Influence of cardiac output on the pseudo-steady state remifentanil and propofol concentrations in swine.

BACKGROUND: The propofol concentration during constant infusion is affected by a change in cardiac output, but the effect of this change on remifentanil, which is frequently used in combination with propofol, is unclear. METHODS: Ten swine were anaesthetised through inhalation of isoflurane and maintained with 1.5% isoflurane. After infusion of remifentanil (0.5 µg/kg/min) and propofol (6 mg/kg/h after 2 mg/kg bolus infusion) for 60 min (baseline 1), cardiac output was increased by continuous infusion of dobutamine and termination of isoflurane (high cardiac output state). Dobutamine infusion was then stopped, 1.5% isoflurane was restarted, and cardiac output was allowed to return to baseline (baseline 2). Finally, cardiac output was decreased by administration of 3% isoflurane (low cardiac output state). Blood samples were collected from the femoral artery at 10, 30, and 60 min after the change to each haemodynamic state. RESULTS: An inverse relationship was found between cardiac output and the plasma remifentanil and propofol concentrations. The plasma drug concentrations were given by the following equations: [remifentanil] (ng/ml) = 17.5/cardiac output (l/min) + 4.52; and [propofol] (µg/ml) = 3.34/cardiac output + 1.17. The influence of changes in cardiac output on remifentanil were similar to those for coadministered propofol and the influence on the concentration of each drug was greater with decreasing cardiac output. CONCLUSIONS: The plasma remifentanil concentration is influenced by cardiac output in a similar manner to that of propofol during remifentanil and propofol anaesthesia, although the metabolic sites are different.

Influence of haemorrhage on the pseudo-steady-state remifentanil concentration in a swine model: a comparison with propofol and the effect of haemorrhagic shock stage.

BACKGROUND: The increase in remifentanil concentration during haemorrhagic shock and the difference between this effect and that for propofol are not fully understood. We investigated the influence of haemorrhage on the pseudo-steady-state remifentanil concentration in a porcine model and compared the changes with those for propofol. METHODS: After infusion of remifentanil (0.5 µg kg⁻¹ min⁻¹) and propofol (6 mg kg⁻¹ h⁻¹ after 2 mg kg⁻¹ bolus infusion) for 60 min, nine swine [mean (standard deviation) body weight=26.3 (1.3) kg] were studied using a stepwise haemorrhage model (10% of estimated blood volume removed every 30 min until 1.5 h, and stepwise removal of 5% every 30 min thereafter until circulatory collapse). Haemodynamic and metabolic variables and plasma remifentanil and propofol concentrations were measured at every step. RESULTS: A mean volume of 913 (82) ml of blood was drained before reaching circulatory collapse. The increases in plasma concentrations from the prehaemorrhagic value fitted the following equations: % increase in remifentanil=2.1 × cumulative blood loss (% of initial blood volume) and % increase in propofol = 0.7 × cumulative blood loss during compensated shock; and % increase in remifentanil = 27.4 × cumulative blood loss-897 and % increase in propofol = 9.5 × cumulative blood loss-306 during uncompensated shock. Remifentanil concentrations were highly correlated with the reciprocal of cardiac output. CONCLUSIONS: During haemorrhage, the plasma remifentanil concentration showed a three-fold greater increase than that of propofol in administration by continuous infusion.

Do the kidneys contribute to propofol elimination?

BACKGROUND: Propofol is mainly metabolized in the liver, but extrahepatic clearance may also be important since systemic propofol clearance exceeds hepatic clearance. Recent reports suggest that the kidneys contribute to propofol elimination in humans and here we investigated renal elimination of propofol in a controlled animal study. METHODS: Seventeen swine were anaesthetized with 5% isoflurane induction and 2% isoflurane maintenance. After a left subcostal incision, the left kidney and renal pedicle were exposed by an approach via the retroperitoneum and the renal vein was identified for blood sampling. Propofol was then administered via the right jugular vein at a rate of 2 mg kg(-1) h(-1). After 120 min of pseudo-steady-state infusion of propofol (Baseline 1), cardiac output (CO) was increased by continuous infusion of dobutamine for 30 min (high-CO state). Thirty minutes after stopping dobutamine (Baseline 2), CO was decreased by bolus administration of propranolol (low-CO state). Blood samples were collected simultaneously from the renal vein (direct puncture) and the femoral artery at Baseline 1, in the high-CO state, at Baseline 2, and in the low-CO state. RESULTS: There was no significant difference in propofol concentration between femoral arterial and renal venous blood in all states. The propofol concentration significantly decreased with increased CO, but renal extraction was not observed in any state. CONCLUSIONS: The kidneys are a minor site of propofol elimination in a swine model.

Effects of using two airway exchange catheters on laryngeal passage during change from a double-lumen tracheal tube to a single-lumen tracheal tube.

BACKGROUND: A thin airway exchange catheter (AEC) is often used for changing from a double-lumen tracheal tube (DLT) to a single-lumen tracheal tube. However, passage of the tube into the trachea is often difficult. The purpose of this study was to evaluate the effectiveness of using two AECs for tracheal tube exchange. METHODS: In Study 1, 30 patients were randomly allocated to two groups and one AEC was inserted into the trachea in one group, and two AECs in the other group. A tracheal tube was advanced into the pharynx over the AEC(s). A blinded observer assessed the difficulty of passing the tube into the trachea. In Study 2, another group of 30 patients (whose airways had been managed with DLTs) were randomly allocated to two groups, and either one or two AECs were inserted into the DLT depending upon the group allocation. The difficulty of passing the tube into the trachea was assessed and the time required for exchange was measured. RESULTS: The use of two AECs reduced the incidence of impingement of the tube into the trachea during the AEC-guided tracheal intubation (Study 1) from 93 to 33% (P < 0.05) and during exchange from a DLT to a single-lumen tracheal tube (Study 2) from 100 to 27% (P < 0.05). The exchange time was similar: 106 (7) and 116 (4) s [mean (SD)] for one and two AECs, respectively. CONCLUSION: The use of two AECs reduces the incidence of impingement of the tube into the trachea during tracheal tube exchange.

Landiolol, an ultra-short-acting beta 1-adrenoceptor antagonist, does not alter the electroencephalographic effect of isoflurane in swine model.

BACKGROUND: beta-Adrenergic blocking agents may interact with anaesthetics, and several studies suggest that beta-blockers attenuate electroencephalographic responses during general anaesthesia. We have investigated the influence of landiolol, an ultra-short-acting beta 1-adrenoceptor antagonist, on the electroencephalographic effect of isoflurane in pigs. METHODS: Ten swine were anaesthetized through inhalation of 2% isoflurane. The inhalational concentration was then decreased to 0.5% and maintained for 25 min, before being returned to 2% and maintained for a further 25 min (control period). After control measurements, infusion of landiolol (at 0.125 mg kg(-1) min(-1) for 1 min, and then at 0.04 mg kg(-1) min(-1)) was started. After a 20 min stabilization period, the inhalational concentration was varied as in the control period (40 gamma landiolol). Finally, infusion of landiolol was increased from 0.04 to 0.2 mg kg(-1) min(-1), and after a 20 min stabilization period, the inhalational concentration was again varied as in the control period (200 gamma landiolol). End-tidal isoflurane concentrations and spectral edge frequencies were recorded throughout the study. Analysis of the pharmacodynamics was performed using a sigmoidal inhibitory maximal effect model for spectral edge frequency vs effect-site concentration. RESULTS: There were no significant differences in the effect of isoflurane among the conditions used. Landiolol did not shift the concentration-effect relationship [the effect-site concentration that produced 50% of the maximal effect was 1.35 (0.17)% under control conditions, 1.30 (0.12)% at 40 gamma landiolol, and 1.38 (0.30)% at 200 gamma landiolol]. CONCLUSION: Landiolol does not alter the electroencephalographic effect of isoflurane.

Cronkhite-Canada syndrome. A case report and analytical review of 23 other cases reported in Japan.

A case study is presented of a 57-year-old male who showed typical clinical features of Cronkhite-Canada syndrome. Numerous polypoid lesions were found in the stomach, duodenum, ileum, colon and rectum accompanied with characteristic ectodermal changes. Tests indicated a protein-losing gastroenteropathy. Intestinal lactase deficiency was demonstrated by the lactose tolerance test. Scanning electronmicroscopy of the gastric and colonic mucosa revealed prominent secretion of mucoid substances and distortion in the gastric pits and colonic crypts. These abnormal findings were interpreted as having a direct relationship to the loss of protein into the gastrointestinal tract.