Thoracic Surgery, Pulmonary Physiology, Obesity, and Hemoglobin Flashcards
What are important considerations in the preoperative evaluation of a patient for thoracic surgery?
- Focus on the extent and severity of pulmonary disease and cardiovascular involvement.
- Inquire about: dyspnea, cough, cigarette smoking, exercise tolerance, risk factors for acute lung injury.
What are pack years?
The #of packs smoked/day x the # of years
On physical examination of the thoracic surgery patient, what signs are you looking for?
Presence of cyanosis and clubbing, breathing pattern, type of breath sounds (wet- crackles, dry- wheezes).
Look for midline trachea- if displaced, consider difficult intubation.
T or F: one important factor in the evaluation of a thoracic surgery patient is the presence of an increase in PVR 2/2 to a fixed reduction in the x-sectional area of the pulmonary vascular bed.
True- pulmonary circulation is normally a low-pressure, high-compliance system capable of handling an increase in blood flow by recruitment of normally underperfused vessels. This acts as a compensatory mechanism that normally prevents an increase in pulmonary arterial pressure.
In COPD, there is distention of the pulmonary capillary bed with decreased ability to tolerate an increase in blood flow (decreased compliance). These patients demonstrate an increase in PVR when cardiac output increases because of a decreased ability to compensate for an increase in pulmonary blood flow –> results in pulmonary HTN.
T or F: An increase in PVR is of significance in the management of the patient during anesthesia because factors such as acidosis, sepsis, hypoxia, and application of PEEP, all further increase the PVR and increase the likelihood of right ventricular failure.
True
Common features on ABG analysis of COPD patients.
Hypoventilation and CO2 retention.
BLUE BLOATERS: cyanotic, hypercarbic, hypoxemic, overweight, in a state of chronic respiratory failure with decreased ventilatory response to CO2. In these patients, the high PaCO2 increases CSF HCO3 concentrations, and the medullary chemoreceptors become reset to a higher level of CO2. Sensitivity to CO2 is decreased. These patients hypoventilate when given high oxygen concentrations to breathe because of a decreased hypoxic drive.
PINK PUFFERS: pts with emphysema, thin, dypneic, pink, normal ABG values. Have increase in minute ventilation to maintain normal PaCO2, which explains increase in work of breathing and dyspnea. Preoperative PaO2 correlates with intraoperative PaO2 during one lung ventilation.
What are three goals in performing PFTs in a patient scheduled for lung resection?
1- identify the patient at risk for increased postoperative morbidity and mortality.
2- identify patient who will need short-term or long-term postoperative ventilatory support.
3- evaluate the beneficial effect and reversibility of airway obstruction with use of bronchodilators. (PFTs are usually performed before and after bronchodilator therapy to assess the reversibility of airway obstruction –> a 12% improvement in PFTs may be considered a positive response to bronchodilator therapy and indicates that this therapy should be initiated before surgery. )
What is FEV1?
Forced expired volume in 1 second.
When referring to FEV1, indicate the % of predicted value, rather than just using the actual results in liters.
The % of predicted value takes into account the age and size of the patient, and the number may have a different implication in another patient.
Why is the ratio of FEV1/FVC useful?
Allows to differentiate between restrictive and obstructive lung disease.
Restrictive lung disease: normal FEV1/FVC
Obstructive lung disease: decreased FEV1/FVC because FEV1 is markedly decreased
What is DLCO? Why is it important?
The ability of the lung to perform gas exchange is reflected by the diffusing capacity for CO.
DLCO is impaired in disorders such as interstitial lung disease, which affects the alveolar-capillary site.
PREDICTED POSTOPERATIVE DIFFUSING CAPACITY PERCENT IS THE STRONGEST SINGLE PREDICTOR OF RISK OF COMPLICATIONS AND MORTALITY AFTER LUNG RESECTION.
High-risk patients, or patients unlikely to recover from pneumonectomy are cited as:
PaCO2 > 45, PaO2 < 50 on room air
FEV < 25%
FEV1 < 2L preoperatively or < 0.8L or < 40% of predicted postoperatively
FEV1/FVC < 50% of predicted
maximum breathing capacity < 50% predicted
maximum VO2 < 10 mL/kg/min
What is important in the preoperative care of a COPD patient?
- optimize lung function
- address bronchospasm (with bronchodilators), infections (with antibiotics), smoking cessation
- Patients who smoke should be advised to stop smoking at least 2 months prior to an elective operation to decrease the risk of postoperative pulmonary complications (PPCs)
What is a hallmark feature in advanced emphysema?
dynamic hyperinflation, intrinsic PEEP
What concerns must you have during mechanical ventilation in an emphysematous patient?
Be concerned for worsening intrinsic PEEP leading to respiratory and hemodynamic consequences such as barotrauma, reduced CO, and impaired gas exchange.
How does positive pressure ventilation affect the cardiopulmonary system?
1- increased mean intrathoracic pressure reduces venous return and therefore reduces CO
2- hyperexpanded lungs may cause tamponade of the heart, especially the thin-walled right ventricle.
3- Increased PVR and shunting of blood to nonventilated lung causes hypoxia
4- Dilation of the RV reduces LV diastolic compliance
All of the above reduce oxygen delivery and cause mismatch between supply and demand.
What are reasonable maneuvers to minimize intrinsic PEEP?
1- low tidal volume
2- reduce respiratory rate
3- low I:E ratio (such as 1:3 and 1:4)
4- increase inspiratory flow to deliver tidal volume in a short time to reduce the I:E ratio an dincrease expiratory time.
What are three causes for hyperventilation?
1- arterial hypoxemia
2- metabolic acidosis
3- central etiologies (eg intracranial hypertension, hepatic cirrhosis, anxiety, pharmacologic agents)
T or F: During spontaneous ventilation, the ratio of alveolar ventilation to dead space ventilation is 2:1. The alveolar-to-dead space ventilation ratio during positive-pressure ventilation is 1:1. Thus, minute ventilation during mechanical ventilatory support must be greater than that during spontaneous ventilation to achieve the same PaCO2
True
T or F: PaCO2 ≥ PETCO2 unless the patient inspires or receives exogenous CO2.
True- the difference between PaCO2 and PETCO2 is due to dead space ventilation. The most common reason for an acute increase in dead space ventilation is decreased cardiac output –> you will see your end-tidal CO2 dramatically decrease in hypotension.
T or F: When FRC is reduced, lung compliance falls and results in tachypnea, and venous admixture increases, creating arterial hypoxemia
True
T or F: There is no compelling evidence that defines rules or parameters for ordering preoperative pulmonary function tests.
True- rather, they should be obtained to ascertain the presence of reversible pulmonary dysfunction (bronchospasm) or to define the severity of advanced pulmonary disease.
T or F: During ventilation, the predominant changes in thoracic diameter occur in the anteroposterior direction in the upper thoracic region and in the lateral or transverse direction in the lower thorax.
True
T or F: The ventilatory muscles include the diaphragm, intercostal muscles, abdominal muscles, cervical strap muscles, SCM muscles, and the large back and intervertebral muscles of the shoulder girdle.
True
