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Biomedical subjects

P Coriat

Publications and source records attributed to P Coriat.

At least 73 records · Page 4Linked to original sources
PubMed2000

Evaluation of transesophageal echocardiography for diagnosis of traumatic aortic injury.

BACKGROUND: Traumatic aortic injury is a frequent cause of death after blunt trauma, but few patients survive to reach a trauma center. The role of transesophageal echocardiography (TEE) in the diagnosis of traumatic aortic injury remains debated. METHODS: Over a 9-yr period, 209 blunt trauma patients (mean age, 34 +/- 13 yr) were suspected of having traumatic aortic injury because of enlarged mediastinum and/or sudden deceleration, and underwent TEE and angiography (aortography and/or contrast-enhanced computed tomography. RESULTS: Traumatic aortic injury was diagnosed in 42 patients (20%). Angiography (aortography and/or contrast-enhanced computed tomography) was less accurate (sensitivity, 83%; specificity, 100%) than TEE (sensitivity, 98%; specificity, 100%) for the diagnosis of aortic injury because it failed to diagnose most minor injuries (intramural hematoma or limited intimal flap, n = 7). However, when considering only patients with major aortic injury (n = 33; i.e., those who might need surgery), angiography (sensitivity, 97%; specificity, 100%) and TEE (sensitivity, 97%; specificity, 100%) were equivalent. CONCLUSION: Transesophageal echocardiography is an accurate method for diagnosis of traumatic aortic injury. Nevertheless, the clinical implications of limited aortic injuries diagnosed by the technique have yet to be determined.

Accidental Falls↗
PubMed1999

[Postoperative patient management. Perioperative myocardial infarct].

A FREQUENT AND SEVERE EVENT: The incidence and the pathogenic mechanisms of cardiac complications in general surgery patients are now well described. Acute myocardial necrosis, the most frequent complication, is observed in 3 to 5% of patients at risk. Most are silent subendocardial lesions, but may have a short-term or mid-term life-threatening effect in these surgery patients. EARLY POSTOPERATIVE PERIOD: In most patients, cardiac events occur within 48 hours of surgery. Diagnosis is confirmed by elevated troponin I. The immediate postoperative period is characterized by increased left ventricular load and metabolic disturbances, increased release of catecholinergic mediators and hypercoagulability, factors related to the effect of anesthesia on circulation and surgical stimuli. These modifications compromise the energy balance in the myocardium and favor the development of left ventricular failure. ECG RECORDINGS: Continuous recordings in the postoperative period have shown that although the number of episodes of myocardial ischemia is not affected during surgery, their number doubles during the postoperative period, a factor predicting postoperative infarction. OPTIMAL CARE: Cardiovascular and anti-aggregate therapy should be adapted in patients with an underlying heart or coronary condition. Postoperative circulatory load and hyperaggregability should be controlled. This involves preventing hypothermia, intensive analgesia and, in some cases, cardiovascular therapy using beta blockers or alpha 2 agonists.

Combined Modality Therapy↗
PubMed1999

Impact of hepatitis B and C virus on kidney transplantation outcome.

The impact of hepatitis B (HBV) and C (HCV) on patient survival after kidney transplantation is controversial. The aims of this study were (1) to assess the independent prognostic values of HBsAg and anti-HCV in a large renal transplant population, (2) to compare infected patients with noninfected patients matched for factors possibly associated with graft and patient survival, and (3) to assess the prognostic value of biopsy-proven cirrhosis. Eight hundred thirty-four transplanted patients were included: 128 with positive HBsAg (group I), 216 with positive anti-HCV (group II), and 490 without serological markers of HBV and HCV (group III). Fifteen percent and 29% of patients were HBsAg-positive and anti-HCV-positive, respectively. Ten-year survivals of group I (55 +/- 6%) and group II (65 +/- 5%) were significantly lower than survival of group III (80 +/- 3%, P <.001). At 10 years, among overall patients with HCV screening (n = 834), four variables had independent prognostic values in patient survival: age at transplantation (P <.0001), year of transplantation (P =.02), biopsy-proven cirrhosis (P =.03), and presence of HCV antibodies (P =.02). In the case control study, comparison of infected patients with their matched control patients showed that age at transplantation (P <.05), HBsAg (P =.005), and anti-HCV (P =.005) were independent prognostic factors. HCV, biopsy-proven cirrhosis, and age are independent prognostic factors of 10-year survival in patients with kidney grafts. The case-control study showed that anti-HCV and HBsAg were independently associated with patient and graft survivals. In infected patients, a routine liver histological analysis would improve selection of patients for renal transplantation.

Adult↗
PubMed1999

Cardiac troponin I cutoff values to predict postoperative cardiac complications after circulatory arrest and profound hypothermia.

OBJECTIVE: Cardiac failure and myocardial infarction are complications of thoracic aorta, thoracoabdominal aorta, or aortic arch surgery, especially when surgery is performed using profound hypothermia and circulatory arrest (PHCA). Moreover, the diagnosis of non-Q-wave postoperative myocardial infarction (PMI) is challenging because there is no gold standard. The aims of this study were to determine values for cardiac troponin I (cTnl) in patients undergoing aortic arch or thoracoabdominal aortic surgery with PHCA who were free of cardiac complications in the postoperative period, and to test the validity of cutoff values of cTnl to predict postoperative cardiac complications in such patients. DESIGN: Prospective, nonrandomized study. SETTING: Single university hospital; Departments of Anesthesiology, Biochemistry and Vascular Surgery. PARTICIPANTS: Fifty-two consecutive patients were studied over a 2-year period. None was excluded, even patients who underwent emergency surgery. INTERVENTIONS: Patients undergoing aortic arch or thoracoabdominal aortic surgery with PHCA were studied. Thirty patients undergoing coronary artery bypass grafting (CABG) in the same period constituted a control group. MEASUREMENTS AND MAIN RESULTS: The cTnl concentrations were determined using an immunoenzymofluorometric assay on a Stratus analyzer (Dade, Massy, France) on blood samples obtained at recovery and on day 1 (D1) and D2. Seventeen patients developed a cardiac complication, which was lethal in 10 patients. In patients without cardiac complication, the peak level for cTnl was observed on D1. Cutoff values of cTnl were identical in both the CABG control group (11 .6 microg/mL) and the sternotomy group (12.2 microg/mL), but were significantly greater (20.5 microg/mL) in patients with a thoracotomy approach. Sensitivity and specificity of these cutoff values were high in both groups (control group, sensitivity = 100%, specificity = 100%; sternotomy group, sensitivity = 78%, specificity = 100%; thoracotomy group, sensitivity = 100%, specificity = 94%). CONCLUSION: In patients who underwent surgery using PHCA for aortic arch or descending aorta repair, myocardial damage related to cardiac arrest, vents or fibrillation explains the increased cutoff value (12.2 microg/mL). This value is similar to patients undergoing CABG surgery through a sternotomy approach with cardioplegia administration. In contrast, and probably related to the absence of cardioplegia, patients undergoing surgery through a left thoracotomy approach had a greater cutoff value (20.5 microg/mL). Values of cTnl greater than these respective cutoff values were closely related to cardiac complications during the postoperative period.

Adult↗
PubMed1999

Does desflurane alter left ventricular function when used to control surgical stimulation during aortic surgery?

BACKGROUND: Although desflurane is commonly used to control surgically induced hypertension, its effects on left ventricular (LV) function have not been investigated in this clinical situation. The purpose of the present study was to evaluate the LV function response to desflurane, when used to control intraoperative hypertension. METHODS: In 50 patients, scheduled for vascular surgery, anesthesia was induced with sufentanil 0.5 microg/kg, midazolam 0.3 mg/kg and atracurium 0.5 mg/kg. After tracheal intubation, anesthesia was maintained with increments of drugs with controlled ventilation (N2O/O2=60/40%) until the start of surgery. A 5 Mhz transesophageal echocardiography (TEE) probe was inserted after intubation. Pulmonary artery catheter and TEE measurements were obtained after induction (to)(control value), at surgical incision (t1) if it was associated with an increase in systolic arterial pressure (SAP) greater than 140 mmHg (hypertension) and after control of hemodynamic parameters by administration of desflurane (return of systolic arterial pressure to within 20% of the control value) (t2) in a fresh gas flow of 31/ min. RESULTS: Sixteen patients developed hypertension at surgical incision. SAP was controlled by desflurane in all 16 patients. Afterload assessed by systemic vascular resistance index (SVRI), end-systolic wall-stress (ESWS) and left-ventricular stroke work index (LVSWI) increased with incision until the hypertension returned to post-induction values with mean end-tidal concentration of 5.1+/-0.7% desflurane. No change in heart rate, cardiac index, mean pulmonary arterial pressure, stroke volume, end-diastolic and end-systolic cross-sectional areas, fractional area change and left ventricular circumferential fiber shortening was noted when desflurane was added to restore blood pressure. CONCLUSION: This study demonstrates that in patients at risk for cardiac morbidity undergoing vascular surgery, desflurane is effective to control intraoperative hypertension without fear of major cardiac depressant effect.

Anesthetics, Inhalation↗
PubMed1999

Effects of propofol, propofol-nitrous oxide and midazolam on cortical somatosensory evoked potentials during sufentanil anaesthesia for major spinal surgery.

Recording of cortical somatosensory evoked potentials (CSEP) enables monitoring of spinal cord function. We studied the effects of propofol, propofol-nitrous oxide or midazolam during sufentanil anaesthesia on CSEP monitoring during major spinal surgery. Thirty patients with normal preoperative CSEP were allocated randomly to one of the following anaesthesia regimens: propofol (2.5 mg kg-1 followed by 10-6 mg kg-1 h-1) with or without nitrous oxide, or midazolam (0.3 mg kg-1 followed by 0.15 mg kg-1 h-1) combined with sufentanil 0.5 microgram kg-1 h-1 in the propofol and midazolam groups, or 0.25 microgram kg-1 h-1 in the propofol-nitrous oxide group. CSEP were elicited by alternate right and left tibial posterior nerve stimulation and recorded before and after induction (15 min, 1, 2 and 3 h), and during skin closure. CSEP latencies were not significantly modified in the three groups. CSEP amplitude decreased significantly in the propofol-nitrous oxide group (from mean 2.0 (SEM 0.3) to 0.6 (0.1) microV; P < 0.05) but not in the propofol (from 1.8 (0.6) to 2.2 (0.3) microV) or midazolam (1.7 (0.5) to 1.6 (0.5) microV) groups. The time to the first postoperative voluntary motor response (recovery) delay was significantly greater in the midazolam group (115 (19) min) compared with the propofol and propofol-nitrous oxide groups (43 (8) and 41 (3) min, respectively). Consequently, the use of propofol without nitrous oxide can be recommended during spinal surgery when CSEP monitoring is required.

Adult↗
PubMed1999

Minimum alveolar anesthetic concentration of volatile anesthetics in normal and cardiomyopathic hamsters.

UNLABELLED: Minimum alveolar anesthetic concentrations (MAC) values of volatile anesthetics in cardiovascular diseases remain unknown. We determined MAC values of volatile anesthetics in spontaneously breathing normal and cardiomyopathic hamsters exposed to increasing (0.1%-0.3% steps) concentrations of halothane, isoflurane, sevoflurane, or desflurane (n = 30 in each group) using the tail-clamp technique. MAC values and their 95% confidence interval were calculated using logistic regression. In normal hamsters, inspired MAC values were: halothane 1.15% (1.10%-1.20%), isoflurane 1.62% (1.54%-1.69%), sevoflurane 2.31% (2.22%-2.40%), and desflurane 7.48% (7.30%-7.67%). In cardiomyopathic hamsters, they were: halothane 0.89% (0.83%-0.95%), isoflurane 1.39% (1.30%-1.47%), sevoflurane 2.00% (1.85%-2.15%), and desflurane 6.97% (6.77%-7.17%). Thus, MAC values of halothane, isoflurane, sevoflurane, and desflurane were reduced by 23% (P < 0.05), 14% (P < 0.05), 13% (P < 0.05), and 7% (P < 0.05), respectively in cardiomyopathic hamsters. IMPLICATIONS: Minimum alveolar anesthetic concentrations of volatile anesthetics were significantly lower in cardiomyopathic hamsters than in normal hamsters.

Anesthetics, Inhalation↗
PubMed1999

Treatment of intraoperative refractory hypotension with terlipressin in patients chronically treated with an antagonist of the renin-angiotensin system.

UNLABELLED: The goal of the present study was to determine whether terlipressin, an agonist of the vasopressin system, could counteract perioperative hypotension refractory to common vasopressor therapy and to analyze its circulatory effects. We enrolled 51 consecutive vascular surgical patients chronically treated with angiotensin-converting enzyme inhibitors or antagonists of the receptor of angiotensin II, who received a standardized opioid-propofol anesthetic. Of these 51 patients, 32 had at least one episode of hypotension, which responded to epinephrine or phenylephrine. In 10 other patients, systolic arterial pressure (SAP) did not remain above 100 mm Hg for 1 min, despite three bolus doses of ephedrine or phenylephrine. In these patients, we injected a bolus of 1 mg of terlipressin, repeated twice if necessary. Hemodynamic and echocardiographic variables were recorded every 30 s over 6 min. In eight patients, arterial pressure was restored with one injection of terlipressin; in two other patients, three injections were necessary. One minute after the last injection of terlipressin, the SAP increased from 88+/-3 to 100+/-4 mm Hg and reached 117+/-5 mm Hg (P = 0.001) 3 min after the injection and remained stable around this value. This increase in SAP was associated with significant changes in left ventricular end-diastolic area (17.9+/-2 vs 20.2+/-2.2 cm2; P = 0.003), end-systolic area (8.1+/-1.3 vs 9.6+/-1.5 cm2; P = 0.004), end-systolic wall stress (45+/-8 vs 66+/-12; P = 0.001), and heart rate (60+/-4 vs 55+/-3 bpm; P = 0.001). Fractional area change and velocity of fiber shortening did not change significantly. No additional injection of vasopressor was required during the perioperative period. No change in ST segment was observed after the injection. IMPLICATIONS: Terlipressin is effective to rapidly correct refractory hypotension in patients chronically treated with antagonists of the renin-angiotensin system without impairing left ventricular function.

Aged↗
PubMed1999

The effects of dantrolene on the contraction, relaxation, and energetics of the diaphragm muscle.

UNLABELLED: Dantrolene is used in patients with muscle spasticity and is the only known effective treatment for malignant hyperthermia. However, its effects on muscle relaxation and energetics are unknown and may have important consequences in diaphragmatic function. We studied the effects of dantrolene (10(-8) to 10(-4) M) on diaphragm muscle strips (n = 12) in the hamster in vitro (Krebs-Henseleit solution, 29 degrees C, 95% oxygen/5% carbon dioxide) in response to tetanic stimulation (50 Hz). We studied contraction and relaxation under isotonic and isometric conditions, as well as energetics. Data are mean +/- SD. Dantrolene induced a negative inotropic effect in the hamster diaphragm (active force at 10(-4) M: 34% +/- 7% of baseline; P < 0.05) but did not significantly modify the curvature of the force-velocity relationship. Dantrolene did not significantly modify isotonic relaxation. Dantrolene, up to 10(-5) M, did not significantly impair isometric relaxation. In conclusion, dantrolene induced a marked negative inotropic effect on diaphragm muscle without affecting myothermal efficiency and relaxation. IMPLICATIONS: Dantrolene induced a significant and concentration-dependent negative inotropic effect on diaphragm muscle but did not modify isotonic relaxation, which suggests no alteration of the calcium reuptake by the sarcoplasmic reticulum; up to 10(-5) M dantrolene did not alter isometric relaxation, i.e., myofilament calcium sensitivity. Dantrolene did not modify the energetics of diaphragm muscle.

Animals↗
PubMed1999

Pericardial cardiac troponin I release after coronary artery bypass grafting.

UNLABELLED: Pericardial fluid can reflect the composition of cardiac interstitium in myocardial ischemia. This study investigated the hypothesis that pericardial cardiac troponin I (CTnI) measurements could be a more accurate marker of perioperative myocardial infarction (MI) than serum CTnI after coronary artery bypass grafting (CABG). Postoperative arterial and pericardial blood samples were taken in 102 subjects undergoing elective CABG allocated to one of three groups according to the 12-lead electrocardiogram (ECG) abnormalities observed during the first postoperative 24 h: Group 1 = normal ECG; Group 2 = nonspecific ECG abnormalities; and Group 3 = perioperative Q-wave MI. Peak pericardial CTnI concentrations were much higher than peak serum concentrations in all subjects and significantly greater in Group 3 than in Groups 1 and 2 (1,318 +/- 1,810 ng/mL vs 367 +/- 339 ng/mL and 558 +/- 608 ng/mL, respectively; P < 0.01). However, no significant difference between groups occurred at any time for pericardial/serum CTnI ratios, indicating that time courses of CTnI were not different in pericardial fluid and serum. A significant correlation was found between serum and pericardial CTnI concentrations (R = 0.70, P < 0.001). Pericardial CTnI was not more accurate than serum CTnI in predicting Q-wave MI as shown by the low value of the area under the receiver-operator characteristic curve (= 0.71). Peak and early pericardial CTnI were also not accurate in predicting an increase of serum CTnI greater than a cutoff value of 19 ng/mL. Thus, pericardial CTnI measurements were less useful than serum CTnI measurements in the diagnosis of perioperative MI after CABG. IMPLICATIONS: Although cardiac troponin I concentrations were much higher in pericardial fluid than in serum and significantly increased in subjects who experienced perioperative Q-wave myocardial infarction, pericardial cardiac troponin I measurements were of less value than serum cardiac troponin I measurements for the diagnosis of perioperative myocardial infarction after coronary artery bypass grafting and cannot be recommended in routine clinical practice.

Aged↗
PubMed1999

The hemodynamic effects of anesthetic induction in vascular surgical patients chronically treated with angiotensin II receptor antagonists.

UNLABELLED: The use of angiotensin II receptor subtype-1 antagonists (ARA), recently introduced as antihypertensive drugs, is becoming more prevalent. We studied the prevalence and severity of hypotension after the induction of general anesthesia in 12 patients treated with ARA until the morning of surgery. The hemodynamic response to induction was compared with that of patients treated with beta-adrenergic blockers (BB) and/or calcium channel blockers (CB) (BB/CB group, n = 45) and angiotensin-converting enzyme inhibitors (ACEI) (ACEI group, n = 27). A standardized anesthesia induction protocol was followed for all patients. Hypotension occurred significantly (p < or = 0.05) more often in ARA-treated patients (12 of 12) compared with BB/CB-treated patients (27 of 45) or with ACEI-treated patients (18 of 27). There was a significantly (P < or = 0.001) increased ephedrine requirement in the ARA group (21+/-3 mg) compared with the BB/CB group (10+/-6 mg) or the ACEI group (7+/-4 mg). Hypotension refractory to repeated ephedrine or phenylephrine administration occurred significantly (P < or = 0.05) more in the ARA group (4 of 12) compared with the BB/CB group (0 of 45) or the ACEI group (1 of 27), but it was treated successfully by using a vasopressin system agonist. Treatment with angiotensin II antagonism until the day of surgery is associated with severe hypotension after the induction of anesthesia, which, in some cases, can only be treated with an agonist of the vasopressin system. IMPLICATIONS: Hypotensive episodes occur more frequently after anesthetic induction in patients receiving Angiotensin II receptor subtype-1 antagonists under anesthesia than with other hypotensive drugs. They are less responsive to the vasopressors ephedrine and phenylephrine. The use of a vasopressin system agonist was effective in restoring blood pressure when hypotension was refractory to conventional therapy.

Adrenergic beta-Antagonists↗
PubMed1999

Role of the hematocrit in a rabbit model of arterial thrombosis and bleeding.

BACKGROUND: A decrease in hematocrit lengthens bleeding time. The authors studied the role of hematocrit variations in an experimental model of arterial thrombosis and bleeding. METHODS: The Folts model was used in 24 rabbits. After anesthesia was induced and common monitors were positioned, the right common carotid artery was exposed and a 60% stenosis was induced. A compression injury of the artery was then produced, which triggered a series of cyclic episodes of thrombosis and clot lysis (cyclic flow reductions [CFRs]). After counting the number of CFRs that occurred in 20 min (CFR1), the animals were assigned randomly to one of three groups (n = 8 in each group): control, hemodilution with rabbit homologous platelet-rich plasma, and hemodilution with gelatin solution and then reinfusion of the shed blood. The effect of hemodilution with replacement by platelet-rich plasma or by colloid was observed by recording the number of CFRs during another 20-min period (CFR2). A third period of observation (CFR3) followed shed blood reinfusion in the gelatin solution group. Ear immersion bleeding time was recorded after each CFR period. RESULTS: In the two experimental groups, the decrease in hematocrit (from 36 +/- 3% to 23 +/- 2% and from 38 +/- 3% to 23 +/- 2%, respectively; mean +/- SD) abolished CFRs (from a median of 4 to 0 and 7 to 0, respectively) and significantly lengthened bleeding time (from 76 +/- 24 s to 114 +/- 36 s and from 84 +/- 37 s to 127 +/- 29 s, respectively). Blood reinfusion in the group that received the gelatin solution caused CFR to reappear (CFR3 = 4). CONCLUSIONS: Decreases in hematocrit reduced the cyclic arterial thrombosis rate and increased the bleeding time in the rabbits in this study. Hematocrit normalization caused thrombosis to reappear.

Animals↗
PubMed1999

Interaction of halogenated anesthetics with dobutamine in rat myocardium.

BACKGROUND: Halogenated anesthetics potentiate the positive inotropic effects of alpha- and beta-adrenoceptor stimulations, but their interactions with dobutamine remain unknown. METHODS: The effects of halothane, isoflurane, sevoflurane, and desflurane (1 and 2 minimum alveolar concentration) on the inotropic responses induced by dobutamine (10(-8)-10(-4) M) were studied in rat left ventricular papillary muscles in vitro. Inotropic effects were studied under low (isotony) and high (isometry) loads. The authors also studied the lusitropic effects in isotonic (R1) and isometric (R2) conditions. Data are the mean percentage of baseline +/- SD. RESULTS: Dobutamine induced a positive inotropic effect (active isometric force: 185+/-36%, P < 0.001) and a positive lusitropic effect under low load (R1: 78+/-9%, P < 0.001), but not under high load (R2: 95+/-21%, not significant). Halothane, isoflurane, and sevoflurane did not modify the positive inotropic effect of dobutamine. Even in the presence of alpha-adrenoceptor blockade, isoflurane did not potentiate the positive inotropic effect of dobutamine. Desflurane significantly enhanced the positive inotropic effect of dobutamine (active isometric force: 239+/-35%, P < 0.001), but this potentiation was abolished by pretreatment with reserpine. In contrast to halothane, isoflurane, sevoflurane, and desflurane did not significantly modify the lusitropic effects of dobutamine. CONCLUSIONS: Halogenated anesthetics, except desflurane, did not modify the positive inotropic effects of dobutamine. Desflurane enhanced the positive inotropic effect of dobutamine, but this effect was related to the desflurane-induced release in intramyocardial catecholamine stores.

Adrenergic beta-Agonists↗
PubMed1999

A simple automated method for measuring pressure-volume curves during mechanical ventilation.

Measurement of respiratory compliance is advocated for assessing the severity of acute respiratory failure (ARF). Recently, the administration of an automated constant flow of 15 L/min was proposed as a method easier to implement at the bedside than supersyringe or inspiratory occlusions methods. However, pressure-volume (P-V) curves were shifted to the right because of the resistive properties of the respiratory system. The aim of this study was to compare the P-V curves obtained using two constant flows-3 and 9 L/min-during volume-controlled mechanical ventilation with those obtained with the supersyringe and the inspiratory occlusions methods. Fourteen paralyzed patients with ARF were studied. The supersyringe and the inspiratory occlusions methods were performed according to usual recommendations. The new automated method was performed during volume-controlled mechanical ventilation by setting the inspiratory:expiratory ratio at 80%, the respiratory frequency at 5 breaths/min, and the tidal volume at 500 or 1,500 ml. These peculiar ventilatory settings were equivalent to administering a constant flow of 3 or 9 L/min during a 9.6-s inspiration. Esophageal and airway pressures were recorded. P-V curves obtained by the 3-L/min constant-flow method were identical to those obtained by the reference methods, whereas the P-V curve obtained by the 9-L/min constant flow was slightly shifted to the right. The slopes of the P-V curves and the lower inflection points were not different between all methods, indicating that the resistive component induced by administering a constant flow equal to or less than 9 L/min is not of clinical relevance. Because the 3-L/min constant-flow method is not artifacted by the resistive properties of the respiratory system and does not require any other equipment than a ventilator, it is an easy-to-implement, inexpensive, safe, and reliable method for measuring the thoracopulmonary P-V curve at the bedside.

Acute Disease↗
PubMed1999

A scanographic assessment of pulmonary morphology in acute lung injury. Significance of the lower inflection point detected on the lung pressure-volume curve.

The goal of this study was to assess lung morphology in patients with acute lung injury according to the presence or the absence of a lower inflection point (LIP) on the lung pressure-volume (P-V) curve and to compare the effects of positive end-expiratory pressure (PEEP). Eight patients with and six without an LIP underwent a spiral thoracic CT scan performed at zero end-expiratory pressure (ZEEP) and at two levels of PEEP: PEEP1 = LIP + 2 cm H2O and PEEP2 = LIP + 7 cm H2O, or PEEP1 = 10 cm H2O and PEEP2 = 15 cm H2O in the absence of an LIP. The volumes of air and tissue within the lungs were measured from the gas-tissue ratio and the volumes of overdistended and normally, poorly, and nonaerated lung areas were determined by the analysis of the frequency histogram distribution. In the ZEEP condition, although total lung volume, volume of gas, and volume of tissue were similar in both groups, the percentage of normally aerated lung was lower (24 +/- 22% versus 55 +/- 12%, p < 0.05) and the percentage of poorly aerated lung was greater (40 +/- 12% versus 23 +/- 8%, p < 0.05) in patients with an LIP than in patients without an LIP. Lung density histograms of patients with an LIP showed a unimodal distribution with a peak at 7 Hounsfield units (HU). Lung density histograms of patients without an LIP had a bimodal distribution, with a first peak at -727 HU and a second peak at 27 HU. Total respiratory system and lung compliances were lower in patients with an LIP whereas all other cardiorespiratory parameters were similar in the two groups. In both groups, PEEP induced an alveolar recruitment that was associated with lung overdistension only in patients without an LIP. The amount of lung overdistension was related to the volume of lung parenchyma, characterized by a CT number less than -800 HU before PEEP implementation (y = 0.52x + 4, R = 0.87, and p < 0.0001). This study shows that the presence or the absence of an LIP on the lung P-V curve is associated with differences in lung morphology. In patients without an LIP on the lung P-V curve, normally aerated lung areas coexist with nonaerated lung areas and increasing levels of PEEP result in lung overdistension rather than in additional alveolar recruitment. In patients with an LIP, air and tissue are more homogeneously distributed within the lungs and increasing levels of PEEP result in additional alveolar recruitment without lung overdistention.

Acute Disease↗
PubMed1999

Expiratory washout versus optimization of mechanical ventilation during permissive hypercapnia in patients with severe acute respiratory distress syndrome.

The aim of this study was to compare three ventilatory techniques for reducing PaCO2 in patients with severe acute respiratory distress syndrome treated with permissive hypercapnia: (1) expiratory washout alone at a flow of 15 L/min, (2) optimized mechanical ventilation defined as an increase in the respiratory frequency to the maximal rate possible without development of intrinsic positive end- expiratory pressure (PEEP) combined with a reduction of the instrumental dead space, and (3) the combination of both methods. Tidal volume was set according to the pressure-volume curve in order to obtain an inspiratory plateau airway pressure equal to the upper inflection point minus 2 cm H2O after setting the PEEP at 2 cm H2O above the lower inflection point and was kept constant throughout the study. The three modalities were compared at the same inspiratory plateau airway pressure through an adjustment of the extrinsic PEEP. During conventional mechanical ventilation using a respiratory frequency of 18 breaths/min, respiratory acidosis (PaCO2 = 84 +/- 24 mm Hg and pH = 7.21 +/- 0.12) was observed. Expiratory washout and optimized mechanical ventilation (respiratory frequency of 30 +/- 4 breaths/min) had similar effects on CO2 elimination (DeltaPaCO2 = -28 +/- 11% versus -27 +/- 12%). A further decrease in PaCO2 was observed when both methods were combined (DeltaPaCO2 = -46 +/- 7%). Extrinsic PEEP had to be reduced by 5.3 +/- 2.1 cm H2O during expiratory washout and by 7.3 +/- 1.3 cm H2O during the combination of the two modes, whereas it remained unchanged during optimized mechanical ventilation alone. In conclusion, increasing respiratory rate and reducing instrumental dead space during conventional mechanical ventilation is as efficient as expiratory washout to reduce PaCO2 in patients with severe ARDS and permissive hypercapnia. When used in combination, both techniques have additive effects and result in PaCO2 levels close to normal values.

Acidosis, Respiratory↗