Larry McNicol

The aetiology and pathogenesis of cardiopulmonary bypass-associated metabolic acidosis using polygeline pump prime.

Objective: The pathogenesis of the metabolic acidosis of cardiopulmonary bypass (CPB) is not fully understood. New quantitative methods of acid-base balance now make it possible to describe it more clearly. Accordingly, we studied acid-base changes during CPB with polygeline pump prime and defined and quantified the factors which contribute to metabolic acidosis. Design: Prospective cohort study. Setting: Tertiary institution. Participants: 10 cardiac bypass graft surgery patients. Interventions: Sampling of arterial blood at four time intervals: post-induction, on CPB during cooling and rewarming, and at skin closure. Measurement of serum Na+, K+, Mg+ +, Ca+ +, Cl–, bicarbonate, and phosphate concentrations, arterial blood gases, and serum albumin, lactate, and pyruvate concentrations at each collection point. Analysis of findings according to quantitative physicochemical principles, including calculation of the strong ion difference apparent, the strong ion difference effective, and the strong ion gap (SIG). Measurements and main results: All patients developed a mild metabolic acidosis. The median serum standard bicarbonate concentration decreased from 25.0 mEq/l post-induction to 22.3 mEq/l at cooling and 22.2 mEq/l at rewarming (p < 0.05). The standard base excess decreased from a median of 1.55 mEq/l prior to CPB, to –2.50 mEq/l at cooling, –1.65 mEq/l at rewarming and, –0.85 mEq/l at skin closure (p < 0.001). This mild metabolic acidosis occurred despite a decrease in the median serum lactate concentration from 3.20 mEq/l post-induction to 1.83, 1.80, and 1.58 mEq/l at the three other time points. The increase in the median serum chloride concentration from 104.9 mEq/l post induction to 111.0, 111.1, and 110.0 mEq/l at the subsequent time points (p < 0.0001) was the main cause of the acidosis. There was also a significant increase in the SIG of 3.8 mEq/l at cooling and rewarming (p < 0.0001), suggesting a role for other unmeasured anions (polygeline) in the genesis of this acidosis. Conclusions: Using quantitative biophysical methods, it can be demonstrated that, in patients receiving a pump prime rich in chloride and polygeline, the metabolic acidosis of CPB is mostly due to iatrogenic increases in serum chloride concentration and unmeasured strong anions (SIG). Its development is partially attenuated by iatrogenic hypoalbuminaemia. Changes in lactate concentrations did not play a role in the development of metabolic acidosis in our patients.

Major Complications Related to the Use of Transesophageal Echocardiography in Cardiac Surgery

OBJECTIVE The purpose of this study was to determine the incidence of injury associated with transesophageal echocardiography (TEE injuries) in cardiac surgery. DESIGN Retrospective. SETTING University-affiliated hospitals. PARTICIPANTS Four thousand seven hundred eighty-four patients, 89% of all public hospital cardiac surgery patients in Victoria, from the Australasian Society of Cardiac and Thoracic Surgeons (ASCTS) database undergoing cardiac surgery with TEE between July 1, 2005, and June 30, 2007. Because ASCTS did not record TEE use before July 2005, it was assumed that 89% of an additional 11,719 cardiac surgery patients between July 2001 and June 2005 also had TEE. INTERVENTIONS The authors searched the ASCTS database for cardiac surgery patients who also had endoscopy and/or noncardiac surgery. The files of these patients were screened for possible esophageal or gastric tears or perforations. An expert panel determined likely TEE injuries. MEASUREMENTS AND MAIN RESULTS There were 6 TEE complications from July 1, 2005, to June 30, 2007 (13/10,000 patients). There were a further 8 TEE complications before June 30, 2005, an extrapolated overall rate of 9/10,000 TEE (95% confidence interval, 5-16/10,000). TEE complications were more frequent in patients more than 70 years old (relative risk [RR], 3.7; p = 0.03) and women (RR, 6.5; p < 0.001). Three patients with TEE injury died (2/10,000). CONCLUSIONS TEE is associated with an incidence of major injuries of about 1 per 1,000 patients, with older women having a much higher risk. TEE use in cardiac surgery should be evaluated in the light of practice guidelines and morbidity and mortality data and not considered routine.

Markers of splanchnic perfusion and intestinal translocation of endotoxins during cardiopulmonary bypass: effects of dopamine and milrinone.

OBJECTIVES To investigate markers of splanchnic perfusion and the extent of endotoxemia during cardiopulmonary bypass (CPB) and to compare the effects of dopamine and milrinone on both splanchnic perfusion and endotoxemia. DESIGN Prospective, randomized, blinded study. SETTING University teaching hospital. PARTICIPANTS Twenty-four patients scheduled for elective coronary artery bypass graft surgery (CABG). INTERVENTIONS Patients were allocated to receive placebo (eight patients), dopamine (eight patients), or milrinone (eight patients) during CPB, and at seven times intraoperatively assays were performed of arterial and hepatic venous endotoxin levels, as well as measurements and/or calculations of intramucosal gastric pH (pHi), arterial and hepatic venous lactate-pyruvate ratio (lac/pyr), and hepatic venous oxygen saturation (S(HV)O2). MEASUREMENTS AND MAIN RESULTS Both splanchnic and systemic endotoxin levels increased significantly, and this was unaffected by either dopamine or milrinone. Gastric pHi did not change, and there were only modest increases in lac/pyr, which remained within the normal range of less than 10 in both splanchnic and systemic blood. In the placebo group, S(HV)O2 decreased at the onset of CPB and also significantly decreased during rewarming and at the end of CPB and surgery. In the dopamine-treated patients, S(HV)O2 was greater compared with placebo and milrinone during both hypothermic and rewarming phases. CONCLUSION Endotoxemia occurs during routine CPB. Neither pHi nor lac/pyr values showed adverse change, but hepatic venous oximetry may be a more sensitive indicator of splanchnic dysoxia in that S(HV)O2 was reduced during rewarming. Whether dopamine or milrinone confer protection against splanchnic ischemia remains uncertain.

Role of the splanchnic circulation in acid-base balance during cardiopulmonary bypass.

OBJECTIVE The role of the splanchnic circulation in the development of the metabolic acidosis of cardiopulmonary bypass (CPB) is not fully understood. New quantitative methods of acid-base balance now offer the ability to define this phenomenon more accurately. Accordingly, we studied acid-base changes across the splanchnic circulation during CPB and defined and quantified the factors that contributed to acid-base balance. DESIGN Prospective cohort study. SETTING Tertiary institution. PATIENTS Ten patients undergoing CPB for coronary artery bypass surgery. INTERVENTIONS Sampling of arterial and hepatic venous blood at four time intervals: postinduction, on CPB during cooling and rewarming, and at skin closure. MEASUREMENTS Measurement of serum Na+, K+, Mg++, Ca++, Cl-, HCO3-, and phosphate concentrations, arterial and hepatic venous blood gases and serum albumin, and lactate and pyruvate concentrations at each collection point. Analysis of findings according to quantitative physicochemical principles. MAIN RESULTS All patients developed a mild metabolic acidosis with a decrease in median serum bicarbonate concentration from 24.97 mEq/L after induction to 22.29 mEq/L at cooling and 22.23 mEq/L at rewarming (p < .05). Before CPB, the pH decreased by 0.0275 (p < .05) across the splanchnic circulation, representing an increase of 2.26 nmol/L of hydrogen ions. Nevertheless, the splanchnic circulation induced a metabolic alkalosis, with a median transsplanchnic increase in the base excess of 1.50 mEq/L (p < .05). This change was largely due to a decrease in serum chloride and lactate concentration across the splanchnic circulation (p < .05). The acidifying effect of the splanchnic circulation was therefore the result of cell respiration with a median increase in carbon dioxide tension of 5.75 mm Hg (p < .05), causing the strong ion difference effective to increase by 1.94 mEq/L (p < .05). There were no other anions or acids added to the circulation by splanchnic organs (no change in strong ion gap). During and after CPB the splanchnic metabolic alkalinizing effect continued and the respiratory acidifying effect was reduced. This caused the splanchnic circulation to be pH neutral at these times. CONCLUSIONS Using quantitative biophysical methods it can be demonstrated that the splanchnic circulation does not contribute to the metabolic acidosis of CPB, and that it continues to have a metabolic alkalinizing effect involving significant lactate extraction. However, its respiratory acidifying effect continues, although at a reduced rate.

Size variation between contralateral infraclavicular axillary veins within individual patients-implications for subclavian venous central line insertion.

Objective:Vein size and use of dynamic ultrasound guidance have been shown to be directly related to a reduction in insertion failure and complication rates during subclavian vein catheterization. We hypothesized that contralateral infraclavicular axillary vein sizes are significantly different within the same patient. We also aimed to demonstrate the relationship of subject’s anthropomorphic indices with vein size and contralateral vein size difference. Design:Prospective observational study. Setting:Operating theatre of a tertiary hospital. Patients:Fifty adult elective and emergency surgical patients. Interventions:The largest dimensions of each patient’s left and right infraclavicular axillary veins were measured with two-dimensional cross-sectional ultrasound examinations. The absolute difference between sides in individual patients was calculated using a paired difference t test and the relationship between hand dominance and vein size calculated by a paired difference t test of dominant side vein size minus nondominant side vein size Measurements and Main Results:Forty-five patients (90%) of patients were right hand dominant. The mean proportional cross-sectional area difference between left and right sides in individual patients was 59.7% (SEM 9.2%), with absolute cross-sectional area difference of 26.7 mm2 (SEM 2.8 mm2). All test statistics reached statistical significance at p < 0.0001. There was no relationship between right hand dominance and ipsilateral infraclavicular axillary vein size (p = 1.0), nor was there any clinically significant correlation between subject’s anthropomorphic indices and ipsilateral infraclavicular axillary vein size or contralateral vein size difference (largest Pearson’s r = 0.22). Conclusions:Contralateral infraclavicular axillary vein sizes within the same patient are significantly different in the adult surgical population and bear no clear relation to patient hand dominance. The magnitude of contralateral difference or absolute ipsilateral infraclavicular axillary vein size cannot be predicted by a subject’s anthropomorphic indices. All patients in whom subclavian central line insertion is planned should have both sides examined by ultrasound to determine which side has the largest vessel.

Comparative Evaluation of Crystalloid Resuscitation Rate in a Human Model of Compensated Haemorrhagic Shock

Introduction: The most effective rate of fluid resuscitation in haemorrhagic shock is unknown. Methods: We performed a randomized crossover pilot study in a healthy volunteer model of compensated haemorrhagic shock. Following venesection of 15 mL/kg of blood, participants were randomized to 20 mL/kg of crystalloid over 10 min (FAST treatment) or 30 min (SLOW treatment). The primary end point was oxygen delivery (DO2). Secondary end points included pressure and flow-based haemodynamic variables, blood volume expansion, and clinical biochemistry. Results: Nine normotensive healthy adult volunteers participated. No significant differences were observed in DO2 and biochemical variables between the SLOW and FAST groups. Blood volume was reduced by 16% following venesection, with a corresponding 5% reduction in cardiac index (CI) (P < 0.001). Immediately following resuscitation the increase in blood volume corresponded to 54% of the infused volume under FAST treatment and 69% of the infused volume under SLOW treatment (P = 0.03). This blood volume expansion attenuated with time to 24% and 25% of the infused volume 30 min postinfusion. During fluid resuscitation, blood pressure was higher under FAST treatment. However, CI paradoxically decreased in most participants during the resuscitation phase; a finding not observed under SLOW treatment. Conclusion: FAST or SLOW fluid resuscitation had no significant impact on DO2 between treatment groups. In both groups, changes in CI and blood pressure did not reflect the magnitude of intravascular blood volume deficit. Crystalloid resuscitation expanded intravascular blood volume by approximately 25%.

Interpleural analgesia for attenuation of postoperative pain after hepatic resection

We performed a prospective randomised trial to evaluate the analgesic efficacy of interpleural analgesia in patients undergoing hepatic resection. The control group (n = 25) received multimodal analgesia with intravenous morphine patient‐controlled analgesia; in addition, the interventional group (n = 25) received interpleural analgesia with a 20‐ml loading dose of levo bupivacaine 0.5% followed by a continuous infusion of levobupivacaine 0.125%. Outcome measures included pain intensity on movement using a visual analogue scale over 24 h, cumulative morphine and rescue analgesia requirements, patient satisfaction, hospital stay and all adverse events. Patients in the interpleural group were less sedated and none required treatment for respiratory depression compared to 6 (24%) in the control group (p< 0.01). Patients in the interpleural group also had lower pain scores during movement in the first 24 h. Patients’ satisfaction, opioid requirements and duration of hospital stay were similar. We conclude that continuous interpleural analgesia augments intravenous morphine analgesia, decreases postoperative sedation and reduces respiratory depression after hepatic resection.

Pilot alternating treatment design study of the splanchnic metabolic effects of two mean arterial pressure targets during cardiopulmonary bypass

BACKGROUND The arterial pressure target for optimal splanchnic function during cardiopulmonary bypass (CPB) is uncertain. Thus, we aimed to compare the effects of two different arterial pressure targets during CPB on trans-splanchnic oxygenation, acid-base regulation, and splanchnic interleukin-6 (IL-6) and interleukin-10 (IL-10) flux. METHODS Sixteen patients undergoing cardiac surgery with CPB in a university affiliated hospital were subjected to a prospective alternating treatment design interventional study. We measured arterial and hepatic vein blood gases, electrolytes, IL-6, and IL-10 while targeting a mean arterial pressure (MAP) of between 60 and 65 mm Hg for 30 min, a MAP of between 80 and 85 mm Hg for 30 min (using norepinephrine infusion), and finally 60-65 mm Hg MAP target for 30 min. RESULTS The MAP targets were achieved in all patients [65 (4), 84 (4), and 64 (3) mm Hg, respectively; P<0.001] with a greater dose of norepinephrine infusion during the higher MAP target (P<0.001). With longer time on CPB, hepatic vein O2 saturation decreased, while magnesium, lactate, glucose, IL-6, and IL-10 increased independent of MAP target. The decrease in hepatic vein saturation was greater as the temperature increased (re-warming). Overall, there was trans-splanchnic oxygen, chloride, lactate, and IL-6 removal during CPB (P<0.001) and carbon dioxide, bicarbonate, glucose, and IL-10 release (P<0.001). Such removal or release was not affected by the MAP target. CONCLUSIONS Targeting of a higher MAP during CPB by means of norepinephrine infusion did not affect splanchnic oxygenation, splanchnic acid-base regulation, or splanchnic IL-6 or IL-10 fluxes. Australian and New Zealand Clinical Trial Registry ACTRN 12611001107910.

Endoscopically Assisted Transesophageal Echocardiographic Probe Insertion

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Sodium bicarbonate infusion in patients undergoing orthotopic liver transplantation: a single center randomized controlled pilot trial

Liver transplantation‐associated acute kidney injury (AKI) carries significant morbidity and mortality. We hypothesized that sodium bicarbonate would reduce the incidence and/or severity of liver transplantation‐associated AKI.