Hypotension during gradual blood loss: waveform variables response and absence of tachycardia.

BACKGROUND: Variation in arterial pressure and plethysmographic waveforms has been shown to be predictors of cardiac output response to fluid challenge. The objective of this study was to evaluate the ability of arterial and plethysmographic waveform variables to predict hypotension during blood loss. METHODS: Patients undergoing autologous haemodilution were studied. After anaesthesia induction, blood was withdrawn in steps of 2% of estimated circulating blood volume (ECBV). Arterial and plethysmographic waveforms were recorded and analysed offline at each step of blood withdrawal. RESULTS: Thirty-four (29%) out of 118 studied patients tolerated 20% ECBV withdrawal without hypotension. Patients who tolerated 20% ECBV withdrawal were younger than those who did not [mean (sd): 53.8 (11.1) vs 62.7 (10.7); P<0.0001]. Patients with hypertension developed hypotension earlier than healthier patients did. There were no differences at the baseline in arterial and plethysmographic waveform variables between those who did and those who did not tolerate 20% of ECBV withdrawal. All values of variables increased significantly from the baseline after the withdrawal of 4% of ECBV (P<0.005). There were no changes in heart rate (HR), 73 (12) at the baseline and 76 (13) after 20% of ECBV withdrawal (P=0.4). CONCLUSIONS: Arterial and plethysmographic waveform variables were augmented with increasing blood loss in all patients. Older patients, patients who received anti-hypertensive drugs, or both developed hypotension earlier than others. Baseline values were weak predictors of hypotension during stepwise blood withdrawal. No clinically significant increase in HR was observed, regardless of tolerance of arterial pressure to blood withdrawal.

The effect of helium on ventilator performance: study of five ventilators and a bedside Pitot tube spirometer.

OBJECTIVE: To assess in vitro the performance of five mechanical ventilators-Siemens 300 and 900C (Siemens-Elma; Solna, Sweden), Puritan Bennett 7200 (Nellcor Puritan Bennett; Pleasanton, CA), Evita 4 (Dragerwerk; Lubeck, Germany), and Bear 1000 (Bear Medical Systems; Riverside CA)-and a bedside sidestream spirometer (Datex CS3 Respiratory Module; Datex-Ohmeda; Helsinki, Finland) during ventilation with helium-oxygen mixtures. DESIGN: In vitro study. SETTING: ICUs of two university-affiliated hospitals. METHODS AND MEASUREMENTS: Each ventilator was connected to 100% helium through compressed air inlets and then tested at three to six different tidal volume (VT) settings using various helium-oxygen concentrations (fraction of inspired oxygen [FIO(2)] of 0.2 to 1.0). FIO(2) and VT were measured with the Datex CS3 spirometer, and VT was validated with a water-displacement spirometer. MAIN RESULTS: The Puritan Bennett 7200 ventilator did not function with helium. With the other four ventilators, delivered FIO(2) was lower than the set FIO(2). For the Siemens 300 and 900C ventilators, this difference could be explained by the lack of 21% oxygen when helium was connected to the air supply port, while for the other two ventilators, a nonlinear relation was found. The VT of the Siemens 300 ventilator was independent of helium concentration, while for the other three ventilators, delivered VT was greater than the set VT and was dependent on helium concentration. During ventilation with 80% helium and 20% oxygen, VT increased to 125% of set VT for the Siemens 900C ventilator, and more than doubled for the Evita 4 and Bear 1000 ventilators. Under the same conditions, the Datex CS3 spirometer underestimated the delivered VT by about 33%. CONCLUSIONS: At present, no mechanical ventilator is calibrated for use with helium. This investigation offers correction factors for four ventilators for ventilation with helium.

Blast lung injury from an explosion on a civilian bus.

OBJECTIVE: To assess clinical signs and management of primary blast lung injury (BLI) from explosions in an enclosed space and to propose a BLI severity scoring system. DESIGN: Retrospective analysis. PATIENTS: Fifteen patients with primary BLI resulting from explosions on two civilian buses in 1996. RESULTS: Ten patients were extremely hypoxemic on admission (PaO2 < 65 mm Hg with oxygen supplementation). Four patients remained severely hypoxemic (PaO2/fraction of inspired oxygen (FIO2) ratio of < 60 mm Hg) after mechanical ventilation was established and pneumothoraces were drained. Initial chest radiographs revealed bilateral lung opacities of various sizes in 12 patients (80%). Seven patients (47%) had bilateral pneumothoraces and two patients had a unilateral pneumothorax. Five (33%) had clinically significant bronchopleural fistulae. After clinical and laboratory data were collected, a BLI severity score was defined based on hypoxemia (PaO2/FIO2 ratio), chest radiographic abnormalities, and barotrauma. Severe BLI was defined as a PaO2/FIO2 ratio of < 60 mm Hg, bilateral lung infiltrates, and bronchopleural fistula; moderate BLI as a PaO2/FIO2 ratio of 60 to 200 mm Hg and diffuse (bilateral/unilateral) lung infiltrates with or without pneumothorax; and mild BLI as a PaO2/FIO2 ratio of > 200, localized lung infiltrates, and no pneumothorax. Five patients developed ARDS with Murray scores > 2.5. Respiratory management included positive pressure ventilation in the majority of the patients and unconventional methods (ie, high-frequency jet ventilation, independent lung ventilation, nitric oxide, and extracorporeal membrane oxygenation) in patients with severe BLI. Of the four patients who had severe BLI, three died. All six patients with moderate BLI survived, and four of five with mild BLI survived (one with head injury died). CONCLUSIONS: BLI can cause severe hypoxemia, which can be improved significantly with aggressive treatment. The lung damage may be accurately estimated in the early hours after injury. The BLI severity score may be helpful in determining patient management and prediction of final outcome.

Recovery from blast lung injury: one-year follow-up.

BACKGROUND: Blast injury to the lung is one of the devastating threats facing victims of an explosion. Although the pathogenesis of blast injury has been studied, little is known about the long-term effects on lung function in survivors. OBJECTIVE: To examine the pulmonary function of survivors 1 year after sustaining a blast injury. DESIGN: Prospective study. SETTING: Pulmonary function test laboratory at Hadassah Medical Center, Jerusalem. PARTICIPANTS: Eleven surviving victims of a blast injury sustained during a bus terrorist explosion. MEASUREMENTS: Twelve months after the injury, physical examinations, lung function tests, and progressive cardiopulmonary exercise examinations were conducted, and chest radiographs were obtained. RESULTS: The average age was 28 +/- 9.8 years. Most of the victims had multiple injuries in addition to the lung injury. Ten patients received mechanical ventilation, and 6 patients required chest drainage. All patients were treated in the ICU, with an average stay of 11.8 +/- 9 days. The patients were discharged to their homes or to a rehabilitation center 32.4 +/- 27. 3 days after the explosion. One year later, none had any pulmonary-related complaints. Physical examination of the lungs was normal. Most of the patients demonstrated normal lung function tests and complete resolution of the chest radiograph findings. CONCLUSION: Most patients who survive lung blast injury will regain good lung function within a year.

The effect of tidal volume and intravascular volume state on systolic pressure variation in ventilated dogs.

Both tidal volume and effective blood volume may affect the variation in the arterial pressure waveform during mechanical ventilation. The systolic pressure variation (SPV), which is the difference between the maximal and minimal systolic pressure values following one positive pressure breath was analyzed in 10 anesthetized and ventilated dogs, during ventilation with tidal volumes of 15 and 25 ml/kg. The dogs were studied during normovolemia, hypovolemia (after bleeding of 30% of estimated blood volume) and hypervolemia (after retransfusion of shed blood with additional 50 ml/kg of plasma expander). The SPV reflected hemodynamic changes and was maximal during hypovolemia and minimal during hypervolemia. Unlike all other hemodynamic parameters it was also affected by the tidal volume and significantly increased at higher tidal volumes during each volume state. We conclude that the SPV and its components are useful parameters in evaluating the intravascular volume state. They also reflect the magnitude of the tidal volume employed.

Foregoing life-sustaining treatment in an Israeli ICU.

OBJECTIVE: To determine whether physicians in Israel withhold and/or withdraw life-sustaining treatments. DESIGN: A prospective, descriptive study of consecutively admitted patients. Patients were prospectively evaluated for diagnoses, types and reasons for foregoing life-sustaining treatment, mortality and times from foregoing therapy until mortality. SETTING: A general intensive care unit of a university hospital in Israel. RESULTS: Foregoing life-sustaining treatment occurred in 52 (13.5%) of 385 patients admitted and 5 (1%) had cardiopulmonary resuscitation. Withholding therapy occurred in 48 patients. Four patients with brain death had all treatments withdrawn. No patient had antibiotics, nutrition or fluids withheld or withdrawn. Time from foregoing therapy until death was 2.9 +/- 0.6 days. Thirty-one of 48 (65%) patients who had therapy withheld died within 48 h. CONCLUSIONS: Withholding life-prolonging treatments is common in an Israeli intensive care unit whereas withdrawing therapy is limited to brain dead patients. Terminal patients die soon after withholding, even if the therapy is not withdrawn. Withholding treatments should be an option for patients and professionals who object to withdrawing therapies.

Novel thermoregulation system for enhancing cardiac function and hemodynamics during coronary artery bypass graft surgery.

BACKGROUND: Myocardial ischemia, arrhythmias, and coagulopathies are associated with postoperative hypothermia. This study assessed the efficacy of a novel thermoregulation system in alleviating these events during coronary artery bypass graft (CABG) surgery. METHODS: Elective CABG surgery patients were randomized into either Allon thermoregulation (AT, n = 40) or routine thermal care (RTC, n = 20) groups in whom the maintenance of normothermia during the nonbypass phases of the operation was compared. The AT used patients' rectal temperature as reference data to monitor the maintenance of the water temperature circulating at 37 degrees C in a garment. Rectal temperature, patient hemodynamics, and cardiac-specific troponin I (cTnI) levels were assessed at the induction of anesthesia, 30 minutes into surgery, at discontinuation of bypass, end of surgery, and 2 hours postoperatively. RESULTS: Body temperature was higher in the AT group compared to the RTC group at all five time points. Cardiac index (CI) (L/min) was higher in the AT group, 2.5 +/- 0.5, 2.6 +/- 0.5*, 3.2 +/- 0.6*, 3.3 +/- 0.5*, 3.1 +/- 0.7 at the respective time points, compared to the RTC group, 2.3 +/- 0.6, 2.1 +/- 0.2, 2.6 +/- 0.7, 2.7 +/- 0.7, 2.7 +/- 0.7 (*p < 0.05). Systemic vascular resistance (SVR) (dyne x s)/cm5) was consistently lower in the AT patients. Enzyme levels were elevated in both groups but were less so in the AT patients. CONCLUSIONS: The AT system can efficiently maintain normothermia. The beneficial effects are expressed by reduced SVR, elevated CI, and lower levels of cTnI, which may show a possible attenuation of myocardial injury.

Effect of haemofiltration on pathological fibrinolysis due to severe sepsis: a case report.

Bleeding due to coagulopathy is a frequent complication of severe sepsis, especially in burn patients. The primary treatment is aimed at the underlying cause but additional supportive measures, consisting mainly of coagulation factor replacement, are frequently necessary. We describe the salutary effect of continuous veno-venous haemofiltration (CVVH) with predilution on diffuse haemorrhage in a patient with severe septic shock and renal failure. The diffuse haemorrhage was initially treated with replacement of coagulation factors. Prothrombin time and partial thromboplastin time became normal while diffuse bleeding continued and the thrombelastogram showed evidence of fibrinolysis. A short period of CVVH lead to the cessation of bleeding which was reflected by a normal thrombelastogram.

Urgent abdominal aortic aneurysm repair in patients over the age 80.

We present three patients with successful surgical repair of abdominal aortic aneurysms with signs of imminent rupture in octogenarians. The patients presented with evidence of severe left ventricular dysfunction and reduced compliance either before or during surgery. Extremely cautious delivery of fluids and of after-load reducing agents was employed under the guidance of measurements of cardiac output and filling pressures from a pulmonary arterial catheter inserted prior to surgery.

Systolic pressure variation predicts the response to acute blood loss.

STUDY OBJECTIVE: To evaluate systolic pressure variation (SPV), defined as the difference between the maximum and minimum systolic blood pressure measured during a controlled mechanical respiratory cycle, as a predictor of the cardiac output (CO) response to an acute decrease in ventricular preload. DESIGN: Prospective study with each subject serving as his or her own control. SETTING: Cardiac surgery operating rooms of a university medical center. PATIENTS: 15 adults with good ventricular function undergoing coronary artery bypass grafting. INTERVENTION: During stable anesthetic conditions and before surgical stimulation, 500 ml of blood was removed from each patient over 10 minutes. MEASUREMENTS AND MAIN RESULTS: CO, central venous pressure (CVP), pulmonary artery diastolic pressure, and pulmonary artery occlusion pressure (PAOP), and SPV before and after phlebotomy were recorded. Phlebotomy was associated with significant decreases in CVP, PAOP, and CO, and an increase in SPV. Of these variables, SPV was the best predictor of the percent decrease in CO resulting from blood loss. CONCLUSION: SPV is a dynamic measurement, which, by revealing the response to small cyclical changes in left ventricular preload that occur during the controlled mechanical respiratory cycle, is a better predictor than central filling pressures of the response of CO to acute decreases in preload that occur as a result of acute blood loss.

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)

QRS-activated ventilation during general anesthesia for extracorporeal shock wave lithotripsy.

High frequency ventilation has been claimed to improve the efficiency of extracorporeal shock wave lithotripsy (ESWL) by minimizing the movement of urinary stones during the procedure. A ventilatory mode, QRS-activated ventilation, was developed in which the stones remain motionless during the delivery of shock waves. As the shock wave is triggered to occur approximately 20 milliseconds after the R wave of the QRS complex, the mechanical breath was synchronized to occur approximately 150 ms later. QRS-activated ventilation is used in 16 patients undergoing ESWL under general anesthesia. Tidal volume was set at 3 ml/kg (234 +/- 36 ml; mean +/- SD) at a rate that equaled the heart rate (71 +/- 9 beats/min). The time between the R wave and the initiation of mechanical breath (T1) was 124 +/- 25 ms, time of mechanical breath itself (T2) was 431 +/- 67 ms, and time between end of T2 and next R wave (T3) was 264 +/- 84 ms. End-tidal CO2 measured by the large breath technique was 28.1 +/- 4.8 mmHg. During the clinical use of QRS-activated ventilation and during earlier studies using an EKG simulator and a test lung, the shock wave occurred invariably at end-expiration even at high heart rates.

Systolic pressure variation in hemodynamic monitoring after severe blast injury.

Fluid management in patients following blast injury is a major challenge. Fluid overload can exacerbate pulmonary dysfunction, whereas suboptimal resuscitation may exacerbate tissue damage. In three patients, we compared three methods of assessing volume status: central venous (CVP) and pulmonary artery occlusion (PAOP) pressures, left ventricular end-diastolic area (LVEDA) as measured by transesophageal echocardiography, and systolic pressure variation (SPV) of arterial blood pressure. All three patients were mechanically ventilated with high airway pressures (positive end-expiratory pressure 13 to 15 cm H2O, pressure control ventilation of 25 to 34 cm H2O, and I:E 2:1). Central venous pressure and PAOP were elevated in two of the patients (CVP 14 and 18 mmHg, PAOP 25 and 17 mmHg), and were within normal limits in the third (CVP 5 mmHg, PAOP 6 mmHg). Transesophageal echocardiography was performed in two patients and suggested a diagnosis of hypovolemia (LVEDA 2.3 and 2.7 cm2, shortening fraction 52% and 40%). Systolic pressure variation was elevated in all three patients (15 mmHg, 15 mmHg, and 20 mmHg), with very prominent dDown (23, 40, and 30 mmHg) and negative dUp components, thus corroborating the diagnosis of hypovolemia. Thus, in patients who are mechanically ventilated with high airway pressures, SPV may be a helpful tool in the diagnosis of hypovolemia.