolemia, normovolemia, and 25% and 50% hypervolemia. PEPV, ΔPEP, pulse pressure variation (PPV), central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) were measured before each volume expansion. Results: Sensitivity was 89% and specificity was 93% for PEPV, 78% and 93% for ΔPEP, 89% and 100% for PPV, 78% and 93% for CVP, and 89% and 87% for PAOP. Conclusion: PEPV predicts fluid responsiveness in low tidal volume ventilated piglets.     

Hemodynamic monitoring

The goal of hemodynamic monitoring is to maintain adequate tissue perfusion. Classical hemodynamic monitoring is based on the invasive measurement of systemic, pulmonary arterial and venous pressures, and of cardiac output. Since organ blood flow cannot be directly measured in clinical practice, arterial blood pressure is used, despite limitations, as estimate of adequacy of tissue perfusion. A mean arterial pressure (MAP) of 70 mm Hg may be considered a reasonable target, associated with sign of adequate organ perfusion, in most patients. In the approach to hypotension, which is the most common cause of hemodynamic instability in critical ill patients, increasing levels of monitoring may be used. Assuming that central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) are adequate estimates of the volume of the systemic and pulmonary circulation respectively, the following decision tree is suggested: 1) make a working diagnosis based on the relationship between pressure (CVP and PAOP) and cardiac output or stroke volume (CO or SV); 2) consider conditions that may alter reliability of CVP and PAOP in estimate adequately circulating volumes such as abnormal pressure/volume relationship (compliance) of the RV or LV, increased intrathoracic pressure (PEEP, autoPEEP, intra-abdominal pressure), valvular heart disease (mitral stenosis); 3) look at the history; 4) separating RV and LV by reciprocal variations of CVP, PAOP and SV. CVP is often used as sole parameter to monitor hemodynamic. However CVP alone may not differentiate between changes in volume (different venous return curve) or changes in contractility (different starling curve). Finally, other techniques such as echocardiography, transesophageal Doppler and volume-based monitoring system are now available.     

Systolic blood pressure variation is a sensitive indicator of hypovolemia in ventilated dogs subjected to graded hemorrhage

Systolic pressure variation (SPV) is defined as the difference between the maximum and minimum values of systolic blood pressure following a single positive pressure breath. An increase in the SPV is known to occur clinically during hypovolemia. This study aims to quantify SPV during graded hemorrhage in ventilated dogs, and to compare its reliability relative to other hemodynamic indicators of hypovolemia. Ten anesthetized dogs were mechanically ventilated with a fixed tidal volume. A continuously inflated vest was applied around the chest to maintain the ratio of lung to chest wall compliance similar to that of humans (0.83 +/- 0.12). SPV was further divided into delta up and delta down components relative to apneic (5 s) systolic blood pressure. Dogs were bled 5, 10, 20, and 30% of their estimated blood volume. The measured parameters best correlated to the amount of bleeding were SPV (rs = 0.993), delta down (rs = 0.981), and cardiac output (rs = 0.976). The SPV and its delta down component correlated to the degree of hemorrhage as well as the CO and the pulmonary capillary wedge pressure, and significantly better than the central venous pressure and the mean systemic blood pressure. Thus, SPV and its delta down component are accurate indicators of hypovolemia in ventilated dogs subjected to hemorrhage.     

The effects of positive expiratory pressure on peritoneovenous shunt flow.

Cirrhotic patients with peritoneovenous shunts may require mechanical ventilation. Despite the importance of flow to shunt patency and the relevance of intrathoracic pressure to that flow, the relationship between shunt flow and positive airway pressure has not been documented. To study the effects of positive expiratory pressure (PEEP) on shunt flow, models of ascites (n = 8) were created in adult male mongrel dogs. Each animal was anesthetized, intubated, and mechanically ventilated. Peritoneovenous shunts with in-line electromagnetic flow meters were surgically placed. Shunt flow, central venous pressure (CVP), and intraabdominal pressure (IAP) were monitored. Initial intraabdominal pressures were adjusted by infusion of warmed saline and positive expiratory airway pressures were added in increments. Changes in pressures (IAP, CVP) and shunt flow were tabulated and analyzed with linear and polynomial regression. Intraabdominal and central venous pressures increased linearly with PEEP at different rates such that IAP-CVP varied inversely with PEEP. Shunt flow varied inversely as a polynomial function of PEEP. Analyses of these relationships allowed creation of a nomogram which can be interpolated to indicate required intraabdominal pressure needed to maintain shunt flow throughout the clinically useful range of positive airway pressure.     

Monitoring intravascular volumes for postoperative volume therapy

BACKGROUND AND OBJECTIVE: The feasibility of monitoring measured intravascular volumes and the cardiac filling pressures were compared to reflect the optimal volume status of postoperative patients. METHODS: In a prospective clinical study, 14 hypovolaemic adult patients were included after cardiac surgery. All patients received 1,000 mL hydroxyethyl starch after meeting the authors' criteria for hypovolaemia. Pressures were measured by use of a pulmonary artery catheter and volumes were determined by double-indicator dilution technique. RESULTS: Stroke volume index (SVI), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), intrathoracic blood volume index (ITBVI) and total circulating blood volume (TBVIcirc) increased significantlyaftervolumeloading(30.7 +/- 9.8 to 41.7 +/- 9.6 mLm(-2), 4.9 +/- 1.7 to 9.1 +/- 2.3mmHg, 6.6 +/- 1.3 to 10.6 +/- 1.9 mmHg, 858 +/- 255 to 965 +/- 163 mLm(-2), and 1,806 +/- 502 to 2,110 +/- 537 mLm(-2), respectively). During the subsequent 1 h steady-state period, CVP and PAOP decreased significantly (9.1 +/- 2.2 to 7.4 +/- 2.2 mmHg and 10.6 +/- 1.9 to 9.2 +/- 2.0 mmHg, respectively), whereas SVI and intravascular volumes remained unchanged. The changes of CVP and PAOP did not correlate with changes in stroke volume during volume loading (r2 = 0.06 and 0.03, respectively) and during steady-state (r2 = 0.17 and 0.00 respectively). On the other hand, a significant correlation was found between changes of the intrathoracic blood volume and changes in stroke volume during the volume loading (r2 = 0.67) and also during the steady-state phase (r2 = 0.83). CONCLUSIONS: Intrathoracic blood volume reflects more accurately the preload dependency of cardiac output in postoperative patients than left/right-sided cardiac filling pressures.     

Estimation of cardiac preload changes by systolic pressure variation in pigs undergoing pneumoperitoneum

BACKGROUND: Variations in systolic pressure arterial waveform (SPV) and its component have been shown to be a reasonable indicator of left ventricular preload. Creation of a pneumoperitoneum (PMOP) by insufflation of CO2 increases intrathoracic pressure, leading to overestimation of preload as assessed by pressure methods. The purpose of this study was to compare SPV with other standard methods in anaesthetized pigs. METHODS: We measured SPV and its DeltaDown component (deltaDown), pulmonary artery occlusion pressure (PAOP) and left ventricular short-axis cross-sectional area using transthoracic echocardiography (TTE) in 7 pigs, at baseline, after 12 mmHg PMOP and after an intravascular load with 10 ml/kg hydroxylethylstarch (HES). RESULTS: PMOP increased SPV from 12.9+/-4.9 to 16.9+/-5.5 mmHg (P<0.05) and decreased pulmonary compliance, with no change in PAOP or end-diastolic area assesssed by TTE. Intravascular volume loading significantly decreased SPV from 16.9+/-5.5 to 11.2+/-4.9 mmHg and deltaDown from 9.9+/-7.1 to 5.2+/-4.5 (P<0.05), and increased PAOP and end-diastolic area. Significant correlation between changes in deltaDown and EDA was noted following HES (r=0.78, P<0.05). CONCLUSION: In anaesthetized pigs, the creation of a PMOP alters SPV, likely by decreasing lung compliance. Once PMOP is established, changes in cardiac preload could be estimated by SPV analysis.     

Subjective assessment of left ventricular preload using transesophageal echocardiography: corresponding pulmonary artery occlusion pressures.

OBJECTIVE: To record pulmonary artery occlusion pressures (PAOPs) in patients whose left ventricular preload reserve was subjectively determined using transesophageal echocardiography (TEE). DESIGN: Prospective, blinded, nonrandomized. SETTING: University hospital. PARTICIPANTS: Twenty-three patients with well-preserved left ventricular function during nonemergent cardiac surgery. INTERVENTIONS: After separation from cardiopulmonary bypass, patients received repeated boluses of fluid volume through the aortic inflow cannula while being monitored with TEE. The endpoint for this fluid administration was a plateau in left ventricular fractional area change and end-diastolic area. This point at which additional fluid failed to cause noticeable increases in left ventricular end-diastolic area and fractional area change was defined as the preload reserve volume. After reaching the preload reserve volume, the PAOP was measured, as were the systolic blood pressure, left ventricular fractional area change, and end-diastolic area. MEASUREMENTS AND MAIN RESULTS: The mean PAOP for all patients at the time of achieving preload reserve volume was 18.6 +/- 2.9 mmHg. In 8 patients, the PAOP corresponding to preload reserve volume was elevated (20 to 25 mmHg). The remaining 15 patients had PAOPs ranging from 13 to 19 mmHg. When these 2 groups were compared with respect to left ventricular end-diastolic area, fractional area change, and systolic blood pressure, there were no significant differences between groups. The left ventricular wall thickness was significantly greater, however, in the group with elevated PAOP (1.37 +/- 0.04 cm) when compared with the group with normal ventricular filling pressures (1.05 +/- 0.15 cm) (p = 0.001). CONCLUSIONS: In patients with well-preserved left ventricular function and normal wall thickness, preload reserve volumes subjectively determined by TEE corresponded to a range of filling pressures historically targeted to maximize cardiac performance (13 to 19 mmHg). In a subset of patients with increased wall thickness, however, subjective determination of preload reserve was associated with filling pressures that were higher than traditionally considered optimal (20 to 25 mmHg). Similarities in left ventricular fractional area change and end-diastolic area between these 2 groups suggest that patients with elevated filling pressures had decreased ventricular compliance and were managed correctly with higher than usual PAOPs.     

Correlation of peripheral venous pressure and central venous pressure in surgical patients

OBJECTIVE: To determine the degree of agreement between central venous pressure (CVP) and peripheral venous pressure (PVP) in surgical patients. DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: Patients without cardiac dysfunction undergoing major elective noncardiac surgery (n = 150). MEASUREMENTS AND MAIN RESULTS: Simultaneous CVP and PVP measurements were obtained at random points in mechanically ventilated patients during surgery (n = 100) and in spontaneously ventilating patients in the postanesthesia care unit (n = 50). In a subset of 10 intraoperative patients, measurements were made before and after a 2-L fluid challenge. During surgery, PVP correlated highly to CVP (r = 0.86), and the bias (mean difference between CVP and PVP) was -1.6 +/- 1.7 mmHg (mean +/- SD). In the postanesthesia care unit, PVP also correlated highly to CVP (r = 0.88), and the bias was -2.2 +/- 1.9 (mean +/- SD). When adjusted by the average bias of -2, PVP predicted the observed CVP to within +/-3 mmHg in both populations of patients with 95% probability. In patients receiving a fluid challenge, PVP and CVP increased similarly from 6 +/- 2 to 11 +/- 2 mmHg and 4 +/- 2 to 9 +/- 2 mmHg. CONCLUSION: Under the conditions of this study, PVP showed a consistent and high degree of agreement with CVP in the perioperative period in patients without significant cardiac dysfunction. PVP -2 was useful in predicting CVP over common clinical ranges of CVP. PVP is a rapid noninvasive tool to estimate volume status in surgical patients.     

Comparison of external jugular and central venous pressures in mechanically ventilated patient

We compared central venous pressures, measured via a 150 mm triple lumen catheter in the internal jugular vein with simultaneous external jugular venous pressures, measured with a 5 mm cannula in the external jugular vein, in 24 patients undergoing major surgery. Patients were mechanically ventilated in the supine position. Six sets of paired measurements of mean central venous pressure and mean external jugular venous pressure were taken by a blinded observer, in random order and at end-expiration at 30-min intervals during surgery. Four patients were not studied because of a failure to cannulate the external jugular vein. The remaining 20 patients yielded 111 sets of paired measurements. The mean difference between external jugular venous pressure and central venous pressure was 0.3 mmHg over a range of central venous pressure of 0-22 mmHg. Limits of agreement were 3.6 to +3.0 mmHg (95% CI 4.1 to +3.5 mmHg). We conclude that external jugular venous pressure is an accurate estimate of central venous pressure in surgical patients undergoing mechanical ventilation.     

Effects of initiation of continuous renal replacement therapy on hemodynamics in a pediatric animal model

There are no studies analyzing the initial hemodynamic impact of continuous renal replacement therapy (CRRT) in children. We have performed a prospective observational study in 34 immature Maryland pigs to analyze the initial hemodynamic changes during venovenous CRRT. The heart rate, blood pressure, central venous pressure (CVP), pulmonary arterial occlusion pressure (PAOP), pulmonary capillary wedge pressure, temperature, and cardiac output (CO), simultaneously by pulmonary arterial thermodilution and femoral arterial thermodilution, were measured at 30-min intervals during 2 h. Venovenous CRRT induced an initial significant diminution of volemic hemodynamic parameters (intrathoracic blood volume, global end-diastolic volume, stroke volume index, PAOP, and CVP). Simultaneously, a significant increase in systemic vascular resistance index and left ventricular contractility, and a decrease in CO, was observed. We conclude that CRRT in a pediatric animal model induces initial hypovolemia, and a systemic cardiovascular response with vasoconstriction and increase in ventricular contractility.     

Effects of Initiation of Continuous Renal Replacement Therapy on Hemodynamics in a Pediatric Animal Model

There are no studies analyzing the initial hemodynamic impact of continuous renal replacement therapy (CRRT) in children. We have performed a prospective observational study in 34 immature Maryland pigs to analyze the initial hemodynamic changes during venovenous CRRT. The heart rate, blood pressure, central venous pressure (CVP), pulmonary arterial occlusion pressure (PAOP), pulmonary capillary wedge pressure, temperature, and cardiac output (CO), simultaneously by pulmonary arterial thermodilution and femoral arterial thermodilution, were measured at 30-min intervals during 2 h. Venovenous CRRT induced an initial significant diminution of volemic hemodynamic parameters (intrathoracic blood volume, global end-diastolic volume, stroke volume index, PAOP, and CVP). Simultaneously, a significant increase in systemic vascular resistance index and left ventricular contractility, and a decrease in CO, was observed. We conclude that CRRT in a pediatric animal model induces initial hypovolemia, and a systemic cardiovascular response with vasoconstriction and increase in ventricular contractility.     

Hemodynamic Response of Modified Fluid Gelatin Compared with Lactated Ringer's Solution for Volume Expansion in Emergency Resuscitation of Hypovolemic Shock Patients: Preliminary Report of a Prospective, Randomized Trial

The objective of this study was to compare the cardiac and hemodynamic responses to a rapid infusion of 1000 ml of modified fluid gelatin (group A) or 1000 ml of lactated Ringer's solution (group B) in emergency room patients suffering from shock. This prospective, randomized, open, noncrossover study was performed at a medical center university hospital in a surgical resuscitation room in the emergency department. The subjects were 34 patients with either hypovolemic or neurogenic shock who were admitted to the emergency room. A resuscitation protocol according to Advanced Trauma Life Support (ATLS) with an additional central venous line or Swan-Ganz catheters for hemodynamic monitoring was used. Physical parameters and hemodynamic variables were measured at baseline and 15 minutes, 30 minutes, and 1 hour after the infusion of each fluid. In both groups the mean arterial blood pressure (MAP), systolic and diastolic pressure, central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) increased significantly. The CVP and PAOP increased significantly more in the modified fluid gelatin resuscitation group. In patients with traumatic or neurogenic shock due to acute volume deficiency, there was significantly better hemodynamic improvement, judged by CVP and PAOP measurements using the modified fluid gelatin for volume replacement than with lactated Ringer's solution during the first hour of resuscitation.     

Respiratory variations in pulse oximeter waveform amplitude are influenced by venous return in mechanically ventilated patients under general anaesthesia

BACKGROUND AND OBJECTIVES: Respiratory variations in pulse oximetry plethysmographic waveform amplitude (DeltaPOP) are related to respiratory variations in arterial pulse pressure (DeltaPP) in the critical care setting. The aims of this study were to test the hypothesis that in mechanically ventilated patients undergoing general anaesthesia, DeltaPOP calculation is feasible and can detect changes in preload. METHODS: Twenty-five mechanically ventilated patients were studied immediately after induction of general anaesthesia. Haemodynamic data (mean arterial pressure [MAP], central venous pressure [CVP], DeltaPP and DeltaPOP) were recorded at baseline, before and after tilting the patient from anti-Trendelenburg to Trendelenburg position in order to induce preload changes. RESULTS: Change from anti-Trendelenburg to Trendelenburg position induced changes in MAP (58 +/- 9 to 67 +/- 10 mmHg, P < 0.05), CVP (4 +/- 4 to 13 +/- 5 mmHg, P < 0.05), DeltaPP (14 +/- 8 to 7 +/- 5%, P < 0.05) and DeltaPOP (17 +/- 12 to 9 +/- 5%, P < 0.05). There was a significant relationship between DeltaPOP in anti-Trendelenburg position and percent change in MAP after volume expansion (r = 0.82; P < 0.05). CONCLUSIONS: DeltaPOP can be determined in the operating room and is influenced by changes in preload. This new index has potential clinical applications for the prediction of fluid responsiveness.     

Detection of intraoperatiye myocardial ischaemia — a comparison among electrocardiographic,myocardial metabolic,and haemodynamic measurements in patients with reduced ventricular function

This study determined the sensitivity and specificity of haemodynamic and ECG monitors to detect the development of intraoperative myocardial ischaemia utilizing myocardial lactate production as the standard. In 29 patients with reduced ejection fraction (0.27–0.50) undergoing coronary artery revascularization, measurements were made at the awake, post-induction, post-intubation, first skin incision, post-sternotomy, preprotamine, immediately post-cardiopulmonary bypass, and skin suture intervals. At each interval, measurement of a haemo-dynamic profile (including pulmonary artery occlusion (PAOP) and central venous (CVF) pressures, heart rate, and pressure rate quotient); myocardial lactate extraction and flux; changes in ST segments in ECG leads, V₅ and II utilizing a Siemens 1280® intraoperative monitor, and a Marquette 8500® Hotter monitor utilizing leads V₅, V₂, and AVF were made. “Ischaemia” was considered to be present when myocardial lactate production (MLP) occurred, PAOP or CVP increased by 5 mmHg above the baseline value, the pressure rate quotient was <1, or ST segment deviation (>1 mm) occurred in any lead for >1 min. Variables positive when MLP was positive were the pressure rate quotient (sensitivity 32.8%, specificity 71.9%), CVP (sensitivity 10.9%, specificity 92.6%), and PAOP (sensitivity 1.6%, specificity 99.2%). Holter monitoring had a 100% positive predictive value but poor sensitivity (1.6%). The ECG (Lead V₅ + II) measures of ischaemia were insensitive (17.5%) and relatively non-specific (87.7%). We conclude that, in this patient group and using myocardial lactate production as the standard, the pressure rate quotient, elevations in CVP or PAOP, or ST segment changes are insensitive measures of intraoperative myocardial ischaemia.     

气道加压对全麻患者右颈内静脉穿刺置管术的影响

目的 探讨气道加压对全麻患者右颈内静脉穿刺置管术的影响.方法 需要进行右颈内静脉穿刺置管的全麻患者125例,随机分为对照组(C组,n=60)和气道加压组(P组,n=65).超声引导下于环状软骨平面,C组在暂停机械通气时、P组手控呼吸维持气道压力20 cm H2O时进行右颈内静脉穿刺置管.暂停机械通气时测定两组右颈内静脉横截面积和穿刺成功后CVP,P组患者气道压力20 cm H2O时测定颈内静脉横截面积和CVP,记录穿刺次数、颈内静脉管壁至皮肤的最短距离、进针深度、进针和退出过程中回抽血液通畅情况,气道加压前测定HR和MAP,并记录气道加压过程中的最低值,观察两组患者的穿刺置管情况.结果 P组气道压力20 cm H2O时颈内静脉横截面积和CVP较气道加压前增加(P＜0.01);与C组比较,P组进针深度降低,1次穿刺成功率、30 s内穿刺成功率、进针过程中回抽血液通畅率升高(P＜0.01),心动过缓、低血压发生率升高(P＜0.05).结论 气道加压有助于超声引导下右颈内静脉穿刺置管术的成功.     

The effect of the prone position on venous pressure and blood loss during lumbar laminectomy.

STUDY OBJECTIVE: To determine the effects of three different prone support systems (Andrews spinal surgery frame, Cloward surgical saddle, and longitudinal bolsters) on inferior vena cava (IVC) and superior vena cava (SVC) pressures; the validity of measuring central venous pressure (CVP) for the determination of ideal positioning of the patient; and the relationship among frame type, blood loss, and hemodynamic measurements. DESIGN: Prospective, randomized study of the hemodynamic effects of the prone position. SETTING: Inpatient surgery at a university hospital (regional spinal cord injury treatment center). PATIENTS: Eighteen patients free of significant coexisting disease (ASA physical status I and II) undergoing elective lumbar laminectomy. INTERVENTIONS: Patients were assigned to one of three support frames and measurement of SVC pressure, IVC pressure, and mean arterial pressures (MAP) were obtained supine, prone, and after repositioning. These pressures and measured blood loss were obtained every 15 minutes during the surgical laminectomy portion of the procedure. MEASUREMENTS AND MAIN RESULTS: Patients positioned on the Andrews frame had decreased mean SVC and IVC pressures from 8.7 mmHg and 8.4 mmHg in the supine position to 3.3 mmHg and 1.8 mmHg in the prone position, respectively (p less than 0.001). Prone position CVP also was significantly lower in the Andrews group compared with that in the other two groups (p less than 0.001). Repositioning efforts did not significantly decrease CVP. Blood loss was higher in the Cloward group (1,150 +/- 989 ml) than in the Andrews (245 +/- 283 ml) and bolsters (262 +/- 188 ml) groups (p less than 0.02). CONCLUSIONS: Increased blood loss was not associated with increased SVC or IVC pressure, nor was there any significant correlation between any demographic or hemodynamic variable and blood loss. There was no evidence that CVP is useful in determining the ideal prone position in patients undergoing lumbar laminectomy.     

The adverse hemodynamic effects of laparoscopic cholecystectomy

Recent studies suggest that significant physiologic derangements can occur during laparoscopic surgery. Eighteen patients admitted for laparoscopic cholecystectomy were studied. The mean age was 46.7 (range 19–78). A standard anesthetic technique, reverse Trendelenburg positioning, and an abdominal insufflation pressure of 15 mmHg with CO₂ were used with all subjects. Central venous pressure (CVP) and arterial pressures were measured invasively. Stroke volume and cardiac index were calculated using quantitative transesophageal echocardiography. Baseline measurements were taken after induction. Additional measurements were taken at 15-min intervals throughout the procedure. There was a statistically significant increase in mean arterial pressure (15.9%), systolic blood pressure (11.3%), diastolic blood pressure (19.7%), and CVP (30.0%) from control baseline values. Significant decreases in stroke volume (29.5%) and cardiac index (29.5%) occurred within 30 min of the induction of pneumoperitoneum and positioning (P<0.05, ANOVA). Laparoscopic cholecystectomy significantly and reversibly decreases cardiac performance. Compromised patients may be at increased risk for complications not previously recognized with this procedure.     

The use of systolic pressure variation in hemodynamic monitoring during deliberate hypotension in spine surgery

The systolic pressure variation (SPV), which is the difference between the maximal and minimal systolic blood pressure (SP) during one ventilatory cycle, was studied in ten patients during posterior spine fusion. To minimize the blood loss, deliberate hypotension to a mean blood pressure of 50 mmHg was introduced by a continuous infusion of sodium nitroprusside. SPV was further divided into two components, delta up and delta down, using SP during a short apnea as a reference point. All hemodynamic parameters were measured at the beginning of anesthesia, 15 minutes after induction of hypotension, before cessation of nitroprusside infusion, and 15 minutes after the end of the hypotensive period. During the hypotensive period (166 +/- 53 minutes), cardiac output (CO) decreased significantly from 4.83 +/- 1.36 L/min to 3.86 +/- 1.07 L/min (p less than 0.05). Heart rate (HR), central venous pressure (CVP), and pulmonary capillary wedge pressure (PCWP) did not change during this period and bore no correlation to the changes in CO. The only variables that changed during the hypotensive period, in addition to CO, were SPV (from 13.1 +/- 4.9 mmHg to 16.9 +/- 5.1 mmHg, p less than 0.02), and delta down (from 6.0 +/- 3.8 mmHg to 9.9 +/- 6.3 mmHg, p less than 0.05). The delta down segment was the only hemodynamic variable whose changes during the hypotensive period showed a significant (p less than 0.018) correlation with the changes in CO. delta down reflects the degree of decrease in left ventricular stroke output in response to a positive pressure breath, and thus is a sensitive indicator of preload.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison between systolic pressure variations under mechanical ventilation and classic pressure parameters in predicting fluid responsiveness in patients after coronary surgery

Evaluation of the value of the systolic pressure variations (SPV) under mechanical ventilation and of its components (delta down and delta up) in predicting fluid responsiveness in patients after coronary surgery by comparison with classic parameters. A prospective,randomized study, on 50 patients who underwent CABG surgery, in the early postoperative period (the first two hours). We assessed the following parameters: CO, CI, CVP, PCWP, SAP, DAP, MAP, SVP, delta down and delta up. The including criteria were: sinus rhythm, CI < or = 2,5 l/min/m2, PCP < 18 mmHg. All the patients underwent a fluid challenge (500 ml of colloids in 10 min). Three patients were excluded: 3 for a PCWP > 18 mm Hg, 1 for loosing the sinus rhythm and 1 for an early return in the OR for bleeding. After a new assessment of the same parameters the patients were divided in two groups: group A (28 pts) with a raise of CI > 15%, and group B (22 pts) with a CI variation < 15%. In each group was statistically analyzed the variation of each parameter. Results Both parameters provided by SPV analysis are able to predict the fluid responsiveness with a great accuracy: the positive predictive value of a SPV > 12 mmHg is above 92,85% and of a delta down > 5 mm Hg is above 96,42%; the negative predictive value of a SPV < or = 12 mmHg is above 90,90% and of a delta down = 5 mm Hg is above 95,45%. None of the "classic" pressure parameters (MAP, CVP, PCWP) used in hemodynamic assessment have revealed a statistical significant variation. The SVP method's parameters are superior to classic pressure parameters (MAP, CVP, PCWP) in predicting fluid responsiveness in patients after coronary surgery.