Monitoring and Interpretation of Vital Signs in the High-Risk Surgical Patients

Abstract

Vital signs connect physiological concepts and clinical practice. Traditional vital signs include heart rate, arterial pressure, body temperature, and respiratory rate. For four decades, peripheral oxyhemoglobin saturation (SpO2) as measured by pulse oximeter has been added to heart and respiratory rate, blood pressure, and temperature measurement, so becoming the fifth vital sign. The present chapter gives a throughout analysis of the physiological meaning of the five vital signs together with insights about their usefulness in clinical practice. Special attention has been provided to respiratory rate, the most neglected but perhaps most accurate predictor of adverse events. The importance of respiratory rate has been stressed in relation to its bounds with the breathing pattern and the magnitude of respiratory work. Arterial blood pressure has been analyzed in relation to the pressure–flow relationship so giving the basic tools for essential cardiovascular analysis. Heart rate has been analyzed in function of its compensatory role during increased O2 demand and/or dysfunction/failure of the cardiovascular system. Temperature regulation has been analyzed in relation to the cardiorespiratory changes associated with hyperthermia and hypothermia. Finally, the main aspects of the SpO2 and oxyhemoglobin saturation curve have been dealt together with the most frequent pitfalls concerning inaccurate SpO2 readings.