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Signa Vitae

Journal of Intensive Care and Emergency Medicine

Multimodal monitoring (MMM) in the perioperative period

Abstract

Routine anaesthesia monitoring until the mid-1980s often consisted of just a finger on the pulse, primitive ECG and intermittent blood pressure (MAP) measurement using a cuff and aneroid gauge or mechanical oscillotonometer. Then in quick succession an explosion of new monitors was introduced including pulse oximetry (SpO2), end tidal carbon dioxide (EtCO2) and anaesthetic agent monitoring as well as automated non-invasive blood pressure (NIBP) machines. These were all routinely in place in many hospitals by the late 1980’s, but then progress came to a halt with no advances in routine anaesthetic monitoring for over 25 years.

This paper concentrates on three classes of non- or minimally invasive monitors which have become additionally available in the last 10 to 15 years and if used in combination their potential impact on improving outcome following surgery in high risk patients:

  1. Monitors which calculate stroke volume (SV, and thus cardiac output, CO) from a standard radial arterial line (e.g. LiDCO, UK), oesophageal probe (Deltex, UK), ECG pads or even from the finger
  2. Monitors which assess the degree of cortical suppression (e.g. BIS, Medtronic, USA) produced by anaesthetics thus potentially allowing the administrator to “fine tune” anaesthesia for individual patients
  3. Monitors which assess tissue oxygenation, usually of the brain (e.g. Invos, Medtronic, USA)

If used together they provide complementary information which should improve perioperative haemodynamic management and outcome and form part of a multi-modal monitoring (MMM) strategy which is the subject of this article.

Key words: cardiac output, minimally invasive, tissue oxygenation, depth of anaesthesia, multi-modal monitoring

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Measurement of skeletal muscle tissue oxygenation in the critically ill

Abstract

Shock is a state of acutely reduced tissue oxygenation. In cardiogenic shock oxygen delivery (DO2) is reduced, but oxygen extraction is preserved. In septic shock DO2 is preserved, but oxygen extraction is decreased because of microvascular changes and disturbed metabolism. Global assessment of DO2 and oxygen consumption does not tell us enough about adequacy of regional perfusion. The aim of this study was to assess the value of near infrared spectroscopy (NIRS) in detecting skeletal muscle tissue oxygenation (StO2) in critically ill patients.
Patients in cardiogenic shock (n=17), septic shock (n=14), without shock but with localized infection (n=14) and healthy volunteers (n=15) were included. Thenar StO2 was measured with NIRS before (baseline StO2, %), between (downward StO2 slope, %/min) and after 90 seconds of upper arm stagnant ischemia (hyperemic StO2, %). Muscle oxygen extraction (mOER) was calculated as follows: mOER (%) = (1-baselineStO2/hyperemic StO2)*100. Repeatability was assessed using the Bland Altman method (95 % of values within limits of agreement), comparing 55 pairs of measurements performed in 5-minute intervals.
Repeatability of measurements was clinically acceptable. Compared to septic shock patients, cardiogenic shock patients had lower baseline StO2 (68.9 ± 10.0 % vs. 84.3 ± 10.4 %; p < 0.05) and hyperemic StO2 (80.8 ± 7.8 % vs. 91.8 ± 8.3 %; p < 0.05), and a higher downward StO2 slope (-17.4 ± 31.7 %/min vs. -9.1 ± 2.6 %/min; p < 0.05). mOER was higher in healthy volunteers (11.9 ± 3.8 %) and volunteers with cardiogenic shock (14.8 ± 7.3 %) compared to septic shock patients (8.1 ± 7.8 %) and those with localized infection (7.6 ± 5.4 %) (p < 0.05).
Repeatability of baseline StO2 and hyperemic StO2 is clinically acceptable. Results support the hypothesis that skeletal muscle oxygen extraction capability is preserved and extraction is increased in cardiogenic shock compared to septic shock.

Key words: repeatability, NIRS, tissue oxygenation, cardiogenic shock

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