Stephanie J Poustie

Role of pump prime in the etiology and pathogenesis of cardiopulmonary bypass-associated acidosis.

BackgroundThe development of metabolic acidosis during cardiopulmonary bypass (CPB) is well recognized but poorly understood. The authors hypothesized that the delivery of pump prime fluids is primarily responsible for its development. Accordingly, acid–base changes induced by the establishment of CPB were studied using two types of priming fluid (Haemaccel, a polygeline solution, and Ringer’s Injection vs. Plasmalyte 148) using quantitative biophysical methods. MethodsA prospective, double-blind, randomized trial was conducted at a tertiary institution with 22 patients undergoing CPB for coronary artery bypass surgery. Sampling of arterial blood was performed at three time intervals: before CPB (t1), 2 min after initiation of CPB at full flows (t2), and at the end of the case (t3). Measurements of Na+, K+, Mg2+, Cl−, HCO3−, phosphate, Ca2+, albumin, lactate, and arterial blood gases at each collection point were performed. Results were analyzed in a quantitative manner. ResultsImmediately on delivery of pump prime fluids, all patients developed a metabolic acidosis (base excess: 0.95 mEq/l (t1) to −3.65 mEq/l (t2) (P < 0.001) for Haemaccel–Ringer’s and 1.17 mEq/l (t1) to −3.20 mEq/l (t2). The decrease in base excess was the same for both primes (−4.60 vs. −4.37; not significant). However, the mechanism of metabolic acidosis was different. With the Haemaccel–Ringer’s prime, the metabolic acidosis was hyperchloremic (&Dgr; Cl−, +9.50 mEq/l; confidence interval, 7.00–11.50). With Plasmalyte 148, the acidosis was induced by an increase in unmeasured anions, most probably acetate and gluconate. The resolution of these two processes was different because the excretion of chloride was slower than that of the unmeasured anions (&Dgr; base excess from t1 to t3 = −1.60 for Haemaccel–Ringer’s vs. +1.15 for Plasmalyte 148;P = 0.0062). ConclusionsCardiopulmonary bypass–induced metabolic acidosis appears to be iatrogenic in nature and derived from the effect of pump prime fluid on acid–base balance. The extent of such acidosis and its duration varies according to the type of pump prime.

Complications and mortality in older surgical patients in Australia and New Zealand (the REASON study): a multicentre, prospective, observational study*

We conducted a prospective study of non‐cardiac surgical patients aged 70 years or more in 23 hospitals in Australia and New Zealand. We studied 4158 consecutive patients of whom 2845 (68%) had pre‐existing comorbidities. By day 30, 216 (5%) patients had died, and 835 (20%) suffered complications; 390 (9.4%) patients were admitted to the Intensive Care Unit. Pre‐operative factors associated with mortality included: increasing age (80–89 years: OR 2.1 (95% CI 1.6–2.8), p < 0.001; 90+ years: OR 4.0 (95% CI 2.6–6.2), p < 0.001); worsening ASA physical status (ASA 3: OR 3.1 (95% CI 1.8–5.5), p < 0.001; ASA 4: OR 12.4 (95% CI 6.9–22.2), p < 0.001); a pre‐operative plasma albumin < 30 g.l−1 (OR: 2.5 (95% CI 1.8–3.5), p < 0.001); and non‐scheduled surgery (OR 1.8 (95% CI 1.3–2.5), p < 0.001). Complications associated with mortality included: acute renal impairment (OR 3.3 (95% CI 2.1–5.0), p < 0.001); unplanned Intensive Care Unit admission (OR 3.1 (95% CI 1.9–4.9), p < 0.001); and systemic inflammation (OR 2.5 (95% CI 1.7–3.7), p < 0.001). Patient factors often had a stronger association with mortality than the type of surgery. Strategies are needed to reduce complications and mortality in older surgical patients.

Effect of an anaesthesia department led critical care outreach and acute pain service on postoperative serious adverse events.

We examined whether a combined critical care outreach and acute pain service comprising both medical and nursing staff from the Department of Anaesthesia would decrease the incidence of postoperative serious adverse events in a hospital with an established Medical Emergency Team. We called this combined service IMPACT: Inpatient Management of acute Pain and Advice on Clinical Treatment. We conducted a prospective, before‐and‐after trial with a baseline phase (319 patients) of standard acute pain management followed by the IMPACT phase (271 patients), during which the IMPACT team systematically reviewed high‐risk postoperative patients for the first three days after their return to the general wards. The incidence of serious adverse events decreased from 23 events per 100 patients to 16 events per 100 patients. The 30‐day mortality decreased from 9% to 3%, p = 0.004. An acute pain service providing critical care outreach may improve postoperative outcome but the workload is considerable.

Quantitative physical chemistry analysis of acid−base disorders in critically ill patients

Compared with the Henderson−Hasselbalch approach, the Stewart approach may better describe the mechanisms of acid−base physiology and disorders. We prospectively examined the acid−base disorders of 100 routine blood samples from critically ill patients using Stewarts physical chemistry analysis. The median results were pH 7.45, Paco2 5.5 kPa, bicarbonate 27.2 mmol.l−1 and base excess 3 mmol.l−1. The median reference strong ion difference was 46.0 meq.l−1 and the measured median was 45.5 meq.l−1. The median reference total weak‐acid concentration was 11.1 mmol.l−1. The measured median total weak‐acid concentration was 6.8 mmol.l−1. From Stewarts approach, the most likely explanation for the overall alkalosis was decreased total weak‐acid concentration resulting from decreased plasma albumin concentration.

The effect of critical care outreach on postoperative serious adverse events

We proposed that critical care outreach would decrease the incidence of postoperative serious adverse events and so conducted a sequential cohort study with a surveillance‐only phase (baseline) followed by an intervention phase. We studied high‐risk patients in a large Australian hospital. A critical care qualified nurse reviewed patients for the first three days after return to the general wards. During the intervention phase the nurse intervened in patient care where appropriate. We examined the incidence of 11 categories of serious adverse events per 100 patients during the first three days on the general wards during the surveillance and intervention phases. The surveillance phase had 319 patients and the intervention phase 345 patients. In a subgroup analysis, there were four myocardial infarctions per 100 patients in the surveillance phase and seven per 100 patients during the intervention phase (95% confidence interval: 1–7 infarctions per 100 patients increase). For the other 10 serious adverse events there were 19 per 100 patients in the surveillance phase and 11 per 100 patients in the intervention phase (95% confidence interval: 4–11 serious adverse events per 100 patients decrease). Outreach may have led to greater detection of myocardial infarctions while reducing the incidence of other serious adverse events.

Estimating unmeasured anions in critically ill patients: Anion‐gap, base‐deficit, and strong‐ion‐gap

Summary We used 100 routine blood samples from critically ill patients to establish whether correcting the anion‐gap and base‐deficit for decreased plasma albumin improves agreement with the strong‐ion‐gap for estimating unmeasured anions and whether the modifications increase the proportion of samples with levels of anion‐gap or base‐deficit above the reference ranges. We used Bland− Altman analyses to compare the methods of estimating unmeasured ions. Compared with the strong‐ion‐gap, modification reduced the limits of agreement for both the anion‐gap and the base‐deficit. The bias for the base‐deficit was also reduced but the bias for the anion‐gap was increased. The proportion of samples with an anion‐gap > 22 meq.l−1 increased from 4 to 29% (p < 0.001), and the proportion with a base‐deficit > 5 meq.l−1 in creased from 8 to 42% (p < 0.001). Consequently, metabolic acidosis from unmeasured ions in critically ill patients maybe more frequent than often recognised.

Changes in plasma creatinine concentration after cardiac anesthesia with isoflurane, propofol, or sevoflurane: a randomized clinical trial.

BackgroundRenal impairment often follows cardiac surgery. The authors investigated whether sevoflurane produces greater increases in plasma creatinine concentration than isoflurane or propofol after elective coronary artery surgery. MethodsAs part of maintenance anesthesia, including during cardiopulmonary bypass, patients were randomly allocated to receive one of three agents: isoflurane (n = 118), sevoflurane (n = 118), or propofol (n = 118). Fresh gas flows were 3 l/min. The preoperative plasma creatinine concentration was subtracted from the highest creatinine concentration in the first 3 postoperative days. A median maximum increase greater than 44 &mgr;m (0.5 mg/dl) was regarded as clinically important. Data were analyzed on an intention-to-treat basis. Subgroup analyses were performed on per-protocol patients and those with preoperative renal impairment (creatinine concentration > 130 &mgr;m [1.47 mg/dl] or urea > 7.7 mm [blood urea nitrogen, 21.6 mg/dl]). ResultsThe differences between the groups were small, clinically unimportant, and not statistically significant for the primary analysis and subgroups. The proportions of patients with creatinine increases greater than 44 &mgr;m were 15% in the isoflurane group, 17% in the sevoflurane group, and 11% in the propofol group (P = 0.45). The median increases were 8 &mgr;m in the isoflurane group, 4 &mgr;m in the sevoflurane group, and 6 &mgr;m in the propofol group. The differences between the three median maximum increases were 1–4 &mgr;m (P > 0.45). In the subgroup with preoperative renal impairment, the median increases were 10 &mgr;m in the isoflurane group, 15 &mgr;m in the sevoflurane group, and 5 &mgr;m in the propofol group (P = 0.72). ConclusionsSevoflurane did not produce greater increases in creatinine than isoflurane or propofol after elective coronary artery surgery.

Inconsistent survey reporting in anesthesia journals.

BACKGROUND: As with other types of research, there are concerns about reporting of survey research in anesthesia journals. We hypothesized that use of survey reporting items would be inconsistent in survey research reported in anesthesia journals. METHODS: After a literature review we constructed a 17-item reporting list for a limited systematic review of survey reporting in 6 anesthesia journals. We identified survey reports by MEDLINE (PubMed) search for January 2000 to April 2009. RESULTS: The initial search identified 347 publications. Of these, we excluded 107 because they were not questionnaire surveys (often audits), were reviews, or were letters. We therefore identified 240 surveys published as full survey reports. From the 17-item reporting list, the median number of items recorded was 9 (interquartile range: 7 to 10; range 2 to 15). The number (and percentage) of surveys reporting specific items ranged widely for different items: from 9 surveys (4%; 95% confidence interval [CI]: 2% to 7%) for sample size to 240 surveys (100%; 95% CI: 98% to 100%) for response rate. In addition to sample size, the 5 least frequently reported items included the following: reporting confidence intervals, 21 surveys (9%; 95% CI: 6% to 13%); stating a hypothesis, 23 of 240 surveys (10%; 95% CI: 7% to 14%); accounting for nonresponders, 61 surveys (25%; 95% CI: 20% to 31%); and survey design, 67 surveys (28%; 95% CI: 33% to 34%). CONCLUSIONS: Inconsistent reporting may compromise the transparency and reproducibility of survey reports.

Non-invasive measurement of intrapulmonary shunt during inert gas rebreathing

We tested the agreement between non-invasive measurement of intrapulmonary shunt, using oxygen uptake and pulmonary capillary blood flow measurement obtained by nitrous oxide rebreathing, with that measured using mixed venous blood sampling. Nine patients were recruited pre- and post-cardiac surgery resulting in 20 sets of measurements overall. Mean shunt fraction was 12.5%, and bias between methods (+/-95% confidence limits) was -0.7% (+/-0.8%). The standard deviation of the difference was 1.7% with limits of agreement between the two methods of +2.6% and -3.9%. Correlation coefficient r was 0.90. Agreement with the invasive standard was less accurate and precise where cardiac output was measured by bolus thermodilution (mean bias +1.6%, standard deviation of the difference 2.2%, limits of agreement between the two methods of +5.8% and -2.8%, r = 0.86). Good agreement was demonstrated between the non-invasive method and the invasive reference standard.

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.