Diagnostic approach and monitoring

Monitoring is required to determine the adequacy of management designed to restore perfusing pressures and the underlying cause of the hypotension.

A primary assessment, including history and physical examination, must be undertaken in an ordered way. Inspection should be initially directed at pulse rate and quality, respiratory rate, skin circulation, and mental status. Hypotension is associated with a typical constellation of clinical signs with some differentiation according to the underlying cause (Table...!). It is important to remember that clinical findings may also be modified by pre-existing diseases. For example, an elderly or diabetic patient may not exhibit tachycardia because of a diminished cardiac response to sympathetic stimulation.

Table 1 Clinical signs common to three frequent causes of hypotension.

During ebb phase resuscitation the clinician also needs to decide on the monitoring and diagnostic approaches which facilitate early restoration of arterial perfusing pressures and to establish the cause of hypotension. Key to this early management phase is adequate monitoring of the perfusing pressures. Shock in the previously normotensive patient is defined as a systolic blood pressure above 90 mmHg, but, as the sphygmomanometer can be an unreliable tool in patients with shock and pre-existing vascular disease, confirmatory evidence by clinical examination is mandatory. Signs of clinically significant hypotension include a cool vasoconstricted periphery, oliguria (since skin and renal blood flows are redirected to the core circulation), and obtundation or restlessness (since cerebral blood flow is depressed). As a previously hypertensive patient is accustomed to elevated perfusing pressures, shock in this type of patient is defined when the blood pressure has fallen by at least 30 mmHg from previously recorded levels. We recommend inserting an arterial line (radial or femoral) if restoration of arterial perfusing pressures might be protracted and if this can be performed rapidly—time should not be spent trying to insert an arterial line to the exclusion of prompt management of the hypotension. An arterial line also provides access for rapid blood sampling or in-line biochemistry monitoring.

Other monitoring and diagnostic technologies that might be considered during ebb phase management are considered in Table 2. The principal objectives are to determine the adequacy of restoration of arterial perfusing pressures and to find clues to the underlying cause of the shock. Pulse oximetry and end-tidal CO 2 monitoring provide a non-invasive assessment of the integration of the respiratory and circulatory systems. However, in vasoconstricted shock pulse oximetry may be unreliable because capillary blood flows are impeded. End-tidal CO 2 monitoring has been used as a surrogate for circulatory function, particularly in cardiac arrest situations where restoration of core blood flows is accompanied by increases in end-tidal CO 2. Laboratory tests may provide diagnostic information about the etiology of hypotension and give an important baseline assessment of organ function. Leukocytosis or leukopenia can occur in sepsis, although in non-septic patients they may indicate a late stage of shock. Thrombocytopenia may be found in sepsis and after acute hemorrhage. Coagulation parameters need not be routinely measured unless there is clinical suspicion of a coagulopathy. Diagnostic blood sampling also provides an opportunity to perform early cross-matching for possible blood transfusion needs.

Table 2 Monitoring the hypotensive patient

During flow phase resuscitation, the aim of monitoring is to determine whether O2 delivery is adequately meeting the body's needs. Measuring arterial lactate may be useful in tracking the balance between whole-body O2 supply and demand. Although many factors contribute to arterial lactate concentrations, the trend is useful over short periods of time as a surrogate marker of the adequacy of the whole-body O 2 supply-demand relationship. Thus, if lactate is increasing, the prevailing O 2 delivery is likely to be insufficient for ongoing metabolic needs. In this circumstance, treatments which increase O 2 delivery can be used as a diagnostic test: if the lactate falls after O2 delivery is elevated, this is reasonable presumptive evidence of perturbation of the whole-body O 2 supply-demand balance. Ideally, this balance should be determined at the level of individual organs, since any test which represents the sum of all organs (as happens with arterial lactate) may obscure the presence of significant ischemia in individual organs. Gastric tonometry measures gastric intramucosal PCO2 (PiCO2); the difference between PaCO2 and PiCO2 is currently being evaluated as a surrogate of the adequacy of oxygenation in the gastrointestinal circulation. Urine PO2 measurements have also been proposed to monitor the O2 supply-demand balance in the core circulation.

The next issue in flow phase resuscitation is to determine how to improve O 2 delivery further when indicated. Figure,! shows a treatment algorithm for increasing systemic O2 delivery. Crucial to circulatory management is the assessment of the adequacy of ventricular preload. If it is low, fluid infusion to augment intravascular volume is appropriate. If it is high, inotropes and/or dilators are more appropriate as fluid therapy may promote pulmonary edema, thereby further depressing the arterial O2 content. At this point the clinician must decide about the usefulness of right heart catheterization. If uncertainty remains regarding the status of ventricular preload, and hence whether fluid or inotropic therapy is the most appropriate, we recommend pulmonary artery catheter insertion. As no clinical trial has satisfactorily demonstrated that information provided by the pulmonary artery catheter leads to improved patient outcome, this recommendation must be regarded as opinion only.

hPHH

Fig. 1 General treatment algorithm for increasing systemic O2 delivery during flow phase resuscitation (after restoration of blood pressure) in patients with inadequate O2 delivery. PEEP, positive end-expiratory pressure; RBC, red blood cell.

When early evaluation of the patient does not identify the cause of hypotension, specific diagnostic procedures must be considered ( Table,, , 3).

Table 3 Specific diagnostic techniques

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