page 2 introduction physiological aspects monitoring requirements

IntroductionIntroduction

Physiological Aspects Physiological Aspects

Monitoring RequirementsMonitoring Requirements

Thoracic anesthesia is challengingThoracic anesthesia is challenging

Patient Patient Procedure Procedure

““V" - ventilation V" - ventilation - the air which reaches the lungs

"Q" - perfusion "Q" - perfusion - the blood which reaches the lungs

Normal V is 4 L of air per minute.

Normal Q is 5L of blood per minute.

So Normal V/Q ratio is 4/5 or 0.8. Normal V/Q ratio is 4/5 or 0.8.

When the V/Q is higher than 0.8, it means ventilation exceeds perfusion.

When the V/Q is < 0.8, there is a VQ mismatch caused by poor ventilation

An area with no ventilation (and thus a V/Q of zero) is termed "shunt." "shunt."

An area with no perfusion (and thus a V/Q of infinity) is termed “dead space”“dead space”

A change in volume divided by a change in transpulmonary pressure.

(CL = ΔV / ΔPL)(CL = ΔV / ΔPL)

A typical value of compliance is 200 ml/cm H20

Pulmonary blood flow distribution relative to the Pulmonary blood flow distribution relative to the alveolar pressurealveolar pressure

Ven

tilation

Ven

tilation

Patient awake spontaneously breathing

The dependent lung is betterVentilated than the

Nondependent lung,˙V/˙ Q still is well matched.

The principle physiologic change of Oprinciple physiologic change of OLV is the redistribution of lung perfusion between the ventilated (dependent) and blocked (nondependent) lung

Many factors contribute to the lung perfusion, the major determinants of them are hypoxic pulmonary hypoxic pulmonary vasoconstriction, HPV and gravity. vasoconstriction, HPV and gravity.

HPV is a widely conserved, homeostatic, vasomotor response of precapillary smooth muscle in the PAs to alveolar hypoxia. HPV mediates ˙V/˙Q matching and, by reducing shunt fraction, optimizes systemic pO2.

Reduces the surface area available for gas exchangeReduces the surface area available for gas exchange

Reduced arterial oxygen tensionReduced arterial oxygen tension

Maintaining oxygenationMaintaining oxygenation and and

elimination of carbon dioxide elimination of carbon dioxide is the greatest challengeis the greatest challenge

Use of Monitoring to Detect and Diagnose Use of Monitoring to Detect and Diagnose Intraoperative EventsIntraoperative Events

RespirationRespiration

OxygenationOxygenation

VentilationVentilation

Cardiovascular functionCardiovascular function

ElectrocardiographyElectrocardiography

Arrhythmia, ischemia

Intraarterial catheterIntraarterial catheter

Hypotension or hypertension

Arterial compression

Pulmonary artery catheterPulmonary artery catheter

Pulmonary hypertension, filling pressures, assess

cardiac performance

SvO2SvO2

Adequacy of cardiac output

Transesophageal EchocardiographyTransesophageal Echocardiography

Ischemia, volume status, right ventricular dysfunction

Failure to check the equipment properlyFailure to check the equipment properly before induction of anesthesia isbefore induction of anesthesia is

responsible for 22% of theresponsible for 22% of the critical incidents that occur during anesthesiacritical incidents that occur during anesthesia

Healthy patients no special intraopertive conditionsHealthy patients no special intraopertive conditions

Sick patients special intraopertive conditionsSick patients special intraopertive conditions

Tier ITier I

ProcedureProcedure PatientPatient

Gas exchange

Airway mechanics

Endotracheal tube position

PA pressures

Cardiovascul-ar status

Color of tissues and shed blood Spo2, PETCO2

Feel of the breathing bag, stethoscope,PIP, PETCO2

EBBS Ballotable balloon in SSN, FOB afterplaced in LDP

Not measured NIBP, pulse oximeter waveform, ECG, PETco2esophageal stethoscope,± CVP, ± invasive arterialpressure monitoring



Tier IITier II


Gas exchange

Airway mechanics


PA pressures


As above plus frequent ABG studies

As above plus spirometry. Individual and whole-lungcompliance

FOB to verify tube position while in supine position, as well as in the LDP

Measure Ppa if lobectomy or lung resection

As above, plus invasive arterial pressure monitoring, + CVP, + PA catheter (if poor EF, PA,HTN), ± TEE

SpirometrySpirometry is a non-invasive monitor device which measures volume, pressure and flow volume, pressure and flow in the airway.

These measurements may be used to construct :

a pressure-volume curve (PV) and

a flow-volume curve (FV).

The constructed curves will give important information about the peri-operative respiratory function.peri-operative respiratory function.



Tier IIITier III


Gas exchange

Airway mechanics


PA pressures


As above plus Qs/Qt, VD/Vtfrequent VBGs

As above plus airway resistance

As above plus frequent rechecksto verify position

Measure PA ,Q , PVR , SVR, Dao2 –Dvo2

As above plus PA , TEE

Measured values:Measured values:

CVPCVP: 1-6 mm Hg (reflects right atrial pressure).

PAPPAP: Systolic 15-30mm Hg, Diastolic 6-12mm Hg.

PCWPPCWP: 6 - 12mm Hg. Estimates left atrial heart pressure and left ventricular end diastolic pressure.

COCO: 3.5 - 7.5 L/min

Sv02:Sv02: (70 - 75%). Drawn from the end of the pulmonary artery catheter. Used to calculate how well oxygen is extracted by the tissues.

the LDP is important with regard to pulmonary artery catheter the LDP is important with regard to pulmonary artery catheter monitoring in three situationsmonitoring in three situations.

The catheter is in the nondependent collapsed lung, the measured cardiac output and mixed venous blood (pvo2) may be decreased.decreased.

When the nondependent lung is ventilated with PEEP and the catheter is in the nondependent lung, Ppaw may not equal , Ppaw may not equal Pla.Pla.

When the catheter is in the dependent lung, Ppaw will be a Ppaw will be a faithful index of Plafaithful index of Pla, even if PEEP is used

Monitors are useful adjuncts, But they alone Monitors are useful adjuncts, But they alone cannot replacecannot replace

Careful observation by AnaesthesiologistCareful observation by Anaesthesiologist.

page 2 introduction physiological aspects monitoring requirements

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