Non-Invasive Monitoring CRITICAL CARE TECHNIQUES Components of NonInvasive Monitoring Pulse-oximetry Capnography Transcutaneous Monitoring (a.k.a. T-Com) Pulse Oximetry Pulse oximetry provides an estimate of SaO2 by utilizing selected wavelengths of light to non invasively determine the saturation of pulsed blood (SpO2) Uses two LEDS to transmit light through capillary bed to photodiode detector at different wavelengths. Ex. One diode (Red) – emits light at 660nm Second diode (infared)– emits light at 940nm (Lights flashing several hundred times per second! 3 Principle of absorption Pulse Oximetry Indications Monitor - the adequacy of arterial oxyhemoglobin saturation Quantify response - of arterial oxyhemoglobin saturation to therapeutic intervention or to diagnostic procedures, such as bronchoscopy To comply - with mandated regulations or recommendations by authoritative groups Contraindications The ongoing need for actual measurements of pH, PaCO2, total hemoglobin, and abnormal hemoglobins may be a relative contraindication to pulse oximetry 5 Pulse Oximetry False high or low readings can be caused by several factors. Factors affecting SpO2 accuracy include Motion Abnormal hemoglobin such as CARBOXYHEMOGLOBIN!!! POX will read high! Intravascular dyes Skin pigmentation Nail polish Low perfusion states – such as cold hands, low BP, & hypovolemia. 6 Pulse Oximetry (Cont.) 7 Pulse Oximetry Remember POX does not measure CaO2 or PCO2; patients suspected of having O2 transport issues or hypoventilation should have an ABG 8 Capnography Defined as the measurement of C02 in an expired gas. Two main types of Capnography Qualitative Quantitative Qualitative Devices Also referred to as “chemical” capnometry Color change on litmus denotes at least a 5% change in C02 levels. Used in RSI Not for trending Quantitative Capnography Take sample of exhaled gas and provides a number display and graphic display of results Two types exist Side stream Mainstream Mainstream vs. Sidestream Sidestream Sample is collected via a small port that feeds to outside sensor (monitor). Mainstream Sample chamber attaches directly between ETT and Y adapter, so there is a continuous reading of PetC02 Mainstream vs. Sidestream 13 Mainstream Sidestream Nasal Cannula w/EtCO2 Continuous Waveform Capnography Can be breath to breath This is the gold standard for endotracheal intubation If a square is seen, the ETT cannot be anywhere other than in the trachea. Auscultate bilaterally. Can also be viewed as a trend https://www.youtube.com/watch?v=_KKliTT3DSo Normal SBc02 waveform Normal value End tidal C02 (PetC02) ◦ Normal = 35-40 torr ◦ a-e diff. (PaCO2-PetCO2) Can be used to estimate dead space ventilation. ◦ Normal a-e diff. = 2-5 mmHg ◦ The a-e difference can never be 0 ◦ https://www.youtube.com/watch?v=mrQ8pghnC94 Increased Vd More wasted ventilation = more deadspace results in a widened (a-e diff) Example: PaC02 50 and PetC02 20 An a-e diff of 30 is huge! https://www.youtube.com/watch?v=sB3J3DhhUT0 Widening a-e diff. Example: PaC02 is 45 and PetC02 is 30 difference is 15 torr (widened or increased) Examples of when this may happen COPD who is air-trapping Pulmonary emboli Over-distended alveoli or excessive PEEP or pulmonary HTN LHF blood backs up to pulmonary capillary beds and less C02 is excreted T-com Monitor https://www.youtube.com/watch?v=7d7XNtQNllA Transcutaneous Monitoring Provides continuous, noninvasive estimates of PO2 and PCO2 using skin sensor More commonly used in neonates Sensor warms underlying skin to increase arterial blood flow Two most important factors influencing accuracy of transcutaneous measurements: age and perfusion status Low perfusion and increasing age reduce agreement between PtcO2 and PaO2 Agreement between PtCO2 and PaCO2 is better because CO2 is more diffusible through skin 23 Transcutaneous Monitoring Most common sites for electrode placement for infants and children are abdomen, chest, and lower back Should compare monitor readings with those obtained with concurrent ABG Validation with ABG should be repeated any time patient’s status undergoes major change 24 Transcutaneous Monitoring Indications The need to monitor continuously the adequacy of arterial oxygenation or ventilation The need to quantify the real-time responses to diagnostic and therapeutic interventions, as evidenced by PtCO2 or PtCO2 values Contraindications There are no absolute contraindications. In patients with poor skin integrity or adhesive allergy, alternative devices should be considered 25 Transcutaneous Monitoring Hazards and possible complications False-negative or false-positive results may lead to inappropriate treatment. Tissue injury Erythema (redness) Blisters Burns 26
