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 during acute exacerbations to prevent mortality.

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 at home and during clinical encounters 1.
• Patients should record PEF twice daily (morning and evening) at the same times, maintaining a chart over several weeks 1.
• Normal PEF values vary by age, sex, and height—compare measurements against standardized charts 1.
• A variability of >10% in adults and >13% in children between daily measurements is diagnostic of asthma 1.
• Calculate daily diurnal variation as: (highest PEF - lowest PEF) ÷ mean PEF for the day, averaged over one week 1.

Respiratory Rate

• Respiratory rate >25 breaths/min in adults indicates severe asthma requiring immediate treatment 1.
• This parameter is frequently underestimated but is a critical marker of severity 1.
• Respiratory rate correlates with accessory muscle use and dyspnea as a distinct dimension of asthma severity 2.

Heart Rate

• Heart rate >110 beats/min in adults signals severe asthma 1.
• Heart rate monitoring is essential because beta-blockers can mask tachycardia, one of the key warning signs of severe exacerbation 3.
• Heart rate correlates with wheezing as a separate factor in asthma assessment 2.

Oxygen Saturation (SpO2)

• SpO2 <94% is associated with increased severity of asthma attacks 4.
• SpO2 ≤92% carries a 6.3-fold greater relative risk for requiring additional treatment 4.
• SpO2 correlates positively with spirometric values (FEV1 and FEF25-75) and negatively with clinical scores 4.
• Critical pitfall: Never assume normal oxygen saturation excludes severe asthma exacerbation, especially in patients on beta-blockers 3.

Advanced Monitoring During Acute Exacerbations

Arterial Blood Gas Analysis

• Arterial blood gases must always be measured in patients with acute severe asthma admitted to hospital 1.
• A normal (5-6 kPa or 38-45 mmHg) or elevated PaCO2 in a breathless asthmatic patient is a life-threatening marker indicating impending respiratory failure 1, 3, 5.
• This represents a critical pitfall: a "normal" PaCO2 during an asthma exacerbation is NOT reassuring—it indicates severe respiratory compromise 5.
• Severe hypoxia: PaO2 <8 kPa (60 mmHg) irrespective of oxygen treatment indicates life-threatening attack 1.
• A low pH value (or high H+) marks very severe, life-threatening attack 1.
• Repeat arterial blood gas measurements within 2 hours of starting treatment if initial PaCO2 was normal or raised 5.

Spirometry (When Available)

• Spirometry provides more reliable and reproducible results than PEF alone 1.
• Measure FEV1, FVC, and FEV1/FVC ratio (should be >70-80% in healthy adults, >90% in healthy children) 1.
• An increase of FEV1 by >12% from baseline (adults and children) or >200ml after bronchodilator (adults) indicates significant reversibility 1.
• Avoid short-acting beta-agonists within 4 hours or long-acting beta-agonists within 15 hours before testing 1.

Severity Classification Based on Vital Parameters

Severe Asthma Features

• Too breathless to complete sentences in one breath 1
• Respiratory rate >25 breaths/min 1
• PEF <50% of predicted normal or personal best 1
• Heart rate >110 beats/min 1

Life-Threatening Features

• PEF <33% of predicted normal or personal best 1
• Silent chest, cyanosis, or feeble respiratory effort 1
• Bradycardia or hypotension 1
• Exhaustion, confusion, or coma 1
• Normal or elevated PaCO2 in a breathless patient 1, 5

Clinical Monitoring Algorithm

For Stable Asthma

1. Daily home PEF monitoring (morning and evening) with charted results 1, 6
2. Periodic spirometry in outpatient settings (every 3-6 months or as needed) 1
3. Assessment of symptom frequency and variability 6

For Acute Presentations

1. Immediate measurement of respiratory rate, heart rate, and PEF 1
2. Pulse oximetry (SpO2) for all patients 4
3. Arterial blood gas analysis for any patient requiring hospital admission 1
4. Reassessment 15-30 minutes after bronchodilator administration 1

Critical Pitfall to Avoid

The severity of asthma attacks is often underestimated by patients, relatives, and doctors due to failure to make objective measurements 1, 5. Never rely solely on subjective assessment—always obtain objective vital parameter measurements, particularly PEF and respiratory rate 1, 7.