James O. M. Plumb

Re-designing the pathway to surgery: better care and added value

The case for radical pathway re-design before surgery is in part driven by healthcare system pressures which are in turn the result of continuously rising demand in the face of tightly constrained resources. Such circumstances tend to drive revolutionary, rather than incremental, change. The current approach to preoperative assessment, that typically occurs in the weeks leading up to surgery, but is all too often only a few days before surgery, results in a lost opportunity for perioperative physicians to improve patient care. Re-engineering this process based on a patient-focused, pathway-driven vision of perioperative medicine offers a means of exploiting this opportunity. This review explores drivers for change, the opportunity offered by pathway re-design, and suggests a variety of strategies to add value in the preoperative pathway, each of which is facilitated by early engagement between perioperative physician and patient: collaborative decision-making, collaborative behavioural change, targeted comorbidity management as well as expectation management and psychological preparation for surgery including surgery schools.

Hemoglobin concentration, total hemoglobin mass and plasma volume in patients: implications for anemia

In practice, clinicians generally consider anemia (circulating hemoglobin concentration < 120 g.l−1 in non-pregnant females and < 130 g.l−1 in males) as due to impaired hemoglobin synthesis or increased erythrocyte loss or destruction. Rarely is a rise in plasma volume relative to circulating total hemoglobin mass considered as a cause. But does this matter? We explored this issue in patients, measuring hemoglobin concentration, total hemoglobin mass (optimized carbon monoxide rebreathing method) and thereby calculating plasma volume in healthy volunteers, surgical patients, and those with inflammatory bowel disease, chronic liver disease or heart failure. We studied 109 participants. Hemoglobin mass correlated well with its concentration in the healthy, surgical and inflammatory bowel disease groups (r=0.687–0.871, P<0.001). However, they were poorly related in liver disease (r=0.410, P=0.11) and heart failure patients (r=0.312, P=0.16). Here, hemoglobin mass explained little of the variance in its concentration (adjusted R2=0.109 and 0.052; P=0.11 and 0.16), whilst plasma volume did (R2 change 0.724 and 0.805 in heart and liver disease respectively, P<0.0001). Exemplar patients with identical (normal or raised) total hemoglobin masses were diagnosed as profoundly anemic (or not) depending on differences in plasma volume that had not been measured or even considered as a cause. The traditional inference that anemia generally reflects hemoglobin deficiency may be misleading, potentially resulting in inappropriate tests and therapeutic interventions to address ‘hemoglobin deficiency’ not ‘plasma volume excess’. Measurement of total hemoglobin mass and plasma volume is now simple, cheap and safe, and its more routine use is advocated.

Total haemoglobin mass, but not haemoglobin concentration, is associated with preoperative cardiopulmonary exercise testing-derived oxygen-consumption variables

Background. Cardiopulmonary exercise testing (CPET) measures peak exertional oxygen consumption (Symbol) and that at the anaerobic threshold (Symbol at AT, i.e. the point at which anaerobic metabolism contributes substantially to overall metabolism). Lower values are associated with excess postoperative morbidity and mortality. A reduced haemoglobin concentration ([Hb]) results from a reduction in total haemoglobin mass (tHb‐mass) or an increase in plasma volume. Thus, tHb‐mass might be a more useful measure of oxygen‐carrying capacity and might correlate better with CPET‐derived fitness measures in preoperative patients than does circulating [Hb]. Symbol. No caption available. Symbol. No caption available. Methods. Before major elective surgery, CPET was performed, and both tHb‐mass (optimized carbon monoxide rebreathing method) and circulating [Hb] were determined. Results. In 42 patients (83% male), [Hb] was unrelated to Symbol at AT and Symbol (r=0.02, P=0.89 and r=0.04, P=0.80, respectively) and explained none of the variance in either measure. In contrast, tHb‐mass was related to both (r=0.661, P<0.0001 and r=0.483, P=0.001 for Symbol at AT and Symbol, respectively). The tHb‐mass explained 44% of variance in Symbol at AT (P<0.0001) and 23% in Symbol (P=0.001). Conclusions. In contrast to [Hb], tHb‐mass is an important determinant of physical fitness before major elective surgery. Further studies should determine whether low tHb‐mass is predictive of poor outcome and whether targeted increases in tHb‐mass might thus improve outcome.

Mobilising Oedema in the Oedematous Critically Ill Patient with ARDS: Do We Seek Natriuresis Not Diuresis?

In the treatment of the acute respiratory distress syndrome in the intensive care unit, one of the aims is to achieve a negative fluid balance. Traditional use of sole-agent loop diuretics such as furosemide often results in the loss of free water, dehydration, hypernatraemia and metabolic alkalosis, with therapeutic failure once water is replaced. A more rational approach is to induce natriuresis with loss of sodium in the urine to reduce extracellular and interstitial fluid volume, not total body water. Polypharmacy with a loop diuretic combined with other weak diuretics to prevent tubules modifying glomerular filtrate, promotes natriuresis with large volume urinary losses and minimal electrolyte disturbance, and the excretion of urine with a composition comparable to plasma.

Replicating measurements of total hemoglobin mass (tHb‐mass) within a single day: precision of measurement; feasibility and safety of using oxygen to expedite carbon monoxide clearance

Hemoglobin concentration ([Hb]) is a function of total hemoglobin mass (tHb‐mass) and plasma volume. [Hb] may fall by dilution due to plasma volume expansion and changes in the perioperative period may therefore correlate poorly with blood loss. A simple, reliable, repeatable way to measure plasma volume and tHb‐mass would have substantial clinical utility. The “optimized carbon monoxide re‐breathing method” (oCOR) meets these criteria. However, it is recommended that a minimum of 12 h (when breathing room air) is left between repeat measurements. Twenty‐four subjects underwent 3 days of testing. Two oCOR tests were performed (T1 and T2), 3 h apart, with a different CO clearance method employed between tests aiming to keep the carboxyhemoglobin level below 10%. The primary aim was to ascertain whether tHb‐mass testing could be safely repeated within 3 h if carboxyhemoglobin levels were actively reduced by breathing supplemental oxygen (PROCA). Secondary aims were to compare two other clearance methods; moderate exercise (PROCB), or a combination of the two (PROCC). Finally, the reliability of the oCOR method was assessed. Mean (SD) tHb‐mass was 807.9 ± (189.7 g) (for T1 on day 1). PROCA lowered the carboxyhemoglobin level from the end of T1 (mean 6.64%) to the start of T2 (mean 2.95%) by a mean absolute value of 3.69%. For PROCB and PROCC the mean absolute decreases in carboxyhemoglobin were 4.00% and 4.31%, respectively. The fall in carboxyhemoglobin between T1 and T2 was greatest in PROCC; this was statistically significantly lower than that of PROCA (P = 0.0039) and PROCB (P = 0.0289). The test‐retest reliability for the measurement of total hemoglobin mass was good with a mean typical error (TE) of 2.0%. The oCOR method is safe and can be repeated within 3 h when carbon monoxide is suitably cleared between tests. Using oxygen therapy alone adequately achieves this.