Editorial

Let’s get the numbers!

O. F. M. Sellevold1,2, I. Kirkeby-Garstad

1,2 and P. Pelosi3

1Department of Cardiothoracic Anaesthesiology and Intensive Care, St Olavs University Hospital, 2Department of Circulation and MedicalImaging, Norwegian University of Science and Technology, Trondheim, Norway and 3Department of Surgical Sciences and IntegratedDiagnostics, University of Genoa, Genoa, Italy

Measure what is measurable, and make measur-able what is not so.Galileo Galilei (Pisa, 15 February 1564 – Arcetri, 8January 1642) – Italian physicist, mathematician,astronomer, and philosopher

Alf Prøysen, the Norwegian storyteller forchildren, told about the clever little billy-goat

kid who counted his fellow animals at the farm:I am one and the calf is two. . . . Not knowing thepurpose of counting, animosity arose among theother animals; they ran along chasing him to makehim stop. Eventually, they all ended up in greatdanger where the kid’s knowledge of countinghelped save their day. The tale illustrates our oppo-sition to numbers when the benefits are obscure. Inanaesthesiology and intensive care, we continu-ously make decisions on management and are inneed of reliable and precise information – whichmay come from numbers. We routinely monitorphysiological variables like heart rate, arterial bloodpressure, arterial oxygen saturation, and venousblood pressures. Some decades ago the extendedmonitoring with the pulmonary artery catheter(PAC) prompted a new understanding of criticalillness and boosted the interest in clinical physiol-ogy of the very sick patients.1,2 Large amounts ofknowledge have been accumulated from variousfields of intensive care and perioperativemedicine.3–6 The numbers allow us to calculateadvanced physiological indices like left and rightventricular work and systemic and pulmonary vas-cular resistance. We construct patients’ Starlingcurves and calculate the balance between oxygenconsumption and delivery. These figures appear rel-evant and pertinent for guiding treatment of a criti-

cal care patient, and we use them according to ourcurrent understanding: when a haemodynamicallyunstable patient appears to be on the left side of theStarling curve, we give volume; low peripheralresistance may lead to vasoconstrictive drugs andwith depressed cardiac function, the treatment maybe inotropes. However, while the objective of ourtreatment is to secure tissue oxygenation, these vari-ables represent only requirements for tissue oxy-genation – they do not guarantee it. It has not beeneasy to cash in the numbers into proven better out-comes. On the contrary, several studies and reviewshave questioned the usefulness of the pulmonaryartery catheter.7 After analysis of the literatureHarvey and colleagues stated that: ‘The economicevaluation, using decision analysis techniques ratherthan conventional hypothesis testing, suggests thatthe withdrawal of the PAC from routine clinicalpractice in the NHS would be considered cost-effective in the current decision-making climate,and might result in lives or life-years being saved atmodest cost’.7

Why does not better monitoring lead to bettertreatment? First, monitoring is not a treatmentmodality and the direct complications are few.Second, since more information has not been docu-mented fully to improve outcome, the relevance andthe use of information should be examined. A wholeset of information must be put together. The Goal-directed therapy that was launched by Rivers et al.focused not only on which parameters should bemonitored but also on the timing of the monitor-guided therapeutic measures.4 Many colleagueshave been discouraged by the lack of documentedbenefit of extended haemodynamic monitoring.Sweeping away their PACs, they did not have anydocumented alternative substitution. It then comes

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easy to rely on clinical judgement alone. It is,however, difficult to assess the haemodynamics byclinical evaluation. Iregui et al. examined inten-sivists’ clinical judgement of haemodynamics in106 mechanically ventilated patients using nurse-obtained transoesophageal Doppler measurementsas reference.8 They found that the physicians hadless than 50% correct estimation of Cardiac Index,while there was a reasonable correlation betweenthe aortic oesophageal Doppler (AOD) and PACmeasurements and of circulatory failure. This oldclinical trick of diagnosis ex iuvantibus confirms thediagnosis from the outcome. This is like manoeu-vring in the dark without map or compass. The mostserious consequence of such defeatism is the conse-quent failure of continuous haemodynamic analysis.

There are, however, several other tools at handwhen not using the pulmonary artery catheter.Ultrasound technology is increasing in importance.Echocardiography was first established in cardiacanaesthesia and has proved efficient in monitoringbut also in changing the course of surgery. It is nowcraving its place in intensive care.9 The high qualityimages produced supports the clinicians’ under-standing of the pathophysiology. Another way toexploit ultrasound technology is through AOD. ADoppler probe is introduced into the oesophagusand the oesophageal diameter and the velocity ofdescending aorta blood flow is measured. The prox-imity to the structures makes high quality imagesand measurements possible. This information isentered into algorithms resulting in estimation ofamong others, cardiac output. The limited spaceavailable for this comment does not allow a detailedanalysis of the technique, but there are several pit-falls. These underline the need for a highly qualifiedstaff and a prudent evaluation of the data. In thisissue of Acta Anaesthesiologica Scandinavica,Robert et al. show that both Intensive Care Unit(ICU) residents and nurses can be trained in the useof AOD.10 Six residents and three nurses under-went a 1-day training programme consisting oftheory and practice. Their results were compared tothe measurements done by one experienced physi-cian. The training consisted of more than 12 proberepositioning in the ICU. Quality criteria of theDoppler signal were a sharp and well-definedDoppler wave associated with the highest value ofaortic flow velocity and complete detection of theanterior and posterior descending aortic wall. Theperformance for both groups was good confirmingthat a relative short training period is sufficient forobtaining quality data in stable patients with this

method. Thus, haemodynamic values may beobtained frequently and treatment could be directedaccordingly.

The question remains whether the results mirrorthe relevant physiology. Sharma and colleaguesfound poor correlation between measurementsfrom AOD and PAC in 35 patients after cardiacsurgery and concluded that AOD could not be usedas the sole indicator of cardiac output after cardiacsurgery.11 The AOD probe in their study did notmeasure the diameter of the descending aorta – afigure of great importance in the calculations. Well-trained intensive care nurses are important qualitymeasures for any critical care unit; and training ICUnurses to do measurements and to understand algo-rithms may add value to the system. Health carefinances are under pressure all over the world. Thor-ough examination of new monitoring devices forefficiency and cost is pertinent. But so far, no moni-toring method has gained overall acceptance andnone have proven – beyond doubt – that it is deci-sive for improved outcome. While the search for theoptimal information goes on, the question remainswhether this enhanced understanding justifies theextra cost and work. However, we must seek moreand better information. It may improve the outcomefor the individual patient, but it is vital for the ana-lytical attitude in the intensive care.

The day in the ICU may be busy and stressful.Training of nurses is important but should not be anexcuse for reduction of the number of intensivists.No patient is quite like the other, and there arenumerous protocols for management. Monitoringphysiological parameters cannot adequately guidepatient therapy. Critical care treatment is to integratedata from the monitoring into the clinical context.Thus, the treatment should not be decided and runby algorithms. It is vital that the intensivists arebeing present in unit to integrate information anddecide the course of treatment. Intensive care medi-cine is to have an open mind for alternative diag-noses through continuous observation.

Let’s get the numbers – is an apparently superficialattitude but the second part has its reason – becauseit promotes analysis. Thus, the title of this commentfocuses on the necessity to find the mechanismsbehind the disease. The skilled clinician is the hub ofthe wheel of treatment in anaesthesia and intensivecare and should be present at the bedside. A nega-tive attitude towards monitoring will reduce theinterest in haemodynamic understanding andundermine the progress of intensive care. If thenumbers we obtain through monitoring do not lead

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to improved outcome, we should remember thewise words of Galilei cited above. If we do not getthe numbers, progress is at stake.

Acknowledgement

Conflicts of interest: There are no conflicts of interest.

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8. Iregui MG, Prentice D, Sherman G, Schallom L, Sona C,Physicians KMH. estimates of cardiac index and intravascu-lar volume based on clinical assessment versus transesopha-geal Doppler measurements obtained by critical care nurses.Am J Crit Care 2003; 12: 336–42.

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Address:Olav F. M. SellevoldDept of Cardiothoracic Anaesthesiology and Intensive CareSt Olavs University HospitalAHL SenterPrinsesse Kristinas gt 3NO 7030 TrondheimNorwaye-mail: Olav.Sellevold@ntnu.no

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