Anesthesia and analgesia
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Anesthesia and analgesia · Dec 2002
Comparative StudyThe detection of changes in heparin activity in the rabbit: a comparison of anti-xa activity, thrombelastography, activated partial thromboplastin time, and activated coagulation time.
Thrombelastography (TEG) has been used to detect both exogenous and endogenous circulating heparin activity in clinical and laboratory settings. Thus, in this study I sought to compare the sensitivity of TEG, activated partial thromboplastin time (aPTT), and activated coagulation time (ACT) values with changes in anti-Xa activity after small-dose heparin administration in rabbits. Conscious rabbits (n = 11) had blood obtained from ear arteries for hematological analyses after the administration of 0, 10, 20, and 30 U/kg of IV heparin. Anti-Xa activities after the administration of 0, 10, 20, and 30 U/kg of heparin were, respectively, 38 +/- 9 mU/mL, 74 +/- 15 mU/mL, 105 +/- 14 mU/mL, and 134 +/- 17 mU/mL; all values were significantly different from each other. TEG variables (R and alpha) significantly (P < 0.05) changed between 0, 10, and 20 U/kg heparin doses, but a difference between 20 and 30 U/kg could not be discerned secondary to loss of a detectable clot. The aPTT was significantly (P < 0.05) different between 0, 20, and 30 U/kg doses. ACT values were significantly different between the 0 U/kg heparin dose and all other doses; however, there were no significant differences between the 10, 20, and 30 U/kg heparin doses. Changes in anti-Xa activity were significantly linearly related to R (r = 0.81, P < 0.0001), alpha (r = -0.85, P < 0.0001), aPTT (r = 0.74, P < 0.0001), and ACT (r = 0.41, P = 0.005). In this model of small-dose heparin administration, TEG variables were more sensitive to changes in heparin activity than aPTT and ACT. ⋯ Changes in thrombelastography (TEG) variables more sensitively reflect changes in circulating heparin activity than activated partial thromboplastin time (aPTT) and activated coagulation time (ACT) after small-dose heparin administration in rabbits. Thus, TEG may be more helpful than aPTT and ACT in the detection of heparin in both laboratory and clinical settings wherein heparin may play a role in coagulopathy.
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Anesthesia and analgesia · Dec 2002
Vasopressor response in a porcine model of hypothermic cardiac arrest is improved with active compression-decompression cardiopulmonary resuscitation using the inspiratory impedance threshold valve.
During normothermic cardiac arrest, a combination of active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) with the inspiratory threshold valve (ITV) significantly improves vital organ blood flow, but this technique has not been studied during hypothermic cardiac arrest. Accordingly, we evaluated the hemodynamic effects of ACD + ITV CPR before, and after, the administration of vasopressin in a porcine model of hypothermic cardiac arrest. Pigs were surface-cooled until their body core temperature was 26 degrees C. After 10 min of untreated ventricular fibrillation, 14 animals were randomly assigned to either ACD CPR with the ITV (n = 7) or to standard (STD) CPR (n = 7). After 8 min of CPR, all animals received 0.4 U/kg vasopressin IV, and CPR was maintained for an additional 10 min in each group; defibrillation was attempted after 28 min of cardiac arrest, including 18 min of CPR. Before the administration of vasopressin, mean +/- SEM common carotid blood flow was significantly higher in the ACD + ITV group compared with STD CPR (67 +/- 13 versus 26 +/- 5 mL/min, respectively; P < 0.025). After vasopressin was given at minute 8 during CPR, mean +/- SEM coronary perfusion pressure was significantly higher in the ACD + ITV group, but did not increase in the STD group (29 +/- 3 versus 15 +/- 2 mm Hg, and 25 +/- 1 versus 14 +/- 1 mm Hg at minute 12 and 18, respectively; P < 0.001); mean +/- SEM common carotid blood flow remained higher at respective time points (33 +/- 8 versus 10 +/- 3 mL/min, and 31 +/- 7 versus 7 +/- 3 mL/min, respectively; P < 0.01). Without active rewarming, spontaneous circulation was restored and maintained for 1 h in three of seven animals in the ACD + ITV group versus none of seven animals in the STD CPR group (not significant). During hypothermic cardiac arrest, ACD CPR with the ITV improved common carotid blood flow compared with STD CPR alone. Moreover, after the administration of vasopressin, coronary perfusion pressure was significantly higher during ACD + ITV CPR, but not during STD CPR. ⋯ New strategies are needed to improve the efficiency of cardiopulmonary resuscitation (CPR) in hypothermic cardiac arrest. Active compression-decompression CPR with the inspiratory threshold valve improved carotid blood flow (and coronary perfusion pressure with vasopressin) compared with standard CPR.
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Anesthesia and analgesia · Dec 2002
Influence of rate and volume of infusion on the kinetics of 0.9% saline and 7.5% saline/6.0% dextran 70 in sheep.
We examined whether volume kinetic variables obtained during infusion of a short bolus of 0.9% saline (NS) or 7.5% saline/6.0% dextran 70 (HSD) predict the dilution-time curve resulting from a 20-min infusion of the same fluid. Each of six conscious, splenectomized sheep (mean body weight, 36 +/- 3 kg), on 4 different days, in a random order, received each of 4 IV boluses: NS at a rate of 1.2 mL. kg(-1). min(-1) over 5 min or 20 min or 4.0 mL/kg of HSD over 2 min or 20 min. One, 2, and 3-volume kinetic models were fitted to the dilution of the arterial hemoglobin concentration and the urinary excretion as sampled during 180 min. The maximum dilution of arterial plasma at the end of the 5-min and 20-min infusions of NS was approximately 10% and 22%, respectively, and after the 2-min and 20-min infusions of HSD, maximum dilution was 24% and 21%, respectively. The median absolute performance error was virtually identical when the mean variable estimates from the 5-min infusion of NS were used to predict the individual dilution-time curves of the 5-min (mean, 0.027 dilution units) and 20-min (mean, 0.027) infusions and when the 2-min infusion of HSD was used to predict the dilution during the individual 2-min (mean, 0.050) and 20-min infusions (mean, 0.047). Computer simulations indicated that the difference at the end of infusion between the volume effects of NS and HSD is larger after longer infusions. We concluded that the volume kinetic variables obtained during a short infusion can be used to predict the outcome of a longer one, even if the longer infusion also delivers a larger volume. ⋯ Kinetic analysis of a short infusion of 7.5% saline/6% dextran or 0.9% saline accurately predicts the effects of a longer infusion of the same volume (7.5% saline/6% dextran) or of a larger volume (0.9% saline).
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Anesthesia and analgesia · Dec 2002
Needle electrodes can be used for bispectral index monitoring of sedation in burn patients.
We present the results of a study examining the agreement of bispectral index values obtained using original sensor and subdermal needle electrodes in burn patients. Both types of electrodes can be used interchangeably to monitor depth of sedation.
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Anesthesia and analgesia · Dec 2002
Maximum minute ventilation test for the ProSeal laryngeal mask airway.
One of the distinguishing features of the ProSeal laryngeal mask airway (PLMA) is that it can cause upper airway obstruction, even when it is correctly inserted behind the cricoid cartilage. We used a hyperventilation test, the maximum minute ventilation test (MMV test), to aid in the diagnosis of upper airway obstruction after PLMA insertion. The patient was briefly hyperventilated for 15 s yielding a MMV value equal to 4 x (breaths/15 s) x (exhaled tidal volume). MMV values were collected in 317 adult women and men over 6 mo. Critical MMV values were obtained in 17 of 317 patients, 15 of 317 (4.7%) of which were due to insertion of the PLMA. The PLMA was removed in seven of 317 (2.2%) patients. The most common cause of upper airway obstruction due to the PLMA was laryngeal obstruction. This refers to compression of supraglottic and glottic structures with resulting narrowing and compromise of the airway. A second, much less common, form of airway obstruction was bilateral cuff infolding with or without downfolding of the epiglottis. Finally, we discuss the margin of safety for minute ventilation, defined as the excess of the MMV over and above basal minute ventilation requirements for the patient. With critical MMV, the margin of safety is drastically reduced or nonexistent. ⋯ One of the distinguishing features of the ProSeal laryngeal mask airway (PLMA) is that it can cause upper airway obstruction, even when it is correctly inserted behind the cricoid cartilage. We used a hyperventilation test, the maximum minute ventilation test, to aid in the diagnosis of upper airway obstruction after PLMA insertion.