Cardiopulmonary Monitoring During Anesthesia
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Guidelines to the practice of anesthesia and patient monitoring: § § §
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Qualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care. A completed pre-anesthetic checklist - history, physical exam, lab investigations, NPO An anesthetic record - In general, major regional anesthesia, or monitored IV conscious sedation HR and BP should be measured every 5 min. Also time, dose and route of drugs and fluids should be charted During all anesthetics, the patient’s oxygenation, ventilation, circulation and temperature shall be continually evaluated.
Required Anesthesia Equipment and Supplies §
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Only state of the art, currently calibrated anesthetic delivery and support equipment, supplies and pharmaceuticals will be employed by our medical professionals to provide the safest in reliable anesthesia. An Anesthesia Machine with the following : § Ability to deliver medicinal Oxygen. § Ability to accommodate administration of volatile agents. § Annual calibration of the machine and vaporizer. § If the machine requires electricity then a back up battery is essential. § An oxygen concentration monitor to test the purity of oxygen supply on site § A Secure oxygen supply with an alarm warning of hypoxic mixture and an appropriate back up supply in the operating room Equipment appropriate for the ages of the patients being treated that includes § Ventilation masks; Appropriate endotracheal tubes with stylets; Oral and nasopharyngeal airways; Laryngoscopes § A positive pressure ventilation system with a peep valve § IVF administration equipment including pediatric volumetric administration devices § Non invasive monitoring equipment for the measurement of § Electrocardiography, blood pressure, pulse oximetry, capnography, and temperature § Appropriate equipment must be included to manage an unanticipated difficult airway § Emergency equipment as well as a defibrillator (with pediatric paddles) § Equipment for administration of fluids through the intra-osseous route § Sevoflurane is the only volatile anesthesia agent that should be used. § Dantrolene should be available at every surgical site. § Resuscitation cardiac drugs of appropriate concentrations including a resuscitation dosage schedule should be available.
Elements to Monitor : I. Anesthetic Depth: § Patients with local or regional anesthesia provide verbal feedback regarding well being. § Onset of general anesthesia signaled by lack of response to verbal commands, in addition to loss of blink reflex to light touch. § Inadequate anesthesia can be signaled by : Facial grimacing or movement of arm or leg. But with muscle relaxants ( fully paralysis), it can be signaled by : Hypertension, tachycardia, tearing or sweating. § Excessive anesthesia can be signaled by : Cardiac depression, bradycardia, and Hypotension. And also may result in hypoventilation, hypercapnia and hypoxemia when muscle relaxants is not given. II. Oxygenation: § Clinically, monitored by patient color ( with adequate illumination ) and pulse oximetry. § Quantitatively monitored by using oxygen analyzer, equipped with an audible low oxygen concentration alarm. III. Temperature § Continuous temperature measurements monitoring is mandatory if changes in temperature are anticipated or suspected. IV. Circulation § Clinically, monitored by pulse palpation, heart auscultation and monitoring intraarterial pressure or oximetry. § Quantitatively using ECG signals and arterial blood pressure measurements every 5 min. V. Ventilation • Clinically, monitored through a correctly positioned endotracheal tube, also observing chest excursions, reservoir bag displacement, and breath sounds over both lungs. • Quantitatively by ETCO2 analysis, equipped with an audible disconnection alarm. Monitoring: 1. Electrocardiogram ECG: § 3 or 5 lead electrode system is used for ECG monitoring in the OR. § The 3 lead system has electrodes positioned on the right arm, left arm and chest position. ( placed in the left anterior axillary line at the 5th interspace, referred to as V5 ). Lead 2 is usually monitored by this system. § The 5 lead system adds a right leg and left leg electrodes, which allows monitoring v1, v2, v3, AVR, AVL, AVF and V5.
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Identification of P waves in lead 2 and it’s association with the QRS complex is useful in distinguishing a sinus rhythm from other rhythms. Analysis of ST segment is used as an indicator of MI. ( Dep.-ischemia / elev.-infarction ) Over 85% of ischemic events can be detected by monitoring ST seg. of leads 2 and V5.
2. Pulse Oximetry § Allows beat to beat analysis of oxygenation. § Depends on differences in light absorption between oxyHb and deoxyHb. § Red and Infra-red light frequencies transmitted through a translucent portion. (finger-tip or earlobe) § Microprocessors then analyze amount of light absorbed by the 2 wavelengths, comparing measured values, then determining concentrations of oxygenated and deoxygenated forms. (oxy- and deoxy-) § After all data is processed, oxygen saturation can be calculated. § Pulse plethysmograph (visual analysis of pulse waveform), while an audible form (auditory assessment of oxygenation status). § Pulse oximetry (SpO2) measures oxy-, deoxy-, met-, and carboxyHb. § CO poisoning gives an overestimation of the true O2 saturation(SaO2). E.g. Burn victims. § Inaccurate measurements seen in poor tissue perfusion (shock or cold extremities), movement, dysrhythmias, or with electrical interference (surgical cautery unit). 3. Blood Pressure BP: Methods of BP measurement: § Simplest method of BP measurement, estimating the SBP, is by palpating the return of arterial pulse as cuff is deflated. § Auscultation of the Kortokoff sounds on deflation (providing both SBP and DBP) § Mean Arterial Pressure (MAP) = DBP + 1/3(SBP – DBP)
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Automated non-invasive BP measurements.
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METHODOLOGY: a microprocessor controlled oscillometer (Dinamap®) which is used routinely intraoperatively. It allows automatic inflation of the BP cuff at preset time intervals, sending readings into a pressure transducer that digitalizes them. This technique gives rapid, accurate (± 9 mmHg) measurements of SBP, DBP, MAP and HR several times a minute. LIMITATIONS: Errors occur due to movements, arrhythmias or BP fluctuations due to respiration. 3 – 5 minutes intervals is recommended to prevent compressive peripheral nerve injury due to repeated rapid measurements.
Invasive BP measurements. (Arterial BP): Indications: § § § § § § § §
Rapid moment to moment BP changes
Frequent blood sampling Major surgeries (cardiac, thoracic, vascular) Circulatory therapies: vasoactive drugs, deliberate hypotension Failure of indirect BP: burns, morbid obesity Sever metabolic abnormalities Major trauma The radial artery at the wrist is the most common site for an arterial catheter. Alternatives are femoral, brachial and dorsalis pedis.
4. Capnography and EtCO2 § § § § §
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Capnometry: is the numerical measurement of CO2 concentration during inspiration and expiration. Capnogram: refers to the continuous display of the CO2 concentration waveform sampled from the patient’s airway during ventilation. Capnography: is the continuous monitoring of a patient’s capnogram. End-tidal CO2 monitoring is standard for all patients undergoing GA with mechanical ventilation. It is an important safety monitor and a valuable monitor of the patient’s physiologic status, and it has been an important factor in reducing anesthesia-related mortality and morbidity. Co2 monitoring is considered the best method for verifying successful intubation and extubation procedures. It helps in assessment of the adequacy of ventilation and an indirect estimate of PaCO2. Also it aids in diagnosis of PE, recognition of a partial airway obstruction, and indirect measurement of airway reactivity (bronchospasm). ETCO2 levels have also been used to predict outcome of resuscitation.
Measurement of ETCO2 § Sampling the patient’s respiratory gases near the airway. § Using infra-red gas analysis or mass spectrometry on the values and concentrations obtained. § Provided that when sampling, inspired CO2 value should be near zero. (i.e. ETCO2 value is a function of CO2 production, alveolar ventilation and pulmonary circulation; excluding inspired CO2). § During general anesthesia, with absence of ventilation perfusion abnormalities, difference between PaCO2 and ETCO2 is about 5 mm Hg (PaCO2 = 40 mmHg, ETCO2 = 35 mmHg) § Increases or decreases in ETCO2 values maybe the result of increases or decreases Factors affecting ETCO2:
5. Monitoring Temperature Objective: aid in maintaining appropriate body temperature Application: readily available method to continuously monitor temperature if changes are intended, anticipated or suspected Methods: thermostat, temperature sensitive chemical reactions § §
Potential heat loss or risk of hyperthermia necessitates continuous temperature monitoring
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Temperature below 34C may lead to significant morbidity Hypothermia develops when thermoregulation fails to control balance of metabolic heat production and environment heat loss Normal response to heat loss is impaired during anesthesia Those at high risk are elderly, burn patients neonates, spinal cord injuries
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Normal heat loss during anesthesia averages 0.5 - 1 C per hour, but usually not more that 2 - 3 C
Hyperthermia Causes § Malignant hyperthermia § Endogenous pyroxenes (IL1) § Excessive environmental warming § Increases in metabolic rate secondary to: o Thyrotoxicosis o Pheochromocytoma Monitoring Sites § Tympanic § Esophagus § Rectum § Nasopharynx
Suggested Reading: Life Saving Anesthetic Skills for Plastic Surgery of the Face - Operation Smile Anesthesia Manual. Operation Smile (2011)