GOMEZ 9/16/25 INTERN Respiratory
Sputum culture, sampling, and laboratory custody
Distinguish phlegm vs sputum
Phlegm: mucus not in contact with mouth/cavity
Sputum: material expectorated from lower airways after contact with oral cavity
Purpose of sputum sample
Used for culture and sensitivity to identify causative bacteria and determine antibiotic sensitivity
Guides targeted antibiotic therapy rather than broad-spectrum empiric therapy
Sampling methods
Have patient cough up sputum OR obtain sputum via deep suction
Important to avoid contamination from mouth/oral secretions
Custody and labeling requirements (lab procedures)
Include patient name, initials, source of sample, date and time collected
Do not necessarily record the amount, but can indicate approximate volume; lab will see volume
Time and source are critical for lab processing and interpretation
If any field is missing, the lab may return the sample
Practical lab handling issues
A sticker on the specimen is essential (e.g., labeling for proper custody); lab inspectors require proper labeling
Proper custody ensures the lab knows who collected the sample and when
Why this matters for patient safety
Mislabeling or missing information can delay results, affecting care and patient satisfaction
Distinguishing mucus from true infectious secretions helps avoid unnecessary procedures or misinterpretation
When to consider low platelets or bleeding risk
Suctioning, lavage, or invasive sampling carries bleeding risk; assess bleeding risk before sampling
If secretion is mostly fluid rather than mucus, or if lab data suggests fluid overload or edema, reassess sampling strategy
Interpreting culture results and treatment implications
Lab returns list of organisms and antibiotics to which they are sensitive (sensitivity profile)
If patient is on prior antibiotics, culture helps tailor the regimen
Infectious disease consultation for recurrent or difficult infections may be indicated
Practical nurse/therapist guidance during sampling
Donβt gross the lab with an excessive volume; collect an adequate inoculum with a sterile technique
Communicate to the team that a culture and sensitivity sample has been sent and awaiting results
Summary
Culture and sensitivity of sputum identify bacteria and guide antibiotic choice
Ensure proper specimen collection, labeling, custody, and timely delivery to the lab
Consider patient-specific factors (bleeding risk, fluid status) when deciding on sampling method
Imaging tests in respiratory evaluation
Computed Tomography Pulmonary Angiography (CTPA)
Specialized CT scan with contrast to visualize pulmonary arteries
Primary use: rule out pulmonary embolism (PE) in patients with shortness of breath or suspected clot
Noninvasive diagnostic tool; provides direct visualization of clots in the pulmonary vasculature
Pre-procedure considerations: assess kidney function (creatinine) because contrast is nephrotoxic
If creatinine is elevated or there is contrast allergy, discuss alternatives or risk/benefit with the team
Chest X-ray (CXR)
First-line imaging to assess chest structures
Indications include: pneumonia, pneumothorax (collapsed lung), pleural effusion (fluid in pleural space), pulmonary edema, COPD-related changes
Advantages: fast, bedside availability, digital now with rapid read
What you look for on CXR (quick read approach): lung symmetry, air in pleural space, lung markings, signs of consolidation, effusions, collapse, edema, line/tube positions
Relationship of imaging choices to clinical questions
CTPA when PE is suspected; CXR for broad differential (pneumonia, effusion, pneumothorax, edema, chronic lung disease)
Use CXR for initial assessment in chest pain or SOB while reserving CTPA for PE suspicion
Practical considerations and caveats
CT dyes require renal clearance; verify creatinine and hydration status
Consider age, allergies, pregnancy status as part of imaging decisions
Quick practical takeaways
CTPA: rule out PE (clot in lung)
CXR: check pneumonia, pneumothorax, effusion, lung structure
Pulmonary function tests (PFTs) and DLCO
Diffusing capacity of the lung for carbon monoxide (DLCO)
A PFT that measures how well gas transfers from the lungs into the blood via the alveolar-capillary membrane
Abbreviated as DLCO
Key uses: diagnoses and monitors interstitial lung disease; evaluates COPD progression and effects of COPD/COVID-related lung injury; helps assess gas exchange efficiency
Test concept: patient inhales a small, safe amount of carbon monoxide, then the amount absorbed is measured
Clinical relevance: particularly useful in evaluating COVID-related lung injury, cystic fibrosis, pulmonary fibrosis, and other interstitial processes
Common implications: reduced DLCO suggests diffusion impairment; relatively preserved DLCO may point away from diffusion-limited disease
Other pulmonary function test measures mentioned
Forced Vital Capacity (FVC): total volume exhaled after a deep breath; helps differentiate obstructive vs restrictive patterns
Forced Expiratory Volume (FEV) and Peak Expiratory Flow (PEF): indicators of airway obstruction and effort
How PFTs fit into the care plan
Indicated when there is suspicion of COPD, COPD exacerbation, interstitial disease, or after illnesses like COVID to assess diffusion and lung capacity
Provide context for treatment decisions and prognosis
Other respiratory function tests and exertion-related assessments
Six-minute walk test (6MWT) / dyspnea with exertion
Walk test used to assess functional status and exertional dyspnea
Monitoring oxygen saturation during activity helps determine need for home oxygen or additional support
Medicare criterion for oxygen: saturation below 90% during exertion can justify home oxygen therapy
Dyspnea on exertion assessment
How well a patient tolerates walking or stair climbing informs disease severity and activity level
Peak flow monitoring and expiratory flow concepts
Peak Expiratory Flow (PEF) and other flow-based measures used in asthma and obstructive disease monitoring
Ventilation basics and ventilator-related concepts
Tidal Volume (VT)
The amount of air inhaled or exhaled in a normal breath
Normal adult VT β
500 ext{ mL}
Minute Volume (MV)
The total volume of air moved in and out in one minute
Formula: MV = VT imes RR
Example: VT β 500 mL, RR β 12 breaths/min β MV β 500 imes 12 = 6000 ext{ mL/min} = 6 ext{ L/min}
Dead space ventilation and alveolar ventilation
Anatomic dead space (VD) β 150 mL in adults (no gas exchange occurs here)
Alveolar ventilation: VA = (VT - VD) imes RR
Ventilation and lung protection considerations
On mechanical ventilation, too large a VT can cause overdistension (volutrauma)
VT and RR are adjusted to support gas exchange while minimizing lung injury; use patient-specific factors (lung size, disease state)
Forced Vital Capacity (FVC) and Forced Expiratory Volume (FEV)
FVC: total forced breath after deep inspiration; FEV: volume exhaled in a set time during forced expiration
Useful for differentiating obstructive vs restrictive disease (e.g., obstruction lowers FEV1 relative to FVC)
Minute volume and respiratory effort in disease states
High minute volume due to tachypnea or increased VT indicates high ventilatory demand and can reflect respiratory distress or attempts to clear CO2
Excessive drive to breathe can decrease venous return due to high intrathoracic pressure (see next section)
Practical example and interpretation guidance
If a patient sits at rest with SpO2 around 92% but fatigues with activity, perform 6MWT and monitor SpO2 and vitals
When ventilated, consider how changes in VT and RR impact overall gas exchange and patient effort
Cardiopulmonary interactions: intrathoracic pressure, venous return, and cardiac output
Intrathoracic pressure and venous return
Repeated chest movements and high intrathoracic pressures can push on the vena cava, reducing venous return to the heart
Reduced venous return lowers preload and stroke volume, thereby decreasing cardiac output if compensation is insufficient
Cardiac output basics
Cardiac Output (CO) = Heart Rate (HR) Γ Stroke Volume (SV)
Typical adult values: SV β 70 mL/beat; HR β 60β100 beats/min; CO β 4β8 L/min
Interplay during respiratory distress or high work of breathing
High respiratory rate and increased VT raise intrathoracic pressure, reduce venous return, and can lower CO
When the lungs and heart are both stressed (e.g., ARDS, pneumonia with sepsis, COPD with exacerbation), they compete for oxygen delivery; insufficient oxygen delivery can worsen overall function
Right heart strain and pulmonary circulation
Hypoxia can provoke pulmonary vasoconstriction, increasing right ventricular afterload (pulmonary hypertension) and potentially leading to right heart strain or cor pulmonale
This worsens venous return and can create a cycle of reduced oxygen delivery
Practical clinical implications
Monitoring minute volume, intrathoracic pressure, and hemodynamics helps guide ventilator settings and diuretic decisions
Early intervention to optimize oxygen delivery protects both lungs and heart from secondary injury
Acid-base balance and renal-lung interplay
Key blood gas concepts (basic overview mentioned in the lecture)
Blood pH normal around
7.40; acceptable range roughly
7.35-7.45Bicarbonate (HCO3^-) normal range about
22-26 ext{ mEq/L}Base excess normal around a small range near zero (typical clinical norm: approximately -2 to +2); large negative base excess indicates metabolic acidosis
Kidneyβlung interaction maintains acid-base homeostasis: lungs adjust CO2; kidneys adjust bicarbonate and acid excretion
Practical numbers observed in lecture
Base excess example discussed: -30 (severe metabolic acidosis) signals substantial metabolic compensation or pathology
Changes in acid-base balance can take time (metabolic changes can take days to reflect in base excess), whereas respiratory changes can occur more rapidly
Clinical implications in respiratory care
In respiratory failure, CO2 retention leads to acidosis; adequate ventilation is needed to remove CO2 and normalize pH
When failing to clear CO2 and manage pH, multi-organ function is affected, including cardiac function and perfusion
Dialysis and fluid management context
In patients with kidney failure or significant acid-base disorders, dialysis may be used to correct electrolyte and acid-base imbalances when the kidneys cannot compensate adequately
Summary points
The body maintains pH via a coordinated effort between lungs (CO2) and kidneys (bicarbonate and acid excretion)
Disturbances in ventilation or renal function can push the system out of balance, leading to metabolic or respiratory acidosis/alkalosis
Understanding base excess and bicarbonate levels helps determine whether primary pathology is metabolic or respiratory and guides treatment decisions
Intensive care unit (ICU) considerations and respiratory support
ICU role in respiratory care
ICU provides constant specialized monitoring for patients with respiratory failure or high-acuity respiratory needs
Patients with ARDS, severe pneumonia/sepsis, post-major surgery, or requiring advanced support are managed there
Ventilatory support options
Invasive ventilation with endotracheal tube when mechanical ventilation is required
Noninvasive ventilation (BiPAP) for partial support on the floor or in the ICU when appropriate
BiPAP can be used to bridge patients who may later be extubated or to stabilize them before escalation or withdrawal of support
Clear criteria for escalation and weaning
Document and communicate patient response to ventilatory support; look for decreasing ventilator requirements as readiness to wean increases
Weaning criteria include decreasing minute volume needed and improving lung mechanics; readiness to wean is often associated with a reduction in ventilatory support needs to a manageable level (e.g., minute volumes approaching lower thresholds, decreasing support pressures, etc.)
Conditions commonly encountered in respiratory ICU care
Acute Respiratory Distress Syndrome (ARDS)
Severe pneumonia and sepsis
Acute lung injury and post-operative respiratory management
Difficult-to-wean patients and those requiring lifelong ventilatory support in certain settings
Overall teaching point
Respiratory therapists must understand how to interpret ventilator data, adjust settings, and communicate with the team to prevent delayed weaning or failure to rescue
Practical takeaways and problem-solving approach
Culture and imaging align with clinical questions
Sputum culture and sensitivity informs antibiotic choice; sample collection must be timely and properly labeled
Chest X-ray provides quick structural information; CTPA investigates suspected PE; lab tests guide therapy decisions
Functional testing informs prognosis and management
DLCO helps diagnose diffusion limitations and monitor interstitial/covid-related changes
FVC/FEV/PEF help define obstructive vs restrictive pathology
6MWT and exertion assessment guide oxygen therapy decisions and rehabilitation planning
Ventilation concepts to remember
VT β 500 mL; RR determinesMV via MV = VT Γ RR
Dead space β 150 mL; VA = (VT β VD) Γ RR
High minute volume increases intrathoracic pressure, reduces venous return, and may depress cardiac output if not carefully managed
Cardiac output = HR Γ SV; normal CO ~ 4β8 L/min; SV β 70 mL/beat
Oxygenation and perfusion considerations
Hypoxia vs hypoxemia: tissue-level oxygen deficit vs blood-level oxygen deficit
Pulmonary vasoconstriction in hypoxia can raise right heart workload; watch for signs of cor pulmonale in chronic lung disease
Ethical and practical clinical mindset
Experience and situational awareness are crucial; anticipate deterioration and be prepared for escalation or extubation
Documentation and communication with the care team are essential for timely interventions and patient safety
Quick-reference formulas and numbers (LaTeX)
Tidal volume: VT \approx 500\,\text{mL}
Minute volume: MV = VT \times RR
Example: MV \approx 500\,\text{mL} \times 12\,\text{/min} = 6000\,\text{mL/min} = 6\,\text{L/min}
Dead space: VD \approx 150\,\text{mL}
Alveolar ventilation: VA = (VT - VD) \times RR
Stroke volume: SV \approx 70\,\text{mL/beat}
Cardiac output: CO = HR \times SV; \quad CO \approx 4-8\,\text{L/min}
Normal blood pH: \text{pH} \approx 7.40\; \; 7.35-7.45
Bicarbonate: \text{HCO}_3^- \approx 22-26\,\text{mEq/L}
Base excess: normal roughly around -2 \text{ to } +2 (example severe metabolic acidosis with base excess β -30)
Oxygenation threshold for some Medicare decisions: SpO_2 < 90\% during exertion