What vital parameters should be monitored in adults and children with a known history of asthma?

Vital Parameters to Monitor in Asthma Patients

In adults and children with asthma, the essential vital parameters to monitor are respiratory rate, heart rate, peak expiratory flow (PEF), and oxygen saturation, with arterial blood gas analysis (particularly PaCO2) being critical in acute severe exacerbations.

Core Vital Parameters for Routine Monitoring

Peak Expiratory Flow (PEF)

• PEF is the single most important objective measure for asthma monitoring and should be measured regularly in all asthmatic patients 1, 2
• Normal PEF values vary by age, sex, and height; patients should know their personal best value 1
• Daily variability >10% in adults or >13% in children is diagnostic of asthma 1
• Patients should measure PEF twice daily (morning and evening) and record values over several weeks 1
• PEF <50% of predicted or personal best indicates severe asthma requiring immediate treatment 1
• PEF <33% of predicted or personal best is a life-threatening feature 1

Respiratory Rate

• Respiratory rate >25 breaths/min in adults indicates severe asthma 1
• This parameter is frequently underutilized despite being readily available 1
• Respiratory rate correlates with accessory muscle use and dyspnea severity 3

Heart Rate

• Heart rate >110 beats/min in adults indicates severe asthma 1
• Tachycardia is a key warning sign of severe exacerbation 4
• Critical caveat: Beta-blockers can mask tachycardia, making this parameter unreliable in patients on these medications 4

Oxygen Saturation (SpO2)

• Pulse oximetry should be measured in all patients during acute exacerbations 5
• SpO2 <94% is associated with increased severity of asthma attack 5
• SpO2 ≤92% carries a 6.3-fold greater risk for requiring additional treatment 5
• SpO2 correlates positively with spirometric values (FEV1 and FEF25-75) and negatively with clinical severity scores 5

Critical Parameters in Acute Severe Asthma

Arterial Blood Gas Analysis

• Arterial blood gases must always be measured in patients with acute severe asthma admitted to hospital 1, 6
• A normal (5-6 kPa or 35-45 mmHg) or elevated PaCO2 in a breathless asthmatic patient is a marker of life-threatening attack 1, 4, 6
• This finding indicates impending respiratory failure and potential need for intensive care 6
• Severe hypoxia: PaO2 <8 kPa (60 mmHg) despite oxygen therapy is life-threatening 1
• A low pH or high H+ indicates severe respiratory acidosis 1

Clinical Assessment Parameters

• Inability to complete sentences in one breath indicates severe asthma 1
• Silent chest, cyanosis, or feeble respiratory effort are life-threatening features 1
• Bradycardia, hypotension, exhaustion, confusion, or coma indicate life-threatening asthma 1

Spirometry for Severity Classification

FEV1 and FEV1/FVC Ratio

• Spirometry provides more reliable and reproducible data than PEF alone 1
• FEV1/FVC ratio should be >70-80% in healthy adults and >90% in healthy children 1
• FEV1 <70-80% of predicted with reversibility >12% (and >200ml in adults) after bronchodilator confirms asthma 1

Severity Classification Based on Lung Function

• Severe persistent: PEF <60% of predicted or continuous symptoms 2
• Moderate persistent: PEF 60-79% of predicted or daily symptoms 2
• Mild persistent: PEF ≥80% with symptoms more than once weekly 2
• Intermittent: PEF ≥80% with symptoms less than once weekly 2

Common Pitfalls to Avoid

• Never assume a "normal" PaCO2 in an acute asthmatic exacerbation is reassuring—it actually indicates severe respiratory compromise 6
• The severity of asthma attacks is frequently underestimated by patients, families, and physicians due to failure to obtain objective measurements 1, 6
• Never assume normal oxygen saturation excludes severe asthma in patients on beta-blockers 4
• Subjective assessment of chest symptoms by patients is often poor; objective measurements are essential 1
• Avoid using fixed FEV1/FVC ratios in older adults (may cause false-positive obstruction) and younger adults (may miss obstruction) 1

Monitoring Frequency

• Home monitoring: PEF should be measured twice daily at consistent times 1
• During acute exacerbations: Reassess PEF 15-30 minutes after bronchodilator treatment 1
• If initial PaCO2 was normal or elevated, repeat arterial blood gases within 2 hours of starting treatment 6
• All patients require follow-up within one week of an acute exacerbation 1